Plasma growth hormone concentrations in female mithun (Bos frontalis) of different ages: relations with age and body weight

The role of growth hormone (GH) in postnatal somatic growth is well established. Its basal level and relation to growth performance in different age group mithun (Bos frontalis), a semiwild ruminant has not been characterized until now. To estimate the normal blood GH level and also to assess the influence of age and body weight (BW) on blood GH level in captive mithuns, a total of 65 female mithuns was divided into six age groups (group I, 0-6 months; group II, >6-12 months; group III, >1-2 years; group IV, >2-2.5 years; group V, >2.5-3.0 years and group VI, >3.0 years). Blood samples collected weekly for six consecutive weeks were assayed for GH. GH was also estimated in the samples collected from six growing mithuns at -60, -45, -30, -15, -10, -5 and 0 min prior to GH-releasing hormone (GHRH) administration for calculation of basal GH level and at 5, 10, 15, 30 min and thereafter at 15-min interval up to 8 h post-GHRH to assess blood GH response following GHRH administration in growing mithuns. For calculation of basal plasma GH in adult mithuns, GH was measured in blood samples collected at 30-min interval for 24 h from four animals. BW of all animals was recorded on two consecutive days per week and average of weekly BW was considered for growth rate calculation. It was found that both mean GH and GH per 100 kg BW between the age groups differ (p < 0.01). With increasing age and BW, GH and GH per 100 kg BW both decreased (p < 0.01). The age group with higher plasma GH and GH per 100 kg BW showed higher growth rates (r = 0.83 and 0.97 respectively). Interestingly, mean plasma GH for six consecutive weeks in all the groups showed much greater GH concentration (group I, 86.6 +/- 9.7 ng/ml to group VI 33.2 +/- 5 ng/ml) than reported in other species. Mean basal plasma GH calculated in growing and adult mithuns was 29.6 +/- 4.01 ng/ml and around 25 +/- 3.6 ng/ml respectively. The GH peak (444 +/- 21.3 ng/ml) was registered at 15 min post-GHRH administration in growing mithuns. In conclusion, age and BW influence plasma GH and GH per 100 kg BW but the latter is a better indicator of growth. The basal plasma GH and GH response to GHRH administration is six to eight and four to five times higher in mithun than in other species reported so far. An accurate assessment of the relationship between GH profiles and protein metabolism, proper receptor level study for GH action at the cellular level and the interaction of GH with other growth factors awaits better understanding of higher GH in this unique species.     

Effect of human growth hormone-releasing factor and(or) thyrotropin-releasing factor on hormone concentrations in dairy calves

To determine the effect of chronic treatment with human growth hormone-releasing factor (1-29)NH2 (GRF) and(or) thyrotropin-releasing factor (TRF), 20 calves averaging 70.2 kg BW were divided into four groups (n = 5) according to a 2 X 2 factorial design. For 86 d, calves in each group received twice daily s.c. injections of either .9% NaCl, GRF (5 micrograms/kg BW), TRF (1 microgram/kg BW) or GRF (5 micrograms/kg BW) plus TRF (1 microgram/kg BW). On d 87, all calves received a s.c. injection of GRF (5 micrograms/kg BW) plus TRF (1 microgram/kg BW). Blood samples were collected every 20 min for 18 h on d 1, 29, 57 and 85, and for 8 h on d 87. Hormone responses were measured as area under the hormone concentration curve over time. GRF and TRF acted in synergy (P less than .10) on GH release throughout the treatment period. Growth hormone responsiveness to GRF and(or) TRF decreased (P less than .01) with days of treatment, but this decrease was due to aging rather than to chronic treatment, because GH response to GRF plus TRF was similar (P greater than .10) between control and treated calves on d 87. TRF increased prolactin (Prl) concentration until the end of the treatment period (P less than .01). The response of thyroid-stimulating hormone (TSH) to TRF disappeared (P greater than .10) after 1 mo of treatment, whereas the thyroxine (T4) response decreased (P less than .01) throughout the treatment period. GRF did not induce nor did it interact with TRF on TSH and T4 release.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of long-term administration of human growth hormone-releasing factor and (or) thyrotropin-releasing factor on hormone concentrations in lactating dairy cows

Fifteen cows (87 +/- 8 d in lactation; 641 +/- 33 kg BW) were randomly assigned to treatment and then subjected for 182 d to daily sc injection (1000 hr), in the cervical area, of saline (control), thyrotropin-releasing factor (TRF: 1 micrograms/kg BW), growth hormone-releasing factor (1-29)NH2 (GRF; 10 micrograms/kg BW) or GRF plus TRF (10 and 1 micrograms/kg BW, respectively) according to a 2 x 2 factorial design. On days 1, 31, 88 and 179, jugular blood samples were collected from 2 hr before to 6 hr after injection. Samples were also collected for 5 consecutive days after cessation of treatment. GRF always induced growth hormone (GH) release (600 vs 7925 ng.min/ml) with augmentation of response with time (interaction GRF * day; P less than .001). TRF did not affect (P greater than .25) GH release; there was no interaction (P greater than .25) with time. There was no significant interaction (P greater than .25) between GRF and TRF on GH release. However, the amount of GH release with GRF plus TRF was always greater than with GRF alone (9419 vs 6431 ng.min/ml). TRF induced a significant release of prolactin (23769 vs 42175 ng.min/ml) but GRF reduced the amount of prolactin release on the last day of sampling. TRF induced thyroid stimulating hormone (TSH) release only on the first day of injection while triiodothyronine (T3) and thyroxine (T4) continued to respond to TRF throughout the treatment period. Concentrations of T3 and T4 fell below control levels after cessation of TRF injection. In conclusion, GRF-induced GH release and TRF-induced Prl and thyroid hormone release were maintained over a 6-mo treatment period. TRF induced TSH release only on the first day of injection. Overall, these results raised the possibility of a direct effect of TRF on the thyroid gland.     

Serological evidence of Neospora caninum infection in mithun (Bos frontalis) from India

Studies conducted on mithuns maintained at National Research Centre on mithun, Indian Council of Agricultural Research (ICAR), Nagaland, India and mithuns found in free-ranging condition of Nagaland revealed that the overall prevalence of antibodies to Neospora caninum in mithun was 10% (95% CI=5-15) when detected by a commercially available competitive enzyme-linked immunosorbent assay test. Highest (prevalence rate=16, 95% CI=8-24) seroprevalence was found in mithuns above 3 years of age and lowest (prevalence rate=2, 95% CI=0-6) in mithuns of 2-12 months old. No statistically significant difference was observed between male (prevalence rate=7, 95% CI=0-14) and female (prevalence rate=12, 95% CI=6-18) seroprevalences. The seroprevalence was found to be higher (prevalence rate=20, 95% CI=9-31) in mithuns found in free-ranging condition in comparison to mithuns kept in semi-intensive system (prevalence rate=5, 95% CI=1-9). This is probably the first report on serological evidence of N. caninum infection in mithun. The possible role of sylvatic fauna in the epidemiology of N. caninum infection mithun is also discussed in brief.     

Oral administration of peptidergic growth hormone (GH) secretagogue KP102 stimulates GH release in goats

To assess the oral activity of KP102 (also known GHRP-2) on growth hormone (GH) release in ruminant animals, 5 or 10 mg/kg body weight (BW) of KP102 dissolved in saline was orally administered twice at 2 hr-intervals to either 1- or 3-mo-old goats (n = 5-6). Plasma GH concentrations in the 1-mo-old goats were elevated at 15 min after the first administration of both 5 and 10 mg/kg BW of KP102. Significant elevation of GH concentrations continued until 180 min after 10 mg/kg BW of KP102, whereas the elevated GH levels after the administrations of 5 mg/kg BW of KP102 subsided to basal concentrations within 90 min. The second administration of 10 mg/kg BW of KP102 failed to elevate the GH concentration, but 5 mg/kg BW of KP102 abruptly stimulated GH release. Plasma GH concentrations in the 3-mo-old goats were also significantly elevated after the administration of both 5 and 10 mg/kg BW of KP102. The plasma GH responses to 5 and 10 mg/kg BW of KP102 were almost identical. The elevated GH levels after the first administration of KP102 tended to be maintained throughout the experiment, and a transient increase in plasma GH levels was observed after the second administration. However, the stimulatory effect of KP102 on GH release in the 3-mo-old goats was small and less abrupt than that in the 1-mo-old goats. The concentrations of insulin-like growth factor-I were not increased by KP102 during the brief sampling periods used in this experiment. These results show that the oral administration of the peptidergic GH secretogogue KP102 stimulates GH release in a ruminant species, and that the oral activity of KP102 on GH release is modified by the age.     

Effect of human growth hormone-releasing factor on bone and mineral metabolism in growing pigs

Little information is available on the effects of growth hormone (GH) and growth hormone-releasing factor (GRF and GHRH) treatment on bone metabolism in pigs. Thus, tibial bending moments and ash contents were studied in 12, 6-wk-old pigs weighing 13 +/- .2 kg. Six pigs (GRF group) were injected s.c. twice daily with 75 micrograms GRF (hGRF [1-29] NH2)/kg BW for 52 d and six remained untreated (control group, C). Average daily gain was slightly (5%; P less than .10) increased in treated pigs. At slaughter, plasma measurements related to calcium homeostasis, such as concentrations of Ca, inorganic P, and vitamin D metabolites (25-OH and 1,25-(OH)2 vitamin D3), were not changed by GRF injection. At slaughter, plasma GH levels were 3.3 times greater in treated (11.3 +/- 3 ng/ml) than in untreated pigs (3.4 +/- .5 ng/ml, P less than .02), whereas those of insulin-like growth factor I were increased by approximately 38%. No difference was observed between the two groups at slaughter in tibial weight, density, bending moment, ash relative to bone volume (29 +/- 1 vs 30 +/- 2 g/100 cm3, GRF vs C), total ash content, or ash relative to dry matter in cortical or medullary bone. Our GRF treatment did not affect bone and mineral metabolism in young, growing pigs.     

Effects of growth hormone-releasing factor on growth hormone response, growth and feed conversion efficiency in buffalo heifers (Bubalus bubalis)

The aim of this study was to determine the benefits of growth hormone-releasing factor (GRF) on growth and feed conversion efficiency (FCE) in buffaloes. Twelve Murrah buffalo heifers (Bubalus bubalis) of mean age 24.8 months and mean body weight 302.4kg were divided into two groups (treatment and control) with six animals in each group. The buffaloes were given intravenous injections of bovine GRF (bGRF) at a dose rate of 10microg/100kg body weight or an equal volume of saline at 15-day intervals for a period of 9 months. Plasma growth hormone (GH) responses to bGRF challenge were measured in blood samples collected at 90-day intervals on days 1, 90, 180 and 270 and samples were taken at -60, -30, 0, +10, +20, +30, +60, +120 and +180min relative to bGRF injection. Blood samples were also collected weekly by jugular venepuncture for the quantification of plasma GH. The average growth rate (AGR) and FCE of all animals were recorded at 15-day intervals. Plasma GH concentrations increased (P=0.001) steadily following bGRF challenge, peaking 10-20min after challenge and declining to baseline by 180min. In the treatment group, there were no significant differences (P>0.05) in either the peak heights of the GH response or the area under the curve (AUC) of the GH response after bGRF challenge on any of the four occasions of intensive bleeding. There were overall increases in plasma GH concentrations (P<0.01), AGR (P<0.01) and FCE (P=0.05) in the treatment group compared with the control animals. The study showed that GH responsiveness to administration of bGRF at 15-day intervals over 9 months of treatment remained unchanged in buffalo heifers. Exogenous bGRF treatment for a long period can therefore enhance GH release leading to higher growth rates and better feed conversion efficiency in buffalo heifers.     

Role for des-acyl ghrelin in the responsiveness of plasma hormones and metabolites to ghrelin in Holstein steers

Gastric-derived peptide hormone ghrelin is known for its potent growth hormone (GH) stimulatory effects. The acyl-modification on N-terminal Ser(3) residue is reported to be important to stimulate the ghrelin receptor, GH secretagogue-receptor type1a (GHS-R1a). However, major portion of circulating ghrelin lacks in acylation, and some biological properties of des-acyl ghrelin have been reported in monogastric animals. In the present study, the responsiveness of plasma hormones and metabolites to ghrelin in steers was characterized, and role for des-acyl ghrelin in these changes was investigated. The repeated intravenous administrations of bovine ghrelin (1.0 microg/kg BW) every 2h for 8h to Holstein steers significantly increased the plasma acylated ghrelin, total ghrelin, GH, insulin and NEFA levels. The GH responses in peak values and area under the curves (AUCs) were attenuated by repeated injections of ghrelin, however, the responses of plasma total ghrelin were similar. Plasma insulin AUC decreased after fourth injection of ghrelin while plasma NEFA AUCs gradually increased by repeated injections of ghrelin. Pretreatment of des-acyl ghrelin (10.0 microg/kg BW) 5 min prior to the single injection of ghrelin (1.0 microg/kg BW) did not affect the ghrelin-induced hormonal changes. Moreover, the responses of plasma GH to bovine and porcine ghrelin, which differ in C-terminal amino acid residues, were similar in calves. These data show that (1) GH release was attenuated by repeated administration of ghrelin, (2) ghrelin regulates glucose and fatty acid metabolism probably via different pathway, and (3) des-acyl ghrelin is unlikely the antagonist for ghrelin to induce endocrine effects in Holstein steers.     

The effects of growth hormone-releasing peptide-2 (GHRP-2) on the release of growth hormone and growth performance in swine

The effects of GHRP-2 (also named KP102), a new growth hormone-releasing peptide, on the release of growth hormone (GH) and growth performance were examined in swine. The single intravenous (i. v.) injection of GHRP-2 at doses of 2, 10, 30 and 100 microg/kg body weight (BW) to cross-bred castrated male swine stimulated GH release in a dose-dependent manner, with a return to the baseline by 120 min. The peak GH concentrations and GH areas under the response curves (GH AUCs) for 180 min after the injections of GHRP-2 were higher (P < 0.05) than those after the injection of saline. The GH responses to repeated i.v. injections of GHRP-2 (30 microg/kg BW) at 2-h intervals for 6 h were decreased after each injection. The chronic subcutaneous (s.c.) administration of GHRP-2 (30 microg/kg BW) once daily for 30 days consistently stimulated GH release. The GH AUCs for 300 min after the injections on d 1, 10 and 30 of treatment in GHRP-2-treated swine were higher than those in saline-treated swine. However, chronic administration of GHRP-2 caused a partial attenuation of GH response between d 1 and 10 of treatment. The chronic s.c. administration of GHRP-2 also increased average daily gain for the entire treatment period by 22.35% (P < 0.05) and feed efficiency (feed/gain) by 20.64% (P < 0.01) over the saline control values, but did not significantly affect daily feed intake. These results indicate that GHRP-2 stimulates GH release and enhancing growth performance in swine.     

Effect of human growth hormone-releasing factor and(or) thyrotropin-releasing factor on growth, carcass composition, diet digestibility, nutrient balance, and plasma constituents in dairy calves

Sixty male dairy grain-fed calves, raised from 70 to 223 kg BW in individual crates, were used in a 2 X 2 factorial arrangement to determine the effect of administration of human growth hormone-releasing factor (1-29)NH2 (GRF) and(or) thyrotropin-releasing factor (TRF). Calves received twice-daily s.c. injections of .9% NaCl (control), GRF (5 micrograms/kg BW), TRF (1 micrograms/kg BW) or GRF (5 micrograms/kg BW) plus TRF (1 micrograms/kg GTRF). Average daily gain and days on feed were not affected by treatments, but TRF treatment increased (P less than .05) total intake of dry matter (DM) and feed conversion ratio: 3.00, 3.02, 3.08, and 3.22 kg DM/kg weight gain for control, GRF, TRF, and GTRF, respectively. During two 7-d periods, after 66 and 75 d of treatment, feces and urine were collected from 40 calves (5 per treatment per period). Treatment with GRF increased (P less than .05) digestibility of DM, nitrogen (N), and energy and tended (P less than .20) to increase N retention. At slaughter, withers height was increased (P = .05) by GRF and carcass length was increased (P less than .05) by TRF. Pituitary and liver weights were increased (P less than .05) by TRF. The combination of GRF and TRF slightly increased (P less than .10) protein content and decreased (P less than .05) fat content of the 9-10-11th rib section. After d 1, GRF treatment chronically increased (P less than .05) insulin concentrations and also increased (P less than .10) IGF-I concentrations on d 29 and 57. In summary, chronic treatment with GRF and(or) TRF did not improve growth or efficiency, although GRF increased digestibility of DM, N, and energy and the GRF plus TRF combination resulted in slightly leaner carcasses.     

Changes in plasma non-esterified fatty acids, glucose and alpha-amino nitrogen and their relationship with body weight and plasma growth hormone in growing buffaloes (Bubalus bubalis)

A study was undertaken to investigate the changes of plasma non-esterified fatty acids (NEFA), glucose and alpha-amino nitrogen and their relationship with age, body weight (BW) and plasma growth hormone (GH) in growing buffaloes. For the purpose, six growing female Murrah buffalo calves of 6-8 months of age were selected on the basis of their BW and fed according to Kearl standard (Nutrient Requirements of Ruminants in Developing Countries, International Feedstuffs Institute, Utah State University, Utah, USA, 1982, p. 89) for growing buffaloes (target growth rate 500 g/day) to meet energy and protein requirement of the animals. Blood samples collected at fortnight intervals for 1 year were analysed for plasma NEFA, glucose, alpha-amino nitrogen and GH. The animals were also weighed at fortnight intervals. Plasma NEFA and glucose levels were found to decrease (p < 0.01) with age. Unlike plasma NEFA and glucose, plasma alpha-amino nitrogen level increased (p < 0.01) as the buffaloes become older. Plasma NEFA and glucose concentrations in growing buffaloes were found to be positively correlated with plasma GH (r = 0.379 and 0.420 respectively), but these were non-significant (p > 0.01). However, plasma NEFA and glucose showed a good correlation (p < 0.01; r = 0.780 and 0.652 respectively) with plasma GH per 100 kg live weight. Plasma alpha-amino nitrogen exhibited non-significant (p > 0.01) negative correlation (r = -0.295) with plasma GH but a negative correlation (p < 0.01; r = -0.641) with GH per 100 kg BW. So, plasma metabolites showed a definite pattern of change during growth and these have a significant (p < 0.01) correlation with plasma GH per 100 kg BW than GH.     

Stimulated growth hormone release in juvenile cattle genetically selected for high and low milk yield

The purpose of the present study was to test if plasma growth hormone (GH) concentrations in juvenile male and female cattle before or after intravenous stimulation with secretagogues was affected by selection for high (H) vs. low (L) milk yield in lines of Norwegian cattle. In the first of two experiments (A), 32 yearling heifers (16 H and 16 L, at 307–424 days of age) were tested by use of four doses of growth hormone releasing factor (GRF); 0.02, 0.10, 0.50 and 2.50 μg/kg live weight, on 4 consecutive days. The animals were fed ad libitum on a silage-based ration before and during the experiment. Growth hormone was assayed in plasma from blood samples taken at ?15, ?5, 0, 5, 10, 15, 20, 30, 45 and 60 min from stimulation. Plasma GH concentrations were log transformed before statistical analyses. Response variables were; PRIOR (mean of ?15, ?5 and 0 min samples) and PEAK (mean of 10, 15 and 20-min samples). In experiment B, 37 calves (19 H+18 L, 22 males and 15 females, age 114–259 days) were subjected daily to one of three intravenous stimulation tests (GRF, 0.10 and 0.50 μg/kg or thyrotrophin releasing hormone (TRH) at 0.20 μg/kg live weight) on each of 3 consecutive days. Feeding was restricted to cover estimated maintenance requirements only. Rations were given once daily during the test days and 3 days prior to first test. Blood sampling and variables followed those of experiment A. Selection line did not significantly affect GH variables in experiments A or B at any dose of GRF or TRH. GH response increased with increasing dose of GRF up to 0.50 μg/kg. At the highest GRF dose, the response was delayed and persisted longer. Doses giving intermediate to large response increased repeatability of GH measurements. It is concluded that GH secretion in juvenile cattle can be accurately assessed using GRF based stimulation tests combined with restricted and controlled feeding, but it is not affected by selection for milk yield in Norwegian cattle.     

Effects of Long-term Growth Hormone-releasing Factor Administration on Plasma Growth Hormone, Luteinizing Hormone and Progesterone Profiles in Growing Female Buffaloes (Bubalus bubalis)

To investigate the effects of long-term growth hormone-releasing factor (GRF) administration on plasma growth hormone (GH), LH and progesterone and body weight gain in growing buffalo calves, 12 female Murrah buffaloes within the age group of 6-8 months of age were divided into two groups (treatment and control groups) of six each in such a way so that average body weights between the groups did not differ (p > 0.05). Control buffaloes were not given any hormonal treatment and treatment group buffaloes were treated with synthetic bovine GRF [bGRF (1-44)-NH(2)] at the rate of 10 microg/100 kg body weight intravenously at an interval of 15 days from week 6 (5-week pre-treatment period) till 18 injections were completed (week 6-42 treatment period) and thereafter, effect of exogenous GRF were observed for 10-week post-treatment period. Jugular blood samples were drawn twice a week at 3-4-day intervals for plasma GH, LH and progesterone quantification. Body weight of all animals was recorded twice a week. During pre-treatment period, mean plasma GH, LH and progesterone did not differ (p > 0.05) between the groups. But during treatment as well as post-treatment period, mean plasma GH levels were found to be significantly (p < 0.01) higher in treatment than control group of buffaloes. Administration of GRF for longer term sustained a higher level of plasma GH even after cessation of treatment. GRF-treated buffaloes attained higher (p < 0.01) body weight than the controls. Repeated GRF administration for long-term significantly (p < 0.01) increased plasma LH and progesterone. In conclusion, repeated long-term exogenous GRF administration induces and even enhances GH release without any sign of refractoriness. GRF may, therefore, be used to induce daily GH release without loss of responsiveness over an extended period of time in young growing female buffaloes and it may assist these animals to grow faster.     

Effects of the administration of growth hormone-releasing peptide-2 (GHRP-2) orally by gavage and in feed on growth hormone release in swine

The experiments were conducted to determine the effects of the administration of growth hormone-releasing peptide-2 (GHRP-2, also named KP102), both orally by gavage and in feed, on the release of growth hormone (GH) in swine and to investigate whether attenuation of the GH response occurs after short-term treatment with the peptide in feed. In the first experiment, saline or GHRP-2 at doses of 1, 4.5 and 9 mg/kg body weight (BW) was dissolved in 15 ml saline and administered orally as a bolus by gavage to cross-bred castrated male swine (n = 6). Orally administered GHRP-2 stimulated dose-related increases in peak concentrations of GH, with a return to basal by 120 min. After administering GHRP-2 orally, peak concentrations of GH and areas under the GH response curves (GH AUCs) for 180 min were higher (P < 0.05) than those in saline controls. In Experiment 2, GHRP-2 at doses of 0 (served as control), 1, 4.5 and 9 mg/kg BW was mixed in 150 g of feed and offered to cross-bred castrated male swine (n = 6) at 0900 hr and 1700 hr daily for a 3-d period. Administration of 1 mg/kg BW GHRP-2 to swine in feed failed to stimulate the release of GH, but GHRP-2 at doses of 4.5 and 9 mg/kg BW significantly (P < 0.05) increased plasma concentrations of GH after initial and final treatments at 0900 hr on Days 1 and 3 of treatment, respectively. Peak concentrations of GH and GH AUCs for 180 min after the initial and final treatments in the 4.5 and 9 mg/kg BW GHRP-2-treated swine were higher (P < 0.05) than those in controls. After 3 d of treatment with GHRP-2 in feed at doses of 4.5 and 9 mg/kg BW, GH responses to the peptide were maintained. The results of the present study indicate that the administration of GHRP-2 orally by gavage and in feed stimulates the release of GH in swine, and that the GH-releasing effect of the peptide does not become desensitized after short-term administration in feed.     

Effect of age and intake on growth hormone kinetics in dairy heifers.

The effects of aging and intake on growth hormone (GH) kinetics and GH-releasing factor (GRF)-induced GH concentrations were studied in two groups of 12 Holstein heifers each (80 d, 85 kg: young; and 273 d of age, 246 kg: old). Each group was then equally subdivided into full-fed (FF) and restricted-fed (RF) subgroups. After 11 d of intake treatment, animals were infused for 3 hr with GH (1.5 mg/hr) in order to calculate GH metabolic clearance rate (MCR), secretion rate (SR) and half-life (t 1/2). Two d later, total plasma volume was determined and the following day, all heifers received a GRF challenge (5 micrograms/kg i.v.). The following values are LSM +/- SE for young-FF, young-RF, old-FF and old-RF. Rate of secretion was not affected by any treatment, averaging 1.51, 1.25, 1.34, and 1.40 +/- .23 micrograms/min. Aging increased (P < .01) MCR (186, 159, 382, and 300 +/- 21 ml/min) and increased plasma volume (P < .01), which resulted in lower basal GH concentrations. Aging also decreased (P < .01) the area under the GH response curve following GRF injection (AUC: 12442, 21114, 5155, and 6308 +/- 1776 ng.min/ml) but did not affect average GH quantity in the plasma after the GRF challenge. Feed restriction decreased (P < .05) MCR, but not enough to affect basal GH concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)     

Serum growth hormone and nitrogen metabolism responses in young bull calves infused with growth hormone-releasing factor for 20 days

Intravenous infusion of growth hormone (GH)-releasing factor (GRF) sustains elevated serum GH for at least 5 days in young Holstein steers, but the effects of extended infusion of GRF on serum GH and nitrogen (N) metabolism have not been determined. Thirteen Dutch-Friesian bull calves (148 +/- 1.5 kg) were assigned randomly to receive daily either 0 or 3.6 mg GRF (hGRF1-44NH2; U-68420) in saline as a continuous infusion for 20 days. Calves were fed milk replacer twice daily while housed indoors in wooden-slatted floor box crates (metabolism cages). Nitrogen determinations were made on daily feed, feces, and urine samples which were pooled for days 9 to 14 of treatment. Concentrations of GH were quantified in blood samples collected at 20 min intervals for 8 hr on day 1, 10 and 20. The infusion of GRF increased baseline GH (P less than .07), the number of GH pulses (P less than .0001), the amplitude of the GH pulses (P less than .001), and area under the GH response curve (P less than .0002). Within GRF-infused calves baseline GH (P less than .0001) and area under the GH response curve (P less than .006) were greater on day 20 than on day 1 or 10 (day X treatment interaction, P less than .04). Area under the GH response curve was similar on each sampling day in saline-infused calves, but baseline GH was higher (P less than .03) on day 20 than either day 1 or 10. Infusion of GRF increased episodic GH secretion in spite of limited pulsatile activity in saline-infused calves.(ABSTRACT TRUNCATED AT 250 WORDS)     

N-methyl-d,l-aspartate stimulates growth hormone and prolactin but inhibits luteinizing hormone secretion in the pig.

The effects of n-methyl-d,l-aspartate (NMA), a neuroexcitatory amino acid agonist, on luteinizing hormone (LH), prolactin (PRL) and growth hormone (GH) secretion in gilts treated with ovarian steroids was studied. Mature gilts which had displayed one or more estrous cycles of 18 to 22 d were ovariectomized and assigned to one of three treatments administered i.m.: corn oil vehicle (V; n = 6); 10 micrograms estradiol-17 b/kg BW given 33 hr before NMA (E; n = 6); .85 mg progesterone/kg BW given twice daily for 6 d prior to NMA (P4; n = 6). Blood was collected via jugular cannulae every 15 min for 6 hr. Pigs received 10 mg NMA/kg BW i.v. 2 hr after blood collection began and a combined synthetic [Ala15]-h GH releasing factor (1-29)-NH2 (GRF; 1 micrograms/kg BW) and gonadotropin releasing hormone (GnRH; .2 micrograms/kg BW) challenge given i.v. 3 hr after NMA. NMA did not alter LH secretion in E gilts. However, NMA decreased (P < .02) serum LH concentrations in V and P4 gilts. Serum LH concentrations increased (P < .01) after GnRH in all gilts. NMA did not alter PRL secretion in P4 pigs, but increased (P < .01) serum PRL concentrations in V and E animals. Treatment with NMA increased (P < .01) GH secretion in all animals while the GRF challenge increased (P < .01) serum GH concentrations in all animals except in V treated pigs. NMA increased (P < .05) cortisol secretion in all treatment groups. These results indicate that NMA inhibits LH secretion and is a secretagogue of PRL, GH and cortisol secretion with ovarian steroids modulating the LH and PRL response to NMA.     

Effect of daily injections of growth hormone-releasing factor and thyrotropin-releasing hormone on growth and endocrine parameters in chickens

The control of growth is a complex mechanism regulated by several metabolic hormones including growth hormone (GH) and thyroid hormones. In avian species, as well as in mammals, GH secretion is regulated by hypothalamic hypophysiotropic hormones. Since thyrotropin-releasing hormone (TRH) and growth hormone-releasing factor (GRF) are potent GH secretagogues in poultry, we were interested in determining the influence of daily intravenous administration of either peptide or both simultaneously on circulating GH and IGF-I concentrations and whether an improvement in growth rate or efficiency would be obtained.

Male broiler chicks were injected once daily for a period of 21 days with either GRF (10 μg/kg), TRH (1 μg/kg) or both GRF and TRH (10 and 1 μg/kg respectively) between four and seven weeks of age. On the last day of the experiment, following intravenous injection of TRH, GRF or a combination of GRF and TRH, plasma GH levels were significantly (P<.05) increased to a similar extent in control chicks and in those which had received daily peptide injections for the previous 21 days. Circulating GH levels between 10 and 90 min post-injection were significantly (P<.05) greater and more than additive than GH levels in chicks injected with both GRF and TRH when compared to those injected with either peptide alone. Mean plasma T₃ concentrations during that same time period were significantly elevated (P<.05) above saline-injected control chick levels in birds treated with TRH or GRF and TRH respectively, regardless of whether the chicks had received peptide injections for the previous 21 days. There was no evidence of pituitary refractoriness to chronic administration of either TRH or GRF injection in terms of growth or thyroid hormone secretion.

Despite the large elevation in GH concentration each day, growth rate, feed efficiency and circulating IGF-I concentrations were not enhanced. Thus the quantity or secretory pattern of GH secretion induced by TRH or GRF administration was not sufficient to increase plasma IGF-I concentration or growth.     

Oestrous Behaviour and Timing of Ovulation in Relation to Onset of Oestrus and LH Peak in Mithun (Bos frontalis) Cows

The objectives of the study were to evaluate the oestrus behaviour and to determine the timing of ovulation in relation to onset of oestrus and the pre-ovulatory LH surge in mithun (Bos frontalis). For this purpose, the blood samples collected at 15-min intervals for 9 h period following onset of oestrus and thereafter, at an interval of 2 h till 4 h post-ovulation for three consecutive cycles from 12 mithun cows were assayed for plasma LH and progesterone. Ovulation was confirmed by palpation of ovaries per rectum at hourly intervals. Various signs of behavioural oestrus were also recorded. The common signs of oestrus and their frequency of occurrence in mithuns were following and mounting by male mithuns (100%), standing to be mounted (100%), frequent urination (62.33%), raising of tail (65.23%), swelling of vulva (54.26%) and congestion of vulvar mucous membrane (69.87%). The pre-ovulatory LH surges consisted of several pulses (2.92 +/- 0.26 pulses/animal; range, 1-4). The mean (+/-SEM) peak level of LH for individual mithun varied from 6.99 +/- 0.44 to 12.69 +/- 2.10 ng/ml and the mean pooled LH peak concentration was 9.10 +/- 0.60 ng/ml. The highest peak (highest amplitude of LH during LH surge) was 10.83 +/- 0.76 ng/ml (range, 8.07-16.49 ng/ml). The duration of LH surge was 6.98 +/- 0.22 h (6-8 h). Onset of LH surge was at 1.23 +/- 0.17 h post-oestrus onset (range, 0.25-2.25 h). Mean plasma progesterone stayed low (<0.24 ng/ml) during the entire duration of sampling. Ovulation occurred at 26.92 +/- 0.31 (range, 26-29 h) after the onset of oestrus and 18.63 +/- 0.35 h (range, 17-20.75 h) after the end of LH surge. The occurrence of the highest LH peaks within a narrow time frame of 2- to 5-h post-oestrus onset in mithuns could have contributed to the animals ovulating within a narrow time interval. These results are very promising from a practical standpoint of potential success when AI program in this species is implemented in a big way. Furthermore, the results of the occurrence of LH pulses during pre-ovulatory LH surges, which are required for ovulation in this species of animals, is unique and species specific.     

Seroprevalence of brucellosis in mithuns (Bos frontalis) in India

Studies conducted on the seroprevalence of brucellosis in 98 mithuns maintained at the National Research Centre on Mithun, Nagaland, India revealed that the number of animals found positive for brucellosis in avidin-biotin enzyme-linked-immunosorbent assay, standard tube-agglutination test and Rose-Bengal plate test were 34, 20 and 11%, respectively. Highest prevalence of brucellosis was observed in the Mizoram mithun strain. The relative sensitivity and specificity of the standard tube-agglutination test were 61 and 100%, respectively; the corresponding values of the Rose-Bengal plate test were 33 and 100%, respectively.