Effects of cimaterol administration on plasma concentrations of various hormones and metabolites in friesian steers

The aim of the experiment was to determine the acute and chronic effects of the β-agonist, cimaterol, on plasma hormone and metabolite concentrations in steers. Twelve Friesian steers (liveweight = 488 ± 3 kg) were randomly assigned to receive either 0 (control; n=6) or .09 mg cimaterol/kg body weight/day (treated; n=6). Steers were fed grass silage ad libitum. Cimaterol, dissolved in 140 ml of acidified distilled water (pH 4.2), was administered orally at 1400 hr each d. After 13 d of treatment with cimaterol or vehicle (days 1 to 13), all animals were treated with vehicle for a further 7 d (days 14 to 20). On days 1, 13 and 20, blood samples were collected at 20 min-intervals for 4 hr before and 8 hr after cimaterol or vehicle dosing. All samples were assayed for growth hormone (GH) and insulin, while samples taken at −4, −2, 0, +2, +4, +6 and +8 hr relative to dosing were assayed for thyroxine (T₄), triiodothyronine (T₃), cortisol, urea, glucose and non-esterified fatty acids (NEFA). Samples taken at −3 and +3 hr relative to dosing were assayed for IGF-I only. On day 1, cimaterol acutely reduced (P<.05) GH and urea concentrations (7.6 vs 2.9 ± 1.4 ng/ml; and 6.0 vs 4.9 ± 0.45 mmol/l, respectively; mean control vs mean treated ± pooled standard error of difference), and increased (P<.05) NEFA, glucose and insulin concentrations (160 vs 276 ± 22 μmol/l, 4.1 vs 6.2 ± 0.15 mmol/l and 29.9 vs 179.7 ± 13.9 μU/ml, respectively). Plasma IGF-I, T₃, T₄ and cortisol concentrations were not altered by treatment. On day 13, cimaterol increased (P<.05) GH and NEFA concentrations (7.7 vs 14.5 ± 1.4 ng/ml and 202 vs 310 ± 22 mEq/l, respectively) and reduced (P<.05) plasma IGF-I concentrations (1296 vs 776 ± 227 ng/ml). Seven-d withdrawal of cimaterol (day 20) returned hormone and metabolite concentrations to control values. It is concluded that : 1) cimaterol acutely increased insulin, glucose and NEFA and decreased GH and urea concentrations, 2) cimaterol chronically increased GH and NEFA and decreased IGF-I concentrations, and 3) there was no residual effect of cimaterol following a 7-d withdrawal period.     

The effect of dietary yeast and protected methionine on performance and trace minerals status of growing Awassi lambs

Eighteen growing Awassi lambs were used in this study to determine the effect of supplementing two levels of yeast and methionine (cyc-methionine) on the trace elements bioavailability, growth rate, and general performance. The lambs were divided to three groups. The dietary treatments were the control diet (C), control diet plus 2 g cyc-methionine/lamb/day (T₁) and control diet plus 4 g cyc-methionine/lamb/day (T₂).

Lambs fed 2 g/day of cyc-methionine (T₁) showed a significantly higher (P < 0.05) copper, zinc, and cobalt concentrations in liver and meat tissues, but not the same trend in kidney. No significant (P > 0.05) effect of time and time × treatment interaction on copper, zinc, cobalt, and manganese concentrations in blood serum, but cobalt and manganese concentration showed significant (P < 0.05) change by time. Moreover, a significantly (P < 0.05) higher total body gain, average daily gain, dressing percentage, and lower feed conversion were detected in lambs from T₁ compared with the control and T₂ groups.

Feeding 2 g of cyc-methionine to growing lambs increased the net profit by $6.017/lamb and only $3.52/lamb fed 4 g cyc-methionine/day when compared with the control group.

In conclusion, feeding growing Awassi lambs yeast and methionine in a form of cyc-methionine, with a low level of 2 g/day, improve the bioavailability of copper, zinc, and cobalt by growing lambs and their growth performance.     

Effect of progressive cachectic parasitism and growth hormone treatment on hepatic 5'-deiodinase activity in calves

Thyroid status is compromised in a variety of acute and chronic infections. Conversion of thyroxine (T₄) into the metabolically active hormone, triiodothyronine (T₃), is catalyzed by 5′-deiodinase (5′D) mainly in extrathyroidal tissues. The objective of this study was to examine the effect of protozoan parasitic infection (Sarcocystis cruzi) on hepatic 5′D (type I) activity and plasma concentrations of T₃ and T₄ in placebo- or bovine GH (bGH)-injected calves. Holstein bull calves (127.5±2.0 kg BW) were assigned to control (C, ad libitum fed), infected (I, 250,000 S. cruzi sporocysts per os, ad libitum fed), and pair-fed (PF, non-infected, fed to intake of I treatment) groups placebo-injected, and three similar groups injected daily with pituitary-derived bGH (USDA-B-1, 0.1 mg/kg, i.m.) designated as C_GH, I_GH and PF_GH. GH injections were initiated on day 20 post-infection (PI), 3–4 days prior to the onset of clinical signs of the acute phase response (APR), and were continued to day 56 PI at which time calves were euthanized for liver collection. Blood samples were collected on day 0, 28, and 55 PI. Alterations in nutritional intake did not affect type I 5′D in liver. Treatment with bGH increased (P<0.05) 5′D activity in C (24.6%) and PF (25.5%) but not in I calves. Compared to PF calves, infection with S. cruzi reduced 5′D activity 25% (P<0.05) and 47.8% (P<0.01) in placebo- and bGH-injected calves, respectively. Neither nutrition nor bGH treatment significantly affected plasma concentrations of T₄ and T₃ on day 28 and 55 PI. However, plasma thyroid hormones were reduced by infection. On day 28 PI, the average plasma concentrations of T₃ and T₄ were reduced in infected calves (I and I_GH) 36.4% (P<0.01) and 29.4% (P<0.05), respectively, compared to pair-fed calves (PF and PF_GH). On day 55 PI, plasma T₃ still remained lower (23.7%, P<0.01 versus PF) in infected calves while plasma T₄ returned to control values. The data suggest that parasitic infection in growing calves inhibits both thyroidal secretion and extrathyroidal T₄ to T₃ conversion during the APR. After recovery from the APR, thyroidal secretion returns to normal but basal and bGH-stimulated generation of T₃ in liver remains impaired.     

Relationships between the thyroid and somatotropic axes in steers I: Effects of propylthiouracil-induced hypothyroidism on growth hormone, thyroid stimulating hormone and insulin-like growth factor I

The effects of propylthiouracil (PTU)-induced thyroid hormone imbalance on GH, TSH and IGF-I status in cattle were examined. In the first study, four crossbred steers (avg wt 350 kg) were fed a diet dressed with PTU (0, 1, 2 or 4 mg/kg/d BW) in a Latin square design with four 35-d periods. On day 29 in each period, steers were challenged with an intrajugular bolus of thyrotropin releasing hormone (TRH, 1.0 μg/kg). Blood samples were obtained to assess the change in plasma GH and TSH as affected by PTU. Plasma IGF-I was measured from blood samples obtained before and after (every 6 hr for 24 hr) intramuscular injection of bovine GH (0.1 mg/kg, day 31). Doses of 1 and 2 mg/kg PTU increased plasma T₄ (P<.01). At 4 mg/kg, PTU depressed T₄ concentrations to 30% of control (P<.01). Plasma T₃ linearly decreased with increasing doses of PTU (P<.01). Plasma TSH increased when PTU was fed at 4 mg/kg (P<.05) while the TSH response to TRH declined with increasing PTU (P<.02). Neither basal nor TRH-stimulated plasma concentration of GH was affected by PTU; the IGF-I response to GH tended to increase at the 1 and 2 mg/kg PTU (P<.01). In a second study 24 crossbred steers were fed PTU (1.5 mg/kg) for 119 d in a 2 × 2 factorial design with implantation of the steroid growth effector, Synovex-S (200 mg progesterone + 20 mg estradiol), as the other main effect. Basal plasma GH and IGF-I were not affected by PTU treatment. Synovex increased plasma concentration (P<.01) of IGF-I without an effect on plasma GH. The data suggest that mild changes in thyroid status associated with PTU affects regulation of T₃, T₄ and TSH more than GH or IGF-I in steers.     

Cimaterol-induced muscle hypertrophy and altered endocrine status in lambs

The objectives of this study were 1) to determine how cellular growth of skeletal muscle is altered by the repartitioning agent cimaterol and 2) to determine if cimaterol alters endocrine status in association with its repartitioning effects. Thirty Dorset wether lambs were randomly assigned to a pre-treatment baseline group or received 0 or 10 ppm cimaterol in a complete, mixed, high-concentrate diet for 7 or 12 wk. Weights of biceps femoris (BF), semimembranosus (SM) and semitendinosus (ST) muscles were 32.8, 27.1 and 31.5% greater, respectively, in treated lambs at 7 wk, and were 22 to 24% greater at 12 wk. Longissimus (LD) cross-sectional area was 26 and 32% greater at these treatment intervals. Percent type I fibers declined significantly over the course of the experiment in ST, SM and LD, and cimaterol caused a small but significant reduction in percent type I fibers in the ST at 7 and 12 wk. Muscles from lambs fed cimaterol contained 50 and 75% more fibers that exhibited negative staining for phosphorylase activity. Mean cross-sectional area of type I and type II fibers in the combined portions of the ST were 30.4 and 29.3% greater, respectively, in cimaterol-fed lambs after 12 wk, while type I and type II fiber areas in the longissimus were only 13 and 15% greater, respectively. Cimaterol-induced hypertrophy of the ST resulted in both protein and RNA content being 30 to 35% greater (P less than .01) at 7 and 12 wk, while DNA concentration was 22% less (P less than .01) at 7 wk. DNA concentration returned to normal by 12 wk. These results indicate that cimaterol elicits a rapid increase in muscle RNA and protein accretion without concurrent incorporation of satellite cell nuclei. Plasma insulin and insulin-like growth factor-1 (IGF-1) concentrations were 55 and 34% lower, respectively, in cimaterol-fed lambs. Plasma somatotropin concentration and area under the curve were 2.3 times greater (P less than .01) in lambs fed cimaterol for 6 wk, while plasma cortisol, prolactin and glucose concentration were unaffected at 6 or 12 wk. The significant changes in endocrine status may be important in the mechanism(s) of cimaterol in altering muscle accretion.     

Perturbed metabolism and hormonal profiles in calves infected with Sarcocystis cruzi

Plasma concentrations of growth hormone (GH), thyroid stimulating hormone (TSH), insulin (IN), thyroxine (T₄), and triiodothyronine (T₃) in addition to metabolic parameters [N balance (NB), urinary 3-methylhistidine (TMH), urinary creatinine (CR), and urinary hydroxyproline (HP)] were measured in 4-mo-old Holstein steers divided equally among groups infected with Sarcocystis (I), noninfected ad libitum fed (C), and noninfected pair fed to I (PF) (7 steers per treatment). Effects of infection on these parameters beyond those attributable to altered dietary intake were determined using orthogonal contrasts (effect of intake, C vs I + PF; effect of infection, PF vs I). NB was higher in C than I and PF (P<.05) and lower in I than PF (P<.02). Hydroxyproline and CR were influenced by intake (P<.05) and HP excretion was reduced in association with infection (P<.05). Reduced intake was associated with lowered mean basal plasma concentrations of GH, IN, T₃ and T₄ (P<.05). Infection further reduced (P<.001) plasma T₃ concentration.

Triiodothyronine and T₄ responses following an intravenous bolus of thyrotropin releasing hormone (TRH) were measured. The magnitude of the responses in I and PF were lower than those observed in C (P<.05). Plasma T₃ responses were further reduced in association with infection (P<.05). Insulin responses to intravenous arginine infusion (ARG) were also low in association with reduced intake. Growth hormone responses to TRH or ARG were affected by the level of feed intake only. These data suggest that hormonal perturbations associated with the insult of infection further compromise metabolism and the direction of nutrient partitioning that would ordinarily be associated with developmental growth in young steers beyond those responses anticipated from solely the reduction of feed intake.     

Administration of recombinant porcine somatotropin (rpST) changes hormone and metabolic status during early pregnancy

The objective of this study was to examine the effects of somatotropin (ST) on porcine reproductive and metabolic statuses during early pregnancy. Four pregnant crossbred gilts received 6 mg of recombinant porcine somatotropin (rpST) daily from days 10 to 27 after artificial insemination while six pregnant gilts served as controls. Blood samples were taken on days 8, 10, 12, 14, 18, 22, and 27 prior to rpST injections (8:00 h) and subsequently at 9:00, 10:00, 12:00, 14:00, 16:00, 18:00, and 20:00 h. On all remaining days of treatment, samples were taken once daily before injections (8:00 h). The samples were assayed for the metabolic hormones: ST, insulin-like growth factor I (IGF-I), insulin, thyroxine (T₄), triiodothyronine (T₃), and cortisol; for metabolites: free fatty acids (FFA) and glucose; and for the reproductive hormones: luteinizing hormone (LH), progesterone, estradiol-17β, estrone sulfate, and prostaglandin F₂. Delivery of rpST daily induced a 20- to 40-fold increase in plasma ST concentrations. Moreover, repeated administration of rpST resulted in a continuous increase in plasma IGF-I concentration (P<0.001), from 191.0±22.3–340.0±15.3 ng/mL 24 h after initial injection to 591.3±46.8 ng/mL after final injections. Mean serum insulin tended to be greater in rpST-treated gilts. Blood concentrations of T₄ were reduced (P<0.05) from day 14 of gestation in treated gilts while T₃ concentrations remained unchanged. Concentrations of both glucose and FFA were greater (P<0.01) and cortisol concentrations were unchanged in treated gilts. Changes in reproductive steroid hormones were minimally affected. Circulating progesterone (P=0.078), and estradiol-17β (P=0.087) concentrations tended to be lower in treated animals. These data show that treatment of pregnant gilts with rpST during early gestation mainly impacts metabolic rather than reproductive status.     

The effect of insulin and relaxin upon mitosis (in vitro) in mammary tissue from pregnant and lactating pigs

The rate of cellular proliferation in the mammary glands of pigs during late gestation and lactation was assessed by measuring the incorporation of ³H-thymidine (T₁) into the DNA of mammary gland explants in vitro. The T₁ showed a linear response over the first 9 hr in vitro, and was not affected by the addition of 500 ng insulin/ml medium. From day 100 to parturition the T₁ rose, reached a peak at 2 d after parturition and declined during lactation to the lowest levels seen at day 21 of lactation.

The inclusion of 0–1000 ng relaxin/ml medium on T₁ at 24–72 hr in vitro had no effect in stimulating T₁ in mammary tissue explants taken from either pregnant or lactating pigs.     

Extrathyroidal thyroxine-5′-monodeiodinase activity in cattle

The monodeiodination of thyroxine (T₄) to triiodothyronine (T₃) was studied in vitro using liver, kidney, and muscle obtained from two-year old Angus and Hereford steers. Tissues were homogenized in .1 M phosphate buffer-.25 M sucrose - 5 mM EDTA, pH 7.5, and centrifuged at 2000 × g for 30 min. Supernatants were incubated with T4 (1.3 μM) at 37 C and T₃ generated was measured by radioimmunoassay of an ethanol extract of the incubation mixture. The T₄ to T₃ conversion in Angus liver homogenate was dependent upon pH, temperature, duration of incubation (5–120 min), homogenate (.025–.20 g-eq tissue/ml), and substrate concentration (.32–6.43 μM T₄). The apparent K_m and V_max of the conversion were .64 μM T₄ and 1.87 ng T₃ generated/hr/mg protein, respectively. Mean T₄ to T₃ conversion in Angus liver and kidney was 1.37 and .22 ng T₃/hr/mg protein. The presence of 2 mM dithiothreitol (DTT), a sulfhydryl protective agent, significantly increased T₃ generation in liver and kidney (5.12 and 4.58 ng/hr/mg protein) and also revealed activity in muscle (05 ng/hr/mg protein). In liver and kidney from Hereford steers conversion activity was 2.89 and .48 in absence and 10.91 and 5.38 ng T₃/hr/mg protein in presence of DTT, respectively. These results demonstrate the presence of a very active enzymatic system responsible for the peripheral 5′-monodeiodination of T₄ to T₃ in cattle.     

Basal and hormone-stimulated metabolism in lambs varies with breed and diet quality

The present study investigated the effects of breed and diet quality on basal and hormone-stimulated energy metabolism in lambs. Twenty-four 7-mo-old merino (MM; n = 12) and second-cross (2X; n = 12) lambs were maintained indoors and fed ad libitum either a low-quality (7.8% crude protein [CP] and 8.1 MJ metabolizable energy [ME]/kg dry matter [DM]) or a moderate-quality (17.6% CP and 9.1 MJ ME/kg DM) diet in a crossover design. After 3 wk of feeding, lambs were injected intravenously with insulin (10 μg/kg body weight [BW]) and epinephrine (0.8 μg/kg BW) on consecutive days and blood samples were collected at -30, -15, -1, 3, 6, 10, 15, 20, 30, 45, 60, 90, and 120 min relative to time of injection. Lambs fed the low-quality diet had lower DM (P < 0.001), CP (P < 0.01), and ME (P < 0.001) intakes than lambs fed the moderate-quality diet. Baseline nonesterified fatty acid (NEFA) concentrations were higher (P < 0.001) in lambs fed a low-quality diet than in those fed a moderate-quality diet but there were no breed differences. Second-cross lambs had higher basal plasma concentrations of glucose (P < 0.001), lactate (P < 0.001), and cortisol (P < 0.02) than the MM lambs, although there was no effect of diet on any of these plasma variables. Insulin injection caused a rapid hypoglycemic response in all lambs but the response was more pronounced (P < 0.01) in MM lambs compared with 2X lambs. The cortisol response to insulin was twice as great (P < 0.05) in MM lambs compared with 2X lambs. There was a rebound in plasma NEFA concentrations after approximately 30 min postinjection that was most pronounced (P < 0.01) in MM lambs. Epinephrine injection caused a rapid increase in plasma NEFA, which tended to be lower in lambs fed the moderate-quality diet (P = 0.07) than in those fed the low-quality diet, but did not differ between breeds. Epinephrine injection caused rapid hyperglycemia, with the response being lower (P < 0.006) in lambs fed the moderate-quality diet compared with those fed the low-quality diet and greater (P < 0.050) in 2X than in MM lambs. Epinephrine injection caused a rapid increase in plasma lactate that tended to be greater (P = 0.07) in 2X lambs compared with MM lambs. The present study demonstrated clear breed differences in basal and hormone-stimulated metabolism, such that the 2X lambs appeared to be less sensitive to insulin and more sensitive to epinephrine than the MM lambs. These metabolic differences may be related to the fundamental differences in physiology that are associated with meat and wool production from 2X and MM breeds, respectively. They may also be related to adaptation of the MM breed to harsh environments through the ability of the body to metabolize fat resources, which are an efficient source of energy for survival.     

Inhibition of endogenous nitric oxide production influences ovine hindlimb metabolism independently of insulin concentrations

The hindlimb arteriovenous difference (AVD) model was used to determine whether 30 mg/ kg of the nitric oxide synthase (NOS) inhibitor L-NGnitroarginine methyl ester (hydrochloride; L-NAME) inhibited ovine NO synthesis and influenced muscle metabolism. Eight Border Leicester x Merino cross lambs (50 to 55 kg BW) were infused with saline (control) or saline containing L-NAME via an indwelling jugular vein catheter in a balanced randomized crossover design with 3 d between treatments. The abdominal aorta and deep femoral vein were catheterized for assessment of AVD of hind limb metabolism. Arterial hematocrit and insulin concentration and both arterial and venous concentrations of nitrate/nitrite (NOx), glucose, lactate, NEFA, and urea were determined. Infusion of L-NAME decreased arterial NOx concentrations (P = 0.049), indicating inhibition of systemic NO synthesis. Treatment had no effect on arterial (3.5 vs. 3.6 +/- 0.19 mmol/L for control and L-NAME lambs, respectively; P = 0.39) or venous (3.3 vs. 3.4 +/- 0.16 mmol/L, P = 0.55) plasma glucose concentrations or on glucose AVD (0.19 vs. 0.27 +/- 0.065 mmol/L, P = 0.20). There was an interaction (P = 0.038) between time and treatment, such that L-NAME initially increased the AVD of glucose (up to 180 m) divergent from control lambs. The response was then decreased before a possible inflection beyond 240 min. Infusion of L-NAME increased hindlimb venous NEFA (222 vs. 272 +/- 13.2 micromol/L, P = 0.007) and NEFA AVD (79.4 vs. -13.3 +/- 31.5 micromol/L, P = 0.018). These metabolic changes were independent of plasma insulin concentrations, which were not affected by L-NAME infusion (25.3 vs. 27.8 +/- 3.62 mU/L, P = 0.85). The increase in hindlimb lipolysis after L-NAME infusion does not seem to be due to increased lipolysis of plasma triacylglycerol because circulating arterial (155 vs. 142 +/- 20.8 micromol/L, P = 0.58), venous (154 vs. 140 +/- 20.5 micromol/L, P = 0.50), and AVD (1.0 vs. 2.9 +/- 3.17 micromol/L, P = 0.38) triacylglycerol concentrations were unaffected by L-NAME infusion. In conclusion, these data indicate that infusion of 30 mg of L-NAME/kg inhibits NO synthesis, which in turn influences fat and carbohydrate metabolism in the ovine hindlimb independently of plasma insulin concentrations.     

Relationship of thyroid status to growth hormone and insulin-like growth factor-I (IGF-I) in plasma and IGF-I mRNA in liver and skeletal muscle of cattle

Steers were made hyperthyroid or hypothyroid to study the effects of physiological alterations in thyroid hormone status on plasma growth hormone (GH) profiles, plasma insulin-like growth factor-I (IGF-I) concentrations, and relative abundance of IGF-I mRNA in skeletal muscle and liver. Eighteen yearling crossbred steers (360 to 420 kg) were randomly allotted to hyperthyroid (subcutaneous injection 0.6 μg/kg BW L-thyroxine for 10 d), hypothyroid (oral thiouracil; 0.25% diet plus 12.5 g capsule/d for 17 d), or control (subcutaneous injection 0.9% NaCl) treatment groups. Blood samples were taken for measurement of GH, IGF-I, thyroxine (T₄) and triiodothyronine (T₃) by RIA. Samples of liver and skeletal muscle were taken by biopsy for measurement of IGF-I mRNA by solution hybridization. Steers receiving thiouracil had 57 and 53% (P<.05) lower T₄ and T₃, respectively, than control steers (84.1 and 1.7 ng/ml). The hyperthyroid steers had 228 and 65% greater (P<.05) T₄ and T₃ than control steers. Neither increased nor decreased thyroid status had any significant effects on plasma GH profiles, liver IGF-I mRNA, or plasma concentration of IGF-I. There was no effect of thyroid hormone alteration on skeletal muscle IGF-I mRNA concentrations. The results of this study suggest that short-term changes in thyroid status of cattle had no major impact on the GH-IGF-I axis or skeletal muscle IGF-I mRNA.     

The influence of methimazole on the thyrotrophic and peripheral activity of thyrotrophin and thyrotrophin-releasing hormone in the chick embryo and growing chicken

Plasma concentrations of thyroxine (T₄) and triiodothyronine (T₃) were profoundly depressed both in chick embryos and growing chickens after methimazole (MMI) treatment. There was no response of T₄ and T₃ levels to TRH or TSH injections in the MMI group, either in embryos or growing chickens.

Peroxidase activity measured in the thyroid gland was significantly higher in embryos and growing chickens treated with MMI. However, neither TRH nor TSH affected this activity 2 hr after injection in either control or the MMI-treated group.

Hepatic 5′-monodeiodinase activity was significantly stimulated in the MMI-treated groups of embryos and growing chickens but only when additional sulphydryl groups (DTT) were provided. In embryos, monodeiodination activity 2 hr after TSH injection was not significantly different from control values for either DTT-stimulated or unstimulated conditions within the control and MMI-infused groups. However, in both control and MMI-treated embryos monodeiodination activity significantly increased 2 hr after TRH injection. In the growing chickens, monodeiodination activity 2 hr after TRH or TSH injection was not significantly different from control values in either stimulated or unstimulated conditions of each group.     

Enhanced non-esterified fatty acids and corticosterone in blood plasma of chickens treated with insulin are significantly depleted by reverse T: minor changes in hypoglycaemia

Previously, it has been observed that dexamethasone or adrenaline-induced hyperlipaemia in blood of chicken was significantly reduced after administration of reverse triiodothyronine (rT3). The present experiment was performed on chicken to determine the altered circulating non-esterified fatty acids (NEFA) induced by physiologically enhanced endogenous corticosterone and catecholamines may also be influenced by rT3. Rise of both hormones were induced by insulin administration. Changes in circulating glucose, corticosterone and catecholamines were additionally measured. Following insulin injection blood glucose fell on the average by 32.7% below control at 2 h of the experiment. Additional treatment with rT3 (rT3 + insulin group) gradually attenuated this decrease and at 4 and 6 h of the experiment it was 17.1% and 12.9% below control, respectively, suggesting on slight inhibition by rT3 of insulin-stimulated glucose utilization. Exposure to insulin significantly increased NEFA levels to about 670% above control group. Additional treatment with rT3 reduced this increase to 309% of control, suggesting inhibition of lipolysis by rT3. Similar alterations were observed in plasma corticosterone levels. Insulin treatment peaked the corticosterone levels maximally by 507.6% above control. Additional treatment with rT3 abolished this rise in the averages to 194.2% above control, possibly by interaction of rT3 with hypothalamo-adrenal axis. Insulin injection increased plasma catecholamines on the average by 21.5% and 53.4% for adrenaline and noradrenaline respectively. Supplementary treatment with rT3 intensified this rise by 55.6% and 71.6% respectively. The obtained results suggest on inhibitory effect of rT3 on hypoglycaemia, hyperlipaemia and plasma corticosterone concentrations in chickens treated with insulin. Contrary to this, rT3 enhanced the rise of plasma catecholamines due to insulin treatment. The obtained data favour the assumption that hypometabolic properties of rT3 depends mainly upon reduced supply of NEFA as a result of restricted lipolysis and to a lesser extent upon the supply of glucose.     

The effects of beta agonists on muscle cells in culture

Increases in protein synthesis of 12% were found with two myogenic cell lines (L6 and G8-1) on treatment for 6 hr with the beta-adrenergic agonist cimaterol. In L6 cells, propranolol blocked the effect. Protein breakdown measured over 18–24 hr was unchanged. The K_d for cimaterol binding to the L6 beta-receptor was 26 nM which was compatible with its EC₅₀ for the stimulation of protein synthesis (approx 5 nM). Evidence provided with muscle cell lines indicatesa direct effect of cimaterol on protein synthesis, which may contribute to muscle accretion in cimaterol-fed animals.     

Effect of exogenous thyrotropin-releasing hormone (TRH) administration on plasma levels of triiodothyronine (T3), thyroxine (T4) and growth hormone (GH) in chronically catheterized suckling piglets.

The purpose of the present study was to determine experimental conditions to stimulate secretion of thyroid hormones (T₃ and T₄) with thyrotropin-releasing hormone (TRH) injections in suckling piglets during the first weeks of postnatal life. Three consecutive experiments were conducted. Four 10–20 d old piglets were i.m. injected with 0, 20, 100, 500 μg (experiment 1) or 0, 4, 20, 100 μg TRH/kg BW (experiment 2) according to a 4 × 4 latin square design involving different litters in each experiment. Blood samples were taken −15, −1, 15, 30, 45, 60, 90, 120 180 and 300 min after TRH injection in experiment 1, and −.25, −.08, .25, .5, 1, 2, 4, 6, 8, 12, 24, 30, 36, 48, 60 and 72 hr after TRH injection in experiment 2. T₃ and T₄ levels were significantly (P<.01) increased as soon as 30 and 45 min after TRH injection, respectively. Maximal levels of T₃ and T₄ were obtained 2 and 4 hr after the injection of 100 μg TRH. T₃ and T₄ returned to basal levels within 6 and 8 hr post injection, respectively. Plasma pGH levels were significantly (P<.001) increased 15 min after TRH injection in piglets injected with 500 μg. In experiment 3, 100 μg TRH/kg BW were injected i.m. either daily or every other day from .0 to 23 days of age. Results showed that T₄ response to TRH did not decrease after repeated injections. These results indicate that daily i.m. injections of 100 μg TRH/kg BW can be used to increase thyroid hormone levels for at least 13 d in the young suckling piglet.     

Addition of fat to the diets of lactating sows: II. Effects on hormone-sensitive lipase activity, energy mobilization in response to epinephrine, and plasma insulin and glucose concentrations.

Four experiments were conducted to determine the effects of dietary fat on lipolysis in lactating sows. In Exp. 1, a 6 x 6 Latin square was used to determine the optimal dosage of epinephrine for use in a subsequent epinephrine challenge. Peak concentrations of plasma glucose and response area increased linearly (P < .10) with epinephrine dosage. However, plasma NEFA peak and response area were quadratically affected (P < .05 and .06, respectively) by epinephrine dosage, with a minimum NEFA peak concentration observed at .4 microg/kg and a maximum at 1.6 microg/kg. In Exp. 2, the effect of dietary tallow on the response to epinephrine infusion (1.6 microg/kg BW) was examined. No differences (P > .10) between treatments were observed in NEFA, glycerol, or peak concentrations of plasma glucose following epinephrine administration. In Exp. 3, the effect of dietary fat on hormone-sensitive lipase activity was examined. Sows (n = 36) were fed diets containing either 0 or 10% added tallow. Hormone-sensitive lipase activity on d 28 of lactation was increased by the addition of tallow to the diet (P = .06). No effect of dietary tallow was observed on hormone-sensitive lipase activity of adipose tissue on d 21 of lactation (P > .10) in Exp. 3 (n = 16 sows) and Exp. 4 (n = 30 sows). In summary, diets containing 10% added tallow did not alter the rate of lipolysis, as measured by exogenous epinephrine challenge, in adipose tissue of lactating sows.     

Total and free iodothyronine levels of growing Thoroughbred foals: Effects of weaning and gender

The aim of this study was investigate the effect of growing associated with different gender on circulating total and free iodothyronine concentrations during the first 13 mo of age in foals. In addition, we investigated the evolution of circulating concentrations of thyroid hormones during the first 3 d of weaning. Blood was collected from 13 clinically healthy Thoroughbred foals every month. All foals were weaned at the 4 mo and blood samples were taken also at 24, 48 and 72 h after weaning. The results obtained showed growing effects for tri-iodothyronine (T₃), thyroxine (T₄), free tri-iodothyronine (fT₃) and free thyroxine (fT₄) values (P < .001).

Serum T₃ concentrations averaged respectively 2.89 and 0.29 nmol/L at 7 and 9 mo. Serum T₄ concentrations averaged respectively 100.17 and 21.77 nmol/L at 1 and at 10 mo. Serum fT₃ concentrations averaged respectively 6.96 and 1.50 pmol/L at 1 and 4 mo. Serum fT₄ concentrations averaged respectively 31.40 and 4.93 pmol/L at 1 and 9 mo. Significant correlations between T₃, T₄, fT₃ and fT₄ with body weight (BW) and between T₃, T₄ and fT₄ with age were observed.

Weaning effects (P < .001) were shown for T₃ and fT₄ levels. No differences (P > .05) in T₄ and fT₃ levels were observed over the 3-day period. Gender effects (P < .001) were shown for T₃, T₄, fT₃, and fT₄ levels. Significant correlations between T₄ and fT₄ with BW and age were observed in colts and fillies. T₃ concentrations were correlated with age only in colts and fT₃ with BW only in colts. The results obtained seem to lend support to the recognized effects of growing and weaning in modulating the thyroid function of Thoroughbred foals. In fact, significant and differentiated effects of growing and weaning on total and free iodothyronine levels have been demonstrated.     

Effect of cimaterol on sheep adipose tissue lipid metabolism

Effects of dietary cimaterol (5 mg/kg) on adipose tissue metabolism of wether lambs were studied. Lipogenesis, lipolysis, fatty acid composition and adipocyte size and number were measured. Cimaterol feeding increased lipogenesis; however, this effect was not statistically significant. Insulin (1,000 microU/ml) stimulated lipogenesis of adipose tissue from control sheep. However, this elevated rate was abolished by in vitro cimaterol. Insulin had no stimulatory effect on lipogenesis in cimaterol-fed sheep. Lipolysis was depressed by cimaterol feeding. However, 10(-4) M cimaterol stimulated lipolysis in the adipose tissue from both control and cimaterol-fed sheep. Insulin inhibited stimulated lipolysis in adipose tissue from control sheep but had no effect on the stimulated lipolysis in cimaterol-fed sheep. Mean adipocyte diameter was smaller (from 74 to 70 microns) and adipocyte size distribution also was changed in the cimaterol-fed sheep. Adipocyte number per gram of tissue was not affected by cimaterol. There was a significant increase in percentage of unsaturated fatty acids in adipose tissue from cimaterol-fed sheep. These results indicate that lipogenic and lipolytic responses to insulin and cimaterol in sheep adipose tissue were altered by cimaterol feeding. The carcass fat content decrease in cimaterol-fed sheep may be attributed to the reduction in adipocyte size.