Effect of naloxone on serum luteinizing hormone, cortisol and prolactin concentrations in anestrous beef cows

Two experiments were conducted with the opioid antagonist naloxone to determine the effect of opioid receptor blockade on hormone secretion in postpartum beef cows. In Exp. 1, nine anestrous postpartum beef cows were used to measure the effect of naloxone on serum luteinizing hormone (LH), cortisol and prolactin concentrations. Cows received either saline (n = 4) or 200 mg naloxone in saline (n = 5) iv. Blood samples were collected at 15-min intervals for 2 h before and after naloxone administration. Serum LH concentrations increased (P less than .01) in naloxone-treated cows from 1.8 +/- .04 ng/ml before treatment to 3.9 +/- .7 ng/ml and 4.2 +/- .5 ng/ml at 15 and 30 min, respectively, after naloxone administration. In contrast, LH remained unchanged in saline-treated cows (1.6 +/- .3 ng/ml). Serum cortisol and prolactin concentrations were not different between groups. In Exp. 2, 12 anestrous postpartum beef cows were used to examine the influence of days postpartum on the serum LH response to naloxone. Four cows each at 14 +/- 1.2, 28 +/- .3 and 42 +/- 1.5 d postpartum received 200 mg of naloxone in saline iv. Blood samples were taken as in the previous experiment. A second dose of naloxone was administered 2 h after the first, and blood samples were collected for a further 2 h. Serum LH concentrations increased (P less than .01) only in cows at 42 d postpartum.(ABSTRACT TRUNCATED AT 250 WORDS)     

Regression of induced corpora lutea in mature cyclic gilts by human chorionic gonadotropin.

This study was conducted to determine whether chronic hCG treatment would cause regression of induced corpora lutea (CL) in mature cyclic gilts. Thirty-two mature gilts that had displayed one or more estrous cycles of 18 to 22 d were used. Sixteen gilts were hysterectomized (HYSTX) on d 6 to 9 (d 0 = onset of estrus) and their CL were marked with charcoal (spontaneous group). Sixteen gilts (induced group) were injected with 1,500 IU of pregnant mare's serum gonadotropin (PMSG) on d 6 and 500 IU of hCG on d 9 (day of hCG = d 0 of the induced cycle). Ovulation was assumed to occur on d 2 of the induced cycle. Induced gilts were HYSTX on d 8 to 9 (d 17 to 18 of the original spontaneous cycle) and their CL were marked with charcoal. Only gilts (n = 14) in which induced CL were present and in which the original CL had regressed were then subjected to treatment with saline or hCG. From d 10 to 29, gilts with spontaneous CL were injected daily with 500 IU of hCG (n = 8) or saline (n = 8). From d 10 to 29 of the induced cycle, induced gilts were injected daily with 500 IU of hCG (n = 6) or saline (n = 8). Jugular blood samples were collected every other day from all gilts beginning on the 1st d of daily hCG treatment and quantified for estradiol and progesterone by RIA. On the day after the last hCG injection, the number of charcoal-marked CL and charcoal-marked corpora albicantia (CA) were determined.(ABSTRACT TRUNCATED AT 250 WORDS)     

N-methyl-d,l-aspartate modulation of pituitary hormone secretion in the pig: Role of opioid peptides

Sixteen ovariectomized (OVX) mature gilts, averaging 139.6 ± 3.1 kg body weight (BW) were assigned randomly to receive either progesterone (P, 0.85 mg/kg BW, n=8) or corn oil vehicle (OIL, n=8) injections im twice daily for 10 d. On the day of experiment, all gilts received either the EAA agonist, N-methyl-d,l-aspartate (NMA; 10 mg/kg BW, iv) alone or NMA plus the EOP antagonist, naloxone (NAL, 1 mg/kg BW, iv), resulting in the following groups of 4 gilts each: OIL-NMA, OIL-NMA-NAL, P-NMA and P-NMA-NAL. Blood samples were collected via jugular cannula every 15 min for 6 hr. All pigs received NMA 5 min following pretreatment with either 0.9% saline or NAL 2 hr after blood collection began and a GnRH challenge 3 hr after NMA. Administration of NMA suppressed (P<0.03) LH secretion in OIL-NMA gilts and treatment with NAL failed to reverse the suppressive effect of NMA on LH secretion in OIL-NMA-NAL gilts. Similar to OIL-NMA gilts, NMA decreased (P<0.03) mean serum LH concentrations in P-NMA gilts. However, in P-NMA-NAL gilts, serum LH concentrations were not changed following treatment. All gilts responded to GnRH with increased (P<0.01) LH secretion. Additionally, administration of NMA increased (P<0.01) growth hormone (GH) and prolactin (PRL) secretion in both OIL-NMA and P-NMA gilts, but this increase in GH and PRL secretion was attenuated (P<0.01) by pretreatment with NAL in OIL-NMA-NAL and P-NMA-NAL gilts. Serum cortisol concentrations increased (P<0.01) in all gilts and the magnitude of the cortisol response was not different among groups. In summary, results of the present study confirmed previous findings that NMA suppresses LH secretion in both oil- and P-treated OVX gilts, but we failed to provide definitive evidence that EOP are involved in the NMA-induced suppression of LH secretion. However, NMA may, in part, activate the EOP system which in turn increased GH and PRL secretion in the gilt.     

Associated luteinizing hormone-releasing hormone and luteinizing hormone secretion in ovariectomized gilts.

The secretion of luteinizing hormone-releasing hormone (LHRH) and its temporal association with pulses of luteinizing hormone (LH) was examined in ovariectomized prepuberal gilts. Push-pull cannulae (PPC) were implanted within the anterior pituitary gland and LHRH was quantified from 10 min (200 microliters) perfusate samples. Serum LH concentrations were determined from jugular vein blood obtained at the midpoint of perfusate collection. Initial studies without collection of blood samples, indicated that LHRH secretion in the ovariectomized gilt was pulsatile with pulses comprised of one to three samples. However, most pulses were probably of rapid onset and short duration, since they comprised only one sample. Greater LHRH pulse amplitudes were associated with PPC locations within medial regions of the anterior pituitary close to the median eminence. In studies which involved blood collection, LH secretion was not affected by push-pull perfusion of the anterior pituitary gland in most gilts, however, adaptation of pigs to the sampling procedures was essential for prolonged sampling. There was a close temporal relationship between perfusate LHRH pulses and serum LH pulses with LHRH pulses occurring coincident or one sample preceding serum LH pulses. There were occasional LHRH pulses without LH pulses and LH pulses without detectable LHRH pulses. These results provide direct evidence that pulsatile LHRH secretion is associated with pulsatile LH secretion in ovariectomized gilts. In addition, PPC perfusion of the anterior pituitary is a viable procedure for assessing hypothalamic hypophyseal neurohormone relationships.     

Opioid inhibition stimulates luteinizing hormone and prolactin secretion in the gilt

Ten gilts on day 6·11 of the estrous cycle (onset of estrus = day 0) were given 115 mg of naloxone (NAL), an opioid antagonist, in saline i.v. (n = 5) or saline Lv. (n = 5). Jugular blood was collected at 15 min intervals for 2 hr before and 4 hr after treatment. Serum LH concentrations were 0.4 ± 0.1 ng/ml before NAL treatment, increased (P<.01) to 4.3 ± 0.7 ng/ml at 15 min following NAL treatment and returned to control concentrations by 75 minutes. Serum PRL concentrations were 5.0 ± 0.1 ng/ml before NAL treatment, increased (P<.05) to 14.8 ± 2.9 ng/ml at 30 min following NAL treatment and returned to control concentrations by 120 minutes. Serum LH and PRL concentrations were 0.5 ± 0.1 ng/ml and 5.2 ± 0.4 ng/ml, respectively, at 15 min following saline treatment and remained unchanged throughout the blood sampling period. Four of the 5 NAL treated gilts responded with an increase in both serum LH and PRL concentrations. The mean of serum progesterone concentrations, quantitated in samples taken every 2 hr, were similar for controls (22.7 ± 1.8 ng/ml) and NAL (26.5 ± 1.4 ng/ml) treated gilts. The gilt which failed to respond to NAL had nondetectable concentrations of serum progesterone and was excluded from analysis. These data indicate that the opioids modulate LH and PRL secretion during the luteal phase of the estrous cycle.     

Comparison of physiological indicators of chronic stress in confined and nonconfined gilts

Two experiments were conducted to determine if confinement-induced delayed puberty in gilts was due to chronic physiological stress imposed by confinement housing. In both experiments, crossbred gilts, raised in total confinement, were moved to an outside dirt lot (nonconfined) or to a single pen in a confinement finishing unit (confined) at 100 to 110 d of age. Beginning at 150 d of age, estrus was checked daily with a boar to determine age at first estrus. Gilts were necropsied at 270 d of age. In Exp. I, 19 confined and 19 nonconfined gilts were cannulated by jugular puncture at 185 d of age. The day after cannulation, blood samples were collected for 4 h, 200 IU porcine adrenocorticoptropic hormone (ACTH) was injected via the cannulae and blood samples were collected for an additional 8 h. Serum cortisol, progesterone, luteinizing hormone (LH) and prolactin (PRL) concentrations were determined. In Exp. II, both jugular veins of six confined and six nonconfined gilts were cannulated at 204 d of age. The day after cannulation, blood samples were collected for 4 h and cortisol was continuously infused for the last 2 h of the blood collection period. Cortisol metabolic clearance rate (MCR) and secretion rate (SR) were determined. By 270 d of age, 21 of 28 (75%) nonconfined gilts and 11 of 31 (35.5%) confined gilts (P less than .01) in Exp. I and 18 of 25 (72%) nonconfined gilts and 12 of 25 (48%) confined gilts (P less than .06) in Exp. II had exhibited estrus and ovulated.(ABSTRACT TRUNCATED AT 250 WORDS)     

Orexin-B modulates luteinizing hormone and growth hormone secretion from porcine pituitary cells in culture

To test the hypothesis that orexin-B acts directly on the anterior pituitary to regulate LH and growth hormone (GH) secretion, anterior pituitary cells from prepuberal gilts were studied in primary culture. On day 4 of culture, 10(5) cells/well were challenged with 0.1, 10 or 1000 nM GnRH; 10, 100 or 1000 nM [Ala15]-hGRF-(1-29)NH2 or 0.1, 1, 10 or 100 nM, orexin-B individually or in combinations with 0.1 and 1000 nM GnRH or 10 and 1000 nM GRF. Secreted LH and GH were measured at 4 h after treatment. Basal LH and GH secretion (control; n = 6 pigs) was 183 +/- 18 and 108 +/- 4.8 ng/well, respectively. Relative to control at 4 h, all doses of GnRH and GRF increased (P < 0.0001) LH and GH secretion, respectively. All doses of orexin-B increased (P < 0.01) LH secretion, except for the 0.1 nM dose. Basal GH secretion was unaffected by orexin-B. Addition of 1, 10 or 100 nM orexin-B in combinations with 0.1 nM GnRH increased (P < 0.001) LH secretion compared to GnRH alone. Only 0.1 nM (P = 0.06) and 100 nM (P < 0.001) orexin-B in combinations with 1000 nM GnRH increased LH secretion compared to GnRH alone. All doses of orexin-B in combination with 1000 nM GRF suppressed (P < 0.0001) GH secretion compare to GRF alone, while only 0.1 nM orexin-B in combination with 10 nM GRF suppressed (P < 0.01) GH secretion compared to GRF. These results indicate that orexin may directly modulate LH and GH secretion at the level of the pituitary gland.     

Antimicrobial resistance in Clostridium perfringens isolates from broilers in Belgium

The antimicrobial susceptibility of Clostridium perfringens strains isolated from Belgian broilers between May and September 2007 was investigated. All 39 tested isolates were sensitive to enrofloxacin, erythromycin, tylosin, florfenicol and bacitracin. Twenty-six (66%) and 24 (61%) out of the 39 tested isolates showed acquired resistance to tetracycline and lincomycin, respectively. The C. perfringens isolates were also screened by PCR for the presence of the resistance genes tet(K), tet(L), tet(M), tetB(P), tet(O), tet(W), lnu(A) and lnu(B). In 22/26 tetracycline resistant strains and 7/24 lincomycin resistant strains, resistance could be attributed to one or more of these genes. An extended frequency distribution range of MICs was seen for ampicillin. These data are consistent with data derived from studies carried out in 1980 and in 2004, indicating that no changes in antimicrobial resistance patterns have taken place during time in C. perfringens isolates from broilers in Belgium.     

Influence of clay minerals on the formation of humic substances by Epicoccum nigrum and Stachybotrys chartarum

The influence of montmorillonite, kaolinite and finely ground quartz on the formation of humic acid-type polymers by Epicoccum nigrum and Stachybotrys chartarum was studied. The fungi were grown in shake and in deep (4 cm) or shallow (1.5 cm) stationary cultures. In general, clay shortened the time required for the formation of dark colored substances and increased the amounts of humic acid-type polymers in the culture solutions or extracted from the cells with NaOH. In some tests, the time of maximum humic polymer accumulation was much earlier in the presence of clay but total amounts formed in check cultures eventually equalled that of the cultures with clay additions. The ratios of the total humic acid to the total cell substance or to the glucose consumed were also generally increased by montmorillonite. Kaolinite and quartz exerted a similar but less pronounced effect. In deep stationary cultures of S. chartarum, total growth and humic acid formation was sometimes depressed by the higher concentrations of montmorillonite but in shallow cultures biomass and humic acid formation were increased. In cultures with an initial pH of 6.0, humic acid polymers were formed in the cells before they appeared in the solutions. During autolysis, some of the cellular polymers were either released into the medium or became more readily extractable with NaOH. The clays did not appreciably alter the chemical properties of the humic polymers, namely, C and N contents, exchange capacity, COOH groups, total acidity, or phenols released upon sodium amalgam reduction. In the presence of clays, phenols were formed more quickly in the culture solutions, but the kinds and relative amounts did not appear to be altered. Clays did not significantly affect oxygen consumption during autoxidation of phenol mixtures. The observations indicate that, by affecting growth and metabolism, the clays indirectly influence phenolic polymer formation.