Concentrations of luteinizing hormone, follicle stimulating hormone and prolactin following transection of the pituitary stalk in ovariectomized ewes

Two experiments (Spring and Fall) were conducted in ovariectomized ewes to determine changes in pituitary hormone secretion immediately after pituitary stalk-transection. Ewes underwent either pituitary stalk-transection (SS), sham-transection (SH) or administration of anesthesia only (AO). Stalk-transected, but not sham-operated or anesthetized ewes had polyuria and polydipsia for 7 to 14 days after surgery. Concentrations of luteinizing hormone (LH), follicle stimulating hormone (FSH) and prolactin were measured in peripheral blood samples collected every 10 minutes for a six-hour period. Results were comparable for each season. During the six hours following surgery or removal from anesthesia, concentrations of LH declined in all ewes, but more slowly in SS ewes. No differences in patterns or mean concentrations of FSH were observed. Immediately after surgery, concentrations of prolactin were elevated, then declined in SH and SS ewes. The decrease was greater in SH than SS ewes. Data are consonant with the view that hypothalamic inhibition as well as LHRH stimulation regulate gonadotropin release by the pituitary.     

Concentrations of ovarian and pituitary hormones following prostaglandin F2 alpha-induced luteal regression in ewes varies with day of the estrous cycle at treatment

Prostaglandin F2 alpha (PGF2 alpha) was injected on d 5, 8 or 11 postestrus in ewes to determine how stage of the estrous cycle would affect PGF2 alpha-induced changes in concentrations of ovarian and pituitary hormones and intervals to the onset of estrus and the preovulatory surge of luteinizing hormone (LH). Initial concentrations of progesterone and average values during the 12 h after PGF2 alpha were related positively to the day of cycle on which PGF2 alpha was administered. Patterns of decline in progesterone after injection of PGF2 alpha were similar among the 3 d. Concentrations of LH in plasma increased in a similar manner from 0 to 12 h in all ewes. After 12 h LH continued to increase, plateaued or declined in ewes treated on d 5, 8 or 11, respectively. Initial concentrations of follicle stimulating hormone (FSH) in plasma were related positively to day of treatment. After treatment with PGF2 alpha, FSH increased within 2 h on d 5 but declined by that time on d 8 or 11. Concentrations of estradiol following treatment did not vary with day. The onset of estrus and the preovulatory surge of LH occurred at 36 and 35, 40 and 45, and 48 and greater than 48 h in ewes treated on d 5, 8 or 11, respectively. It is concluded that: 1) the initial increase in LH is dependent on a decrease in plasma progesterone and 2) differences in patterns of secretion of gonadotropins before the preovulatory surge of LH might be caused by differences in progesterone or progesterone:-estradiol ratio when luteal regression is induced on different days of the estrous cycle.     

Gonadotropin concentrations, follicular development, and luteal function in pituitary stalk-transfected ewes treated with bovine follicular fluid.

Two experiments, each arranged as a 2 x 2 factorial, were conducted in ewes to examine direct effects of bovine follicular fluid (bFF) on follicular development and luteal function and to further characterize follicular development and luteal function after pituitary stalk transection (SS). In Exp. 1, ewes were sham-operated or SS on d 6 of an estrous cycle and received 5 ml of saline or bFF three times daily on d 5 through 11 of the same cycle. In Exp. 2, all ewes were SS on d 6 of an estrous cycle and treated with saline or bFF three times daily on d 5 through 11 and with ovine FSH (60 micrograms; NIADDK-oFSH-16) or saline (1.2 ml) from d 7 to 11. In Exp. 2, ewes were ovariectomized on d 11 to assess effects of treatments on follicular development and luteal function. In both experiments, concentrations (ng/ml) of FSH on d 7 were suppressed (P less than or equal to .005) by bFF compared with saline (.50 +/- .17 vs 1.63 +/- .15) and remained suppressed (P less than or equal to .005) through d 11 (.46 +/- .12 vs 1.54 +/- .12). Replacement therapy (oFSH) restored concentrations of FSH. Concentrations of LH were not affected by bFF but were elevated (P less than or equal to .05) 1 d after SS (d 7; .88 +/- .09 vs .56 +/- .09) and remained elevated (P less than or equal to .05; 1.31 +/- .20 vs .65 +/- .11) from d 6 through 11. Concentrations of progesterone were unaffected by SS.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of dopamine, norepinephrine and serotonin on secretion of luteinizing hormone, follicle-stimulating hormone and prolactin in ovariectomized, pituitary stalk-transected ewes

Two experiments were conducted in ovariectomized, pituitary stalk-transected ewes to determine if dopamine (DA), norepinephrine (NE) or serotonin (5-HT) alter secretion of luteinizing hormone (LH), follicle-stimulating hormone (FSH) and prolactin (PRL). In experiment 1, ewes were infused (iv) with saline (control), DA (66 micrograms/kg/min), NE (6.6 micrograms/kg/min) or 5-HT (6.6 micrograms/kg/min). Treatments did not alter pulse frequency, but 5-HT increased (P less than .05) amplitude of pulses of LH and mean concentrations of LH, DA and NE were without effect on basal secretion of LH. DA but not NE or 5-HT decreased (P less than .05) the release of LH in response to gonadotropin hormone-releasing hormone (GnRH, 25 micrograms, im). Concentrations of FSH were not affected by treatments. Secretion of PRL was reduced (P less than .05) by treatment with DA and NE but not 5-HT. Each amine reduced (P less than .05) the release of PRL in response to thyrotropin-releasing hormone (TRH; 3 micrograms, im). In experiment 2, ewes were given DA at doses of 0, 0.66, 6.6 or 66.0 micrograms/kg/min, iv. No dose altered basal LH, but each dose reduced (P less than .05) basal and TRH-induced release of PRL. Key findings from these studies include direct pituitary action for: (1) 5-HT enhanced basal secretion of LH, (2) suppression of GnRH-induced secretion of LH by DA. (3) DA and NE inhibition of PRL secretion, and (4) DA, NE and 5-HT inhibition of release of PRL in response to TRH.     

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.     

Androgen and estradiol effects on gonadotropin secretion and response to GnRH in ovariectomized pony mares

In Exp. 1, 16 long-term ovariectomized pony mares were used to determine the effects of treatment with estradiol benzoate (EB) and dihydrotestosterone (DHT) benzoate alone, and in combination, on secretion of follicle stimulating hormone (FSH) and luteinizing hormone (LH) in daily blood samples and after three consecutive injections of gonadotropin releasing hormone (GnRH). Administration of EB alone, or in combination with DHT, every other day for 11 d reduced (P less than .05) concentrations of FSH and increased (P less than .05) concentrations of LH in daily blood samples, and increased (P less than .05) the secretion of both gonadotropins after administration of GnRH. Treatment with DHT alone had no effect (P greater than .10) on LH or FSH concentrations in daily blood samples and no effect on the LH response to exogenous GnRH. There was no interaction (P greater than .10) between DHT and EB treatment for any hormonal characteristic. In Exp. 2, the control mares and mares treated with DHT in Exp. 1 were equally allotted to treatment with vehicle or testosterone propionate (TP) every other day for six injections, and then GnRH was administered as in Exp. 1. Treatment with TP had no effect (P greater than .10) on LH or FSH concentrations in daily blood samples but increased (P less than .05) the FSH response to exogenous GnRH, confirming our findings in previous experiments. It is concluded that the TP-induced stimulation of FSH secretion after exogenous GnRH in ovariectomized mares may involve estrogens produced from aromatization of the injected androgen.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of suckling, progestogen-impregnated pessaries or hysterectomy on ovarian function in autumn-lambing postpartum ewes

In three experiments, we examined the effects of suckling, progestogen treatment, hysterectomy or exogenous gonadotropin releasing hormone (GnRH) on ovarian function in autumn-lambing, postpartum ewes. In each experiment, GnRH was injected on approximately d 25 postpartum. Suckling reduced (P less than .01) GnRH-induced release of luteinizing hormone (LH) but not of follicle stimulating hormone (FSH), and reduced (P less than .05) the proportion of ewes that developed corpora lutea in response to GnRH. Suckling had no effect on duration (8.8 d) of GnRH-induced luteal phases. Progestogen prior to GnRH increased (P less than .01) the duration of the first luteal phase (10.1 vs 7.6 d; progestogen-treated ewes vs control ewes), but progestogen did not affect the release of LH or FSH. Progestogen treatment did not alter the interval from parturition to the first detected estrus (42.6 d). The concentration of 13,14-dihydro-15-keto-PGF2 alpha (PGFM) just after lambing was greater than 400 pg/ml of jugular plasma, but concentrations of PGFM declined thereafter. Hysterectomy the day after lambing hastened (P less than .001) the decline in concentrations of PGFM, indicating that prostaglandins from the postpartum uterus probably caused the high concentrations of PGFM in jugular plasma. Hysterectomy reduced (P less than .05) the interval from parturition to detectable luteal function (19.6 vs 25.3 d) and enhanced (P less than .001) luteal production of progesterone. This study of autumn-lambing ewes indicates that the uterus has a negative effect on ovarian function and that suckling and progestogen affect ovarian response to GnRH.     

Anovulation and plasma hormone concentrations after administration of dexamethasone during the middle of the luteal phase in sows undergoing estrous cycles

The effect of glucocorticoids on early follicular growth in sows undergoing normal estrous cycles was evaluated by administration of dexamethasone during the middle of the luteal phase. Plasma specimens were obtained for measurement of luteinizing hormone (LH), follicle-stimulating hormone (FSH), progesterone, and estradiol-17 beta concentrations. Fifteen sows were used. Control sows (n = 5) were given physiologic saline solution twice daily from day 9 to day 14 of the estrous cycle. Sows of the second group (n = 5) were given dexamethasone (30 micrograms/kg of body weight, IM) similarly, and those of the third group (n = 5) were given dexamethasone plus gonadotropin-releasing hormone (GnRH; 50 micrograms at 6-hour intervals, IV). Plasma specimens, obtained twice daily from day 8 through day 26, indicated that progesterone production and luteal regression were not inhibited by any of the 3 treatment regimens. Although preovulatory plasma estradiol concentration increased in control sows, such was not observed in the sows treated with dexamethasone or dexamethasone plus GnRH (P less than 0.01). Ovulation, with formation of corpora lutea, occurred in gilts given saline solution. Dexamethasone administration resulted in persistence of 19 to 41 follicles/ovary (2 to 4 mm in diameter), and dexamethasone-plus-GnRH treatment resulted in 6 to 18 follicles/ovary (5 to 6 mm in diameter). Plasma was obtained at 15-minute intervals for 12 hours to compare the effect of treatment on hormone concentrations on day 12 of the estrous cycle with the values on day 8.(ABSTRACT TRUNCATED AT 250 WORDS)     

Increased ovulation rate of adult ewes treated with anti-bovine LH antiserum during the normal breeding season

Adult Suffolk ewes (n = 14) were treated on d 10 of the estrous cycle with anti-bovine luteinizing hormone (LH) antiserum. Control ewes (n = 10) were treated with normal horse serum. Estrous behavior and the number of corpora lutea and ovarian follicles were examined at the subsequent estrous cycle. Daily plasma concentrations of progesterone (P4), follicle stimulating hormone (FSH) and estradiol were determined before and after treatment. Ewes treated with antiserum had a higher (P less than .05) ovulation rate (2.7 +/- .2) than did controls (2.1 +/- .1). No differences were found in the numbers of large (greater than 5 mm) or small (less than 5 mm) follicles between treatment groups. Estrus was delayed (P less than .025) approximately .6 d/in ewes treated with antisera. Immunoreactive FSH increased (P less than .05) within 1 d after treatment and remained higher than the controls for 5 d. Peak estradiol concentrations occurred on d 17 for treated ewes compared with peak concentrations on d 15 or 16 for control ewes. The P4 concentrations were generally less (P less than .025) in treated ewes throughout the luteal phase of the treatment cycle. These data demonstrate that ovulation rate is increased in ewes treated with LH antiserum. The marked increase in plasma FSH suggests a possible mechanism whereby ovulation rate is enhanced.     

Suppressive action of gonadotropin-releasing hormone and luteinizing hormone on function of the developing ovine corpus luteum

Experiments were conducted to examine the effects of exogenous GnRH and LH on serum concentrations of progesterone (P4) in the ewe. Ewes in Exp. 1 and 2 were laparotomized on d 2 of an estrous cycle and ewes with corpora lutea (CL) in both ovaries were unilaterally ovariectomized. Ewes with CL in one ovary only were not ovariectomized. While they were anesthetized, ewes (n = 5) were injected with 25 micrograms GnRH (Exp. 1) or 50 ng GnRH (Exp. 2) into the artery supplying the ovary bearing the CL. Control ewes (n = 5 in each experiment) were injected similarly with saline. In Exp. 3, six ewes were injected i.v. (jugular) on d 2 with 100 micrograms oLH (t = 0) and 50 micrograms oLH at 15, 30 and 45 min; six control ewes were injected similarly with saline. Jugular blood was collected from all ewes at frequent intervals after treatment for LH analysis and on alternate days of the cycle through d 10 or 11 for P4 analysis. Treatment with 25 micrograms GnRH increased serum concentrations of LH at 15, 30, 45 and 60 min postinjection (P less than .001) and reduced serum concentrations of P4 on d 7 through 11 (treatment x day interaction; P less than .05). Injection with 50 ng GnRH caused a slight increase in serum concentrations of LH at 15 min but had no effect on serum concentrations of P4.(ABSTRACT TRUNCATED AT 250 WORDS)     

The role of noradrenaline in the generation of the preovulatory LH surge in the ewe

Increasing plasma estrogen (E) levels during the follicular phase of the estrous cycle trigger the pre-ovulatory surge of gonadotropin-releasing hormone (GnRH)/LH. Noradrenaline (NA)-producing cells of the brain stem are involved in regulating GnRH cells and project to the preoptic area (POA) and bed nucleus of stria terminalis (BnST). Input to GnRH cells may be direct or indirect, via relay neurons in the POA/BnST. To investigate this, we ascertained whether an ₁-adrenergic antagonist would block/delay the LH surge in ovariectomised (OVX), E-treated ewes. E benzoate (EB) (50 μg) was injected (i.m.) and Doxazosin (100 nmol/h) or vehicle was infused into the third ventricle 2–26 h after EB injection. Doxazosin reduced the magnitude of the LH surge, but did not affect timing. To determine if NA is released in the POA/BnST of cyclic ewes, we immunostained dopamine-β-hydroxylase (DBH) in terminal fields. Reduced numbers of varicosities staining for DBH indicates release of NA. The number of varicosities immunostained for DBH was reduced in the dorsal and lateral BnST during the follicular phase and during the preovulatory LH surge compared to the luteal phase. These data suggest that noradrenergic mechanisms are involved in generation of the GnRH/LH surge via projections to the BnST and relay to GnRH cells. Since Doxasozin reduced the magnitude of the LH surge in the E-treated OVX ewe, and release of NA in cyclic ewes occurred during the follicular phase of the estrous cycle, we speculate that NA is a permissive factor in surge generation. Thus, increased noradrenergic activity is not a trigger mechanism for initiation of the surge.     

Response of the bovine corpus luteum to increased secretion of luteinizing hormone induced by exogenous gonadotropin releasing hormone

Two experiments were conducted to investigate the response of the bovine corpus luteum to surges of luteinizing hormone (LH) induced by natural gonadotropin-releasing hormone (GnRH) administered twice during the same estrous cycle. In experiment 1, eight mature beef cows, each cow serving as her own control, were injected intravenously (iv) with saline on days 2 and 8 of the cycle (day of estrus = day 0 of the cycle), then with 100 micrograms GnRH on days 2 and 8 of the subsequent cycle. Jugular blood samples were taken immediately prior to an injection and at 15, 30, 45, 60, 120 and 240 min postinjection, to quantitate changes in serum luteinizing hormone. Blood was also collected on alternate days after an injection until day 16 of the cycle, to characterize changes in serum progesterone concentrations. Although exogenous GnRH caused release of LH on days 2 and 8 of the cycle, the quantity of LH released was greater on day 8 (P less than .025). Serum levels of progesterone after treatment with GnRH on day 8 of the cycle did not differ significantly from those observed during the control cycles of the heifers. Because exposure of the bovine corpus luteum to excess LH, induced by GnRH early during the estrous cycle, causes attenuated progesterone secretion during the same cycle, these data suggest that a second surge of endogenous LH may ameliorate the suppressive effect of the initial release of LH on luteal function. Duration of the estrous cycle was not altered by treatment (control, 20.4 +/- .5 vs. treated, 20.4 +/- .4 days).(ABSTRACT TRUNCATED AT 250 WORDS)     

Pituitary receptors for GnRH and estradiol, and pituitary content of gonadotropins in beef cows. I. Changes during the estrous cycle

To further characterize the endocrinological changes in the hypothalamo-hypophyseal axis thoughout the bovine estrous cycle, cycling beef heifers (n = 24) were randomly assigned to six groups. These heifers were slaughtered 6, 12, 18, 19, 20 or 21 days following their previous estrus (day 0). Anterior pituitaries and hypothalami were collected. Hypothalami were divided into the preoptic area and medial basal hypothalamus, and content of gonadotropin-releasing hormone (GnRH) was quantified by radioimmunoassay. Contents of luteinizing hormone (LH) and follicle stimulating hormone (FSH) in the anterior pituitary gland were quantified by radioimmunoassay. Membrane receptors for GnRH were quantified by a standard curve technique and receptors for estradiol in anterior pituitary cytosol were quantified by saturation analysis. There was no significant change in content of GnRH in the hypothalamus or content of FSH in the anterior pituitary on any of the days examined; however, content of GnRH in the preoptic area was lower (P less than .1) on day 19 postestrus. Cytosolic receptors for estradiol increased (P less than .05) on day 18 post-estrus and returned to baseline by day 19. Content of LH and the number of receptors for GnRH in the anterior pituitary gland decreased (P less than .01) on day 19 postestrus, and the number of receptors for GnRH remained low through day 21 postestrus. The reduction in anterior pituitary content of LH was transient indicating that synthesis of LH restores pituitary content to preovulatory levels before the number of receptors for GnRH returns to normal.     

Pituitary responsiveness to GnRH, hypothalamic content of GnRH and pituitary LH and FSH concentrations immediately preceding puberty in gilts

To determine whether pituitary concentrations of luteinizing hormone (LH), follicle-stimulating hormone (FSH) or hypothalamic content of gonadotropin releasing hormone (GnRH) change before puberty, 40 prepubertal gilts averaging 7 mo of age were slaughtered before or on the second, third or fourth day after relocation and boar exposure. Some gilts responded to relocation and boar exposure as indicated by swollen vulvae, turgid uteri and enlarged ovarian follicles at the time of slaughter. Pituitary concentrations of LH and FSH and hypothalamic content of GnRH were similar between gilts that responded to relocation and boar exposure and gilts that did not respond. In addition, boar exposure and relocation had no effect on pituitary concentrations of LH and FSH or on hypothalamic content of GnRH. To determine whether pituitary responsiveness to GnRH changes before puberty, a third experiment was conducted in which 72 gilts were injected with 400 micrograms of GnRH either before or on the second, third or fourth day after relocation and boar exposure. In gilts that subsequently responded (i.e., ovulated) as a result of relocation and boar exposure, pituitary responsiveness to GnRH was reduced as compared with gilts that failed to ovulate after relocation and boar exposure. Peak concentrations of serum LH after GnRH injection were 4.6 +/- 1.3 vs 9.8 +/- .8 ng/ml for responders vs nonresponders. Peak serum FSH after GnRH injection was also lower for responders than for nonresponders (29.5 +/- 4.2 vs 41.2 +/- 2.4 ng/ml). When compared with controls, relocation and boar exposure did not significantly affect GnRH-induced release of LH and FSH.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of dihydrotestosterone administration with and without estradiol pretreatment on gonadotropin secretion in ovariectomized pony mares

Twenty ovariectomized pony mares were used to determine if dihydrotestosterone propionate (DHTP) administration, with or without estradiol benzoate (EB) pretreatment, would have the same effects on follicle stimulating hormone (FSH) and luteinizing hormone (LH) secretion as testosterone propionate (TP) administration. All mares were given an initial injection of gonadotropin releasing hormone (GnRH) to characterize their LH and FSH response, and then two groups of mares (n = 4/group) were administered EB (22 micrograms/kg of body weight), two groups were administered vehicle (safflower oil) and a fifth group was administered TP (175 micrograms/kg of body weight) daily for 10 days. Following a second injection of GnRH, one group of EB-treated mares and one group of oil-treated mares were administered DHTP (175 micrograms/kg of body weight) daily for 10 days; the other EB- and oil-treated mares were administered oil and the TP-treated mares were continued on the same dose of TP for 10 days. A final injection of GnRH was then given. Treatment with EB increased (P less than .01) concentrations of LH in daily blood samples and increased (P less than .05) the LH response to exogenous GnRH. Administration of TP or DHTP reduced (P less than .05) both daily LH concentrations and the LH response to exogenous GnRH. Concentrations of FSH in daily blood samples were reduced (P less than .05) and the FSH response to exogenous GnRH was increased (P less than .05) by administration of EB alone, DHTP alone or TP.(ABSTRACT TRUNCATED AT 250 WORDS)     

Testosterone propionate treatment of stallions: Effects on secretion of luteinizing hormone and follicle stimulating hormone in daily samples and after administration of gonadotropin releasing hormone

Ten stallions were used to determine if the stallion responds to administration of testosterone propionate (TP) with an increase in follicle stimulating hormone (FSH) secretion after administration of gonadotropin releasing hormone (GnRH) as has been previously observed for geldings and intact and ovariectomized mares. Five stallions were treated with TP (350 μg/kg of body weight) in safflower oil every other day for 11 days; control stallions received injections of safflower oil. The response to GnRH (1.0 μg/kg of body weight) was determined for all stallions before the onset of treatment (GnRH I) and at the end of treatment (GnRH II). Blood samples were also withdrawn daily from 3 days prior to treatment through GnRH II. Treatment with TP decreased (P<.10) concentrations of FSH in daily blood samples. However, treatment with TP did not affect (P>.10) the GnRH-induced secretion of FSH. Concentrations of luteinizing hormone (LH) decreased (P<.05) in daily blood samples averaged over both groups of stallions and were lower (P<.10) in TP-treated stallions than in controls during the latter days of treatment. We conclude that TP administration to stallions does not alter the FSH response to GnRH as has been observed for geldings and for mares of several reproductive states.     

Follicle stimulating hormone pattern and luteal function in ewes receiving bovine follicular fluid during three stages of the estrous cycle

The objectives of this study were to determine 1) the ability of charcoal-extracted bovine follicular fluid (bFF) to suppress endogenous follicle stimulating hormone (FSH) at various stages of the estrous cycle and 2) the effects of suppression of FSH on luteal function and lengths of the current and subsequent estrous cycles. Twenty-six mature ewes were assigned randomly to receive 5 ml of either bFF or saline, subcutaneously, at 8-h intervals on d 1 through 5 (bFF n = 6; saline n = 3), d 6 through 10 (bFF n = 6; saline n = 3) or d 11 through 15 (bFF n = 6; saline n = 2) of the estrous cycle (d 0 = estrus). Blood was collected daily beginning at estrus and continued until the third estrus (two estrous cycles) or 40 d; more frequent samples were collected 2 h prior to initiation of treatment (0600), hourly for the first 8 h of treatment, then every 4 h until 0800 on the first day after treatment, and finally at 1600 and 2400 on that day. Plasma concentrations of FSH were lower (P less than .001) in bFF-treated than in saline-treated ewes. Treatment with bFF reduced (P less than .05) plasma concentrations of progesterone during the current but not during the subsequent estrous cycle. Treatment with bFF did not affect plasma concentrations of estradiol-17 beta. Administration of bFF on d 11 through 15 of the estrous cycle lengthened the interval from the decline in progesterone to estrus and the inter-estrous interval by approximately 3 and 4 d, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)     

BMPR-IB基因对绵羊外周血生殖激素水平的影响

为研究不同BMPR-IB基因型多胎萨福克羊外周血中生殖激素水平的差异,以培育的发情期多胎萨福克母羊为实验对象,应用PCR-RFLP技术检测个体的BMPR-IB基因型,ELISA方法检测绵羊外周血中E2、FSH、LH、PRL和P4的含量,分析BMPR-IB基因型与5种生殖激素水平的相关性.结果表明：多胎萨福克羊群体中存在BMPR-IB基因的BB、B＋和＋＋三种基因型.＋＋基因型个体的平均E2含量和P4含量显著低于B＋基因型和BB基因型个体（P＜0.05）,3种基因型个体间平均FSH含量、LH含量和PRL含量差异均不显著（P＞0.05）.BMPR-IB基因突变导致发情期母羊的雌二醇和孕酮的分泌量增加.研究结果可为合理利用BMPR-IB基因培育多胎肉羊提供依据.     

Gonadotropin secretion in ovariectomized pony mares treated with dexamethasone or progesterone and subsequently with dihydrotestosterone

Twelve long-term ovariectomized (OVX) pony mares were used to determine the effects of dexamethasone (DEX) or progesterone (PR) on concentrations of follicle stimulating hormone (FSH) and luteinizing hormone (LH) in daily blood samples and after administration of gonadotropin releasing hormone (GnRH). All mares were subsequently administered dihydrotestosterone (DHT) to determine if DEX or PR treatment altered the FSH or LH response to this androgen. Daily blood sampling was started on day 1. After a pretreatment injection of GnRH on day 5, four mares were administered DEX at 125 micrograms/kg of body weight (BW), four mares were administered PR at 500 micrograms/kg of BW and four mares were administered vehicle. Injections were given subcutaneously in vegetable shortening daily through day 14. After a second injection of GnRH on day 15, all mares were administered DHT in shortening at 150 micrograms/kg of BW. Injections of DHT were given daily through day 24. A final injection of GnRH was given on day 25. Treatment of mares with DEX 1) reduced (P less than .01) daily LH secretion and briefly increased (P less than .05) daily FSH secretion and 2) increased (P less than .01) the FSH response to exogenous GnRH. Treatment of mares with PR had no effect on daily LH secretion but increased (P less than .05) daily FSH secretion and increased (P less than .01) the FSH response to exogenous GnRH.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of sodium pentobarbital on release of gonadotropins in ewes immediately after ovariectomy and after treatment with gonadotropin-releas ing hormone

Two experiments were conducted with ewes 9 to 11 days after estrus to determine whether the secretion of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) are controlled differentially. In experiment 1, gonadotropin-releasing hormone (GnRH) was injected (100 (μg/ewe) at time = 0 min into ewes in four treatment groups. The treatment groups (9 ewes/group) were: 1) periodic iv sodium pentobarbital (NaPen) vehicle from 0 min; 2) periodic iv NaPen from 0 min; 3) vehicle iv for 120 min then iv NaPen from 120 min; 4) vehicle iv for 150 min then iv NaPen from 150 min. A surgical plane of anesthesia was maintained from the initiation of NaPen injection until the experiment ended. Jugular blood was sampled at 30-min intervals from ?30 to + 210 min for LH and FSH assays, and profiles of hormone concentrations were compared by time-trend analyses. GnRH released LH (P<.001) and FSH (P<.001), but NaPen did not affect the profiles of hormone concentrations; this indicated that NaPen did not reduce the ability of the pituitary to secrete gonadotropins in response to GnRH. Experiment 2 was a 2x2 factorial with ovariectomy (time = 0 hr) and NaPen as the main effects. One group of ovariectomized (n = 6) and one group of sham ovariectomized (n = 6) ewes were anesthetized only during surgery, while a group of ovariectomized (n = 7) and a group of sham ovariectomized (n = 6) ewes were kept at a surgical plane of anesthesia until 10 hr after surgery. Patterns of LH and FSH were compared in jugular blood collected hourly from 0 hr until 10 hr after surgery and in samples collected at 24 hr intervals from -24 to +72 hr of surgery. After ovariectomy, LH increased (P<.001) hourly and daily, but anesthesia suppressed (hourly, <.001 and daily, P<.005) these increases, which resulted in an interaction (hourly, P<.001 and daily, P<.01) of ovariectomy and anesthesia. FSH after ovariectomy increased hourly and daily (hourly, P<.02 and daily, P<.001), but the effect of anesthesia and interaction of ovariectomy and anesthesia were not significant. Because NaPen did not alter secretion of LH or FSH after exogenous GnRH in experiment 1 while it blocked the postovariectomy increase in LH but not FSH in experiment 2, we concluded that the postovariectomy increase in LH resulted from increased hypothalamic secretion of GnRH. The mechanisms responsible for the postovariectomy increase in FSH secretion are not identical to those for LH. The mechanisms that control the postovariectomy secretion of FSH might involve factors that are not suppressible by NaPen or, alternatively, the differences in LH and FSH release after ovariectomy might reflect the removal of ovarian factors that suppress FSH but not LH secretion in intact ewes.