LHRH receptor, LH and FSH concentrations in anterior pituitaries of cycling, noncycling and early pregnant heifers

In domestic animals limited data are available concerning levels of pituitary luteinizing hormone-releasing hormone (LHRH) receptors during various physiological states. The objectives of this study were to quantify anterior pituitary gonadotropin and LHRH receptor concentrations in cycling, noncycling and early pregnant beef heifers. To accomplish these objectives, five heifers each were slaughtered, after synchronization with prostaglandin F2 alpha (PGF2 alpha), on d 0 (estrus), 7 and 14 of the estrous cycle and d 40 of pregnancy. Four heifers determined to be noncycling were also slaughtered. Pituitaries were collected and analyzed for LHRH receptor and gonadotropin concentrations. Pituitary luteinizing hormone (LH) concentrations were low on d 0 (1.4 +/- .2 micrograms/mg pituitary, mean +/- SE) and remained low on d 7 (1.4 +/- .1 micrograms/mg pituitary) before increasing (P less than .01) on d 14 (2.6 +/- .5 micrograms/mg pituitary). Luteinizing hormone concentrations, compared with d 0, were also elevated (P less than .01) in noncycling (NC; 2.6 +/- .2 micrograms/mg pituitary) animals and in 40-d pregnant (PG; 2.5 +/- .2 micrograms/mg pituitary) heifers. Pituitary follicle stimulating hormone (FSH) concentrations, though similar (P greater than .05) for all groups, paralleled changes in LH concentration. Pituitary LHRH receptor binding affinity did not differ (P greater than .05) among groups, with an overall Kd = .64 +/- .02 X 10(-9) M. Luteinizing hormone-releasing hormone receptor concentrations were highest on d 0 (1.09 +/- .12 fmol/mg pituitary) and fell (P less than .01) to low levels on d 7 (.75 +/- .11 fmol/mg pituitary).(ABSTRACT TRUNCATED AT 250 WORDS)     

Regional differences in concentrations of LHRH receptors,LH and FSH in the bovine adenohypophysis

Pituitaries from intact luteal phase (INT) and ovariectomized (OVX) cows were collected at slaughter to determine whether differences exist among regions of the bovine adenohypophysis in the concentrations of luteinizing hormone (LH), follicle stimulating hormone (FSH) and receptors for luteinizing hormone releasing hormone (LHRH). Each adenohypophysis was divided into three paired regions (anterior, AT; medial, M; posterior, PT) by first making a midsagittal cut followed by two transverse cuts of approximately equal size. Values for all variables were similar between paired regions. Mean LHRH receptor, LH and FSH concentrations were greater in OVX than INT adenohypophyseal regions. Receptor and gonadotropin concentrations differed among all three regions and were greatest in the AT, intermediate in the M and lowest in the PT regions of the adenohypophysis. There were significant correlations between LHRH receptor concentrations and concentrations of LH and FSH among the three adenohypophyseal regions for both INT and OVX cows. Therefore, to accurately characterize LHRH receptors from the bovine adenohypophysis, a midsagittal-half of the gland should be used for analysis.     

Effects of intermittent injections of LHRH on secretory patterns of LH and FSH and ovarian follicular growth during postpartum anovulation in suckled beef cows

Changes in numbers of ovarian follicles and coincident secretion of pituitary gonadotropins were characterized in suckled, anovulatory beef cows injected iv with 500 ng of luteinizing hormone-releasing hormone (LHRH) every 2 h for 48 or 96 h, starting 21.4 +/- .4 d after parturition. Two hours after the last injection, all cows were ovariectomized. Compared with saline-injected controls, LHRH had no effect on baseline or overall concentrations of luteinizing hormone (LH) in serum (P greater than .10), but increased (P less than .05) frequency and decreased (P less than .05) amplitude of LH pulses. Luteinizing hormone-releasing hormone increased (P less than .05) baseline concentration of follicle stimulating hormone (FSH) in serum and frequency of FSH pulses, but decreased (P less than .05) pulse amplitude. Overall concentrations of FSH increased 20% (P less than .10). Exogenous LHRH did not affect diameter of the two largest follicles or numbers of follicles 1.0 to 3.9 mm, 4.0 to 7.9 mm or greater than or equal to 8.0 mm in diameter. These data suggest that increasing the frequency of episodic LH and FSH pulses in postpartum cattle by intermittent administration of LHRH did not increase mean circulating levels of LH, or alter size and numbers of ovarian follicles within the 96-h period of injections. Thus, induction of ovulation in anovulatory cows treated with low-dose injections of LHRH cannot be explained on the basis of an increase in mean concentrations of LH or numbers of antral follicles within 96 h after initiation of injections.     

Effect of dietary energy, body condition and calf removal on pituitary gonadotropins, gonadotropin-releasing hormone (GnRH) and hypothalamic opioids in beef cows

Beef cows (n = 64) were slaughtered to evaluate effects of dietary energy and calf removal (CR) on hypothalamic and adenohypophysial endocrine characteristics. From d 190 of gestation until parturition, cows received maintenance (ME; n = 32) or low (LE; n = 32) energy diets (ME = 100%, LE = 70% NRC recommendations). After parturition, half (n = 16) of each prepartum diet group received low (LE; n = 32) or high (HE = 130% NRC; n = 32) energy diets. At 30 d postpartum, cows were slaughtered 0 or 48 hr after CR. Hypothalami [preoptic area (POA), hypothalamus (HYP), stalk-median eminence (SME)] and pituitaries were collected. Basal and K(+)-induced release of GnRH from SME, and pituitary luteinizing hormone (LH) and follicle stimulating hormone (FSH) did not differ among groups (P greater than .05). Hypophyseal LH was correlated (P less than .01) with body condition score (BCS) at parturition and slaughter (r = .36 and .47, respectively). Prepartum LE diet increased (P less than .05) met-enkephalin in POA compared to prepartum ME (.59 +/- .05 vs. .44 +/- .04 pmol/mg) regardless of postpartum diet or suckling status. Concentrations of beta-endorphin in combined HYP + POA were decreased (P less than .05) by 48 hr CR (15.1 +/- 1.1 vs. 18.1 +/- 0.7 fmol/mg).(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of intermittent injections of LHRH on specific binding of 125I-labeled gonadotropins to granulosa and theca, and concentrations of steroids in serum and ovarian follicles during postpartum anovulation in suckled beef cows

To examine ovarian follicular response to low-dose injections of luteinizing hormone-releasing hormone (LHRH), 32 anovulatory, suckled beef cows were allotted to one of four treatment groups and injected with either saline or 500 ng LHRH every 2 h for 48 or 96 h, starting 21.4 +/- .4 d after parturition. Two hours after the last injection of LHRH, cows were ovariectomized and 10 to 15 ovarian follicles per pair of ovaries were removed and categorized by diameter as small (1.0 to 3.9 mm), medium (4.0 to 7.9 mm) or large (greater than or equal to 8.0 mm). Injections of LHRH did not affect (P greater than .10) steroid levels in small follicles or numbers of gonadotropin receptors in small and medium follicles. Concentrations of progesterone in fluid of medium follicles increased 1.5-fold (P less than .05) after 96 h of LHRH, whereas concentrations of estradiol and androstenedione were unchanged. In fluid of large follicles, concentrations of progesterone were fourfold greater (P less than .05) in LHRH-treated than in control cows at 48 h, but by 96 h progesterone was twofold greater (P less than .05) in control than LHRH-treated cows. In large follicles, concentrations of estradiol were unchanged (P greater than .10) after 48 h of LHRH injections but after 96 h estradiol was twofold greater (P less than .05) in LHRH-treated than control cows. Increased concentrations of estradiol in large follicles coincided with increased numbers of binding sites for human chorionic gonadotropin (hCG) but not follicle stimulating hormone (FSH) in granulosa and theca.(ABSTRACT TRUNCATED AT 250 WORDS)     

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)     

Pituitary receptors for GnRH and estradiol, and pituitary content of gonadotropins in beef cows. II. Changes during the postpartum period

Pregnant beef heifers (n = 24) were assigned randomly to four groups and slaughtered at day 1, 15, 30 or 45 postpartum. The day prior to slaughter blood samples were taken from each cow every 15 min for 8 hr. The anterior pituitary gland, preoptic area (POA) and medial basal hypothalamus (HYP) were collected from each cow. Contents of gonadotropin-releasing hormone (GnRH) in extracts of POA and HYP, and luteinizing hormone (LH) and follicle-stimulating hormone (FSH) in extracts of anterior pituitary were quantified by radioimmunoassay. In the anterior pituitary gland, membrane receptors for GnRH were quantified by a standard curve technique and cytosolic receptors for estradiol were quantified by saturation analysis. Concentrations of LH, FSH and prolactin in serum were quantified by radioimmunoassay. Only one cow of eight had a pulse of LH during the 8 hr bleeding period on day 1 postpartum. This increased to 8 pulses in 6 cows on day 30 postpartum. Contents of GnRH in POA (15.0 +/- 3.2 ng) and HYP (14.0 +/- 2.0 ng) did not change significantly during the postpartum period. Pituitary content of LH was low following parturition (.2 +/- .1 mg/pituitary) and increased significantly through day 30 postpartum (1.2 +/- .1 mg/pituitary). Pituitary content of FSH did not change over the postpartum period. Receptors for both GnRH (.9 +/- .2 pmoles/pituitary) and estradiol (5.0 +/- .9/moles/pituitary) were elevated on day 15 postpartum, possibly increasing the sensitivity of the anterior pituitary gland to these hormones and leading to an increased rate of synthesis of LH that restored pituitary content to normal by day 30 postpartum.     

Adenohypophyseal receptors for LHRH, pituitary content of gonadotropins and plasma concentrations of LH in cyclic, pregnant and postpartum beef cows

Adenohypophyseal concentrations of LHRH receptors, pituitary content of LH and FSH, and plasma concentrations of LH were determined in thirty Hereford, Angus or Hereford-Angus heifers that were randomly assigned by breed and weight to five periods including day 3 of the estrous cycle (CY), pregnant day 120 (P120), 200 (P200), 275 (P275), or day 2 postpartum (PP). Jugular blood samples were collected at 10-min intervals for 8 hr from all cows. Within 2 hr after completion of blood sampling, animals were slaughtered and the pituitary gland frozen at −196 C. LH pulse frequency/8 hr was reduced (P<.05) during gestation (.5, .2, and 1.5 ± .5/8 hr, for P120, P200, and P275, respectively) and PP (.5 ± .5/8 hr) compared to CY (7.8 ± .5/8 hr). Frequency of LH pulses/8 hr was not different (P>.1) among P120, P200 or PP periods but was different (P<.05) between P200 and P275. There were no differences in LH pulse height (P>.1) among periods; however, pulse amplitude was greatest (P<.05) at P120 (1.3 ± .2 ng/ml) and lowest between P200 and PP (.6 to .8 ± .2 ng/ml). Baseline concentrations of plasma LH did not differ (P>.1) among P and PP periods (.3 ± .1 ng/ml), but were lower (P<.05) than in CY animals (.7 ± .1 ng/ml). Concentration of adenohypophyseal LHRH receptors was approximately two-fold greater (P<.05) at P120 (25.85 ± 2.2 fmol/mg) than at all other periods (9.5 to 14.9 ± 2.2 fmol/mg). Pituitary content of LH was greatest at P120 (1.56 ± .11 ug/mg) and lowest (P<.05) at P275 and PP (0.46 to 0.52 ± .11 ug/mg). Pituitary content of FSH was greatest (P<.05) in P (12.7 to 17.0 ± 1.4 ug/mg) and PP (18.3 ± 1.4 ug/mg) vs CY (5.0 ± 1.4 ug/mg) cows and increased from P120 to PP (P<.05). Results indicate that physiological changes occurring during gestation may have an effect on subsequent function of the adenohypophysis in beef cows.     

Effect of dosage and frequency of injection of luteinizing hormone releasing hormone on release of luteinizing hormone and follicle stimulating hormone in estradiol-treated steers

The objective was to determine how estradiol (0 vs 1 mg) and changes in the dosage of luteinizing hormone releasing hormone (LHRH; 1,000 ng/steer vs 1 ng/kg body weight) and frequency of LHRH injection (25 vs 50 min) affect LH and follicle stimulating hormone (FSH) release in steers. In steers pretreated with estradiol peak concentrations of LH in serum after LHRH averaged 14.4 ng/ml, which was greater (P less than .001) than peak concentrations in steers given oil (7.4 ng/ml). Increasing the dosage of LHRH from 1 ng/Kg body weight (approximately or equal to 300 ng/steer) to 1,000 ng/steer increased (P less than .001) peak LH values from 7.5 to 14.4 ng/ml. Furthermore, increasing the frequency of LHRH injections from once every 50 min to once every 25 min increased (P less than .001) LH release, but only in steers given estradiol. Estradiol reduced basal concentrations of FSH by 65% and then increased LHRH-induced FSH release by 276% (P approximately .07) relative to values for steers given oil. Only when 1,000 ng LHRH was given every 25 min to steers pretreated with estradiol were LH and FSH release profiles similar to the preovulatory gonadotropin surges of cows in magnitude, duration and general shape. The results demonstrate that increases in the dosage or frequency of LHRH pulses increase LHRH-induced release of LH, but not of FSH. Furthermore, these results are consistent with the hypothesis that in cows, estradiol increases responsiveness of the gonadotrophs to LHRH and then increases the magnitude and frequency of pulses of LHRH secretion beyond basal levels, thereby causing the preovulatory gonadotropin surges.     

Reduced postpartum anestrus of suckled beef cows treated with microencapsulated luteinizing hormone-releasing hormone analog.

This study evaluated the effect of microencapsulated LHRH agonist (D-Trp6-LHRH) on gonadotropin release and occurrence of estrus in early postpartum beef cows. Angus cows (n = 54) were assigned randomly to two treatment groups at d 5 postpartum. Group 1 received a single i.m. injection of D-Trp6-LHRH (LHRH-A) encapsulated in poly-DL-lactide-coglycolide, calculated to release 15 micrograms of LHRH-A per day for 30 d (n = 23). Group 2 received vehicle only (control, n = 31). Blood samples (15-min intervals for 6 h) were obtained on d 5, 10, 20, 30, and 40 postpartum for evaluation of LH and FSH concentrations (n = 12 per group). Days to first postpartum estrus were reduced by treatment with LHRH-A (Group 1, 43.7 +/- 4.2 d vs Group 2, 55.9 +/- 4.7 d; P < .05). However, days to conception were similar between groups (68.9 +/- 7.9 vs 76.7 +/- 6.7 d, respectively). On the day of treatment, cows treated with LHRH-A had higher mean concentrations of LH and FSH than did controls (8.3 +/- 1.4 vs 2.0 +/- .4 ng/mL for LH and 211.0 +/- 8.6 vs 51.2 +/- 2.7 ng/mL for FSH (P < .05). There were no differences in mean concentrations of LH or FSH between treatment groups on d 10, 20, 30, and 40 postpartum. Cows given LHRH-A had more (P < .05) LH pulses on d 10 and 30 postpartum than did controls. This study demonstrated that microencapsulated D-Trp6-LHRH reduced the postpartum anestrous interval in suckled beef cows.     

Influence of nutrition and body condition on pituitary, ovarian, and thyroid function of nonlactating beef cows

Nonpregnant Hereford cows (n = 70) were used to determine the effect of nutrient intake and body condition on reproductive and thyroid function. Body condition scores (BCS; 1 = emaciated; 9 = obese) of cows averaged 5.0 +/- .2 on July 1, and cows were fed for 4 mo either to lose weight and BCS (thin; n = 22), to maintain weight and BCS (moderate; n = 24), or to gain weight and BCS (fat; n = 24). After November 1, cows received a complete ration to maintain weight and BCS. Cows were slaughtered in December (six thin, eight moderate, and eight fat cows) or the subsequent March (16 cows per group). Before slaughter, cows were given two injections of prostaglandin F2 alpha (PGF) 11 d apart. Six days after the second PGF injection, cows were simultaneously treated with 100 micrograms of gonadotropin releasing hormone (GnRH; i.m.) and 100 micrograms of thyrotropin releasing hormone (TRH; i.v.) and serum samples were obtained. The BCS of cows at slaughter (8 d after PGF) averaged 3.4, 5.3, and 7.1 (P less than .01) and carcass energy content averaged 243, 432, and 714 Mcal (P less than .01) for thin, moderate, and fat cows, respectively. Wet ovarian (P less than .001) and corpora lutea (P less than .01) weights were heavier for fat cows. Content of LH in the pituitary gland and concentrations of thyroxine (T4) in serum after GnRH/TRH were not influenced by nutrient intake or BCS. However, thin cows had greater concentrations (P less than .05) of LH in serum after GnRH/TRH than did moderate or fat cows. We conclude that nutrient intake and body energy reserves of beef cows influenced ovarian function and LH in serum after treatment with GnRH.     

Pituitary concentrations of gonadotropins and receptors for GnRH in suckled beef cows at various intervals after calving

Mature beef cows were slaughtered at 5 (n = 6), 10 (n = 6), 20 (n = 6) or 30 (n = 5) d after calving to identify endocrine events that may affect the duration of postpartum anestrus. Additional cows (n = 6) were slaughtered 12 to 14 d after their first postpartum estrus (luteal phase cows). Anterior pituitary concentrations of luteinizing hormone (LH) were low at d 5 (383 +/- 69 micrograms/g), averaged 445 +/- 103 and 682 +/- 207 micrograms/g at d 10 and 20, respectively, and were elevated (P less than .05) by d 30 (1,097 +/- 174 micrograms) to a concentration similar to luteal phase cows (1,208 +/- 148 micrograms/g). Concentrations of follicle-stimulating hormone (FSH) averaged 12.4 +/- 1.1, 9.6 +/- 2, 8.6 +/- 1.8 and 7.4 +/- 3.3 mg/g at d 5, 10, 20 and 30, respectively. Affinity (1.6 +/- .2 X 10(9) M-1) of anterior pituitary receptors for the GnRH (gonadotropin-releasing hormone) analog (DAla6; des-Gly10, [D-Ala6]-LH-RH ethylamide) and weights (2.1 +/- .1 g) of the anterior pituitaries did not differ among groups (P greater than .05). Number of receptors for GnRH averaged 37 +/- 7, 39 +/- 9, 25 +/- 5 and 23 +/- 5 X 10(-14) M/mg protein at d 5, 10, 20 and 30, respectively. Anterior pituitaries from luteal phase cows contained 22 +/- 2 X 10(-14) M/mg protein of receptors for GnRH.(ABSTRACT TRUNCATED AT 250 WORDS)     

Testosterone administration to mares during estrus: duration of estrus and diestrus and concentrations of LH and FSH in plasma

To study the possible role of ovarian androgens in regulation of follicle stimulating hormone (FSH) secretion in the cycling mare, five mature, intact mares were treated with testosterone (20 micrograms/kg of body weight) daily during estrus; five control mares received safflower oil on the same schedule. Mares were teased for estrus and samples of jugular blood were drawn daily through one full estrous cycle. Concentrations of FSH in plasma were measured by a newly developed radioimmunoassay based on anti-ovine FSH serum and radioiodinated equine FSH. Testosterone treatment during estrus had no effect on duration of estrus, diestrus or the total cycle. Concentrations of FSH in plasma during estrus were unaffected by testosterone treatment. However, FSH concentrations in testosterone-treated mares were elevated (P less than .05) compared with controls during mid-diestrus (d 6 through 11). The magnitude and timing of the LH peaks were unaffected by treatment, as was the day on which the first elevated progesterone concentration occurred. These data are consistent with a model of FSH secretion in which ovarian androgens cause an accumulation of FSH in the pituitary during estrus in preparation for the surges that occur in FSH secretion during diestrus.     

Changes in hormonal profiles during the estrous cycle in old lactating beef cows

Patterns of concentrations of luteinizing hormone (LH), follicle stimulating hormone (FSH), progesterone (P4) and estradiol-17 beta (E2) during an estrous cycle were compared between 15 lactating beef cows 5 to 7 years of age (young) and 15 cows greater than or equal to 12 years of age (old). Length of estrous cycle did not differ between young and old cows (P = .06). No differences due to age were found for LH. Patterns of concentrations of P4 during the first 15 days of the cycle, of FSH during days 6 through 12 and of E2 during the follicular phase differed with age (P less than .05). An earlier (P less than .025) midcycle elevation of FSH was associated with an earlier rise and greater concentration of E2 (P less than .05) during the follicular phase in old than in young cows. Differences in FSH and P4, although subtle, were consistent with an earlier or more advanced follicular development in old cows, leading to greater secretion of E2 from the preovulatory follicle.     

Effects of charcoal-extracted follicular fluid on reproductive function in postpartum cows

In order to determine the role of follicle-stimulating hormone (FSH) on the resumption of ovarian function in cows early postpartum (PP), bovine follicular fluid (FF) was used to selectively suppress concentrations of FSH. Calves were removed from all cows within 24 hr of birth. Follicular fluid that was treated with charcoal to remove steroids (15 ml; n = 14) or serum (S) from an ovariectomized cow (15 ml, n = 14) was injected i.m. twice daily from days 1 to 10 PP. Blood samples were collected before each injection and frequent samples (every 15 min for 6 hr) taken on days 5 and 10 PP. Eight cows from each group (FF and S) were slaughtered on the morning of day 11 PP and pituitaries and ovaries collected. The remaining cows (n = 6) were observed for estrus. Treatment with FF delayed follicular growth (P less than 0.01), as evidenced by the largest follicle per cow observed at time of slaughter (3.6 +/- 0.42 vs 11.5 +/- 1.77 mm dia; FF vs S). The intervals from parturition to first estrus (P less than 0.11) and to first progesterone rise (25.3 +/- 1.97 vs 18.0 +/- 3.62 d; P less than 0.06) tended to be delayed by treatment with FF vs S. Many of the cows treated with S ovulated by day 10 PP, they were divided retrospectively into those that had ovulated by (n = 9) or after (n = 5) day 10 PP for analysis. Cows treated with FF had lower (P less than 0.05) and less variable (P less than 0.01) serum FSH concentrations while levels of luteinizing hormone (LH) tended (P less than 0.08) to be greater on days 5 and 10 PP. Follicular fluid decreased levels of FSH (P less than 0.001), but not LH (P less than 0.15), in the samples obtained twice daily compared to S-treated cows that did not ovulate by day 10 PP. Anterior pituitaries were dissociated, and cells from each cow were cultured in order to ascertain whether treatment with FF in vivo would affect gonadotropin secretion in vitro. Estradiol-17 beta (E) was incubated with pituitary cells to determine the effect of E on gonadotropin secretion from cells of PP cows, and to ascertain whether treatment with FF in vivo and with E in vitro would interact to affect secretion of FSH and LH in culture. After 2 d of incubation, cells were treated with 10(-9) M E or vehicle (1% ethanol).(ABSTRACT TRUNCATED AT 400 WORDS)     

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.     

Follicular fluid concentrations of estradiol-17 beta and progesterone and secretory patterns of LH and FSH in prepubertal gilts reared in confinement or outdoor lots

One-hundred-twenty crossbred gilts from two experiments were assigned randomly to a 2 X 5 factorial experiment. Gilts were reared in two environments (confinement or outside) and assigned to be slaughtered at 4, 5, 6, 7 or 8 mo of age. Beginning at 6 mo of age, blood samples were taken at weekly intervals from each gilt via venipuncture. Serum concentrations of progesterone were analyzed to determine when gilts attained puberty. On the day prior to slaughter, six pigs within a treatment group were cannulated and blood samples were taken at 20-min intervals for 4 h. At slaughter, follicular fluid (FF) was aspirated and the volume determined from those follicles having a diameter of at least 4 mm. No effect of environment was found on the proportion of gilts that attained puberty by 8 mo of age. For the 12 gilts that reached puberty during the study, the age at puberty for gilts reared in outdoor lots (202 +/- 5 d) was less (P less than .05) than those reared in confinement (224 +/- 8 d). Mean concentrations of serum luteinizing hormone (LH; P = 98) and number of secretory spikes of LH (P = .76) were similar between gilts reared in confinement and those reared in outdoor lots. No differences in average serum concentrations of follicle stimulating hormone (FSH) or number of secretory spikes of FSH were found between gilts subjected to these environments (P = .95). Concentrations of estradiol-17 beta in FF were not affected by environment or age (P greater than .25).(ABSTRACT TRUNCATED AT 250 WORDS)     

Hypothalamic control of gonadotropin secretion by LHRH,FSHRF, NO,cytokines, and leptin

Gonadotropin secretion by the pituitary gland is under the control of luteinizing hormone-releasing hormone (LHRH) and the putative follicle stimulating hormone-releasing factor (FSHRF). Lamprey III LHRH is a potent FSHRF in the rat and seems to be resident in the FSH controlling area of the rat hypothalamus. It is an analog of mammalian LHRH and may be the long sought FSHRF. Gonadal steroids feedback at hypothalamic and pituitary levels to either inhibit or stimulate the release of LH and FSH, which is also affected by inhibin and activin secreted by the gonads. Important control is exercised by acetylcholine, norepinephrine (NE), dopamine, serotonin, melatonin, and glutamic acid (GA). Furthermore, LH and FSH also act at the hypothalamic level to alter secretion of gonadotropins. More recently, growth factors have been shown to have an important role. Many peptides act to inhibit or increase release of LH and the sign of their action is often reversed by estrogen. A number of cytokines act at the hypothalamic level to suppress acutely the release of LH but not FSH. NE, GA, and oxytocin stimulate LHRH release by activation of neural nitric oxide synthase (nNOS). The pathway is as follows: oxytocin and/ or GA activate NE neurons in the medial basal hypothalamus (MBH) that activate NOergic neurons by alpha₁ (α₁) receptors. The NO released diffuses into LHRH terminals and induces LHRH release by activation of guanylate cyclase (GC) and cyclooxygenase. NO not only controls release of LHRH bound for the pituitary, but also that which induces mating by actions in the brain stem. An exciting recent development has been the discovery of the adipocyte hormone, leptin, a cytokine related to tumor necrosis factor (TNF) α. In the male rat, leptin exhibits a high potency to stimulate FSH and LH release from hemipituitaries incubated in vitro, and increases the release of LHRH from MBH explants. LHRH and leptin release LH by activation of NOS in the gonadotropes. The NO released activates GC that releases cyclic GMP, which induces LH release. Leptin induces LH release in conscious, ovariectomized estrogen-primed female rats, presumably by stimulating LHRH release. At the effective dose of estrogen to activate LH release, FSH release is inhibited. Leptin may play an important role in induction of puberty and control of LHRH release in the adult as well.     

Influence of estradiol,progesterone, and nutrition on concentrations of gonadotropins and GnRH receptors,and abundance of mRNA for GnRH receptors and gonadotropin subunits in pituitary glands of beef cows

Nutritionally induced anovulatory cows (n = 28) were used to determine the effect of steroids on regulation of synthesis and secretion of gonadotropins. Anovulatory cows were ovariectomized and received intravaginal inserts containing estradiol (E2), progesterone (P4), E2 and P4 (E2P4), or a sham intravaginal insert (C) for 7 d. Concentrations of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) were quantified in serum and E2 and P4 were quantified in plasma. Cows were exsanguinated within 1 to 2 h after removal of intravaginal inserts and pituitary glands were collected and stored at -80 degrees C until messenger ribonucleic acid (mRNA) for gonadotropin-releasing hormone receptor (GnRH-R) and gonadotropin subunits, pituitary content of GnRH-R, and LH and FSH were quantified. Pituitary glands from five proestrous cows were harvested to compare gonadotropin characteristics between ovariectomized, anovulatory cows and intact cows. Plasma concentrations of E2 were greater (P < 0.05) in E2-treated cows than in sham-treated cows. Concentrations of P4 were greater (P < 0.05) in cows treated with P4 than in sham-treated cows. Mean serum concentrations of LH and FSH were not significantly influenced by steroid treatments. However, frequency of LH pulses of ovariectomized, nutritionally induced anovulatory cows was increased (P < 0.05) by treatment with E2 and amplitude of LH pulses was greater (P < 0.05) in cows treated with E2 or P4 than in cows treated with E2P4 or sham-treated. Quantity of mRNA for LHbeta in the pituitary gland was greater when cows were treated with P4. Concentrations of LH in the pituitary gland were not affected by steroid treatments; however, pituitary concentrations of FSH were less (P < 0.1) in E2 cows than in sham-treated cows. The number of GnRH-R was increased (P < 0.05) in cows treated with E2, but P4 treatment did not influence the number of GnRH-R. Abundance of mRNA for GnRH-R, common alpha-subunit, and FSHbeta were not affected by treatments. Pituitary concentrations of LH were greater (P < 0.05) and concentrations of FSH were less (P < 0.05) in proestrous cows than in ovariectomized, anovulatory cows treated with or without steroids. Abundance of mRNA for GnRH-R, common alpha-subunit, LHbeta and FSHbeta were similar for proestrous and anovulatory cows. We conclude that treatment of nutritionally induced anovulatory cows with progesterone and estradiol may cause pulsatile secretion of LH.     

Measurement of the amount of mRNA for gonadotropins during an estradiol-induced preovulatory-like surge of LH and FSH in ovariectomized ewes

The amount of messenger RNA (mRNA) for luteinizing hormone beta-subunit (LH beta), follicle-stimulating hormone beta-subunit (FSH beta) and alpha-subunit was measured during estradiol-17 beta (E) positive feedback in ovariectomized (OVX) ewes. During the anestrous season, OVX ewes were given an i.m. injection of E (25 micrograms: n = 5) or oil (control; n = 4) and hourly blood samples were collected for 16 hr. After blood collection, ewes were killed and anterior pituitary glands were removed for analysis of hormone and mRNA content. Preovulatory-like increases in serum concentrations of LH and FSH were measured in E-treated OVX ewes. In two E-treated OVX ewes the serum concentrations of LH and FSH were still increasing, whereas in the remaining three E-treated OVX ewes, serum concentrations of LH were on the decreasing portion of the E-induced preovulatory-like surge. Pituitary content of LH was lower (P less than .10) in E-treated OVX ewes when serum concentrations of LH were decreasing than that measured in control ewes or E-treated OVX ewes in which serum concentrations were still increasing. Pituitary content of FSH and prolactin were similar (P greater than .05) among all groups. The amount of mRNA for LH beta-subunit was similar (P greater than .05) in ewes in which serum concentrations of LH were increasing and in control ewes, but was lower (P less than .05) in ewes with decreasing levels of LH. The amount of mRNA for FSH beta-subunit was lower (P less than .05) in all E-treated OVX ewes (independent of whether serum concentrations of FSH were increasing or decreasing) than that measured in control ewes. There was no difference (P greater than .05) in the amount of mRNA for alpha-subunit among any groups. Thus, amounts of mRNA for the beta-subunits of gonadotropins are reduced, while amounts of mRNA for alpha-subunit are unchanged during estradiol positive feedback in OVX ewes.