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.     

Ovine luteinizing hormone: isoforms in the pituitary during the follicular and luteal phases of the estrous cycle and during anestrus.

Pituitaries were collected from late follicular phase (n = 5), mid-luteal phase (n = 5), and anestrous ewes (n = 4) to assess changes in intrapituitary LH heterogeneity at selected reproductive states. After homogenization, an aliquot of each pituitary extract was desalted by flow dialysis against water and chromtofocused on a pH 10.5 to 4.0 gradient. Concentrations of LH in pituitary extracts and chromatofocusing fractions were determined by RIA. The LH in pituitary extracts resolved into 13 isoforms during chromatofocusing, which were coded with letters beginning with the most basic isoform. Follicular and mid-luteal phase ewes exhibited similar distributions of intrapituitary LH among its isoforms. Relative to follicular and luteal phase ewes, anestrous ewes had lower percentages of isoforms D and E as well as higher percentages of isoforms G, H, J and K. Isoform F, the predominant molecular form of LH, constituted a similar percentage in all treatment groups (P > .05). Thus, the distribution of intrapituitary LH among its isoforms did not change significantly between the mid-luteal and follicular phases of the estrous cycle, but higher percentages of the weakly basic and acidic forms of LH were present during anestrus. These observations suggest that intrapituitary LH heterogeneity changes minimally throughout the estrous cycle of ewes during the breeding season.     

Ovine luteinizing hormone heterogeneity: Androgens increase the percentage of less basic isohormones

The heterogeneity of luteinizing (LH) is hormonally regulated with androgens having been reported to increase the percentage of extremely basic LH isohormones in the ovine pituitary. This study re-examined the effects of androgens on the heterogeneity of LH in the ovine pituitary because the extremely basic isoforms of LH reported previously were subsequently demonstrated to be artifacts resulting from the conditions used for chromatofocusing. Pituitary extracts from wethers, rams, and dihydrotestosterone (DHT)-implanted wethers were desalted by flow dialysis and chromatofocused on pH 10.5 to 7.0 gradients. LH was quantitated by radioimmunoassays. When compared with rams, wethers had increased percentages of LH isoforms eluting between pH 9.6 and 10. Patterns of intrapituitary LH isohormones were comparable in rams and DHT-implanted wethers except that rams had a higher percentage of LH eluting at pH 9.2 (20.9 ± 2.1% vs. 13.3 ± 1.3%). In contrast to what was previously reported, rams and DHT-implanted wethers had higher percentages of ovine LH isoforms eluting at pH's 9.4 or lower. Thus, androgens alter LH heterogeneity yielding increased percentages of isohormones eluting at pH's of 9.4 or lower.     

Suckling inhibits release of luteinizing hormone-releasing hormone from the bovine median eminence following ovariectomy

The effect of suckling on depletion of hypothalamic LHRH from the median eminence (ME) following ovariectomy (OVX) was determined in cattle. Multiparous, postpartum Holstein cows were assigned randomly to three groups: intact, nonsuckled (INT, n = 4); ovariectomized (3 to 5 d after parturition), nonsuckled (OVX, n = 4); and ovariectomized (3 to 5 d after parturition) and suckled by three calves (OVX-S, n = 5). Blood samples were collected at three periods (1 to 7 d before parturition and 3 to 5 d and 31 to 37 d after parturition) to determine plasma LH concentration. At 31 to 37 d after parturition, all cows were slaughtered and each ME was collected and mid-sagitally sectioned. The left half of each ME was used to determine content and concentration of LHRH. Concentrations of LH and LHRH were determined by RIA. Plasma LH concentration was similar among the three groups at 1 to 7 d before parturition and 3 to 5 d after parturition; however, at 31 to 37 d after parturition, OVX cows had a greater (P less than .05) concentration of LH (2.25 +/- .64 ng/ml) than either INT (.47 +/- .10 ng/ml) or OVX-S (.92 +/- .14 ng/ml) cows. Content of LHRH in the ME of INT (80.12 +/- 15.0 ng) and OVX-S 109.8 +/- 16.4 ng) cows was similar but was greater (P less than .05) than that in OVX cows (48.95 +/- 5.9 ng).(ABSTRACT TRUNCATED AT 250 WORDS)     

Possible role of histamine in the regulation of secretion of luteinizing hormone in the ewe

Concentrations of histamine were quantified by an enzymatic isotopic assay in different regions of the brain and pituitary gland of gonadal-intact and chronically ovariectomized ewes during the anestrous season. Sera concentrations of LH were confirmed to be elevated in ovariectomized compared with intact animals immediately before tissues were obtained. Areas of the brain that were examined included cerebral cortex, thalamus, pineal gland, hypothalamus (rostral, medial basal, median eminence), midbrain, cerebellum and brain stem. Concentrations of histamine were greatest within the thalamus, pineal gland, medial basal hypothalamus and median eminence. Histamine within the medial basal hypothalamus was greater (P less than .05) in ovariectomized than in ovarian-intact animals. Further experiments were designed to determine the effect of antihistaminic drugs on secretion of LH. Ovariectomized ewes were treated every 6 h (i.m.) for 24 h with diphenhydramine (an antagonist of the H1-receptor for histamine), cimetidine (an H2-receptor antagonist), a combination of the drugs, or vehicle. Twelve hours after initiation of treatments, animals were injected with estradiol. Diphenhydramine depressed (P less than .01) basal serum concentrations of LH and the positive feedback effect of estradiol on serum concentrations of LH. Cimetidine did not influence the pattern of secretion of LH. Diphenhydramine did not alter LHRH-induced release of LH in ovariectomized ewes or basal serum concentrations of LH in ovarian-intact anestrous ewes. We suggest that histamine acts at the level of the central nervous system through an H1-receptor mechanism to control secretion of LH in female sheep.     

Effects of immunization against luteinizing hormone-releasing hormone and treatment with trenbolone acetate on reproductive function of beef bulls and steers

The objectives of this study were 1) to evaluate the ability of trenbolone acetate (TBA) administered in tandem with LHRH immunization to suppress reproductive function in bulls and 2) to examine the effects of LHRH and androgen (TBA) signaling on pituitary gland function. Forty-four Angus × Hereford crossbred calves (BW=225 ± 2 kg; age=187 ± 6 d) received castration, LHRH immunization, or TBA administration in a 2 × 2 × 2 factorial design. Treatment groups receiving LHRH immunization contained 6 animals, whereas other treatment groups contained 5 animals. Animals immunized against LHRH received a primary injection and 2 booster injections of ovalbumin-LHRH-7 fusion protein on d 0, 42, and 196, respectively. Animals treated with TBA were implanted on d 224. Serum LHRH antibodies increased (P<0.05) after each booster for immunized animals, but were negligible in nonimmunized animals throughout the experiment. Serum testosterone concentration (P<0.001) and scrotal circumference (P<0.05) were depressed in LHRH-immunized bulls compared with nonimmunized bulls by d 84 and 168 of the experiment, respectively. Treatment with TBA tended (P=0.08) to decrease serum testosterone concentrations of nonimmunized bulls. Weights of testes at slaughter were decreased (P<0.001) for LHRH-immunized (232 ± 41 g) compared with nonimmunized (752 ± 45 g) bulls, but did not differ (P=0.80) between TBA-implanted (500 ± 49 g) and nonimplanted bulls (484 ± 36 g). Both LHRH immunization and castration decreased pituitary gland stores of LH and FSH (P<0. 001). There was no effect (P>0.10) of TBA on pituitary gland FSH content and only a tendency (P=0.09) to increase pituitary gland LH content. Immunization against LHRH decreased expression of LH β-subunit and common α-subunit genes (P<0.001). Castration increased expression of LH β-subunit and common α-subunit genes (P=0.02). Treatment with TBA further suppressed (P=0.04) α-subunit mRNA expression in LHRH-immunized steers. In summary, LHRH immunization decreased synthesis and storage of LH and decreased storage, but not synthesis of FSH in bulls. The increased synthesis of LH and FSH in nonimmunized, but not LHRH-immunized steers suggests that castration removes the negative feedback on gonadotropin synthesis but that LHRH is still needed for release of these hormones. Androgen replacement with TBA did not restore the negative feedback control of gonadotropin synthesis.     

Calcium involvement in luteinizing hormone-releasing hormone release from the bovine infundibulum

Bovine infundibular (stalk median eminence) explants were incubated in vitro to test the hypothesis that calcium (Ca) is involved in the release of luteinizing hormone-releasing hormone (LHRH) from LHRH neuron terminals in cattle. Right and left infundibular halves from individual heifers and/or steers were randomly assigned to either control or treated (EGTA [a Ca chelator] or verapamil [an L-type Ca channel antagonist]) groups. Each half was incubated in 600 μl of KrebsRinger bicarbonate medium (KRB) in the presence or absence of a treatment agent for 180 min. At 30-min intervals, 500-μl samples were removed from each incubate and replaced with fresh media. Spontaneous (basal) and depolarization-induced (60 mM potassium) LHRH release was evaluated by radioimmunoassay of the LHRH content in the media incubated from 91 to 120 and 121 to 150 min of culture, respectively. The effect of treatment on depolarization-induced LHRH release was analyzed by comparing the differences between spontaneous and depolarization-induced LHRH release in control and treated groups. Spontaneous LHRH release was not different between control and 1.25 mM EGTA- or 100 μM verapamil-treated halves from steers. In contrast, steer infundibular halves incubated with EGTA (replacing Ca in KRB and chelating any Ca in the media) released less LHRH during depolarization than did control halves. In addition, verapamil-treated (to block Ca uptake by the terminal) infundibular halves from steers or heifers released less LHRH in response to depolarization than did control halves. In conclusion, these results: 1) support the hypothesis that Ca is involved in LHRH release from the bovine infundibulum, 2) suggest that the involvement of Ca may be independent of the reproductive state, and 3) demonstrate that bovine infundibular halves incubated in vitro are useful for studying selected mechanisms regulating bovine hypothalamic neurohormone release (exocytosis) from neuron terminals.     

FSH分泌细胞在皖西白鹅脑垂体中的分布与定位

采用免疫组化SABC法并结合DAB显色技术时皖西白鹩脑垂体结构和促卵泡素(follicular stimulating hormone,FSH)分泌细胞进行了研究和定位.结果发现,皖西白鹅的垂体前叶由远侧部和结节部构成,没有中间部.垂体FSH免疫阳性细胞分布广泛,但前叶远侧部分布较多,从而表明皖西白鹅整个垂体都有FSH分泌,主要分泌部位在垂体前叶的远侧部.     

Orexin‐B‐like immunoreactivity in pituitary αMSH‐producing cells and median eminence GnRH‐containing fibres of the flat‐tailed house gecko

We examined the distribution of the orexin‐like peptides in the pituitary and median eminence of the flat‐tailed house gecko (Hemidactylus platyurus) using immunohistochemistry. Orexin‐B‐like, but not orexin‐A‐like, immunoreactivity was detected in the pituitary, specifically in the pars intermedia, and these cells corresponded to alpha‐melanocyte‐stimulating hormone (αMSH)‐producing cells. Orexin‐B and αMSH secreted from pars intermedia may modulate secretion of adenohypophyseal cells in the pars distalis. In the median eminence, orexin‐B‐immunoreactive puncta and fibres were observed, and these structures corresponded to gonadotropin‐releasing hormone (GnRH)‐immunoreactive puncta and fibres. Orexin‐B secreted from GnRH‐containing neurons in the hypothalamus may affect thyrotropin‐releasing hormone‐containing neurons resulting in modulation of αMSH secretion of melanotrophs in the pars intermedia.     

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.     

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.     

Effect of luteinising hormone releasing hormone and its analogues on plasma luteinising hormone concentrations in incubating bantam hens

The ability of synthetic vertebrate luteinising hormone releasing hormones (LHRHs) and their long-acting analogues to maintain elevated plasma luteinising hormone (LH) concentrations and to stimulate ovarian growth was investigated in incubating bantam hens. Chicken LHRH-II (pGlu1-His2-Trp3-Ser4-His5-Gly6-Trp7-Tyr8-Pro9-G ly10-NH2) was more effective than chicken LHRH-I (pGlu1-His2-Trp3-Ser4-Tyr5-Gly6-Leu7-Gln8-Pro9-Gly10-N H2) or porcine LHRH (pGlu1-His2-Trp3-Ser4-Tyr5-Gly6-Leu7-Arg8-Pro9-Gly10-N H2) in stimulating the release of LH. Long-acting analogues of chicken LHRHs (chLHRHs) were created by substituting D-amino acids in position 6. An intravenous injection (10 micrograms/bird) of D-Arg6-chLHRH-II or of a long-acting mammalian analogue of LHRH (buserelin) resulted in a sustained release of LH for up to 8 h. Less sustained releases of LH were observed after the same doses of D-Ala6-chLHRH-I or of D-Trp6-chLHRH-I. Repeated subcutaneous injections of D-Arg6-chLHRH-II or buserelin at 7 to 9 h intervals for 9 d resulted in loss of pituitary gland responsiveness to these analogues. For this reason, the treatment failed to maintain elevated plasma LH concentrations and did not stimulate the growth of the ovary or oviduct.     

Response to luteinizing hormone releasing hormone in postpubertal boars with large testes

The objective of the present study was to determine if postpubertal boars (12-13 months of age; 156 +/- 8 kg) with large testes had altered hypothalamic control of secretion of luteinizing hormone (LH). Seven boars with the highest estimated 150 d, paired testis weights from a line selected for large testes (769 +/- 60 g = mean weight of excised testes) and 8 boars from a control group (control, 544 +/- 20 g) were tethered in stalls and fitted with indwelling jugular catheters. Males were bled when they were intact, 14 days after castration and during administration of sodium pentobarbital anesthetic (subsequent to castration) to block secretion of endogenous LH-releasing hormone (LHRH). Blood samples were collected at 12-min intervals for 6 hr before and 1 hr after intravenous injection of LHRH in intact and castrated males. During anesthesia, LHRH was administered 4 times at 1-hr intervals and blood samples were collected every 6 min. All samples were analyzed for concentrations of LH and pooled samples were analyzed for concentrations of 17-beta estradiol (E2) and testosterone (T). In intact and castrated males, mean concentrations of LH, frequency and amplitude of pulses of LH, and concentrations of E2 and T were not different between boars of the two groups (P greater than .10). Response to exogenous LHRH was less (P less than .05) in intact males with large testes than in corresponding males from the control group (P less than .05). Fourteen days after castration, males that had larger testes before castration had less of a response to LHRH than males from the control group (P less than .05).(ABSTRACT TRUNCATED AT 250 WORDS)     

妊娠期山羊腺垂体中催乳素促卵泡素和促黄体素的分布特点

为了阐明妊娠期垂体中催乳素(PRL)、促卵泡素(FSH),促黄体素(LH)的分布和三者之间协调关系.本试验采用免疫组化SP法检测了PRL、FSH,LH三种激素在妊娠各期山羊的腺垂体细胞中免疫反应产物的分布特点.结果显示,在山羊妊娠过程中,腺垂体中PRL阳性细胞多存在于远侧部,数量逐渐增多,胞质呈强阳性;FSH和LH阳性细胞分布在远侧部和结节部,FSH胞质内颗粒着色深浅不一,LH多核膜着色;相对表达量都逐渐升高,而升高程度不同,表现为妊娠后期LH表达量急剧升高,FSH则变化较小,除了FSH的相对表达量在妊娠前期和中期之间无显著差异(P>0.05)外,3种激素的相对表达量在妊娠前期、中期和后期3个时期之间都存在显著差异(P<0.05),妊娠前、中期FSH的相对表达量均高于PRL和LH,妊娠后期LH的表达量最高.FSH次之,PRL最低.提示PRL,FSH和LH三种激素相互协同以促进胚胎着床并维持妊娠,而且在妊娠早期PRL起主要作用,之后协同FSH和LH维持妊娠.     

Effects of estradiol-17β, para-chlorophenylalanine and quipazine on tonic and LHRH-induced secretion of luteinizing hormone in ovariectomized ewes

Changes in metabolism of serotonin (5-HT) might mediate the reduced tonic luteinizing hormone (LH) and increased pituitary responsiveness to luteinizing hormone releasing hormone (LHRH) caused by estradiol-17β (estradiol). Two experiments were conducted to determine effects of estradiol, para-chlorophenylalanine (PCPA), an inhibitor of synthesis of 5-HT, and quipazine, an agonist of 5-HT, on tonic and LHRH-induced secretion of LH in ovariectomized ewes during the summer. Tonic levels of LH were reduced, the interval from LHRH to peak of the induced surge was longer and the magnitude of release of LH was greater in ovariectomized ewes treated with estradiol than in controls. Neither PCPA nor quipazine affected tonic secretion of LH. In ovariectomized ewes not receiving estradiol, PCPA and quipazine increased the magnitude of the LHRH-induced release of LH. However, PCPA reduced pituitary sensitivity to LHRH when administered concomitantly with estradiol; treatment with quipazine attenuated this effect of PCPA. The interval to the peak of the induced surge of LH was not affected by PCPA or quipazine in estradiol-treated or control ovariectomized ewes. Based on these results it appears that 5-HT mediates or is required for estradiol to increase pituitary responsiveness to LHRH.     

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.     

Observations on the Equine Hypophysial Portal System

The blood supply to the equine pituitary gland, with special attention to its portal system, was studied by the aid of vascular injections and histological serial sections. The primary capillary plexus of the median eminence was supplied by the rostroventral and rostrodorsal infundibular arteries, which were branches of the internal carotid arteries and the ramus communicans caudalis, respectively. The neural lobe was supplied by the caudal infundibular arteries, which originated from the arteria intercarotica caudalis. Dorsal and ventral groups of the portal vessels were described. Their regional distribution into the sinusoidal capillaries of the pars distalis was discussed. Results of this investigation indicated that the portal vessels were the sole supply to the equine pars distalis. No direct arterial supply to this part of the adenohypophysis was observed.     

The Effect of Parity of the Dam on Sexual Maturation,Serum Concentrations of Metabolic Hormones and the Response to Luteinizing Hormone Releasing Hormone in Bull Calves

The objectives of this study were to determine the effect of parity of the dam on age at which a scrotal circumference (SC) ≥ 28 cm was attained and the LH response to Luteinizing Hormone Releasing Hormone (LHRH) in bull calves. We also wanted to confirm, in a large group of bull calves, that the LH response to LHRH could be used to select early maturing bulls. Body weight and SC of the bull calves were measured every other week. At 15, 20 and 25 weeks of age, calves received 4.12 nm /kg body weight of LHRH ischio‐rectally and blood samples were taken every 15 min for 4 h. Calves from primiparous and multiparous dams were separated into two sub‐groups based on age at which an SC ≥ 28 cm was attained (early or late). An SC ≥ 28 cm was attained earlier in calves born to multiparous as compared with primiparous dams (p < 0.05). At 20 and 25 weeks of age, peak serum LH concentrations (LH‐peak) and area under the LH response curve (LH‐AUC) in response to LHRH were higher (p < 0.01) in calves born to multiparous as compared with primiparous dams. In calves born to multiparous dams the LH‐peak at 15 and 25 weeks of age and the LH‐AUC at 15 weeks of age were lower (p < 0.05) in calves that attained an SC ≥ 28 cm early as compared with late. The LHRH‐challenge test sensitivity and specificity ranged from 46% to 86%. We concluded that parity of the dam affected age at which SC ≥ 28 cm was attained and the LH response to LHRH in bull calves. Serum LH responses to LHRH at 15 and 25 weeks of age, in calves born to multiparous dams, show some promise for development into a test to select early maturing bull calves.     

Differential responses in anterior pituitary luteinizing hormone (LH) content and LHβ- and α-subunit MRNA, and plasma concentrations of LH and testosterone, in bulls treated with the LH-releasing hormone agonist deslorelin

Anterior pituitary gland contents of LH and LHß- and α-subunit mRNAs, and circulating concentrations of LH and testosterone, were determined in bulls treated with the LH-releasing hormone (LHRH) agonist deslorelin. Brahman (Bos indicus) bulls (14-month-old) were allocated to two groups and received the following: Control (n = 5), no treatment; Deslorelin (n = 4), four deslorelin implants (approximately 200 μg total deslorelin/day) for 36 d. Plasma concentrations of LH were higher in bulls treated with deslorelin on Day 1, had returned to typical levels by Day 8, and did not differ for control bulls and bulls treated with deslorelin from Day 8 to Day 29. Pituitary content of LH on Day 36 was reduced (P < 0.001) in bulls treated with deslorelin (33 ± 4 ng/mg) compared with control bulls (553 ± 142 ng/mg). Relative pituitary content of LHß-subunit mRNA was also reduced on Day 36 in bulls treated with deslorelin (Control, 0.65 ± 0.10; Deslorelin, 0.22 ± 0.04; P = 0.003). However, α-subunit mRNA relative content did not differ (Control, 0.73 ± 0.15; Deslorelin, 1.06 ± 0.12; P > 0.05). Plasma concentrations of testosterone were increased over the period of the experiment in the bulls treated with deslorelin compared with control bulls. This is the first demonstration of reduced pituitary content of LHß-subunit mRNA and LH, and unaltered content of α-subunit mRNA, in bulls treated with LHRH agonist. This was associated with apparently typical plasma concentrations of LH and elevated plasma testosterone. The anterior pituitary in bulls treated with LHRH agonist, therefore, undergoes classical desensitization and downregulation, but plasma LH and testosterone are not suppressed.     

Protein and mRNA expression of follicle‐stimulating hormone receptor and luteinizing hormone receptor during the oestrus in the yak (Bos grunniens)

Follicle‐stimulating hormone (FSH) and luteinizing hormone (LH) have a central role in follicle growth, maturation and oestrus, but no clear pathway in the seasonal oestrus of yak (Bos grunniens) has been found. To better understand the role of FSH and LH in seasonal oestrus in the yak, six yaks were slaughtered while in oestrus, and the pineal gland, hypothalamus, pituitary gland, and gonads were collected. Using real‐time PCR and immunohistochemical assays, we determined the mRNA and protein expression of the FSH and LH receptors (FSHR and LHR) in these organs. The analysis showed that the FSHR mRNA expression level was higher in the pituitary gland tissue compared with LHR (p < .01) during oestrus. By contrast, there was low expression of FSHR and LHR mRNA in the pineal gland and hypothalamus. FSHR mRNA expression was higher than that of LHR (p < .05) in the ovary, whereas LHR mRNA expression was higher than that of FSHR (p < .01) in the uterus. FSHR and LHR proteins were located in the pinealocyte, synaptic ribbon and synaptic spherules of the pineal gland and that FSH and LH interact via nerve fibres. In the hypothalamus, FSHR and LHR proteins were located in the magnocellular neurons and parvocellular neurons. FSHR and LHR proteins were localized in acidophilic cells and basophilic cells in the pituitary gland, and in surface epithelium, stromal cell and gland epithelium in the uterus. In the ovary, FSHR and LHR protein were present in the ovarian follicle. Thus, we concluded that FSHR and LHR are located in the pineal gland, hypothalamus, pituitary and gonad during oestrus in the yak. However, FSHR was mainly expressed in the pituitary gland and ovaries, whereas LHR was mainly expressed in the pituitary gland and uterus.