Plasma LH Concentrations Research Articles

Seasonal and photoperiodic regulation of secretion of hormones associated with reproduction in Magang goose ganders

This study examined the reproductive endocrine profile under natural and artificial photoperiods in Magang goose ganders. Group 1 ganders ( n = 8) served as non-treated controls and were exposed to natural photoperiod throughout the experiment from 13th January to 17th December 2004. Group2 ganders ( n = 8) were exposed to 18 h long daily photoperiod for 60 days from 13 January till 15 March 2004 and again to 16 h photoperiod for 75 days till 10th October 2004, and the 11 h short photoperiod in the remainder periods of the experiment. In control ganders, plasma LH concentrations were high in normal breeding seasons (August–March) and decreased to low levels in non-breeding season from April to July. Testosterone concentrations changed similarly to that of LH throughout the seasons. Seasonal pattern of PRL concentrations was opposite to those of LH and testosterone, with low values in breeding season and high values in non-breeding season. In artificial photoperiod treated ganders, increasing photoperiod increased PRL and decreased LH and testosterone concentrations, while decreasing photoperiod reversed these changes. There were no seasonal or photoperiod caused changes in plasma T3 concentrations in both control ganders and artificial photoperiod treated ganders. These results demonstrated that in Magang goose ganders that long photoperiod stimulates PRL secretion and decreases LH secretion, which terminates reproductive season in spring and early summer, and short photoperiod stimulates LH secretion and inhibits PRL secretion rendering ganders enter into reproductive season.

Reproduction in high body condition mares with high versus low leptin concentrations

Previous results from our laboratory indicated that a majority of mares with high body condition scores (BCS) displayed estrous cycles or had considerable follicular activity during the winter. Among these high BCS mares, about 35% of them exhibited a persistent hyperleptinemia and hyperinsulinemia. The current experiment was designed to compare the reproductive characteristics of high BCS mares with hyperleptinemia to those with normal (low) plasma concentrations of leptin during the winter and the first estrous cycle (or the first full cycle encountered for those already cycling). Light horse mares with high BCS (6–8.5) were assigned to groups based on leptin concentrations (8/group): low (<5ng/mL) and high (>10ng/mL). Beginning 7 January, mares were assessed every 3d for follicular activity and then daily once a follicle >25mm was detected. Mares were subsequently monitored through their first and second ovulations. Leptin concentrations remained higher (P<0.001) in mares in the high leptin group over the duration of the experiment. Also, high leptin mares had greater (P<0.0001) insulin response to glucose infusion and a faster (P<0.05) rate of glucose clearance. One mare with high leptin and three mares with low leptin had progesterone concentrations indicative of the presence of a corpus luteum at the onset of the experiment. Plasma concentrations of LH, FSH, and progesterone did not differ between groups (P>0.1) during the first estrous cycle occurring after 7 January. Date of first ovulation after 7 January and interovulatory interval were similar (P>0.1) for the two groups, as were estimates of follicular numbers on the ovaries (small, medium, and large; P>0.1). It is concluded that the perturbations in leptin and insulin secretion observed in some high BCS mares are not associated with alterations in ovarian activity or the estrous cycle during winter and into the period of vernal transition.

Effect of various photoperiods on testicular weight, weekly sperm output and plasma levels of LH and testosterone over the reproductive season in male turkeys

The effects of duration and variation in photoperiod on testis weight, testicular sperm production, semen output, and hormone status over the reproductive season in male turkeys were investigated. In Experiment 1, four groups of males raised from 17 to 23 wk of age under a constant short photoperiod were subjected to a constant short (Group 1: 7L:17D; Group 2: 10.5L:13.5D), constant long (Group 3: 14L:10D) or progressively increasing photoperiod (Group 4: 7L:17D to 14L:10D) up to 60 wk of age. In Experiment 2, four groups of males first raised as in Experiment 1 up to 23 wk of age were placed under a constant short (Group 5: 10.5L:13.5D), constant long (Group 6: 14L:10D), or night-interrupted photoperiod (Group 7: 6L:2.5D:1L:14.5D, referred to as subjective 9.5L:14.5D; Group 8: 6L:3.5D:1L:13.5D), referred to as subjective 10.5L:13.5D) up to 60 wk of age. Males in Groups 2–4 had similar reproductive characteristics, whereas sexual maturity was delayed from 29 to 49 wk in males from Group 1. In Experiment 2, males in Groups 5 and 8 had similar reproductive characteristics, whereas sexual maturity was delayed in males in Group 7 in a manner similar to that observed in Group 1. In both experiments, plasma LH and testosterone concentrations were poor indicators of testis development and semen production, irrespective of age and photoperiod. We conclude that a moderately short photoperiod such as 10.5L:13.5D or subjective 10.5L:13.5D may stimulate reproductive characteristics of male turkeys in a manner comparable to constant long or increasing photoperiods. We inferred the existence of a threshold of photosensitivity in male turkeys for photoperiods longer than 9.5L:14.5D, but shorter than or equal to 10.5L:13.5D.

Gonadotropin-Inhibitory Hormone Inhibits Gonadal Development and Maintenance by Decreasing Gonadotropin Synthesis and Release in Male Quail

Until recently, any neuropeptide that directly inhibits gonadotropin secretion had not been identified. We recently identified a novel hypothalamic dodecapeptide that directly inhibits gonadotropin release in quail and termed it gonadotropin-inhibitory hormone (GnIH). The action of GnIH on the inhibition of gonadotropin release is mediated by a novel G protein-coupled receptor in the quail pituitary. This new gonadotropin inhibitory system is considered to be a widespread property of birds and provides us with an unprecedented opportunity to study the regulation of avian reproduction from an entirely novel standpoint. To understand the physiological role(s) of GnIH in avian reproduction, we investigated GnIH actions on gonadal development and maintenance in male quail. Continuous administration of GnIH to mature birds via osmotic pumps for 2 wk decreased the expressions of gonadotropin common alpha and LHbeta subunit mRNAs in a dose-dependent manner. Plasma LH and testosterone concentrations were also decreased dose dependently. Furthermore, administration of GnIH to mature birds induced testicular apoptosis and decreased spermatogenic activity in the testis. In immature birds, daily administration of GnIH for 2 wk suppressed normal testicular growth and rise in plasma testosterone concentrations. An inhibition of juvenile molt also occurred after GnIH administration. These results indicate that GnIH inhibits gonadal development and maintenance through the decrease in gonadotropin synthesis and release. GnIH may explain the phenomenon of photoperiod-induced gonadal regression before an observable decline in hypothalamic GnRH in quail. To our knowledge, GnIH is the first identified hypothalamic neuropeptide inhibiting reproductive function in any vertebrate class.

ICV galanin‐like peptide increases metabolic rate in male rats

Galanin-Like Peptide (GALP) is a hypothalamic neuromediator between metabolism and reproduction. GALP is known to stimulate reproduction and alter food intake and body weight in multiple species. The regulation of body weight involves control of both energy intake and energy expenditure. Since GALP is known to alter food intake, we hypothesized that GALP would increase metabolic rate. Male Sprague Dawley rats were implanted with intracerebroventricular cannulae and abdominal temperature transmitters. Following injection with either 5 nmol of GALP or vehicle, the oxygen consumption of each rat was monitored for 8 hours; and food intake, core temperature, and activity were monitored for 23 hours. GALP significantly increased oxygen consumption without having a significant effect on activity. GALP increased core temperature during the photophase and reduced food intake over 23 hours. In a second set of experiments, the rats were injected with 5 nmol of GALP or vehicle and blood samples obtained two hours later. In these experiments, GALP significantly increased plasma LH concentration without altering plasma corticosterone concentration. GALP appears to increase energy expenditure in addition to decreasing energy input and thus may play an important role in the hypothalamic regulation of body weight. Supported by a Merck/AAAS USRP award, award KO1-DK-066238 from NIH, and NSF REU grant DBI-0139035.

Changes in Plasma Concentrations of LH, FSH, Estradiol 17‐β and Progesterone During Oestrus in Mithun (Bos frontalis)

The objective of the present study was to establish the changes in plasma concentrations of LH, FSH, estradiol 17-beta (E2) and progesterone (P4), as well as to understand their temporal relationships during oestrus in mithun (Bos frontalis). The experiment was conducted on 11 mithuns during third or fourth postpartum oestrous cycle. Since oestrus onset the jugular vein blood samples were collected every 2 h for 72 and 96 h, respectively from the animals without and with standing heat. The LH, FSH, E2 and P4 concentrations were estimated in plasma. The P4 concentration was fluctuated throughout the oestrus period and the average P4 concentration was found significantly (p<0.05) lower on the day of oestrus onset. The multiple rises in LH and FSH concentrations above the basal level in spike like fashion were observed throughout the oestrus period irrespective of the occurrence of standing heat. A significant (p<0.01) gradual increase in the average daily E2 concentration was observed till day 2 following oestrus onset irrespective of the occurrence of standing heat. A significant (p<0.05) simultaneous increase in LH, FSH and E2 concentrations and a transient increase in P4 concentration at approximately the time of standing heat onset were observed. During investigation a definite temporal coupling between LH and FSH rises was absent throughout the oestrus period. The results suggest that (1) the multiple short-duration low-amplitude LH and FSH surges during oestrus may be crucial for the final maturation of ovulatory follicle and subsequent ovulation in mithun; (2) a differential mechanism for controlling LH and FSH secretions probably exists in mithun.

Effects of chronic exposure to sodium arsenite on hypothalamo-pituitary-testicular activities in adult rats: possible an estrogenic mode of action.

BackgroundInorganic arsenic is a major water pollutant and a known human carcinogen that has a suppressive influence on spermatogenesis and androgenesis in male reproductive system. However, the actual molecular events resulting in male reproductive dysfunctions from exposure to arsenic remain unclear. In this context, we evaluated the mode of action of chronic oral exposure of sodium arsenite on hypothalamo-pituitary- testicular activities in mature male albino rats.MethodsThe effect of chronic oral exposure to sodium arsenite (5 mg/kg body weight/day) via drinking water without or with hCG (5 I.U./kg body weight/day) and oestradiol (25 micrograms oestradiol 3-benzoate suspended in 0.25 ml olive oil/rat/day) co-treatments for 6 days a week for 4 weeks (about the duration of two spermatogenic cycle) was evaluated in adult male rats. Changes in paired testicular weights, quantitative study of different varieties of germ cells at stage VII of spermatogenic cycle, epididymal sperm count, circulatory concentrations of hormones (LH, FSH, testosterone and corticosterone), testicular activities of delta 5, 3beta-hydroxysteroid dehydrogenase (delta 5, 3beta-HSD), 17 beta-hydroxysteroid dehydrogenase (17 beta-HSD), sorbitol dehydrogenase (SDH), acid phosphatase (ACP), alkaline phosphatase (ALP), and lactate dehydrogenase (LDH), as well as the levels of biogenic amines (dopamine, noradrenaline and 5-hydroxytryptamine (5-HT)) in the hypothalamus and pituitary were monitored in this study. Hormones were assayed by radioimmuno- assay or enzyme- linked immunosorbent assay and the enzymes were estimated after spectrophotometry as well as the biogenic amines by HPLC electrochemistry.ResultsSodium arsenite treatment resulted in: decreased paired testicular weights; epididymal sperm count; plasma LH, FSH, testosterone and testicular testosterone concentrations; and increased plasma concentration of corticosterone. Testicular enzymes such as delta 5, 3 beta-HSD, 17 beta-HSD, and sorbitol dehydrogenase (SDH) were significantly decreased, but those of acid phosphatase (ACP), alkaline phosphatase (ALP), and lactate dehydrogenase (LDH) were significantly increased. A decrease in dopamine or an increase in noradrenaline and 5-HT in hypothalamus and pituitary were also noted after arsenic exposure. Histological evaluation revealed extensive degeneration of different varieties of germ cells at stage VII of spermatogenic cycle in arsenic exposed rats. Administration of human chorionic gonadotrophin (hCG) along with sodium arsenite partially prevented the degeneration of germ cells and enhanced paired testicular weights, epididymal sperm count, plasma and intratesticular testosterone concentrations, activities of delta 5, 3beta-HSD, 17 beta-HSD and sorbitol dehydrogenase along with diminution in the activities of ACP, ALP and LDH. Since many of the observed arsenic effects could be enhanced by oestradiol, it is suggested that arsenic might somehow acts through an estrogenic mode of action.ConclusionThe results indicate that arsenic causes testicular toxicity by germ cell degeneration and inhibits androgen production in adult male rats probably by affecting pituitary gonadotrophins. Estradiol treatment has been associated with similar effects on pituitary testicular axis supporting the hypothesis that arsenite might somehow act through an estrogenic mode of action.

Adenohypophyseal function in bitches treated with medroxyprogesterone acetate

The aim of this study was to investigate the effects of treatment with medroxyprogesterone acetate (MPA) on canine adenohypophyseal function. Five Beagle bitches were treated with MPA (10 mg/kg, every 4 weeks) and their adenohypophyseal function was assessed in a combined adenohypophyseal function test. Four hypophysiotropic hormones (CRH, GHRH, GnRH, and TRH) were administered before and 2, 5, 8, and 11 months after the start of MPA treatment, and blood samples for determination of the plasma concentrations of ACTH, cortisol, GH, IGF-1, LH, FSH, prolactin, α-MSH, and TSH were collected at −15, 0, 5, 10, 20, 30, and 45 min after suprapituitary stimulation. MPA successfully prevented the occurrence of estrus, ovulation, and a subsequent luteal phase. MPA treatment did not affect basal and GnRH-induced plasma LH concentrations. The basal plasma FSH concentration was significantly higher at 2 months after the start of MPA treatment than before or at 5, 8, and 11 months after the start of treatment. The maximal FSH increment and the AUC for FSH after suprapituitary stimulation were significantly higher before treatment than at 5, 8, and 11 months of MPA treatment. Differences in mean basal plasma GH concentrations before and during treatment were not significant, but MPA treatment resulted in significantly elevated basal plasma IGF-1 concentrations at 8 and 11 months. MPA treatment did not affect basal and stimulated plasma ACTH concentrations, with the exception of a decreased AUC for ACTH at 11 months. In contrast, the maximal cortisol increment and the AUC for cortisol after suprapituitary stimulation were significantly lower during MPA treatment than prior to treatment. MPA treatment did not affect basal plasma concentrations of prolactin, TSH, and α-MSH, with the exception of slightly increased basal plasma TSH concentrations at 8 months of treatment. MPA treatment did not affect TRH-induced plasma concentrations of prolactin and TSH. In conclusion, the effects of chronic MPA treatment on adenohypophyseal function included increased FSH secretion, unaffected LH secretion, activation of the mammary GH-induced IGF-I secretion, slightly activated TSH secretion, suppression of the hypothalamic–pituitary–adrenocortical axis, and unaffected secretion of prolactin and α-MSH.

Effects of Experimental Cryptorchidism on Sperm Motility and Testicular Endocrinology in Adult Male Rats

The effect of induced cryptorchidism on testicular function and sperm motility was investigated. Bilateral cryptorchidism was created surgically in adult male rats (treated group), and sham-operated rats were used as a control group. Five rats from each group were sacrificed on days 1, 3, 5, and 7 after surgery. The percentage of motile spermatozoa began to decrease 1 day after the operation, followed by an abrupt decline 3 and 5 days later in cryptorchid rats. Furthermore, there were significant decreases in the other sperm motility parameters 5 days after inducement of cryptorchidism. In cryptorchid rats, plasma concentrations of LH, FSH, testosterone, and inhibin B were significantly lower than in the control group 1 day after the operation. Thereafter, plasma concentrations of LH, FSH, and testosterone gradually increased in the cryptorchid rats. On the other hand, plasma concentrations of inhibin B showed a further decline from day 3 after the operation onward. Concentrations of immunoreactive (ir)-inhibin, but not testosterone, in testicular interstitial fluid were remarkably increased until 3 days after surgery in the cryptorchid rats, and declined thereafter. Testicular response to human chorionic gonadotropin (hCG) for testosterone release was decreased in the cryptorchid rats compared with the control rats, indicating that heat stress to testes resulted in a reduction of the activity of Leydig cells and Sertoli cells. These results clearly indicate that heat stress to the testes resulted in a significant reduction of sperm activity within 3 days, and this was followed by changes in testicular endocrine function.

Age-related Changes of Reproductive Hormones in Young Meishan Boars

Meishan pigs are known for their early sexual maturity. On the other hand, they grow slowly. There is no information currently available about the combination of these two characteristics in Meishan pigs. To study the developmental characteristics of Meishan pigs, the plasma concentrations of LH, FSH, inhibin, testosterone, estradiol-17beta, progesterone and insulin-like growth factor-I (IGF-I) in young Meishan boars were determined using RIA and ELISA. Inhibin decreased with age in weeks, while testosterone and estradiol-17 beta increased. Testosterone increased gradually, and an increase in estradiol-17beta occurred after sexual maturity. IGF-I increased before puberty and subsequently decreased just after puberty like a pubertal IGF-1 surge. FSH, LH and progesterone did not change with age. There was no significant correlation among the hormones. During the experimental period, the Meishan boars showed large individual differences. These differences may depend on the fact that Meishan boar reach maturity at 12 weeks of age and continue to grow thereafter.

Expression of Inhibin/Activin Subunits in the Ovaries of Fetal and Neonatal Mice

In the present study, the expression of inhibin/activin subunits in the mouse ovary from 13 days post-coitus (dpc) to 30 days postpartum (dpp) was investigated. Circulating FSH, LH, inhibin A, and inhibin B in neonatal to 30 dpp ovaries were measured. Inhibin/activin subunits (alpha, beta(A), beta(B) ) were weakly stained in 13 dpc ovarian stromal cells and increased with age. Inhibin alpha subunit was immunolocalized in follicular granulosa cells at each developmental stage. In 30 dpp ovaries, several large antral follicles were strongly stained for inhibin alpha subunit. Inhibin beta(A) subunit was weakly immunolocalized in granulosa cells until 20 dpp. Moreover, 2 to 3 antral follicles from 20 to 30 dpp were strongly stained for inhibin beta(A) subunit. There was relatively high immunoactivity for inhibin beta(B) subunit in neonatal to 30 dpp mouse ovaries. All three inhibin subunits were stained in theca-interstitial cells from 15 dpp onward. RIA data showed that a temporal increase in circulating FSH occurred around 10 dpp, while the plasma concentrations of LH were sustained at a relatively higher level from 8 to 15 dpp. Inhibin B was detectable in circulation early at 1 dpp (day of birth), and a clear increase in inhibin B occurred around 8 dpp. Circulating inhibin B gradually increased from 20 dpp to 30 dpp, indicating a negative correlation with FSH. Inhibin A levels were only measured on 25 and 30 dpp, and the levels were low. These results suggest that inhibins play an important role in early folliculogenesis in mice. In addition, inhibin B seems to be the main functional isoform from the neonatal to prepubertal stage in the mouse ovary.

Effects of Bilateral Efferent Duct Ligation on Sperm Motility and Secretion of FSH, LH, Inhibin, and Testosterone in Adult Male Rats

Effects of bilateral efferent duct ligation (EDL) on sperm motility and testicular endocrinology were investigated in adult male rats. Bilateral EDL was created surgically in adult male rats (EDL group) and shamoperated rats were used as control (control group). Five rats from each group were killed on d 3, 5, 7, 14, and 35 after the surgery. The sperm motility parameters were determined by a computer-assisted sperm analysis system using sperm collected from the cauda epididymis. Concentrations of spermatozoa in epididymis and testis were counted. The motility of sperm decreased remarkably in EDL rats compared with controls on 5 d after the operation. Four sperm motility parameters-straight velocity (VSL), deviation of the sperm head from the mean trajectory (ALH, mean), the maximum amplitude of lateral head displacement (ALH, max) and curvilinear velocity (VCL)-increased on 3 d after the operation, and followed by a subsequent decline 5 and 7 d later. Concentrations of sperm significantly decreased in both testes and epididymis from 3 and 5 d after the operation. Plasma concentrations of FSH and LH increased significantly in EDL rats from 5 and 7 d after the operation, whereas plasma concentrations of immunoreactive (ir)-inhibin, inhibin B, and testosterone decreased. Testicular content of irinhibin showed an initial increase on 3 d after the operation, followed by a subsequent decline to levels significantly below controls by d 7 postoperation. On the other hand, testicular contents of testosterone were significantly higher in the EDL group than the control group on d 7-35 after the operation, whereas circulating levels of testosterone remained low. In the EDL testes, marked degenerative changes in the Sertoli cells and spermatogonia were observed, whereas Leydig cells showed clear hyperplasia. These results demonstrated that bilateral EDL induced a rapid reduction of sperm motility parameters during a short time. Present results also suggest that EDL first induces impairment of Sertoli cells function and this leads to reduction of sperm activity and secretion of inhibins. On the other hand, circulating levels of testosterone reduced after EDL and this leads to hypersecretion of LH. A large amount of LH resulted in a stimulation of Leydig cells hyperplasia.

Exogenous Melatonin Modifies Rate of Sexual Maturation in Domestic Pullets

Growing pullets were maintained on 14-h photoperiods and given diets supplemented with 25 mg of melatonin (MEL)/kg during the final 7 h of the photo-period to investigate the role of MEL in sexual development. Melatonin diets were fed to 70 d (to mimic a transfer from 7 to 14 h at 70 d), from 105 d onward (to mimic a transfer from 14 to 7 h at 105 d), or throughout the trial (to mimic constant 7-h photoperiods). Control birds, which were fed normal diets, were maintained on 7 or 14 h, transferred from 7 to 14 h at 70 d, or transferred from 14 to 7 h at 105 d. The MEL groups matured 6 to 11 d later than the constant 14-h controls. The group mimicking a transfer from 7 to 14 h matured 35 d later than photostimulated controls, the group mimicking a 14 to 7-h change at 105 d matured 41 d earlier than birds given a decrease in day length; the third group matured 13 d earlier than constant 7-h controls. Although these data suggest that the birds did not perceive the final 7 h of the photoperiod as being part of the night, when given MEL diets, residual plasma MEL during the first 7 h of the photoperiod was atypically high, possibly preventing an interpretation of day and night. However, continuously high plasma MEL did not result in birds responding as if in constant darkness, because birds transferred from darkness to 14 h at 70 d would not have matured at a similar time to birds changed from 14 h to darkness at 105 d. Plasma LH concentrations for birds mimicking a 7 to 14 h change at 70 d were not significantly different from constant 7-h controls after the transfer to normal diets. The later maturity of the experimental groups, compared with constant 14-h controls, clearly indicated that MEL had some influence over hypothalamic activity and gonadal development.

Seasonal changes in semen characteristics, hormonal profiles and testicular activity in Zaraibi goats

Ten Zaraibi buck goats were used to study the effect of season on semen quality. Bucks were housed and fed according to standard recognized practices. Semen was collected twice a week for 7 consecutive weeks (starting from the 3rd to the 9th week) in the mid of the each season. During these periods scrotal circumference was measured fortnightly. The number of mounts terminating in ejaculation and the time interval between the first mount and ejaculation were also recorded. The physical parameters of semen and semen index (semen volume × spermatozoa concentration/ml × live spermatozoa% × progressive motility%) were measured for the first and the second ejaculates of each semen collection during the week. At the end of each season, testicular biopsies were obtained surgically from three bucks for histological evaluation. Plasma testosterone, FSH and LH concentrations were also determined twice weekly. Bucks demonstrated the highest libido in summer, using the least ( P < 0.01) number of mounts and a shorter ( P < 0.01) reaction time. This coincided with a higher ( P < 0.01) level of plasma testosterone (10 ng/ml) and the best semen quality (semen index: 3354 × 10 6). During autumn, bucks recorded the highest ( P < 0.01) ejaculate volume (0.98 ml) and the maximum output of sperm (4565 × 10 6), as well as a lower ( P < 0.01) percentage of sperm abnormalities (8.8%). This was accompanied by high concentrations of plasma LH (average 2.9 mIU/ml). The histological structure of the testis indicated that during autumn (natural breeding season) seminiferous tubules (Sta) occupied the majority of the testicular tissues (76.6%) and the spermatic layers were highest. It can be said that Zaraibi bucks have distinct seasonal activity, with poor semen characteristics during winter and spring—which may be a critical obstacle for implementing intensive systems of three kidding in 2 years when natural mating is applied.

Ghrelin-stimulation test in the diagnosis of canine pituitary dwarfism

This study investigated whether ghrelin, a potent releaser of growth hormone (GH) secretion, is a valuable tool in the diagnosis of canine pituitary dwarfism. The effect of intravenous administration of ghrelin on the release of GH and other adenohypophyseal hormones was investigated in German shepherd dogs with congenital combined pituitary hormone deficiency and in healthy Beagles. Analysis of the maximal increment (i.e. difference between pre- and maximal post-ghrelin plasma hormone concentration) indicated that the GH response was significantly lower in the dwarf dogs compared with the healthy dogs. In none of the pituitary dwarfs, the ghrelin-induced plasma GH concentration exceeded 5 μg/l at any time. However, this was also true for 3 healthy dogs. In all dogs, ghrelin administration did not affect the plasma concentrations of ACTH, cortisol, TSH, LH and PRL . Thus, while a ghrelin-induced plasma GH concentration above 5 μg/l excludes GH deficiency, false-negative results may occur.

Hormonal and metabolic adaptation to fasting: Effects on the hypothalamic–pituitary–ovarian axis and reproductive performance of rabbit does

To assess the impact of acute caloric shortage on reproduction, rabbit does were either fed ad libitum (control, AL), or fasted for 24 (STF) or 48 h (LTF) before induction of ovulation with GnRH injection. Blood samples were collected during the last 3 h of fasting, and the following 4 h after GnRH injection, when feed was provided again, to measure plasma concentrations of LH, estradiol-17β, leptin, insulin, T3, corticosterone, glucose, and NEFA. Before re-feeding, plasma leptin, insulin, and T3 concentrations were lower ( P ≤ 0.01) in both fasted groups than in controls, but then gradually increased following realimentation to match those of controls. During fasting, corticosterone levels were higher ( P ≤ 0.01) in LTF than in STF and AL does, but decreased to control values soon after realimentation. During fasting, plasma glucose concentrations did not differ among groups, but upon re-feeding they markedly increased ( P ≤ 0.01) both in STF and LTF does. NEFA levels were also more elevated ( P ≤ 0.01) in fasted rabbits than in controls, and rapidly decreased ( P ≤ 0.01) after re-feeding. Following GnRH injection, LH peak was lower ( P ≤ 0.01) in LTF than in AL and STF does. Estradiol-17β showed higher pulse frequency and amplitude in AL than in STF and LTF does. Compared to controls, receptivity rate of STF and LTF artificially inseminated does declined respectively by −20.5% ( P ≤ 0.05) and −22.7%, and fertility rate by −23.9% ( P ≤ 0.05) and 21.4%, but no difference was found in ovulation rate. In summary, nutritional status of does, as modified by fasting, greatly influenced fertility, metabolic and reproductive hormones.

Early post-natal exposure to low dose oral di(2ethylhexyl) phthalate affects the peripheral LH-concentration in plasma, but does not affect mating behavior in the post-pubertal boar

In a split-litter design experiment, boars were exposed orally three times weekly to 300 mg/kg of di(2-ethylhexyl) phthalate (DEHP) between 3 and 7 weeks of age. Post-puberty, i.e. at 6 months of age the effects on endocrinology and mating behavior were examined. The response to stimulation with a synthetic GnRH-analogue at 9 months of age resulted initially in lower concentration of LH in the exposed animals, compared to the control animals. We did not find any effects of DEHP on the mating behavior. Also, the effects of DEHP during the treatment period on the plasma concentrations of testosterone, oestradiol and LH were examined. During the exposure period there was a transient decrease in plasma concentrations of LH in the control group, which did not occur in the boars exposed to DEHP. The data suggest that DEHP in low repeated oral doses causes lasting effects on the hypothalamus–pituitary–gonadal axis.

Reducing Estrogen Synthesis Does Not Affect Gonadotropin Secretion in the Developing Boar1

Boars have high concentrations of plasma and testicular estrogens, but how this hormone is involved in feedback regulation of the gonadotropins and local regulation of testicular hormone production is unclear. The present study examined the effects of reducing endogenous estrogens by aromatase inhibition on concentrations of plasma LH and FSH and on testicular and plasma concentrations of testosterone (T) and immunoreactive inhibin (INH). Thirty-six littermate pairs of boars were used. One boar from each pair was assigned to the control group (vehicle); the other boar to the treatment group (aromatase enzyme inhibitor, Letrozole, 0.1 mg/kg body weight [BW]). Weekly oral treatment started at 1 wk of age and continued until castration at 2, 3, 4, 5, 6, 7, or 8 mo. Plasma concentrations of gonadotropins, INH, T, estradiol (E2), and estrogen conjugates (ECs) were determined. Testicular tissue was collected at castration for determination of INH and T and for confirmation of reduced aromatase activity. The acute effects of aromatase inhibition on gonadotropins were monitored in two adult boars treated once with Letrozole (0.1 mg/kg BW). Treatment with the aromatase inhibitor reduced testicular aromatase activity by 90% and decreased E2 and ECs without changing acute, long-term, or postcastration LH and FSH. Plasma T, testicular T, and circulating INH concentrations did not change. Testicular INH was elevated in treated boars compared with controls. In conclusion, estrogen does not appear to play a regulatory role on gonadotropin secretion in the developing boar. This is in direct contrast to findings in males of several other species.

Variation in pituitary expression of mRNAs encoding the putative inhibin co-receptor (betaglycan) and type-I and type-II activin receptors during the chicken ovulatory cycle

Secretion of LH and FSH from the anterior pituitary is regulated primarily by hypothalamic GnRH and ovarian steroid hormones. More recent evidence indicates regulatory roles for certain members of the transforming growth factor beta (TGFbeta) superfamily including inhibin and activin. The aim of this study was to identify expression of mRNAs encoding key receptors and ligands of the inhibin/activin system in the hen pituitary gland and to monitor their expression throughout the 24-25-h ovulatory cycle. Hens maintained on long days (16 h light/8 h dark) were killed 20, 12, 6 and 2 h before predicted ovulation of a midsequence egg (n = 8 per group). Anterior pituitary glands were removed, RNA extracted and cDNA synthesized. Plasma concentrations of LH, FSH, progesterone and inhibin A were measured. Real-time quantitative PCR was used to quantify pituitary expression of mRNAs encoding betaglycan, activin receptor (ActR) subtypes (type I, IIA), GnRH receptor (GnRH-R), LH beta subunit, FSH beta subunit and GAPDH. Levels of mRNA for inhibin/activin betaA and betaB subunits, inhibin alpha subunit, follistatin and ActRIIB mRNA in pituitary were undetectable by quantitative PCR (<2 amol/reaction). Significant changes in expression (P<0.05) of ActRIIA and betaglycan mRNA were found, both peaking 6 h before ovulation just prior to the preovulatory LH surge and reaching a nadir 2 h before ovulation, just after the LH surge. There were no significant changes in expression of ActRI mRNA throughout the cycle although values were correlated with mRNA levels for both ActRIIA (r = 0.77; P<0.001) and beta-glycan (r = 0.45; P<0.01). Expression of GnRH-R mRNA was lowest 20 h before ovulation and highest (P<0.05) 6 h before ovulation; values were weakly correlated with betaglycan (r = 0.33; P = 0.06) and ActRIIA (r = 0.34; P = 0.06) mRNA levels. Expression of mRNAs encoding LH beta and FSH beta subunit were both lowest (P<0.05) after the LH surge, 2 h before ovulation. These results are consistent with an endocrine, but not a local intrapituitary, role of inhibin-related proteins in modulating gonadotroph function during the ovulatory cycle of the hen, potentially through interaction with betaglycan and ActRIIA. In contrast to mammals, intrapituitary expression of inhibin/activin subunits and follistatin appears to be extremely low or absent in the domestic fowl.

Seasonal effects on attempts to synchronize estrus and ovulation by intravaginal application of progesterone-releasing device (PRID™) in mares

To investigate seasonal effects on the efficacy of estrus synchronization in mares, we administered a progesterone-releasing device (PRID™) intravaginally to eight Haflinger mares for 11 days. In January 3 of 8 mares responded to the treatment with estrus and ovulation, in March 7 with estrus and 6 of 7 mares with ovulation, in June 6 of 7 and in October 7 of 8 mares with estrus and ovulation. Follicle distribution patterns at PRID™ insertion were different between January/October, March/June and June/October ( P < 0.05). Number of follicles decreased during PRID™ treatment in January, March and June (difference of number of follicles at Day 12 minus number of follicles at Day 1: −4.2 ± 2.7, −0.9 ± 0.9 and −4.9 ± 1.5 follicles), while it increased in October (3.9 ± 1.2 follicles; P < 0.05). Mean progesterone concentrations were lowest in January (0.3 ± 0.1 ng mL −1) when compared with March (3.5 ± 1.8 ng mL −1; P = 0.063), June (4.4 ± 1.4 ng mL −1; P < 0.05) and October (2.2 ± 0.9 ng mL −1; P < 0.05). At Day 2 of PRID™ treatment, mean progesterone concentrations significantly increased in all mares. Except from January, mean LH concentrations decreased within one day after PRID™ insertion and remained at low levels during treatments in January and March. Total secretion of LH during PRID™-treatment was significantly lower in January and March when compared with June and October. In the 5 of 7 mares that ovulated during PRID™ treatment a distinct increase of plasma LH concentrations after ovulation was detected. Administration of the progesterone releasing intravaginal device PRID™ combined with the PGF2α analogue cloprostenol was able to induce estrus and ovulation in mares at different times of the year. However, efficacy of the treatment was not satisfactory concerning effectiveness in relation to season and synchrony of intervals from removal of PRID™ to ovulation in mares.