Increase In Luteinizing Hormone Secretion Research Articles

Effect of a neurokinin 3 receptor-selective agonist administration on the embryos recovered from superovulated cows.

Superovulation (SOV) treatment of cows results in unovulated follicles and inconsistent quality of the recovered embryos. It has been demonstrated that luteinizing hormone (LH) secretion is suppressed during SOV treatment of cows, which may cause insufficient follicle development and variation in the development of recovered embryos and unovulated follicles. Pulsatile gonadotropin-releasing hormone/LH secretion is controlled by the activity of kisspeptin, neurokinin B and dynorphin (KNDy) neurons in the arcuate nucleus in many mammals. As neurokinin B promotes the activity of KNDy neurons, we hypothesized that senktide, a neurokinin B receptor agonist, has the potential as a therapeutic drug to improve the ovulation rate and quality of recovered embryos in SOV-treated cows via stimulation of LH secretion. Senktide was administered intravenously (30 or 300nmol/min) for 2h, beginning from 72h after the start of SOV treatment. LH secretion was examined before and after administration, and embryos were collected 7 d after estrus. Senktide administration increased LH secretion in SOV-treated cows. The ratios of code 1, code 1 and 2, and blastocyst stage embryos to recovered embryos were increased by senktide (300nmol/min) administration. Moreover, the mRNA levels of MTCO1, COX7C, and MTATP6 were upregulated in recovered embryos of senktide (300nmol/min)-administered animals. These results indicate that the administration of senktide to SOV-treated cows enhances LH secretion and upregulates the expression of genes involved in mitochondrial metabolism in embryos, thereby improving embryo development and embryo quality.

Optogenetic Activation of Arcuate Kisspeptin Neurons Generates a Luteinizing Hormone Surge-Like Secretion in an Estradiol-Dependent Manner.

Traditionally, the anteroventral periventricular (AVPV) nucleus has been the brain area associated with luteinizing hormone (LH) surge secretion in rodents. However, the role of the other population of hypothalamic kisspeptin neurons, in the arcuate nucleus (ARC), has been less well characterized with respect to surge generation. Previous experiments have demonstrated ARC kisspeptin knockdown reduced the amplitude of LH surges, indicating that they have a role in surge amplification. The present study used an optogenetic approach to selectively stimulate ARC kisspeptin neurons and examine the effect on LH surges in mice with different hormonal administrations. LH level was monitored from 13:00 to 21:00 h, at 30-minute intervals. Intact Kiss-Cre female mice showed increased LH secretion during the stimulation period in addition to displaying a spontaneous LH surge around the time of lights off. In ovariectomized Kiss-Cre mice, optogenetic stimulation was followed by a surge-like secretion of LH immediately after the stimulation period. Ovariectomized Kiss-Cre mice with a low dose of 17β-estradiol (OVX+E) replacement displayed a surge-like increase in LH release during period of optic stimulation. No LH response to the optic stimulation was observed in OVX+E mice on the day of estradiol benzoate (EB) treatment (day 1). However, after administration of progesterone (day 2), all OVX+E+EB+P mice exhibited an LH surge during optic stimulation. A spontaneous LH surge also occurred in these mice at the expected time. Taken together, these results help to affirm the fact that ARC kisspeptin may have a novel amplificatory role in LH surge production, which is dependent on the gonadal steroid milieu.

Reduced Luteinizing Hormone Induction Following Estrogen and Progesterone Priming in Female-to-Male Transsexuals.

Anatomical studies have suggested that one of the brain structures involved in gender identity is the bed nucleus of the stria terminalis, though this brain structure is probably not the only one to control gender identity. We hypothesized that, if this brain area also affected gonadotropin secretion in humans, transsexual individuals might produce different gonadotropin levels in response to exogenous stimulation. In the present study, we examined whether estrogen combined with progesterone might lead to a change in luteinizing hormone (LH) secretion in female-to-male (FTM) transsexual individuals. We studied female control subjects (n = 9), FTM transsexual subjects (n = 12), and male-to-female (MTF) transsexual subjects (n = 8). Ethinyl estradiol (50 μg/tablet) was administered orally, twice a day, for five consecutive days. After the first blood sampling, progesterone (12.5 mg) was injected intramuscularly. Plasma LH was measured with an immunoradiometric assay. The combination of estrogen and progesterone resulted in increased LH secretion in female control subjects and in MTF subjects, but this increase appeared to be attenuated in FTM transsexual subjects. In fact, the %LH response was significantly reduced in FTM subjects (P < 0.05), but not in MTF subjects (P > 0.5), compared to female control subjects. In addition, the peak time after progesterone injection was significantly delayed in FTM subjects (P < 0.05), but not in MTF subjects (P > 0.5), compared to female control subjects. We then compared subjects according to whether the combination of estrogen and progesterone had a positive (more than 200% increase) or negative (less than 200% increase) effect on LH secretion. A χ2 analysis revealed significantly different (P < 0.05) effects on LH secretion between female controls (positive n = 7, negative n = 2) and FTM transsexual subjects (positive n = 4, negative n = 8), but not between female controls and MTF transsexual subjects (positive n = 7, negative n = 1). Thus, LH secretion in response to estrogen- and progesterone priming was attenuated in FTM subjects, but not in MTF subjects, compared to control females. This finding suggested that the brain area related to gender identity in morphological studies might also be involved in the LH secretory response in humans. Thus, altered brain morphology might be correlated to altered function in FTM transsexuals.

The Two Populations of Kisspeptin Neurons Are Involved in the Ram-Induced LH Pulsatile Secretion and LH Surge in Anestrous Ewes.

Exposure to a ram during spring stimulates luteinizing hormone (LH) secretion and can induce ovulation in sexually quiescent ewes ("ram effect"). Kisspeptin (Kiss) present in the arcuate nucleus (ARC) and the preoptic area (POA) is a potent stimulators of LH secretion. Our aim was to investigate whether Kiss neurons mediate the increase in LH secretion during the ram effect. With double immunofluorescent detection, we identified Kiss neurons (Kiss IR) activated (Fos IR) by exposure to a ram for 2 hours (M2) or 12 hours (M12) or to ewes for 2 hours (C). The density of cells Kiss + Fos IR and the proportion of Kiss IR cells that were also Fos IR cells were higher in M2 and M12 than in C in ARC (P < 0.002) and POA (P < 0.02). In ARC, these parameters were also higher in M12 than in M2 (P < 0.02 and P < 0.05). Kiss antagonist (P234 10-6M) administered by retrodialysis in POA for 3 hours at the time of introduction of the ram reduced the amplitude of the male-induced increase in LH concentration compared with solvent (P < 0.02). In ARC, P234 had a more limited effect (P < 0.038 1 hour after P234) but pulse frequency increased less than after solvent (P = 0.07). In contrast, Kiss antagonist (P271 10-4M) infused in ARC but not POA 6 to 18 hours after introduction of the ram prevented the LH surge in the ewe (0/6 vs 4/5 and 4/6 in C). These results suggest that both populations of Kiss neurons are involved in the ram-induced pulsatile LH secretion and in the LH surge.

Evidence That Endogenous Somatostatin Inhibits Episodic, but Not Surge, Secretion of LH in Female Sheep

Two modes of gonadotropin-releasing hormone (GnRH) and luteinizing hormone (LH) secretion are necessary for female fertility: surge and episodic secretion. However, the neural systems that regulate these GnRH secretion patterns are still under investigation. The neuropeptide somatostatin (SST) inhibits episodic LH secretion in humans and sheep, and several lines of evidence suggest SST may regulate secretion during the LH surge. In this study, we examined whether SST alters the LH surge in ewes by administering a SST receptor (SSTR) 2 agonist (octreotide) or antagonist [CYN154806 (CYN)] into the third ventricle during an estrogen-induced LH surge and whether endogenous SST alters episodic LH secretion. Neither octreotide nor CYN altered the amplitude or timing of the LH surge. Administration of CYN to intact ewes during the breeding season or anestrus increased LH secretion and increased c-Fos in a subset GnRH and kisspeptin cells during anestrus. To determine if these stimulatory effects are steroid dependent or independent, we administered CYN to ovariectomized ewes. This SSTR2 antagonist increased LH pulse frequency in ovariectomized ewes during anestrus but not during the breeding season. This study provides evidence that endogenous SST contributes to the control of LH secretion. The results demonstrate that SST, acting through SSTR2, inhibits episodic LH secretion, likely acting in the mediobasal hypothalamus, but action at this receptor does not alter surge secretion. Additionally, these data provide evidence that SST contributes to the steroid-independent suppression of LH pulse frequency during anestrus.

Exploring the Role of Pituitary Kisspeptin Receptor on Gonadotrophic Function In Vivo and In Vitro

The hypothalamic‐pituitary‐gonadal (HPG) axis is classically comprised of gonadotropin‐releasing hormone (GnRH) neurons in the hypothalamus that regulate the anterior pituitary gland, stimulating the gonadotrophs to secrete luteinizing hormone (LH) and follicle‐stimulating hormone (FSH) into the bloodstream. LH and FSH after being synthesized and released by the pituitary gland go on to play essential roles in folliculogenesis, ovulation, and steroidogenesis. Kisspeptin (KISS1)/kisspeptin receptor (KISS1R) signaling in GnRH neurons has been shown by our group and others to play an essential role in HPG function. While the gonadotropes of the anterior pituitary express the Kiss1r gene, a physiological role for kisspeptin signaling at the level of the pituitary has not been demonstrated. We knocked out the Kiss1r gene specifically in pituitary gonadotropes by crossing the αGSUCre mouse with the floxed Kiss1r mouse, producing the PKiRKO mouse. Q‐RT‐PCR and immunohistochemistry were used to demonstrate a disruption in pituitary Kiss1r mRNA and KISS1R protein in PKiRKO mice relative to controls. Q‐RT‐PCR demonstrated a reduction in Kiss1r mRNA by 88% and 64% in the pituitary of male and female PKiRKO mice (n=8), respectively, compared with wild type (WT) mice (n=8). Immunostaining for KISS1R protein levels exhibited similar trends for protein knock down as observed for the relative mRNA levels. Our results revealed no difference in the age of puberty between WT and PKiRKO littermates, as assessed by the ages of vaginal opening, and first estrus for female mice, and preputial separation for male mice. Furthermore, we saw no difference in ovarian and testes weight respectively in female and male mice. While there were no differences in basal LH and FSH levels, upon performing a GnRH stimulation test in vivo, we observed a significant attenuation (P&lt;0.05) in stimulated luteinizing hormone (LH) serum of PKiRKO male mice compared with WT male mice, while stimulated LH and FSH levels were no different between WT and PKiRKO female mice. These changes in pituitary sensitivity in males were associated with lower mRNA levels of GnRH receptor and estrogen receptor alpha. To directly study the effects of KISS1 on the pituitary gonadotroph, we sought to develop an in vitro primary culture system. To test the system, a GnRH dose response and time course study was performed on dispersed and adherent pituitary cells harvested from WT male and female mice. Groups of cells were treated with either 5nM, 30nM or 100nM GnRH, for a duration of 30 and 60 minutes. A significant increase in LH levels was observed in both male and female mice pituitary cells when treated with either 30nM or 100nM GnRH for 60 minutes. Female pituitary cells also showed a significant increase in LH secretion at the 30 minute time point. Therefore, a 30nM treatment for 60 minutes is suitable for GnRH stimulation and will be used for future studies. Included in those studies will be; WT and PKiRKO pituitary cells treatment with/without GnRH and with/without different doses of Kp10 (kisspeptin agonist). LH and FSH levels in the media will be measured after a 60 minute incubation. These studies will allow us to assess the direct effects of KISS1 on pituitary gonadotroph function that are mediated via the KISS1R. Overall this work will provide insight into the signaling of kisspeptin and Kiss1r on the gonadotroph neuron and how it contributes to both normal and abnormal reproductive physiology.Support or Funding InformationWe acknowledge support from the following grants 1.) U01HD066432 2.) P30DK079637 3.) R01068777 4.) R01DK101591

Ovarian and hormonal responses to single or continuous peripheral administration of senktide, a neurokinin 3 receptor agonist, during the follicular phase in goats

The present study aimed to investigate the effects of single or continuous administration of a neurokinin 3 receptor agonist, senktide, on hormonal and follicular dynamics in follicular phase goats. Goats were injected with PGF2α in the luteal phase and treated with an intravaginal progesterone device for 10 d. At 12 h after the cessation of progesterone treatment, the goats received a single intravenous injection of senktide (200 nmol, n = 4) or vehicle (n = 4), or continuous intravenous infusion of senktide (20 nmol/min, n = 6) or vehicle (n = 6) for 6 h. Blood sampling and ovarian ultrasonography were performed during the experiment. A single injection of senktide did not influence the number of luteinizing hormone (LH) pulses and mean LH concentration. On the other hand, continuous injection of senktide caused a sustained increase in LH secretion, and mean LH concentration in samples collected at 10-min intervals for 6 h after the start of infusion was higher than that of vehicle-treated goats (2.8 ± 1.3 vs 1.0 ± 0.6 ng/mL, P < 0.01). In 4 of 6 goats, LH concentrations reached their peaks during the 6-h senktide infusion, and ovulation was observed at 48 h after the start of infusion without estrous behavior. The remaining 2 senktide-treated goats and all vehicle-treated goats showed estrus and ovulated at 72 or 96 h after treatment. These results suggest that continuous infusion of senktide in follicular phase goats can cause a sustained increase in LH and advance the time of ovulation.

Kisspeptin signaling in the amygdala modulates reproductive hormone secretion.

Kisspeptin (encoded by KISS1) is a crucial activator of reproductive function. The role of kisspeptin has been studied extensively within the hypothalamus but little is known about its significance in other areas of the brain. KISS1 and its cognate receptor are expressed in the amygdala, a key limbic brain structure with inhibitory projections to hypothalamic centers involved in gonadotropin secretion. We therefore hypothesized that kisspeptin has effects on neuronal activation and reproductive pathways beyond the hypothalamus and particularly within the amygdala. To test this, we mapped brain neuronal activity (using manganese-enhanced MRI) associated with peripheral kisspeptin administration in rodents. We also investigated functional relevance by measuring the gonadotropin response to direct intra-medial amygdala (MeA) administration of kisspeptin and kisspeptin antagonist. Peripheral kisspeptin administration resulted in a marked decrease in signal intensity in the amygdala compared to vehicle alone. This was associated with an increase in luteinizing hormone (LH) secretion. In addition, intra-MeA administration of kisspeptin resulted in increased LH secretion, while blocking endogenous kisspeptin signaling within the amygdala by administering intra-MeA kisspeptin antagonist decreased both LH secretion and LH pulse frequency. We provide evidence for the first time that neuronal activity within the amygdala is decreased by peripheral kisspeptin administration and that kisspeptin signaling within the amygdala contributes to the modulation of gonadotropin release and pulsatility. Our data suggest that kisspeptin is a ‘master regulator’ of reproductive physiology, integrating limbic circuits with the regulation of gonadotropin-releasing hormone neurons and reproductive hormone secretion.

Effects of senktide, a neurokinin 3 receptor agonist, on luteinizing hormone secretion and follicular development in anestrous Shiba goats: a pilot study.

BackgroundRecent studies suggest that neurokinin B and its receptor, neurokinin 3 receptor, have an essential role in the regulation of gonadotropin-releasing hormone and luteinizing hormone (LH) release in several mammalian species. As the first trial, this pilot study reports the effect of intravenous treatment with senktide, a selective agonist of neurokinin 3 receptor, on LH secretion, follicular development in female goats that were clinically diagnosed with anestrus.FindingsAnestrous goats were intravenously administered 200 nmol senktide at 4-h intervals for 24 h. Most of them examined (5/6 cases) showed a pulsatile increase in LH secretion after each injection of senktide, whereas the remaining one case showed a surge-like increase of LH secretion. Ovulation was confirmed in 5/6 cases at the range of 48–96 h after the beginning of treatment.ConclusionsThis pilot study demonstrated that intravenous treatment with senktide has therapeutic action in goats with anestrus by inducing LH release, which could promote follicular development and ovulation.

Effects of intravenous administration of neurokinin receptor subtype-selective agonists on gonadotropin-releasing hormone pulse generator activity and luteinizing hormone secretion in goats.

Recent evidence suggests that neurokinin B (NKB), a member of the neurokinin (tachykinin) peptide family, plays a pivotal role in gonadotropin-releasing hormone (GnRH) pulse generation. Three types of neurokinin receptors (NKRs), NK1R, NK2R and NK3R, are found in the brain. Although NKB preferentially binds to NK3R, other NKRs are possibly also involved in NKB action. The present study examined the effects of intravenous administration of the NKR subtype-selective agonists GR73632 (NK1R), GR64349 (NK2R), and senktide (NK3R) on GnRH pulse generator activity and luteinizing hormone (LH) secretion. Multiple-unit activity (MUA) was monitored in ovariectomized goats (n = 5) implanted with recording electrodes. Characteristic increases in MUA (MUA volleys) were considered GnRH pulse generator activity. Although three NKR agonists dose-dependently induced an MUA volley and an accompanying increase in LH secretion, the efficacy in inducing the volley markedly differed. As little as 10 nmol of senktide induced an MUA volley in all goats, whereas a dose of 1000 nmol was only effective for the NK1R and NK2R agonists in two and four goats, respectively. When the treatment failed to evoke an MUA volley, no apparent change was observed in the MUA or LH secretion. Similar effects of the NK2R and NK3R agonists were observed in the presence of estradiol. The results demonstrated that NK3R plays a predominant role in GnRH pulse generation and suggested that the contributions of NK1R and NK2R to this mechanism may be few, if any, in goats.

Time course and role of luteinizing hormone and follicle-stimulating hormone in the expansion of the Leydig cell population at the time of puberty in the rhesus monkey (Macaca mulatta).

In higher primates, development of the adult population of Leydig cells has received little attention. Here, the emergence of 3β-hydroxysteroid dehydrogenase (HSD3B) positive cells in the testis of the rhesus monkey was examined during spontaneous puberty, and correlated with S-phase labeling in the interstitium at this critical stage of development. In addition, the relative role of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) in initiating the pubertal expansion of Leydig cells was studied by precociously stimulating the juvenile testis in vivo with pulsatile 11-day infusions of recombinant LH and FSH, either alone or in combination. At the time of castration, testes were immersion fixed in Bouin's, embedded in paraffin, and sectioned at 5μm. Leydig cells/testis were enumerated using HSD3B as a Leydig cell marker. Leydig cell number per testis increased progressively during puberty to reach values in the adult approximately 10 fold greater than in early-pubertal animals. The rise in cell number was associated with an increase in nuclear diameter. That the pubertal expansion of Leydig cell number was driven primarily by the increase in LH secretion at this stage of development was suggested by the finding that precocious stimulation of mid-juvenile monkeys with LH, either alone or in combination with that of FSH, resulted in a 20-30 fold increase in the number of HSD3B-positive cells. Interestingly, precocious FSH stimulation, alone, also resulted in appearance of Leydig cells as indicated by the occasional HSD3B-positive cell in the interstitium. The nuclear diameter of these Leydig cells, however, was less than that of those generated in response to LH.

Kisspeptin mediation of estradiol-induced secretion of luteinizing hormone and prolactin

In females, ovulation is coordinated by a complex set of interactions between the hypothalamus, the anterior pituitary and the gonads. Luteinizing hormone (LH) and prolactin (PRL) are pituitary hormones that have complementary roles in reproduction. There is a surge of both hormones prior to ovulation that is essential for adequate reproduction and can be mimicked by estradiol (E2) treatment in ovariectomized (OVX) rats [1], [2]. Both the preovulatory and the E2-induced LH and PRL surges in OVX rats occur at the same time of the day, indicating that circadian signals originating in the suprachiasmatic nucleus (SCN) must provide input to coordinate both LH and PRL secretion, and that response to this input depends on the steroid milieu. Kisspeptin (KISS) is the most potent stimulator of LH release and it has been recently demonstrated to also stimulate PRL release. There are two KISS neuronal populations in the rodent brain, located in the anteroventral periventricular nucleus (AVPV) and the arcuate nucleus (ARC). The ARC population coexpress kisspeptin, neurokinin B and dynorphin and are called KNDy neurons. We have developed a reduced model for kisspeptin control of PRL and LH secretion in animals without (OVX) and with E2 treatment (OVXE), based on experimental data and literature describing the roles of the two kisspeptin subpopulations (KNDy and AVPV) in PRL and LH secretion (Fig ​(Fig1A).1A). Without E2, secretion of PRL and LH remains constant. Dopamine (DA) is released from E2 inhibition and tonically inhibits PRL secretion [3]. The absence of E2 inhibition to KNDy neurons stimulates a tonic increase of LH secretion, while the AVPV subpopulation has a low level of activity, thus preventing an LH surge (Fig ​(Fig1B,1B, left). In the OVXE model, E2 directly induces a PRL surge by increasing the activity of lactotrophs and indirectly inhibiting DA neurons (Fig ​(Fig1B,1B, right). The time-of-day-signal is provided by a brief E2-dependent stimulation from neurons in the SCN. E2 inhibition of KNDy neurons decreases LH basal secretion while stimulation of the AVPV by E2, together with the circadian SCN signal, produces the LH surge (Fig ​(Fig1B,1B, right). The modeling simulation predicts that the two KISS subpopulations have dramatically different effects on the LH surge: ablation of AVPV eliminates the surge without changing basal LH levels, while ablation of KNDY neurons would reduce basal levels and have a modest effect on the LH surge. KNDy ablation would also reduce the PRL surge. Figure 1 A mathematical model reproducing the surges of LH and PRL. (A) Model diagram which was implemented in a system of differential equations. (B) Results of modeling simulations for OVX (left) and OVXE (right). Levels of hormones and neurotransmitters (in ...

Effects of exposure to male goat hair extracts on luteinizing hormone secretion and neuronal activation in seasonally anestrous ewes.

ABSTRACTIn sheep and goats, exposure of seasonally anestrous females to males or their fleece/hair activates the gonadotropin-releasing hormone (GnRH) pulse generator leading to pulsatile luteinizing hormone (LH) secretion. Pheromones emitted by sexually mature males are thought to play a prominent role in this male effect. In the present study, we first aimed to clarify whether the male goat pheromone is effective in ewes. Seasonally anestrous St. Croix ewes were exposed to hair extracts derived from either intact or castrated (control) male Shiba goats. The male goat-hair extract significantly increased LH secretion compared to the control, suggesting that an interspecies action of the male pheromone occurs between sheep and goats. Using the male goat-hair extract as the pheromone source, we then aimed to clarify the neural pathway involved in the signal transduction of the male pheromone. Ewes were exposed to either the goat-hair extract or the control and sacrificed 2 hr after the exposure. Expression of c-Fos, a marker of neuronal activation, was immunohistochemically examined. The male goat-hair extract significantly increased the c-Fos expression compared to the control in regions of the vomeronasal system, such as the accessory olfactory bulb and medial amygdala, and the arcuate nucleus. The main olfactory bulb did not exhibit any significant increase in the c-Fos expression by the male goat-hair extract. This result suggests that the neural signal of the male pheromone is conveyed to the GnRH pulse generator through the activated regions in ewes.

Different types of opioid receptors involved in the suppression of LH secretion in lactating sheep

To learn the involvement of endogenous opioid peptides (EOP) in the regulation of reproductive activity in ruminants, the effects of different opioid antagonists on luteinizing hormone (LH) secretion were determined in sheep during the early stage of lactation. The opioid receptor antagonists: naloxone (all types of receptors, n=5), naloxonazine (μ receptor, n=5), GNTI- (κ receptor, n=5), naltrindole (δ receptor, n=5) or the vehicle (control, n=5) were infused intracerebroventricularly in a series of five 30-min infusions (60μg/60μl) at 30-min intervals. The period of the experiment included the non-suckling (10:00–12.30) and suckling (12.30–15.00) periods. Blood samples were collected from 10.00 to 15.00 at 10-min intervals, and plasma LH concentration was assayed by the radioimmunoassay method. The obtained results showed that blocking of the EOP action within the central nervous system in lactating sheep caused a significant (p<0.001) increase in LH concentration in all treated groups, in comparison to the control. In the naloxone-treated group, a significant (p<0.05) increase in LH secretion also occurred during suckling. The amplitude of LH pulses increased significantly in the naloxonazine- (p<0.01) and naltrindole- (p<0.05) treated ewes compared to the control; there were no significant differences in the frequency of LH pulses among the groups. In conclusion, our study indicates that EOP play a crucial role in the mechanism inhibiting GnRH/LH axis activity in lactating sheep and that the ligands for μ opioid receptor may have the highest inhibitory effect.

Exogenous melatonin after a treatment of artificial long days is able to increase LH secretion during seasonal anoestrus in Payoya goats

One experiment was conducted to determine whether the treatment with artificial long days and exogenous melatonin can increase, by itself, luteinizing hormone (LH) secretion during spring (seasonal anoestrus) in Payoya goats and whether this treatment causes a variation in the reactivation of the LH secretion in the normal breeding season. The experiment started on 4 November and finished on 27 October. A total of 22 ovariectomised-oestradiol treated goats were used. Ten goats were exposed to long days (16 h of light/day) from 14 November to 20 February. On 20 February, they received one s.c. melatonin implant and were exposed to natural photoperiodic changes in an open shed. The control group was located in another open shed with any treatment during the whole experiment. For both groups, plasma samples were obtained twice a week for LH assay. The photoperiodic treatment induced an earlier fall of the LH secretion. However, after the melatonin treatment, a clear increase of LH secretion during the natural seasonal anoestrus in the treated group was observed, and no difference in the onset of the LH secretion at the normal breeding season was observed. We can conclude that, in Payoya goats, the photoperiodic–melatonin treatment is by itself able to induce a clear LH increase during the seasonal anoestrus and does not modify the reactivation of the LH secretion at the normal breeding season.

Embryonic GnRH Signaling Is Necessary for Maturation of the Male Reproductive Axis.

Gonadotropin-releasing hormone (GnRH) signaling regulates reproductive physiology in mammals. GnRH is released by a subset of hypothalamic neurons and binds to its receptor (GnRHR) on gonadotropes in the anterior pituitary gland to control production and secretion of gonadotropins that in turn regulate the activity of the gonads. Central control of reproduction is well understood in adult animals, however GnRH signaling has also been implicated in the development of the reproductive axis. To investigate the role of GnRH signaling during development, we selectively ablated GnRHR expressing cells in mice. This genetic strategy permitted us to identify an essential stage in male reproductive axis development, which depends on embryonic GnRH signaling. Our experiments revealed a striking dichotomy in the gonadotrope population of the fetal anterior pituitary gland. We show, that only luteinizing hormone (LH)- but not follicle-stimulating hormone (FSH)-expressing gonadotropes express the GnRHR at embryonic day 16.75. Furthermore, we demonstrate that an embryonic increase in LH secretion is needed to promote development of FSH-expressing gonadotropes, which might be mediated by paracrine interactions within the pituitary. Moreover, migration of GnRH neurons into the hypothalamus appeared normal with appropriate axonal connections to the median eminence, providing genetic evidence against autocrine regulation of GnRH neurons. Surprisingly, genetic ablation of GnRHR expressing cells significantly increased the number of GnRH neurons in the anterior hypothalamus, suggesting an unexpected role of GnRH signaling in establishing the size of the GnRH neuronal population. Our experiments define a functional role of embryonic GnRH signaling for the first time. (platform)

Altered multihormone synchrony in obese patients with polycystic ovary syndrome

Luteinizing hormone (LH) concentrations and pulsatility are increased in obese women with polycystic ovary syndrome (PCOS). In addition, patients have hyperandrogenemia and insulin resistance. The mechanisms involved in aberrant hormone regulation in PCOS are still unclear. We investigated 15 obese PCOS women with a body mass index between 30 and 54 kg/m2 and 9 healthy obese controls (body mass index, 31-60 kg/m2) with regular menstrual cycles. Subjects underwent 24-hour blood sampling at 10-minute intervals for later measurements of LH, leptin, testosterone, and insulin concentrations. Data were analyzed with a new deconvolution program, approximate entropy (and bivariate approximate entropy), and a cross-correlation network. Patients had increased LH pulse frequency and more than 2-fold greater daily LH secretion, with diminished pattern regularity. Testosterone secretion was increased 2-fold, but pattern regularity was similar to that in controls. In the network construct, insulin was correlated positively with LH, whereas leptin and testosterone were correlated negatively with LH. Bivariate synchrony of LH with insulin was decreased. Short-term caloric restriction paradoxically increased LH secretion by 1.5-fold and pattern irregularity, and reduced interpulse variability. Testosterone secretion and fasting concentrations of estradiol and sex hormone–binding globulin levels remained unchanged. Correlations between LH and insulin, leptin, and calculated free testosterone decreased. This study demonstrates marked alterations in the control of LH secretion in PCOS in the fed and calorie-restricted states. The ensemble results point to abnormal feedback control of not only the GnRH-gonadotrope complex, but also LH's relationships with leptin, insulin, and testosterone.

Embryonic gonadotropin-releasing hormone signaling is necessary for maturation of the male reproductive axis

Gonadotropin-releasing hormone (GnRH) signaling regulates reproductive physiology in mammals. GnRH is released by a subset of hypothalamic neurons and binds to GnRH receptor (GnRHR) on gonadotropes in the anterior pituitary gland to control production and secretion of gonadotropins that in turn regulate the activity of the gonads. Central control of reproduction is well understood in adult animals, but GnRH signaling has also been implicated in the development of the reproductive axis. To investigate the role of GnRH signaling during development, we selectively ablated GnRHR-expressing cells in mice. This genetic strategy permitted us to identify an essential stage in male reproductive axis development, which depends on embryonic GnRH signaling. Our experiments revealed a striking dichotomy in the gonadotrope population of the fetal anterior pituitary gland. We show that luteinizing hormone-expressing gonadotropes, but not follicle-stimulating hormone-expressing gonadotropes, express the GnRHR at embryonic day 16.75. Furthermore, we demonstrate that an embryonic increase in luteinizing hormone secretion is needed to promote development of follicle-stimulating hormone-expressing gonadotropes, which might be mediated by paracrine interactions within the pituitary. Moreover, migration of GnRH neurons into the hypothalamus appeared normal with appropriate axonal connections to the median eminence, providing genetic evidence against autocrine regulation of GnRH neurons. Surprisingly, genetic ablation of GnRHR expressing cells significantly increased the number of GnRH neurons in the anterior hypothalamus, suggesting an unexpected role of GnRH signaling in establishing the size of the GnRH neuronal population. Our experiments define a functional role of embryonic GnRH signaling.

Age- and sex-specific changes in naloxone-induced luteinizing hormone secretion and Fos expression in gonadotropin-releasing hormone neurons of gonadectomized rats

In the present study, we examined sex-specific changes in luteinizing hormone (LH) secretion and Fos expression in gonadotropin-releasing hormone (GnRH) neurons in response to naloxone in young (3 months old) and old (24 months old), gonadectomized male and female rats. We revealed by immunocytochemistry that, regardless of age and sex, naloxone significantly increased the number of GnRH neurons expressing Fos, which was associated with increased LH secretion. Additionally, although the magnitude of the increase in Fos-expressing GnRH neurons did not change in old males compared to young males, it was attenuated by almost half in old females compared to young females. LH levels decreased 60% in old males compared to young males and 15% in old females compared to young females. These results suggest LH secretion is impaired with age, but the ability of GnRH neurons to be stimulated by naloxone is preserved. However, the opioid-controlling mechanism is more fragile in females than males during aging.

Photoperiodic response curves for plasma LH concentrations and age at first egg in female broiler breeders

The objective of this work was to define precisely the response curve for photoinduced luteinizing hormone (LH) release in feed-restricted meat-type (broiler) breeder females and to compare it with the photoperiodic response curve for advance in age at first egg (AFE). Birds with a mean body weight of 2.0 kg at 20 weeks of age were transferred from an 8 to a 9, 9.5, 10, 10.5, 11, 11.5, 12, 12.5, 13, 14 or 18-h photoperiod; change in plasma LH was measured 4 d after photostimulation and subsequent individual AFE recorded. The first significant increase in LH secretion was seen in birds transferred to an 11.5-h photoperiod, but no further significant increases in LH were observed in birds transferred to longer photoperiods. A photoperiodic response curve based on a meta-analysis of changes in photoinduced LH secretion observed in this study and data from an earlier experiment using dwarf broiler breeders indicated a critical daylength of about 9.5 h and a saturation daylength of approximately 13 h. Similarly, the first significant advance in AFE occurred in birds transferred to an 11-h photoperiod, but with no further significant increases seen in birds transferred to photoperiods >11 h. A response curve for photoinduced advances in AFE was produced by meta-analysis using data from the present study and from an earlier investigation involving fewer, more widely spaced photoperiods. It is concluded, in female broiler breeders, that the photoperiodic response curves for photoinduced LH release and AFE are similar, with the point at which the responses begin to rise steeply (classical critical daylength) occurring at 9.5 h and the asymptote (classical saturation daylength) at 13 h. Functionally, however, the minimum photoperiod to achieve a significant change in either LH secretion or advance in AFE is between 11 and 11.5 h.