Inhibiting Kiss1 Neurons With Kappa Opioid Receptor Agonists to Treat Polycystic Ovary Syndrome and Vasomotor Symptoms.

CONTEXT: Recent evidence suggests that vasomotor symptoms (VMS) or hot flashes in the postmenopausal reproductive state and polycystic ovary syndrome (PCOS) in the premenopausal reproductive state emanate from the hyperactivity of Kiss1 neurons in the hypothalamic infundibular/arcuate nucleus (KNDy neurons). OBJECTIVE: We demonstrate in 2 murine models simulating menopause and PCOS that a peripherally restricted kappa receptor agonist (PRKA) inhibits hyperactive KNDy neurons (accessible from outside the blood-brain barrier) and impedes their downstream effects. DESIGN: Case/control. SETTING: Academic medical center. PARTICIPANTS: Mice. INTERVENTIONS: Administration of peripherally restricted kappa receptor agonists and frequent blood sampling to determine hormone release and body temperature. MAIN OUTCOME MEASURES: LH pulse parameters and body temperature. RESULTS: First, chronic administration of a PRKA to bilaterally ovariectomized mice with experimentally induced hyperactivity of KNDy neurons reduces the animals' elevated body temperature, mean plasma LH level, and mean peak LH per pulse. Second, chronic administration of a PRKA to a murine model of PCOS, having elevated plasma testosterone levels and irregular ovarian cycles, suppresses circulating levels of LH and testosterone and restores normal ovarian cyclicity. CONCLUSION: The inhibition of kisspeptin neuronal activity by activation of kappa receptors shows promise as a novel therapeutic approach to treat both VMS and PCOS in humans.

A role for placental kisspeptin in ß cell adaptation to pregnancy.

During pregnancy the maternal pancreatic islets of Langerhans undergo adaptive changes to compensate for gestational insulin resistance. Kisspeptin has been shown to stimulate insulin release, through its receptor, GPR54. The placenta releases high levels of kisspeptin into the maternal circulation, suggesting a role in modulating the islet adaptation to pregnancy. In the present study we show that pharmacological blockade of endogenous kisspeptin in pregnant mice resulted in impaired glucose homeostasis. This glucose intolerance was due to a reduced insulin response to glucose as opposed to any effect on insulin sensitivity. A ß cell-specific GPR54-knockdown mouse line was found to exhibit glucose intolerance during pregnancy, with no phenotype observed outside of pregnancy. Furthermore, in pregnant women circulating kisspeptin levels significantly correlated with insulin responses to oral glucose challenge and were significantly lower in women with gestational diabetes (GDM) compared with those without GDM. Thus, kisspeptin represents a placental signal that plays a physiological role in the islet adaptation to pregnancy, maintaining maternal glucose homeostasis by acting through the ß cell GPR54 receptor. Our data suggest reduced placental kisspeptin production, with consequent impaired kisspeptin-dependent ß cell compensation, may be a factor in the development of GDM in humans.

Gonadotropin-releasing hormone and kisseptin-10 regulate nuclear receptor subfamily 5 group a member 1/catenin beta 1/ nuclear receptor subfamily 0 group B member 1 activity in female rat anterior pituitary gland.

In this study, we tested the hypothesis that modulation of endogenous gonadotropin-releasing hormone (Gnrh) neuronal network activity alters the mRNA expression of nuclear receptor subfamily 5 group A member 1 (Nr5a1), through one of the component of Wnt pathway signaling - catenin beta 1 (Ctnnb1) (its co-activator), and its co-repressor nuclear receptor subfamily 0, group B member 1 (Nr0b1) in the female rat pituitary gland in vivo. Adult ovariectomized rats were given a serial infusion of Gnrh, kisspeptin-10, Gnrh + Gnrh antagonist (Antide), or kisspeptin-10 + kisspeptin antagonist (kisspeptin-234) into the third ventricle of the brain. The anterior pituitary and blood was used to mRNA and protein expression analysis. We demonstrated that Gnrh up-regulates Nr5a1 mRNA expression in the anterior pituitary and induces NR5A1 depletion in gonadotropes. Gnrh administration increased both Ctnnb1 mRNA expression and protein synthesis, and induced activation of cellular Ctnnb1 via translocation from the gonadotropes cytoplasm to nucleus. After kisspeptin-10 treatment, up-regulation of Nr0b1 mRNA and protein expression in the anterior pituitary was observed. These data indicate that Gnrh-neuron-mediated network activity alters Nr5a1 gene transcription and translation in gonadotrope cells and this effect may result from the changes induced in the Ctnnb1 and Nr0b1 gene/protein expression balance.

Effect of kisspeptin antagonist on goat in vitro Leydig cell steroidogenesis.

Kisspeptin is the protein product of Kiss1 gene. In contrast to its fundamental role as GnRH Secretagogue and puberty initiation, its functions in extrahypothalmic tissues such as the testes remain unknown. The objective of this study was to investigate the potential local role of kisspeptin in the Leydig cell culture in goats. Five male Shiba goats were castrated to isolate Leydig cells from the testes. The isolated Leydig cells were then purified and cultured with different concentration of kisspeptin antagonist (0, 5, and 10 nmol; 0KPA, 5KPA, and 10KPA; respectively). After 12 h, 20 IU of hCG was added to some wells (0KPA + hCG, 5KPA + hCG, and 10KPA + hCG; respectively); other wells did not receive hCG (0KPA + Con, 5KPA + Con, and 10KPA + Con; respectively). Media of Leydig cell culture was harvested at 2, 6, 12, and 24 h after addition of hCG for testosterone (T) and estradiol (E2) assays. The contents of some non KPA treated wells (0KPA + Con and 0KPA + hCG wells) were collected and stored at -80 OC for further identification the expression of mRNA encoding Kiss1 and its receptor (GPR54) using real time PCR. Results revealed high expressions of Kiss1/GPR54 mRNAs in the hCG treated (0KPA + hCG) wells compared to non-hCG treated ones (0KPA + Con). KPA significantly reduced the basal T production at 6 h incubation as well as hCG-induced T production in 2, 6, and 24 h incubation. Basal E2 concentrations were significantly lower in the KPA treated wells at 6, and 24 h likewise, KPA significantly attenuated induced E2 production at 12 h compared with its values in non KPA treated wells. In conclusion, kisspeptin antagonist significantly attenuated both basal and hCG-activated T and E2 production by purified Leydig cells in goats. Therefore, involvement of kisspeptin in the steroidogenic capability of Leydig cells is possible in goats.

The anti-androgenic effect of chronic exposure to semicarbazide on male Japanese flounder (Paralichthys olivaceus) and its potential mechanisms.

Semicarbazide (SMC), a new marine pollutant, has anti-estrogenic effects on female Japanese flounder (Paralichthys olivaceus). However, whether SMC also affects the reproductive endocrine system of male marine organisms is currently unclear. In this study, Japanese flounder embryos were exposed to 1, 10, and 100 µg/L SMC for 130 days. Plasma testosterone (T) and 17ß-estradiol (E2) concentrations were significantly decreased in male flounders after SMC exposure. The expression of genes involved in T and E2 synthesis, including steroidogenic acute regulatory protein, cytochrome P450 11A1, 17α-hydroxylase, 17ß-hydroxysteroid dehydrogenase and cytochrome P450 19A, was down-regulated in the gonads, which may explain the decrease in plasma sex hormones levels. Moreover, SMC-mediated changes in the transcription of these steroidogenic genes were associated with reduced levels of follicle-stimulating hormone beta subunit (fshß), luteinizing hormone beta subunit (lhß), follicle-stimulating hormone receptor (fshr) and luteinizing hormone receptor (lhr) mRNA. In addition, down-regulated transcription of fshß and lhß in the SMC exposure groups was affected by reduced mRNA levels of seabream gonadotropin-releasing hormone (sbgnrh), g-protein-coupled receptor 54 (gpr54) in the kisspeptin/gpr54 system, as well as the gamma-aminobutyric acid (GABA) synthesis enzyme glutamic acid decarboxylase (gad). Overall, our results showed that environmentally relevant concentrations of SMC exerted anti-androgenic effects in male flounders via impacting HPG axis, kiss/gpr54 system and GABA synthesis, providing theoretical support for investigating reproductive toxicity of environmental pollutants that interfere with the neuroendocrine system.

Kisspeptin modulates pain sensitivity of CFLP mice.

Kisspeptin, a hypothalamic neuropeptide, is a member of the RF-amide family, which have been known to modify pain sensitivity in rodents. The aim of the present study was to investigate the effect of kisspeptin-13 (KP-13), an endogenous derivative of kisspeptin, on nociception in adult male and female CFLP mice and the possible interaction of KP-13 with morphine on nociception. Mice were injected with different doses of KP-13, 30, 60 and 120 min after of which the nociceptive sensitivity were assessed via the tail-flick test. To investigate the receptor involved in the mediation a kisspeptin receptor antagonist (KP-234) pretreatment was applied before KP-13 administration. Furthermore, we investigated the effect of KP-13 on the acute antinociceptive effect of morphine, on acute morphine tolerance and on naloxone-precipitated withdrawal. Last, the Von Frey test was used in order to assess KP-13's effect on mechanical nociception. Our results showed that KP-13 decreased the nociceptive threshold of both males and females independent of sex, which was prevented by KP-234. Furthermore, KP-13 treatment depressed the acute antinociceptive effect of morphine and attenuated the development of morphine tolerance. KP-13 also induced a mechanical hypersensitivity. These data underlie kisspeptin's hyperalgesic action and argues for the role of kisspeptin receptor 1 in the mediation of its action. Furthermore, our results suggest that central KP-13 administration can modify the acute effects of morphine.

Presence and function of kisspeptin/KISS1R system in swine ovarian follicles.

Kisspeptin and its receptor KISS1R are involved in the neuroendocrine regulation of mammalian reproduction and their role on follicular development and function can be hypothesized. The present work was designed to confirm the immunopresence of kisspeptin and its receptor in the ovary of swine and to study the effects of kisspeptin 10 and its antagonist, kisspeptin 234, on main functional parameters of granulosa cells (i.e. cell proliferation, steroid production, and redox status) as well as their modulatory action on angiogenesis. The immunopresence of kisspeptin and KISS1R were detected in granulosa cells. Kisspeptin 10 stimulated progesterone in vitro production, thus indirectly suggesting that it can have a role in the luteinization process of granulosa cells. Kisspeptin 10 displayed potentiating effects on non-enzymatic scavenging activity, thus supporting its involvement in the control of the antioxidant defense system of ovarian follicles. In addition, results from the angiogenesis bioassay suggest that kisspeptin may have a role in the physiological development of new ovarian vessels. Additional studies are needed to confirm the functional significance of the kisspeptin/KISS1R system within the swine ovary.

Stimulation of growth hormone by kisspeptin antagonists in ewes.

Kisspeptin signalling is indispensable for fertility, stimulating gonadotropin-releasing hormone (GnRH) secretion and mediating gonadal steroid feedback on GnRH neurons. Moreover, kisspeptin neurons have been implicated in other non-reproductive neuroendocrine roles. Kisspeptin appears to also regulate growth hormone secretion but much of the data appear contradictory. We sought to clarify a potential role of kisspeptin in growth hormone (GH) regulation by examining the effect of kisspeptin antagonists on GH secretion in ewes under various physiological conditions. Our data show clear and robust increases in GH secretion following lateral ventricle or third ventricle infusion of kisspeptin antagonists p-234 and p-271 in either ovariectomized or anestrous ewes. Central infusion of kisspeptin-10 had no effect on GH secretion. To determine the level at which kisspeptin may influence GH secretion, we examined expression of the cognate kisspeptin receptor, GPR54, in pituitary cells and showed by immunocytochemistry that the majority of somatotropes express GPR54 while expression was largely negative in other pituitary cells. Overall, we have demonstrated that blocking kisspeptin signalling by antagonists stimulates GH secretion in ewes and that this is likely mediated by inhibiting endogenous kisspeptin activation of GPR54 expressed on somatotropes. The findings suggest that endogenous kisspeptin inhibits GH secretion through GPR54 expressed on somatotropes.

KiSS1 gene as a novel mediator of TGFß-mediated cell invasion in triple negative breast cancer.

The invasive and metastatic phenotypes of breast cancer correlate with high recurrence rates and poor survival outcomes. Transforming growth factor-ß (TGFß) promotes tumor progression and metastasis in aggressive breast cancer. Here, we identified the kisspeptin KiSS1 as a downstream target of canonical TGFß/Smad2 pathway in triple negative breast cancer cells. We also found KiSS1 expression to be required for TGFß-induced cancer cell invasion. Indeed, knockdown expression of KiSS1 blocked TGFß-mediated cancer cell invasion as well as metalloproteinase (MMP9) expression and activity. Interestingly, Kisspeptin-10 (KP-10), the smallest active form of kisspeptin also stimulates cancer cell invasive behavior through activation of MAPK/Erk pathway. We described a positive feedback loop between KiSS1 and p21 downstream of TGFß, further contributing to TGFß-induced cancer cell invasion. Lastly, we explored both the clinical utility of KiSS1 as a lymph node involvement predictive tool and its potential as a therapeutic target. We found KiSS1 high expression to correlate with lymph node positive status. Furthermore, blocking KiSS1 using a specific small peptide antagonist (p234) impaired TGFß-mediated cell invasion and MMP9 induction. Together, our results define an essential role of KiSS1 in regulating TGFß pro-invasive effects and define KiSS1 as a therapeutic new target for triple negative breast cancer.

Contrôle de l'axe gonadotrope : nouveaux aspects physiologiques et thérapeutiques: Control of the gonadotrope axis: new physiologic and therapeutic aspects.

The endocrine and exocrine functions of the gonads are controlled by the gonadotrope axis, whose master regulator is the hypothalamic decapeptide GnRH. The Kisspeptin/Neurokinin B (Kp/NkB) neuronendocrine system is the main physiologic regulator of GnRH neurons. The Kp/NkB system is currently considered the key mediator for the hypothalamic negative feedback exerted by sex steroids and prolactin, as well as by various metabolic signals. Intrinsic alterations or regulatory abnormalities of Kp/NkB system lead to various gonadotrope axis puberty and fertility dysfunctions. Molecular inactivations of Kp/NkB system actors are associated with some forms of congenital hypogonadotropic hypogonadism without anosmia. The Kp/NkB System is also involved in a few forms of precocious puberty. Finally, the Kp/NKB system is also implicated in gonadotrope axis alterations leading to functional hypothalamic amenorrhea or hyperprolactinemia. NkB is particularly and directly involved in vasomotor menopausal hot flushes mechanism. Various Kp/NkB agonist/antagonist compounds have been developed during the last ten years, and are currently being evaluated in humans. These molecules have potential applications not only in rare genetic diseases with Kp/NkB alterations, but also in various gonadotrope axis-related diseases or in vitro fertilization. The administration of NkB antagonists in menopausal women represents a real therapeutic advance because of their impressive effect in controlling vasomotor menopausal hot flushes.

Kisspeptin and Neurokinin B Signaling Network Underlies the Pubertal Increase in GnRH Release in Female Rhesus Monkeys.

Loss-of-function or inactivating mutations in the genes coding for kisspeptin and its receptor (KISS1R) or neurokinin B (NKB) and the NKB receptor (NK3R) in humans result in a delay in or the absence of puberty. However, precise mechanisms of kisspeptin and NKB signaling in the regulation of the pubertal increase in gonadotropin-releasing hormone (GnRH) release in primates are unknown. In this study, we conducted a series of experiments infusing agonists and antagonists of kisspeptin and NKB into the stalk-median eminence, where GnRH, kisspeptin, and NKB neuroterminal fibers are concentrated, and measuring GnRH release in prepubertal and pubertal female rhesus monkeys. Results indicate that (1) similar to those previously reported for GnRH stimulation by the KISS1R agonist (i.e., human kisspeptin-10), the NK3R agonist senktide stimulated GnRH release in a dose-responsive manner in both prepubertal and pubertal monkeys; (2) the senktide-induced GnRH release was blocked in the presence of the KISS1R antagonist peptide 234 in pubertal but not prepubertal monkeys; and (3) the kisspeptin-induced GnRH release was blocked in the presence of the NK3R antagonist SB222200 in the pubertal but not prepubertal monkeys. These results are interpreted to mean that although, in prepubertal female monkeys, kisspeptin and NKB signaling to GnRH release is independent, in pubertal female monkeys, a reciprocal signaling mechanism between kisspeptin and NKB neurons is established. We speculate that this cooperative mechanism by the kisspeptin and NKB network underlies the pubertal increase in GnRH release in female monkeys.

Neurokinin B regulates reproduction via inhibition of kisspeptin in a teleost, the striped bass.

Kisspeptin and neurokinin B (NKB) are neuropeptides co-expressed in the mammalian hypothalamus and coordinately control GnRH signaling. We have found that Nkb and kisspeptin neurons are distinct in the teleost, striped bass (STB) and capitalized on this phenomenon to study the mode of action of Nkb and its related neuropeptide-F (Nkf), both of which are encoded by the tac3 gene. In vitro brain slices and in vivo administration studies revealed that Nkb/f consistently downregulated kiss2, whereas antagonist (AntD) administration restored this effect. Overall, a minor effect was noted on gnrh1 expression, whereas Gnrh1 content in the pituitaries was reduced after Nkb/f treatment and increased with AntD. Concomitantly, immunostaining demonstrated that hypothalamic Nkb neurons border and densely innervate the largest kiss2 neuronal population in the hypothalamus, which also coexpresses Nkb receptor. No expression of Nkb receptor or Nkb neuronal projections was detected near/in Gnrh1 soma in the preoptic area. At the level of the pituitary, however, the picture was more complex: both Nkb/f and AntD upregulated lhb and fshb expression and Lh secretion in vivo Together with the stimulatory effect of Nkb/f on Lh/Fsh secretion from pituitary cells, in vitro, this may indicate an additional independent action of Nkb/f within the pituitary, in which the hypothalamic pathway is more dominant. The current study demonstrates that Nkb/f utilizes multiple pathways to regulate reproduction in the STB and that in the brain, Nkb mainly acts as a negative modulator of kiss2 to regulate the release of Gnrh1.

Environmental obesogen tributyltin chloride leads to abnormal hypothalamic-pituitary-gonadal axis function by disruption in kisspeptin/leptin signaling in female rats.

Tributyltin chloride (TBT) is a xenobiotic used as a biocide in antifouling paints that has been demonstrated to induce endocrine-disrupting effects, such as obesity and reproductive abnormalities. An integrative metabolic control in the hypothalamus-pituitary-gonadal (HPG) axis was exerted by leptin. However, studies that have investigated the obesogenic TBT effects on the HPG axis are especially rare. We investigated whether metabolic disorders as a result of TBT are correlated with abnormal hypothalamus-pituitary-gonadal (HPG) axis function, as well as kisspeptin (Kiss) action. Female Wistar rats were administered vehicle and TBT (100ng/kg/day) for 15days via gavage. We analyzed their effects on the tin serum and ovary accumulation (as biomarker of TBT exposure), estrous cyclicity, surge LH levels, GnRH expression, Kiss action, fertility, testosterone levels, ovarian apoptosis, uterine inflammation, fibrosis, estrogen negative feedback, body weight gain, insulin, leptin, adiponectin levels, as well as the glucose tolerance (GTT) and insulin sensitivity tests (IST). TBT led to increased serum and ovary tin levels, irregular estrous cyclicity, and decreased surge LH levels, GnRH expression and Kiss responsiveness. A strong negative correlation between the serum and ovary tin levels with lower Kiss responsiveness and GnRH mRNA expression was observed in TBT rats. An increase in the testosterone levels, ovarian and uterine fibrosis, ovarian apoptosis, and uterine inflammation and a decrease in fertility and estrogen negative feedback were demonstrated in the TBT rats. We also identified an increase in the body weight gain and abnormal GTT and IST tests, which were associated with hyperinsulinemia, hyperleptinemia and hypoadiponectinemia, in the TBT rats. TBT disrupted proper functioning of the HPG axis as a result of abnormal Kiss action. The metabolic dysfunctions co-occur with the HPG axis abnormalities. Hyperleptinemia as a result of obesity induced by TBT may be associated with abnormal HPG function. A strong negative correlation between the hyperleptinemia and lower Kiss responsiveness was observed in the TBT rats. These findings provide evidence that TBT leads to toxic effects direct on the HPG axis and/or indirectly by abnormal metabolic regulation of the HPG axis.

Engineering a gene silencing viral construct that targets the cat hypothalamus to induce permanent sterility: An update.

The intent of this contribution is to provide an update of the progress we have made towards developing a method/treatment to permanently sterilize cats. Our approach employs two complementary methodologies: RNA interference (RNAi) to silence genes involved in the central control of reproduction and a virus-based gene therapy system intended to deliver RNAi selectively to the hypothalamus (where these genes are expressed) via the systemic administration of modified viruses. We selected the hypothalamus because it contains neurons expressing Kiss1 and Tac3, two genes essential for reproduction and fertility. We chose the non-pathogenic adeno-associated virus (AAV) as a vector whose tropism could be modified to target the hypothalamus. The issues that must be overcome to utilize this vector as a delivery vehicle to induce sterility include modification of the wild-type AAV to target the hypothalamic region of the brain with a simultaneous reduction in targeting of peripheral tissues and non-hypothalamic brain regions, identification of RNAi targets that will effectively reduce the expression of Kiss1 and Tac3 without off-target effects, and determination if neutralizing antibodies to the AAV serotype of choice are present in cats. Successful resolution of these issues will pave the way for the development of a powerful tool to induce the permanent sterility in cats.

Galanin Activates G Protein Gated Inwardly Rectifying Potassium Channels and Suppresses Kisspeptin-10 Activation of GnRH Neurons.

GnRH neurons are regulated by hypothalamic kisspeptin neurons. Recently, galanin was identified in a subpopulation of kisspeptin neurons. Although the literature thoroughly describes kisspeptin activation of GnRH neurons, little is known about the effects of galanin on GnRH neurons. This study investigated whether galanin could alter kisspeptin signaling to GnRH neurons. GnRH cells maintained in explants, known to display spontaneous calcium oscillations, and a long-lasting calcium response to kisspeptin-10 (kp-10), were used. First, transcripts for galanin receptors (GalRs) were examined. Only GalR1 was found in GnRH neurons. A series of experiments was then performed to determine the action of galanin on kp-10 activated GnRH neurons. Applied after kp-10 activation, galanin 1-16 (Gal1-16) rapidly suppressed kp-10 activation. Applied with kp-10, Gal1-16 prevented kp-10 activation until its removal. To determine the mechanism by which galanin inhibited kp-10 activation of GnRH neurons, Gal1-16 and galanin were applied to spontaneously active GnRH neurons. Both inhibited GnRH neuronal activity, independent of GnRH neuronal inputs. This inhibition was mimicked by a GalR1 agonist but not by GalR2 or GalR2/3 agonists. Although Gal1-16 inhibition relied on Gi/o signaling, it was independent of cAMP levels but sensitive to blockers of G protein-coupled inwardly rectifying potassium channels. A newly developed bioassay for GnRH detection showed Gal1-16 decreased the kp-10-evoked GnRH secretion below detection threshold. Together, this study shows that galanin is a potent regulator of GnRH neurons, possibly acting as a physiological break to kisspeptin excitation.

The effects of kisspeptin agonist canine KP-10 and kisspeptin antagonist p271 on plasma LH concentrations during different stages of the estrous cycle and anestrus in the bitch.

Kisspeptin (KP) plays a key role in the regulation of the hypothalamic-pituitary-gonadal axis via the release of GnRH. As normal KP signaling is essential for reproductive function, it could be an interesting new target for therapeutic interventions, e.g., nonsurgical contraception in dogs. The aims of the present study were to investigate the effect of KP-10 administration on plasma LH concentration in different stages of the reproductive cycle and to investigate the suitability of p271 as KP antagonist in the bitch. Two groups of six adult Beagle bitches were used. In one group, plasma LH concentration was determined before (40 and 0 minutes) and 10, 20, 40, and 60 minutes after the intravenous administration of 0.5-µg/kg body weight (BW) canine KP-10. In the other group, the bitches received a continuous intravenous infusion with p271 (50 µg/kg BW/h) for 3 hours, and 0.5-µg/kg BW canine KP-10 was administered intravenously 2 hours after the start of the p271 infusion. Their plasma LH concentration was determined before (-40 and 0 minutes) and 30, 60, 90, 120, 130, 140, 160, and 180 minutes after the start of the p271 infusion. In both groups, the experiments were performed during the follicular phase, the first and second half of the luteal phase, and during anestrus. Canine KP-10 induced an increase of plasma LH concentration during all estrous cycle stages and anestrus. There was no difference in LH response between the two groups. The lowest LH response was seen during the follicular phase and the highest response during anestrus. The area under the curve (AUC) for LH and LH increment in the follicular phase were lower than those in anestrus. The AUC LH and LH increment in the first half of the luteal phase were lower than those in the second half of the luteal phase and anestrus. The AUC LH and LH increment in the second half of the luteal phase were not different from those in anestrus. Continuous administration of the antagonist p271 did not alter basal plasma LH concentration and could not prevent or lower the LH response to KP-10 in any of the cycle stages and anestrus. It can be concluded that the LH response to KP-10 is dependent on estrous cycle stage and that peripheral administrated p271 cannot be used as KP antagonist in the dog. This provides new insight in reproductive endocrinology of the bitch, which is important when KP signaling is considered for therapeutic interventions, such as for estrus induction or nonsurgical contraception in the bitch.

The Increase in Signaling by Kisspeptin Neurons in the Preoptic Area and Associated Changes in Clock Gene Expression That Trigger the LH Surge in Female Rats Are Dependent on the Facilitatory Action of a Noradrenaline Input.

In rodents, kisspeptin neurons in the rostral periventricular area of the third ventricle (RP3V) of the preoptic area are considered to provide a major stimulatory input to the GnRH neuronal network that is responsible for triggering the preovulatory LH surge. Noradrenaline (NA) is one of the main modulators of GnRH release, and NA fibers are found in close apposition to kisspeptin neurons in the RP3V. Our objective was to interrogate the role of NA signaling in the kisspeptin control of GnRH secretion during the estradiol induced LH surge in ovariectomized rats, using prazosin, an α1-adrenergic receptor antagonist. In control rats, the estradiol-induced LH surge at 17 hours was associated with a significant increase in GnRH and kisspeptin content in the median eminence with the increase in kisspeptin preceding that of GnRH and LH. Prazosin, administered 5 and 3 hours prior to the predicted time of the LH surge truncated the LH surge and abolished the rise in GnRH and kisspeptin in the median eminence. In the preoptic area, prazosin blocked the increases in Kiss1 gene expression and kisspeptin content in association with a disruption in the expression of the clock genes, Per1 and Bmal1. Together these findings demonstrate for the first time that NA modulates kisspeptin synthesis in the RP3V through the activation of α1-adrenergic receptors prior to the initiation of the LH surge and indicate a potential role of α1-adrenergic signaling in the circadian-controlled pathway timing of the preovulatory LH surge.

Therapeutic Neuroendocrine Agonist and Antagonist Analogs of Hypothalamic Neuropeptides as Modulators of the Hypothalamic-Pituitary-Gonadal Axis.

Reproductive hormones play a role at all stages of life and affect most tissues of the body. Gonadotropin-releasing hormone (GnRH) synthesized in the hypothalamus stimulates the secretion of gonadotropins which in turn stimulate gonadal sex hormone production and gamete formation. This hypothalamic-pituitary-gonadal (HPG) axis has, therefore, been the target for the development of numerous drugs which regulate it at various points. These include sex steroid agonists and antagonists, inhibitors of sex steroid biosynthesis, and GnRH agonists and antagonists, which have found extensive applications in treating numerous conditions such as precocious puberty, delayed puberty, prostate cancer, benign prostatic hyperplasia, endometriosis, uterine fibroids and also in in vitro fertilization protocols. The novel neuroendocrine peptides, kisspeptin (KP) and neurokinin B (NKB), were recently discovered as upstream regulators of GnRH, and inactivating mutations of KP and NKB ligands or receptors result in a failure to progress through puberty. Agonists and antagonists of KP and NKB are being developed as more subtle modulators of the HPG axis. These new drugs offer additional and alternative therapeutic options in pediatric and adult hormone-dependent diseases.

Kisspeptin is involved in ovarian follicular development during aging in rats.

We have previously reported that kisspeptin (KP) may be under the control of the sympathetic innervation of the ovary. Considering that the sympathetic activity of the ovary increases with aging, it is possible that ovarian KP also increases during this period and participates in follicular development. To evaluate this possibility, we determined ovarian KP expression and its action on follicular development during reproductive aging in rats. We measured ovarian KP mRNA and protein levels in 6-, 8-, 10- and 12-month-old rats. To evaluate follicular developmental changes, intraovarian administration of KP or its antagonist, peptide 234 (P234), was performed using a mini-osmotic pump, and to evaluate FSH receptor (FSHR) changes in the senescent ovary, we stimulated cultured ovaries with KP, P234 and isoproterenol (ISO). Our results shows that KP expression in the ovary was increased in 10- and 12-month-old rats compared with 6-month-old rats, and this increase in KP was strongly correlated with the increase in ovarian norepinephrine observed with aging. The administration of KP produced an increase in corpora lutea and type III follicles in 6- and 10-month-old rats, which was reversed by P234 administration at 10 months. In addition, KP decreased the number and size of antral follicles in 6- and 10-month-old rats, while P234 administration produced an increase in these structures at the same ages. In ovarian cultures KP prevented the induction of FSHR by ISO. These results suggest that intraovarian KP negatively participates in the acquisition of FSHR, indicating a local role in the regulation of follicular development and ovulation during reproductive aging.

Kisspeptin Antagonists Reveal Kisspeptin 1 and Kisspeptin 2 Differential Regulation of Reproduction in the Teleost, Morone saxatilis.

The importance of kisspeptin in regulating vertebrate reproduction has been well established, but the exact mechanism continues to unfold. Unlike mammals, many lower vertebrates possess a dual kisspeptin system, Kiss1 and Kiss2. To decipher the roles of the kisspeptins in fish, we identified two potential kisspeptin antagonists, pep 234 and pep 359, by screening analogs for their ability to inactivate striped bass Kiss1 and Kiss2 receptors expressed in COS7 cells. Pep 234 (a mammalian KISS1 antagonist) antagonizes Kiss1r signaling activated by Kiss1 and Kiss2, and pep 359 (a novel analog) antagonizes Kiss2 activation of both receptors. In vitro studies using brain slices demonstrated that only Kiss2 can upregulate the expression of the hypophysiotropic gnrh1, which was subsequently diminished by pep 234 and pep 359. In primary pituitary cell cultures, the two antagonists revealed a complex network of putative endogenous and exogenous regulation by kisspeptin. While both kisspeptins stimulate Fsh expression and secretion, Kiss2 predominately induces Lh secretion. Pep 234 and 359 treatment of spawning males hindered sperm production. This effect was accompanied with decreased brain gnrh1 and gnrh2 mRNA levels and peptide content in the pituitary, and increased levels of pituitary Lh, probably due to attenuation of Lh release. Strikingly, the mRNA levels of arginine-vasotocin, the neurons of which in the preoptic area coexpress kiss2r, were dramatically reduced by the antagonists. Our results demonstrate differential actions of Kiss1 and Kiss2 systems along the hypothalamic-pituitary axis and interactions with other neuropeptides, and further reinforce the importance of kisspeptin in the execution of spawning.