Development and validation of sensitive sandwich ELISAs for two investigational nonapeptide metastin receptor agonists, TAK-448 and TAK-683

KNDy neurons as the GnRH pulse generator: Recent studies in ruminants

This review considers three aspects of recent work on the role of KNDy neurons in GnRH pulse generation in ruminants. First, work on basic mechanisms of pulse generation includes several tests of this hypothesis, all of which support it, and evidence that Kiss1r-containing neurons form a positive feedback circuit with the KNDy neural network that strengthen the activity of this network. The second section on pathways mediating external inputs focuses on the influence of nutrition and photoperiod, and describes the evidence supporting roles for proopiomelanocortin (POMC) and agouti-related peptide (AgRP) afferents to KNDy cells in each of these. Finally, we review studies exploring the potential applications of manipulating signaling by kisspeptin, and the other KNDy peptides, to control reproductive function in domestic animals and conclude that, although these approaches show some promise, they do not have major advantages over current practices at this time.

GnRH and the photoperiodic control of seasonal reproduction: Delegating the task to kisspeptin and RFRP-3

Synchronization of mammalian breeding activity to the annual change of photoperiod and environmental conditions is of the utmost importance for individual survival and species perpetuation. Subsequent to the early 1960s, when the central role of melatonin in this adaptive process was demonstrated, our comprehension of the mechanisms through which light regulates gonadal activity has increased considerably. The current model for the photoperiodic neuroendocrine system points to pivotal roles for the melatonin-sensitive pars tuberalis (PT) and its seasonally-regulated production of thyroid-stimulating hormone (TSH), as well as for TSH-sensitive hypothalamic tanycytes, radial glia-like cells located in the basal part of the third ventricle. Tanycytes respond to TSH through increased expression of thyroid hormone (TH) deiodinase 2 (Dio2), which leads to heightened production of intrahypothalamic triiodothyronine (T3) during longer days of spring and summer. There is strong evidence that this local, long-day driven, increase in T3 links melatonin input at the PT to gonadotropin-releasing hormone (GnRH) output, to align breeding with the seasons. The mechanism(s) through which T3 impinges upon GnRH remain(s) unclear. However, two distinct neuronal populations of the medio-basal hypothalamus, which express the (Arg)(Phe)-amide peptides kisspeptin and RFamide-related peptide-3, appear to be well-positioned to relay this seasonal T3 message towards GnRH neurons. Here, we summarize our current understanding of the cellular, molecular and neuroendocrine players, which keep track of photoperiod and ultimately govern GnRH output and seasonal breeding.

An administration of TAK-683 at a minimally effective dose for luteinizing hormone stimulation under the absence of the ovary induces luteinizing hormone surge in ovary-intact goats

The present study aimed to evaluate hormonal responses and their association with the TAK-683 blood concentrations in goats administered TAK-683 at a low dose, which had been previously determined as the minimally effective dose for luteinizing hormone (LH) stimulation in ovariectomized goats. In Experiment 1, 5 µg of TAK-683 treatment had no significant stimulatory effect on LH secretion in ovariectomized Shiba goats (n = 4). In Experiment 2, cycling goats received the treatment of prostaglandin F_2α and progesterone-releasing controlled internal drug releasing (CIDR) to induce the follicular phase, then they were treated with 5 µg of TAK-683 (hour 0) intravenously (n = 4, IV) or subcutaneously (n = 3, SC) or with vehicle intravenously (n = 4, control) at 12 h after CIDR removal. Blood samples were collected at 10-min (–2–6 h), 2-h (6–24 h), or 6-h (24–48 h) intervals. Ovarian ultrasonographic images were assessed daily to confirm ovulation after the treatment. A surge-like release of LH was immediately observed after injection in all animals in the IV (peak time: 4.2 ± 0.6 h, peak concentration: 73.3 ± 27.5 ng/ml) and SC (peak time: 4.6 ± 0.4 h, peak concentration: 62.6 ± 23.2 ng/ml) groups, but not in the control group. Ovulation was detected within 3 days after TAK-683 injection in all animals in the IV and SC groups, and the interval period from TAK-683 administration to ovulation in the IV group was significantly (P < 0.05) shorter than that of the control group. No significant changes were observed between the IV and SC groups in terms of luteal diameter and blood progesterone levels after ovulation. The present findings suggest that the involvement of one or more ovarian factor(s) is indispensable for a TAK-683-induced LH surge leading to ovulation in goats.

Effect of investigational kisspeptin/metastin analog, TAK-683, on luteinizing hormone secretion at different stages of the luteal phase in goats

This study aimed to examine the response of luteinizing hormone (LH) secretion and ovarian steroid profile to TAK-683, an investigational metastin/kisspeptin analog, through treatment during different stages of the luteal phase in goats. Nine cycling Shiba goats (4.4 ± 2.3 years old) were assigned to early luteal phase (ELP, n = 4), mid-luteal phase (MLP, n = 4), and control (n = 5) groups. The ELP and MLP groups were administered 50 µg of TAK-683 intravenously on either day 5 or between days 7–14 after ovulation, respectively. The control group received vehicle between days 7–14 after ovulation. Blood samples were collected at 10-min (2–6 h), 2-h (6–24 h), and 24-h (24–96 h) intervals after treatment. Significant increases in plasma LH concentration were detected during the periods of 3 to 5 h and 2 to 5 h in the ELP and MLP groups, respectively. Estradiol concentrations continuously increased with the rise of basal LH secretion after TAK-683 treatment in two goats of the ELP group with a surge-like release of LH, but not in the goats without LH surge, i.e. the MLP and control group ones. Plasma progesterone concentration and the lengths of estrous cycle in all groups did not change significantly from the time before and after treatment. Present findings indicate that the responses of LH and ovarian steroids to treatment with TAK-683 depend on the stage of the luteal phase of the estrous cycle. We suggest that the stimulatory effects of TAK-683 on LH secretion are reduced in the process leading to the mid-luteal phase in cycling goats.

In vivo and vitro characterization of the effects of kisspeptin-13, endogenous ligands for GPR54, on mouse gastrointestinal motility

Kisspeptin (KP), the endogenous ligand of GPR54, is a mammalian amidated neurohormone, which belongs to the RF-amide peptide family. However, in contrast with the related members of the RF-amide family, little information is available regarding its role in the gastrointestinal motility. With regard to the recent data suggesting KP play an important role in food intake, and while gastrointestinal motility are closely related to it. Thus, in the present work, effects of central administration of KP-13, one of the endogenous active isoforms, on gastrointestinal motility were investigated. The results indicated that intracerebroventricular (i.c.v.) infused of KP-13 significantly facilitated gastrointestinal transit, bead expulsion and fecal pellet output, respectively, while has no effect on gastric emptying. The effects were significantly reversed by GPR54 antagonist 234, but not GnRH receptor antagonist Cetrorelix. However, i.p. injected of KP-13 or compound 5 (10mg/kg), a high metabolic stability kisspeptin analog, did not affect gastrointestinal transit, suggesting that KP-13 or compound 5 facilitated gastrointestinal transit through the activation of central GPR54. Then the gastrointestinal motility-enhancing effects were also presented after infusion of KP-13 into the hypothalamus. In vitro, KP-13 (10^-6M) also modulated colonic contraction, but not in the stomach and small intestine. Similarly, KP-13 (10^-6M)-induced contractions of circular and longitudinal colonic muscle were significantly attenuated by antagonist 234 (10^-6M). In conclusion, all the results indicated that KP-13 promoted gastrointestinal motility through the activation of GPR54, which implicate that KP/GPR54 system might be a new target to treat gastrointestinal function disorder.

Ovarian and hormonal responses to follicular phase administration of investigational metastin/kisspeptin analog, TAK-683, in goats

This study evaluated the effects of follicular phase administration of TAK-683, an investigational metastin/kisspeptin analog, on follicular growth, ovulation, luteal function and reproductive hormones in goats. After confirmation of ovulation by transrectal ultrasonography (Day 0), PGF2α (2 mg/head of dinoprost) was administered intramuscularly on Day 10 to induce luteal regression. At 12 h after PGF2α administration, intravenous administration of vehicle or 35 nmol (50 μg)/head of TAK-683 was performed in control (n = 4) and treatment (n = 4) groups, respectively. Blood samples were collected at 6-h intervals for 96 h and then daily until the detection of subsequent ovulation (second ovulation). After the second ovulation, ultrasound examinations and blood sampling were performed every other day or daily until the subsequent ovulation (third ovulation). Mean concentrations of LH and FSH in the treatment group were significantly higher 6 h after TAK-683 treatment than those in the control group (12.0 ± 10.7 vs 1.0 ± 0.7 ng/ml for LH, 47.5 ± 28.2 vs 15.1 ± 3.4 ng/ml for FSH, p < 0.05), whereas mean concentrations of oestradiol in the treatment group decreased immediately after treatment (p < 0.05) as compared with the control group. Ovulation tended to be delayed (n = 2) or occurred early (n = 1) in the treatment group as compared with the control group. For the second ovulation, ovulatory follicles in the treatment group were significantly smaller in maximal diameter than in the control group (3.8 ± 0.5 vs 5.4 ± 0.2 mm, p < 0.05, n = 3). Administration of TAK-683 in the follicular phase stimulates gonadotropin secretion and may have resulted in ovulation of premature follicles in goats.

The effects of chronic subcutaneous administration of an investigational kisspeptin analog, TAK-683, on gonadotropin-releasing hormone pulse generator activity in goats

The continuous activation of the kisspeptin receptor by its agonists causes the abrogation of kisspeptin signaling, leading to decreased pulsatile luteinizing hormone (LH) secretion. Employing this phenomenon as a tool for probing kisspeptin action, this study aimed to clarify the role of kisspeptin in gonadotropin-releasing hormone (GnRH) pulse generation in goats. We examined the effects of chronic administration of TAK-683, an investigational kisspeptin analog, on LH secretion, GnRH immunostaining, pituitary responses to exogenous GnRH, and GnRH pulse generator activity, reflected by a characteristic increase in multiple-unit activity (MUA volley). An osmotic pump containing TAK-683 was subcutaneously implanted on day 0. TAK-683 treatment dose-dependently suppressed pulsatile LH secretion on day 1. Higher doses of chronic TAK-683 profoundly suppressed pulsatile LH secretion but had little effect on GnRH immunostaining patterns and pituitary responses to GnRH on day 5. In ovariectomized goats, MUA volleys occurred at approximately every 30 min on day -1. On day 5 of chronic TAK-683 administration, pulsatile LH secretion was markedly suppressed, whereas MUA volleys were similar to those observed on day -1. Male pheromones and senktide (neurokinin B receptor agonist) induced an MUA volley but had no effect on LH secretion during chronic TAK-683 administration. The results indicate that the chronic administration of a kisspeptin analog profoundly suppresses pulsatile LH secretion without affecting GnRH content, pituitary function or GnRH pulse generator activity, and they suggest an indispensable role for kisspeptin signaling in the cascade driving GnRH/LH pulses by the GnRH pulse generator.

Differential effects of continuous exposure to the investigational metastin/kisspeptin analog TAK-683 on pulsatile and surge mode secretion of luteinizing hormone in ovariectomized goats

The aim of the present study was to determine if the estradiol-induced luteinizing hormone (LH) surge is influenced by the constant exposure to TAK-683, an investigational metastin/kisspeptin analog, that had been established to depress the pulsatile gonadotropin-releasing hormone (GnRH) and LH secretion in goats. Ovariectomized goats subcutaneously received TAK-683 (TAK-683 group, n=6) or vehicle (control group, n=6) constantly via subcutaneous implantation of an osmotic pump. Five days after the start of the treatment, estradiol was infused intravenously in both groups to evaluate the effects on the LH surge. Blood samples were collected at 6-min intervals for 4 h prior to the initiation of either the TAK-683 treatment or the estradiol infusion, to determine the profiles of pulsatile LH secretion. They were also collected at 2-h intervals from –4 h to 32 h after the start of estradiol infusion for analysis of LH surges. The frequency and mean concentrations of LH pulses in the TAK-683 group were remarkably suppressed 5 days after the start of TAK-683 treatment compared with those of the control group (P<0.05). On the other hand, a clear LH surge was observed in all animals of both groups. There were no significant differences in the LH concentrations for surge peak and the peak time of the LH surge between the TAK-683 and control groups. These findings suggest that the effects of continuous exposure to kisspeptin or its analog on the mechanism(s) that regulates the pulsatile and surge mode secretion of GnRH/LH are different in goats.