Differential changes in luteinizing hormone secretion after administration of the investigational metastin/kisspeptin analog TAK-683 in goats

This study aimed to evaluate the hormonal and ovarian responses to the administration of a metastin/kisspeptin analog (TAK-683) under the endocrine environments of luteal and follicular phases in goats. Five estrous cycling goats received a prostaglandin F2α injection followed by 10 days of progesterone treatment by CIDR. The TAK-683 (35 nmol) was intravenously administered (Hour 0) on 3 days after CIDR insertion (luteal phase condition; LC) and at 12 h after CIDR removal (follicular phase condition; FC). Blood samples were collected at 10 min (−2 to 6 h), 2 h (6–24 h) or 6 h intervals (24–48 h). In the LC, small increases in the basal concentrations of LH were observed after TAK-683 administration from 0 to 6 h, which were associated with an increase in estradiol concentration, followed by a surge-like release of LH with a peak at 12.5 ± 1.0 h (n = 4) after TAK-683 administration. In the FC, a surge-like release of LH occurred immediately after TAK-683 administration with a peak at 6.0 ± 3.5 h (n = 5), which was earlier than that in the LC (P < 0.01). The peak concentration of estradiol did not differ between the two conditions, whereas the time interval from TAK-683 treatment to estradiol peak in the LC was longer than that in the FC (12.0 ± 0.0 compared with 6.0 ± 4.2 h, P < 0.05). These findings suggest that the timing of surge-like release of LH after TAK-683 administration is associated with blood estradiol concentration at the time of treatment.