Peripheral administration of κ-opioid receptor antagonist stimulates gonadotropin-releasing hormone pulse generator activity in ovariectomized, estrogen-treated female goats.

Pulsatile gonadotropin-releasing hormone (GnRH) secretion is indispensable for reproduction in mammals. Kisspeptin neurons in the hypothalamic arcuate nucleus (ARC), referred to as KNDy neurons because of the coexpression of neurokinin B and dynorphin A, are considered as components of the GnRH pulse generator that produces rhythmic GnRH secretion. The present study aimed to investigate if peripheral administration of PF-4455242, a κ-opioid receptor (KOR, a dynorphin A receptor) antagonist, facilitates pulsatile luteinizing hormone (LH) secretion and GnRH pulse generator activity in estrogen-treated ovariectomized Shiba goats to determine the possibility of using KOR antagonists to artificially control ovarian activities. PF-4455242 was intravenously infused for 4 h (1 or 10 μmol/kg body weight/4 h) or as a single subcutaneous injection (1 or 10 μmol/kg body weight). In a separate experiment, the same KOR antagonist (10 μmol/kg body weight/4 h) was intravenously infused during the recording of multiple unit activity (MUA) in the ARC that reflects the activity of the GnRH pulse generator to test the effects of KOR antagonist administration on GnRH pulse generator activity. Intravenous infusion and single subcutaneous injection of the KOR antagonist significantly increased the frequency of LH pulses compared with controls. Intravenous infusion of KOR antagonist also significantly increased the frequency of episodic bursts in the MUA. The present study demonstrates that peripherally administered KOR antagonist stimulates pulsatile LH secretion by acting on the GnRH pulse generator, and peripheral administration of PF-4455242 can be used to facilitate pulsatile LH secretion, which in turn facilitates ovarian activities in farm animals.