Patterns of Ovulation-Inducing LH Release Following Coitus, Electrical Stimulation and Exogenous LH-RH in the Rabbit¹

Abstract

Ovulation was induced in mature New Zealand White rabbits by copulation, electricalstimulation of the amygdaloid complex, or iv luteinizing hormone-releasing hormone (LH-RH). Blood was withdrawn by heart puncture from unanesthetized animals before and at intervals for 4 hr after stimulation, and serum LH patterns were quantitated by a radioimmunoassay (RIA) procedure. In estrogen-primed rabbits (50 µg estradiol benzoate daily for 2 days) copulation was followed by two peaks in serum LH, the first at 30 min, the second at 120 min after coitus. Only the 30 min peak occurred after LH-RH and only the 120-min peak was detected after amygdaloid excitation. In rabbits (not primed with estrogen) 250 ng/kg LH-RH, given either as a single injection or infused iv over a 30-min period, induced ovulation in 8/11 rabbits. Although 2 µg/kg doses of LH-RH iv, given to estrogen-primed animals, resulted in much larger increments in serum LH (a 250-fold increase at 30 min) than either copulation or amygdaloid stimulation, a double peak was never detected and LH values declined rapidly thereafter. Estrogenpriming itself caused a significant but non-ovulatory peak in serum LH 8 hr after the first administration. Results indicate that each of the ovulation-inducing procedures evokes a characteristic pattern of LH release: LH-RH produces the most rapid and shortlived responses; coitus, a rapid yet sustained elevation with two peaks (at 30 and 120 min); and electrical stimulation of theamygdala, a slow and sustained response.(Endocrinology95: 247, 1974)