PARENT SESSION
SLIDE SESSION 4: NEUROENDOCRINOLOGY
Chairs: Donal Skinner, Fred Karsch, Heather Billings (Trainee)
Univ Ottawa-Arts Hall 257
2:30 PM-4:30 PM

CHOLINERGIC REGULATION OF THE COITUS-INDUCED LUTEINIZING HORMONE (LH) AND PROLACTIN (PRL) RELEASE IN OVARIECTOMIZED, ESTROGEN-TREATED RABBITS.

Pau, K.-Y. Francis¹, ¹

ABSTRACT- In rabbits, coital signals are transmitted to the brainstem where they are transformed into GnRH-stimulating signals that project to the hypothalamus. Two of these signals are likely to be norepinephrine (NE) and acetylcholine (Ach) since either NE or Ach antagonist blocks ovulation (Sawyer et al., 1947). However, Ach has not been established as a key component of the coital signaling pathway. We utilized the ovariectomized, estrogen-treated (OVX+E) rabbit as a model to test the hypothesis that blockade of Ach receptors in the hypothalamus alters the release of LH and PRL induced by coitus. Ventricular (3rd) cannula and femoral vein catheter were implanted into OVX+E females. At 10-min before coital attempts, animals received intraventricular injection of 50 l artificial cerebrospinal fluid (KRP) that contained either nothing (n=5), -bungarotoxin (BTX, a nicotinic Ach antagonist) at dosages of 5 g (n=5) or 20 g (n=5), or scopolamine (Scop, a muscarinic Ach antagonist, 250 M, n=5). Coitus was achieved by pairing females with a stud male for < 10 min. Blood samples were taken once before the drug injection, and at 10-min intervals for 4 hours after mating. The rate of successful mating in these OVX+E rabbits was > 85%. In control animals after coitus, plasma LH rose from < 1 ng/ml to, and maintained at, ~4 ng/ml for at least 120 min. In animals treated with 5 g BTX, coitus induced a similar pattern of LH but the levels were maintained at ~2 ng/ml. After 20 g BTX or 250 M Scop, plasma LH rose to about 2-3 ng/ml within 30 min before it gradually declined. In contrast, 5 g BTX slightly increased the coitus-induced PRL release (peaked at ~80 ng/ml) as compared to ~70 ng/ml in untreated females. Both the higher dose of BTX and Scop increased PRL release with peak levels at ~100 ng/ml. These results, which showed that activation of both muscarinic and nicotinic Ach receptors enhanced LH and inhibited PRL release in OVX+E rabbits after coitus, support the hypothesis that Ach is one component of the coital signaling pathway between the brainstem and hypothalamus. Alteration of brain Ach transmission may disrupt the normal functioning of reproduction in young and aging mammalian species, including the rabbit. Supported by NIH grants HD-30316 and RR-00163.

KEY WORDS: acetylcholine, luteinizing hormone, prolactin, coitus