NICOTINE GIVEN INTRACEREBROVENTRICULARLY DOES NOT INHIBIT THE PREOVULATORY SURGE OF LH AND PRL SECRETION IN FEMALE RATS

To determine the effect of nicotine on LH and PRL secretion, nicotine bitartrate (nicotine) dissolved in saline was administered at 1400 h, just before the critical period for the preovulatory surge of LH and P RL secretion, either intracerebroventricularly (icv) or intravenously (iv) in female rats in proestrus. Nicotine neither at a dose of 5 mu g nor at a dose of 10 mu g injected icy at 1400 h caused significant ch anges in the surge of LH and PRL secretion. When nicotine was given iv at a dose of 100 mu g, a significant decrease in LH and PRL concentra tions occurred immediately, lasting for 2 h. After 1700 h, LH and PRL concentrations as high as that observed after 1700 h in saline-injecte d control rats were recovered, just as if nicotine caused a transient deficit of the surge secretion of these hormones. The results indicate that nicotine does not inhibit the preovulatory surge of LH and PRL s ecretion by acting at the hypothalamic level accessible via the third ventricle, but inhibits it by acting at certain other site(s).