Abstract
To determine the effect of nicotine on LH and PRL secretion, nicotine bitartrate (nicotine) dissolved in saline was administered at 1400h, just before the critical period for the preovulatory surge of LH and PRL secretion, either intracerebroventricularly (icv) or intravenously (iv) in female rats in proestrus. Nicotine neither at a dose of 5μg nor at a dose of 10μg injected icv at 1400h caused significant changes in the surge of LH and PRL secretion. When nicotine was given iv at a dose of 100 μg, a significant decrease in LH and PRL concentrations occurred immediately, lasting for 2h. After 1700h, LH and PRL concentrations as high as that observed after 1700h in saline-injected 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 secretion by acting at the hypothalamic level accessible via the third ventricle, but inhibits it by acting at certain other site(s).
