Intravenous injections of nicotine decrease the pulsatile secretion of LH by inhibiting the gonadotropin-releasing hormone (GnRH) pulse generator activity in female rats.

Whether nicotine inhibits the electrical activity of the gonadotropin-releasing hormone (GnRH) pulse generator to suppress pulsatile LH secretion, and whether this suppression of LH secretion by nicotine is mediated by opioid neurons, were studied in ovariectomized rats by examining changes in LH secretion and the multiunit activity (MUA) of the medial basal hypothalamus. Intravenous (i.v.) injection of nicotine (nicotine bitartrate, 100 micrograms) significantly increased the interval between characteristic increases (volleys) in MUA and LH pulses. This inhibitory effect of nicotine on the GnRH pulse generator activity was not blocked by the prior injection of an opiate receptor antagonist naloxone (naloxone hydrochlolide, 2 mg/kg bw), which was effective in significantly decreasing the interval between MUA volleys. The results suggest that nicotine alters the activity of the GnRH pulse generator, and that cholinergic neurons appear to be directly involved in suppressing pulsatile secretion of LH.