Nicotine injected intravenously or on pituitary in vivo stimulated maturational
gonadotropin (GtH2) secretion in domperidone (D-2 receptor antagonist) pretreated carps.
The effective dose was 1 mg·kg−1 and 100
μg·kg−1, respectively. No stimulatory effects of nicotine
were observed in normal (non-treated) carps. When nicotine was injected together with
gonadotropin releasing hormone (GnRH) analogs (D-Arg6 sGnRH or
D-Ala6 LHRH) a clear potentiation effect of nicotine on GnRH analogs' action
was observed. This potentiation was seen even in normal fish where nicotine itself had no
effect on GtH2 release. A synergism between nicotine and GnRH analogs appeared when low
doses of GnRH analogs were used. In domperidone pretreated fish, this synergism occurred
after injection of 1 μg·kg−1 of sGnRHa. In normal fish, the same phenomenon was observed after injection of 5 μg·kg−1 of sGnRHa or 20 μg·kg−1 of LHRHa. Higher doses of GnRH analogs mask this effect. Results confirm previous in vitro findings on the stimulatory action of nicotine on GtH2 secretion. They also indicate a possible synergy between nicotine and GnRH as well as an inhibitory influence of dopamine on nicotine's action.