NICOTINE STIMULATED GTH2 SECRETION IN-VIVO IN MALE COMMON CARP (CYPRINUS-CARPIO) - POTENTIATION OF GNRH ACTION AND POSSIBLE INTERACTION WITH DOPAMINERGIC SYSTEM

Nicotine injected intravenously or on pituitary in vivo stimulated mat urational gonadotropin (GtH2) secretion in domperidone (D-2 receptor a ntagonist) pretreated carps. The effective dose was 1 mg.kg(-1) and 10 0 mu g.kg(-1), respectively. No stimulatory effects of nicotine were o bserved in normal (non-treated) carps. When nicotine was injected toge ther with gonadotropin releasing hormone (GnRH) analogs (D-Arg(6) sGnR H or D-ALa(6) LHRH) a clear potentiation effect of nicotine on GnRH an alogs' 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 anal ogs were used. In domperidone pretreated fish, this synergism occurred after injection of 1 mu g.kg(-1) of sGnRHa. In normal fish, the same phenomenon was observed after injection of 5 mu g.kg(-1) of sGnRHa or 20 mu g.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 dopami ne on nicotine's action. (C) Ifremer/Elsevier, Paris.