Nicotine stimulated GtH2 secretion in vivo in male common carp (Cyprinus carpio); Potentiation of GnRH action and possible interaction with dopaminergic system

¹ Dept of Ichthyobiology & Fisheries, Agricultural Academy of Cracow, ul. Spiczakowa 6, 30149 Cracow-Mydlniki, Poland
² Laboratory of Fish Physiology INRA, Campus de Beaulieu, 35042 Rennes, France
³ Inst. of Zoology, Catholic University of Leuven, Naamsestraat 59, B3000 Leuven, Belgium

Received: 12 March 1998
Accepted: 2 June 1998

Abstract

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.