EFFECTS OF EXTRACELLULAR CALCIUM ON THE GTH RELEASE IN COMMON CARP, CYPRINUS CARPIO, INDUCED BY PULSATILE AND CONTINUOUS ADMINISTRATION OF SLMON GnRH AGONIST

Two-min pulse of 10nmol/L sGnRH-A(Arg6Trp7Leu8pro9NEt-LHRH)stimulated a rapid and significant release of GtH from perifused pituitary fragments ofcommon carp.The GtH level then decreased and to its basal level within 30-minafter the introduction of the sGnRH-Apulse. The continuous exposure of perifusedpituitary fragments to 10nmol/L sGnRH-A for 4hrs resulted in desensitization in-cluding two phases:an initial pcak phase of GtH release and a followed lowerlevel phase of GtH release. The perifusion of the pituitary fragments with Ca++freeHanks salt solution or the salt solution containing EGTA(1.25 and 5mmol/L)didnot influence the basal GtH release,but resulted in a significant decrease in GtHrelease if stimulated by 2-min pulses of 10nmol/L sGnRH-A and in disappearance ofdesensitization of GtH release which is induced by continuous administration ofof 10nmol/L sGnRH-A.