EFFECTS OF EXTRACELLULAR CALCIUM AND POTASSIUM ON GROWTH HORMONE SECRETION FROM COMMON CARP PITUITARY IN VITRO

The effects of extracellular Ca²⁺ and K⁸ on the basal and salmonGnRH (sGnRH)-stimulated growth hormone (GH) release from pituitary of com-mon carp were studied using an in vitro perifusion system for pituitary fragmen-ts. The basal and sGnRH-stimulated GR secretion from erifused pituitary ofcommon carp were extracellular Ca²⁺-dependent. In the absence of extracellularCa²⁺, the significant reduction in the basal GH secretion and almost disappearan-ce in the GH release responses to 2--min pulses of sGnRH (1, 10 and 100nM)were observed. Voltage-sensitive calcium channels (VSCC) antagonist verapam il(VER) significantly inhibited the basal GH release and CH release responses to2- min pulses of sGnRH (1,10 and 100nM) in a dose--dependent manner, indica-ting that the effects of extracellular Ca²⁺ on the basal and sGnRH-stimulated GHrelease are, at least partially, via the action of VSCC. 50mM K⁸ significantlystimulated the basal GR release from perifused pituitary of common carp, andmarkedly potentiated the action of pulses of high dose of sGnRH (100nM) on GHsecretion. The effects of elevated K⁸ were extracellular Ca²⁺--dependent.