STUDIES ON MECHANISMS OF RELEASING PITUITARY GONADOTROPIN (GtH2) FROM CARP (Cyprinus carpio) HYPOPHYSIS

Abstract

Levels of GtH2 and of GnRH in carp females and males were investigated during a 4 year period in relation to the gonadal maturation. GtH in males remained at the level of 10-20 ng ml^-1 and maximum occurred at the commencement of spermination. The level of GtH in the pituitary gland increased with the fish age. The GtH2 level in females changed slightly (9.97 - 33.25 ng ml^-1) during the investigation except at the oocyte vacuolisation stage (161.4 - 214.51 ng ml^-1). GtH2 accumulation in the pituitary gland increased since the 13th month, from 2.64 to 617.35 ng/ml of the homogenate, and of GnRH since the 33rd month, from 0.6 to 9.55 ng/ml. The in vivo experiments on gonadotropin (GtH2) release from carp hypophysis proved that NPY alone raised gonadotropin secretion and intensified GnRH action, but GABA affected GtH2 secretion through the dopaminergic system decreasing the hormone secretion. Stress induced by capture and injections during artificial spawning did not influence the level and rhythm of GtH2 release from pituitary glands, thus allowing to disregard this factor in assessing artificial spawning success.