Role of calcium ions in action of gonadotropin-releasing hormone on gonadotropin secretion in the African catfish, Clarias gariepinus.

The aim of the present study was to establish the role of calcium ions in the mechanism of action of gonadotropin-releasing hormone (GnRH) in stimulating gonadotropin (GTH) release in the African catfish, Clarias gariepinus. For that purpose, GTH release from pituitary fragments was monitored in a perifusion system. GTH release, induced by the GnRH analog Buserelin, was strongly diminished in the absence of Ca2+, as well as in the presence of the Ca2+ channel antagonist nifedipine. In addition, the Ca2+ ionophore A23187 stimulated GTH secretion in the absence of GnRH. These results indicate that calcium ions play an intermediate role in the mechanism of action of GnRH in the African catfish.