Calcitropic effect of recombinant prolactins in Oreochromis mossambicus

Homologous recombinant tilapia prolactins 1 and 2 were tested for calcitropic activity in tilapia Oreochromis mossambicus. Injection of both PRLs induced hypercalcemia that resulted for an enhanced calcium influx via the gills and a decreased calcium efflux. Both PRLs increased the density of the Ca2+-transporting Ca2+-adenosinetriphosphatase in a plasma membrane preparation of the branchial epithelium. Dose-response studies demonstrated that the PRL-1 was roughly twofold more potent than PRL2 in inducing hypercalcemia, in enhacing basal levels of cortisol and in stimulating opercular ionocyte density. But both PRL were equipotent in stimulating the dermal mucocyte frequency.