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Am J Physiol. 1994 Apr;266(4 Pt 2):R1302-8.

Calcitropic effects of recombinant prolactins in Oreochromis mossambicus.

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Department of Animal Physiology, Faculty of Science, University of Nijmegen, The Netherlands.


Homologous recombinant tilapia prolactin-188 (PRL-I) and tilapia prolactin-177 (PRL-II) were tested for calcitropic activity in tilapia, Oreochromis mossambicus. Injection of PRL-I and PRL-II (4 injections, 12.5 pmol/g, over an 8-day period) induced hypercalcemia that resulted from an enhanced calcium influx via the gills and a decreased calcium efflux. Both PRLs increased the density of the Ca(2+)-transporting Ca(2+)-adenosinetriphosphatase in a plasma membrane preparation of the branchial epithelium. Dose-response studies (doses tested: 0.75-12.5 pmol/g) demonstrated that PRL-I was roughly twofold more potent than PRL-II in inducing hypercalcemia, in enhancing basal levels of cortisol, and in stimulating opercular ionocyte density. PRL-I and PRL-II were equipotent in stimulating the dermal mucocyte frequency. We conclude that in this species PRL-I and PRL-II have calcitropic effects, and that PRL-I is more potent than PRL-II in this respect. We postulate that PRL has corticotrophic activity in this fish.

[Indexed for MEDLINE]

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