RAPID ACTION OF TESTOSTERONE AND DIETHYLSTILBESTROL ON ENZYMES OF OSMOREGULATION IN A FRESHWATER FISH OREOCHROMIS MOSSAMBICUS

Abstract

The rapid action of sex steroids on enzymes of osmoregulation has not been studied in teleosts. In vivo administration of 0.1 µg/g body wt. of testosterone and diethylstilbestrol (DES) significantly enhanced branchial Na⁺–K⁺ ATPase, Ca²⁺ ATPase, and Na⁺, K⁺, and Ca²⁺ ions as early as 30 minutes in a freshwater teleost Oreochromis mossambicus. Treatment with 10⁻⁶ M testosterone significantly stimulated Na⁺–K⁺ ATPase as early as 5 minutes in vitro. The same dose of DES also stimulated Na⁺–K⁺ ATPase activity within 10 minutes of incubation in a gill culture study. Administration of the transcriptional inhibitor, actinomycin D (0.1 µg/g body wt. in vivo and 10⁻⁶ M in vitro), prior to hormone treatment, did not prevent the steroid-induced ATPase activity both in vivo and in vitro. It seems that stimulation of Ca²⁺ ion may be responsible for the hormonal effects to increase enzyme activity. A possible nongenomic mode of action for testosterone and DES is suggested in Oreochromis.

ACKNOWLEDGMENTS

We thank the University Grants Commission for providing a fellowship under FIP IX plan to Francis Sunny, the University of Kerala for laboratory facilities and Government of Kerala for deputation to FS.