Rapid action of testosterone and diethylstilbestrol on enzymes of osmoregulation in a freshwater fish Oreochromis mossambicus.

The rapid action of sex steroids on enzymes of osmoregulation has not been studied in teleosts. In vivo administration of 0.1 microg/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 microg/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.