Rapid action of glucocorticoids on branchial ATPase activity in Oreochromis mossambicus: an in vivo and in vitro study

The rapid action of cortisol and corticosterone on branchial Na +–K + ATPase, Ca 2+ ATPase activity and Na +, K + and Ca 2+ ion contents was studied both in vivo and in vitro employing transcription inhibitor actinomycin D in Oreochromis mossambicus. Cortisol and corticosterone administration had significantly increased the activity of branchial Na +–K + ATPase and Ca 2+ ATPase in vivo after 30 min of injection, and the trend continued for 60 and 120 min for cortisol. The ionic contents were also significantly increased after 30 min in vivo. Na +–K + ATPase activity was significantly increased 5 min after hormone application in the in vitro system. Actinomycin D did not inhibit the effect of glucocorticoids on ATPase activity both in vivo and in vitro. It is concluded from the present study that cortisol and corticosterone produced a rapid stimulatory effect on branchial ATPase activity and ions in O. mossambicus both in vivo and in vitro. This effect could be due to a non-genomic action of these hormones since the enzyme activity was insensitive to actinomycin D.