Stimulation of Sodium Transport Across the Isolated Toad Bladder by 1α-Hydroxycorticosterone from an Elasmobranch

Abstract

The mineralocorticoid activity of 1α-hydroxycorticosterone, an interrenal steroid in elasmobranch fish, was determined by the in vitro toad bladder bioassay. It stimulated the transport of sodium across the toad bladder at concentrations of 10⁻⁶, 10⁻⁷, and 10⁻⁸ M. The elasmobranch steroid had approximately 80% of the activity of d-aldosterone; it was slightly less active than aldosterone and corticosterone at the lower concentrations. Protein binding alone does not seem to explain the relative potencies of the two steroids. The concentrations of 1α-hydroxycorticosterone required to stimulate sodium transport across the toad bladder are comparable with those reported in the peripheral blood plasma of Raja radiata and R. ocellata. A seasonal variation in the number of positive responses was observed.