The Effects of Steroids on the Sodium, Urea and Water Permeability of the Toad Bladder

Abstract

Using the bladder of toad Bufo bufo japonicus the effects of steroids on the water, urea and sodium permeability of the biological membrane were examieed. As mineralocorticoid (aldosterone) and gluco corticoid (cortisol) were administered separatelyy to a bladder which had been made steroid-free by 14 hours' incubation, the effects of these two steroids on the permeability were examined independently. Mearsueing 11-OHCS in the bladder tissue, it is proved that the steroids are significantly decreased in. the bladder membrane. Sodium transport across the membrane was measured by the short-circuit current (SCC) technique with the method of Ussing and Zerahn. Urea permeability across the membrane was measured by ¹⁴C-urea. Water tranrfer of the toad bladder was measured volumetrically and isotopically. Trritiated water was used for the determination of water permeability of the toad bladder. Na. K-dependent ATPase activity of the homogenate of the toad bladdetr was measured with the method of Fiske-SabbaRow. Aldosterone started to increase the SCC after about 90 minutes' time-lag at the concentration of 7.5X 10^-7M. The SCC was increased continuously during 5 or 6 hours. Aldosterone did not affect the water permeability of the toad bladder. As both steroids did not affect the Na, K-dependent ATPase activity of the homogenate of the bladder membrane, the SCC increasing effect of aldosterone seemed not to concern with the ATPase activity. Cortisol reduced the water permeability of the membrane in about 90 minutes after addition of it when the measurment carried out both volumetrical and isotopic techniques. The results show that cortisof affects diffusion permeability and osmotic flow of water across the membrane either. Cortisol did not affect the urea permeability and the short-circuit current of the toad bladder. Antagonistic action beween cortisol and vasopressin was not observed by measuring SCC and water influx. Accoding to the double barrier series theory, the results suggest that cortisol affects the porous barrier of the membrane.