Mineralocorticoid effects on cation transport by cortical collecting tubules in vitro

Abstract

Previous studies indicated that the function of cortical collecting tubules in vitro may be conditioned by the state of the animals from which they are obtained. The purpose of the present studies was to evaluate such conditioning of Na and K transport and its role in control of urinary Na and K. In 10 different groups of rabbits urinary Na and K concentrations were altered by dietary and pharmacologic manipulation. Cortical collecting tubules from all the groups were studied under the same conditions in vitro. When plasma aldosterone was suppressed to zero by a high Na, low K diet, Na absorption by the isolated collecting tubules decreased to 50% of control and K secretion to 26% of control. When plasma aldosterone was increased 18-fold by a low Na diet plus furosemide, Na absorption by the isolated tubules increased to 163% of control and K secretion to 208% of control. Na and K transport was highly correlated with plasma aldosterone level. Changes in urinary sodium-to-potassium ratio did not correlate with changes in the transport of Na and K in vitro in 4 treatment groups, including DOCA (DOCA [deoxycorticosterone acetate] escape). Cation transport by the cortical collecting tubule in vitro varies with the physiological state of the animals from which the tubules are obtained, the effect is mediated primarily by the action of endogenous aldosterone and Na and K transport as measured in vitro is not necessarily correlated with urinary cation composition. Therefore, either transport by the cortical collecting tubule in vivo is affected by other factors in addition to aldosterone, and/or other tubule segments play a more important role in the control of urinary cation excretion under some conditions.