Additive effects of aldosterone with vasopressin or angiotensin

Rat tail arteries were incubated overnight in potassium (K)-free physiological saline solution (PSS) at 10 degrees C, then returned to normal aerated PSS at 37 degrees C for a 3-hour recovery period followed by standard chemical analysis. Cell sodium (Na) was measured following replacement of extracellular Na by lithium (Li) at 3 degrees C. The addition of aldosterone at 10(-7) M reduced free cell Na by about 3 mmol/kg dry weight (about 20%). Arginine vasopressin also lowered cell Na to the same degree. The minimal effective dose was about 25 pM (25 pg/ml, 0.01 mU/ml), and the maximal dose was about 250 pM. No effect was seen with higher doses (greater than 1.5 nM or 0.5 mU/ml). Tissues incubated in media containing 10(-7) M aldosterone showed an exaggerated response to vasopressin evidenced by a near doubling of the maximum fall in cell Na produced by a tenfold smaller dose (25 pM). No significant change in cell K was observed while cell water tended to increase with lower doses. Angiotensin produced a similar reduction of cell Na at the same dose levels as vasopressin and was similarly additive with aldosterone. We suggest that these hormones enhance the transport of Na from luminal to basal sides of polarized cells and from cells to environment in symmetrical cells.