Role of angiotensin II and potassium in the long-term regulation of aldosterone secretion in intact conscious dogs.

The aldosterone response to long-term infusion of angiotensin II and potassium was studied in intact conscious dogs. Plasma aldosterone concentration (PAC), plasma renin activity (PRA), and plasma cortisol concentration (PCC) were determined by radioimmunoassay. In ten dogs maintained on angiotension II infusion (5 ng/kg min-1) for 14 days, PAC increased from 6.9 plus or minus 2.9 to 18.6 plus or minus 4.7 ng/100 ml plasma (mean plus or minus SE) within ten minutes after beginning the infusion, reached a maximum level of 28.3 plus or minus 6.8 ng/100 ml plasma by one hour, and returned to control levels by six hours. PCC increased from 0.6 plus or minus 0.2 to 3.9 plus or minus 1.0 mu-g/ 100 ml plasma within one hour after angiotensin II infusion and returned to control levels by six hours. During the next 14 days of angiotensin infusion, PAC remained at control levels, PRA was undetectable by radioimmunoassay, and mean arterial blood pressure was elevated 29 plus or minus 4 mm Hg above control levels. In ten dogs maintained on KCL infusion (250 mEg/day) for 15 days, PAC increased from 6.8 plus or minus 2.4 to 13.6 plus or minus 3.4 ng/100 ml plasma within 24 hours, averaged 22.4 plus or minus 4.3 ng/100 ml plasma by 48 hours, and remained elevated for the next 12 days, averaging 21.8 plus or minus 5.6 ng/100 ml plasma. During the next 14 days of KCL infusion, serum Kn increased from 4.1 plus or minus 0.3 to 4.9 plus or minus 0.5 ME1/L, and PRA decreased from 1.25 plus or minus 0.3 to 0.65 plus or minus 0.2 ng/ml/hr. PCC averaged 0.73 plus or minus 0.4 mu-g/100 ml plasma in the control samples and failed to change significantly during KCL infusion. These data indicate that chronic angiotensin II infusion into intact conscious dogs at rates capable of maintaining elevated arterial blood pressure results in a transient increase in aldosterone secretion that lasts only a few hours, while chronic infusion of potassium ions at rates that produce a minor increase in serum Kn results in a sustained increase in aldosterone secretion.