Chronic effects of ACTH and cortisol excess on arterial pressure in normotensive and hypertensive dogs.

The chronic effects of ACTH and cortisol on mean arterial pressure (MAP) and related variables were studied in normotensive dogs and, subsequently, in the same dogs after they had been made hypertensive by chronic infusion of angiotensin II (All). MAP was recorded continuously, 24 hours/day, and sodium intake was 71 mEq/day. In both normotensive and hypertensive dogs, 8 to 10 days of ACTH infusions caused natriuresis, kaliuresis, diuresis, hypernatremia, and hypokalemia; additionally, plasma renin activity (PRA) was suppressed to undetectable levels. During ACTH infusion there was a sustained 12-fold increase in plasma cortisol concentration, but only a transient elevation in plasma aldosterone concentration; this steroidogenic response occurred even in dogs with All hypertension where plasma AH concentration was maintained at elevated levels by infusion. In normotensive dogs, increases in MAP were not consistently observed during ACTH infusion, whereas, in dogs with AH hypertension, ACTH invariably exacerbated the hypertension (AMAP = + 16 mm Hg). Cortisol infusion, like ACTH infusion, caused a 12-fold increase in plasma cortisol concentration, and negative sodium and water balance; however, cortisol did not produce kaliuresis, hypokalemia, suppression of PRA, or hypertension. In fact, cortisol induced chronic hypotension (AMAP = — 7 mm Hg) when infused in normotensive dogs, and in dogs with AH hypertension there were no detectable changes in MAP during cortisol treatment. Thus, the changes in plasma cortisol concentration and PRA that accompany ACTH infusion do not mediate, but seem actually to oppose, the hypertensive effects of ACTH. Indeed, when ACTH was infused in hypertensive dogs with fixed plasma levels of All, the hypertensive effects of ACTH were manifested. Finally, failure of chronic ACTH administration to maintain an elevated secretion rate of aldosterone cannot be attributed to suppression of PRA. (Hypertension 4: 652-661, 1982)