Angiotensin II attenuates reflex decrease in heart rate and sympathetic activity in man

Summary. Circulatory variables and hormone concentrations in arterial plasma were measured in six normal subjects during angiotensin II (ANG II) step-up infusion of 0·25 and 1·00 ng kg^-1× min. During the 1·00 ng kg^-1× min infusion ANG II plasma concentrations increased from 11 ± 2 to 48 ± 6 pg ml^-1; i.e., similar to those obtained during acute hypotensive hypovolemia in man. Mean arterial pressure increased (P<0·05) from a resting value of 89±3 to 97±5 mmHg. Heart rate and catecholamine concentrations did not change. Plasma aldosterone increased (P<0·05) from 36 ± 4 to 77 ± 10 pg ml^-1 during the infusion. Plasma concentrations of vasopressin, adrenalin and pancreatic polypeptide did not change during the investigation. During the 0·25 and 1·00 ng kg^-1× min infusion subcutaneous blood flow decreased (P= 0·06) to 67 ±20 and 66 ±26%, respectively, of control. It is concluded that: (1) ANG II in physiological doses in man may augment the sympathetic activity on the circulatory system since compensatory decreases in heart rate or in plasma catecholamines were not observed during the increased arterial pressure; (2) ANG II does not induce a general decrease in vagal tone as plasma pancreatic polypeptide concentrations were unchanged; (3) the obtained plasma concentrations of ANG II do not stimulate the release of vasopressin to plasma; and (4) the threshold for reducing the subcutaneous blood flow is reached within relatively small increments in plasma ANG II.