Hyper-responsiveness to low-dose epinephrine infusion in mild essential hypertension.

The present study was undertaken to evaluate the effects of intravenous infusion of small amounts of epinephrine on haemodynamics, renal electrolyte excretion and blood platelets in essential hypertension. Arterial plasma epinephrine concentrations were increased during the infusion to approximately 2.5 nmol/l both in a group of 40-year-old men with untreated mild essential hypertension (blood pressure 154 +/- 3/100 +/- 3 mmHg, n = 12) and in a group of age-matched male controls (124 +/- 3/78 +/- 2 mmHg, n = 11). In the hypertensive group only, mean blood pressure decreased, forearm blood flow increased, forearm vascular resistance decreased (P less than 0.001 for all) and the urinary excretion of sodium and potassium increased (P less than 0.01 for both). The hypertensive group also responded with an increase in plasma beta-thromboglobulin (P less than 0.05), blood platelet size (P less than 0.05) and a higher increase in platelet counts than in the normotensive group (P less than 0.05). Thus, in several ways the hypertensive patients showed a hyper-responsiveness to amounts of epinephrine which corresponds well to the plasma concentration achieved during psychological and physical activity.