Interactions of sympathomimetic and sympatholytic agents in normotensive and hypertensive subjects.

Sympathomimetic agents and their blocking agents were administered drop wise intravenously alone or in various combinations to 9 normotensive subjects and 16 patients with essential hypertension. Their effects on the cardiovascular reaction (heart rate and blood pressure) were compared in order to estimate the degree of stimulation of a and ƒÀ-receptors respectively. When the a and fl receptor stimulating effects of so-called a and ƒÀ-receptor stimulators were com pletely blocked by corresponding blocking agents respectively, ƒÀ-effect in the ƒ¿ -stimulator and ƒ¿-effect in the ƒÀ-stimulator remained in effect without any modification in the degree of responses. Simultaneous injection of ƒ¿-stimulator and ƒÀ-blocker caused no change in the heart rate (ƒÀ-effect), but produced additive increase in the blood pressure (ƒ¿-effect) already raised by single treat ment of the ƒ¿-stimulator. A similar additive effect was observed also in the ( effect when ƒÀ-stimulator and ƒ¿-blocker were injected simultaneously. Such an increase in the a or ƒÀ-effect seemed to be due to conversion of f or ƒ¿-effect blocked by f or ƒ¿-blocker respectively, but it was not attributable to the a or ƒÀ-effect of the blockers themselves. The ƒÀ-effect induced in this way, that is, the reactivity of ƒ¿-receptor was greater in hypertensive patients than in nor motensives, and the ƒÀ-effect induced in the same way was greater in normotensives than in hypertensive patients.