Haemodynamic Studies with Methyldopa: Effect on Cardiac Output and Response to Pressor Amines.

Methyldopa has been shown to be an effective hypotensive agent both in animals and in man (Oates et al., 1960), and valuable in the treatment of hypertension, particularly in the management of mild or moderately severe cases (Dollery and Harington, 1962; Bayliss and Harvey-Smith, 1962). Pharmacological activity resides entirely in the L-isomer (Gillespie et al., 1962). The mechanism of the anti-hypertensive action of methyldopa is not fully understood. Although known to be an inhibitor of decarboxylase (Sourkes, 1954), and thus potentially capable of reducing the biosynthesis of noradrenaline and other pressor amines, there is evidence that the cardiovascular effects of the drug are independent of this mechanism, and more closely related to depletion of noradrenaline from sympathetic nerve endings (Hess et al., 1961). The present paper reports certain further observations on the clinical pharmacology of methyldopa, in particular measurements of the cardiac output before and after treatment, and the effect of the drug on the response to pressor amines.