Comparison between the effects of ST 600 and clonidine

The effects of the antihypertensive imidazoline compounds 2-(5 fluor-0-toluidine)-2-imidazoline hydrochloride (ST 600) and 2-(2, 6 dichlorophenylamine)-2-imidazoline hydrochloride (ST 155, clonidine, Catapres) on intra-arterial pressure, cardiac output, stroke volume, heart rate, total peripheral resistance, renal blood flow, glomerular filtration rate, renal vascular resistance, plasma volume, plasma renin and aldosterone concentration were studied in five patients with essential hypertension. The antihypertensive action of both compounds was similar and was accompanied by a reduction in heart rate and in cardiac output, total peripheral resistance being unchanged. There was no significant decrease in renal blood flow and glomerular filtration rate. Plasma volume and plasma concentrations of renin and aldosterone also did not change significantly. In the face of similar reductions in blood pressure, no differences were observed between cardio-renal haemodynamic responses after ST 600 and clonidine. However ST 600 had a longer lasting effect (8-12 hours).