Clonidine Lowers Blood Pressure by Reducing Vascular Resistance and Cardiac Output in Young, Healthy Males

Abstract

Purpose: Clonidine is a classical sympatholytic drug that is widely used for the treatment of hypertension. Experimental and clinical studies suggest that Clonidine may activate baroreflex. The aim of this study was to determine the hemodynamic response to Clonidine under physiological conditions and to test the hypothesis that Clonidine would reduce cardiac output and blood pressure resulting in an increase in total peripheral resistance. Methods: Clonidine’s hemodynamic effect was evaluated in 28 young, healthy subjects after a single i.v. dose of 1 μ g × kg^{− 1}. Impedance cardiography, systolic time intervals and pulse wave analysis were used to characterize myocardial and vascular function. Results: Clonidine lowered blood pressure, heart rate, left ventricular ejection time, and pulse wave velocity and increased pre-ejection period. Stroke volume and cardiac output decreased gradually over the investigation time of 240 min. Central systolic blood pressure (SBP) was lowered to a larger extent than peripheral SBP. Total peripheral resistance was characterized by an immediate fall of short duration followed by a continuous rise above baseline after 120 min. Placebo did not have any significant effect on hemodynamic parameters. Conclusions: Clonidine’s blood pressure lowering effect is mediated by both an immediate decrease in vascular resistance and a prolonged decrease in cardiac output, and Clonidine lowers central SBP more than peripheral SBP.