Acute and Chronic Effects of the Loop Diuretic, Piretanide, on Baroreflex Set Point and Sensitivity in Hypertensive Man

Intra-arterial blood pressure (IABP), baroreflex sensitivity and set point were measured in nine patients with essential hypertension during a control period and then after acute (4 h after a 12 mg oral dose) and chronic (after 3 months) treatment with the loop diuretic piretanide, mean dose 10 mg. Acutely, there was a fall in mean systolic IABP (P less than 0.05) associated with a reduction in pulse interval (P less than 0.01). Chronically, mean systolic IABP remained significantly reduced (P less than 0.01) but pulse interval returned to control values. There were no significant changes in baroreflex sensitivity, either acutely or chronically. These results demonstrate acute deactivation of the vagal efferent limb of the baroreflex followed by a chronic resetting of the baroreflex-heart rate mechanism. We conclude that changes in baroreflex sensitivity are not responsible for the hypotensive effects of this drug and that resetting of the reflex arc is likely to be due to physiological adaptation rather than to any direct drug effect.