Decreased venous distensibility and reduced renin responsiveness in hypertension

Abnormalities of renin release and of venous distensibility have been described in essential hypertension. We have postulated that decreased venous distensibility could contribute to the blunted renin response to upright posture in hypertension. Stiffer veins might prevent venous pooling in the lower extremities, which in turn might affect the stretch on cardiopulmonary mechanoreceptors, thereby influencing the reflex release of renin. We investigated this hypothesis in the present study of 47 patients with mild hypertension and 26 (male) healthy volunteers of similar age and race. To induce isolated changes in the stretch of cardiopulmonary mechanoreceptors, systemic hemodynamics were measured before and after thigh cuff inflation at 60 mm Hg for 30 minutes. Cardiac output was determined by dye dilution. Before the intervention, variable thigh cuff pressures were used to measure venous pressure volume with mercury-in-Silastic strain gauge plethysmography. Venous distensibility was diminished in hypertension, as evidenced by a shift in the calf venous volume/pressure curve toward the pressure axis. During the 30-minute experiment, the hypertensive subjects had less blood pooling in their legs in response to thigh cuff inflation, as compared with the control subjects. The hemodynamic and renin responses reflected this diminished effect of thigh cuff inflation on venous return. The smaller increase of renin in the hypertensive group was associated with a smaller fall in the stroke index and right atrial pressure; the reflex rise in the heart rate was also decreased. By pooling blood in the lower extremities, thigh cuff inflation simulates upright posture. It is customary to classify the renin status of hypertensive patients according to the renin response to upright posture.(ABSTRACT TRUNCATED AT 250 WORDS)