REVERSAL OF MICROVASCULAR RAREFACTION AND REDUCED RENAL MASS HYPERTENSION

This study examined the microcirculatory and renin-angiotensin system changes following the reversal of hypertension in reduced renal mass r ats. Nine-week-old Sprague-Dawley reduced renal mass rats were placed on a low or high sodium diet for 4 or 8 weeks or a combination of 4 we eks of high sodium followed by 4 weeks of low sodium. Blood pressure w as directly measured during the development of hypertension and its re versal. Plasma renin activity, angiotensin-converting enzyme activity, and angiotensin II concentrations were measured throughout the experi ment. The cremaster and hindlimb muscles were removed, and microvascul ar density was determined by quantitative stereology. Four weeks of hi gh sodium increased blood pressure (152+/-7 mm Hg) and reduced microve ssel density (13.7%). Reduced renal mass hypertension was rapidly reve rsed after the rats were returned to a low sodium diet (124+/-7 mm Hg after 3 days), and microvascular density returned to control levels. A fter 4 weeks of high sodium, circulating plasma renin activity and ang iotensin II fell by 94% and 82%, respectively. Plasma angiotensin-conv erting enzyme activity was increased after 2 weeks of high sodium but returned to control levels after 4 weeks of high sodium. This study de monstrates that microvascular density is reduced in reduced renal mass hypertensive rats following exposure to high sodium diet and this is associated with a fall in circulating plasma renin activity and angiot ensin II levels. Microvascular density can return to normal levels aft er a reactivation of the circulating renin-angiotensin system. This st udy provides further evidence for the hypothesis that modulation of th e renin-angiotensin system is important in the regulation of microvasc ular structure.