BLOOD-PRESSURE AND ITS REGULATION IN SPONTANEOUSLY HYPERTENSIVE RATS BRED ON THE LOWEST SODIUM DIET FOR NORMAL GROWTH

To investigate the effects of dietary sodium restriction from concepti on to adulthood on blood pressure and its regulatory mechanisms, male offspring were derived from inbreeding in spontaneously hypertensive r ats fed a diet containing sodium of 175 mu mol/g food (control) or 22 mu mol/g (low sodium), which is the least sodium content for normal gr owth. While urinary sodium excretion was markedly less, the low sodium diet did not inhibit body growth and failed to blunt the development of hypertension. Neither plasma catecholamine concentration nor depres sor response to hexamethonium was different between the two groups at any age examined (8, 12, and 20 weeks). Plasma renin concentration was not elevated, whereas urinary excretion of aldosterone was increased at any age in the low sodium group compared with that in the control g roup. Other sets of rats were fed a diet containing sodium of 175 mu m ol/g plus mefruside (a diuretic) of 0.001% in the same manner as in th e other two groups. Urinary sodium excretion per creatinine was higher than in the other groups. The diuretic treatment inhibited body growt h and suppressed adult blood pressure. While the sympathetic function was not affected, both plasma renin concentration and urinary excretio n of aldosterone were elevated. These results indicate that dietary so dium restriction with the least podium for normal growth from concepti on cannot blunt either the sympathetic nervous function or the develop ment of hypertension in spontaneously hypertensive rats. Aldosterone a ppears to play an important role in maintaining sodium hemeostasis und er the dietary sodium restriction.