Effect of angiotensin on the renal transport of sodium in essential hypertension.

SUMMARY The renal function, including sodium excretion rates, were studied in 27 patients with early essential hypertension, before and during angiotensin infusions. The patients had a preparatory period of salt loading for four days taking a supplement of 7 g of NaCl. Determinations were made during two 30-minute periods before the angiotensin and for two 30-minute periods afterward. Arterial blood pressure was increased in all 27 patients and renal plasma flow decreased in 25. The glomerular filtration rate changes were not statistically significant, showing some increase in 15 and a decrease in 11 patients. When the group was divided into those in w,hich there was a decrease in sodium excretion (11 patients), and those in which there was an increase in sodium excretion (16 patients), with angiotensin infusion, a correlation with the control blood pressure was evident. The patients in whom an increase occurred had a control mean blood pressure greater than 136 mm Hg, and those exhibiting a decrease of sodium excre-tion, a blood pressure less than 136 mm Hg. Salt excretion did not correlate with the increment in blood pressure or renal resistance changes. The minor changes in glom-erular filtration of sodium of the two groups could not explain the different excretory patterns which are attributed to an alteration of the tubular transport of sodium. ANGIOTENSIN reduces urinary sodium excretion and glomerular filtration rate in normotensive subjects and increases sodium excretion in hypertensive patients.1 2 Although the glomerular filtration rate remains unchanged by the substance in most hypertensives, this function has been observed to rise in some and drop in others under its effect.' This makes it difficult to determine whether or not natriuresis is due to inhibition of tubular transport of sodium. Furthermore, it has been asserted that in essential hyper-tension increased sodium excretion is not the result of a tubular factor inasmuch as its excretion fraction remains unchanged.3 The purpose of this study was to investigate whether the rise in sodium excretion observed in patients with essential hypertension under the effect of angiotensin is the result of changes in glomerular filtration rate, inhibition of tubular reabsorption, or both. Methods A study was made of 27 patients in the early stage of essential arterial hypertension. For 4 days before the study was carried out, patients received 7 g of sodium chloride daily in their diet and a placebo. Renal function was studied during two 30-minute periods before …