[Influence of arterial pressure and plasma renin activity on tubular reabsorption of sodium]. / Influencia de la presión arterial y de la actividad de renina plasmática sobre la reabsorción tubular de sodio.

BACKGROUND: With the aim of confirming the possible existence of an increase in the fractional proximal reabsorption of sodium in the development of essential hypertension, the tubular dynamics of sodium were compared by the lithium clearance technique in a group of hypertensive patients and controls. METHODS: Following a week of drug suspension 186 patients with slight or moderate essential hypertension and 37 normal subjects with homogeneous sodium ingestion were studied. A clearing period of 90 minutes prior to the administration of a tracing doses of lithium was considered to calculate the fractional proximal and distal reabsorption of sodium in terms of glomerular filtration. In addition to global comparison of the measurements, the hypertensives were classified and compared according to mean arterial pressure (MAP) and percentages of plasma renin activity (PRA). RESULTS: No differences were found in tubular dynamics of sodium between hypertensive and normotensive patients. Neither did the degree of hypertension induce differences. However, upon classifying the patients according to PRA, it was found that those with PRA higher than 0.5 ng/ml-1/h-1 had less secondary natriuresis to a greater fractional distal reabsorption of sodium (p < 0.05). CONCLUSIONS: The findings of the this study do not support the possible existence of a primary defect of the transport of sodium in the proximal tubule in the origin and/or maintenance of essential arterial hypertension.