The intrarenal distribution of blood flow measured by the 183 xenon washout method and the renin activity of renal venous blood were determined in 16 patients with early essential hypertension. None of the patients had evidence of systemic disease except for the elevation in blood pressure (> 150/100 mm Hg). Fifteen of the subjects received a controlled sodium diet during 7 to 9 days before study, at the time of renal angiography. An inverse relationship was noted between the cortical component of the renal blood flow and renin activity of renal venous blood (r = 0.64, P <0.02). Renin secretion rates were also calculated in 12 patients confirming the inverse relationship between cortical distribution of blood flow and renin secretion (r = 0.763, P<0.01). The cortical renal blood flow in 10 patients on a low salt intake was 79.6% ± 2.6 (SE) of the total renal blood flow. The cortical blood flow in five patients on a high salt diet was 87.6%±1.9 (SE); the statistical difference between the two groups is significant (P<0.05). A direct relationship was noted between cortical blood flow and the logarithm of the 24-hour urinary sodium excretion from the day preceding the study (r = 0.54, P<0.05). Renin secretion rate and renin in renal venous blood were directly correlated (r = 0.813, P<0.01). Changes in corticomedullary distribution of flow were inversely related to the changes in cortical distribution. The degree of reduction of cortical renal blood flow correlated with the degree of increase in renin secretion and in renin activity in renal venous blood. Our data are compatible with reduced cortical renal blood flow mediating renin release or vice versa. Either mechanism would result in more efficient conservation of salt and water by the kidney. ADDITIONAL KEY WORDSrenin release human hypertension low salt intake sodium excretion xenon washout cortical blood flow corticomedullary blood flow• The majority of pathologic conditions which are accompanied by consistent alterations in renal blood flow are also associated with changes in peripheral renin activity. Renovascular hypertension (1), acute renal failure (2), and hemorrhagic hypotension (3) are each associated with increased peripheral renin activity and with a reduction in the total

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