1.In 91 essential hypertensive patients cumulative sodium balance was studied during the first week after they were taken into hospital. Sodium intake was fixed at 55 mmol/day. 2.After the first week, when sodium equilibrium was achieved, haemodynamic and endocrinological studies were carried out (cardiac output, renal plasma flow, plasma volume, measurements of plasma concentrations of total and active renin, aldosterone and noradrenaline). 3. On the basis of cumulative sodium balance a discrimination could be made between three groups. Group I (23 patients) accumulated sodium (52 mmol) before attaining equilibrium; group I1 (35 patients) were in balance from the beginning; group I11 (33 patients) exhibited a negative balance and lost on the average 125 mmol before equilibrium was attained. 4. On admission blood pressure and other characteristics were similar in the three groups. The decrease in blood pressure over the first 24 h period was equal. After that, the group characterized by a negative cumulative sodium balance (111) continued to exhibit a fall in blood pressure whereas groups I and II did not. 5.After sodium equilibrium had been attained, the haemodynamic profiles were somewhat different between groups. Group I (with a positive balance) showed greater systemic and renal vascular resistances than the other groups. 6.It is concluded that sodium loss contributes to the decrease in blood pressure on the second day EA Rotterdam, The Netherlands. of hospital admission and after. The blood pressure reduction during the first day is due to an independent mechanism, e.g. a decrease in sympathetic nervous tone. 7.It is also apparent that the attainment of sodium equilibrium during clinical investigations constitutes no guarantee that subjects are physiologically comparable; the preceding sodium balance has to be taken into account.

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1. 20 subjects with uncomplicated essential hypertension were studied, 10 of whom were on propranolol treatment. Several blood samples for determination of total and active renin were drawn simultaneously from the renal artery and vein after angiographic studies.2. In all patients renal blood flow was measured by Hippuran-clearance at the time of blood sampling. Intrarenal blood flow was assessed by xenon-washout.3. The results indicate that under basal conditions renin is secreted mainly in the active form, although secretion of inactive renin does occur. During propranolol treatment there is a tendency for secretion of active renin to be reduced.

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1. To investigate whether reduced activity of pressor systems could explain the spontaneous drop in pressure upon hospitalization, 5 1 subjects with uncomplicated essential hypertension were admitted to hospital. Sodium intake was fixed at 55 mmol/day.2. Blood samples for noradrenaline, adrenaline, active renin, angiotensin I1 and aldosterone were drawn on each morning of the first 3 days of hospitalization; blood pressure was measured at 2 h intervals and values were averaged for each day.3. Subjects were divided in two groups depending on whether they became normotensive (group 1; n = 12) or remained hypertensive (group 2; n = 39). This distinction was thought to reflect mild and more severe hypertensive groups respectively. 4. Although both groups showed a comparable fall in blood pressure during hospitalization, noradrenaline levels fell more consistently in group 1, whereas adrenaline levels fell only in group 2. The components of the reninangiotensin-aldosterone system rose, but more conspicuously in group 1. 5. It is concluded that withdrawal of sympathetic activity can only partly explain the hypotensive response to hospitalization. The renin-angiotensin system behaves only passively and appears to be counterproductive to alterations in blood pressure.