Study of the renin-angiotensin system in essential hypertension

320 patients with essential hypertension divided into three groups (minor, medium and major severty) were studied against 50 normal controls. Plasma renin activity (PRA) was estimated in case of normal and low Na intake, furthermore, of low Na intake in association with administration of chlorothiazide, in the recumbent position as well as at the end of 4-hr walk. The hypertensive group of medium severity (Group II) revealed a significant decrease in PRA, compared with the controls and with the hypertensive group of minor severity (Group I), in each period of observation. A significant increase of PRA in response to insulin hypoglycaemia was demonstrable in all three groups and in the controls, but the increase was of significantly lesser degree in Group II than either in the controls or in Group I. The plasma catecholamine concentrations were found lower in Group II than in the controls and in Group I. An elevation of the plasma catecholamine levels was demonstrable in response to insulin hypeglycaemia, but it was of lesser degree in Group II than a Group I and in the controls. The poor responsiveness of the RAS in Group II is attributed to an inadequate adrenergic activity and to an increased mean arterial pressure in that group, but the higher age of patients and longer duration of hypertensive disease, both characteristic of the group of medium severity, may also effect the renin-angiotensin system.