1. To evaluate the effects of converting-enzyme inhibition on the sympathetic nervous system, on renin and on the other known regulators of aldosterone secretion, we measured blood pressure, heart rate, plasma noradrenaline, adrenaline, renin activity, aldosterone, cortisol and serum potassium in 15 sodium-repleted hypertensive patients in supine position and during 30 min of 65° head-up tilt before and during treatment with SQ 14 225. 2. SQ 14 225 produced significant decreases in supine blood pressure and plasma aldosterone and significant increments in plasma renin activity and potassium; in contrast, heart rate, noradrenaline, adrenaline and cortisol were unchanged. 3. While in control tilt studies blood pressure was always maintained, during treatment three of 15 patients had vasovagal syncopes. In the remaining 12 blood pressure was maintained during tilt on SQ 14 225; however, while the tilt-induced responses in heart rate and adrenaline were as in control studies, the 30 min increments in noradrenaline were significantly higher. 4. Both before and during treatment the responses of plasma renin activity and aldosterone to tilt were parallel, and correlated with each other, and cortisol and potassium changed only slightly. 5. It is concluded that the SQ 14 225-induced fall in blood pressure occurs without a concomitant rise in sympathetic nervous activity; thus the increase in supine plasma renin activity, being a reflection of the interruption of the angiotensin feedback mechanism on renin release, indicates an effective suppression of angiotensin II formation. 6. During SQ 14 225 the persistence of aldosterone response to tilt and its relationship with renin activity suggest that the enzymatic blockade is over-ridden; however, in the presence of a reduced formation of angiotensin II a more pronounced response of the sympathetic nervous system is required to defend blood pressure against postural changes.

1. The pulse-wave velocity along the brachial radial artery was measured in 38 subjects and volume distensibility values were calculated. 2. Measurements made at each subject's resting blood pressure showed that those with high blood pressure had higher pulse-wave velocity values and hence less distensible arteries. 3. An acute rise in arterial distending pressure was accompanied by a rise in pulse-wave velocity. 4. When pulse-wave velocity was remeasured in all subjects at identical arterial distending pressures, no difference was found between hypertensive and normal subjects. 5. It appears that poor distensibility of large arteries in hypertensive subjects is a consequence of the elevated distending pressures and not due to irreversible structural changes in the arterial wall.

1. Serial studies of the baroreflex control of heart rate (baroreflex sensitivity) were made in thirty-two patients on long-term haemodialysis by relating the reflex slowing of the heart to the arterial pressure rise produced by repeated sudden injections of phenylephrine. 2. Baroreflex sensitivity was less in the older patients and in those with higher pressures. The response was about 50% of that found previously for other subjects of comparable ages and arterial pressures without renal failure. 3. Haemodialysis improved reflex sensitivity over the long term, but did not have any consistent immediate effect. 4. Patients who had malignant hypertension in the past had lower reflex sensitivities than others (with similar ages and pressures at the time of study) whose blood pressures had never been raised, but there were individual exceptions. 5. Reflex sensitivity changed very little with different blood pressures in any one subject. 6. Three patients in whom hypertension was thought to have preceded renal failure had reflex sensitivities similar to eleven others in whom the hypertension was secondary to renal disease. 7. Reflex sensitivity was no different in three patients whose blood pressure could be controlled only by bilateral nephrectomy from that in others in whom the pressure could be controlled by salt restriction. 8. Reflex sensitivity was slightly reduced in two patients studied in the diuretic phase of acute renal failure; it was markedly reduced in a third who was also pregnant.