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A B S T R A C T Continuous 6-h infusions of the beta adrenergic blockers dl-propranolol or oxprenolol significantly reduced plasma renin activity (PRA) and mean blood pressure in the resting rabbit and prevented the stimulatory effects of isoproterenol on renin release and heart rate. These actions were due to blockade of beta receptors, for the inactive isomer, d-propranolol, had no effect. Despite sustained high plasma concentrations of dl-propranolol (0.2 Ag/ml) in the unstimulated animal, PRA did not fall below 36% of control values, suggesting that basal renin secretion is maintained partly by factors other than beta adrenergic mechanisms.Prindolol, another beta blocker, also abolished the effects of isoproterenol on renin and on the heart, and reduced blood pressure in the resting animal. However, prindolol increased resting PRA and heart rate, and in animals already receiving dl-propranolol, it raised PRA and heart rate without further altering blood pressure. This suggests that the effect on PRA of prindolol was due to its intrinsic sympathomimetic activity and not hypotension-mediated mechanisms. The observation that the blood pressure-lowering effect of prindolol was associated with a rise in PRA, while another beta antagonist, H 35/25, lowered PRA but had no effect on blood pressure, indicates that the hypotensive action of beta blockers is unrelated to their effects on renin release.In both unstimulated and isoproterenol-challenged animals, only blockers possessing beta-i receptor affinity (d,t-propranolol, oxprenolol, prindolol, practolol, and metoprolol) affected heart rate, while effects on PRA were more prominent with agents possessing beta-2 activity (dl-propranolol, oxprenolol, prindolol, and H 35/25). Thus, the changes in PRA caused by the beta adrenergic blockers appear to be dependent upon the summation of their direct effects, antagonistic or sympathomimetic, on beta-2 adrenergic receptors regulating renin release.

Wales 2000 G S STOKES, MD, FRACP, cardiorenal physician R M GRAHAM, MB, BS, fellow in cardiorenal diseases J M GAIN, SRN, SRM, research nurse P R DAVIS, MB, BS, registrar occurred in five out of seven patients given 2 mg prazosin and in two out of four given a 05-mg dose, whereas those taking 2 mg or 0 5 mg and a 250-mmol sodium intake experienced no postural symptoms. These findings indicate that particular care should be taken in starting prazosin treatment in sodium-depleted patients.

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In hypertensive patients with unilateral renal artery stenosis, intravenous diazoide increased renal vein renin activity more on the involved side than on the contralateral side, whereas, in a group with predominantly unilateral renal parenchymal disease, the increase in renal vein was similar for both kidneys. In patients with bilateral renal artery stenosis, the use of diazoxide was helpful in lateralizing the dominant ischaemic lesion. Diazoide administration appears to be a safe, rapid and convenient method of increasing the sensitivity of the renal vein renin test used in predicting the outcome of surgical treatment of renovascular hypertension. Bilateral renal vein renin determination of established value in the diagnosis of functional renal ischaemia. 1-4 However, in the use of this procedure to predict the efficacy of corrective surgery, false positive and false negative results still occur. Thus, various manoeuvres which stimulate renin release have been employed to improve the sensitivity of the test. 5-7 We report a new application the practical approach to of this procedure in the diagnosis of renal hypertension, which both basal and stimulated levels of renal venous renin activitity can be measured during a brief period of bilateral renal vein catherization.

Clonidine (Catapres) administered intramuscularly in a dose of 150 microng produced a satisfactory reduction in blood pressure in 13 of 16 hypertensive patients. Its effect occurred within five minutes, was maximal at 75 minutes and persisted for five hours. In six patients who received two doses (150 microng and 300 microng), the response was shown to be dose-related. No serious side effects were noted. Intramuscular administration of clonidine thus appears to be safe and effective. It has a place in the management of uncontrolled hypertension when a rapid reduction in blood pressure is undesirable and in the maintenance of blood pressure control when oral therapy cannot be tolerated.