In rats anesthetized with urethane, intravenous injection of oxprenolol, propranolol, and d-propranolol increases arterial pressure, while practolol is ineffective. These changes of arterial pressure occur in rats previously treated with phentolamine or phenoxybenzamine, indicating that the pharmacological block of alpha receptors does not prevent vasoconstriction by oxprenolol and propranolol. On the contrary, beta receptor blocking agents have little effect on the arterial pressure of rats treated with a ganglion blocker (pentolinium).The pressor action of adrenaline and angiotensin is significantly depressed by alpha blockers, but small doses of oxprenolol restore completely the action of angiotensin and, in part, that of adrenaline. Adrenaline produces a biphasic effect on the blood pressure of anesthetized rats. Both phases of the effect are eliminated by alpha blockers while ganglion blocker abolishes the hypotensive phase only. Administration of small doses of oxprenolol and propranolol (1–10 μg/kg) in untreated rats or in animals treated with alpha blockers increases significantly the blood pressure, but does not modify the biphasic effect of adrenaline.The results indicate that the pressor effect of small doses of beta blocker may not be entirely related to the elimination of the beta inhibitory effect of exogenous adrenaline on the vascular system. No changes of blood pressure occur when beta blockers are administered to animals treated with ganglion blockers, suggesting that the vasoconstriction produced by propranolol and oxprenolol is not due to a direct effect on the vascular smooth muscles.

SUMMARYIn 10 patients with coarctation of the aorta, plasma renin activity was measured after recumbency and orthostatism in peripheral venous blood and, in some cases, in renal venous blood also. In nine of these patients, basic plasma renin values and those obtained under stimulatory conditions lay within normal range, and only in one patient were the values elevated. However, since this patient displayed the lowest gradient of mean arterial blood pressure proximal and distal to the stenosis, it can be regarded as improbable that the elevation in plasma renin activity was caused by the coarctation. Plasma renin activity in the renal venous blood of both kidneys, which was measured in three patients, showed no elevation.On the basis of observations of other authors and of our own studies it can be concluded that the kidneys can contribute to the development of prestenotic hypertension in acute constriction of the aorta in experiments with animals, but in chronic coarctation in animals or in man the humoral or renal theory has no importance to the pathogenesis of hypertension.

Scornik und Paladini (36) stellten zum Beispiel nach intravenösen Infusionen von Noradrenalin einen signifikanten Anstieg des Plasma-Angiotensins fest. Wathen und Mitarbeiter (49) fanden bei Tierexperimenten eine Reninstimulation, wenn die Katecholamine direkt in die Nierenarterie gegeben wurden, bei intravenösen Gaben blieb die Stimulation des Renins jedoch aus. Vander (45) sah demgegenüber auch nach intravenöser Verabreichung von Katecholaminen eine deutliche Reninerhöhung bei Hunden.

Oxprenolol, a new beta adrenergic blocking drug, was used as the sole antihyperteTl8ive agent for a minimum of 14 weeks in 20 patients with mild to moderate essential hypertension. The results demonstrate a definite, but not prominent, antihypertensive activity of this drug. Oxprenolol does not lower the blood pressure sufficiently in an unselected group of patients, but its effect is clinically satisfactory and well tolerated in some cases of mild "borderline" hypertension. In the latter, low doses of oxprenolol influence equally the systolic and diastolic blood pressure in both supine and standing position. The decrease in heart rate is relatively small. No maior side effects were noted.