The intravenous infusion of I.C.I. 50172 in doses up to 20 mg reduced, although not significantly, the increase in heart rate produced by the infusion of isoprenaline in healthy volunteers; the response to adrenaline was significantly reduced. The infusion of 1 mg propranolol abolished these responses After the pre‐treatment of subjects with atropine or hexamethonium, I.C.T. 50172 produced a significant reduction in an isoprenaline tachycardia. This reduction was not competitive and did not exceed 50%. The intravenous injection of 4 mg I.C.I. 50172 reduced an exercise tachycardia; its effect was less than that of 4 mg propranolol. This difference became greater as the doses of the two drugs were increased. The dextro isomer of propranolol had no effect on the exercise tachycardia; I.C.I. 45763 reduced it to the same extent as propranolol. The intravenous injection of I.C.I. 50172 reduced the increase in heart rate produced by tilting a normal subject from the supine to 80° head‐up position. After the administration of atropine, I.C.I. 50172 almost abolished the response. In the presence of atropine, I.C.I. 50172 was as active as propranolol in reducing the increase in heart rate on tilting. The reason for the differences in the effects of I.C.I. 50172 on the increases in heart rate brought about by the three procedures is not clear. The increase in forearm blood flow produced by the infusion of isoprenaline into the brachial artery was not reduced by the intra‐arterial administration of I.C.I. 50172.

It has been suggested that poststenotic weakening of arterial walls is caused by arterial wall vibration and structural fatigue initiated by pressure disturbances in turbulent blood flow. We examined the frequency spectra of wall vibration downstream from experimental arterial stenoses and compared them with the natural resonant vibration characteristics of the artery walls. Spectra of arterial wall displacement of isolated perfused dog and human arteries were measured with a noncontacting capacitance transducer during conditions of fluid flow through the artery; resonant vibration characteristics were determined during pure sine and random sound stimulation of the artery walls in the absence of flow. It is concluded that fluid flow through isolated arteries with an experimental stenosis excites the artery wall to vibrate over a wide range of frequencies within which are discrete frequencies that coincide with the resonant frequencies of the artery wall.

The central and peripheral vascular haemodynamic effects of glucagon were studied in 29 and peripheral haemodynamic effects of glucagon in patients with organic heart disease. Patients and MethodsA total of 29 patients was studied; they were divided into the following groups: (i) the acute phase of myocardial infarction (8 patients); (2) chronic rheumatic heart disease (II patients); (3) a selection of I0 patients chosen for measurement of forearm and calf blood flow. As the technique varied for each group the methods and results will be described for each in turn.

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