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SUMMARY The intravenous injection of isoprenaline and glucagon in anaesthetized dogs increased heart rate and stroke volume. Isoprenaline was 60 and 500 times more potent than glucagon in increasing heart rate and stroke volume respectively. Isoprenaline, but not glucagon, dilated the femoral blood vessels and increased ventricular automaticity. Propranolol blocked the cardiac actions of isoprenaline but not those of glucagon. The actions of glucagon do not appear to be mediated through beta adrenoceptive receptors.

Seventeen patients with thyrotoxicosis have been treated with relatively small doses of iodine-131 and their thyrotoxic symptoms have been controlled with propranolol. This use of propranolol, which does not interfere with thyroid-function tests, may allow an earlier and better differentiation of those patients who will respond effectively to a small dose of therapeutic radioactive iodine.

Plasma-gastrin levels measured by radioimmunoassay were found to be elevated in two patients with phaeochromocytoma. Both the administration of phenoxybenzamine and the later removal of the tumour reduced the fasting plasma-gastrin level to normal. The intravenous infusion of adrenaline in dogs produced a rise in plasma-gastrin level. It is concluded that catecholamines stimulate gastrin release.

The effect of propranolol on radioiodine utilization by the thyroid gland has been studied in 18 patients. All parameters of iodine uptake by the thyroid – initial 5–20 minutes after intravenous administration, 2, 4, 24 and 48 hours after oral administration were unaltered by propranolol administration. In three of four patients studied an increase in isotopically labelled serum PBI was observed after 8 days propranolol therapy.

Propranolol reduced heart-rate in 10 patients with hyperthyroidism by 17.5 beats per minute and in 5 patients with hypothyroidism by 11.4 beats per minute. The heart-rate after propranolol in the two groups was 74.2 and 47.2 beats per minute respectively. The intrinsic heart-rate was greater than expected in 14 of 15 patients with hyperthyroidism and less than expected in 7 patients with hypothyroidism. It was concluded that the differences in heart-rate between patients with hyperthyroidism and hypothyroidism are mainly due to thyroxine acting directly on the heart and not to its potentiation of the action of catecholamines.