1. Intravenous infusion of propranolol (3·86 μmol h —1 kg —1 ) for 2 h lowered arterial pressure in the conscious rabbit whereas similar infusions of practolol (37·6 μmol h —1 kg —1 ) did not. 2. The fall in blood pressure produced by propranolol was accompanied by a decrease in splanchnic nerve activity. Practolol did not change splanchnic nerve activity. 3. A centrally mediated decrease in sympathetic nervous activity makes an important contribution to the hypotensive action of propranolol in the rabbit. This effect is not shown by practolol.

1. The mechanism by which pretreatment of rats with intracisternal 6-hydroxydopamine prevents the onset of deoxycorticosterone hypertension has been studied. 2. Rats pretreated with central 6-hydroxydopamine increase their consumption of 0.17 mol/l sodium chloride-0.03 mol/l potassium chloride (‘saline’) less than normal rats when implanted with deoxycorticosterone. 3. Intact rats restricted to the equivalent consumption of saline of rats pretreated with 6-hydroxydopamine develop hypertension despite this restriction. 4. It is suggested that the prevention of deoxycorticosterone hypertension by central 6-hydroxydopamine does not depend on reduced saline consumption.

1. The effects of propranolol and R03-4787, a new beta-adrenoceptor antagonist with a partial agonist activity, have been studied in a blind, cross-over comparison with placebo. 2. In ten patients who completed the study, the two drugs produced a similar reduction in blood pressure; the reduction in heart rate with propranolol was significantly( P 0.001)greater than that produced by R03-4787. 3. Plasma renin activity averaged 4.13 ± 1.37 ng h −1 ml −1 on placebo, fell to 3.64 ± 1.47 ng h −1 ml −1 on propranolol and to 2.50 ± 1.39 ngh −1 ml −1 on R03-4787. 4. No correlation was demonstrable between the log plasma concentration of either propranolol or R03-4787 and change in blood pressure.

1. Depletion of brain catecholamines by injection of 6-hydroxydopamine (6-OH D) into the cisterna magna in rabbits significantly diminished the rise in arterial pressure following the wrapping of both kidneys in cellophane, 6-OHD treated animals having a mean arterial pressure of 100 mmHg at 6 weeks after wrapping, compared with 122 mmHg in control animals. 2. In rabbits with established cellophane perinephritis hypertension, intracisternal 6-OHD significantly lowered the arterial pressure from 124 to 103 mmHg. 3. The pressor response to intraventricular angiotensin (100 ng) was decreased in normotensive rabbits pretreated with intracisternal 6-OHD from a pressure rise of 20 mmHg in 1 min to 10 mmHg in 1 min.