Guinea-pigs: In one series of experiments, 5 mg/kg of pronethalol was injected, and in another 15 mg/kg. Pronethalol (5 mg/kg), increased the dose of ouabain required to produce extrasystoles, completely prevented fibrillation, and significantly raised the lethal dose of ouabain. When fibrillation had already been produced by ouabain, pronethalol (3 to 4 mg) administered slowly restored a regular rhythm, but rapid injection sometimes produced cardiac arrest. As much as 20 to 25 mg/kg of pronethalol could be given to animals deeply anaesthetized with urethane or pentobarbitone, but with light chloroform or ether anaesthesia, 5 mg/kg of pronethalol caused a large fall in blood pressure and complete heart-block.

Pronethalol (6.8 x 10(-5)M) reversed the alpha-receptor blockade by dibenamine, ergotamine and phentolamine of responses to adrenaline, noradrenaline and phenylephrine in guinea-pig seminal vesicle.