The Effect of Propranolol on the Cardiovascular Responses to Isoprenaline, Adrenaline and Noradrenaline in the Anaesthetized Dog

In 1948 Ahlquist suggested that there were two types of catechol amine receptor, which he designated a and 8. The first compound shown to block selectively the ,8-receptors was dichloroisoprenaline They also found that dichloroisoprenaline itself increased heart rate and cardiac contractile force and reduced arterial pressure. These effects were attributed to a sympathomimetic action, which has been demonstrated in isolated heart preparations, conscious and anaesthetized animals and in man (Furchgott, 1959; Black Glover, Greenfield & Shanks, 1962). Recent studies suggest that pronethalol may possess intrinsic sympathomimetic activity, but to a much lesser extent than dichloroisoprenaline. Donald, Kvale & Shepherd (1964) found that in anaesthetized dogs pronethalol increased cardiac output and stroke volume, and in conscious dogs with cardiac denervation it increased heart rate. In all dogs there was a fall in arterial pressure. Similar results were obtained in anaesthetized dogs by