INTERACTIONS OF ADRENERGIC BETA-RECEPTOR BLOCKADE (OXPRENOLOL) AND Pco2 IN THE ANAESTHETIZED DOG: INFLUENCE OF INTRINSIC BETA-SYMPATHOMIMETIC ACTIVITY

Effects of change in Pa_co2 on systemic and coronary haemodynamicsand on coronary sinus blood-gases have been studied in 10 open-chesteddogs in which the lungs were ventilated with 0.8% halothanein oxygen, before and after administration of oxprenolol 0.3mg kg^–1 i.v. The hyperdynamic response of the circulationto hypercapnia was only marginally reduced after oxprenolol(cardiac output increased by 10% as opposed to 16% before oxprenolol).Before and after oxprenolol, hypocapnia caused large reductionsof coronary blood flow (–24% and –20% respectively),while hypercapnia caused large increases of coronary blood flow(+59% and +34% respectively). Oxprenolol does not appear tomodify significantly the circulatory response to arterial carbondioxide tension.