The haemodynamic effects of adrenergic receptor blockade or stimulation druing nitrous oxide anaesthesia in dogs

The effects of ventilation with normoxic and hyperoxic nitrous oxide on systemic, pulmonary and coronary haemodynamics before and after adrenergic receptor blockade or stimulation were investigated in 15 dogs. To evaluate a blocking or stimulating effect of nitrous oxide on the alpha-adrenergic receptors, the animals were given phenoxybenzamine or noradrenaline, respectively. The effects of beta-adrenergic receptor blockade or stimulation were studied after injection of propranolol or isoproterenol, respectively. The experiments showed that in spite of the lack of alpha-receptor blocking properties and despite the tendency to produce beta-receptor blockade, nitrous oxide induced vasodilation. The findings of the present study, together with the increase in cardiac output and peripheral vasodilation, suggest that the cardiovascular effects of nitrous oxide are extra-adrenergic.