Effect of alpha-adrenergic blockade on the cardiovascular responses to hypoxemia and hypercapnic acidosis in conscious dogs

In order to evaluate the role of the alpha-adrenergic system in the systemic and renal hemodynamic changes of the acute combined blood gas derangement, seven conscious mongrel dogs in careful sodium balance (80 mEq/day for 4 days) were evaluated. Each animal was evaluated during combined acute hypoxemia (PaO2 = 35 +/- 1 mm Hg) and hypercapnic acidosis (PaCO2 = 56 +/- 2 mm Hg; pH = 7.18 +/- 0.01) with (i) vehicle (D5W) alone and (ii) alpha 1-adrenergic blockade with prazosin, 0.1 mg/kg iv. Mean arterial pressure increased during the combined blood gas derangement with vehicle. In contrast, mean arterial pressure fell during combined acute hypoxemia and hypercapnic acidosis with alpha 1-adrenergic blockade. The mechanism for abrogation of the rise in mean arterial pressure during the combined blood gas derangement by alpha 1-adrenergic blockade appeared to be through attenuation of the rise in cardiac output rather than an exaggerated fall in total peripheral resistance. These observations suggest that the alpha-adrenergic system is important in circulatory homeostasis during the combined blood gas derangement.