Effect of α -Adrenergic Blockade on the Cardiovascular Responses to Hypoxemia and Hypercapnic Acidosis in Conscious Dogs

Abstract

In order to evaluate the role of the α-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) α 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 α ₁-adrenergic blockade. The mechanism for abrogation of the rise in mean arterial pressure during the combined blood gas derangement by α 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 α-adrenergic system is important in circulatory homeostasis during the combined blood gas derangement.