Intrapulmonary bronchial circulation during hemorrhage

Experiments were conducted on 119 anesthetized and artificially ventilated rats to evaluate effects of a physiological stimulus (hemorrhage) to the sympothoadrenal system on the bronchial circulation. In the presence of a sufficient dose of a vasopressin V1-receptor antagonist, moderate (81 mmHg on average, 33 rats) or severe hypotension (69 mmHg, 28 rats) was produced by controlled hemorrhage (11 or 9 rats, respectively), or by treatment with phenoxybenzamine (0.1 mg/kg, i.v., 12 rats, or 1.0 mg/kg, 10 rats), or the highly selective alpha1-adrenoceptor antagonist, bunazosin (0.01 mg/kg i.v., 10 rats, or 0.1 mg/kg, 9 rats). During hypotension, the intrapulmonary bronchial blood flow (microsphere method) was decreased in a dose-dependent manner in the two antagonist-treated groups. However, these decreases were only of a moderate degree compared to the severe decrease in the hemorrhage group. Although the bronchovascular resistance was not significantly changed after treatment with either antagonist, this variable was greatly elevated during severe hemorrhagic hypotension, reaching 240±51% (P<0.001 with either antagonist study) of its baseline level. Changes in the pulmonary arterial and left atrial pressures, plasma vasopressin concentration, and renin activity were found to be less influential on these responses in 58 rats. Overall, we concluded that the sympathoadrenal mechanism powerfully increased the resistance and decreased the blood flow of the intrapulmonary bronchial circulation.