SYMPATHETIC MODULATION OF HYPOXIC PULMONARY VASOCONSTRICTION IN INTACT DOGS

Background: The effects of the sympathetic nervous system on hypoxic p ulmonary vasoconstriction (HPV) have been reported variably. We studie d the effects of adrenergic receptor blockade and epidural blockade on HPV in 32 pentobarbital-anaesthetised intact dogs. Methods: Pulmonary arterial flow-pressure relationships were determined in hyperoxia and hypoxia, at baseline and after alpha-blockade (phentolamine 2 mg/kg 50 mu g.kg(-1).h(-1)), beta-blockade (propranolol 2 mg/kg), alpha bet a-blockade, epidural blockade (lignocaine 20 mg/kg), and alpha beta- p lus epidural blockade. Results: At reference flow of 3.51.min(-1).m(-2 ), the mean hypoxic response (hypoxia-induced increase in transpulmona ry pressure gradient, each n = 8) changed from 6.0 +/- 0.9 to 3.5 +/- 1.0 mmHg after alpha-blockade, from 5.8 +/- 0.9 to 7.3 +/- 0.7 mmHg af ter beta-blockade, from 4.1 +/- 0.8 to 9.0 +/- 1.4 mmHg after alpha be ta-blockade, and from 3.4 +/- 1.0 to 4.3 +/- 0.9 mmHg after epidural b lockade (all P < 0.05), and was not affected by epidural blockade afte r alpha beta-blockade. Conclusions: In pentobarbital-anaesthetised dog s, (1) HPV is attenuated by alpha- and enhanced by beta-, alpha beta- and epidural blockade, and (2) epidural blockade has no significant ad renergic-unrelated effect on the pulmonary vasculature.