Sympathetic modulation of hypoxic pulmonary vasoconstriction in intact dogs

Background: The effects of the sympathetic nervous system on hypoxic pulmonary vasoconstriction (HPV) have been reported variably. We studied 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 beta-blockade, epidural blockade (lignocaine 20 mg/kg), and alpha beta- plus epidural blockade. Results: At reference flow of 3.51.min(-1).m(-2), the mean hypoxic response (hypoxia-induced increase in transpulmonary 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 after beta-blockade, from 4.1 +/- 0.8 to 9.0 +/- 1.4 mmHg after alpha beta-blockade, and from 3.4 +/- 1.0 to 4.3 +/- 0.9 mmHg after epidural blockade (all P < 0.05), and was not affected by epidural blockade after alpha beta-blockade. Conclusions: In pentobarbital-anaesthetised dogs, (1) HPV is attenuated by alpha- and enhanced by beta-, alpha beta- and epidural blockade, and (2) epidural blockade has no significant adrenergic-unrelated effect on the pulmonary vasculature.