Pulmonary hypoxic vasoconstriction: not affected by chemical sympathectomy

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Abstract
The influence of chemical sympathectomy with 6-hydroxydopamine (6-OHDA) on regional alveolar hypoxic vasoconstriction and on global hypoxic pulmonary vasoconstriction was investigated. In 8 dogs a double-lumened endotracheal tube allowed ventilation of 1 lung with nitrogen as an alveolar hypoxic challenge while ventilation of the other lung with 100% O2 maintained adequate systemic oxygenation. Distribution of perfusion to the 2 lungs was determined with 133Xe and external counters. Mean perfusion to the test lung was 50.9 .+-. 4.9% of total lung perfusion on room air and decreased by 32.4% (P < 0.01) during alveolar hypoxia. Following 6-OHDA the test lung continued to reduce perfusion during alveolar hypoxia by 27.3%. In 5 dogs global hypoxia induced a 106% increase in pulmonary vascular resistance (PVR) prior to 6-OHDA and a 90% increase in PVR after 6-OHDA. After 6-OHDA no rise in PVR or systemic blood pressure occurred in response to tyramine, confirming effective sympathectomy by the 6-OHDA. Thus, sympathectomy with 6-OHDA failed to substantially block regional alveolar hypoxic vasoconstriction or global hypoxic pulmonary vasoconstriction.