Journal of Applied Physiology, Vol 60, Issue 1 32-37, Copyright © 1986 by American Physiological Society
Chemical sympathectomy decreases alveolar hypoxic vasoconstriction in lambs but not in sheep
J. R. Custer and C. A. Hales
We studied the role of the sympathetic nervous system in the augmented
vasoconstrictor response of the newborn lamb, compared with the adult
sheep, by producing a chemical sympathectomy with 6-hydroxydopamine
(6-OHDA). Seven lambs, age 4-16 days, and five sheep, age 2 yr, were
anesthetized and intubated with a double-lumen endotracheal tube, allowing
ventilation of one lung with O2 to maintain systemic oxygenation while the
contralateral lung was ventilated with N2 as a hypoxic challenge.
Distribution of perfusion to each lung was evaluated using positron
scintigraphy after inferior vena caval injections of 13N, a
positron-emitting isotope. In the lambs, prior to 6-OHDA, distribution of
perfusion to the test lung was 43 +/- 3% of total lung perfusion during
bilateral O2 ventilation and fell with hypoxia to 24 +/- 2%, a reduction of
44 +/- 3% during N2 ventilation as compared with O2 ventilation. After
6-OHDA, hypoxic challenge reduced perfusion by only 22 +/- 2% (P less than
0.01 compared with pre-6-OHDA). In the adult sheep, hypoxic
vasoconstriction reduced perfusion to the test lung by 28 +/- 2% but was
unaffected by 6-OHDA. Absence of rise in pulmonary vascular resistance
(PVR) or femoral artery pressure (Pfa) in response to Tyramine infusions
after 6-OHDA confirmed complete sympathectomy in lambs and sheep.
Persistent increases in PVR and Pfa to infusions of prostaglandin F2 alpha
before and after 6-OHDA showed that the loss of alveolar hypoxic
vasoconstriction in the lamb was specific. Thus sympathetic innervation may
contribute to the greater strength of alveolar hypoxic vasoconstriction
found in lambs than in sheep.
