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Background. Adult respiratory distress syndrome is characterized by hypoxia and acute pulmonary
hypertension. Therefore we examined the effect of acute hypoxia on the mechanisms
of pulmonary vasodilation.
Methods. Isolated rat pulmonary artery rings were suspended on tensiometers in a balanced
salt solution. A normoxic gas mixture was bubbled through the solution (21% O2, 5% CO2, 74% N2). Rings were preconstricted with phenylephrine, and the following mechanisms of pulmonary
vascular smooth muscle relaxation were studied in a random order: (1) endothedial-dependent
cyclic guanosine monophosphate-mediated (acetylcholine, 10−9 to 10−6 mol/L), (2) endothelial-independent cyclic guanosine monophosphate-mediated (nitroprusside,
10−9 to 10−6 mol/L), and (3) β-adrenergic receptor cyclic adenine monophosphate-mediated (isoproterenol,
10−9 to 10−6 mol/L). Separate rings were preconstricted with phenylephrine, and the gas was switched
to a hypoxic mixture (0% O2, 5% CO2, 95% N2). After vasoconstriction to hypoxia reached a plateau, the response to the maximal
effective dose of the above vasodilators (10−6 mol/L) was determined in a random order. Statistical analysis was done with one-way
analysis of variance with post hoc Bonferroni-Dunn correction. A p value of less than
0.05 was accepted as significant.
Results. Endothelial-dependent and-independent cyclic guanosine monophosphate-mediated relaxation
was the same in normoxia and hypoxia. On the other hand, hypoxia inhibited β-adrenergic
receptor cyclic adenine monophosphate-mediated pulmonary vasorelaxation (97.5%±2.5%
versus 71.5%±2.3% in hypoxia; p<0.01).
Conclusions. These data suggest that hypoxia selectively inhibits β-adrenergic cyclic adenine
monophosphate-mediated pulmonary vasorelaxation. This dysfunction of the normal mechanism
of pulmonary vasodilation may contribute to the pulmonary hypertension seen in adult
respiratory distress syndrome.
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Article info
Publication history
Accepted:
June 9,
1994
Footnotes
1Supported by National Institutes of Health grants R29HL49398 (D.A.F.) and R29HL43696 (A.B.).
Identification
Copyright
© 1995 Mosby-Year Book, Inc. Published by Elsevier Inc.
