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Departments of Pediatrics and Neurology, Medical College of Wisconsin and Zablocki Veterans Affairs Medical Center, Milwaukee, Wisconsin 53226
Alkalosis-induced relaxation was measured in
precontracted arterial rings from 1-wk-old piglets exposed to normoxia
or to 3 days of chronic hypoxia. In normoxic piglet arteries,
alkalosis-induced relaxation was blunted in arteries without functional
endothelium and in arteries treated with nitric oxide synthase or
guanylate cyclase inhibitors but not in arteries treated with
cyclooxygenase inhibitors or Ca2+-
and ATP-dependent K+-channel
inhibitors. Inhibition of voltage-dependent
K+ channels with
10
3 M 4-aminopyridine also
failed to block alkalosis-induced relaxation. 4-Aminopyridine at
10
2 M did
block the response, but this may have been due to sustained vascular
smooth muscle depolarization. Arteries from hypoxic piglets exhibited
greater contraction to the thromboxane mimetic U-46619, decreased
endothelium-dependent relaxation, and blunted alkalosis-induced relaxation. The residual relaxation was eliminated by nitric oxide synthase but not by cyclooxygenase or voltage-dependent
K+-channel inhibition.
Alkalosis-induced relaxation of newborn piglet pulmonary arteries
appears to be mediated by the nitric oxide-cGMP pathway and is
attenuated after 3 days of hypoxia, likely because of decreased nitric
oxide activity.
pulmonary hypertension; newborn; endothelium-derived relaxing factors; potassium channels
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