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Am J Physiol Regul Integr Comp Physiol 279: R1813-R1820, 2000;
0363-6119/00 $5.00
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Vol. 279, Issue 5, R1813-R1820, November 2000

Chronic hypoxia increases the NO contribution of acetylcholine vasodilation of the fetal guinea pig heart

Loren P. Thompson, Kripamoy Aguan, Gerard Pinkas, and Carl P. Weiner

Department of Obstetrics, Gynecology and Reproductive Sciences, University of Maryland School of Medicine, Baltimore, Maryland 21158

To investigate the effect of chronic hypoxia (HPX) on vasodilation of the fetal heart, we exposed pregnant guinea pigs to room air or 12% O2 for 4, 7, or 10 days. We excised hearts from anesthetized fetuses (60 ± 3 days; 65-day gestation = term) and measured changes in both the coronary artery pressure of the isolated constant-flow preparation and endothelial nitric oxide synthase (eNOS) mRNA of fetal ventricles. Dilator responses to cumulative addition (10-9-10-5 M) of acetylcholine and sodium nitroprusside in prostaglandin F2alpha (5 × 10-6 M)-constricted hearts were similar among normoxia (NMX), 4-, 7-, and 10-day HPX (control). Nitro-L-arginine (L-NA, 10-4M), a NOS inhibitor, inhibited maximal acetylcholine dilation of hearts exposed to 10-day HPX greater than NMX, 4-, and 7-day HPX. Hypoxia (after 7 and 10 days) increased eNOS mRNA of fetal ventricles compared with NMX and 4-day HPX. 4-Aminopyridine (3 mM), a voltage-dependent K+-channel inhibitor, inhibited acetylcholine- but not sodium nitroprusside-induced dilation of NMX and 10-day HPX hearts to a similar magnitude. Glibenclamide (10-5 M), an ATP-sensitive K+-channel inhibitor, had no effect on vasodilation. We conclude that chronic HPX increases the contribution of NO but does not alter K+-channel activation in response to acetylcholine-stimulated coronary dilation. Thus increases in NO production via upregulation of eNOS gene expression may be an adaptive response to chronic HPX in the fetal coronary circulation.

coronary microcirculation; endothelial nitric oxide; K+ channel; endothelium-dependent hyperpolarizing factor


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