Submitted on March 2, 2009
Revised on April 9, 2009
Accepted on April 24, 2009
Age-Dependent Modulation of Soluble Guanylate Cyclase Activity by Chronic Hypoxia in Ovine Cerebral Arteries
William J. Pearce1*, James M. Williams1, Charles R. White2, and Thomas Michael Lincoln3
1 Loma Linda University
2 University of California San Diego
3 University of South Alabama
* To whom correspondence should be addressed. E-mail: wpearce{at}llu.edu.
A broad variety of evidence obtained largely in pulmonary vasculature suggests that chronic hypoxia modulates vasoreactivity to NO. The present study explores the general hypothesis that chronic hypoxia also modulates cerebrovascular reactivity to NO, and does so by modulating the activity of soluble guanylate cyclase (sGC), the primary target for NO in vascular smooth muscle. Pregnant and non-pregnant ewes were maintained at either sea level or at 3820 m for the final 110 of gestation, at which time middle cerebral arteries from term fetal lambs and non-pregnant adults were harvested. In both fetal and adult arteries, NO-induced vasodilatation was attenuated by chronic hypoxia and completely inhibited by 10 µM ODQ, a selective inhibitor of sGC. sGC abundance (in ng sGC/mg protein) measured via Westerns was approximately 10-fold greater in fetal (17.6±1.6) than adult (1.7±0.3) arteries, but was not affected by chronic hypoxia. The specific activity of soluble guanylate cyclase (in pmol cGMP/µg sGC/min) was similar in fetal (255±64) and adult (280±75) arteries, and was inhibited by chronic hypoxia in both fetal (120±10) and adult (132±26) arteries. Rates of cGMP degradation (in pmol cGMP/mg protein/min) were similar in fetal (159±59) and adult (134±36) arteries but were not significantly depressed by chronic hypoxia in either fetal (115±25) or adult (108±25) arteries. The cGMP analogue 8-pCPT-cGMP was a more potent vasorelaxant in fetal (pD2=4.7±0.1) than adult (pD2=4.3±0.1) arteries, but its ability to promote vasodilatation was not affected by chronic hypoxia in either age group. Together, these results reveal that hypoxic inhibition of NO-induced vasodilatation is attributable largely to attenuation of the specific activity of soluble guanylate cyclase and does not involve significant changes in soluble guanylate cyclase abundance, cGMP-phosphodiesterase activity, or the vasorelaxant activity of protein kinase G.
