1. Fetal cerebral and peripheral circulatory responses to hypoxia after nitric oxide synthase inhibition.
- Author
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Harris AP, Helou S, Gleason CA, Traystman RJ, and Koehler RC
- Subjects
- Analysis of Variance, Animals, Blood Circulation drug effects, Cerebrovascular Circulation drug effects, Enzyme Inhibitors pharmacology, Female, Gestational Age, Nitric Oxide Synthase antagonists & inhibitors, Oxygen metabolism, Pregnancy, Sheep, Vascular Resistance drug effects, Blood Circulation physiology, Blood Pressure drug effects, Cerebrovascular Circulation physiology, Fetal Hypoxia physiopathology, Fetus physiology, NG-Nitroarginine Methyl Ester pharmacology, Nitric Oxide Synthase metabolism
- Abstract
The increase in cerebral blood flow (CBF) during hypoxia in fetal sheep at 0.6 gestation is less than the increase at 0.9 gestation when normalized for differences in baseline CBF and oxygen consumption. Nitric oxide (NO) synthase (NOS) catalytic activity increases threefold during this period of development. We tested the hypothesis that administration of the NOS inhibitor N(omega)-nitro-L-arginine methyl ester (L-NAME) decreases the CBF response to systemic hypoxia selectively at 0.9 gestation. We also tested whether any peripheral vasoconstriction during hypoxia is potentiated by L-NAME at 0.9 gestation. Administration of L-NAME increased arterial blood pressure and decreased microsphere-determined CBF during normoxia in fetal sheep at both 0.6 and 0.9 gestation. With subsequent reduction of arterial oxygen content by approximately 50%, the percent increase in forebrain CBF in a control group (57 +/- 11%; +/- SE) and L-NAME-treated group (51 +/- 6%) was similar at 0.6 gestation. Likewise, at 0.9 gestation, the increase in CBF was similar in control (90 +/- 25%) and L-NAME (80 +/- 28%) groups. At 0.9 gestation, L-NAME treatment attenuated the increase in coronary blood flow and increased gastrointestinal vascular resistance during hypoxia. We conclude that NO exerts a basal vasodilatory influence in brain as early as 0.6 gestation in fetal sheep but is not an important mechanism for hypoxic vasodilation in brain at either 0.6 or 0.9 gestation. Thus the developmental increase in NOS catalytic capacity does not appear to be responsible for developmental increases in the CBF response to hypoxia during this period. In contrast, NO modulates the vascular response to hypoxia in heart and gastrointestinal tract.
- Published
- 2001
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