Hemodynamic responses to alpha-adrenergic blockade during hypoxemia in the fetal lamb. |
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Authors: | R P Paulick R L Meyers C D Rudolph A M Rudolph |
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Affiliation: | Cardiovascular Research Institute, University of California, San Francisco 94143. |
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Abstract: | The mechanisms responsible for the increase in umbilical venous and hepatic vascular resistance during hypoxemia are poorly understood. To assess the relative importance of alpha-adrenergic receptors, we produced an acute, severe hypoxemia in chronically instrumented fetal sheep. While fetal arterial oxygen saturation was maintained at the same level, we then injected phentolamine, a selective alpha-adrenoreceptor blocker. We found that the hypoxemia-induced vasoconstriction of the umbilical veins and hepatic vasculature was reversed by alpha blockade. Thus, alpha-adrenergic stimulation is necessary to maintain vasoconstriction of the umbilical veins and hepatic vasculature during acute fetal hypoxemia. Furthermore, alpha-adrenergic stimulation is responsible for the hypoxemia-induced vasoconstriction of the gut, spleen, and lower carcass. Thus, the alpha-adrenergic system mediates important fetal hemodynamic adaptations to acute hypoxemia. However, the alpha-adrenergic system is not responsible for the hypoxemia-induced constriction of the renal vasculature. |
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