Adenosine produces changes in cerebral hemodynamics and metabolism as assessed by near-infrared spectroscopy in late-gestation fetal sheep in utero.

Abstract

Rises in fetal adenosine during hypoxia may have a metabolic inhibitory role that helps the fetus adapt to periods of low arterial partial pressure of oxygen (P(a)O(2)). We examined the fetal cerebral hemodynamic and metabolic responses to exogenous adenosine infusion and compared this with previous studies. Six fetal sheep at ca. 125 d gestation were instrumented under general anesthesia with catheters, flow probes, and near-infrared optodes and allowed to recover. After 3 d, adenosine was infused at a level known to reproduce fetal levels during hypoxia. Fetal hemodynamics and cerebral near-infrared spectroscopic (NIRS) variables were monitored and paired blood samples taken for oxygen delivery and consumption calculation. Fetal heart rate, mean arterial pressure, and carotid flow showed no change during adenosine infusion. Cerebral oxyhemoglobin (HbO(2)), deoxyhemoglobin (Hb), and blood volume rose, suggesting venous pooling in the brain. Cerebral cytochrome oxidase (CcO) became more oxidized, indicating reduction in electron flow down the mitochondrial electron transfer chain and, thus, a fall in metabolic rate. Blood sample analysis revealed that there was no change in oxygen delivery to the head but that cerebral oxygen consumption fell during adenosine infusion. These data indicate that fetal cerebral metabolism fell during infusion of adenosine at a level known to reproduce fetal plasma concentrations during hypoxia.