Purinergic contribution to circulatory, metabolic, and adrenergic responses to acute hypoxemia in fetal sheep

This study investigated the effects on femoral vascular resistance, blood g lucose and lactate levels, and plasma catecholamine concentrations of fetal treatment with an adenosine receptor antagonist during acute hypoxemia in fetal sheep during late gestation. Under anesthesia, seven fetal sheep were instrumented between 117 and 118 days gestation (term is similar to 145 da ys) with vascular and amniotic catheters and an ultrasonic probe around a f emoral artery. Six days after surgery, all fetuses were randomly subjected to a 3-h experiment consisting of 1 h of normoxia, 1 h of hypoxemia, and 1 h of recovery. This was done during either intravenous infusion of vehicle or the adenosine receptor antagonist [8-(p-sulfophenyl)-theophylline; 8- SP T] dissolved in vehicle. During vehicle infusion, all fetuses responded to hypoxemia with bradycardia, an increase in arterial blood pressure, and fem oral vasoconstriction. Increases in blood glucose and lactate concentration s and in plasma epinephrine and norepinephrine concentrations also occurred in all fetuses during hypoxemia. Fetal treatment with 8-SPT markedly atten uated the bradycardic, hypertensive, vasoconstrictor, glycemic, and adrener gic responses to hypoxemia, but it did not affect the increase in blood lac tate concentrations during hypoxemia. These data show that adenosine is inv olved in the mechanisms mediating fetal cardiovascular, metabolic, and adre nergic responses to hypoxemia in fetal sheep. Fetal treatment with 8-SPT mi mics the effects of carotid sinus nerve section on fetal cardiovascular fun ction during hypoxemia, suggesting a role for adenosine in mediating fetal cardiovascular chemoreflexes.