ADENOSINE MEDIATES METABOLIC AND CARDIOVASCULAR-RESPONSES TO HYPOXIA IN FETAL SHEEP

1. In seven unanaesthetized fetal sheep (> 80% term), isocapnic hypoxi a (arterial partial pressure of O-2, P-a,P-O2, similar to 15 mmHg) was induced for 1 h by lowering maternal inspired P-O2. Fetal hypoxia was also produced during intra-arterial administration of the adenosine r eceptor antagonist 8-(p-sulphophenyl)-theophylline (8-SPT). The fetal 8-SPT infusion was begun just prior to hypoxia and was stopped when fe tal P-a,P-O2 was returned to normal. 2. Hypoxia induced a progressive fetal acidosis, a rise in mean arterial pressure, a transient fall in heart rate and a decrease in breathing movements. 8-SPT signivicantly reduced the metabolic acidosis and abolished the hypertension and brad ycardia without altering hypoxic inhibition of fetal breathing. Admini stration of the vehicle for 8-SPT during hypoxia did not significantly affect the normal fetal metabolic and cardiovascular responses to acu te O-2 deprivation. 3. It is concluded that adenosine mediates the fet al bradycardia and hypertension produced by hypoxia, indicating that a denosine modulates fetal autonomic responses to acute oxygen deficienc y Secondly, adenosine contributes to fetal metabolic acidaemia, sugges ting that adenosine also modulates fetal glycolytic responses to hypox ia.