Role of adenosine in regulation of brain temperature in fetal sheep

OBJECTIVE: The purpose of this study was to test adenosine's possible suppr ession of heat production by the ovine fetal brain during acute hypoxia. STUDY DESIGN: Hypoxia was induced by occluding the umbilical cord for 5 min utes in 8 fetal sheep with and without an adenosine receptor blocker, theop hylline, and fetal brain arid core temperatures were recorded. RESULTS: In 8 untreated fetuses, card occlusion induced severe but reversib le hypoxemia (decrease in carotid arterial PO2 from 23 +/- 1 to 5 +/- 1 mm Hg (P < .01), a 2.3-fold increase in plasma adenosine, and an increase in b ody core temperature of 0.19 degrees C +/- 0.03 degrees C (P < .01), yet br ain temperature remained constant. However, after cord occlusion with prior and continuing administration of theophylline, brain temperature did not i ncrease as hypothesized but rather decreased, suggesting marked reductions in cerebral metabolic rate. This response occurred despite similar degrees of hypoxemia and similar increases in plasma adenosine and body core temper ature. CONCLUSION: We conclude that the temperature of the fetal ovine brain remai ns constant or decreases during severe reversible hypoxemia by mechanisms o ther than those dependent on adenosine.