Adenosine modulates corticotropin and cortisol release during hypoxia in fetal sheep

OBJECTIVE: This study was designed to determine the role of adenosine in th e hypoxic release of corticotropin in fetal sheep. STUDY DESIGN: The adenosine receptor antagonist 8-phenyltheophylline or the vehicle was infused intraarterially to chronically catheterized fetal shee p (>0.8 term) during an hour of fetal hypoxemia (Pao(2) congruent to 14 mm Hg). Control studies were also performed in which 8-phenyltheophylline or t he vehicle was administered to normoxic fetuses. RESULTS: 8-Phenyltheophylline abolished hypoxia-induced bradycardia and hyp ertension and produced a nearly 5-fold greater rise in fetal plasma concent rations of corticotropin and approximately a 3-fold greater increase in pla sma cortisol levels. During normoxia 8-phenyltheophylline increased plasma cortisol concentrations by 2-fold without altering corticotropin levels, me an arterial blood pressure, or heart rate. CONCLUSION: Adenosine blunts fetal corticotropin release during hypoxia, wh ich in turn reduces cortisol secretion. At lower corticotropin concentratio ns, adenosine also appears to dampen the cortisol response through direct e ffects on the adrenals. (Am J Obstet Gynecol 1999;180:1272-7).