Suppressive action of endogenous adenosine on ovine fetal nonshivering thermogenesis

Karen T. Ball, Tania R. Gunn, Peter D. Gluckman, and Gordon G. Power Center for Perinatal Biology, School of Medicine, Loma Linda University, Loma Linda, California 92350; and Department of Pediatrics, School of Medicine, University of Auckland, Auckland, New Zealand Received 19 May 1995; accepted in final form 6 August 1996. Ball, Karen T., Tania R. Gunn, Peter D. Gluckman, and Gordon G. Power. Suppressive action of endogenous adenosine on ovine fetal nonshivering thermogenesis. J. Appl. Physiol. 81(6): 2393-2398, 1996. Nonshivering thermogenesis is not initiated when the fetal sheep is cooled in utero but appears to require the removal of an inhibitor of placental origin at birth. To test whether adenosine is such an inhibitor, we examined the effect of the adenosine antagonist theophylline on the initiation of nonshivering thermogenesis during sequential cooling, ventilation, and umbilical cord occlusion in utero. Theophylline (18 mg/kg bolus and 0.6 mg · kg 1 · min 1 thereafter) was infused for 90 min before and 90 min after cord occlusion. Theophylline enhanced the nonshivering thermogenic free fatty acid (FFA) and glycerol responses before cord occlusion, raising FFA concentrations 99% to 415 ± 60 µeq/l ( P