Journal of Applied Physiology, Vol 63, Issue 5 1896-1901, Copyright © 1987 by American Physiological Society
Oxygen supply and the placenta limit thermogenic responses in fetal sheep
G. G. Power, T. R. Gunn, B. M. Johnston and P. D. Gluckman
Department of Pediatrics, University of Auckland, New Zealand.
The aim of this study was to assess the individual effects of cooling,
increased oxygenation, and umbilical cord occlusion on nonshivering
thermogenesis in utero. A cooling coil was placed around eight fetal sheep
of 132-145 days gestation; thermistors were placed in the fetal esophagus
and maternal iliac artery, vascular catheters and a tracheal catheter were
inserted, and a snare was placed loosely around the umbilical cord. The
next day cold water was circulated through the coil for 5 h. During the 1st
h of cooling alone, fetal core temperature fell 2.79 degrees C, but indexes
of brown fat activity increased only slightly. After ventilation with O2,
plasma free fatty acid concentration (FFA) rose 7.4-fold to 244 +/- 42 mu
eq/l, glycerol concentration rose fourfold to 376 +/- 85 microM, and the
difference between brown fat and core temperature widened to 0.60 +/- 0.10
degrees C. Ventilation with N2-enriched air did not evoke similar
responses. After snaring the umbilical cord while ventilation was
continued, FFA rose to 554 +/- 95 mu eq/l, glycerol rose to 684 +/- 76
microM, and the temperature difference widened to 0.77 +/- 0.13 degrees C.
Whole-body O2 consumption peaked at 19.6 ml.min-1.kg-1 of fetal tissue. We
conclude that fetal thermogenic responses are limited in part by O2
delivery to brown fat and are augmented by occlusion of the umbilical cord.
