Brain temperature and metabolic responses during umbilical cord occlusion in fetal sheep.

The purpose of this study was to compare core body and brain temperatures after complete but intermittent occlusions of the umbilical cord. Thermocouple probes were placed in the parasagittal parietal cortex, ascending aorta, and jugular vein of eight near-term fetal sheep and in the maternal descending aorta. Three days later, after an initial control period, the umbilical cord was occluded for 5 min, followed by a 30-min recovery period, and this cycle was repeated 4 times. Temperature changes, blood gases, and plasma glucose, lactate and adenosine were measured. In the first occlusion period, body core temperature increased 0.12 degreesC over control, and then declined to baseline after cord release, and this pattern was repeated with subsequent occlusions. Brain temperature, however, did not increase in response to any of the cord occlusions. Plasma adenosine increased 2.4-fold during the first occlusion, but not during subsequent occlusions, despite a continuing pattern of constant brain temperature, a result which minimizes adenosine's importance as a continuing regulator of cerebral metabolism. We conclude that brain temperature fails to increase because of diminished heat production by the brain and increases in cerebral blood flow, responses which delay complete depletion of adenosine 5'-triphosphate stores in brain tissue.