AJP - Regulatory, Integrative and Comparative Physiology, Vol 245, Issue 5 730-R736, Copyright © 1983 by American Physiological Society
Cerebral metabolism in hypoglycemic and hyperglycemic fetal lambs
B. S. Richardson, A. R. Hohimer, J. M. Bissonnette and C. M. Machida
To investigate the mechanism whereby glucose affects fetal breathing
movements (FBM), cerebral metabolism was studied in 12 unanesthetized fetal
lambs, during fasting-induced hypoglycemia and after a subsequent fetal
infusion of glucose. Preductal arterial and sagittal sinus blood samples
were analyzed for glucose and oxygen concentrations and for blood gases and
pH. Measurements of regional brain blood flow were made with radioactive
microspheres. Maternal fasting of 24- to 36-h duration resulted in a
decrease in fetal blood glucose from 1.061 +/- 0.085 mmol X l-1 to 0.664
+/- 0.053 (P less than 0.001). Although cerebral glucose and O2 uptake
remained unchanged, sagittal sinus CO2 partial pressure (Pco2) and [H+]
were significantly decreased and may have contributed to the observed
decrease in FBM. A 2-h infusion of glucose to the fetuses of fasted animals
resulted in an increase in blood glucose to 2.452 +/- 0.173 mmol X l-1.
Cerebral O2 consumption was again unchanged; however, cerebral glucose
consumption was significantly increased as were sagittal sinus Pco2 and
[H+], which may have contributed to the observed increase in FBM. These
findings are consistent with the hypothesis that glucose affects the
incidence of FBM in part by altering the environment of central
chemoreceptors.
