ALLOCATION OF SYSTEMIC GLUCOSE PRODUCTION TO CEREBRAL GLUCOSE UTILIZATION AS A FUNCTION OF INTRAUTERINE CANINE GROWTH

Abstract

Hypoglycemia in intrauterine growth retardation may be due to an imbalance between glucose production (GP) and cerebral glucose needs. We investigated relationships between GP, cerebral glucose uptake (CMRG), brain and body weight in 16 fasted 3 hr old term pups weighing 263 g (170-345 g). Brain wt 6.1±0.3 g was 2.3% of body wt, while liver wt 11.8±1.5 g was 4.4% of body wt. Brain wt:liver wt ratio was 0.66 for the entire group. Mean pH 7.23, pCO2 48.4, pO2 90.0, blood glucose 3.36 mM (1.45-10.77mM), steady state GP 49.6 umol/kg/min, cerebral blood flow (CBF) 0.83 ml/g/min, CMRC 0.60 umol/g/min, and cerebral O2 uptake (CMRO2) 1.76 umol/g/min. The brain utilized 36.6±7.9% of total body GP. To test the effect of growth status at term upon brain glucose utilization, we analyzed these data as a function of birth wt. Both brain and liver wt increased as a function of body wt. However, brain:liver (r=-0.6, p<0.02) and brainibody (r= -0.63, p<0.01) ratios were greatest in smaller pups. Although CBF increased, CMRO2, CMRG, and GP did not correlate with body wt. However, the % of GP used by the brain increased exponentially with body wt (r=0.50, p<0.05).CONCLUSION: In small pups a smaller % of GP was used by brain despite the fact that the brain represents a larger % of body wt. These data suggest that smaller pups do not use a disproportionately larger % of GP to maintain their normal rates of cerebral glucose utilization. Within the range of wt there was no imbalance between GP and CMRG.