Cerebral utilization of glucose, ketone bodies and oxygen in starving infant rats and the effect of intrauterine growth retardation.

Cerebral arteriovenous differences of acetoacetate, D-beta-hydroxybutyrate, glucose, lactate and oxygen and brain DNA content was measured at 20 days of age in intrauterine growth retarded (IUGR) rats and normal littermates after 48 and 72 h of starvation. Cerebral blood flow (CBF) was measured with labeled microspheres in other comparable groups of IUGR and control rats. CBF was similar in IUGR and normal littermates (0.57+/-0.09 and 0.58+/-0.10 ml/min respectively). After 48 h of starvation, arterial glucose was significantly lower in IUGR than control animals but the arterial concentrations of ketone bodies were similar. After 48 h of starvation, cerebral arteriovenous difference of beta-hydroxybutyrate was significantly higher in control than IUGR rats also when expressed per mg brain DNA as was the fractional uptake of D-beta-hydroxybutyrate. After 72 h of starvation, arterial concentrations of ketone bodies were significantly lower in IUGR rats than controls but the fractional uptake of D-beta-hydroxybutyrate was increased compared to IUGR rats starved for 48 h. The average percentage of calculated total substrate uptake (mumol/min) accounted for by ketone bodies increased in control animals from 31.1% after 48 h of starvation to 41.0% after 72 h of starvation. In IUGR rats these percentage values were 26.5 and 25.7 respectively. After 72 h of starvation the fraction of total cerebral uptake of substrates accounted for by ketone bodies was significantly higher in control that IUGR rats. As total cerebral uptake of substrates was similar between IUGR and control animals it is concluded that IUGR rats are more dependent on glucose as a substrate for the brain during starvation.