Tissue glycogen and glucose 6-phosphatase levels in fetal and newborn foals.

Glycogen and glucose 6-phosphatase levels were measured in a variety of tissues from fetal, newborn and adult pregnant mares. Hepatic and renal glucose 6-phosphatase activities increased with increasing gestational age and rose further in the 24 h after birth to values similar to those observed in maternal tissues. The glycogen content of fetal liver and skeletal muscle also increased in late gestation, whereas that of fetal lung and cardiac muscle decreased toward term. No significant change in renal glycogen content with fetal age was observed. The values of hepatic glycogen and glucose 6-phosphatase found in the fetal foal near term were less than those observed previously in fetal sheep and pigs at a similar stage of gestation. These observations suggest that, in late gestation, the fetal foal has a limited glucogenic capacity compared with other domestic species and may have difficulty maintaining an adequate glucose supply during adverse conditions.