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Tissue glycogen and glucose 6-phosphatase levels in fetal and newborn foals
A L Fowden1, L Mundy, J C Ousey
1Physiological Laboratory, Cambridge, U.K.
Insights
Fetal foal liver and kidney glucose 6-phosphatase activity and glycogen levels increase with gestation. However, near term, these levels are lower than in other species, suggesting limited glucogenic capacity in fetal foals.
Area of Science:
- Comparative physiology
- Equine neonatal adaptation
- Metabolic regulation
Background:
- Glucose homeostasis is critical for fetal and neonatal survival.
- Understanding species-specific metabolic development aids in identifying potential vulnerabilities.
- Maternal-placental glucose transfer is the primary source for fetal energy, but endogenous glucose production becomes crucial near term.
Purpose of the Study:
- To investigate the developmental changes in hepatic and renal glucose-6-phosphatase (G6Pase) activity and tissue glycogen content in fetal and neonatal horses.
- To compare the glucogenic capacity of the fetal foal with that of other precocial species.
- To assess the potential for glucose dysregulation in late-gestation and neonatal foals.
Main Methods:
- Measurement of glycogen content and glucose-6-phosphatase (G6Pase) activity in liver, kidney, skeletal muscle, cardiac muscle, and lung tissues.
- Tissues were collected from fetal, newborn (24 hours postpartum), and adult pregnant mares.
- Data were analyzed in relation to gestational age and compared with previously published data from fetal sheep and pigs.
Main Results:
- Hepatic and renal G6Pase activities increased with gestational age and further post-birth, reaching maternal levels.
- Fetal liver and skeletal muscle glycogen increased in late gestation; lung and cardiac muscle glycogen decreased.
- Near-term fetal foal hepatic glycogen and G6Pase levels were lower than those reported for fetal sheep and pigs.
Conclusions:
- The fetal foal exhibits a developing, but limited, endogenous glucogenic capacity in late gestation compared to other domestic species.
- Neonatal foals may be more susceptible to hypoglycemia during periods of stress or inadequate nutrient supply.
- Further research into equine neonatal hypoglycemia and metabolic adaptation is warranted.
Abstract:
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.