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Glycogen metabolism in neonatal liver of the rat
Insights
Newborn rat liver mobilizes hepatic glycogen stores for energy before feeding begins. Enzyme activity changes regulate glycogen breakdown and synthesis, adapting to the early postnatal nutritional shifts.
Area of Science:
- Biochemistry
- Developmental Biology
- Physiology
Background:
- Fetal rats accumulate significant hepatic glycogen before birth.
- This glycogen is crucial for sustaining newborns in the early postnatal period until suckling and gluconeogenesis commence.
- The liver plays a key role in managing nutrient supply through glycogen metabolism.
Purpose of the Study:
- To investigate the dynamic changes in hepatic glycogen metabolism during the early postnatal period in rats.
- To understand the enzymatic regulation of glycogen synthesis and breakdown in neonatal liver.
- To elucidate the liver's adaptation to nutrient availability following birth and the onset of feeding.
Main Methods:
- Analysis of hepatic glycogen levels.
- Measurement of glycogen synthase (GS) and glycogen phosphorylase (GP) activities, key enzymes in glycogenesis and glycogenolysis.
- Assessment of phosphatase activities associated with glycogen metabolism.
Main Results:
- Hepatic glycogen stores are mobilized postnatally, reflected by decreased active glycogen synthase and increased active glycogen phosphorylase.
- Activities of smooth endoplasmic reticulum (SER)-associated phosphatases decline from prenatal levels, influencing enzyme activation.
- Following suckling (1-4 h), hepatic glycogen levels increase slightly, followed by significant glycogenolysis (6-12 h).
- By 24 h post-birth, glycogen levels rise again, indicating adaptation to meal feeding.
Conclusions:
- The neonatal rat liver undergoes significant metabolic adjustments in glycogen utilization and synthesis shortly after birth.
- Enzymatic regulation, including shifts in phosphatase activity, is critical for managing hepatic glycogen during the transition from fetal to neonatal life.
- The liver adapts its glycogen metabolism to accommodate the changing nutrient supply from maternal circulation to suckling and meal feeding.
Abstract:
Prior to birth the fetus of the rat accumulates large quantities of hepatic glycogen, with these stores mobilized as glucose in the early postnatal period to sustain the newborn until the onset of suckling and gluconeogenesis. The liver acts to mobilize glycogen in the early neonatal period and gradually adjusts to the alternating supply of nutrients that results from the onset of a feeding cycle. Early postnatal glycogen mobilization is reflected in the decreased active form of glycogen synthase (GS), the rate-limiting enzyme of glycogenesis, and increased activation of glycogen phosphorylase (GP), the rate-limiting enzyme of glycogenolysis. Levels of smooth endoplasmic reticulum (SER)-associated synthase phosphatase and phosphorylase phosphatase activities are diminished from high prenatal levels, contributing to these changes in activation of GS and GP. With the onset of suckling at 1-4 h after birth the liver again accumulates small quantities of glycogen. The period of 6 to 12 h after birth is characterized by large scale glycogenolysis. Glycogen levels are again increased at 24 h after birth, reflecting hepatic adaptation to the onset of meal feeding.