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Myocardial enzyme activities in guinea pigs during development
Insights
Cardiac metabolism shifts significantly after birth in guinea pigs. Key enzymes involved in glycolysis and fatty acid oxidation change activity, supporting adaptation to extrauterine life.
Area of Science:
- Biochemistry
- Cardiovascular Physiology
- Developmental Biology
Background:
- The transition from fetal to neonatal life requires substantial metabolic adjustments in the heart.
- Understanding the enzymatic changes in cardiac metabolism is crucial for comprehending heart development and function.
Purpose of the Study:
- To investigate the developmental changes in key metabolic enzyme activities in the guinea pig myocardium from the fetal stage through the first month of postnatal life.
- To characterize the shift in energy substrate utilization during cardiac adaptation after birth.
Main Methods:
- Enzyme activity assays were performed on myocardial tissue samples from fetal, newborn, and 1-month-old guinea pigs.
- Specific enzymes measured included hexokinase, glycolytic enzymes, lactate dehydrogenase (LDH) subunits, glycogen phosphorylase, beta-hydroxyacylcoenzyme A dehydrogenase, succinate dehydrogenase, malate dehydrogenase, aspartate aminotransferase, and palmitylcarnitine transferase.
Main Results:
- Glycolytic enzyme activities (hexokinase, glucose-6-phosphate dehydrogenase) were higher in fetal myocardium than at birth, decreasing postnatally.
- The ratio of alpha-hydroxybutyrate dehydrogenase (alphaHBDH) to lactate dehydrogenase (LDH) increased after birth, indicating a shift in LDH subunit composition.
- Activities of enzymes involved in fatty acid oxidation and the Krebs cycle (beta-hydroxyacylcoenzyme A dehydrogenase, succinate dehydrogenase, malate dehydrogenase, aspartate aminotransferase) were low in the fetus but reached adult levels by birth.
- Palmitylcarnitine transferase activity increased significantly in the first two weeks after birth.
Conclusions:
- The guinea pig heart undergoes a significant metabolic transition from fetal to neonatal life, characterized by a decrease in glycolytic capacity and an increase in oxidative metabolism.
- These enzymatic adaptations support the heart's transition to utilizing fatty acids as a primary energy source in the postnatal period.
Abstract:
The activities of hexokinase, glucose-6-phosphate dehydrogenase, and glycolytic enzymes were higher in the fetal myocardium of the guinea pig than at birth and fell progressively during the 1st mo of life. The alphaHBDH/LDH ratio of H to M subunits of lactate dehydrogenase, was low in the fetus and continued to rise during the 1st mo after birth. The distinction between the left and right ventricular activities of lactate dehydrogenase, which is clear in adult guinea pigs, was absent in the fetus and appeared during postnatal development. Glycogen phosphorylase activity was low in the fetus and at birth. The activities of beta-hydroxyacylcoenzyme A dehydrogenase, succinate dehydrogenase, malate dehydrogenase, and aspartate aminotransferase were low in the fetus, but had reached, or even temporarily exceeded, normal adult levels at birth. Palmitylcarnitine transferase activity was also low in the fetal heart compared with the newborn but continued to increase substantially during the first 2 wk after birth.