Myocardial enzyme activities in guinea pigs during development.

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.