Ontogeny and kinetics of carnitine palmitoyltransferase in liver and skeletal muscle of the domestic felid (Felis domestica)

The ontogeny of carnitine palmitoyltransferase (CPT) was examined in liver and muscle throughout growth and development of the domestic felid. Homogenates from animals in six age categories (newborn, 24-h, 3-, 6- and 9-week-old, and adult) were examined. Hepatic CPT specific activity increased progressively from birth to 6 weeks and then declined slightly into adulthood, with maximal values for animals greater than 24 h of age [171 nmol/(min g wet tissue)] being 70% higher than for newborns [99 nmol/(min g wet tissue)] (P<.05). Specific activity in adults was similar to that in 6- and 9-week-old juveniles. Total hepatic CPT activity [nmol/(min liver)] increased linearly with age, but the activity expressed per kg body weight [nmol/(min kg BW)] declined after 3 weeks. In contrast, skeletal muscle CPT-specific activity remained unchanged from birth to 3 weeks and then increased significantly, with maximal values at 9 weeks being 90% greater than those for young animals (newborn to 3 weeks; P<.05), whereas specific activity in adults was 50% lower than that observed in 9-week-old animals (P<.05). Hepatic and muscle apparent Km's for carnitine averaged 440 μM and did not vary with age. Hepatic carnitine concentrations remained relatively constant during development, but were lower in adult lactating females, whereas skeletal muscle concentrations increased markedly with age. Hepatic concentrations were 20-50% higher than apparent K(m)'s for carnitine in young and growing animals, but concentrations were similar to the apparent K(m) at 6 weeks and significantly lower than the apparent K(m) in adults. Carnitine concentrations in skeletal muscle were 37% lower than apparent K(m) during the neonatal period, but significantly higher in cats >3 weeks of age. We conclude that postnatal increases in CPT activity support increased capacity for fatty acid oxidation in the developing felid and that dietary carnitine may be required to maximize enzyme activity.