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Biochemical, Molecular, and Genetic Mechanisms

Ontogeny of Carnitine Palmitoyltransferase I Activity, Carnitine-K_m, and mRNA Abundance in Pigs throughout Growth and Development^1,2

³ Department of Animal Science, ⁴ Interdepartmental Nutrition Program, and ⁵ Functional Genomics Program, North Carolina State University, Raleigh, NC 27695 and ⁶ Lonza, Inc., Fairlawn, NJ 07410

^* To whom correspondence should be addressed. E-mail: jack_odle{at}ncsu.edu.

Carnitine palmitoyltransferase (CPT) I catalyzes an important regulatory step in lipid metabolism; however, no studies, to our knowledge, have evaluated the molecular and kinetic [maximal velocity and Michaelis constant (K_m) for carnitine] ontogeny of CPT I and prevailing tissue concentrations of carnitine in pigs. To this end, hepatic and skeletal muscle tissues were examined at various ages: birth; 24 h; 1, 3, 5, and 8 wk of age; and adult. Hepatic and skeletal muscle CPT I specific activities were low at birth and increased 100 and 70%, respectively, during the first week of life (P < 0.05). Skeletal muscle transcript amounts were 2.7-fold greater (P < 0.001) in 24-h-old pigs relative to newborns, whereas hepatic CPT I mRNA remained constant at each age studied. The apparent K_m for carnitine decreased 48% (P < 0.05) during the initial 3 wk of life in liver and decreased 40% (P < 0.05) during the first week of life in skeletal muscle. Plasma and liver free carnitine concentrations increased 95 and 62%, respectively, within 24 h after birth (P < 0.05) and hepatic carnitine concentrations remained constant through 5 wk of age. Consequently, hepatic carnitine concentrations were 20–80% greater (P < 0.05) than the K_m for carnitine during the suckling period. Skeletal muscle carnitine met or exceeded the apparent K_m for carnitine at each stage of development. Collectively, these findings suggest that postnatal increases in CPT I activity during the suckling period are accompanied by increased tissue carnitine; however, the lack of hepatic CPT I mRNA induction and low activity reported in both tissues prior to 1 wk of age may limit postnatal lipid utilization during the piglet's transition to extra-uterine life.