Effect of age, muscle and insulin-like growth factor-II genotype in pigs on muscle proteolytic and lipolytic enzyme activities

¹ Laboratory for Animal Nutrition and Animal Product Quality, Department of Animal Production, Ghent University, Proefhoevestraat 10, 9090 Melle, Belgium
² Laboratory of Livestock Physiology, Immunology and Genetics, KULeuven, Kasteelpark 30, 3001 Heverlee, Belgium

^* To whom correspondence should be addressed. E-mail: Stefaan.DeSmet{at}UGent.be.

	Abstract

Recently, a paternally expressed QTN (quantitative trait nucleotide) in the regulatory sequence of the IGF-II gene with effects on muscle growth and fat deposition was discovered in the pig. This QTN is also known as the IGF-II intron3 G3072A mutation. The aim of the current study was to determine the effects of age, muscle and IGF-II genotype (Apat, mutant allele vs. Gpat, wild type allele) on muscle proteolytic and lipolytic enzyme activities. At approximately 4, 8, 16, and 26 wk of age, boars (n = 6 to 15 per genotype x age group) were slaughtered and µ- and m-calpain (CALP), calpastatin (CAST), cathepsins (CATH) B+L and H, acid lipase, and phospholipase activities were measured in Longissimus thoracis et lumborum, Semimembranosus, and Triceps brachii muscle samples taken early after slaughter. Activities of CATH B+L and H, µ- and m-CALP, and acid lipase were not affected by the IGF-II genotype. Activity of CAST was greater (P < 0.005) and m-CALP / CAST was less (P < 0.05) in Apat animals. Because it is known that CAST activity and m-CALP / CAST are related to protein degradation and/or satellite cell fusion, it is likely that differences in proteolytic enzyme activities are involved in the greater percentage of muscle mass in Apat animals. Age and muscle influenced proteolytic and lipolytic enzyme activities (P < 0.05) except for µ- and m-CALP (no effect of muscle) and acid lipase (no effect of age). The same pattern in µ-CALP, CAST, and m-CALP / CAST with age was found during growth for the 3 muscles, although clear differences (P < 0.05) between muscles existed. In general and in agreement with previous reports, greater enzyme activities were found in the more oxidative Triceps brachii muscle compared with the other two muscles. A remarkable increase (P < 0.05) from 16 to 26 wk of age in µ-CALP, CAST, µ-CALP / CAST, and CATH H and a large decrease (P < 0.05) in acid phospholipase and m-CALP / CAST was found. For m-CALP and CATH B+L, a gradual decrease (P < 0.05) was found with age. Although age effects on enzyme activities could only partly be interpreted biologically in relation to muscle growth rate, this study showed that proteolytic and lipolytic enzyme activities evolve during growth.

Key Words: Growth, Insulin-like growth factor-II, Muscle, Pig, Proteolytic and lipolytic enzymes