Causes of Sex Differences in Serum Cholesterol and Triglyceride Levels in Meishan Pigs

To clarify the causes of sex differences (male < female) in the serum total cholesterol (TCHO) and triglyceride (TG) levels in Meishan pigs, we examined the sex differences in mRNA levels of key hepatic enzymes involved in the biosynthesis/metabolism of cholesterol and TG using real-time RT-PCR. There were no sex differences in mRNA levels of 3-hydroxy-3-methylglutaryl-CoA reductase and CYP51A1 for cholesterol biosynthesis, or of the rate-limiting enzyme CYP7A1 for bile acid synthesis from cholesterol. By contrast, sex differences (male < female) were observed in mRNA levels of glycerol-3-phosphate acyltransferase 1 (GPAT1), a rate-limiting enzyme for TG biosynthesis. However, the sex differences in mRNA levels of carnitine palmitoyltransferase 1A (CPT1A) and acyl-CoA dehydrogenase long chain (ACADL), key enzymes for the oxidation of the fatty acids that are structural components of TG, were the opposite (male > female). Castration of male pigs led to an increase in the mRNA level of GPAT1 and decreases in those of CPT1A and ACADL. Furthermore, testosterone propionate (TP)-treatment of castrated males and intact females restored and changed, respectively, these mRNA levels to those of intact males. Notably, castration and TP-treatment increased and decreased, respectively, serum and hepatic TG levels. These findings suggest that sex differences in the serum and hepatic TG levels in Meishan pigs are closely correlated with differences in testosterone-associated mRNA expression levels of the key enzymes (GPAT1, CPT1A, and ACADL) involved in the TG biosynthesis process, although no causes of sex differences in serum and hepatic TCHO levels could be found.