Enhanced mRNA levels for intestinal type II arginase (ARG II), argininosuccinate synthase (ASS) and lyase (ASL) in postweaning pigs.
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We have recently demonstrated enhanced intestinal metabolism of arginine in postweaning pigs, but the molecular mechanism involved is not known. The objective of this study was to determine whether weaning caused increases in the activities and mRNA levels for key enzymes of arginine metabolism. Jejunum was obtained from 29-d-old weaned pigs treated with 0 or 10 mg RU486/kg body wt and from suckling pigs. mRNA levels for ARG II, ASS and ASL were measured by northern blot analysis of total RNA isolated from jejunum. Relative mRNA levels for each enzyme were expressed relative to the level of -actin mRNA. The mRNA levels for ARG Il and ASL increased (P<0.01) by 135% and 65%, respectively, in jejunum of untreated weaned pigs compared with suckling pigs. RU486 completely prevented the induction of ARG II and ASL mRNAs in weaned pigs. ASS mRNA levels did not differ between suckling and weaned pigs. Activities of ARG II, ASL and ASS increased (P<0.05) by 635%, 56% and 106%, respectively, in jejunum of untreated weaned pigs compared with suckling pigs. RU486 attenuated (P<0.01) the enhanced activities of ARG II and ASL by 74% and 54%, respectively, in weaned pigs, but had no effect (P>0.05) on ASS activity. These results suggest that intestinal ARG II, ASS and ASL are regulated at both transcriptional and posttranslational levels in weaned pigs and that glucocorticoids play a major role in the postweaning induction of ARG II and ASL.