Lactase synthesis is pretranslationally regulated in protein-deficient pigs fed a protein-sufficient diet

The in vivo effects of protein malnutrition and protein rehabilitation on l actase phlorizin hydrolase (LPH) synthesis were examined. Five-day-old pigs were fed isocaloric diets containing 10% (deficient, n = 12) or 24% (suffi cient, n = 12) protein. After 4 wk, one-half of the animals in each dietary group were infused intravenously with [ C-13(1)]leucine for 6 h, and the j ejunum was analyzed for enzyme activity, mRNA abundance, and LPH polypeptid e isotopic enrichment. The remaining animals were fed the protein-sufficien t diet for 1 wk, and the jejunum was analyzed. Jejunal mass and lactase enz yme activity per jejunum were significantly lower in protein-deficient vs. control animals but returned to normal with rehabilitation. Protein malnutr ition did not affect LPH mRNA abundance relative to elongation factor-1 alp ha, but rehabilitation resulted in a significant increase in LPH mRNA relat ive abundance. Protein malnutrition significantly lowered the LPH fractiona l synthesis rate (FSR; %/day), whereas the FSR of LPH in rehabilitated and control animals was similar. These results suggest that protein malnutritio n decreases LPH synthesis by altering posttranslational events, whereas the jejunum responds to rehabilitation by increasing LPH mRNA relative abundan ce, suggesting pretranslational regulation.