Characterization of glutaminase in the developing rat small intestine.

As a primary substrate in the small intestine, glutamine is a very important source of energy. Glutaminase (GA) is the enzyme involved in the deamination of glutamine to glutamate, which is utilized for energy production via the TCA cycle. Although the enzymatic activity of GA in the small intestine is known to undergo maturational changes, the tissue localization of the protein and its mRNA, the intracellular processing of this enzyme and levels of its mRNA in the small intestine at different maturational stages have not yet been described. In this study, using immuno-histochemical staining, we confirm previous studies using other techniques that suggested GA is localized in the epithelial layer of the rat small intestine. Some GA is also found in cells of the lamina propria and crypt epithelium. Using in situ hybridization studies, we have corroborated the presence of the protein in the epithelial cells of the villi by localizing the mRNA of this protein to the same layer and its precursor layer in the crypt region. An ontogenic analysis of GA mRNA and protein from rat small intestines, using RNA dot blots, gel blots and protein immunoblotting revealed differences in immunoreactive GA protein and mRNA during maturation. Immunoreactive GA and steady-state levels of GA mRNA increased around the 3rd wk of life, coincident with weaning and the endogenous glucocorticoid surge. Whether these findings have nutritional or pathophysiological implications remains speculative.