Species differences in the distribution of gamma-glutamyl transpeptidase in choroid plexus of lateral ventricle and microvessels of adjacent brain.

The distribution of gamma-glutamyl transpeptidase in different vascular compartments of the central nervous system was evaluated in several common laboratory animals, i.e., hamster, gerbil, guinea pig, rat and mouse, by enzyme-histochemistry. Microvascular endothelium of the periventricular brain tissue stained positively in all five species. In contrast, the vascular endothelium of the choroid plexus stained positively only in the gerbil, and was negative in the other four species. Positive reactions for the transpeptidase was also found in choroid plexus epithelial cells in guinea pig, rat, and mouse; however no activity could be demonstrated in these cells of hamster and gerbil. The results demonstrate clear species differences in localization of the enzyme and suggest that gamma-glutamyl transpeptidase-promoted amino acid transport in choroid plexus is different in various animal species. It is also suggested that in gerbil, transpeptidase-aided amino acid transport takes place in endothelial cells of choroid plexus, whereas in guinea pig, rat and mouse this occurs in epithelial cells of choroid plexus. In the case of hamster, such aided transport is absent in endothelial as well as in epithelial cells of the choroid plexus. Thus, the hamster and the gerbil showed differences in gamma-glutamyl transpeptidase distribution, whereas the guinea pig, rat, and mouse showed similar enzyme distributions.