Developmental changes of enzymes involved in peptide degradation in isolated rat brain microvessels.

The specific activities of aminopeptidase A (APA), aminopeptidase M (APM), and dipeptidyl-aminopeptidase IV (DP IV) were determined in isolated brain microvessels and in brain homogenate of rats with different ages (between 1 and 8 weeks old). In addition, the blood-brain barrier (BBB)-specific enzymes gamma-glutamyltranspeptidase (gamma-GT) and alkaline phosphatase (ALP) were measured. As similarly described by others, gamma-GT activity increased during this time period by fourfold, whereas ALP increased between weeks 1 and 2 and declined thereafter. DP IV activity increased fivefold during the first 8 weeks after birth and APM activity increased by twofold. A decrease of APA activity was found between weeks 1 and 2 after birth followed by an increase thereafter. The development of aminopeptidase activities responsible for the processing of specific neuropeptides acting on brain microvessels may be important in the development of regulation processes for cerebral blood flow and BBB permeability in the maturing animal.