Postnatal development of gamma-GT activity in rat brain microvessels corresponds to capillary growth and differentiation.

It has been demonstrated histochemically that endothelial cells of the cerebral capillaries show a high activity in gamma-glutamyl transpeptidase (gamma-GT), an enzyme which takes part in the transfer of large neutral amino acids across the blood-brain barrier. Reports of the disappearance of enzyme activity in endothelial cells (EC) grown in culture suggest that the presence of astroglial cells (AG) is required for the expression of gamma-GT in these cells. The present study deals with the developmental changes in gamma-GT activity in capillaries of rat cerebral cortex during ontogenesis (i.e. on days 2, 7, 11, 14, 21 and 60 after birth). gamma-GT activity is determined by measuring the enzyme kinetics of the histochemical reaction on isolated brain capillaries using a flying spot microscope densitometer. Enzyme activity is expressed as an increase in relative optical density (at 500 nm) in arbitrary units/min/micron 2 during the 2 min immediately after initiating incubation and corresponds to the gamma-GT active area (in micron 2) of the capillary segment. During early postnatal development, a biphasic change of gamma-GT activity in capillaries of rat cerebral cortex is observed. The first phase (i.e. the postnatal period between the 2nd and 12th day) is characterized by a significant decrease in gamma-GT activity, which coincides with the onset of the rapid mitotic proliferation of cortical endothelial cells. During the second phase (i.e. the postnatal period between the 12th and 21st day), a fast increase in the gamma-GT activity can be measured. Then enzyme activity reaches the adult level between the 21st and 60th postnatal day.(ABSTRACT TRUNCATED AT 250 WORDS)