DISTRIBUTION AND ONTOGENY OF THYROTROPIN-RELEASING-HORMONE DEGRADING ENZYMES IN RATS

The distribution and ontogeny of tissue prolyl endopeptidase and pyroglutamyl peptidase I activities were studied in the rat from the 7th day before birth to adulthood. While low levels of prolyl endopeptidase activity were demonstrable in many fetal tissues, activity in brain cortex, hypothalamus, lung, and kidney increased dramatically during the 2 wk after birth, gradually returning to adult levels. In adult rats, levels of tissue prolyl endopeptidase activity were highest in kidney, when compared with the intermediate levels in brain cortex, hypothalamus, and liver. Pyroglutamyl peptidase activity was widely distributed in adult rat tissues with high levels in kidney and liver that exceeded intermediate levels in brain cortex and hypothalamus. Pyroglutamyl peptidase activities in fetal gut, brain, and lung tissue were elevated above adult values. In contrast to the developmental changes in prolyl endopeptidase activities, pyroglutamyl peptidase activity remained elevated above adult levels only during the first week of life. These results indicate that both prolyl endopeptidase and pyroglutamyl peptidase activities in the rat are developmentally regulated.