Ontogeny of cell proliferation and DNA synthesis in rat colon: role of glucocorticoids.

This study was undertaken to determine whether the rat colon exhibits ontogenic changes in epithelial cell proliferation and DNA synthesis during growth. DNA synthesis was measured at intervals after birth in four colonic segments by the incorporation rates of [3H]thymidine. The labeled crypt cell index was determined by radioautography. New findings from our study are that 1) in each colonic segment of suckling rats, [3H]thymidine incorporation rate overshot the adult levels (49-119%) with a peak occurring at day 14 postpartum, 2) between days 14 and 20, the incorporation rates declined sharply to adult values and remained thereafter unchanged until adulthood; during the same period, the labeled and mitotic index decreased, respectively, from 52 to 19% and from 3.58 to 1.43%, 3) the decrease in DNA synthesis and in cell proliferation rates was concomitant with an upsurge in plasma total corticosterone initiated on day 14, and 4) treatment of 10-day-old sucklings with physiological doses of hydrocortisone for 4 consecutive days significantly depressed (P less than 0.01) colonic DNA content and DNA synthesis rates to levels about 45-67% of the control values. These data indicate that growth of the colon may be under the control of glucocorticoid secretion at the weaning period.