Ontogeny of 11 beta-hydroxysteroid dehydrogenase in rat brain and kidney.

Close regulation of circulating corticosteroid levels during the early postnatal period is crucial for normal development and maturation of the central nervous system. In the first weeks of life cerebral glucocorticoid receptor concentrations are low and the hypothalamic-pituitary-adrenal axis is relatively unresponsive to stress, which might, in part, protect the developing brain from elevated corticosteroid levels. However, central mineralocorticoid receptors are at near adult levels and free glucocorticoid concentrations may approximate adult values as corticosteroid binding globulin is absent. Thus other mechanisms controlling cerebral exposure to corticosteroids may be of importance. 11 beta-Hydroxysteroid dehydrogenase (11 beta-OHSD) determines the access of corticosterone to peripheral mineralocorticoid and glucocorticoid receptors in adults in vivo by metabolizing corticosterone to inactive 11-dehydrocorticosterone. The enzyme has recently been demonstrated in brain subregions and may modulate local corticosteroid-receptor interactions. We therefore examined 11 beta-OHSD bioactivity and messenger RNA (mRNA) expression in the brain, compared with kidney, during the neonatal period. 11 beta-OHSD bioactivity (expressed as the percentage conversion of corticosterone to 11-dehydrocorticosterone) was moderately high in hippocampus and parietal cortex at birth (46 +/- 4% and 48 +/- 5%, respectively), fell significantly to a nadir (32 +/- 1% and 30 +/- 1%, respectively) at postnatal day 10 and then gradually rose to adult values (52 +/- 3% and 58 +/- 3%). By contrast, 11 beta-OHSD activity in cerebellum was high at birth (60 +/- 3%), rose significantly to a peak at postnatal day 10 (74 +/- 3%), and then fell to adult values by postnatal day 15 (64 +/- 3%). Renal 11 beta-OHSD activity was moderately high (69 +/- 3%) at birth and reached adult values (80 +/- 2%) by postnatal day 5. Northern blots showed high and similar expression of a single species of 11 beta-OHSD mRNA from birth to adulthood in the hippocampus. Only low expression of 11 beta-OHSD (two or three separate species) was found in the kidney during the first 2 weeks of life, whereas, in adults high expression of 11 beta-OHSD mRNA was detected in kidney (four species). Using in situ hybridization high 11 beta-OHSD mRNA expression was localized to the neuronal layers of the postnatal hippocampus, neocortex, and cerebellum, and low but detectable expression was found in the neonatal renal cortex. Thus, 11 beta-OHSD is highly expressed in rat brain subregions in the early postnatal period with specific developmental patterns of activity.(ABSTRACT TRUNCATED AT 400 WORDS)