Postnatal development of cholesterol ester hydrolase activity in the rat adrenal.

In certain circumstances the activity of cholesterol ester hydrolase (CEH) activity is believed to be rate-limiting for corticosterone production by the adrenal. The principal aim of the current study was to determine whether the activity of CEH displays a developmental increase in the infant rat which could, in part, account for the marked increase in serum corticosterone which begins at the end of the second postnatal week. The data show that the specific activity of CEH (units/mg cytosolic protein) during development is actually a mirror image of the pattern seen for serum corticosterone, i.e. CEH activities are high when serum corticosterone concentrations are low and then fall when serum corticosterone is rising. Even when total activities of CEH in the adrenal were calculated, there was no increase in parallel with the initial rise of serum corticosterone. At each age studied, stressed pups displayed significant increases of serum corticosterone; however, their CEH activities were no different from those in the non-stressed littermates. It is concluded that the activity of CEH is not the rate-determining factor for the developmental surge of basal concentrations of serum corticosterone nor for stress-induced elevation of corticosterone during the developmental period. A second aim of the current study was to address the more general question of whether steroidogenesis in the developing adrenal is limited by substrate supply. Measurement of the cholesterol content of adrenal mitochondria showed no ontogenic increase, suggesting that substrate supply, from any source, is not rate-limiting for steroidogenesis at these ages.