Adrenal phenylethanolamine N-methyltransferase induction in relation to glucocorticoid receptor dynamics: evidence that acute exposure to high cortisol levels is sufficient to induce the enzyme

Abstract

Glucocorticoids (GCs) are thought to regulate, in a permissive fashion, the basal activity of adrenal medullary phenylethanolamine N-methyltransferase (PNMT). However, it is unclear whether a large short-term increase in GC release, such as occurs during an acute stress response, may also play a role in PNMT regulation. The present study investigated how the GC influence over PNMT activity varies in relation to dynamic changes in the hormone-receptor signal. Using [3H]dexamethasone (DEX) and [3H]RU 28362 as radioligands, we have confirmed the presence of GC receptors in bovine adrenal medullary cells. A concentration-dependent decline in soluble GC receptor sites and an increase in nuclear uptake of [3H]DEX were found in response to GC levels as low as 5 x 10(-8) M. The loss of soluble sites plateaued between 5 x 10(-8) and 10(-6) M cortisol, with further losses occurring at 10(-5) and at 10(-4) M. The functional consequence of GC receptor binding was confirmed by measuring PNMT activity following 3-day exposure to cortisol. The pattern of PNMT induction was similar to that seen with GC receptor occupancy; at cortisol concentrations between 10(-8) and 10(-5) M, PNMT induction was at a plateau, with a further increase in activity at 10(-4) M. The increase in PNMT activity following 3-day exposure to low (10(-7) M) and high (5 x 10(-5), 10(-5) M) cortisol was blocked by the GC receptor antagonist RU 38486, suggesting a GC receptor-mediated event. Finally, a short (2 h) pulse of GC, which mimics the time course of physiological elevation of GC following acute stress, elevated adrenal medullary PNMT activity measured 3 days later. Therefore, our results provide novel evidence that short-term exposure of adrenal medullary cells to high cortisol levels can elevate PNMT activity.