| Abstract: | The implication of polyamines in cellular growth and differentiation processes and the existence of a polyamine-mediated protein phosphorylation system in adrenocortical cells suggest that polyamines may be examined as potential intracellular messengers in the pleiotypic action of ACTH. Bovine adrenocortical cells in culture exhibit a specific, energy-dependent, partly sodium-supported, inward polyamine transport system, independent of the A, L, and N aminoacid uptake systems. Steroidogenic concentrations of ACTH (10(-12) to 10(-9)M) induced a rapid activation of the polyamine uptake, resulting in a 2- to 3-fold increase in intracellular polyamine content, over 1 h. The ACTH dose-response curves for steroidogenic activity and for polyamine uptake were similar. Other adrenocortical effectors such as angiotensin II, acetylcholine, and the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA) activated polyamine uptake with a pattern parallel to their steroidogenic potency (i.e. ACTH greater than angiotensin II greater than acetylcholine, TPA). Steroidogenic concentrations of 8-bromo-cAMP displayed no effect on the adrenocortical polyamine uptake, suggesting that cAMP does not mediate this action of ACTH. On the other hand, ACTH induced a large increase in ornithine decarboxylase (ODC) activity in bovine adrenocortical cells, after a 6- to 8-h lag period, resulting in an average 2-fold increase in cell putrescine, spermidine, and spermine content. However, when the cells were previously polyamine loaded, ACTH-dependent ODC induction was suppressed. Adrenocortical cell polyamine content thus appears to be under hormonal control. ACTH may act through two possible pathways: 1) the rapid activation of the cell polyamine accumulation from an extracellular source and 2) the delayed increase in polyamine biosynthesis secondary to induction of ODC activity, when the cells are relatively depleted of the polyamines. These observations suggest that polyamines may function as intracellular messengers for some of the ACTH effects in bovine adrenocortical cells. |
