ADRENOCORTICOTROPIN INCREASES INTERLEUKIN-6 RELEASE FROM RAT ADRENAL ZONA GLOMERULOSA CELLS

Interleukin-6 (IL-6) is produced by adrenal zona glomerulosa cells; its release is stimulated by several secretagogues, including IL-1-alpha, IL-1-beta, and angiotensin II. The present study reports that ACTH (0.1-100 nM) increased the release of IL-6 from primary cultures of rat adrenal cells in a concentration-dependent manner. This increase was accompanied by an increase in cAMP content in cell extracts and in the incubation medium. The dynamics of IL-6 release from the adrenal cells also were investigated using a perifusion system; approximately 50 min were required for the effects of IL-1-alpha, IL-1-beta, and ACTH on IL-6 release to become apparent. Following withdrawal of the secretagogues, IL-6 release returned to basal levels within 90-120 min. In some experiments, the adrenal zona glomerulosa was separated from the zona fasciculata/reticularis to determine the origin of secretagogue-stimulated IL-6 release. PGE2 and forskolin increased IL-6 release from both cell types, but maximal release from zona glomerulosa cells was more than 10-fold greater than that from zona fasciculata/reticularis cells. ACTH (0.1-100 nM) increased intracellular cAMP levels in cells from both cell types in a concentration-dependent manner, but increased IL-6 release only from zona glomerulosa cells. Dexamethasone, an inhibitor of IL-6 production in several tissues, had no effect on either basal or stimulated IL-6 production in the adrenal. Because IL-1-beta is produced primarily by tissues of the immune system, whereas ACTH is a classical endocrine hormone, we investigated the effect of interaction of these proteins on IL-6 release from the adrenal. Together, IL-1-beta and ACTH stimulation of IL-6 release was greater than the sum of the effects of each substance separately; however, IL-1-beta did not potentiate the effect of ACTH on cAMP levels. Similarly, IL-1-beta potentiated IL-6 release stimulated by forskolin and (Bu)2cAMP. Thus, the adrenal may be an important convergence point between the immune and endocrine systems, and because IL-6 release is regulated by IL-1-alpha, IL-1-beta, ACTH, and angiotensin II, and this cytokine stimulates corticosterone release, IL-6 may play an important paracrine role in integrating the signals derived from these systems.