Interleukin-3 and interleukin-6 stimulate bovine adrenal cortisol secretion through different pathways

Several interleukins have been reported to play a major role in the regulat ion of steroid secretion at all three levels of the hypothalamic-pituitary- adrenal axis. The objective of this study was to investigate the effect of interleukin-3 (IL-3) and interleukin-6 (IL-6) on cortisol secretion of bovi ne adrenocortical cells in primary culture under serum-free conditions. Bot h IL-3 and IL-6 stimulated basal cortisol secretion dose-dependently to a s imilar extent at a similar time course. After incubation with IL-3 or IL-6 at concentrations of 100 mu g/l, a maximum 4.1-fold increase of the cortiso l secretion was reached after 12 h (P < 0.01). Coincubation of IL-3 and IL- 6 (100 mu g/l) revealed no significant synergism. To elucidate a possible i nvolvement of arachidonic acid metabolites in the signal transduction, we c oincubated IL-3 or IL-6 together with the cyclo-oxygenase inhibitor indomet acin or the lipoxygenase inhibitor nordihydroguaiaretic acid (NDGA). Coincu bation with indometacin completely abolished the stimulatory effect of IL-6 but had no effect on IL-3 stimulated cortisol secretion. In contrast, spec ific inhibition of the lipoxygenase system by nordihydroguaiaretic acid blo cked IL-3 stimulated steroidogenesis while the effect of IL-6 was not affec ted. Neither IL-3 nor IL-6 altered cAMP levels significantly, whereas ACTH significantly induced cAMP levels in parallel to its steroidogenic effect. In conclusion, our data indicate that IL-3 and IL-6 stimulate the steroid s ecretion of bovine adrenocortical cells to a similar extent and with a simi lar time course. However, the effects of IL-3 and IL-6 are mediated through different, cAMP-independent pathways. While the stimulatory effect of IL-3 seems to be dependent on the lipoxygenase pathway, the effect of IL-6 on a drenocortical cortisol secretion is mediated through the cyclo-oxygenase pa thway.