The M₃ muscarinic receptor mediates acetylcholine-induced cortisol secretion from bovine adrenocortical zona fasciculata/reticularis cells

In order to characterize the receptor subtype mediating acetylcholine (ACh)-induced cortisol secretion from purified bovine adrenocortical zona fasciculata/reticularis cells in primary culture, the potencies of a range of selective muscarinic antagonists of ACh-induced steroidogenesis were assessed by Schild analysis. Basal secretion of cortisol was 10.2 ± 1.4 pmol/well/30min. ACh stimulated a dose-dependent increase in cortisol secretion and was maximally effective at 10^-5 M, at which concentration cortisol secretion was 143.4 ± 12.9 pmol/well/30 min. Hexahydro-sila-difenidol and para-fluoro-hexa-hydro-sila-difenidol were potent competitive antagonists of ACh-stimulated cortisol secretion, with pA₂ values of 8.68 ± 0.28 and 7.96 ± 0.29, respectively. Pirenzepine (pA₂ = 6.95 ± 0.28) and methoctramine (pA₂ = 6.06 ± 0.27) were relatively weak competitive antagonists. The pA₂ values determined in this study are characteristic of the M₃ muscarinic receptor, and we conclude that this receptor subtype mediates ACh-induced cortisol secretion from bovine zona fasciculata/reticularis cells.