Acth stimulation of adrenal steroidogenesis is sensitive to trypsin inhibitors

Various trypsin inhibitors (lima bean, soybean, and p-tosyl-L-lysine chloromethyl ketone (TLCK)) decrease the sensitivity of rat adrenocortical cells isolated from the inner zones to ACTH-stimulated corticosterone production. Basal steroidogenesis is not affected. The inhibitors produce dose-dependent effects at concentrations greater than 10 μ M. Dibutyryl cAMP stimulation of this system also is antagonized by TLCK, though not by lima bean trypsin inhibitor. When various steroid intermediates are added to the incubations as sources of substrate, the inhibitory effect of TLCK on corticosterone production decreases in parallel with the number of hydroxylation reactions required to generate corticosterone. These results suggest that trypsin inhibitors may block specific ACTH-linked proteolytic events in the adrenal cortex. Alternatively, they may interfere non-specifically with ACTH binding and/or adrenocortical metabolism. In either case, the common practice of including a trypsin inhibitor in adrenal cell incubations should be approached with caution.