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When rat adrenal whole capsules, containing the zona glomerulosa, were incubated, addition of the protein kinase C inhibitors TMB-8 (10 µmol/l), W7, H7, polymyxin-B and sphingosine (all 1 µmol/l) was found to inhibit the steroidogenic response to trypsin. Aldosterone and 18-hydroxycorticosterone were strongly, and corticosterone moderately, affected, while the production of 18-hydroxydeoxycorticosterone was neither stimulated by trypsin nor inhibited by the protein kinase C inhibitors. Addition of neomycin, which prevents substrate interaction with phospholipase C, also inhibited the response to trypsin, while addition of phospholipase C itself stimulated aldosterone, 18-hydroxycorticosterone and corticosterone production with the same tissue sensitivity as trypsin. Addition of phospholipase A₂ had no effect. Direct assay of protein kinase C activity showed that trypsin stimulation effected the translocation of Ca²⁺/phospholipid-activated protein kinase C from the cytosolic to the membrane fraction. When glomerulosa tissue was incubated with [³²P]ATP, and cytosolic proteins were subjected to isoelectric focusing on polyacrylimide gels, autoradiography showed that incorporation of ³²P into several protein components was increased by trypsin stimulation.

It was concluded that trypsin exerts its stimulatory effects on steroidogenesis by activating protein kinase C; not, however, by generating the Ca²⁺/phospholipid-independent fragment, but possibly by enhancing the activity of phospholipase C.