Effects of protein kinase C activation on cyclic AMP and testosterone production of rat Leydig cells in vitro.
The role of protein kinase C in modulation of the endocrine function of rat Leydig cells was studied. Percoll-purified rat Leydig cells were stimulated with hCG, forskolin, cholera toxin, pertussis toxin and 8-bromo-cAMP in the presence and absence of two activators of protein kinase C, 12-0-tetradecanoylphorbol 13-acetate (TPA) or 1-oleoyl-2-acetyl-sn-glycerol (OAG). The two activators had no effect on basal cAMP, but decreased hCG-stimulated, and increased cholera toxin- and forskolin-stimulated cAMP production. Cells pre-incubated with pertussis toxin showed enhanced rate of cAMP production in response to forskolin, but were no more responsive to TPA and OAG stimulation. These findings suggest that protein kinase C activation may on one hand inhibit the LH-receptor and Gs-protein coupling and on the other hand inhibit the Gi-protein mediated suppression of adenylyl cyclase activity. TPA and OAG effects on testosterone production were measured in the absence and presence of 8-bromo-cAMP stimulation. TPA enhanced basal testosterone production, but this effect was shifted to inhibition when steroidogenesis was stimulated by 8-bromo-cAMP. The OAG effect on testosterone production was inhibitory throughout the dose-response curve of 8-bromo-cAMP. The basal stimulation of testosterone production by TPA was probably due to a marginal increase of cAMP caused by inhibition of the Gi-protein, since a similar effect was observed by pertussis toxin, and thereafter TPA was without effect on testosterone. The inhibition of stimulated testosterone production by TPA and OAG indicates that protein kinase C activity also affects steroidogenesis at a step(s) beyound cAMP formation.
Nikula
H
H
Department of Physiology, University of Turku, Finland.
Huhtaniemi
I
I
D000818:Animals; D000242:Cyclic AMP / Q000096:biosynthesis*; D004075:Diglycerides / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects; D007985:Leydig Cells / Q000378:metabolism*; D008297:Male; D011493:Protein Kinase C / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D013739:Testosterone / Q000096:biosynthesis*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
D004075:Diglycerides; D013739:Testosterone; C038237:1-oleoyl-2-acetylglycerol; D000242:Cyclic AMP; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate