Comparative involvement of cyclic nucleotide phosphodiesterases and adenylyl cyclase on adrenocorticotropin-induced increase of cyclic adenosine monophosphate in rat and human glomerulosa cells

The present study investigated the role and identity of cyclic nucleotide p hosphodiesterases (PDEs) in the regulation of basal and ACTH-stimulated lev els of intracellular cAMP in human and rat adrenal glomerulosa cells. Compa rative dose-response curves indicated that maximal hormone-stimulated cAMP accumulation was 11- and 24-fold higher in human and rat cells, compared wi th cAMP production obtained in corresponding membranes, respectively. Simil arly to 3-isobutyl-1-methyl-xanthine, 25 mu M erythro-9-[2-hydroxy-3-nonyl] adenine (EHNA, a specific PDE2 inhibitor), caused a large increase in ACTH- stimulated cAMP accumulation; by contrast, it did not change cAMP productio n in membranes. Moreover, in membrane fractions, addition of 10 mu M cGMP i nhibited ACTH-induced cAMP production, an effect completely reversed by add ition of 25 mu M EHNA. These results indicate that PDE2 activity is involve d in the regulation of cAMP accumulation induced by ACTH, and suggest that ACTH inhibits this activity. Indeed, time-course studies indicated that ACT H induced a rapid decrease in cGMP production, resulting in PDE2 inhibition , which in turn, contributed [with adenylyl cyclase (AC) activation] to an accumulation in cAMP for 15 min. Thereafter, cAMP content decreased, becaus e of cAMP-stimulated PDE2, as confirmed by measurement of PDE activity that was activated by ACTH, but only after a 10-min incubation. Hence, we demon strate that the ACTH-induced increase in intracellular cAMP is the result o f a balance between activation of AC and direct modulation of PDE2 activity , an effect mediated by cGMP content. Although similar results were observe d in both models, PDE2 involvement is more important in rat than in human a drenal glomerulosa cells, whereas AC is more stimulated in human than in ra t glomerulosa cells.