Cyclic AMP-dependent synthesis and release of adrenomedullin and proadrenomedullin N-terminal 20 peptide in cultured bovine adrenal chromaffin cells

Adrenomedullin and proadrenomedullin N-terminal 20 peptide are peptides wit h multiple physiological functions and are most abundant in adrenal medulla . We studied whether the cAMP-dependent pathway is involved in the regulati on of synthesis and release of adrenomedullin and proadrenomedullin N-termi nal 20 peptide in cultured bovine adrenal chromaffin cells. Exposure of the cells to dibutyryl cAMP (dbcAMP) increased a progressive accumulation of i mmunoreactive-adrenomedullin and immunoreactive-proadnnomedullin N-terminal 20 peptide in the extracellular medium, while reciprocally decreasing thei r cellular content in a time-dependent manner. The decrease of levels of bo th peptides in the cells was much greater in extent than the increase of th e peptides in the medium. H89, an inhibitor of cAMP-dependent protein kinas e attenuated these changes, induced by dbcAMP. The resulting changes by dbc AMP and H89 were similar to those of chromogranin B, a marker peptide of ch romaffin granule. Northern blot analysis showed that the mRNA encoding thes e peptides, detected as a band of 1.6 kb, was decreased by the treatment wi th dbcAMP. The effect of dbcAMP on mRNA was attenuated by H89, and was reve rsible as the decreased mRNA level caused by dbcAMP could be returned to co ntrol levels by culturing cells after removal of dbcAMP. These results sugg est that the cAMP-dependent protein kinase pathway stimulates the release o f adrenomedullin and proadrenomedullin N-terminal 20 peptide, whereas it lo wers synthesis of these peptides via the reduction of their transcript leve l.