Expression and function of adrenomedullin and its receptors in Conn's adenoma cells

Adrenomedullin (ADM) is a hypotensive peptide, that derives from the proteo lytic cleavage of pro(p)ADM and acts through two subtypes of receptors, cal led L1-receptor (L1-R) and calcitonin receptor-like receptor (CRLR). CRLR m ay function as a calcitonin gene-related peptide or a selective ADM recepto r depending on the expression of the subtype 1 or the subtypes 2 and 3 of a family of proteins, named receptor-activity modifying, proteins (RAMPs). R everse transcription (RT)-polymerase chain reaction (PCR) allowed the detec tion of pADM mRNA in dispersed cells of eight Conn's adenomas (aldosteronom as). These cells also expressed peptidyl-glycine , alpha -amidating monooxi genase, the enzyme converting immature ADM to the mature form, and containe d sizeable amounts of ADM-immunoreactivity as measured by radioimmunoassay. RT-PCR also demonstrated the presence in aldosteronoma cells of the specif ic mRNAs of LI-R, CRLR and RAMPs 1-3. ADM (10(-8) M) inhibited angiotensin- II (10(-9) M)-simulated aldosterone secretion from cultured aldosteronoma c ells, without affecting basal production. ADM (10-8 M) also enhanced basal proliferation rate of cultured cells, as estimated by the 5-bromo-2'-deoxyu ridine immunocytochemical technique. Both effects of ADM were annulled by t he ADM-receptor selective antagonist ADM(22-52) (10(-7) M). In conclusion, our study provides evidence that aldosteronoma cells express both ADM and A DM(22-52)-sensitive receptors. These findings, coupled with the demonstrati on that ADM exerts an aldosterone antisecretagogue action and a proliferoge nic effect on cultured aldosteronoma cells, make it likely that endogenous ADM system plays a potentially important role in the paracrine or autocrine functional control of Conn's adenomas.