Adrenomedullin enhances cell proliferation and deoxyribonucleic acid synthesis in rat adrenal zona glomerulosa: Receptor subtype involved and signaling mechanism

The effect of adrenomedullin (ADM) on the proliferative activity of the rat adrenal cortex has been investigated in vivo, using an in situ perfusion t echnique of the intact left gland. ADM and other chemicals were dissolved i n the perfusion medium, and the perfusion was continued for 180 min. ADM in fusion concentration dependently increased the mitotic index and [H-3]thymi dine incorporation into DNA in the zona glomerulosa (ZG; the maximal effect ive concentration was 10(-8) M), but not in inner adrenocortical layers, wh ere basal proliferative activity was negligible. The effect of 10(-8) M ADM was equipotently counteracted by both the calcitonin gene-related peptide (CGRP) type 1 receptor antagonist CGRP-(8-37) and ADM-(22-52). The adenylat e cyclase inhibitor SQ-22536 (10(-4) ha), the cAMP blocker Rp-cAMP-S (10(-3 ) M), and the protein kinase A inhibitor H-89 (10(-5) M), although countera cting the ZG proliferogenic action of 10(-9) kz ACTH, did not affect the 10 (-8) M ADM-elicited increase in ZG DNA synthesis. Similar results were obta ined using the phospholipase C inhibitor U-73122 (10(-5) M), the inositol-1 ,4,5-trisphosphate antagonist D,L-myo-inositol-1,4,5-trisphosphothiate (10( -4) M), and the protein kinase C inhibitor calphostin C (10(-5) M), which, however, significantly inhibited the ZG proliferogenic effect of 10(-9) M a ngiotensin II. The growth-promoting action of 10(-8) M ADM was not affected by the phospholipase A2 inhibitor AACOCF3 (10(-5) M), the cyclooxygenase ( COX) inhibitor indomethacin (10(-5) h r), or the mixed COX/lipoxygenase inh ibitor phenidone (10(-9) M). In contrast, the ZG proliferogenic effect of 1 0(-8) M ADM was abolished by either the tyrosine kinase (TK) inhibitor tyrp hostin-23 (10(-5) M) or the mitogen-activated protein kinase (MAPK) antagon ists PD-98059 and U0216 (10(-4) M). ADM (10(-8) M) stimulated TK and p42/p4 4 MAPK activity in dispersed ZG, but not ZF, cells, and the effect was reve rsed by either 10(-6) M CGRP(8-37) and ADM-(22-52) or preincubation with 10 (-5) M tyrphostin-23. Collectively, our findings indicate that 1) ADM stimu lates cell proliferation in the rat ZG, through CGRP-(8-37)- and ADM(22-52) -sensitive receptors, probably of the CGRP1 subtype; and 2) the mitogenic e ffect of ADM is mediated by activation of the TK-MAPK cascade, without any involvement of the adenylate cyclase/protein kinase A-, phospholipase C/pro tein kinase C-, and COX- or lipoxygenase-dependent signaling pathways.