Intermedin/adrenomedullin-2 (IMD/AM2) relaxes rat main pulmonary arterial rings via cGMP-dependent pathway: Role of nitric oxide and large conductance calcium-activated potassium channels (BKCa)

The present study was designed to investigate the effects of rat intermedin/adrenomedullin2 (rIMD), an agonist for calcitonin-like calcitonin receptors (CRLR), on the isolated rat pulmonary arterial rings (PA). When PA were precontracted with 9,11-dideoxy-11α,9α-epoxymethanoprostaglandin F2α (U-46619), rIMD (10−11 to 10−6 M) induced concentration-dependent relaxation. The pulmonary vasorelaxant response (PVR) to rIMD in PA were completely inhibited by endothelium removal, NG-nitro-l-arginine-methyl-ester (l-NAME), l-N5-(1-iminoethyl)-ornithine hydrochloride (l-NIO) or 1H-[1,2,4] oxadiazolo[4,3-a]quinoxalin-1-one (ODQ). The PVR to rIMD were also significantly attenuated by a protein kinase inhibitor, Rp-8-bromo-β-phenyl-1,N2-ethenoguanosine 3′:5′-cyclic monophosphorothioate sodium salt hydrate (Rp-8-Br-PETcGMPs), cholera toxin and abolished by tetraethylammonium chloride (TEA), iberiotoxin and precontraction with KCl. The relaxant effect was not affected by 9-(tetrahydro-2-furanyl)-9H-purin-6-amine (SQ22536), (9S,10S,12R)-2,3,9,10,11,12-hexahydro-10-hydroxy-9-methyl-1-oxo-9,12-epoxy 1H diindolo [1,2,3fg:3′,2′,1′kl] pyrrolo [3,4-i] [1,6] benzodiazocine-10-carboxylic acid hexyl ester (KT5720), meclofenamate, glybenclamide or apamin. In parallel with SQ22536 and KT5720 results rolipram pretreatment did not alter the rIMD-induced PVR. The PVR to rIMD was potentialized either in the presence of zaprinast or sildenafil. Since the PVR to rIMD was also significantly reduced by rCGRP8–37 and hADM22–52 and rIMD17–47, the present data suggest that rIMD produces PVR by acting in an indiscriminant manner on functional, and possibly different, endothelial CRLR. In conclusion, rIMD stimulates endothelial CRLR are coupled to release of nitric oxide, activation of guanylate cyclases, and promotion of hyperpolarization through large conductance calcium-activated K+ channels in rat main PA.