Abstract
In contrast to vascular muscles, the contribution of a hypotensive peptide adrenomedullin (AM) to the regulation of visceral smooth muscles is obscure. The content, synthesis, and effects of AM on the muscular tone in rat ileum were explored. It was found that there was immunoreactive AM (301 pg/mg of protein) and AM mRNA expression (162 fg/pg actin mRNA) in the ileum and that AM evoked relaxation in ileal strips (Ki = 0.85 nM) precontracted with serotonin. Antagonists of both AM (AM22-52) and calcitonin gene-related peptide (CGRP8-37) receptors did not affect this AM-induced relaxation, whereas it was suppressed by a selective blocker of β3-adrenoreceptor (SR 59230A). The AM-induced relaxation was accompanied by a production of cAMP. Antagonists of protein kinases A (KT 5720 and H-7) and an inhibitor of the ATP-dependent K+-channels (glibenclamide) attenuated the effect of AM. We suggest that AM is a local regulator of the ileal tone, with an inhibitory action on muscle contraction. AM may activate the β3-adrenoceptors, resulting in protein kinase A activation, which in turn opens the ATP-dependent K+-channels.
Footnotes
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This work was supported by a CRCG grant awarded to F.T.
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DOI: 10.1124/jpet.103.057612.
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ABBREVIATIONS:: AM, adrenomedullin; ir-AM, immunoreactive adrenomedullin; CGRP, calcitonin gene-related peptide; SD rats, Sprague-Dawley rats; PSS, physiological salt solution; NO, nitric oxide; l-NAME, NG-nitro-l-arginine methyl ester); β-AR, β-adrenergic receptor; ICI 118,551, (±)-1-[2,3-(dihydro-7-methyl-1H-inden-4-yl)oxy]-3-[(1-methylethyl)amino]-2-butanol; SR 59230A, 1-(2-ethylphenoxy)-3-[[(1S)-1,2,3,4-tetrahydro-1-naphthalenyl]amino]-(2S)-2-propanol hydrochloride; ZM 226600, N-(4-phenylsulfonylphenyl)-3,3,3-trifluoro-2-hydroxy-2-methylpropanamide; H-7, (±)-1-(5-isoquinolinesulfonyl)-2-methylpiperazine dihydrochloride; KT 5720, (9R, 10S, 12S)-2,3,9,10,11,12-hexahydro-10-hydroxy-9-methyl-1-oxo-9,12-epoxy-1H-diindolo[1,2,3-fg:3′,2′,1′-kl]pyrrolo[3,4-I]benzodiazocine-10-carboxylic acid, hexyl ester; BRL 37344, (R*,R*)-4-[2[(2-(3-chlorophenyl)-2-hydroxyethyl)amino]propyl] phenoxyacetic acid, sodium salt; d-cAMP, dibutyryl-cAMP; TTX, tetrodoxin; PKA, protein kinase A; PIPES, 1,4-piperazinediethanesulfonic acid; RIA, radioimmunoassay.
- Received July 25, 2003.
- Accepted October 8, 2003.
- The American Society for Pharmacology and Experimental Therapeutics
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