Abstract
The mechanisms of relaxation of adrenomedullin were investigated in isolated mesenteric artery from pregnant rats. Adrenomedullin (1 nM–0.3 μM) produced concentration-dependent relaxation of endothelium-denuded mesenteric artery rings precontracted with norepinephrine at a concentration required to produce 70% of maximal response (ED70). The concentration-response curve of adrenomedullin was shifted to the right by adrenomedullin receptor antagonist adrenomedullin22–52 (10 μM) or calcitonin gene-related peptide8–37 (1 μM). Inhibition of adenylate cyclase by 9-(tetrahydro-2-furanyl)-9H-purin-6-amine (SQ22536) (10 μM) or protein kinase A [Rp-cyclic adenosine monophosphorothioate (Rp-cAMP); 10 μM] reduced the adrenomedullin-induced relaxation to the same magnitude. Adrenomedullin increased the intracellular cAMP level from 0.38 ± 0.07 to 2.00 ± 0.47 pmol/mg tissues, which was completely inhibited by adrenomedullin22–52 (100 μM). Extracellular high potassium (80 mM), which inactivates the potassium channels, reduced the adrenomedullin-induced relaxation. Blockade of ATP-sensitive, voltage-gated, or inward rectifier potassium channels did not affect the adrenomedullin-induced relaxation. Blockade of calcium-activated K+ channels (KCa) by tetraethylammonium (1 mM) or iberiotoxin (100 nM) inhibited the adrenomedullin-induced relaxation, whereas there was no additional inhibition by SQ22536 or Rp-cAMP when KCa channels were already inhibited. In conclusion, this study provides evidence that cAMP-dependent protein kinase A and KCa channels seem to mediate as the cellular pathways in the adrenomedullin-induced endothelium-independent relaxation of mesenteric artery from pregnant rats.
Footnotes
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This work was supported in part by the National Institutes of Health Grants HL-58144 and HL-72650.
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doi:10.1124/jpet.106.101790.
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ABBREVIATIONS: KATP, adenosine triphosphate-sensitive potassium channel; PSS, physiological salt solution; CL, calcitonin; RAMP, receptor activity-modifying protein; CGRP, calcitonin gene-related peptide; l-NAME, Nω-nitro-l-arginine methyl ester; AM1, adrenomedullin receptor subtype 1; AM2, adrenomedullin receptor subtype 2; KV, voltage-gated potassium channel; KIR, inward rectifier potassium channel; KCa, calcium-activated potassium channels; Rp-cAMP, Rp-cyclic adenosine monophosphorothioate(s); SQ22536, 9-(tetrahydro-2-furanyl)-9H-purin-6-amine; 4-AP, 4-aminopyridine; ANOVA, analysis of variance.
- Received January 23, 2006.
- Accepted March 17, 2006.
- The American Society for Pharmacology and Experimental Therapeutics
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