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Atypical beta-adrenoceptors mediating relaxation in the human colon: functional evidence for beta3-rather than beta4-adrenoceptors

Atypical beta-adrenoceptors mediating relaxation in the human colon: functional evidence for beta3-rather than beta4-adrenoceptors

Pharmacological Research 39(5): 345-348

The aim of the present functional study was to assess the role of beta3-adrenoceptors in the light of recent findings suggesting the existence of a putative fourth beta-adrenoceptor in adipose and heart tissue. The effect of the non-conventional beta3-adrenoceptor partial agonist CGP12177A is resistant to the effect of the beta3-adrenoceptor antagonist SR59230A. Under isotonic conditions in circular muscle strips of human distal colon, the concentration-effect relationship of CGP12177A and SR59104A (beta3-adrenoceptor agonists), alone and in the presence of CGP20712A (beta1-adrenoceptor antagonist) ICI118551 (beta2-adrenoceptor antagonist) and SR59230A, all 0.1 muM was studied. CGP12177A concentration-dependently relaxed circular muscle strips (pEC50 = 6.16 +- 0.05). This effect was left unchanged by beta1-/beta2-adrenoceptor blockade, but antagonised by SR59230A (pA2 = 8.12 +- 0.02). SR59104A concentration-dependently relaxed circular muscle strips (pEC50 = 5.43 +- 0.01), an effect that was not significantly affected by pretreatment with CGP20712A and ICI118551, but competitively antagonised by SR59230A (pKB = 7.89). Isoprenaline-induced relaxations were antagonised by propranolol with a low pA2 value (7.76 +- 0.16). These results provide further evidence for the presence of functional beta3-adrenoceptors in the human colon, but do not support a role for an atypical beta-adrenoceptor distinct from the beta3-subtype.

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Accession: 010218256

Download citation: RISBibTeXText

PMID: 10328991

DOI: 10.1006/phrs.1998.0440

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