Functional and molecular evidence for beta 1-, beta 2- and beta 3- adrenoceptors in human colon

Br J Pharmacol. 1997 Apr;120(8):1527-35. doi: 10.1038/sj.bjp.0701056.


1. Relaxation of carbachol pre-contracted human colonic muscle to (-)-isoprenaline was examined in circular, longitudinal and taenia coli preparations to determine the beta-adrenoceptor subtypes involved. beta 1-, beta 2- and beta 3-Adrenoceptor mRNAs were also measured in colonic muscle and mucosa. 2. (-)-isoprenaline caused relaxation of longitudinal smooth muscle preparations with pEC50-7.39 +/- 0.12, and this response was inhibited by both propranolol (0.1 microM, pKB 8.55 +/- 0.12) and the selective beta 1-antagonist, CGP 20712A (0.1 microM, pKB 8.80 +/- 0.20), while the selective beta 2-antagonist, ICI 118551 (0.1 microM) failed to inhibit isoprenaline relaxation consistently. 3. (-)-Isoprenaline caused relaxation of taenia coli with a pEC50 of 6.70 +/- 0.17. Propranolol (0.1 microM). CGP 20712A (0.1 microM) and ICI 118551 (0.1 microM) inhibited the isoprenaline response with similar low affinities (pKB values 7.93, 7.71 and 7.54, respectively). Carbachol pre-contracted circular smooth muscle preparations failed to relax consistently to isoprenaline and these responses were not characterized. 4. beta 1- and beta 2-Adrenoceptor mRNAs were present in circular longitudinal muscle samples and taenia coli samples, and lower levels were detected in mucosa. beta 3-mRNA was also present in both muscle preparations but was not detected in human colonic mucosa. 5. In summary, beta 1-adrenoceptors are the predominant subtype mediating isoprenaline-induced relaxation of the thin longitudinal smooth muscle of human colon, while beta 1-receptors do not appear to be involved in these responses. However, beta 3-adrenoceptors may play a role in relaxation of the taenia coli as conventional antagonist affinities are low. beta 3-Adrenoceptor mRNA was present in taenia coli and circular/longitudinal smooth muscle but absent from human colonic mucosa.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adrenergic beta-Agonists / pharmacology
  • Carbachol / pharmacology
  • Colon / drug effects
  • Colon / physiology*
  • Humans
  • In Vitro Techniques
  • Isoproterenol / pharmacology
  • Muscle Contraction / drug effects
  • Muscle Relaxation / drug effects
  • RNA, Messenger / genetics
  • Receptors, Adrenergic, beta / classification
  • Receptors, Adrenergic, beta / genetics
  • Receptors, Adrenergic, beta / physiology*


  • Adrenergic beta-Agonists
  • RNA, Messenger
  • Receptors, Adrenergic, beta
  • Carbachol
  • Isoproterenol