Functional and molecular evidence for beta 1-, beta 2- and beta 3- adrenoceptors in human colon.
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.
Roberts
S J
SJ
Department of Pharmacology, University of Melbourne, Victoria, Australia.
Papaioannou
M
M
Evans
B A
BA
Summers
R J
RJ
D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D002217:Carbachol / Q000494:pharmacology; D003106:Colon / Q000187:drug effects / Q000502:physiology*; D006801:Humans; D066298:In Vitro Techniques; D007545:Isoproterenol / Q000494:pharmacology; D009119:Muscle Contraction / Q000187:drug effects; D009126:Muscle Relaxation / Q000187:drug effects; D012333:RNA, Messenger / Q000235:genetics; D011943:Receptors, Adrenergic, beta / Q000145:classification / Q000235:genetics / Q000502:physiology*
D000318:Adrenergic beta-Agonists; D012333:RNA, Messenger; D011943:Receptors, Adrenergic, beta; D002217:Carbachol; D007545:Isoproterenol