Characterization of beta-adrenoceptor mediated smooth muscle relaxation and the detection of mRNA for beta1-, beta2- and beta3-adrenoceptors in rat ileum.
1. Functional and molecular approaches were used to characterize the beta-AR subtypes mediating relaxation of rat ileal smooth muscle. 2. In functional studies, (-)-isoprenaline relaxation was unchanged by CGP20712A (beta1-AR antagonist) or ICI118551 (beta2-AR antagonist) but shifted by propranolol (pKB=6.69). (+/-)-Cyanopindolol, CGP12177 and ICID7114 did not cause relaxation but antagonized (-)-isoprenaline relaxation. 3. BRL37344 (beta3-AR agonist) caused biphasic relaxation. The high affinity component was shifted with low affinity by propranolol, (+/-)-cyanopindolol, tertatolol and alprenolol. CL316243 (beta3-AR agonist) relaxation was unaffected by CGP20712A or ICI118551 but blocked by SR58894A (beta3-AR antagonist; pA2 = 7.80). Enhanced relaxation after exposure to forskolin and pertussis toxin showed that beta3-AR relaxation can be altered by manipulation of components of the adenylate cyclase signalling pathway. 4. The beta-AR agonist RO363 relaxed the ileum (pEC50=6.18) and was blocked by CGP20712A. Relaxation by the beta2-AR agonist zinterol (pEC50=5.71) was blocked by SR58894A but not by ICI118551. 5. In rat ileum, beta1-, beta2- and beta3-AR mRNA was detected. Comparison of tissues showed that beta3-AR mRNA expression was greatest in WAT>colon=ileum >cerebral cortex>soleus; beta1-AR mRNA was most abundant in cerebral cortex > WAT > ileum = colon > soleus; beta2-AR mRNA was expressed in soleus > WAT > ileum = colon > cerebral cortex. 6. These results show that beta3-ARs are the predominant beta-AR subtype mediating rat ileal relaxation while beta1-ARs may produce a small relaxation. The beta2-AR agonist zinterol produces relaxation through beta3-ARs and there was no evidence for the involvement of beta2-ARs in relaxation despite the detection of beta2-AR mRNA.
Roberts
S J
SJ
Department of Pharmacology, University of Melbourne, Parkville, Victoria, Australia.
Papaioannou
M
M
Evans
B A
BA
Summers
R J
RJ
D037361:Adenylate Cyclase Toxin; D000818:Animals; D005576:Colforsin / Q000494:pharmacology; D004149:Dioxoles / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004983:Ethanolamines / Q000494:pharmacology; D007082:Ileum / Q000502:physiology*; D007545:Isoproterenol / Q000494:pharmacology; D008297:Male; D009126:Muscle Relaxation / Q000187:drug effects*; D037342:Pertussis Toxin; D012333:RNA, Messenger / Q000032:analysis*; D051381:Rats; D017207:Rats, Sprague-Dawley; D011943:Receptors, Adrenergic, beta / Q000235:genetics / Q000502:physiology*; D018342:Receptors, Adrenergic, beta-1 / Q000235:genetics / Q000502:physiology*; D018343:Receptors, Adrenergic, beta-2 / Q000235:genetics / Q000502:physiology*; D022702:Receptors, Adrenergic, beta-3; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D037361:Adenylate Cyclase Toxin; D004149:Dioxoles; D004983:Ethanolamines; D012333:RNA, Messenger; D011943:Receptors, Adrenergic, beta; D018342:Receptors, Adrenergic, beta-1; D018343:Receptors, Adrenergic, beta-2; D022702:Receptors, Adrenergic, beta-3; D010566:Virulence Factors, Bordetella; C076126:disodium (R,R)-5-(2-((2-(3-chlorophenyl)-2-hydroxyethyl)-amino)propyl)-1,3-benzodioxole-2,3-dicarboxylate; D005576:Colforsin; C057368:BRL 37344; D037342:Pertussis Toxin; D007545:Isoproterenol