Relaxation by beta 3-adrenoceptor agonists of the isolated human internal anal sphincter.
OBJECTIVE
In this study, responses of beta(3)-adrenoceptor agonists were examined on human isolated internal anal sphincter (IAS) in order to explore their relaxant effects on hypertonicity of IAS.


METHODS
The relaxant efficacy (E(max)) and potency (-logIC(50)) of BRL37344 and SR58611A, beta(3)-adrenoceptor agonists, were examined in contracted IAS muscle strips. The presence of beta(3)-adrenoceptors, and changes in intracellular calcium and cyclic nucleotide levels in IAS muscle were tested by Western blotting, epifluorescence microscopy and enzyme immunoassay, respectively.


RESULTS
BRL37344 and SR58611A relaxed contracted IAS muscle (E(max)=27+/-3% and 35+/-3%; -logIC(50)=6.26+/-0.24 and 4.87+/-0.13; respectively). These relaxant responses were blocked by SR59230A, a selective beta(3)-antagonist but not by beta(1)/beta(2)-selective antagonists, neuronal inhibitor or inhibition of nitric oxide synthase. The E(max) of beta(3)-agonists was similar to that of beta(2)-selective agonists but smaller than that of isoprenaline (nonselective agonist) or beta(1)-selective agonists. BRL37344 (100 microM) increased cAMP (1.5-fold) without cGMP change, and depressed intracellular calcium signal. beta(3)-Adrenoceptor expression was smaller than that of beta(1)- and beta(2)-adrenoceptors.


CONCLUSIONS
This is the first study demonstrating the presence of beta(3)-adrenoceptor in human IAS muscle and beta(3)-mediated relaxation of augmented sphincter tone. However, direct beta(3)-relaxation appears smaller than that obtained for nonselective agonists which may limit their potential use in the treatment of anorectal hypertonicity disorders.
Ballester
Cristina
C
Department of Surgery, University of Valencia, Valencia, Spain.
Sarriá
Benjamín
B
García-Granero
Eduardo
E
Mata
Manuel
M
Milara
Javier
J
Morcillo
Esteban J
EJ
Lledó
Salvador
S
Cortijo
Julio
J
D058667:Adrenergic beta-3 Receptor Agonists; D000318:Adrenergic beta-Agonists / Q000494:pharmacology*; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001003:Anal Canal / Q000187:drug effects / Q000502:physiology*; D004305:Dose-Response Relationship, Drug; D004983:Ethanolamines / Q000494:pharmacology; D005260:Female; D006801:Humans; D066298:In Vitro Techniques; D008297:Male; D008875:Middle Aged; D009126:Muscle Relaxation / Q000187:drug effects / Q000502:physiology*; D022702:Receptors, Adrenergic, beta-3 / Q000502:physiology*
D058667:Adrenergic beta-3 Receptor Agonists; D000318:Adrenergic beta-Agonists; D004983:Ethanolamines; D022702:Receptors, Adrenergic, beta-3; C057368:BRL 37344