Inhibitory Effect of β3-Adrenoceptor Agonist in Lower Esophageal Sphincter Smooth Muscle: In Vitro Studies

Abstract

We investigated the effects of (R,R)-5-[2-[2-3-chlorophenyl)-2-hydroxyethyl] -amino]propyl] -1,3 -benzodioxole -2 , 2 -dicarboxylate (CL 316243) (a typical ␤ 3 -agonist) on the spontaneously tonic smooth muscle of the lower esophageal sphincter (LES). Studies were carried out in smooth muscle strips and smooth muscle cells (SMCs) of opossum LES. Isometric tension was recorded in the basal state and after CL 316243, and before and after) and nonselective antagonist propranolol. In some experiments, the effects of nonadrenergic noncholinergic (NANC) nerve activation by electrical field stimulation (EFS) were also examined. The effects of CL 316243 were compared with those of nonselective ␤-agonist isoproterenol. CL 316243 caused a concentration-dependent relaxation of the LES smooth muscle. The relaxant action of CL 316243 was determined to be directly at the smooth muscle because it remained unmodified by the neurotoxin tetrodotoxin and other neurohumoral antagonists, and also was observed in the SMCs. L 748337 selectively antagonized the relaxant effect of CL 316243 and, conversely, had no significant effect on the inhibitory actions of isoproterenol. CL 316243 (1 ϫ 10 Ϫ8 M) caused an augmentation of NANC relaxation in the LES. Another ␤ 3 -agonist, (S)-4-[hydroxy-3-phenoxy-propylamino-ethoxy]-N-(2-methoxyethyl)-phenoxyacetamide (ZD 7114), also caused concentration-dependent full relaxation of the LES that was selectively antagonized by ␤ 3 -anatagonist 3-(2-ethylphenoxy)-1-[(1S)1,2,3,4-tetrahydronaphth-1-ylaminol]-(2S)-2-propanol oxalate (SR 59230A). These studies defined the effects of characteristic inhibitory ␤ 3 -adrenoceptors in the spontaneously tonic LES smooth muscle and suggested a potential therapeutic role in the esophageal motility disorders characterized by hypertensive LES.

Angiotensin II-Induced Relaxation of Anococcygeus Smooth Muscle via Desensitization of AT1 Receptor, and Activation of AT2 Receptor Associated with Nitric-Oxide Synthase Pathway

“…For these experiments, two strips from the same donor rat were used to obtain CRC for Ang II in the absence and presence of the inhibitors. The concentrations of different inhibitors used in this study have been previously shown to be selective in their actions (de Godoy and de Oliveira, 2002;Fan et al, 2002;Rattan et al, 2002;Sarma et al, 2003).…”

Tools to study β3-adrenoceptors

“…This was, e.g., based on studies in which it antagonized cAMP formation in rat brown adipose tissue but not in rat brain frontal cortex. Subsequently, it has been used in numerous studies in which inhibition of a functional response by this compound has been taken as evidence for mediation of this response by a β 3 -adrenoceptor (Sarma et al 2003;Yamanishi et al 2002bYamanishi et al , 2003. However, more recent radioligand binding studies with cloned human β-adrenoceptor subtypes have reported that SR 59,230 is not selective for β 3 -adrenoceptors and, if anything, has slightly lower affinity for this subtype than for β 1 -and β 2 -adrenoceptors (Table 2) (Candelore et al 1999;Hoffmann et al 2004;Niclauß et al 2006).…”

“…It is about 100-fold less potent at the rat β 3 -adrenoceptor (Candelore et al 1999). Nevertheless, it was reported to abolish some nadololinsensitive β-adrenoceptor responses in rat heart (Zhang et al 2005) or aorta (Mallem et al 2004) and also to inhibit propranolol-resistant responses in the opossum esophagus (Sarma et al 2003) or anal sphincter . L-748,337 distinguishes the β 3 -adrenoceptor from the propranolol-resistant site of the β 1 -adrenoceptor (Joseph et al 2003).…”

“…CL 316,243 appears to be a rodent-selective agonist, as its potency to stimulate cAMP formation in transfected CHO cells was much higher at the mouse than at the human β 3 -adrenoceptor (pEC 50 8.7 vs. 4.3) (Hutchinson et al 2006). CL 316,243 has repeatedly been used in studies on the rat (Kaidoh et al 2002;Takeda et al 2000Takeda et al , 2002bTakeda et al , 2003Woods et al 2001) and human urinary bladder (Igawa et al 1999(Igawa et al , 2001) and also in the ureter (Murakami et al 2000;Park et al 2000), esophagus (Sarma et al 2003), colon (Kaumann and Molenaar 1996) and blood vessels (Atef et al 1996;Kuratani et al 1994;Leblais et al 2005). In line with the above differences in potency between mouse and human receptors, it also exhibited a consistently higher potency at rat compared with human tissues.…”

Role of Adenylate and Guanylate Cyclases in β1-, β2-, and β3-Adrenoceptor-Mediated Relaxation of Internal Anal Sphincter Smooth Muscle

“…The procedure to describe details of tissue preparation and isometric tension recording in the IAS smooth muscle has been published in a number of our earlier publications (Moummi and Rattan, 1988;Banwait and Rattan, 2003;Rathi et al, 2003;Sarma et al, 2003).…”