Functional, biochemical and molecular biological evidence for a possible β₃‐adrenoceptor in human near‐term myometrium

Abstract

1 The possible existence of a b 3 -adrenoceptor (b 3 -AR) in human near-term myometrium was investigated by in vitro functional and biochemical studies and analysis of mRNA expression. 2 SR 59119A and SR 59104A and CGP 12177 (two selective agonists and a partial agonist, respectively, of the b 3 -AR), salbutamol and terbutaline (b 2 -AR agonists) each produced a concentration-dependent relaxation of the myometrial spontaneous contractions. There were no di erences in pD 2 values for the relaxing potencies of terbutaline, salbutamol, CGP 12177 and SR 59119A. The rank order for their relaxing e cacies was SR 59119A4SR 59104A4terbutali-ne&salbutamol&CGP 12177 (E max =52+7%, 42+12% and&30% respectively). 3 Propranolol, a b 1 -and b 2 -AR antagonist, and ICI 118551, a b 2 -AR antagonist (both at 0.1 mM), did not a ect the SR 59119A-induced relaxation whereas SR 59230A, a selective b 3 -AR antagonist (1 mM), signi®cantly reduced the maximal relaxing e ect of SR 59119A. 4 SR 59119A and salbutamol induced a signi®cant increase in cyclic AMP levels that was antagonized by SR 59230A but not by propranolol for SR 59119A, and by propranolol but not by SR 59230A for salbutamol. 5 The b 3 -AR mRNA was positively expressed in myometrium preparations in a reverse transcription polymerase chain assay. 6 The results presented provide the ®rst evidence for the existence of the b 3 -AR subtype in human near-term myometrium and suggest that the e ects of SR 59119A might be mediated through an increase in cyclic AMP level.

The human near‐term myometrial β3‐adrenoceptor but not the β2‐adrenoceptor is resistant to desensitisation after sustained agonist stimulation

“…In our experimental conditions, we confirmed that, without pretreatment of the myometrial strips, both salbutamol and SR 59119A were able to inhibit spontaneous contractions and to induce cAMP production. These findings provide confirmation of b 2 -and b 3 -AR functional integrity, and positive coupling with the adenylyl cyclase pathway (Bardou et al, 2000). Our functional and biochemical results demonstrate that b 2 -AR undergoes functional desensitisation after long-term exposure to salbutamol, which is associated with a significant decrease in cAMP production.…”

“…We previously determined that maximal effects of salbutamol and SR 59119A were obtained at the concentration of 10 mM (Bardou et al, 2000).…”

“…The 2 g initial tension was chosen according to previous reports including ours (Bardou et al, 2000;Dennedy et al, 2001). One end of each strip was connected to a force-displacement transducer and tension changes were measured with Pioden strain gauges (UF1), amplified (EMKA, Paris, France), and recorded on a pen-writing oscillograph (Linseis, L65514, Munich, Germany).…”

“…During this 5-min time period, 0.5 mM 3-isobutyl-1-methylxanthine (IBMX), a nonselective inhibitor of cAMP-PDE activity, was added in order to prevent cAMP degradation (Fonteh et al, 1993;Bardou et al, 2000;Boulven et al, 2001). cAMP levels (expressed as pmol mg À1 protein) were determined after agonist pretreatments, and were compared with those obtained in time-matched paired strips incubated either in Krebs solution alone (basal value) or in Krebs solution containing the respective solvents of each agonist (solvent value).…”

“…b 3 -AR have been shown to mediate lipolysis in white adipose tissue and thermogenesis in brown adipose tissue (Arch et al, 1984;Zaagsma & Nahorski, 1990;Lonnqvist et al, 1995), and also to inhibit the contractile activity of ileum and colon (Bond & Clarke, 1988;Manara & Bianchetti, 1990;Bardou et al, 1998). The presence of a functional b 3 -AR was recently demonstrated in the human near-term myometrium (Bardou et al, 2000). In this work, the stimulation of myometrial tissue by a specific b 3 -AR agonist led to a higher degree of relaxation than specific stimulation by b 2 -AR agonist, and was associated with a cAMP production.…”