Evidence for a functional β₃‐adrenoceptor in man

Abstract

1. The existence of a functional beta 3-adrenoceptor in man was investigated by studying the lipolytic action of selective beta-adrenoceptor agents in isolated white omental and subcutaneous fat cells. 2. The non-selective beta 1/beta 2-adrenoceptor antagonist, CGP 12177 was lipolytic in both omental and subcutaneous fat cells. The intrinsic activity relative to isoprenaline was greater in omental than in subcutaneous cells. 3. Addition of the beta 2-adrenoceptor antagonist, ICI 118,551 and the beta 1-adrenoceptor antagonist CGP 20712A in combination or the non-selective beta-adrenoceptor antagonist propranolol alone (all 10(-7) M), induced a rightward shift of the dose-response curves for isoprenaline- and BRL37344-stimulated lipolysis of about 4 and 2 log-units, respectively. However, the antagonists did not alter lipolysis induced by CGP12177. 4. Several concentrations of beta-adrenoceptor antagonists were used to determine the pA2 values by Schild analysis. The values for CGP 20712A and ICI 118,551 (6.63 +/- 0.20 and 6.25 +/- 0.12) as antagonists of the lipolytic effects of CGP 12177 were over 2 units lower than the pA2 value for CGP 20712A against the response to the selective beta 1-agonist dobutamine (8.58 +/- 0.23) and the pA2 value for ICI 118,551 against the response to the selective beta 2-agonist terbutaline (9.15 +/- 0.26). 5. beta 3-Adrenoceptor mRNA expression, investigated with a polymerase chain reaction assay, was demonstrated in both types of adipocytes in the same cell preparations that had a lipolytic response to CGP 12177. 6. In conclusion, human white fat cells express an atypical beta-adrenoceptor in addition to beta 1- and beta 2-adrenoceptors. This receptor is stimulated more selectively by the beta1/beta2-antagonist CGP 12177 than by BRL 37344 and is poorly sensitive to blockade by selective beta1- and beta2-antagonists. On the basis of the pharmacological properties and the mRNA analyses, we suggest that this atypical receptor corresponds to the beta 3-adrenoceptor subtype.

Determination of β3‐Adrenoceptor Mediated Lipolysis in Human Fat Cells

“…However, recently, our demonstration of functional 63-adrenoceptors in man (27) has been confirmed by others in isolated mammary fat cells (37) and isolated omental fat cells (8). (25,18,36) and omental fat (40).…”

“…A therapeutic role of B3-adrenoceptor agonists in both obesity and diabetes has been proposed. The expression of B3-adrenoceptors at the mRNA level is today well documented from studies on different human tissues and cells from living subjects (1 1,22,27,34), although negative data also has been reported on a brain-dead donor (39). The human B3 -adrenoceptor mRNA has, predominantly, been detected in adipose tissues.…”

“…All ligands were added simultaneously at the start of the incubation. Increasing concentrations of the following compounds were added to the incubation medium; norepinephrine (non-selective B-adrenoceptor agonist), dobutamine (selective 01-adrenoceptor agonist), terbutaline (selective 4-adrenoceptor agonist), CGP12177 (Bl-and badrenoceptor antagonist and partial B3-adrenoceptor agonist in man) (27), forskolin, acting at the catalytic component of the adenylate cyclase, 8-bromo cyclic AMP, a cyclic AMP analogue and a substrate for phosphodiesterase and the non hydrolysable cyclic AMP analogue dibuturyl cyclic AMP (31). In one set of experiments increasing concentrations of lipolytic antagonists, i.e., CGP 20712A (Bl), ICI 118,551(82) or bupranolol 5-and B3-adrenoceptor antagonist in rodents) were added to cell suspensions that were simultaneously stimulated with either dobutamine, terbutaline or CGP 12177, whereafter the antagonistic properties (pA2) of the three B-adrenoceptor subtypes were calculated.…”

Classical and atypical binding sites for β‐adrenoceptor ligands and activation of adenylyl cyclase in bovine skeletal muscle and adipose tissue membranes

“…More specifically, human subcutaneous adipose tissue shows little or no response to BRL 37344 (Hollenga et al, 1991a;Langin et al, 1991), whereas functional P3-adrenoceptors can be detected in human omental adipose tissue, with a lipolysis assay of appropriate sensitivity (Lonnqvist et al, 1993 (Feve et al, 1991), and with those pK values for cloned human (8.72) and mouse (9.06) V3-adrenoceptors expressed in Chinese hamster ovary (CHO) cells (Feve et al, 1991;Nahmias et al, 1991). In previous papers, we and others discussed further similarities between the 'atypical' ['251I]-ICYP binding site, and the putative rat P3-adrenoceptor (Sillence et al, 1993;Roberts et al, 1993).…”

Lipolytic catecholamine resistance linked to α2-adrenoceptor sensitivity—a metabolic predictor of weight loss in obese subjects

“…17 It should be acknowledged that the possible in¯u-ence of b 3 -adrenoceptor function on the rate of weight loss was not evaluated in this study. This receptor is mainly expressed on a functional basis in visceral fat, 16 a region that for technical and ethical reasons could not be investigated in this type of study. However, subcutaneous adipose tissue is perhaps of greater interest in the present type of study, since it constituted the body's largest fat depot.…”