Format

Send to

Choose Destination
Mol Endocrinol. 1994 Apr;8(4):518-27.

Impaired expression and functional activity of the beta 3- and beta 1-adrenergic receptors in adipose tissue of congenitally obese (C57BL/6J ob/ob) mice.

Author information

1
Department of Medicine (Gastroenterology), Duke University Medical Center, Durham, North Carolina 27710.

Abstract

Adipocytes from genetically obese (ob/ob) mice display an impaired response to beta-adrenergic stimulation, but the molecular defects have not been unequivocally identified. The expression and functional activity of the beta 1-, beta 2-, and beta 3-adrenergic receptor (AR) subtypes in white and brown adipose tissue from genetically lean and obese (ob/ob) mice were compared. Three beta 3AR transcripts of 2.1, 2.6, and 3.5 kilobases were identified in adipose tissue from lean mice by Northern blotting. All three beta 3AR mRNA species were dramatically reduced (by approximately 300-fold) in 12-week-old obese mice compared to those in lean animals. beta 1AR mRNA levels were also reduced (by approximately 4-fold) in obese mice, whereas beta 2AR mRNA levels were not significantly changed. The functional consequences of these changes in beta 3AR and beta 1AR expression were assessed by measuring beta-agonist-stimulated adenylyl cyclase activity in adipocyte plasma membranes with subtype-selective beta-adrenergic agonists and antagonists. Dose-response curves with epinephrine from lean mice were best fit to a two-component model comprised of 23% high affinity (K(act) = 1.42 x 10(-7) M) and 77% low affinity (K(act) = 1.67 x 10(-5) M) components, corresponding to activation of beta 1AR and beta 2AR conjointly, and beta 3AR, respectively. The beta 1AR-selective antagonist CGP20712A reduced the high affinity component to about 10%, whereas the nonselective beta-antagonist propranolol eliminated the high affinity component. The beta 3AR-selective agonist BRL37344 stimulated adenylyl cyclase activity in lean membranes to a slightly lesser extent than epinephrine, but was more potent (73% high affinity component; K(act) = 3.61 x 10(-8) M). In obese mice, stimulation of adenylyl cyclase by all agonists was severely blunted and was best fit to a single class of sites. Studies with CGP20712A or the beta 2AR-selective antagonist ICI118,551 indicated that this residual response was predominantly beta 2AR in character. Expression of beta AR subtypes in both brown and white adipose tissue of weanling obese mice (4-5-weeks of age) was also affected, but to a lesser extent, consistent with the progressive severity of obesity with age. Together the reduction in expression of the beta 3AR and beta 1AR impairs the beta-agonist-stimulated adenylyl cyclase response over a broad concentration range by greatly lowering the maximum stimulation and shifting the adrenergic sensitivity at low concentrations from a mixed beta 1AR/beta 2AR response to predominantly beta 2AR.

PMID:
7914350
DOI:
10.1210/mend.8.4.7914350
[Indexed for MEDLINE]

Publication types, MeSH terms, Substances, Grant support

Supplemental Content

Full text links

Icon for Silverchair Information Systems
Loading ...
Support Center