OBJECTIVES: To investigate whether the β 3-adrenoceptor could be identified by immunohistochemistry in intact human white and brown adipocytes and other human tissues, and to investigate the influence of obesity and its treatment with ephedrine and caffeine on the expression of the β 3-adrenoceptor in adipocytes.

METHODS: Morbidly obese patients were given a hypoenergetic diet (70% of energy expenditure) and some were also treated with ephedrine and caffeine (20/200 mg, three times daily) for 4 weeks. Adipose tissue and other tissues were taken during surgery. Immunohistochemistry was carried out using a monoclonal antibody raised against the human β 3-adrenoceptor.

RESULTS: Staining was localized to the periphery of cells. All white adipocytes were stained. Those from lean subjects and obese subjects treated with ephedrine and caffeine showed more intense staining than those from untreated obese subjects. Staining was more intense in brown than in white adipocytes in perirenal adipose tissue from phaeochromocytoma patients. Staining was also seen in ventricular myocardium, and in smooth muscle of the prostate, ileum, colon and gall bladder.

DISCUSSION: The tissue and subcellular distribution of staining was consistent with it being due to binding of the antibody to the human β 3-adrenoceptor. The presence of the β 3-adrenoceptor in human white adipocytes is consistent with evidence that it can mediate lipolysis in human white adipocytes. The increased expression of the β 3-adrenoceptor in obese subjects treated with caffeine and ephedrine supports the potential of β 3-adrenoceptor agonists in the treatment of obesity and type 2 diabetes. Its expression in ventricular myocardium is consistent with evidence that the β 3-adrenoceptor mediates a negative inotropic effect in this tissue.