Elevated β2-adrenoceptor protein concentration in adipose tissue from obese subjects is closely related to the body mass index and waist/hip ratio

The aim of the present study was to quantify β₂-adrenoceptor protein content in adipose tissue during fasting, and to study the relationships between β₂-adrenoceptor protein and mRNA levels and changes in metabolites related to lipolysis. Groups of male subjects with a body mass index of <25kg/m² or >30kg/m² fasted for 60h. Abdominal subcutaneous fat biopsies were analysed for receptor mRNA levels by reverse transcription–PCR–HPLC. The β₂-adrenoceptor protein concentration was measured by Western blotting using fluorescence laser scanning for detection. The β₂-adrenoceptor protein concentration per cell (on a DNA basis) was higher in obese subjects (P<0.03). There were highly significant relationships between β₂-adrenoceptor protein concentration and both body mass index and waist/hip ratio (P<0.001 for both). Furthermore, there was an inverse relationship between the receptor protein concentration and the serum β-hydroxybutyrate level during fasting (P<0.005). β₂-Adrenoceptor protein levels decreased in both groups during fasting, to a similar degree. Basal β₂-adrenoceptor mRNA levels were similar in the two groups, but there was a smaller increase in the obese group during fasting (P<0.03). The increased β₂-adrenoceptor protein level in obese subjects is likely to be related to the greater plasma membrane area of their adipocytes. The decrease during fasting may be due to increased binding of noradrenaline and subsequent internalization and degradation of the receptor. Elevated levels of less responsive β₂-adrenoceptor protein in obese subjects may contribute to the development of obesity.