Differences in the expression of the adenosine A1 receptor in adipose tissue of obese black and white women

Context: African- American women ( AAW) lose less weight and at a slower rate than Caucasian women ( CAW) under the same weight-loss regimens. A potential cause of this finding is inhibition of lipolysis. Objective: Because alpha-2 and adenosine receptors are directly involved in inhibition of lipolysis, differences in alpha-2 or adenosine A1 receptors in visceral adipose tissue ( VAT) and sc adipose tissue ( SAT) from obese AAW and CAW were determined. Design: Measurements of maximal binding capacity ( Bmax) of alpha-2 and adenosine A1 receptors as well as protein and mRNA levels of the adenosine receptor in VAT and SAT from AAW and CAW were taken. Setting: The study was conducted in the general community. Patients: Patients were selected by body mass index greater than 40 and age matched. Main Outcome Measures: Bmax ( density) of the two receptors and protein and mRNA levels of adenosine receptors were determined in adipose tissue of AAW and CAW. Results: No differences were found for alpha-2 receptor Bmax in either VAT or SAT from AAW and CAW. Bmax ( but not the dissociation constant, Kd) for the adenosine A1 receptor in VAT from AAW was higher ( P < 0.05) than in VAT from CAW. Adenosine receptor protein and mRNA levels were significantly higher in VAT from AAW than VAT from CAW. No racial differences in these parameters were observed in SAT. Conclusions: These data suggest that inhibition of lipolysis by adenosine has the potential to be greater in obese AAW, and this could possibly be one explanation for the observation that obese AAW have more difficulty in losing weight than obese CAW.