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.

Chronic aspartame affects T-maze performance, brain cholinergic receptors and Na+,K+-ATPase in rats.

This study demonstrated that chronic aspartame consumption in rats can lead to altered T-maze performance and increased muscarinic cholinergic receptor densities in certain brain regions. Control and treated rats were trained in a T-maze to a particular side and then periodically tested to see how well they retained the learned response. Rats that had received aspartame (250 mg/kg/day) in the drinking water for 3 or 4 months showed a significant increase in time to reach the reward in the T-maze, suggesting a possible effect on memory due to the artificial sweetener. Using [(3)H]quinuclidinyl benzilate (QNB) (1 nM) to label muscarinic cholinergic receptors and atropine (10(-6) M) to determine nonspecific binding in whole-brain preparations, aspartame-treated rats showed a 31% increase in receptor numbers when compared to controls. In aspartame-treated rats, there was a significant increase in muscarinic receptor densities in the frontal cortex, midcortex, posterior cortex, hippocampus, hypothalamus and cerebellum of 80%, 60%, 61%, 65%, 66% and 60%, respectively. The midbrain was the only area where preparations from aspartame-treated rats showed a significant increase in Na(+),K(+)-ATPase activity. It can be concluded from these data that long-term consumption of aspartame can affect T-maze performance in rats and alter receptor densities or enzymes in brain.

Differences in beta-adrenergic receptor densities in omental and subcutaneous adipose tissue from obese African American and Caucasian women.

African American women lose less weight and at a slower rate than Caucasian women under the same weight loss conditions. This is likely due to decreased mobilization of fat, possibly involving differences in the responsiveness of adipose tissue to adrenergic stimulation. To better understand the causes behind the decreased lipolysis in African American women, this study was initiated to determine if there were differences in the numbers and affinities of beta adrenoreceptors in omental and subcutaneous adipose tissue of obese African American and Caucasian women. We determined the number of beta receptors using a nonselective antagonist and found the total number of receptors in both omental and subcutaneous adipose tissue preparations were higher in African American than Caucasian women. beta(1)(,) beta(2), and beta(3) densities were higher in omental adipose tissue (P <.05), but not different in the subcutaneous tissue of the African American women. No racial differences in kd values for adrenergic agents (agonists and antagonists) were found with regard to beta(1), beta(2), or beta(3) receptors in either the omental or the subcutaneous preparations. beta(1) and beta(2) receptor protein (mass) was significantly increased in African American omental tissue preparations, but not subcutaneous. Our in vitro data demonstrating increased beta receptor numbers in omental tissue from obese African Americans suggest that the potential for lipolysis would be higher in these women. Future studies should determine the biologic significance of the differences in the beta adrenergic receptors in vivo.