Adipocyte blood flow in four distinct adipose tissue depots has been measured in conscious, unrestrained, male Sprague-Dawley rats by using the microsphere technique together with cellularity determinations. Blood flow was determined in young rats (90 days old, 387 g mean body wt), spontaneously obese rats (450 days old, 713 g mean body wt), and long-term calorically restricted rats (450 days old, 390 g mean body wt), therefore allowing the comparison of the relative effects of age and fat mass on adipose tissue blood flow. Results of these experiments indicate that while cardiac index remained constant, cardiac output increased in only the obese group, concomitant with increased body fat mass. Spontaneously obese rats exhibited increased adipose tissue depot weight, fat cell lipid, and fat cell size compared with young and restricted groups. Despite significant differences in cell volume, blood flow per cell was remarkably similar between young and obese rats. Long-term caloric restriction, however, was associated with decreased flow per cell. Interdepot comparisons of flow per unit surface area (mm2) or per unit volume (pl) indicate that mesenteric cells receive significantly more blood than cells of the other depots. Our results suggest that adipocyte blood flow is dependent in part on anatomic location, may be further influenced by age or dietary manipulation, and is not a limiting factor in the enlargement of adipocytes during the development of spontaneous obesity.

The effect of a 21-day program of caloric restriction on cardiac reactivity and beta-adrenoceptor number was investigated in male Sprague-Dawley rats. Rats on the restricted diet (Restricted) exhibited significant decreases in body weight, epididymal fat pad, and retroperitoneal fat pad weight as well as the percent of body fat represented by these adipose tissue depots when compared with rats fed ad libitum (Fed). Fed rats exhibited significantly increased total heart weight and total heart protein, but the percent cardiac protein and ratio of heart weight to body weight were similar in Fed and Restricted rats. Isolated atria from Fed and Restricted rats developed similar chronotropic and inotropic responses over a range of isoproterenol concentrations. Although total beta-adrenoceptor number (fmol/heart) was greater in Fed rats, the concentration of beta-adrenoceptors (fmol/mg protein) was remarkably similar regardless of the dietary regimen. Therefore, despite significant decreases in body weight, body fat, and heart weight, the myocardium of Restricted rats maintained the capability of responding to isoproterenol as that of Fed rats, the mechanism of which is at least partially mediated through maintenance of beta-adrenoceptor concentration.

Increasing BP response to PE infusion suggests improvement in vascular alpha(1)-AR signal transduction with chronic carvedilol therapy. This effect is evident despite no detectable tolerance to preinfusion BP reductions. The varying affinities of alpha(1)-AR subtypes for carvedilol and PE may have contributed to this finding.

No abstract