Adipocyte responses to adrenaline and insulin in active and former sportsmen

Regional differences in adipose tissue metabolism between sedentary and endurance-trained women

Subcutaneous (subc) abdominal and femoral adipose tissue metabolism was studied in sedentary and endurance-trained premenopausal women. Both fat cell weight and lipoprotein lipase (LPL) activity were lower in the subc abdominal depot of trained women compared with controls. Epinephrine- and isoproterenol-stimulated lipolytic responses, as well as the beta-adrenergic sensitivity of subc abdominal adipocytes, were higher in trained than in sedentary women, whereas both the antilipolytic effect of brimonidine (UK-14304) and the alpha 2-adrenoceptor sensitivity were lower in endurance-trained than in sedentary subjects. Maximal lipolysis in the presence of postadrenoceptor agents was also enhanced in subc abdominal adipose cells of trained women compared with sedentary controls. Negative relationships were found between maximal lipolytic responses of subc abdominal fat cells to catecholamines or to postreceptor agents and body fatness as well as abdominal fat distribution indexes. It is concluded that 1) endurance-trained women are characterized by a preferential lipid mobilization from the subc abdominal fat depot, and 2) differences in the metabolic characteristics of subc abdominal adipocytes between trained and sedentary women may involve changes in both LPL activity and the lipolytic cascade that include modifications at receptor and postreceptor levels. However, these alterations appear to be largely resulting from the reduced adipose cell size rather than from exercise training per se.

Effect of training on epinephrine-stimulated lipolysis determined by microdialysis in human adipose tissue

Trained humans (Tr) have a higher fat oxidation during submaximal physical work than sedentary humans (Sed). To investigate whether this reflects a higher adipose tissue lipolytic sensitivity to catecholamines, we infused epinephrine (0.3 nmol.kg-1.min-1) for 65 min in six athletes and six sedentary young men. Glycerol was measured in arterial blood, and intercellular glycerol concentrations in abdominal subcutaneous adipose tissue were measured by microdialysis. Adipose tissue blood flow was measured by 133Xe-washout technique. From these measurements adipose tissue lipolysis was calculated. During epinephrine infusion intercellular glycerol concentrations were lower, but adipose tissue blood flow was higher in trained compared with sedentary subjects (P < 0.05). Glycerol output from subcutaneous tissue (Tr: 604 +/- 322 nmol.100 g-1.min-1; Sed: 689 +/- 203; mean +/- SD) as well as arterial glycerol concentrations (Tr: 129 +/- 36 microM; Sed: 119 +/- 56) did not differ between groups. It is concluded that in intact subcutaneous adipose tissue epinephrine-stimulated blood flow is enhanced, whereas lipolytic sensitivity to epinephrine is the same in trained compared with untrained subjects.