Lipolytic response of adipocytes to epinephrine in sedentary and exercise-trained subjects: sex-related differences

Abstract

Adipose tissue lipolytic activity is increased in endurance-trained subjects, but little is known about the mechanisms of this increase. To understand more fully the mechanisms involved and to discover whether sex-related differences exist, biopsies of fat were performed in the periumbilical region of 20 sedentary subjects (10 women (W) and 10 men (M)) and 20 trained subjects (10 W, 10 M); the in vitro response to epinephrine of the collagenase-isolated fat cells was studied. Glycerol release, chosen as an adipocyte lipolysis indicator, was measured by bioluminescence. Dose-response curves with epinephrine (alpha 2 and beta agonist), with isoproterenol (beta agonist) and epinephrine + propranolol and adenosine deaminase, were studied. Epinephrine-induced lipolysis was enhanced in trained subjects and this was due to an increased efficiency of the beta-adrenergic pathway. However, differences were found between the two sexes. In trained men, the lipolysis increase resulted from the enhancement of the beta-adrenergic pathway efficiency without any significant decrease in the alpha 2-adrenergic pathway efficiency. In trained women, the lipolysis increase was not only due to the enhancement of the beta-adrenergic pathway efficiency (which was greater than in trained men), but also to a significant decrease in the alpha 2-adrenergic pathway efficiency. Despite the decrease, the alpha 2-adrenergic pathway remained more efficient in trained women than in trained men, as was the case in sedentary subjects. It is concluded that endurance training led to better lipid mobilization and that this effect seemed greater in women than in men.

Lipolysis, lipogenesis, and adiposity are reduced while fatty acid oxidation is increased in visceral and subcutaneous adipocytes of endurance-trained rats

“…[1][2][3][4] Importantly, analyses of NEFA rate of appearance (Ra) [4][5][6] during exercise revealed that this variable was significantly reduced as a result of training, which is also in support of a reduction in WAT lipolysis with endurance training. However, at odds with these findings are the results of studies measuring catecholamine-stimulated glycerol release in isolated adipocytes from humans [7][8][9][10][11] and rats, [12][13][14][15] which report increased WAT lipolysis after a period of endurance training. Additional studies have reported lipolysis to be either reduced in isolated rat adipocytes 16 or unaltered when assessed in situ by the microdialysis technique in human WAT 17 following a period of endurance training.…”

“…In fact, there are studies in which the volume of adipocytes in endurance-trained subjects is significantly lower than sedentary controls and lipolysis is expressed per amount of lipid in each incubation. 8,9 In such cases, lipolysis values in the endurance trained condition could derive from a much higher number of fat cells than that of control sedentary adipocytes, making it difficult to establish a clear direct comparison between the conditions. Lipolysis between sedentary and endurance-trained conditions has at times been compared by incubating pieces of rat WAT instead of isolated cells, 12 which does not take into account differences in cell content in each preparation either, despite major differences in fat mass between the 2 groups.…”

Effect of gender on lipid kinetics during endurance exercise of moderate intensity in untrained subjects

“…Several studies that evaluated the direct effects of catecholamines on lipolytic activity have found that adipose tissue lipolytic sensitivity to catecholamines is similar in men and women. Studies performed in vitro in isolated human adipocytes exposed to physiological concentrations of catecholamines (10,33,35,54) and in vivo in human subjects during catecholamine infusion in conjunction with microdialysis (37) or isotope tracer methods (28) found that adipose tissue lipolytic sensitivity was similar in men and women. However, gender differences in ␣-adrenergic receptor activity may have influenced lipolytic rates during exercise.…”

Endurance training increases the β-adrenergic lipolytic response in subcutaneous adipose tissue in obese subjects

“…30 The gender-speci®c and the location-speci®c effects of training were also found in in vitro studies. 4,5,31 Therefore, it is important to note that the traininginduced modi®cations in the present study are speci®c for male subjects and for subcutaneous abdominal deposits.…”