Effect of physical training in humans on the response of isolated fat cells to epinephrine

Abstract

Endurance training helps muscle tissue oxidize lipids and therefore helps conserve glycogen. It was thought interesting to find out if, in addition to this preferential use of fatty acids by muscle tissue, there is an increase in the capacity of adipose tissue to mobilize lipids. So the response to epinephrine of collagenase-isolated fat cells obtained after biopsies of fat performed in the periumbilical region of 10 trained marathon runners (T) and 10 sedentary subjects (S), all males, was studied in vitro. Glycerol release, chosen as adipocyte lipolysis indicator, was measured by bioluminescence. Lipolysis was studied with increased epinephrine concentration. This caused a significant increase in lipolysis only in the T subjects. The dose-response curves were significantly different for T and S subjects at 10(-6) M and above (P less than 0.05). To determine the modification mechanisms observed, lipolysis with isoproterenol and epinephrine plus propranolol were studied. Isoproterenol significantly increased lipolysis in both groups. The dose-response curves were significantly different at 10(-7) M (P less than 0.01) and above. In both groups, epinephrine plus propranolol significantly decreased lipolysis without distinction between T and S. It is concluded that in male subjects endurance training increases the sensitivity of subcutaneous abdominal adipose tissue to the lipolytic action of epinephrine; this effect seems to be related to an increased response of the beta-adrenergic pathways.

Adrenergic-β2 receptor polymorphism and athletic performance

“…14 Savard et al 30 and Wahrenberg et al 31 observed a 20-35% increase in lipolysis in response to catecholamines after 30 and 90 min of aerobic exercise in healthy subjects, respectively. This is supported by the findings of Crampes et al, 55 in which endurance-trained athletes showed increased epinephrine-stimulated lipolysis in adipocytes.…”

Effect of a long-duration physical exercise on fat cell lipolytic responsiveness to adrenergic agents and insulin in obese men

“…15 This difference could be due to the much higher state of training than in our study, as it has been shown that training increases the sensitivity of adipose tissue to the lipolytic action of adrenaline. 28 In the present study, no exercise-induced changes occurred in the adipocyte response to a specific a 2 -adrenergic agonist (UK 14304). However, the a 2 -AR makes an important contribution to the physiological impairment of lipolysis in the adipose tissue of obese men.…”

“…14,15 Moreover, endurance training is reported to enhance the lipolytic activity of catecholamines in lean subjects 28,33,34 as well in obese subjects. 35,36 These two phenomena are of importance for the increase of lipid mobilization from adipose tissue during long-lasting exercises.…”

“…Four of these tubes were used for cell counting and sizing, to estimate the quantity of lipid incubated in each tube and the average cell volume, as previously described. 28 Krebs -Ringer bicarbonate buffer (20 ml) was added to another four tubes, which were immediately placed on ice. They provided an evaluation of the initial quantity of glycerol contained in the medium.…”

The effect of exercise training on β-adrenergic stimulation of fat metabolism in obese men

“…However, cross-sectional in vitro studies in lean subjects found an increased adipocyte lipolytic response in lean trained subjects compared to untrained, which could be explained by an increased badrenergic sensitivity 18,20,22 and a decreased a-adrenoceptor sensitivity. 22 On the other hand, another study found no difference in epinephrine-stimulated in situ lipolysis in adipose tissue of lean trained and untrained subjects.…”