Lipolytic and Cardiac Responses to Various Forms of Stress in Humans

Abstract

The lipolytic and the cardiac responses to 30 min of two different forms of stress - a standardized mental stress test and submaximal bicycle exercise - were investigated in non-obese healthy subjects. This was done by micro-dialysis of the extracellular space in the abdominal subcutaneous adipose tissue in order to determine lipolysis and electrocardiographic recordings of the heart rate. Glycerol concentrations (lipolysis index) in venous plasma and in adipose tissue dialysate as well as plasma catecholamines and determinations of the heart rate showed marked increases during mental stress (p < 0.001) and physical exercise (p < 0.001), but the patterns of response differed during the two forms of stress. All parameters rose gradually during exercise and decreased continuously in the post-exercise period. During mental stress, however, all parameters peaked within the first 20 min of stimulation and then remained at the same level until after the stress period, when they gradually declined. The maximal increase of glycerol in plasma and adipose tissue during mental stress correlated with the corresponding increase during exercise (r = 0.50-0.60). Such a relationship was not observed with plasma catecholamines or heart rate (r = 0.02-0.29). The peak level of plasma noradrenaline was an independent regressor for the peak levels of glycerol in plasma and adipose tissue as well as for the peak heart rate during mental stress and physical exercise (partial r from 0.35 to 0.64), while the peak level of adrenaline was a regressor for heart rate only during mental stress (partial r = 0.45), when multiple regression analysis was used. These results indicate that lipolysis in adipose tissue could be a valuable marker for the characterization of individual responses to various forms of stress. Noradrenaline contributes to lipid mobilization and cardiac activation during both physical and mental stress and the body adapts more rapidly to the later form of stress.

Key words

Fat cell - heart - glycerol - adrenaline - noradrenaline - exercise - mental stress