Circadian Rhythm and Hormonal Sensitivity of Lipoprotein Lipase Activity in Cold Acclimated Rats

Abstract

To delineate the factors that may affect triglyceride capture in brown adipose tissue, we have determined the lipoprotein lipase activity (LPL) under conditions known to modulate this activity in other tissues. Acclimation temperature (28°C or 5°C) had no effect on circadian variations of white adipose tissue and heart LPL activity. LPL activity in brown adipose tissue of 28°C rats was similar to that in white adipose tissue (peak activity between 21:00 and 07:00 h), whereas LPL activity of the former was four times higher in 5°C rats and rhythmicity was altered (peak activity at 17:00 h as for heart). Brown adipose tissue LPL activity was increased in 28°C rats but not in 5°C rats after a single injection of insulin to fasting animals. A single injection of dexamethasone increased brown adipose tissue LPL activity only in 5°C rats, whereas enzyme activity was increased in both 28°C and 5°C rats by a single injection of norepinephrine to fed animals. These variations were discussed with relation to the role of brown adipose tissue at 5°C and 28°C.