The lipoprotein lipase activity of brown adipose tissue during early post-natal development of the normal and hypothyroid rat.

The heparin-releasable LP lipase activity of BAT (brown adipose tissue), and the TG (triglyceride) content of plasma were determined in normal and hypothyroid rats during early post-natal development. The TG content of plasma increased sharply after the onset of suckling and decreased during the weaning period in normal rats, while it stayed at a high level in hypothyroid rats. LP lipase activity was maximal during the perinatal period and decreased later, being practically undetectable in one month old control animals; in contrast, LP lipase activity was still present in cretin rats at this age. The effects of several forms of treatment were also tested in weaned rats: a high-fat diet was not able to maintain the high LP lipase activity of suckling rats, but the activity was high if the animals were bred at a cold temperature. Thyroxine injections had no effect. These results are discussed in terms of the possible factors regulating the LP lipase activity in BAT.