Hormonal regulation of lipoprotein lipase in adipose tissue (studies in the rat and in humans)

Current data strongly suggest the most important role for insulin in the hormonal regulation of adipose tissue LPL activity. It is not clear from the literature what the role is of glucocorticoids in the regulation of the enzyme. Stress hormones as ACTH and adrenalin for example seem to decrease LPL activity or to have no effect at all on the enzyme. One of the reasons for difficulties in interpreting the data obtained so far is the fact that different methods were used to measure LPL activity. Another point is, that biological enzyme activities are measured in vitro, so that one is not informed on what really happens in vivo. We have focussed our attention to the influence of physiologically circulating glucocorticoids, ACTH and insulin on LPL activity in rats. Aims of the study were: - which role have steroid and peptide hormones in the regulation of adipose tissue LPL? - to what degree reflects the adipose tissue LPL activity measured in vitro that prevailing in situ? - what is the balance of in- and efflux of fatty acids in/from adipose tissue under various conditions? - What is the influence of α- and β-adrenergic antagonists on adipose tissue LPL and plasma lipoproteins? In chapter VIII the effects of antagonists of catecholamines on lipoproteins and lipolytic enzymes in post-heparin plasma of humans is shown and discussed. To study the effects of changes in LPL activity in situ on triglyceride metabolism in rats (in different states) the epididymal fat pad was selectively perfused with labeled chylomicrons and VLDL.