Effects of Ca⁺⁺ on Lipolysis in Human Omental Adipose Tissue In Vitro

Abstract

The influence of calcium ions on basal lipolysis as well as on lipolysis stimulated by I-noradrenaline, I-isopropylnoradrenaline, theophylline and the dibutyryl derivate of cyclic AMP in human omental adipose tissue was studied in vitro. Glycerol release was used as an index of lipolysis. Omission of calcium ions from the incubation media slightly inhibited noradrenaline-induced lipolysis. Addition of the calcium complexing agent EGTA to the incubation medium significantly suppressed basal as well as catecholamine-accelerated lipolysis, whereas lipolysis induced by theophylline and dibutyryl cyclic AMP were unaffected.

Depletion of the tissue stores of calcium, obtained by repeated washings with preincubation media containing EGTA, resulted in a significant suppression of the lipolysis with any of the stimulating agents present if calcium was not added to the incubation media.

The present results are interpreted as indicating that Ca⁺⁺ is required at two steps of the lipolytic machinery in human adipose tissue: a) for activation of the adenyl cyclase activity, and b) for activation of the hormone-sensitive lipase by cyclic AMP.

Key words

Lipolysis - Calcium Ions - Catecholamines - Adenylcyclase - Lipase