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
