Journal of Lipid Research, Vol 21, 149-155, Copyright © 1980 by Lipid Research, Inc.
Control of endogenous triglyceride breakdown in the mouse diaphragm
NA Abumrad, HM Tepperman and J Tepperman
The control of endogenous triglyceride breakdown was studied in vitro, in
the incubated intact mouse diaphragm. Isoproterenol (2 microgram/ml)
produced parallel increases in glycerol and free fatty acid release, and in
tissue cyclic AMP levels, suggesting that cyclic AMP mediates the action of
the catecholamine on triglyceride mobilization. In addition to cyclic AMP,
calcium seems to be involved in the action of isoproterenol because
preincubation of hemidiaphragms in the presence of the calcium ionophore
A23187 decreased the lipolytic effect of the drug. Insulin (12.5 mU/ml)
antagonized the action of isoproterenol on triglyceride breakdown (it
decreased glycerol and free fatty acid release) without altering its
stimulatory effect on cyclic AMP levels. On the other hand, no detectable
effect on lipolysis was observed with carbachol in control and denervated
hemidiaphragms, although the latter possess acetylcholine receptors over
the entire surface area of the muscle. It was concluded that catecholamines
control triglyceride breakdown in muscle while the cholinergic system does
not seem to be involved. Cyclic AMP, calcium, and insulin all affect
lipolysis in muscle and the interrelationships remain to be elucidated.