Journal of Lipid Research, Vol 23, 428-436, Copyright © 1982 by Lipid Research, Inc.
Triacylglycerol turnover in large and small rat adipocytes: effects of lipolytic stimulation, glucose, and insulin
JM May
Rates of lipolysis and reesterification were determined under various
conditions in adipocytes from epididymal fat pads of old, spontaneously
obese rats and compared to cells from younger, leaner animals. No
differences were observed in lipolytic responsiveness to several
concentrations (2--50 microM) of the beta-adrenergic agent ritodrine
compared to cells from younger, leaner rats. The large cells showed
diminished rates of lipolysis, reesterification, and glyceride-glycerol
synthesis from glucose of a submaximal but not maximal insulin
concentrations, probably reflecting decreased large cell receptor numbers.
In both cell types reesterification measured in the presence of ritodrine
progressively rose with increasing concentrations of glucose in the medium.
At each glucose concentration (0.5--25 mM) rates of reesterification were
similar in each cell type. When maximal concentrations of insulin (5 nM)
were also added, at low glucose concentrations (less than 5 mM) there was a
similar increase in reesterification in large and small cells. No insulin
effect in either cell type was observed at high concentrations of glucose.
Although fatty acid synthesis from glucose in the large cells was markedly
diminished, glyceride-glycerol synthesis was well maintained, correlating
well with calculated reesterification rates. In fact, reesterification was
found to be quantitatively very important in determining total
triacylglycerol turnover in both cell types. High rates of reesterification
might not only allow maintenance of triacylglycerol stores, but could also
increase metabolic sensitivity to changes in hormonal or substrate
concentrations.