ISSN:
1432-0428
Keywords:
Adipocytes
;
acipimox
;
lipolysis
;
cyclic AMP
;
cyclic AMP-dependent protein kinase
;
hormone-sensitive lipase
;
enzyme translocation
;
insulin
Source:
Springer Online Journal Archives 1860-2000
Topics:
Medicine
Notes:
Summary Acipimox is commonly used to treat hyper-triglyceridaemia in non-insulin-dependent diabetic patients, but its precise mechanism of action has yet to be elucidated. We examined the in vitro effects of acipimox on the lipolytic regulatory cascade in epididymal adipocytes isolated from Wistar rats. Acipimox inhibited the lipolytic rate stimulated by adenosine deaminase (1 U/ml) in a concentration-dependent manner, reaching a near-basal value at 10 Μmol/l acipimox. Lipolysis activated by sub-maximal levels of isoproterenol in combination with adenosine deaminase (20 mU/ml) was significantly (p〈0.05) decreased by 100 Μmol/l acipimox, whereas, in the absence of adenosine deaminase, 100 Μmol/l acipimox showed no significant (p〉0.05) inhibition. These findings suggested that the anti-lipolytic mechanism regulated by adenosine may also be regulated by acipimox. Acipimox diminished the intracellular cyclic AMP level produced by 25 nmol/l isoproterenol in the presence of adenosine deaminase (20 mU/ml) in a concentration-dependent manner. At the same level of stimulation, acipimox inhibited the cyclic AMP-dependent protein kinase activity ratio and lipolytic rate over the same concentration range, with significant (p〈0.05) reductions occurring at and above, 0.5 Μmol/l and 10 Μmol/l acipimox, respectively. Western blotting showed that upon lipolytic stimulation (1 U/ml adenosine deaminase; 100 nmol/l isoproterenol) a threefold increase in the lipolytic rate was accompanied by a significant (p〈0.05) rise in hormone-sensitive lipase associated with the lipid fraction. Acipimox (1 mmol/l) and insulin (1 nmol/l) re-distributed hormone-sensitive lipase back to the cytosol, with a corresponding significant (p〈0.05) loss from the fat cake fraction of adipocyte homogenates. In conclusion, the anti-lipolytic action of acipimox is mediated through suppression of intracellular cyclic AMP levels, with the subsequent decrease in cyclic AMP-dependent protein kinase activity, leading to the reduced association of hormone-sensitive lipase with triacylglycerol substrate in the lipid droplet of adipocytes.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00400412
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