Comparative study on the in vivo and in vitro antilipolytic effects of etofibrate, nicotinic acid and clofibrate in the rat

Treatment of lactating sows with clofibrate as a synthetic agonist of PPARα does not influence milk fat content and gains of litters

Background

In rats, it has been observed that treatment with activators of peroxisome proliferator-activated receptor α (PPARα) disturbs metabolic adaptations during lactation, which in turn lead to a reduction of milk fat content and gains of litters during the suckling period. It has not yet been investigated whether agonists of PPARα are impairing milk production of lactating sows in a similar manner as in rats. Therefore, the present study aimed to investigate the effect of treatment with clofibrate, a strong synthetic agonist of PPARα, on milk composition and litter gains in lactating sows.

Results

Twenty lactating sows received either a basal diet (control group) or the same diet with supplementation of 2 g of clofibrate per kg of diet (clofibrate group). In the clofibrate group, mRNA concentrations of various PPARα target genes involved in fatty acid utilization in liver and skeletal muscle were moderately up-regulated. Fat and energy content of the milk and gains of litters during the suckling period were not different between the control group and the clofibrate group.

Conclusion

It is shown that treatment with clofibrate induces only a moderate up-regulation of PPARα target genes in liver and muscle of lactating sows and in turn might have limited effect on whole body fatty acid utilization. This may be the reason why clofibrate treatment did not influence milk fat content and gains of litters during the suckling period. Thus, the present study indicates that activation of PPARα induced either by native agonists such as dietary polyunsaturated fatty acids or a by negative energy balance might be largely uncritical in lactating sows with respect to milk production and litter gains in lactating sows.

Triglyceridemia and peroxisome proliferator- activated receptor-α expression are not connected in fenofibrate-treated pregnant rats

To investigate the response to fenofibrate in pregnant rats, 0 mg, 100 mg or 200 mg of fenofibrate per kilogram body weight oral doses were given twice a day from day 16 of gestation and studied at day 20. Virgin rats were studied in parallel. Whereas in pregnant rats plasma triglycerides significantly increased, in virgin rats, fenofibrate decreased plasma triglycerides which accumulated in liver. Fenofibrate faithfully modulated the hepatic expression of PPARalpha responsive genes. Fenofibrate increased mRNA contents corresponding to both acyl-CoA oxidase, carnitine palmitoyltransferase (CPT), and peroxisome proliferator-activated receptor alpha (PPAR), and lowered mRNA amounts of apolipoproteins B and C-III, both in virgin and pregnant rats. However, genes related to hepatic lipogenesis, such as PPARy and stearoyl-CoA desaturase (SCD), showed an augmented expression by fenofibrate in virgin rats, but not in pregnant animals. We propose that the opposite effects of fenofibrate treatment in virgin and pregnant rats are a consequence of the enhanced capability for VLDL-triglyceride production in the latter, further promoted by the elevated amount of free fatty acids (FFA), which reach the liver in treated pregnant rats and were not sufficiently oxidized and/or stored, and therefore would have to be canalized as triglycerides to the plasma. Thus, the present study shows how fenofibrate, in spite of efficiently exerting its expected molecular effects in the liver (i.e., to induce fatty acid and lipoprotein catabolism, and to reduce TG-rich lipoprotein secretion), was unable to reverse the typical hypertriglyceridaemia of gestation.

Pantethine stimulates lipolysis in adipose tissue and inhibits cholesterol and fatty acid synthesis in liver and intestinal mucosa in the normolipidemic rat

In vitro effects of pantethine on adipose tissue lipolysis and on both hepatic and intestinal cholesterol and fatty acid synthesis in normolipidemic rats are determined and related to their respective in vivo hypolipidemic effects after acute oral administration. At 3, 5, 7 and 24 h after a single high dose of pantethine to rats, free fatty acids (FFA), cholesterol and triglycerides levels decreased whereas plasma glycerol increased, the effect becoming significant at 7 h. The release of glycerol and FFA by epididymal fat pad pieces from rats was measured in Krebs Ringer bicarbonate-albumin buffer supplemented or not with epinephrine and several concentrations of pantethine (0, 10(-5), 10(-4), or 10(-3) M), and it turned out to be enhanced as pantethine concentration increased. Besides, when glucose was present in the medium, this drug lowered fatty acid re-esterification in a dose-dependent manner, the effect being specially evident in the presence of epinephrine. In vitro synthesis of both cholesterol and fatty acids by slices of liver or intestinal epithelial cells was depressed as the concentration of pantethine increased in the medium. Thus, an inhibition of both cholesterolgenesis and lipogenesis seems to contribute to the hypocholesterolemic and hypotriglyceridemic effects of pantethine. On the other hand, the stimulation of lipolysis and the inhibition of fatty acid re-esterification on adipose tissue caused by pantethine must be counteracted by a high fatty acid oxidation in the liver which would explain the decrease in FFA and the increase in glycerol levels detected in the plasma of the pantethine-treated animals.