Delta-6 desaturase activity and gene expression, tissue fatty acid profile and glucose turnover rate in hereditary hypertriglyceridemic rats.
OBJECTIVE
We have shown previously that the impaired insulin action in hereditary hypertriglyceridemic (hHTg) rat is accompanied by a specific fatty acid (FA) profile in the insulin target tissues, possibly due to a desaturation defect. Thus, the aim of this study was to measure the enzymatic activity and gene expression of delta-6 desaturase in liver of hHTg rats and the tissue FA composition in relation to insulin action.


METHODS
Glucose, triglycerides and insulin in plasma were measured using commercially available enzymatic sets. The hepatic delta-6 desaturase activity in hHTg rats was determined radiometrically in a microsomal fraction using the 1-14C-linoleic acid as substrate. delta-6 Desaturase gene expression was measured by the Northern blot technique using a specific cDNA probe. Tissue FA profile was determined by gas chromatography in the total lipid fraction extracted to chloroform. The glucose turnover rate was measured in conscious freely moving animals with the aid of euglycemic hyperinsulinic clamp method.


RESULTS
Tissue triglycerides showed a high accumulation in skeletal muscle of hHTg rats. In the liver of these animals, a defect in delta-6 desaturase enzymatic activity was found, while the gene expression for delta-6 desaturase was not changed. Such decreased delta-6 desaturase activity in the liver was linked to a decrease of delta-6 desaturase index as calculated from the liver FA composition. Also the concentration of arachidonic acid (a final metabolite in the biosynthesis of polyunsaturated fatty acids of the n-6 series) was significantly decreased in hHTg rat liver. These changes in FA metabolism were accompanied by a decreased glucose infusion rate (a measure of in vivo insulin action) required to maintain euglycemia at hyperinsulinemia in hHTg rats, and correlated with the hepatic delta-6 desaturase activity.


CONCLUSIONS
1. hHTg rats showed a reduced activity of the delta-6 desaturase in liver without any changes in gene expression for this enzyme; 2. such impairment is accompanied by a lower delta-6 desaturase index (18:2n-6/18:3n-6) found in the liver of these animals and by specific FA profiles in the tissues, particularly regarding the amount of long-chain PUFAs and 18:2n-6 metabolites; and (4) these alterations seem to be related to the impaired insulin action of hHTg rats.
Demcakova
E
E
Institute of Experimental Endocrinology, Slovak Academy of Science, Vl rska 3, 833 06 Bratislava, Slovak Republic.
Sebokova
Ukropec
J
J
Gasperikova
D
D
Klimes
I
I
D000818:Animals; D001786:Blood Glucose / Q000378:metabolism*; D015152:Blotting, Northern; D044943:Fatty Acid Desaturases / Q000235:genetics* / Q000378:metabolism*; D005227:Fatty Acids / Q000032:analysis*; D015870:Gene Expression; D015309:Glucose Clamp Technique; D015228:Hypertriglyceridemia / Q000201:enzymology* / Q000235:genetics* / Q000378:metabolism; D007328:Insulin / Q000097:blood; D019787:Linoleic Acid / Q000032:analysis / Q000378:metabolism; D050602:Linoleoyl-CoA Desaturase; D008099:Liver / Q000737:chemistry; D008297:Male; D008862:Microsomes, Liver / Q000201:enzymology; D018482:Muscle, Skeletal / Q000737:chemistry; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D017208:Rats, Wistar; D014280:Triglycerides / Q000032:analysis / Q000097:blood; D017965:gamma-Linolenic Acid / Q000032:analysis
D001786:Blood Glucose; D005227:Fatty Acids; D007328:Insulin; D012333:RNA, Messenger; D014280:Triglycerides; D017965:gamma-Linolenic Acid; D019787:Linoleic Acid; D044943:Fatty Acid Desaturases; D050602:Linoleoyl-CoA Desaturase