Comparison of the conversion rates of alpha-linolenic acid (18:3(n - 3)) and stearidonic acid (18:4(n - 3)) to longer polyunsaturated fatty acids in rats.
The delta 6-desaturase reaction is regarded to be the rate-limiting step in the conversion of linoleic acid (18:2(n - 6)) to arachidonic acid (20:4(n - 6)). The same is probably also the case with the conversion of alpha-linolenic acid (18:3(n - 3)) to eicosapentaenoic acid (20:5(n - 3)). However, there are very few in vivo studies that directly compared the conversion rate between 18:3(n - 3) and stearidonic acid (18:4(n - 3)), which is the delta 6-desaturated product of 18:3(n - 3). We compared this rate by feeding rats on a lipid-free diet supplemented with lard (9%, w/w) and 18:3(n - 3) ethyl ester (1%) diet or on a diet containing lard (9%) and 18:4(n - 3) ethyl ester (1%). A lard (10%)-supplemented diet was used as the control diet. The fatty acid compositions of total phospholipids, triglycerides and free fatty acids of both liver and plasma were measured after 1 or 3 weeks on different diets. The molar ratio of 20:5(n - 3) of most lipid fractions was about 2-fold higher in rats fed the 18:4(n - 3)-supplemented diet than in rats fed the 18:3(n - 3)-supplemented diet. 18:4(n - 3) was found in the liver lipid fraction in only a very small amount, even in the 18:4(n - 3)-supplemented groups. Thus, desaturation at C-6 is suggested to be the rate-limiting step in the conversion of 18:3(n - 3) to 20:5(n - 3).
First Department of Internal Medicine, Toyama Medical and Pharmaceutical University, Japan.
K
K
Yamazaki
M
M
Fujikawa
T
T
Hamazaki
S
S
Yano
T
T
Shono
D000818:Animals; D001835:Body Weight; D004032:Diet; D005230:Fatty Acids, Nonesterified / Q000097:blood; D015525:Fatty Acids, Omega-3 / Q000378:metabolism*; D005231:Fatty Acids, Unsaturated / Q000097:blood / Q000378:metabolism*; D007700:Kinetics; D008042:Linolenic Acids / Q000378:metabolism*; D008297:Male; D010743:Phospholipids / Q000097:blood; D051381:Rats; D011919:Rats, Inbred Strains; D017962:alpha-Linolenic Acid
D005230:Fatty Acids, Nonesterified; D015525:Fatty Acids, Omega-3; D005231:Fatty Acids, Unsaturated; D008042:Linolenic Acids; D010743:Phospholipids; D017962:alpha-Linolenic Acid; C062895:stearidonic acid