Long and very long chain polyunsaturated fatty acids of the n-6 series in rat seminiferous tubules. Active desaturation of 24:4n-6 to 24:5n-6 and concomitant formation of odd and even chain tetraenoic and pentaenoic fatty acids up to C32.
The formation of long and very long chain (VLC) n-6 polyunsaturated fatty acids (PUFA) in isolated rat seminiferous tubules was investigated by following the metabolism of three 1-14C-labeled n-6 tetraenoic fatty acids (20:4, 24:4, and 32:4) and [U-14C]acetate. In contrast to [14C]32:4, which was poorly incorporated and altered, [14C]20:4 and [14C]24:4 were efficiently taken up by the tubules, esterified into lipids, elongated to VLCPUFA, and desaturated to pentaenoic fatty acids; the rate of [14C]24:4 desaturation to [14C]24:5 was notably high. The main products with [14C]acetate as precursor were labeled saturates and VLCPUFA, most of the label in tetraenoic and pentaenoic acids appearing in 24:4 and 24:5, respectively. These two C24 polyenes, connected by a delta 6 desaturation, may play a central role in n-6 PUFA metabolism, in their capacity as potential precursors of longer polyenes via elongation and of shorter ones, such as 22:5n-6, via retroconversion. Triacylglycerols, rich in C22 and C24 polyenes, incorporated the greatest amounts of both [14C] acetate-derived and exogenous 14C-PUFA, suggesting that this lipid class is involved in the traffic and metabolism of testicular PUFA. The detection of a series of unusual odd-chain tetraenoic and pentaenoic acids, also labeled with [U-14C]acetate, suggests that a PUFA chain shortening mechanism occurs in testis involving alpha- in addition to beta-oxidation. We speculate that alpha-oxidation plays a role in the retroconversion of PUFA.
Department of Chemical Pathology, Adelaide Children's Hospital, South Australia.
M I
MI
Aveldaño
B S
BS
Robinson
D W
DW
Johnson
A
A
Poulos
D000085:Acetates / Q000378:metabolism; D019342:Acetic Acid; D000818:Animals; D016718:Arachidonic Acid / Q000378:metabolism; D002250:Carbon Radioisotopes; D002851:Chromatography, High Pressure Liquid; D002855:Chromatography, Thin Layer; D005227:Fatty Acids / Q000378:metabolism; D005230:Fatty Acids, Nonesterified / Q000096:biosynthesis / Q000302:isolation & purification / Q000378:metabolism*; D005231:Fatty Acids, Unsaturated / Q000378:metabolism; D005989:Glycerides / Q000302:isolation & purification / Q000378:metabolism; D007700:Kinetics; D008297:Male; D010743:Phospholipids / Q000302:isolation & purification / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D012671:Seminiferous Tubules / Q000378:metabolism*
D000085:Acetates; D002250:Carbon Radioisotopes; D005227:Fatty Acids; D005230:Fatty Acids, Nonesterified; D005231:Fatty Acids, Unsaturated; D005989:Glycerides; D010743:Phospholipids; D016718:Arachidonic Acid; C065411:tetracosatetraenoic acid; D019342:Acetic Acid