Rat heart cannot synthesize docosahexaenoic acid from circulating alpha-linolenic acid because it lacks elongase-2.
The extent to which the heart can convert alpha-linolenic acid (alpha-LNA, 18:3n-3) to longer chain n-3 PUFAs is not known. Conversion rates can be measured in vivo using radiolabeled alpha-LNA and a kinetic fatty acid model. [1-(14)C]alpha-LNA was infused intravenously for 5 min in unanesthetized rats that had been fed an n-3 PUFA-adequate [4.6% alpha-LNA, no docosahexaenoic acid (DHA, 22:6n-3)] or n-3 PUFA-deficient diet (0.2% alpha-LNA, nor DHA) for 15 weeks after weaning. Arterial plasma was sampled, as was the heart after high-energy microwaving. Rates of conversion of alpha-LNA to longer chain n-3 PUFAs were low, and DHA was not synthesized at all in the heart. Most alpha-LNA within the heart had been beta-oxidized. In deprived compared with adequate rats, DHA concentrations in plasma and heart were both reduced by >90%, whereas heart and plasma levels of docosapentaenoic acid (DPAn-6, 22:5n-6) were elevated. Dietary deprivation did not affect cardiac mRNA levels of elongase-5 or desaturases Delta6 and Delta5, but elongase-2 mRNA could not be detected. In summary, the rat heart does not synthesize DHA from alpha-LNA, owing to the absence of elongase-2, but must obtain its DHA entirely from plasma. Dietary n-3 PUFA deprivation markedly reduces heart DHA and increases heart DPAn-6, which may make the heart vulnerable to different insults.
Igarashi
Miki
M
Brain Physiology and Metabolism Section, National Institute on Aging, NIH, Bethesda, MD 20892, USA. mikii@mail.nih.gov
Ma
Kaizong
K
Chang
Lisa
L
Bell
Jane M
JM
Rapoport
Stanley I
SI
D000123:Acetyltransferases / Q000172:deficiency*; D000818:Animals; D004281:Docosahexaenoic Acids / Q000378:metabolism*; D000081031:Fatty Acid Elongases; D005227:Fatty Acids / Q000097:blood; D008297:Male; D009206:Myocardium / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D011916:Rats, Inbred F344; D017962:alpha-Linolenic Acid / Q000378:metabolism*
D005227:Fatty Acids; D012333:RNA, Messenger; D017962:alpha-Linolenic Acid; D004281:Docosahexaenoic Acids; D000123:Acetyltransferases; D000081031:Fatty Acid Elongases; C531219:elongase-2, rat