Kinetics of different 123-I and 14-C fatty acids in normal and diabetic rat myocardium in vivo

For measuring myocardial metabolism by single photon scintigraphy various iodinated substrate analogues have been proposed. The present study compares in normal and diabetic rats the metabolic pathways of 14-C-palmitic acid (PA), 123-I-para-phenylpentadecanoic acid (I-pPPDA), 123-I-ortho-phenylpentadecanoic acid (I-oPPDA), 14-C-stearic acid (SA) and 123-I-w-heptadecanoic acid (I-ωHDA). In normal and diabetic rats free fatty acids showed a rapid tracer accumulation and an initial rapid, then a slow rate component of release. PA and I-pPPDA were preferentially esterified into triglycerides, whereas SA and I-ωHDA equally distributed between triglycerides and phospholipids. I-oPPDA nearly exclusively labelled the free fatty acid pool. - Turnover of SA and I-ωHDA was similar in triglycerides and phospholipids; yet PA and I-pPPDA continued to increase in triglycerides for 3-5 minutes after injection but decreased in phospholipids. - Following induction of diabetes by Streptocotocin, the primary effect was an inhibition of incorporation of all substrates tested into triglycerides and phospholipids with an initial rapid turnover in the total lipid fraction. - Of the total myocardial activities a considerable fraction was water soluble and another bound to solid tissue residue, with an early maximum and subsequent decline; the values for 14-C-labelled substrates remained below those of radioiodine. Thus different labelled fatty acids behave metabolically differently and promise to be useful for differentiating various intracellular metabolic pathways. External analysis of myocardial fatty acids metabolism requires correction for labelled catabolites. (Author)