Journal of Lipid Research, Vol. 7, 692-697, September 1966
Copyright © 1966 by Lipid Research, Inc.

Metabolism of phytol-U-¹⁴C and phytanic acid-U-¹⁴C in the rat

Charles E. Mize , Joel Avigan , James H. Baxter , Henry M. Fales , and Daniel Steinberg

Laboratory of Metabolism, National Heart Institute, National Institutes of Health, Bethesda, Maryland

The metabolism of uniformly-labeled ¹⁴C-phytol, ¹⁴C-phytenic acid, and ¹⁴C-phytanic acid was studied in the rat. Conversion of both phytol and phytenic acid to phytanic acid was demonstrated. Tracer doses of phytol-U-¹⁴C given orally were well absorbed (30-66%), and approximately 30% of the absorbed dose was converted to ¹⁴CO₂ in 18 hr. After intravenous injection, 20% appeared in ¹⁴CO₂ in 4 hr. Phytanic acid-U-¹⁴C given intravenously was oxidized at a comparable rate (22-37% in 4 hr) and was as rapidly oxidized as palmitic acid-1-¹⁴C (21% in 4 hr).

Metabolism of these substrates was also studied in rats previously maintained on a diet containing 5% phytol by weight, which causes accumulation of phytanic acid, phytenic acid, and, to a lesser extent, phytol in blood and tissues. Despite the large body pools of preformed, unlabeled substrate in these animals, the fraction of an administered dose of phytol-U-¹⁴C or phytanic acid-U-¹⁴C converted to ¹⁴CO₂ was not significantly diminished. These studies indicate that the rat has an appreciable capacity to degrade the highly branched carbon skeleton of phytol and its derivatives.

Twenty-four hours after administration of phytol-U-¹⁴C, the lipid radioactivity remaining in the body was widely distributed among the tissues, highest concentrations being found in liver and adipose tissue. Four hours after intravenous administration of phytanic acid-U-¹⁴C, all of the major lipid classes in the liver contained radioactivity, most in triglycerides and phospholipids and least in cholesterol esters and lower glycerides. There was no demonstrable incorporation of mevalonate-2-¹⁴C or acetate-1-¹⁴C into liver phytanic acid when they were given intravenously to a rat previously fed phytol. Endogenous biosynthesis, if it occurs at all, must be extremely limited.

Supplementary key words phytol-U-¹⁴C • phytanic acid-U-¹⁴C • phytenic acid-U-¹⁴C • absorption • metabolism • oxidation • incorporation • lipid classes • tissue distribution • rat • branched-chain fatty acids and alcohols • dihydrophytol-2,3-³H • Refsum's disease

Submitted on March 21, 1966
Accepted on June 14, 1966

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