Fatty acid composition of myelin lipids from developing rat forebrain and spinal cord: influence of experimental hyperphenylalaninaemia.

The fatty acid composition of individual myelin lipids from rat forebrain and spinal cord was analysed at 20 and 30 days p.p. During this phase of rapid myelination the proportions of C 16:0 and C 18:0 fatty acids decreased whereas the relative amounts of long chain and unsaturated fatty acids increased in most lipid classes. This developmental shift was more pronounced in the forebrain and was different with respect to both magnitude and direction for each myelin lipid. The experimental induction of chronic hyperphenylalaninaemia (hyper-Phe) from day 3 p.p. lead to alterations in the rate of myelination, which were most pronounced in the forebrain. At 20 days, especially in the forebrain, chain elongation and desaturation of fatty acids were delayed. This delay was maximal in sphingomyelin fatty acids, C 18:0 and C 24:1. In hydroxycerebrosides, the shift in the fatty acid composition from C 16:0 to C 22:0 was accelerated in hyper-Phe rats. No significant difference in the fatty acid composition of any myelin lipid was found in the more mature myelin (spinal cord, 30 days p.p.). No evidence was found of a primary effect of hyper-Phe on myelination.