Effect of high carbohydrate and high protein diets on microsomal fatty acid composition, "fluidity" and delta 6 desaturation activity in kidney and lung.

High carbohydrate and high protein diets administered to rats for only three days decreased and increased, respectively, the arachidonate/linoleate ratio (20:4 n6/18:2 n6) in total lipids of lung, kidney, and liver microsomes. In liver and kidney this correlated with a significant decrease in the first dietary condition, and with an increase in the second, of delta 6 desaturase activity, measured by the rate of conversion of 1-14C linoleate n6 to 1-14C linolenate n6. Such an enzymatic activity was not detectable in lung microsomes, probably because of the low capacity of this tissue to produce the coenzyme A ester of the substrate used, since in lung the effects of dietary manipulation on the 20:4/18:2 ratios were as large as in liver. Significant differences were observed in microsomes of the three tissues examined in the steady state fluorescence anisotropy (rs) of diphenylhexatriene, which correlated with their cholesterol/phospholipid ratios. Both were lower in microsomes from liver than from the other two tissues, and both remained unchanged in each tissue under the dietary regimens studied. The results indicate that the observed effects of high carbohydrate and high protein diets on fatty acid delta 6 desaturation activity do not lead to apparent alterations in the physical properties of microsomal membranes.