Effect of sex and gonadal hormones on rat plasma lipids during the development of an essential fatty acid deficiency

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Abstract
Male, female and castrated rats treated with estradiol (30 [mu] g/week) or testosterone (2 [mu]g/week) were given an essential fatty acid-deficient diet containing 10% of hydrogenated coconut oil for 9 weeks. The concentrations and fatty acid composition of plasma phospholipids, cholesteryl esters and triglycerides were determined. Between the 2nd and 3rd weeks of the deficiency, concentrations of plasma cholesteryl esters, phospholipids and triglycerides decreased, then remained relatively constant. There were no significant differences between males and females, but estradiol caused a significant rise in plasma phospholipids and triglycerides as compared with testosterone-treated animals. During the first 2 weeks o of the deficiency, linoleic acid in the plasma lipids of all groups decreased to low concentrations and changed very little thereafter. Female rats maintained higher percentages and concentrations of arachidonic acid and stearic acid in plasma phospholipids and arachi-donic acid in cholesteryl esters than did males. Males had higher proportions of eicosatrienoic acid and oleic acid. There was no sex difference in the fatty acid composition of plasma triglycerides. Estradiol-treated rats had concentrations of cholesteryl and phospho-lipid arachidonate comparable with those of female rats and higher than the testosterone group. Eicosatrienoic acid in the estradiol rats was high and resembled that of the male rats, apparently because of the higher concentration of plasma phospholipids in this group. Supplementation of the essential fatty acid-deficient rats with linoleate restored plasma cholesteryl and phospholipid linoleate and arachidonate nearly to normal concentrations in a single day. The increase in arachidonic acid in these fractions was accompanied by a similar quantitative decrease in eicosatrienoic acid. These sex differences appear to be related to the smaller size of the female rat and to a more direct influence of estradiol on the formation or maintenance of phospholipids rich in arachidonic acid.