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

Abstract

1. Male, female and castrated rats treated with oestradiol (30mug./week) or testosterone (2mg./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. 2. Between the second and third 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 oestradiol caused a significant rise in plasma phospholipids and triglycerides as compared with testosterone-treated animals. 3. During the first 2 weeks of the deficiency, linoleic acid in the plasma lipids of all groups decreased to low concentrations and changed very little thereafter. 4. Female rats maintained higher percentages and concentrations of arachidonic acid and stearic acid in plasma phospholipids and arachidonic 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. 5. Oestradiol-treated rats had concentrations of cholesteryl and phospholipid arachidonate comparable with those of female rats and higher than the testosterone-treated group. Eicosatrienoic acid in the oestradiol-treated rats was high and resembled that of the male rats, apparently because of the higher concentration of plasma phospho lipids in this group. 6. 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. 7. These sex differences appear to be related to the smaller size of the female rat and to a more direct influence of oestradiol on the formation or maintenance of phospholipids rich in arachidonic acid.

Fatty acid composition of serum phospholipid of premenopausal women and postmenopausal women receiving and not receiving hormone replacement therapy

“…While a specific mechanism for increased 20:3n-6 concentrations with oral estrogen use is unknown, it has been suggested that estrogen may increase the biosynthesis of AA from LA. 1,2,4 The results from the present studies do not show significant increases in AA in serum phospholipid, but there was a tendency (P = 0.064) in study B for increased AA levels in the women receiving HRT as compared with women not receiving HRT. The higher level of AA/LA seen in study B, which was also nonsignificantly higher in study A, provides some support for the possibility of increased AA synthesis with oral estrogen use.…”

“…I nfluences of hormone replacement therapy (HRT) on fatty acid compositions of various plasma and serum lipids have been investigated previously, [1][2][3][4][5] but most of this research failed to examine the n-3 polyunsaturated fatty acid (PUFA) levels in serum phospholipid. Levels of n-3 PUFA in serum phospholipid as a physiological biomarker are important as eicosapentaenoic acid (EPA, 20:5n-3), docosapentaenoic acid (DPA, 22:5n-3), and docosahexaenoic acid (DHA, 22:6n-3) have been inversely associated with myocardial infarction and coronary heart disease (CHD) risk.…”

Sex Differences in n-3 and n-6 Fatty Acid Metabolism in EFA-Depleted Rats

“…Female rats retain higher levels of 20:4n-6 (arachidonic acid, AA) in tissues during EFA deficiency (3,7). Female sex hormones may facilitate the conversion of 18:2n-6 (linoleic acid, LA) to AA (7,8).…”

“…Male animals are generally more susceptible than female animals to essential fatty acid (EFA) deficiency (1)(2)(3)(4)(5)(6)(7)(8). Female rats retain higher levels of 20:4n-6 (arachidonic acid, AA) in tissues during EFA deficiency (3,7).…”

Effects of testosterone and estradiol on prostaglandin E synthesis by rat kidney medulla.

“…2). However, a con sistently higher level of arachidonic acid, a precursor of PG's, has been found in female rats, not only in tissues such as liver and heart but also in the plasma (10,11). Moreover, it is generally considered that tissue levels of PG's are regulated by the availability of their precursors, and PG synthesis is initiated by the release of free precursors from phospholipids or triglycerides (12).…”