DIFFERENTIAL EFFECTS OF OESTRADIOL AND ETHYNYL OESTRADIOL ON LIPID METABOLISM IN THE FEMALE RAT

It has recently been shown that ethynyl oestradiol markedly decreases lipase activity in the liver (Valette, Verine, Salers & Boyer, 1977). These observations, along with reports of oestrogen receptors in the liver (Chamness, Costlow & McGuire, 1975) suggest that oestrogens exert considerable influence over the hepatic metabolism of lipids. Previous investigations (DeLorimier, Gordon, Lowe & Carbone, 1965; Gallagher, Mueller & Kappas, 1966) have suggested that the extent of the hepatic changes could be correlated with the molecular nature of the hormonal compound and might depend particularly on the 17\g=a\-alkyl-substitutedgroup in synthetic oestrogens. The influence of the ethynyl function in the 17\g=a\-positionof oestradiol-17\g=b\on the oestrogen-induced changes observed in hepatic lipases and serum levels of triglycerides has therefore been examined. Adult female Sprague-Dawley rats (220-240 g) were allowed free access to food and received oestradiol-17ß or ethynyl oestradiol (6 µg) by s.c. injection in 0-1 ml olive oil daily for 21 days. Controls received olive oil alone. The animals were killed and bled by decapita¬ tion. The liver was immediately excised, rinsed and homogenized at 4 °C with three 1 min passes in a glass-Teflon homogenizer in a solution (10 ml/g) containing 0-25 M-sucrose, 2-5% glycerol and 10 mM-EDTA (pH 7-2). The homogenates were centrifuged sequentially a