Effects of hormone replacement therapy on platelet membrane fatty acid composition

Abstract

Oestrogen replacement therapy has been shown to protect postmenopausal women from ischaemic heart disease, strokes and hypertension. The mechanism of protection conferred by oestrogen, although partly attributable to changes in serum lipoproteins, is not fully understood. The present study was undertaken to assess the effect of hormone replacement therapy on the composition of platelet membrane fatty acids in postmenopausal women. These were analysed by gas-liquid chromatography before and six weeks after continuous conjugated equine oestrogen therapy (0.625 mg daily) combined with cyclical therapy with 75 micrograms L-norgestrel from day 17 to 28 of a 28-day cycle. Each subject acted as her own control. The principal findings of the study were that, following treatment, there was a 16.2% reduction in platelet membrane polyunsaturated fatty acids (P < 0.001), an increase of 9.1 and 7.1% in saturated fatty acids and monounsaturated fatty acids respectively (P < 0.001) and a 17.8% reduction in arachidonic acid (P < 0.003). There was no correlation between changes in membrane fatty acids and serum lipoproteins. This suggests that the changes in membrane composition noted in this study may be a primary effect of hormone replacement therapy, especially oestrogen.

Plasma cholesteryl ester fatty acid composition, insulin sensitivity, the menopause and hormone replacement therapy

“…Fatty acid composition in platelets and plasma cholesteryl esters are often closely related (Boberg et al 1985, Salo et al 1985. However, changes in plasma CEFA composition, and particularly 20:4 n-6 levels, in postmenopausal women during HRT in the present study differed markedly from the reported HRT-induced changes in fatty acid composition in platelets (Raganath et al 1996). It is possible that activation of platelets may account for these disparate changes in fatty acid composition during HRT.…”

“…Combined HRT decreases proportions of polyunsaturated fatty acids and mainly 20:4 n-6 in platelet membranes from postmenopausal women (Raganath et al 1996). Fatty acid composition in platelets and plasma cholesteryl esters are often closely related (Boberg et al 1985, Salo et al 1985.…”

“…Hormone replacement therapy (HRT) reduces proportions of polyunsaturated fatty acids in platelet membranes in postmenopausal women (Raganath et al 1996). However, the influence of HRT on plasma cholesteryl ester fatty acid (CEFA) composition and its relationship with insulin sensitivity has not been studied.…”

Postmenopausal hormone replacement therapy increases plasmatic thromboxane β2

“…Henriksson [17] has demonstrated that there is a decrease in the formation of thromboxane in men, through the use of intra-muscular estrogen therapy in high dosages. Ranganath [18], when studying the effect of hormonal replacement therapy with equine conjugated estrogen in a cyclic scheme associated to l-norgestrel over 6 weeks, observed a reduction in the amount of arachidonic acid on platelet membrane and possibly in the formation of TxA 2 .…”

Fatty acid status of women of reproductive age

“…A sample of 135 healthy women, aged 19 ± 45 y, was recruited. Twenty-one women were excluded for the following reasons: consumption of dietary ®sh-oil or vitamin supplements, hormone replacement therapy (Ranganath et al, 1996) or incomplete data collection. Data were recorded on weight, height, residential postcode, cigarette smoking, alcohol intake, ®sh intake, physical exercise, hormonal contraception and past obstetric history (PObH).…”