ABSTRACT
Fluorescence anisotropy determination were performed on hypotonically lysed red blood cells from 12 healthy, free living, premenopausal and 10 postmenopausal women fed a self-selected diet. Fatty acid composition of phospholipids and cholesterol esters, lipid/lipid and lipid/protein ratios were also determined in erythrocyte ghosts along the menstrual cycle or during hormonal replacemente therapy. The postmenopausal women were treated with transdermal 17-beta estradiol (approx. delivery rate of 50 mug/day) for a 5-week period and with a combination of percutaneous administration of estradiol and orally administered medroxyprogesterone acetate (5 mg/day) for 5 weeks more. Premenopausal women were studied in the mid-follicular and mid-luteal phases of their menstrual cycles. Membrane fluidity in cells from the luteal phase was greater than that observed in the follicular phase. After estradiol treatment, postmenopausal women exhibited a significant raise in the fluorescence anisotropy. The association with progesterone prevented the estrogen-induced increase of the anisotropy values. Estrogen administration also produced an increment in the relative content of cholesterol and membrane proteins that was reverted by progesterone addition. Changes induced by estradiol treatment in the fatty acid pattern of phospholipids and cholesterol esters were characterized by an increment in the monoenoic/saturated fatty acid ratio and linoleic relative content, with a concomitant decrease in the proportion of arachidonic and docosatetraenoic acids. These results suggest that the modification of the desaturase activities may be involved in a mechanism by which these hormonal-induced changes take place. The present study demonstrated that human erythrocyte fluidity is under hormonal control subjected through changes in the proportion and quality of the membrane lipids.