Effects of estradiol on platelet aggregation in cerebral microvessels of mice.

Abstract

SUMMARY Mice were implanted subcutaneously with a pellet containing 0.5 mg estradiol or with a placebo. Eight to 12 days later platelet aggregation was produced in pial arterioles by injuring their endothelium in vivo with a noxious light/dye stimulus. The time between the onset of the noxious stimulus and the appearance of platelet aggregates was significantly shortened (p < .02) by estradiol treatment in young (2 month old) mice. The same treatment had the opposite effect in 4-6 month old mice and significantly delayed the onset of aggregation (p = .01). When platelet rich plasma (PRP) was prepared, aggregation by sodium arachidonate was always inhibited in PRP from estradiol treated mice, irrespective of age. Estradiol treatment had no effect on aggregation induced ex vivo by ADP. Thus the enhanced aggregation observed in pial arterioles of young estradiol treated mice may not reflect direct effects of estradiol on the platelet itself. The data are discussed in light of the literature suggesting enhancement of ischemic vascular disease, including strokes, in patients receiving estrogens, and especially high doses of estrogens.

Effects of Estrogens on Platelets and Megakaryocytes

“…A study published in 1985 has shown that mice treated by an estrogen pellet containing 0.5 mg of E2 and then submitted to a mesenteric endothelial injury exhibited a faster thrombosis response compared to the placebo group [33]. Similar results were found after a cerebral vessels injury induced by a noxious light/dye stimulus [34]. In contrast, we recently reported that a three-week high dose of E2 (200 μg/kg/day) treatment increased the tail-bleeding time, and protected animals against collagen/epinephrine-induced thromboembolism, and against injury-induced carotid artery thrombosis compared to ovariectomized or sham-operated mice [24].…”

Modulatory effects of estrogen in two murine models of experimental colitis

“…Female C57Bl/6 mice were divided into five groups (n ϭ 5-13 per group) that received 17␤-estradiol alone (0.5 mg/pellet) or with tamoxifen (5 mg/pellet), tamoxifen alone (5 mg/pellet), 17␣-estradiol (0.5 mg/pellet), or placebo via 21-day release pellets implanted subcutaneously (IRA, Sarasota, Florida). The dose of 17␤-estradiol used in this study markedly elevates the plasma hormone level in mice (ϳ1,000 pg/ml) by 7 days after implantation, and these levels remain constant for 4 wk (49,50).…”

Migraine: Possible Role of Shear‐Induced Platelet Aggregation With Serotonin Release

“…Estrogens: Fall in premenstrual levels; 110,202,203 oral anticonceptives; 204,205 hormonal replacement therapy 121…”