The Effects of Sex Steroids on Plasma Levels of Marker Proteins of Endothelial Cell Functioning

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Abstract
We studied thirteen male-to-female (M→F) and ten female-to-male (F→M) transsexuals who, for four months, received cross-sex treatment with, respectively, ethinylestradiol and cyproterone acetate, and with testosterone esters. We assessed the effects of treatment on plasma levels of tissue-type plasminogen activator (tPA), von Willebrand factor (vWF), vWF-propeptide (vWF:AgII) and bigendothelin-1 (big-ET-1), four proteins that are markers of endothelial cell functioning. We also measured urokinase-type PA (uPA) and plasminogen activator inhibitor-type 1 (PAI-1), which may not be endothelium-derived but share major clearance pathways with tPA. In M→F transsexuals, mean plasma levels of tPA (minus 4.4 ng/ml), big-ET-1 (minus 0.8 pg/ml), uPA (minus 0.5 ng/ml) and PAI-1 (minus 26 ng/ml) decreased (all Ps ≤0.02). The level of vWF increased (plus 24%; P = 0.005), while vWF:AgII did not change (P = 0.49). In F→M transsexuals, levels of big-ET-1 increased (plus 0.4 pg/ml; P = 0.02), while tPA, uPA and PAI-1 did not change (all Ps >0.25). In this group vWF decreased (minus 14%; P = 0.06), but vWF:AgII did not change (P = 0.38). Estrogens and androgens have clear effects on plasma levels of endothelial marker proteins. The mechanisms behind these effects are complex and appear to involve both altered secretion (big-ET-1) and processing and/or clearance (vWF and possibly tPA). Therefore, effects of hormones on the levels of endothelial marker proteins do not necessarily reflect changes in endothelial cell functioning, at least with regard to changes in vWF level associated with the oral administration of high doses of ethinylestradiol and cyproterone acetate to healthy men and the parenteral administration of testosterone to healthy women.

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