Estrogen increases smooth muscle expression of α2C-adrenoceptors and cold-induced constriction of cutaneous arteries

Raynaud's phenomenon, which is characterized by intense cold-induced constriction of cutaneous arteries, is more common in women compared with men. Cold-induced constriction is mediated in part by enhanced activity of alpha(2C)-adrenoceptors (alpha(2C)-ARs) located on vascular smooth muscle cells (VSMs). Experiments were therefore performed to determine whether 17 beta- estradiol regulates alpha(2C)-AR expression and function in cutaneous VSMs. 17 beta- Estradiol (0.01-10 nmol/l) increased expression of the alpha(2C)-AR protein and the activity of the alpha(2C)-AR gene promoter in human cultured dermal VSMs, which was assessed following transient transfection of the cells with a promoter-reporter construct. The effect of 17 beta-estradiol was associated with increased accumulation of cAMP and activation of the cAMP-responsive Rap2 GTP-binding protein. Transient transfection of VSMs with a dominantnegative mutant of Rap2 inhibited the 17 beta-estradiol-induced activation of the alpha(2C)-AR gene promoter, whereas a constitutively active mutant of Rap2 increased alpha(2C)-AR promoter activity. The effects of 17 beta- estradiol were inhibited by the estrogen receptor (ER) antagonist, ICI- 182780 (1 mu mol/l), and were mimicked by a cell-impermeable form of the hormone (estrogen: BSA) or by the selective ER-alpha receptor agonist 4,4', 4"-(4-propyl-[H-1]-pyrazole-1,3,5-triyl) trisphenol (PPT; 10 nmol/l) or the selective ER-beta receptor agonist 2,3-bis(4-hydroxyphenyl)-propionitrile (DPN; 10 nmol/l). Therefore, 17 beta- estradiol increased expression of alpha(2C)-ARs by interacting with cell surface receptors to cause a cAMP/ Rap2- dependent increase in alpha(2C)-AR transcription. In mouse tail arteries, 17 beta- estradiol (10 nmol/l) increased alpha(2C)-AR expression and selectively increased the cold-induced amplification of alpha(2C)-AR constriction, which is mediated by alpha(2C)-ARs. An estrogen-dependent increase in expression of cold-sensitive alpha(2C)-ARs may contribute to the increased activity of cold-induced vasoconstriction under estrogen-replete conditions.