Estrogen increases smooth muscle expression of α_2C- 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 α_2C-adrenoceptors (α_2C-ARs) located on vascular smooth muscle cells (VSMs). Experiments were therefore performed to determine whether 17β-estradiol regulates α_2C-AR expression and function in cutaneous VSMs. 17β-Estradiol (0.01-10 nmol/l) increased expression of the α_2C-AR protein and the activity of the α_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 17β-estradiol was associated with increased accumulation of cAMP and activation of the cAMP-responsive Rap2 GTP-binding protein. Transient transfection of VSMs with a dominant-negative mutant of Rap2 inhibited the 17β-estradiol-induced activation of the α_2C-AR gene promoter, whereas a constitutively active mutant of Rap2 increased α_2C-AR promoter activity. The effects of 17β-estradiol were inhibited by the estrogen receptor (ER) antagonist, ICI-182780 (1 μmol/l), and were mimicked by a cell-impermeable form of the hormone (estrogen:BSA) or by the selective ER-α receptor agonist 4,4′,4″-(4-propyl-[1H]-pyrazole-1,3,5-triyl)trisphenol (PPT; 10 nmol/l) or the selective ER-β receptor agonist 2,3-bis(4-hydroxyphenyl)- propionitrile (DPN; 10 nmol/l). Therefore, 17β-estradiol increased expression of α_2C-ARs by interacting with cell surface receptors to cause a cAMP/Rap2-dependent increase in α_2C-AR transcription. In mouse tail arteries, 17β-estradiol (10 nmol/l) increased α_2C-AR expression and selectively increased the cold-induced amplification of α₂-AR constriction, which is mediated by α_2C-ARs. An estrogen-dependent increase in expression of cold-sensitive α_2C-ARs may contribute to the increased activity of cold-induced vasoconstriction under estrogen-replete conditions.