Raloxifene relaxes rat pulmonary arteries and veins: Roles of gender, endothelium, and antagonism of Ca²⁺ influx

Effects of raloxifene have been documented in the systemic circulation. However, its impact on the pulmonary circulation is unclear. The present study investigated the role of gender, endothelial modulation, and Ca²⁺ channel in relaxations evoked by raloxifene in rat pulmonary arteries and veins. Vascular responses were studied on isolated pulmonary blood vessels mounted in a myograph and constricted by U46619 (9,11-dideoxy-11α,9α- epoxymethanoprostaglandin F_2α). Constrictions to CaCl ₂ were studied in Ca²⁺-free, 60 mM K⁺ solution. Changes in the intracellular calcium ion concentration ([Ca²⁺] _i) in vascular smooth muscle were measured using a calcium fluorescence imaging method. Raloxifene was more effective in relaxing U46619-constricted pulmonary arteries from male than female rats. Raloxifene-induced relaxation was unaffected by ICI 182,780 [7α-[9-[(4,4, 5,5,5,-pentafluoropentyl)-sulfinyl]nonyl]-estra-1,3,5(10)-triene-3, 17β-diol], inhibition of the nitric oxide (NO) pathway, or removal of the endothelium. In arteries without endothelium, raloxifene attenuated CaCl ₂-induced constriction and CaCl₂-stimulated increase in [Ca²⁺]_i with similar potencies. Raloxifene caused endothelium-independent relaxations in pulmonary veins, albeit to a lesser degree than in pulmonary arteries. The venous responses showed a gender difference because raloxifene was more potent in male veins. In summary, raloxifene relaxed rat pulmonary arteries, and this effect did not involve the endothelium/NO or ICI 182,780-sensitive estrogen receptors. Raloxifene, like nifedipine, reduced constriction and [Ca²⁺]_i increase in response to CaCl₂ in high K⁺ solution. Raloxifene also relaxed high K⁺-constricted pulmonary veins. Our data indicate that raloxifene acutely relaxes rat pulmonary blood vessels primarily via inhibition of Ca²⁺ influx through voltage-sensitive Ca²⁺ channels. Finally, raloxifene induced more relaxation in blood vessels isolated from male than female rats. Copyright © 2005 by The American Society for Pharmacology and Experimental Therapeutics.