Raloxifene relaxes rat intrarenal arteries by inhibiting Ca²⁺ influx

Abstract

Raloxifene may confer vascular benefits without causing estrogen-related side effects. However, its action on renal vascular circulation is unknown. This study aimed to examine the sex difference and roles of the endothelium and Ca 2ϩ channels in rat renovascular relaxation to raloxifene. On isolated intralobar renal artery rings mounted in a myograph and contracted by U-46619, concentration-relaxation curves were constructed for raloxifene and contractions to CaCl 2 were studied. Changes in intracellular Ca 2ϩ concentration levels ([Ca 2ϩ ]i) of vascular smooth muscle (VSM) were measured by fura 2 fluorescence. Raloxifene or 17␤-estradiol was equally effective in relaxing renal arteries from both sexes, with raloxifene being more potent than 17␤-estradiol. Endothelial denudation did not affect raloxifene-or 17␤-estradiol-induced relaxation. N G -nitro-L-arginine methyl ester, charybdotoxin plus apamin, indomethacin, or ICI-182, 780 did not modify the effect of raloxifene. Raloxifene caused similar relaxations in rings contracted by U-46619 and high K ϩ . Nifedipine attenuated the potency of raloxifene. Raloxifene reduced CaCl 2-induced contractions. K ϩ (80 mM) stimulated an increase in VSM [Ca 2ϩ ]i, and raloxifene attenuated this effect. Raloxifene-induced reduction of contraction and increase in VSM [Ca 2ϩ ]i were insensitive to ICI-182, 780. In summary, raloxifene causes relaxation in rat renal arteries; this effect is independent of a functional endothelium and is not mediated by ICI 182, 780-sensitive estrogen receptors. Raloxifene inhibited both contractions and VSM [Ca 2ϩ ]i in response to CaCl2, indicating that raloxifene relaxes rat renal arteries primarily through inhibiting Ca 2ϩ influx via Ca 2ϩ channels. There is little sex difference in raloxifeneinduced relaxation.17␤-estradiol; relaxation; rat renal artery SEX-RELATED DIFFERENCES IN the risk for cardiovascular diseases are generally recognized (1). In pooled analysis, observational studies report that hormone replacement therapy (HRT) reduced the primary risk of cardiovascular disease in healthy menopausal women (27). Despite this evidence, the results from recent randomized clinical trials of HRT for primary or secondary prevention of heart disease have found no overall therapeutic benefit (12,20). Instead, HRT resulted in higher incidences of strokes, heart attacks, and thrombosis (20), although the precise mechanism is unknown. Thus conventional HRT is no longer suitable for prevention of cardiovascular disease (19). Therefore, in recent years, a surge of research has focused on more selective agents that retain beneficial properties of estrogen in bone, lipids, and the cardiovascular system but with antiestrogenic activity in the breast and uterus. Such unique compounds are categorized as selective estrogen receptor modulators (SERMs). SERMs manifest selective agonistic or antagonistic activities in a multitude of estrogen target tissues. Although some SERM members have been known for decades, their tissue specificity has only recen...

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