Chronic treatment of male rats with daidzein and 17 beta-oestradiol induces the contribution of EDHF to endothelium-dependent relaxation.
1. We investigated the effect of chronic (7 days) treatment of male rats with the isoflavone daidzein (0.2 mg kg(-1) sc per day) or 17beta-oestradiol (0.1 mg kg(-1) sc per day) on the contribution of nitric oxide (NO), prostaglandins and endothelium-derived hyperpolarising factor (EDHF) to endothelium-dependent relaxation of isolated aortic rings. 2. The sensitivity and maximum relaxation to acetylcholine (ACh) were significantly greater in aortic rings from rats treated with daidzein or 17beta-oestradiol, in comparison to vehicle-treated rats. Inhibition of nitric oxide synthase with N-nitro-l-arginine (l-NOARG) abolished ACh-induced relaxation in the aortae from vehicle-treated rats, but only attenuated relaxation in aortae from daidzein or 17beta-oestradiol-treated rats. The presence of haemoglobin in addition to l-NOARG did not cause any further inhibition of relaxation. 3. The cyclooxygenase inhibitor indomethacin had no effect on endothelium-dependent relaxation in aortae from any treatment group. Charybdotoxin (ChTX), which blocks large-conductance calcium-activated potassium channels (BK(Ca)) and intermediate-conductance calcium-activated potassium channels (IK(Ca)), plus apamin, which blocks small-conductance calcium-activated potassium channels (SK(Ca)), but not iberiotoxin, which only blocks BK(Ca), attenuated endothelium-dependent relaxation of aortae from daidzein or 17beta-oestradiol-treated rats. Blockade of K(Ca) channels had no effect on the responses to ACh in aortae from vehicle-treated rats. In aortae from daidzein- or 17beta-oestradiol-treated rats, endothelium-dependent relaxation was also attenuated by inhibition of cytochrome P450 (CYP450) epoxygenase with 6-(2-propargylloxyphenyl)hexanoic acid (PPOH) or inhibition of K(IR) channels and Na(+)/K(+)-ATPase with barium and oubain, respectively. 4. This study demonstrates that endothelium-dependent relaxation of male rat aorta is normally entirely mediated by NO, whereas treatment with daidzein or 17beta-oestradiol stimulates a contribution from a non-NO, nonprostaglandin factor acting through the opening of SK(Ca) and IK(Ca) channels, and involving activation of Na/K-ATPase, K(IR) and CYP450 epoxygenase. This pattern of sensitivity to the tested inhibitors is consistent with the contribution of EDHF to relaxation. Thus, EDHF contributes to the enhanced endothelium-dependent relaxation that is observed after chronic treatment with the phytoestrogen daidzein or with 17beta-oestradiol.
Woodman
Owen L
OL
Department of Pharmacology, University of Melbourne, Victoria 3010, Australia. owenlw@unimelb.edu.au
Boujaoude
Mirna
M
D000818:Animals; D001685:Biological Factors / Q000502:physiology*; D004305:Dose-Response Relationship, Drug; D004730:Endothelium, Vascular / Q000187:drug effects* / Q000502:physiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004958:Estradiol / Q000008:administration & dosage*; D007529:Isoflavones / Q000008:administration & dosage*; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley; D014664:Vasodilation / Q000187:drug effects* / Q000502:physiology
D001685:Biological Factors; D004791:Enzyme Inhibitors; D007529:Isoflavones; C067410:endothelium-dependent hyperpolarization factor; D004958:Estradiol; C004742:daidzein