Activation of Ca(2+)-independent nitric oxide synthase by 17beta-estradiol in post-ischemic rat heart.
BACKGROUND
Nitric oxide (NO) donors or facilitation of endogenous NO production is cardioprotective. This study sought to determine whether enhanced myocardial NO production might contribute to estrogen-induced cardioprotection.


METHODS
Ca(2+)-dependent and Ca(2+)-independent NOS activities (pmol min(-1) mg(-1) protein), NOS protein expression (quantitative immunoblot), cGMP content (pmol mg(-1) protein) and LV work (Joules) were measured in hearts isolated from ovariectomized rats that were either untreated or treated chronically with 17beta-estradiol (0.25 mg, 21 day release formulation).


RESULTS
After 14 days, serum levels of 17beta-estradiol were 6+/-1 and 135+/-16 pg ml(-1) in untreated and 17beta-estradiol-treated animals, respectively. After 60 min aerobic working mode perfusion, Ca(2+)-dependent NOS (untreated, 1.47+/-0.36; 17beta-estradiol 1.13+/-0.25) and Ca(2+)-independent NOS (untreated, 0.45+/-0.24; 17beta-estradiol, 0.41+/-0.21) activities, eNOS and iNOS proteins and cGMP content (untreated, 0.64+/-0.08; 17beta-estradiol, 0.76+/-0.12) were not different in the two groups. After 60 min low-flow (0.5 ml min(-1)) ischemia and 30 min reperfusion, Ca(2+)-dependent NOS activities were again similar (untreated, 1.25+/-0.23; 17beta-estradiol, 0.78+/-0.27). However, after reperfusion, Ca(2+)-independent NOS activity (untreated, 0. 39+/-0.10; 17beta-estradiol, 1.36+/-0.36) was 3.5-fold higher (P=0. 008) and cGMP content (untreated, 0.30+/-0.03; 17beta-estradiol, 0. 49+/-0.07) was 1.6-fold higher (P=0.017) in hearts from 17beta-estradiol-treated animals. Although pre-ischemic function was similar, recovery of post-ischemic LV work was 2-fold greater (P=0.024) in the 17beta-estradiol group.


CONCLUSIONS
The ability of ischemia and reperfusion in combination with chronic 17beta-estradiol to increase Ca(2+)-independent NOS activity and cGMP content supports a role for enhanced myocardial NO signaling in 17beta-estradiol-induced cardioprotection.
Fraser
H
H
Department of Physiology, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, Canada.
Davidge
S T
ST
Clanachan
A S
AS
D000818:Animals; D006152:Cyclic GMP / Q000032:analysis / Q000378:metabolism; D004789:Enzyme Activation; D004958:Estradiol / Q000494:pharmacology*; D005260:Female; D015151:Immunoblotting; D017202:Myocardial Ischemia / Q000201:enzymology*; D015425:Myocardial Reperfusion; D009206:Myocardium / Q000201:enzymology*; D019001:Nitric Oxide Synthase / Q000032:analysis / Q000378:metabolism*; D052247:Nitric Oxide Synthase Type II; D052250:Nitric Oxide Synthase Type III; D010052:Ovariectomy; D051381:Rats; D017207:Rats, Sprague-Dawley; D015398:Signal Transduction / Q000187:drug effects*; D018709:Statistics, Nonparametric
D004958:Estradiol; D019001:Nitric Oxide Synthase; D052247:Nitric Oxide Synthase Type II; D052250:Nitric Oxide Synthase Type III; C496318:Nos2 protein, rat; C496316:Nos3 protein, rat; D006152:Cyclic GMP