The direct antiatherogenic effect of estrogen is present, absent, or reversed, depending on the state of the arterial endothelium. A time course study in cholesterol-clamped rabbits.
BACKGROUND
This study further investigated the relationship between estrogen, arterial endothelium, and nitric oxide (NO) in cholesterol-clamped rabbits.


RESULTS
Rabbits were ovariectomized, balloon-injured in the thoracic aorta, and grouped to receive cholesterol-enriched chow together with either 17beta-estradiol or vehicle for 1, 2, 4, or 8 weeks. In the undamaged aorta, cholesterol accumulation of the placebo rabbits was significantly increased from week 4 to 8 (P<0.001). This increase was almost completely inhibited by estrogen (P<0.001). In the balloon-injured aorta, the estrogen and placebo rabbits accumulated similar amounts of cholesterol in the reendothelialized areas. In the deendothelialized areas, the estrogen group surprisingly accumulated significantly more cholesterol than the placebo group. This difference was apparent from week 2 and became significant at week 8 (P<0.01). Circulating nitrite/nitrate were significantly increased by estrogen at weeks 1, 2, and 4 but not at week 8. Similarly, in additional experiments, basal NO release was significantly higher in estrogen-treated than in placebo-treated rabbits after 4 (P<0.05) but not after 8 weeks. Stimulated NO release and endothelial NO synthase activity did not differ between groups. Mononuclear-endothelial cell binding was reduced by 50% by estrogen after 4 weeks (P<0.05). This difference, however, was abolished by coadministration of N(G)-nitro-L-arginine methyl ester, an inhibitor of NO production.


CONCLUSIONS
The direct antiatherogenic effect of estrogen was present, absent, or reversed, depending on the state of the arterial endothelium, and preceded by a transient increase in NO production followed by a reduced mononuclear-endothelial cell binding.
Holm
P
P
Novo Nordisk, Maaloev, Denmark. PHlm@novo.dk
Andersen
H L
HL
Andersen
M R
MR
Erhardtsen
E
E
Stender
S
S
D000704:Analysis of Variance; D000818:Animals; D001013:Aorta, Thoracic / Q000187:drug effects* / Q000502:physiology / Q000503:physiopathology; D001161:Arteriosclerosis / Q000503:physiopathology* / Q000517:prevention & control*; D002784:Cholesterol / Q000378:metabolism; D002791:Cholesterol, Dietary; D004036:Diet, Atherogenic; D004730:Endothelium, Vascular / Q000187:drug effects* / Q000502:physiology / Q000503:physiopathology; D004958:Estradiol / Q000494:pharmacology*; D005260:Female; D009566:Nitrates / Q000097:blood; D009569:Nitric Oxide / Q000378:metabolism; D019001:Nitric Oxide Synthase / Q000378:metabolism; D052250:Nitric Oxide Synthase Type III; D009573:Nitrites / Q000097:blood; D010052:Ovariectomy; D011817:Rabbits
D002791:Cholesterol, Dietary; D009566:Nitrates; D009573:Nitrites; D009569:Nitric Oxide; D004958:Estradiol; D002784:Cholesterol; D019001:Nitric Oxide Synthase; D052250:Nitric Oxide Synthase Type III