Cardiac dysfunction is a major concern after
trauma-
hemorrhage, and increased
IL-6 is one of the underlying causes for producing the dysfunction. Studies have shown that administration of 17beta-estradiol (
estrogen) after
trauma-
hemorrhage normalized cardiac
IL-6 levels and restored cardiac functions under those conditions. Because
hypoxia-inducible factor (HIF) 1 alpha is expressed during
hypoxia and cellular stress and up-regulates the expression of
IL-6, we hypothesized that HIF-1 alpha induces the increased cardiac
IL-6 after
trauma-
hemorrhage and that
estrogen suppresses this induction. To examine this, C3H/HeN mice were subjected to
trauma-
hemorrhage or
sham operation. Vehicle, the HIF-alpha inhibitor YC-1 [3-(5'-hydroxymethyl-2'-furyl)-1-benzylindazole, a novel activator of platelet
guanylate cyclase], or
estrogen was administered to
trauma-
hemorrhage and
sham groups during
resuscitation. Mice were killed at 2 h after
resuscitation, and cardiac
IL-6, HIF-1 alpha, and nuclear factor (
NF) kappaB activities were measured.
IL-6,
NF-kappaB, and HIF-1 alpha levels were markedly elevated after
trauma-
hemorrhage; all of these parameters were normalized by
estrogen as well as YC-1 administration after
trauma-
hemorrhage. Because elevated
IL-6 levels after
trauma-
hemorrhage were decreased with YC-1 treatment, it indicates that
IL-6 expression in cardiomyocytes is induced via HIF-1 alpha. In addition,
estrogen decreased the elevated HIF-1 alpha,
NF-kappaB, and
IL-6 levels after
trauma-
hemorrhage. These results indicate that the beneficial effects of
estrogen on cardiac function after
trauma-
hemorrhage seem to be mediated by the inhibition of HIF-1 alpha expression and activity.