Heart failure after
myocardial infarction (MI) is associated with endothelial dysfunction. There is conflicting evidence on the exact nature of this endothelial dysfunction and how endothelium-dependent vasodilation is affected by
angiotensin-converting enzyme inhibitor (ACE-I)
therapy. Furthermore, consequences of acute ACE-I withdrawal are largely unknown. Therefore, we studied the contribution of
nitric oxide (NO) and endothelium-derived hyperpolarizing factor (
EDHF) to the effects of ACE-I
therapy and its withdrawal on endothelial function in MI rats. Rats were subjected to coronary
ligation to induce MI and were assigned to
quinapril or vehicle from 2 weeks to 8 months post-MI. In parallel, MI rats treated for 14 months with
quinapril were subjected to treatment withdrawal for 0, 4, and 6 weeks.
Acetylcholine (ACh)-induced relaxation and underlying endothelium-derived mediators were studied in isolated aortic rings. Long-term
quinapril (8 months) resulted in markedly improved endothelium-dependent vasodilation in rats with
myocardial infarction, which could be attributed to marked improvement in non-NO/
prostanoid-mediated relaxation (ie,
EDHF). After 14 months of follow-up, maximum vasodilation was still preserved by
quinapril. Withdrawal after 14 months of treatment caused significantly impaired ACh-induced
EDHF-mediated relaxation within 4 weeks. A marked reduction in
EDHF-mediated relaxation caused this impairment. NO-mediated relaxation was unaffected. These findings highlight the importance of
EDHF impairment in development of endothelial dysfunction after
myocardial infarction and the possibility of improving
EDHF-mediated vasodilation with chronic
ACE inhibitor therapy. In addition, withdrawal of chronic ACE inhibition after MI should be considered carefully, as profound endothelial dysfunction may develop rapidly.