A recent study published online by the Journal of Agriculture and Food Chemistry reports on the role of broccoli as a cardioprotector. Broccoli contains high concentrations of selenium (65 nanograms/g broccoli) and glucosinolates, especially isothicyanate sulforaphane (23.6 micrograms/g broccoli). Both selenium and sulforaphane are shown to protect the heart and the cardiovascular system. Sulforaphane induces the redox regulator protein, thioredoxin, which has a cardioprotective role by reducing oxidative stress.
A clinical study reported that eating fresh broccoli sprouts for a week lowered serum low density lipoprotein levels (LDL is the so-called “bad” cholesterol) and a prospective study in Iowa showed a strong association between broccoli consumption and a lowering of the risk of coronary heart disease.
In the study reported in JAFC, rats were either feed, on top of regular rat chow, a broccoli slurry or water for a month before slaughter. At which time the hearts were isolated, stabilized and then subjected to 30 minutes of total ischemia followed by reperfusion*. Heart function was assessed 10, 30, 60, 90 and 120 mins after ischemia finished.
Hearts from rats fed on broccoli slurry showed faster recovery in left ventricular function and aortic flow. Heart rate was not affected by treatment. In addition, hearts from broccoli-fed rats had a smaller myocardial infarct size and the number of cardiomyocytes which under went cell death (apotosis) was reduced.
Hearts from broccoli-fed rats showed a similar response to ischemia as hearts in which thioredoxin had been upregulated. Broccoli possibly limits heart damage by inducing the production of thioredoxin and related proteins. These proteins play important roles in maintaining the inner cell redox potential. Selenium is required as part of the enzymes glutathione peroxidase and thioredoxin reductase, and sulforaphane up-regulates thioredoxin reductase stimulating thioredoxin production and reducing oxidative damage in the cell.
Mukherjee, S.; Gangopadhyay, H.; Das, D. K. Broccoli: A Unique Vegetable That Protects Mammalian Hearts through the Redox Cycling of the Thioredoxin Superfamily. J. Agric. Food Chem. 2007. (online)
From what I scan-read in Wikipedia, ischemia occurs by preventing blood flow to the heart and reperfusion is when blood is allowed back. Reperfusion can cause injury because the sudden influx of oxygen and blood can cause oxidative damage and inflammation.