Red blood cell endothelial cells. Exposure of red blood cells to physiological levels of shear stress activates nitric oxide synthase and export of nitric oxide, which may contribute to the regulation of vascular tonus. Red blood cells can also produce hydrogen sulfide, a signalling gas that acts to relax vessel walls. It is believed that the cardioprotective effects of garlic are due to red blood cells converting its sulfur compounds into hydrogen sulfide. Red blood cells also play a part in the body's immune response: when lysed by pathogens such as bacteria, their hemoglobin releases free radicals, which break down the pathogen's cell
Blood doping or storage is another issue. Contamination was seen in 1 in every 500,000 transfusions of red blood cells in 2002. Blood contamination can lead to septicemia or an infection that affects the whole body. Certain medications used to increase red blood cells can reduce liver function and lead to liver failure, pituitary problems, and increases in cholesterol levels. Blood doping Blood doping is the practice of boosting the number of red blood cells in the bloodstream in order to enhance athletic performance. Because such blood cells carry oxygen from the lungs to the muscles, a higher concentration in the blood