A positive link between laughter and healthy function of blood vessels was first reported in 2005 by researchers at the University of Maryland Medical Center with laughter causing the inner lining of blood vessels, the endothelium, to dilate or expand such to increase blood flow. Drs. Michael Miller (University of Maryland) and William Fry (Stanford), theorize that beta-endorphin like compounds released by the hypothalamus activate receptors on the endothelial surface to release nitric oxide, thereby resulting in dilation of vessels. Other cardio protective properties of nitric oxide include reduction of inflammation and decreased platelet aggregation. The association between laughter and endothelial dilation was recently confirmed by other investigators.