Changes in transmural flow distribution effected of NONLA cannot be ascribed to alterations in the mechanical forces across the wall because no significant changes were observed in left ventricular pressure and heart rate, and the small increase in left ventricular end-diastolic pressure during ischemia was similar before and after administration of NONLA. Because microsphere measurements were done during ischemia at a steady low peripheral coronary pressure, the further decrease in flow produced by inhibition of nitric oxide synthesis cannot be explained by changes in shear stress on the endothelium. A probable explanation is that the larger amount of ischemic tissue is due to the suppression of a signal for nitric oxide release in the endothelium arising in the myocardial cell.Previous reports by Borst and Schrader suggest that ischemia releases purinergic substances from the ischemic cell, and Boeynaems et al reported the existence of purinergic receptors on the endothelial cell. Together these results suggest that ischemia produces coronary vasodilation partly by a regulatory mechanism mediated through the release of purinergic substances in the myocyte, which activates the release of nitric oxide in the endothelium. However, we can not assert whether nitric oxide produced during ischemia is released only by the endothelial cell or also by the ischemic myocardial cell. In this regard it seems that hypoxia induces the production of nitric oxide in the cardiac myocyte . In any case, nitric oxide produced during ischemia is most probably due to activation of constitutive nitric oxide synthetase because of the short period of ischemia that we induced. The internet’s most trusted pharmacy is looking forward to having you among its customers: just see how cheap and easy it can be for you to get buy levlen without any kind of prescription and start your shopping being sure you are protected every time.