Alfred Nobel is best remembered for the Nobel Prizes awarded in his name every year. But he was also the inventor of dynamite, an explosive made from nitroglycerin. This article tells the story of how nitroglycerin (via its derivative nitric oxide, NO) was found to be an effective drug for many ailments (see Nitric Oxide in Biology and Medicine).

The mechanism of blood circulation was not very well understood before the seventeenth century when William Harvey established the heart as the center of the blood system and showed that blood circulates to and from the heart (see The Heart and Blood Pressure). While researching a cure for the heart disease angina, physicians began experimenting with amyl nitrite, which seemed to reduce both angina pain and blood pressure. As its effectiveness was short-lived, they began researching related chemicals, including nitroglycerin (see An Explosive Medication). To understand how nitroglycerin works in the body, scientists had to understand how the chemical signaling system between and within cells worked. While attempting to understand the action of the hormone adrenaline, which is a first messenger molecule, researchers discovered the existence of secondary messenger molecules. The study of a chemical called cGMP led scientists to speculate that the body made NO as a secondary messenger molecule (see Listening to the Cell's Messages).

Meanwhile, scientists studying muscle contraction and relaxation in response to various chemical triggers, found that endothelial cells (which form the lining of blood vessels) formed a relaxing factor in response to a trigger (see The Discovery of EDRF). Extensive research then led scientists to conclude that the relaxing factor was in fact NO and it was an important chemical messenger in the body (see EDRF and NO are United). Further experiments showed that several messenger molecules triggered the production of NO as a secondary biological messenger (see NO Branches Out). The uses for NO and NO-related therapies have expanded as researchers continue to learn about how NO works in the circulatory, immune, and nervous systems (see Future Therapies).

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