NITRIC OXIDE
and Vasodilation etc.

In 1986 it was shown that Nitric Oxide causes vasodilation -- this appears to be why Nitroglycerin can alleviate cardiac angina, and why the "side effects" can include headaches. Nitric Oxide is also the transmitter that results in engorgement of the sexual organs -- the drug Viagra has its effect on the second messenger, cyclic GMP, but other treatments for impotency involve delivery of NO.

Some recent work has indicated that Nitric Oxide can be carried on molecules of Hemoglobin -- specifically the relaxed form, oxyhemoglobin, can form S-Nitrosohemoglobin by reaction with beta-Cys-93. The article by Stamler et al. was published in Science, v. 276, pages 2034-2037, the June 27, 1997 issue. It is titled "Blood Flow Regulation by S-Nitrosohemoglobin in the Physiological Oxygen Gradient."

The Nobel Prize announcement gives a good overview of NO activity and the history of its discovery. And the Nitric Oxide Home Page, while a little daunting, is a good clearing house for information about NO. Below are a few references from that page.