The Nobel Assembly at the Karolinska Institute in Stockholm, Sweden, has awarded the Nobel Prize in Physiology of Medicine for 1998 to Robert F Furchgott, Louis J Ignarro and Ferid Murad for their discoveries concerning "the nitric oxide as a signaling molecule in the cardiovascular system".



Part 1: Dr. Louis Ignarro Explains Nitric Oxide (1/2)



Part 2: Dr. Louis Ignarro Explains Nitric Oxide (2/2)



Nitric oxide (NO) is an important gaseous radical involved in many physiological processes. It is produced from the amino acid L-arginine by the action of nitric oxide synthases (NOS) in what is called the L-arginine/NO pathway. Tracking its metabolic fate in biological fluids is of particular interest as it may indicate how the human body responds in health and disease.
Inspired by pioneering work of Furchgott, Ignarro and Murad, nitric oxide has been becoming one of the most studied molecules since last decade and has been related to numerous diseases.

Nitric Oxide measurements or assessment : The challenge

However, due to its short life span (a few seconds) it is very difficult to accurately monitor any up- or down-regulation in body fluids in vivo.

The detection of NO radicals in biological tissues is particularly difficult due to the short lifetime and concentration of these radicals in tissues. One of the few practical methods is spin trapping of nitric oxide with iron-dithiocarbamate complexes and subsequent detection of the mono-nitrosyl-iron complex with electron paramagnetic resonance (EPR).

A group of fluorescent dye indicators those are also available in acetylated form for intracellular measurements exist. The most common compound is 4,5-diaminofluorescein (DAF-2).

As a consequence, methods have been developed based on the measurement of the NO-derived products nitrite and nitrate or on the substrate of NO, L-arginine and its simultaneously generated product, L-citrulline. Considering only a fraction of the endogenous L-arginine pool is used for the synthesis of NO, NO-production cannot be estimated by measuring changes in the concentrations of L-arginine and/or L-citrulline alone. Instead, to estimate NO-related changes in the L-arginine and/or L-citrulline pools a form of tagging these metabolites for the NOS-mediated reaction is required. The application of stable isotopes is a way to track NOS-mediated changes. The application of various combinations of chromatography and mass spectrometry to measure isotopic enrichments resulting from the conversion of L-arginine to NO and L-citrulline in a one-to-one stoichiometry.

Today, NO effects or responses are well know:

NO enhance the endothelial cell function and decreased the blood pressure and systemic vascular resistance by vasodilation of capillary , small and medium artery and large artery
Decreased the catecholamine's
NO is producing by electrical stimulation of the Post sympathetic cholinergic fibers
NO production is correlated to the fat mass
The ES Complex software measures these data and could be useful to assess Nitric Oxide responses.