Nitric oxide, cell signaling and cell death.

Nitric oxide (NO) is an important bioregulatory molecule in the nervous, immune and cardiovascular systems. NO participates in the regulation of the daily activities of cells as well as in cytotoxic events. It possesses a controversial effect on cell viability by acting both as a protection against apoptogenic stimuli, or by inducing apoptosis when produced at elevated concentrations. The mechanisms of NO in regulating these biological functions can be either through cyclic guanylate cyclase (cGMP)-dependent or cGMP-independent pathways. The purpose of this review is to highlight the implication of NO in cell signalling, synaptic transmission, and cell death. We focus also on the protective role as well as the toxicity of NO. Finally, the adverse effects of inhaled nitric oxide are also depicted in this review.