**1. Introduction**

Since the discoveries of the biological effects of NO on physiological actions mediated by cGMP, delineation of the molecular mechanism of NO actions and understanding of NO activation of guanylate cyclase (GC) and the subsequent signal processes have been greatly advanced [1]. NO can function as an intracellular messenger, an autacoid, a paracrine substance, a neurotransmitter, or as a hormone that can be carried to distant sites for effects [1, 2]. It is therefore a unique simple molecule with diversified physiological functions.
