Natriuretic peptides in the rat olfactory system.

The olfactory system plays an important role in the mobilization of animal behaviour, along with the sense of taste. These functions are mediated by a complex olfactory structure composed of peripheral (olfactory epithelium) and central (olfactory bulb) components. Several neuropeptides are synthesized in the olfactory system and are believed to be involved in olfactive processing. Recently, another bioactive substance, atrial natriuretic peptide (ANP), has been demonstrated in the olfactory system. ANP is a potent diuretic, natriuretic and vasorelaxant hormone which, originally, was isolated from mammalian atria, but its gene is expressed in many loci. ANP is only one member of the natriuretic peptide (NP) family, which includes two other peptides, BNP (brain natriuretic peptide) and CNP (C-type natriuretic peptide) derived from different genes. All three peptides show many common features. A high concentration of ANP-immunoreactive varicose fibers has been detected in the rat olfactory nerve layer and glomerular layer of the olfactory bulb (OB). An important group of perikarya and thin varicose fibers has been observed in the olfactory tubercle. We have demonstrated the presence of both ANP precursor and ANP gene transcript in the rat olfactory bulb. In addition to synthesizing ANP, the OB contains ANP transducing receptors coupled to guanylyl-cyclase system. The immunoreactive ANP has also been detected in the rat olfactory mucosa (OM), where ANP has been localized in secretory cells of Bowman's gland and in the cells of the epithelial layer. The relatively low concentration of ANP in OM (2.5 ng/mg protein) suggests a local role for ANP, a hypothesis which is strengthened by the presence of ANP high affinity receptors in this tissue. Although the role of ANP in the olfactory system is not yet clear, ANP has been shown to modulate olfactory bulb mitochondrial membrane activity and to be involved in the olfactive function.