Immunoreactivity of the Atrial Natriuretic Peptide Family in the Rat Inner Ear

The atrial natriuretic peptide family (ANP family) is comprised of atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP) and C-type natriuretic peptide (CNP). These peptides regulate body fluid and blood pressure homeostasis as a neuropeptide in the central nervous system as well as a cardiac hormone in the periphery. To assess the possible physiological role of the ANP family, we investigated the immunohistochemical localization of these peptides in the rat inner ear. ANP-like and CNP-like immunoreactivities were observed in the spiral ligament just beneath the stria vascularis, spiral limbus, dark cell area, endolymphatic sac, spiral ganglion cells and vestibular ganglion cells. We could not detect specific BNP-like immunoreactivity in the inner ear. These observations were consistent with our previous study concerning the ANP family gene expression. The results suggest that the ANP family influences the metabolism of the inner ear fluid as well as afferent nerve activities in the inner ear.