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Atrial natriuretic peptides (ANP) are a family of humoral compounds released from the heart atria and involved in water and salt homeostasis. ANP immunoreactivity and ANP-binding sites were also found in several areas of the central nervous system including the olfactory bulb. In the present study, the possible involvement of ANP in olfaction was tested by measuring the content and distribution of IR-ANP and ANP-binding sites in rat olfactory bulb in control and rats. The results implicate ANP in the processes leading to olfactory perception.

The binding of atrial natriuretic peptide (ANP) to rat olfactory bulb membranes and synaptosomes was examined. [125I]ANP (rat, 99-126) bound specifically to a single class of binding site on olfactory bulb membrane preparation with dissociation constant (Kd) of 106 pM and maximum binding capacity (Bmax) of 13.6 fmol/mg protein. Comparable results were obtained when the binding was characterized using displacement and kinetic experiments. The ring deleted analog of ANP, C-ANP (rat, 4-23) displaced [125I]ANP only minimally from its binding site in the membrane preparation. Saturation, displacement and blocking experiments on [125I]ANP binding to rat olfactory bulb synaptosomes revealed the presence of two distinct binding sites. Simultaneous analysis of homogeneous and heterogeneous displacement curves and blocking experiments revealed the quantitative characteristics of these receptors to be: Kd1 = 44 pM, Bmax1 = 42 fmol/mg protein and Kd2 = 1050 pM, Bmax2 = 173 fmol/mg protein, for the high and low affinity binding sites, respectively. Kinetic experiments further confirmed the differences between the receptors present in the membranes and the synaptosomes preparations. The demonstration of multiple ANP binding sites in olfactory bulb synaptosomes but not membrane preparations raises the possibility of a particular function of ANP in nerve terminals.