Multiple types of receptors for atrial natriuretic peptide

The binding of atrial natriuretic peptide (ANP) to olfactory bulb, pituitary anterior lobe and thymus gland membranes was examined. [125I]ANP (rat, 99-126) bound specifically to the three types of membranes. However, the affinity for ANP receptor in olfactory bulb was much higher than those in either pituitary or thymus gland. Competitive inhibition of cold ANP (rat, 99-126) with [125I]ANP binding sites on olfactory bulb membranes gave a value of 796 +/- 80 pM (mean +/- S.E.M., n = 4) as a dissociation constant (Kd) of cold ANP (rat, 99-126), while on pituitary and thymus membranes, the competitive curve gave a value of 9.3 +/- 0.4 nM (mean +/- S.E.M., n = 3) and 25.5 +/- 2.2 nM (mean +/- S.E.M., n = 6) as a Kd of cold ANP (rat, 99-126), respectively. Furthermore, a truncated ANP fragment (rat, 111-126) did not inhibit the [125I]ANP binding in olfactory bulb, while this peptide fragment inhibited the [125I]ANP binding in either pituitary or thymus gland with affinities only 2- to 4-fold less potent than ANP (rat, 99-126). These data indicate the possibility of the existence of multiple types of ANP receptors. We propose alpha-receptor in olfactory bulb and beta-receptor in either pituitary anterior lobe or thymus gland.