CHARACTERIZATION OF VASOPRESSIN AND OXYTOCIN RECEPTORS IN AN AUSTRALIAN MARSUPIAL

In this study arginine vasopressin (AVP) and oxytocin (OT) receptors h ave been characterized in the brushtail possum. AVP receptors were cha racterized using [H-3]AVP and the radioiodinated AVP V-1a receptor ant agonist I-125- labelled CH2CO)-O-methyl-D-Tyr-Phe-Gln-Asn-Arg-Pro-Arg- Tyr- NH2] while OT receptors were characterized using the radioiodinat ed OT receptor antagonist I-125-Iabelled d(CH2)(5)[Tyr(Me)(2),Thr(4),O rn(8), Tyr-NH29]-vasotocin. The receptor affinities and densities have been compared with the rat AVP and OT receptors. Low densities of OT receptors were present in the possum ovary and kidney. High densities of AVP-binding sites were found in the possum adrenal, testis, mesente ric artery, ovary and renal medulla and lower densities in the possum liver. The AVP-binding sites showed marked differences in Ligand-bindi ng characteristics from the rat AVP V-1a and V-2 receptors. Receptor a ffinities were similar between tissues, except for a distinctly lower value in the renal medulla. It is concluded that the brushtail possum expresses AVP receptors with distinct ligand specificities from those of the rat AVP V-1a and V-2 receptors.