Characterization of vasopressin receptors of rat urinary bladder and spleen.

By use of tritiated arginine-8-vasopressin (AVP), vasopressin specific binding sites were detected on Sprague-Dawley rat urinary bladder and spleen. In both tissues, one class of high-affinity binding sites was characterized with an equilibrium dissociation constant of 1.61 +/- 0.22 and 1.91 +/- 0.16 nM and a maximal binding capacity of 155 +/- 5 and 110 +/- 11 fmol/mg of protein, for bladder and spleen, respectively. In both tissues, several experimental arguments suggest that these receptors belong to the V1-vascular type: Highly significant correlations were found between the relative agonistic vasopressor activities of eight AVP agonists and their relative abilities to inhibit [3H]AVP binding to the receptors, whereas no such relationship existed when antidiuretic activities were considered. The same profile was also observed with the antagonistic activities of five AVP antagonists. Moreover, AVP (10(-12)-10(-5) M) did not modify the basal cyclic AMP production in either tissue. As cyclic AMP is known to respond to V2 stimulation, the data suggest that the receptors measured are the V1 type. In Dahl rats the receptor characteristics were modulated by salt diet. More interestingly, the number of spleen vasopressin binding sites was always lower in Dahl salt-resistant animals than in the Dahl salt-sensitive animals receiving either a sodium deficient or a 1% NaCl or an 8% NaCl-containing diet. The exploration of vasopressin receptors regulation should facilitate the comprehension of the role played by AVP in different models of experimental hypertension.