Angiotensin AT1 receptor subtypes in the rabbit pulmonary artery. A ligand binding study

The present ligand binding study showed that the rabbit pulmonary artery contained two subtypes of losartan-sensitive angiotensin receptor. The two receptor subtypes are differentially distributed. The high affinity receptor subtype is located predominantly in the cardia end of the artery while the low affinity receptor subtype is found mainly in the pulmonary portion of the artery. The Kd for the high and low affinity receptors for sar1, Ile8-angiotensin II was found to be 0.25 +/- 0.005 and 0.88 +/- 0.02 nM, respectively; and for angiotensin II to be 0.43 +/- 0.001 and 0.96 +/- 0.02 nM, respectively. In the presence of 1 mM GppNHp, the high affinity receptor subtype was converted to the low affinity subtype, indicating that it is G-protein coupled. 1 mM GppNHp had no effect on the low affinity receptor subtype. The present data support the findings of an earlier functional study which also showed the existence and similar differential distribution of two losartan-sensitive angiotensin receptors in the rabbit pulmonary artery. However, the significance of these findings in regard to the regulation of pulmonary circulation in normal and pathological conditions remains to be investigated.