Distribution of a novel binding site for angiotensins II and III in mouse tissues

A novel binding site for angiotensins II and III that is unmasked by parachloromercuribenzoate has been reported in rat, mouse and human brains. Initial studies of this binding site indicate that it is not expressed in the adrenal, liver or kidney of the rat and mouse. To determine if this binding site occurs in other mouse tissues, 8 tissues were assayed for expression of this binding site by radioligand binding assay and compared with the expression of this binding site in the forebrain. Particulate fractions of homogenates of testis, epididymis, seminal vesicles, heart, spleen, pancreas, lung, skeletal muscle, and forebrain were incubated with 125I-sarcosine1, isoleucine8 angiotensin II in the presence or absence of 0.3 mM parachloromercuribenzoate plus 10 µM losartan and 10 µM PD123319 (to saturate AT1 and AT2 receptors). Specific (3 µM angiotensin II displaceable) high affinity binding occurred in the testis > forebrain > epididymis > spleen > pancreas > lung when parachloromercuribenzoate was present. Binding could not be reliably observed in heart, skeletal muscle and seminal vesicles. High affinity binding of 125I-sarcosine1, isoleucine8 angiotensin II was observed in the absence of parachloromercuribenzoate in the pancreas on occasion. This suggests that this novel angiotensin binding site may have a functional role in these tissues.