Angiotensin II binding to tissues of the rainbow trout, Oncorhynchus mykiss, studied by autoradiography.

Tissue slices from seawater-adapted and freshwater-adapted rainbow trout, Oncorhynchus mykiss, were exposed to 125I-angiotensin II (1.01.10(-9) M) and binding sites located by light-microscopic autoradiography. Binding/uptake was significantly inhibited by excess (10(-5) M) unlabelled angiotensin II, suggesting specific binding/uptake of angiotensin II to the ventral and dorsal aorta (smooth muscle), urinary bladder (smooth muscle and epithelial lining), glomeruli and proximal tubules, the gill (lamellae and central filament), skin (epithelium), intestine and oesophagus (mucosal epithelium), liver, heart (ventricular myocytes), adrenocortical tissue and brain (cerebellum and medulla oblongata). The specific binding/uptake of angiotensin II to tissues of freshwater- and seawater-adapted animals were generally similar. However, binding/uptake by the proximal tubules was significantly higher in freshwater-adapted trout than seawater-adapted trout. Specific binding/uptake of angiotensin II by the smooth muscle of the bladder was significantly higher in trout adapted to seawater than trout adapted to freshwater.