Angiotensin II binding sites in the rat pancreas and their modulation after sodium loading and depletion

Specific 125I angiotensin II binding sites were identified in the rat pancreas by radioreceptor assay, autoradiography and immunohistochemistry. Scatchard analysis of the binding in normal rats yielded a Kd of 0.51 +/- 0.23 nM with a Bmax of 15 +/- 3.5 fmol/mg protein (means +/- SD, n = 6). Changed plasma sodium concentration resulted in modifications in the binding affinity and capacity. Sodium loading depressed both Kd (0.36 +/- 0.1 nM) and Bmax (6.4 +/- 0.1 fmol/mg protein), while sodium depletion elevated both Kd (2.03 +/- 0.3 nM) and Bmax (45 +/- 3.5 fmol/mg protein) (means +/- SD, n = 6). Autoradiography using 125I Ang II and immunohistochemistry of the binding sites saturated with unlabeled Ang II and incubated with Ab-Ile5 Ang II, revealed localization of the binding sites on the islet cell membranes and in the exocrine pancreas.