Radioautographic Visualization of in Vivo Insulin Binding to the Exocrine Pancreas*

Two minutes after the iv injection of [125I]insulin, hormone was linked to specific binding sites distributed randomly along the basal and lateral membranes of plasmalemma of pancreatic exocrine cells. The interaction had all of the properties of bona fide binding to a true insulin receptor, and under the described experimental conditions, estimates of receptor densities indicated the exocrine cell plasmalemma to be one of the richest sources of insulin receptors in the male rat.