Evidence from combined immunoassay and radioautography procedures that intact insulin-125-I molecules are concentrated by mouse kidney proximal tubule cells.

Abstract

Tissue samples were obtained from mice sacrificed to 25 min after tail vein injection of mI-labeled beef insulin, 12 μg and 0.1 μc/g or 60 mμg and 0.5 μc/g mouse. The extent to which 125I present in tissues was attached to intact insulin-mI molecules was judged through measurement of the reactivity of 125I in each tissue homogenate with cellulose and with guinea pig anti-insulin serum (AIS), which abolishes insulin reactivity with cellulose. Tissue radioautograms were also prepared. In the liver, the 125I was preferentially concentrated by Kupffer cells and rapidly lost its reactivity to cellulose and, by inference, to AIS also. Kidney 125I concentration continued to increase for at least 10 min; at 5 min and shorter sacrifice times, over 40% of the 125I was still reactive with both cellulose and AIS, i.e., still attached to intact insulin molecules. From the radioautograms, it was judged that by far the greater part of the 125I was in the cortex. This 125I was present at highest concentration in the glom...