The insulin receptor--single function and dual effect

Insulin receptors in human ocular tissues. Immunohistochemical demonstration in normal and diabetic eyes

The alpha- and beta-subunits of the insulin receptor have been localised in human eyes by immunohistochemistry. In the normal eye staining for both receptor subunits was distinct at the same sites of the anterior part of the eye, i.e. cornea, smooth muscle and epithelium of the ciliary body and the lens capsule. In the retina, the receptor was clearly demonstrated in the nerve fibre layer, the ganglion cells and Müller cells, the outer nuclear layer, inner segments of rods and cones, the outer limiting membrane and in the pigment epithelium. In eyes with diabetic retinopathy, the receptor did not stain in the inner segments of the rods and cones and the staining of the other layers was weak. Endothelial cells stained positively in normal and diabetic eyes, but pericytes of normal and new vessels did not stain. The receptor staining did not change in cornea, iris, ciliary body and lens. All together, the study shows that alpha- and beta-subunits of the insulin receptor are present in the retina, and that the staining reaction for the receptor is reduced in diabetes. To what extent these findings are of importance for the development of diabetic retinopathy, remains to be clarified.