Insulin receptors are widely distributed in human brain and bind human and porcine insulin with equal affinity

Insulin receptors differing structurally from those in other tissues have been demonstrated in brain from many species. Subtle differences in binding properties have been reported between insulin receptors in brain and other tissues, including differences in affinity of pig brain receptors for human and porcine insulin. Insulin binding has been demonstrated in human cerebral cortex, but insulin binding has not been characterized in other areas of human brain. We have studied the binding of 125I labelled human insulin, and its displacement by unlabelled human and porcine insulin, in homogenates prepared from human hypothalamus, cerebral cortex and cerebellum obtained post-mortem from eight non-diabetic subjects. Specific binding was demonstrated in all brain regions studied, and displacement curves obtained with unlabelled human and porcine insulin were identical. By contrast, unlabelled insulin-like growth factor-1 did not significantly displace 125I labelled human insulin over the same concentration range. We therefore conclude that insulin receptors are widely distributed in human brain and do not differ in their affinity for human and porcine insulin.