Membrane preparations from monkey and pig hypothalami bound insulin specifically. The binding appeared to be greater by preparations from anterior than posterior portions of the pig hypothalamus. Binding was time dependent, and its dissociation was first order with a half-time at 22°C of 14 min. Desalanine insulin was as effective as native insulin in inhibiting the binding of [125I]insulin, while proinsulin was less effective and desoctapeptide insulin still less effective in accord with their biologic activities. Binding by membranes from cortex and thalamus appeared to be less than from hypothalamus.
[125I]lnsulin was infused into an arterial split monkey brain preparation to determine if insulin that was blood borne bound specifically to the primate hypothalamus. Half the brain was perfused with [125I]insulin alone and the other half with [125I]insulin plus an excess of unlabeled insulin. Radioautography showed specific binding of insulin localized to the median eminence, infundibular nucleus, and microvessels.
Thus, the monkey and pig hypothalami bind insulin with characteristics similar to those reported for known target tissues for insulin. Furthermore, insulin from the blood stream binds to specific anatomical structures in the hypothalamus of the monkey.