CHARACTERIZATION OF GROWTH-HORMONE BINDING-SITES IN RAT-BRAIN

The binding of I-125-labelled rat growth hormone (GH) to different are as in the brain was studied in male Sprague-Dawley rats. A high densit y of GH binding was found in the choroid plexus, hypothalamus, hippoca mpus, pituitary and spinal cord, whereas a lower binding density was o bserved in the cortex. Binding of the hormone to the various brain reg ions was age dependent. Binding was also dependent on time, pH and pro tein concentration. The binding affinity of the labelled hormone to ch oroid plexus was 4.3 per nmol/l and the binding capacity was 33.4 nmol /mg protein. The corresponding figures for binding of I-125-labelled G H to hypothalamus were 5.6 per nmol/l and 21.6 nmol/mg protein. By sod ium dodecyl sulphate electrophoresis of the cross-linked hormone-recep tor complexes, molecular weights of 60,000 and 61,000 were determined for the binding units in the choroid plexus and hypothalamus, respecti vely. It was further indicated that the binding unit for rat GH was di stinct from that for prolactin.