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.