Growth hormone (GH) immunoreactivity in the rodent and primate CNS: Distribution, characterization and presence posthypophysectomy

Abstract Using a specific sensitive radioimmunoassay, the distribution of growth hormone (GH) immunoreactivity in the rodent and primate central nervous system (CNS) was determined. Highest levels of extractable growth hormone-like materials were obtained from the rat amygdaloid nucleus, although other areas including cortex, hippocampus and the thalamus, contained immunoreactive material. Primate hypothalamus showed the highest levels of growth hormone immunoreactivity but it was also detectable in all regions examined. Forty-eight days posthypophysectomy, levels of GH immunoreactivity did not change in most rodent CNS areas studied. Moreover, levels in the amygdaloid nucleus and hypothalamus, although demonstrating an initial fall, actually rose above control levels several weeks following hypophysectomy. Dispersed CNS cells from both intact and hypophysectomized rats continuously release a GH-like material into the growth medium during a 20-day period of tissue culture. This phenomenon was suppressed with the addition of somatostatin to the growth medium. Characterization of this readily extractable GH-like material using column chromatography, parallel displacement curves, and biologic assay in the hypophysectomized rat showed a similarity between the CNS growth hormone-like material and its pituitary counterpart. The blood-brain barrier was found to be most likely intact to circulating pituitary growth hormone lending further support to the CNS origin of this biologically active and immunoreactive GH-like material in the brain.