Distribution of immunoreactive human growth hormone-like material and thyrotropin-releasing hormone in the rat central nervous system: evidence for their coexistence in the same neurons.

The distribution of a substance with human GH (hCG)-like immunoreactivity was studied in the rat brain after rapid fixation with acrolein. Using this method of tissue preparation, the hGH-like material (hGH-LM) was found in several hypothalamic and extrahypothalamic regions of the brain and extended into the spinal cord and posterior pituitary. On serial sections, the distribution of the hGH-LM was observed to be identical to that of TRH throughout the neuraxis. Sequential immunostaining of the hGH-LM and TRH in the same tissue section revealed the coexistence of these two peptides in the same neuronal cell bodies in the hypothalamus and brain stem and in beaded processes in all regions of the central nervous system studied. These findings demonstrate the intimate association between the hGH-LM and TRH in the central nervous system and raise the possibility that the hGH-LM forms part of a precursor hormone from which TRH is derived.