Ultrastructural evidence for endogenous growth hormone-releasing factor-like immunoreactivity in the monkey pituitary...

Growth hormone-releasing factor-like immunoreactivity was visualized in monkey pituitary gland by immunocytochemistry on ultrathin sections obtained by cryoultramicrotomy. Antibodies were raised against synthetic human pancreas growth hormone-releasing factor (1-40). Growth hormone-releasing factor-like immunoreactivity was observed in somatotropes (identified by immunocytochemistry) only. The other pituitary cell types were not immunoreactive. In somatotropes, immunoreactivity was observed at the plasma membrane but only very scarcely, in the cytoplasm (cytoplasmic matrix and secretory granules) and in the nucleus. These results (1) provide immunocytological evidence for the presence of growth hormone-releasing factor or of an immunoreactive fragment of its molecule in the pituitary; (2) indicate the presence of this peptide in one particular pituitary cell type; and (3) provide cytological evidence for direct participation of growth hormone-releasing factor in the regulation of the somatotropic function.