GH-releasing
peptides are a new class of potent GH secretagogs (GHS) in vivo and in vitro. In normal man GHS also elicit low but definite
ACTH and
prolactin secretion. Recently it was shown that patients with pituitary corticotrope
adenomas respond to GHS with a dramatic rise in
ACTH secretion, and it has been suggested that GHS may provide a diagnostic tool to differentiate
Cushing's disease from the
ectopic ACTH syndrome. GHS actions are mediated by a
G protein-coupled receptor recently characterized and cloned in man and rat. In this study we analyzed GHS receptor (GHS-R) expression in various types of
pituitary adenoma and in endocrine and non-endocrine lung
tumors by RT-PCR. GHS-R transcription was detected in all normal pituitaries and GH-secreting
adenomas as expected. The receptor was also transcribed in some
prolactin-secreting
adenomas and non-functioning
adenomas, and, more strikingly, in all 18
ACTH-secreting pituitary adenomas studied. Furthermore, it was frequently expressed in endocrine bronchial
tumors, especially
carcinoids, whereas it was not found or barely detectable in non-endocrine bronchial
tumors. Again
ACTH-secreting
carcinoids of the lung were all positive for GHS-R expression. These results show that GHS-R transcription is a common feature of endocrine
tumors independent of their type and origin.