Octreotide effect on growth hormone and somatostatin subtype 2 receptor mRNAs of the human pituitary somatotroph adenomas

Octreotide, a somatostatin analog used to treat acromegalic patients harbor ing a pituitary tumor, acts via somatostatin subtype 2 receptor (SSTR2) and causes significant decrease of circulating GH levels and sometimes mild to moderate tumor shrinkage. To further elucidate the mechanism of octreotide action, we studied GH and SSTR2 mRNAs by in situ hybridization in densely and sparsely granulated somatotroph adenomas removed by surgery from 14 tre ated and 14 untreated patients. Only in densely granulated adenomas were th e GH and SSTR2 mRNA signals mildly decreased relative to untreated matched adenomas. The decrease of GH mRNA in densely granulated somatotroph adenoma s suggests that they may have a more favorable response to octreotide thera py than sparsely granulated tumors.