Effects of octreotide on morphology of pituitary adenomas in acromegaly

We studied the effects of the long-acting somatostatin analogue octreotide (SMS 201-995, Sandoz, Basel, Switzerland) on the morphology of pituitary adenomas in acromegaly. Of the 29 adenomas examined by light microscopy, 16 had been treated pre-operatively with octreotide. The treated adenomas were compared with the untreated adenomas. 14 adenomas were also studied by electron microscopy. In 23 cases we performed in-situ-hybridization for GH-mRNA. Under light microscopy, we found a decrease in amyloid deposits and a higher amount of cell necroses and fibroses after treatment, mainly in the tumors with shrinkage. Tumor shrinkage was diagnosed when the maximal diameter of the adenoma decreased for at least 1/3 during octreotide treatment in NMR examination. Immunohistochemical examinations showed that treated adenomas, especially those with tumor shrinkage, possessed more GH immunoreactive cells, and after in-situ-hybridization we found a higher content of GH-mRNA. On the ultrastructural level, rough endoplasmic reticulum appeared to be increased in treated adenomas. The increase of GH-mRNA and of rough endoplasmic reticulum suggests the likelihood of an increased secretory activity due to a rebound effect after short-term pre-operative omission of octreotide. Other findings are discussed.