Change in Somatostatinergic Tone of Acromegalic Patients according to the Size of Growth Hormone-Producing Pituitary Tumors

Abstract

The aim of this study was to investigate the relationship between somatostatinergic tone (SST) and the size of growth hormone (GH)-producing pituitary tumors. GH levels of 29 patients with newly diagnosed acromegaly were measured using a 75-gram oral glucose tolerance test (OGTT), an insulin tolerance test (ITT), and an octreotide suppression test (OST). Differences between GH levels during the ITT and the OGTT (ΔGHIO), and between the OGTT and the OST at the same time point (ΔGHOS) were compared according to the size of the tumor and the response pattern to the OST. ΔGHIO of macroadenomas (n=22) was non-significantly higher than those of microadenomas while ΔGHOS of macroadenomas were significantly higher than those of microadenomas. According to further analyses of macroadenomas based on the response pattern to the OST, GH levels during the ITT were significantly higher in non-responders. ΔGHOS showed near-significant differences between responders and non-responders. In conclusion, as the size of the pituitary tumor increases, the effect of glucose on SST appears to be attenuated. Macroadenomas that are non-responders to the OST possess a portion of GH secretion exceeding the range of regulation by SST.

Investigation of Responsiveness to Thyrotropin-Releasing Hormone in Growth Hormone-Producing Pituitary Adenomas

“…Therefore, the presence of this mutation may not be sufficient to explain the relationship between responsiveness of GH to TRH and tumor volume. We previously reported that as the tumor becomes larger, there exists a portion of the GH secretion which escaped physiologic regulation by somatostatinergic tone (SST) [ 25 ]. One of the known hypotheses for the paradoxical response in GH to TRH administration is the inhibition of somatostatin release by TRH [ 13 ].…”