Endocrine Abstracts

Objective: The relationship between the paradoxical response of GH secretion after thyrotropin-releasing hormone (TRH) administration and tumor size has been the subject of only a few studies with conflicting results.

Design: The aim of this study was to investigate how the paradoxical response of GH secretion to TRH changes according to tumor size.

Methods: Patients with newly diagnosed acromegaly were classified as either TRH responders or non-responders according to the results of a TRH stimulation test (TST). GH levels of patients during the TST were compared according to responsiveness to TRH and tumor size. The relationship between ΔGH_max–min (the difference between peak and basal GH levels during the TST) and tumor size was investigated. Lastly, tumor volumes were compared between TRH responders and non-responders.

Results: A total of 112 acromegalic patients who underwent the TST were included in this study. TRH responders showed significantly higher GH levels than non-responders during the entire TST time. ΔGH_max–min during the TST was higher in TRH responders than non-responders, and tumor volumes were likely to be greater in responders than non-responders, although this difference was not statistically significant. Among 69 patients who remained after excluding patients without results of other tests or sellar MR images, those with macroadenomas demonstrated higher GH levels during the entire TST time. Both peak GH levels and ΔGH_max–min during the TST showed significant correlations with tumor volume.

Conclusion: The paradoxical response of GH secretion to TRH in GH-producing pituitary adenomas was positively correlated with tumor size.