Human TRH receptor messenger ribonucleic acid levels in normal and adenomatous pituitary: analysis by the competitive reverse transcription polymerase chain reaction method

Abstract

In patients with functioning pituitary adenomas, hormonal responsiveness to TRH in vivo might not be assessable by TRH receptor mRNA levels in the adenoma cells.

Gene Expression Study of Thyrotropin Releasing Hormone (TRH) Receptor Using RT-PCR: Relationship to Clinical and Immunohistochemical Phenotypes in a Series of Human Pituitary Adenomas

“…TRHR mRNA was detected in 7 patients, whereas it was not demonstrated in the remaining one patient in whom PRL responded 1.7 times the basal value of TRH. As with previous investigators [4][5][6], the present study has confirmed that no significant correlation was observed between PRL response to TRH and TRHR gene expression. The mechanism explaining the poor PRL response to TRH in prolactinoma despite the expression of TRHR gene still remains unclear.…”

“…Several contrary findings have been reported, with respect to the relationship between TRHR gene expression and abnormal hormone responses to TRH in pituitary adenomas. TRHR mRNA has been identified not only in the paradoxical GH responder to TRH but also in the non-responder [4,5], suggesting that GH abnormal response to TRH in acromegaly is owing to a mechanism other than direct TRH action in adenoma cells. By contrast, Kim et al have claimed that there is a significant and positive correlation between the responsiveness for GH to TRH and the level of TRHR1 mRNA expression in 14 GH-producing adenomas [6].…”

“…The present study clearly confirmed the expression of TRHR mRNA in many pituitary adenomas examined other than ACTH cell adenomas. Regarding TRHR mRNA expression in ACTH cell adenomas, only one case has been studied in the literature to date [4], and in this patient low levels of TRHR mRNA were detected by competitive quantitative RT-PCR. However, no TRHR gene expression was identified in any of the five ACTH cell adenomas in our study, including one silent type adenoma.…”

“…Indeed, a variety of abnormal hormone responses to TRH have been reported in patients with pituitary adenomas, but little is known about the mechanism of these abnormal responses to TRH in pituitary adenomas. Moreover, results of the relationship between TRH receptor (TRHR) gene expression and abnormal hormone responses to TRH in pituitary adenomas are not consistent among investigators [4][5][6].…”

Preoperative growth hormone response to thyrotropin-releasing hormone and oral glucose tolerance test in acromegaly: A retrospective evaluation of 50 patients

“…Some investigators have ascribed this paradoxical response to the presence of residual adenomatous tissue, with a de-differentiation and the appearance of specific receptors for TRH, 1 but this hypothesis has not been verified by others. 20,21 However, the GH response to TRH can be also observed in normal subjects after pharmacological manipulation of the complex interactions between the hypothalamus and pituitary or in various pathological situations, other than acromegaly, in which an alteration of these relationships could be present. [2][3][4][5][6][7][8][9] The mechanism of this response in acromegaly remains unknown.…”