HUMAN TRH RECEPTOR MESSENGER-RIBONUCLEIC-ACID LEVELS IN NORMAL AND ADENOMATOUS PITUITARY - ANALYSIS BY THE COMPETITIVE REVERSE TRANSCRIPTION-POLYMERASE CHAIN-REACTION METHOD

OBJECTIVE Little is known about the mechanism of diversity in in-vivo hormonal responsiveness to TRH in patients with functional pituitary a denomas. In order to clarify the relation between the responsiveness t o TRH and TRH receptor messenger ribonucleic acid (mRNA) expression, w e attempted to measure TRH receptor mRNA levels in human pituitary ade noma tissues by competitive reverse transcription polymerase chain rea ction (RT-PCR) method. PATIENTS Pituitary tissue samples were obtained at autopsy from 5 patients without pituitary disease. Pituitary adeno ma tissue samples were obtained at surgery from 18 patients with pitui tary adenoma (4 non-functioning, 8 prolactinoma, 4 acromegaly, 1 Gushi ng's disease and 1 FSH producing adenoma). METHODS Partial TRH recepto r cDNA from a human GH producing adenoma cDNA library was amplified by PGR under low stringency conditions using primers encoding the transm embrane domains III and V1 of pituitary TRH receptor cDNA. The partial sequence of the amplified cDNA determined by a dideoxy-chain terminat ion method was identical to the corresponding sequence of human TRH re ceptor cDNA. A competitor was generated by deleting the inner 111 bp f rom the amplified TRH receptor cDNA and subcloning. RNA extracted from human pituitary was reverse transcribed and co-amplified with competi tor by PGR under higher stringency conditions. The TRH receptor mRNA l evels, expressed as the relative intensity against the amplified level s of competitor, were compared among various pituitary tissues. RESULT S The relative TRH receptor mRNA levels of pituitary tissues in patien ts without pituitary disease were detectable and variable (M +/- SD) ( 0.370 +/- 0.231, n = 5), and slightly but not significantly lower than those in patients with pituitary tumours (0.598 +/- 0.265, n = 18). I n patients with prolactinoma, the relative levels of TRH receptor mRNA were quite variable (0.02-1.170, 0.604 +/- 0.358, n = 8) and not corr elated with PRL responsiveness to TRH (responder 0.457; non-responder 0.340-0.950). In patients with acromegaly, TRH receptor mRNA was detec table not only in the paradoxical GH responder to TRH (0.718) but also in the non-responder (0.758 and 0.765). In one patient with Gushing's disease, a relatively low level of TRH receptor mRNA could be detecte d (0.415). In the patient with a FSH producing tumour whose plasma FSH did not respond to TRH, a small amount of TRH receptor mRNA was detec table (0.447). CONCLUSIONS In patients with functioning pitultary aden omas, hormonal responsiveness to TRH in vivo might not be assessable b y TRH receptor mRNA levels in the adenoma cells.