Effect of TRH on beta-gonadotropin subunits in patients with pituitary microincidentalomas

Objective: To explore the hypothesis that most of the pituitary abnormaliti es compatible with the diagnosis of microadenoma, and detected in about 10% of the normal adult population, represent asymptomatic gonadotropinomas. Design: Patients diagnosed with pituitary microincidentalomas at the Instit ute of Endocrinology of the Tel Aviv Medical Center were evaluated. Circula ting beta-subunits of gonadotropin hormones were measured before and 30, 45 , 60 and 90 min after the intravenous injection of 400 pg TRH. Patients: Twenty-two patients with pituitary incidentaloma and 16 normal vo lunteers were tested. Results: In 16 of the 22 patients, an abnormal beta-s ubunit response was detected after the TRH challenge, Three patients had an abnormal increase in both beta-FSH and beta-LH after TRH administration. I solated pathological beta-FSH or beta-LH responses were demonstrated in fiv e and eight patients respectively, Six patients had normal basal and stimul ated gonadotropin subunit values, raising the possibility that their lesion s were not pituitary microadenomas. There was a significant overall differe nce between the response to TRH of the patient and control groups. In the g onadotropin positive group, comprising 16 patients, serum beta-FSH increase d from 6.4 +/- 1.6 ng/ml to 9.2 +/- 1.3 ng/ml (P=0.042) Ih after TRH stimul ation, whereas no changes were detected in the control group after TRH inje ction (basal: 4.1 +/- 0.8 ng/ml, peak: 5.1 +/- 0.8 ng/ml; P=0.15). Serum be ta-LH increased from 10.5 +/- 3.2 ng/ml to 23.4 +/- 4.9 ng/ml (P=0.0037) at this time, in contrast to a lack of response in controls (basal: 6.4 +/- 1 .5 ng/ml, peak: 8.2 +/- 2.3 ng/ml: P=0.24). Conclusion: In about 73% of patients with pituitary incidentalomas smaller than 10 mm, TRH elicits an increase in gonadotropin beta-subunits, This obs ervation raises the possibility that non-functioning pituitary micro- and m acroadenomas, which share a similar response to TRH, originate in a common ancestor cell type, probably a pituitary gonadotrope.