Secretion of glycoprotein hormone alpha-subunit by pituitary tumors.
Serum glycoprotein hormone alpha-subunit levels were determined in 165 patients with pituitary adenomas. Elevated serum alpha-subunit levels were found in 17 patients (acromegaly, 5 of 58; prolactinoma, 6 of 56; nonfunctioning adenoma, 5 of 32; and ACTH-producing adenoma, 1 of 19), most of whom had normal serum TSH and gonadotropin levels. When TRH (0.5 mg) was injected iv in the 6 prolactinoma patients with elevated serum alpha-subunit levels, serum PRL and alpha-subunit levels increased in only 1 patient. Four acromegalic patients with high serum alpha-subunit levels received TRH; serum GH and alpha-subunit increased in 1 patient and did not change in 2, and only serum GH increased in the remaining patient. Oral administration of bromocriptine (5 mg), on the other hand, consistently decreased serum alpha-subunit and PRL levels in 2 patients with prolactinoma and alpha-subunit and GH levels in 1 acromegalic patient. When serum from 3 patients was subjected to Sephadex G-100 gel filtration, immunoreactive alpha-subunit eluted in a single peak, which emerged in fractions corresponding to [125I]TSH alpha. Concanavalin A (Con A) affinity chromatography revealed that the major portion of immunoreactive alpha-subunit was retained to Con A. A pituitary adenoma removed at surgery from a patient with acromegaly was studied in monolayer cell culture. Secretion of both alpha-subunit and GH from cultured adenoma cells was stimulated by TRH and suppressed by dopamine in a dose-dependent manner. Immunohistochemistry of the pituitary adenomas removed from patients with prolactinoma and acromegaly who had high serum alpha-subunit levels demonstrated alpha-subunit-containing cells as well as PRL- or GH-containing cells. These results suggest that elaboration of glycoprotein hormone alpha-subunit occurs without concurrent production of glycoprotein hormones in a substantial number of patients with pituitary adenomas and that alpha-subunit responses to stimuli in such adenomas are generally parallel with those of the concomitantly produced hormones.
D000172:Acromegaly / Q000378:metabolism; D000236:Adenoma / Q000097:blood* / Q000378:metabolism / Q000473:pathology; D000293:Adolescent; D000328:Adult; D001971:Bromocriptine / Q000494:pharmacology; D002850:Chromatography, Gel; D005260:Female; D015292:Glycoprotein Hormones, alpha Subunit; D013006:Growth Hormone / Q000097:blood; D006801:Humans; D008297:Male; D008593:Menopause; D008875:Middle Aged; D009994:Osmolar Concentration; D010446:Peptide Fragments / Q000378:metabolism*; D010908:Pituitary Hormones, Anterior / Q000378:metabolism*; D010911:Pituitary Neoplasms / Q000097:blood* / Q000378:metabolism / Q000473:pathology; D011388:Prolactin / Q000097:blood / Q000378:metabolism; D013973:Thyrotropin-Releasing Hormone / Q000494:pharmacology
D015292:Glycoprotein Hormones, alpha Subunit; D010446:Peptide Fragments; D010908:Pituitary Hormones, Anterior; D001971:Bromocriptine; D013973:Thyrotropin-Releasing Hormone; D011388:Prolactin; D013006:Growth Hormone