Glycoprotein hormone alpha subunit secretion by pituitary adenomas: influence of external irradiation

In ninety-nine patients with pituitary adenomas, forty-six with acromegaly, the serum level of the glycoprotein hormone alpha subunit was elevated in eighteen cases. Thirteen of these were acromegalic and one had an FSH-producing tumour. Alpha levels varied little during the day, from one day to the next and over a 6 month period. In twenty-five patients with a variety of other hypothalamic-pituitary disorders examined, one patient with a craniopharyngioma had a mildly elevated alpha level. External pituitary irradiation was followed by an acute and often transient fall in alpha level in several of these patients. Of the fifty-four patients with pituitary adenomas who had received external irradiation before testing, only five had elevated alpha subunit levels compared with thirteen patients of the forty-five who had not been irradiated. This difference in incidence of elevated alpha level was statistically significant (P less than 0.025). We conclude that external irradiation may reduce alpha subunit level chronically in many patients with pituitary adenoma.