SERUM FSH BIOACTIVITY AND INHIBIN LEVELS IN PATIENTS WITH GONADOTROPIN SECRETING AND NONFUNCTIONING PITUITARY-ADENOMAS

It has been reported that serum FSH bioactivity and inhibin levels can be used as markers of the presence of true gonadotropin-secreting pit uitary adenoma (Gn-oma). To verify this hypothesis, we have investigat ed the bioactivity of FSH and serum inhibin alpha-alpha and alpha-beta A levels in a series of patients with either Gn-oma or nonfunctioning pituitary adenoma (NFPA). Nine patients with Gn-oma (6 men and 3 wome n), 21 with NFPA (9 men and 12 women) and 30 normal subjects were incl uded in the study. We studied FSH biological activity (FSH-B) by using Sertoli cell aromatase bioassay (SAB) and alpha-alpha and alpha-beta A inhibin levels by two noncompetitive immunometric assays (IEMA). In male patients with Gn-oma, serum immunoreactive FSH (FSH-I) and FSH-B levels ranged from 5.1 to 35.5 U/L and from 8.3 to 48 U/L, respectivel y, FSH B/l ratio being elevated in 2 (2.5 and 4.1; normal male range: 0.3-1.5), while female patients with Gn-oma had serum FSH-I and FSH-B levels ranging from 43.2 to 162 U/L and from 41.2 to 112.8 U/l, respec tively, with a normal FSH B/l ratio. In male patients with NFPA, FSH-I and FSH-B levels ranged from 2.7 to 10.7 U/l and from 2.4 to 11.4 U/l while in females they ranged from 3.4 to 67.9 and from 4.6 to 60.8 U/ l, respectively. FSH B/l ratio was elevated in 1 male (3.3) and normal in the remaining patients with NFPA. Serum a-a inhibin levels were no rmal or low in patients with Gn-oma and NFPA, while a-PA inhibin conce ntrations were slightly elevated in 1 of 6 postmenopausal women (0.9; normal range <0.7 U/ml). The present study confirms and extends previo us reports indicating that male patients with Gn-oma may secrete FSH m olecules with increased bioactivity. However, this abnormality was als o observed in one male patient with NFPA. Moreover, the measurement of inhibin levels does not appear to be a reliable in vivo marker of pit uitary tumors of gonadotroph origin, as it was normal or low in almost all patients with either Gn-oma or NFPA. (J. Endocrinol. Invest. 21: 372-379, 1998) (C)1998, Editrice Kurtis.