Serum FSH bioactivity and inhibin levels in patients with gonadotropin secreting and nonfunctioning pituitary adenomas

Abstract

It has been reported that serum FSH bioactivity and inhibin levels can be used as markers of the presence of true gonadotropin-secreting pituitary adenoma (Gn-oma). To verify this hypothesis, we have investigated 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 women), 21 with NFPA (9 men and 12 women) and 30 normal subjects were included 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, respectively, FSH B/I 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, respectively, with a normal FSH B/I 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/I ratio was elevated in 1 male (3.3) and normal in the remaining patients with NFPA. Serum alpha-alpha inhibin levels were normal or low in patients with Gn-oma and NFPA, while alpha-beta A inhibin concentrations were slightly elevated in 1 of 6 postmenopausal women (0.9; normal range < 0.7 U/ml). The present study confirms and extends previous reports indicating that male patients with Gn-oma may secrete FSH molecules with increased bioactivity. However, this abnormality was also observed in one male patient with NFPA. Moreover, the measurement of inhibin levels does not appear to be a reliable in vivo marker of pituitary tumors of gonadotroph origin, as it was normal or low in almost all patients with either Gn-oma or NFPA.

Testicular enlargement in a patient with a FSH-secreting pituitary adenoma

“…Thus, it is plausible that a gonadotropinoma producing elevated serum levels of FSH in a male could exert a trophic effect on the testicles. Using in vitro assays for FSH bioactivity (aromatase activity in rat granulosa cells or Sertoli cells), FSH from gonadotroph pituitary adenomas have been shown to have normal or even elevated biological activity compared to FSH from healthy controls [8,9].…”

In vitro secretion of FSH by cultured clinically nonfunctioning and gonadotroph pituitary adenomas is directly correlated with locally produced levels of activin A

“…Inhibin A and inhibin B protein levels were low, indicating that there is too little local inhibin production to affect FSH secretion despite readily detectable expression of α‐subunit mRNA. A recent report (Borgato et al ., 1998) also described the lack of correlation between inhibin A and FSH production in Gn‐omas. Although we suggest a possible autocrine role for activin A in the pathogenesis of Gn‐omas and NFAs, recently published data indicate an antiproliferative effect of activin in five out of 16 tested NFAs (Danila et al .…”

Assessing the Presence of Abnormal Regulation of Cortisol Secretion by Membrane Hormone Receptors:In VivoandIn VitroStudies in Patients with Functioning and Non-functioning Adrenal Adenoma

“…Wallac OY, Finland), as previously described [16]. Plasma GIP levels were measured by a commercial RIA method (Peninsula Laboratories, Belmont, CA, USA).…”