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Free Luteinizing-Hormone Beta-Subunit in Normal Subjects and Patients with Pituitary Adenomas

Service d’Endocrinologie et des Maladies de la Reproduction (P.C., J.Y., B.C., G.S.), Hôpital de Bicêtre, 94275 Le Kremlin-Bicêtre; and Département de Biologie Clinique (J.P., J.M.B.), Institut Gustave-Roussy, 94805 Villejuif, France

Address correspondence and requests for reprints to: Philippe Chanson, M.D., Service d’Endocrinologie et des Maladies de la Reproduction, CHU Bicêtre, 78 rue du Général Leclerc, F94275 Le Kremlin, Bicêtre Cedex, France.

Most clinically nonfunctioning pituitary adenomas (NFPA) are found to be gonadotropinomas when assessed by immunocytochemistry. However, they are rarely associated with increased basal plasma levels of FSH, LH and/or -subunit. It has been claimed that the paradoxical free LHß response to TRH may be a useful clinical tool for determining the gonadotropic nature of NFPA. We used a very specific and sensitive immunoradiometric assay (IRMA) for free LHß measurement and another specific IRMA to check the absence of free CGß, to study normal subjects and 26 patients with NFPA. Basal plasma levels of LHß were undetectable in normal men and premenopausal women in the early follicular phase. In contrast, normal postmenopausal women had increased basal plasma LHß, parallel to dimeric LH and -subunit levels. In healthy subjects, stimulation with GnRH elicited an increase in LHß while TRH was ineffective. In patients with NFPA, LHß hypersecretion was found basally and/or after stimulation with TRH in 3 of 16 men, 3 of 5 premenopausal women, and 1 of 5 postmenopausal women, i.e. 7 of 26 patients (26%). In 3 of these 7 cases, -subunit and/or FSH levels were also increased. The LHß measurement was thus truly informative on the gonadotropic nature of NFPA in only 4 out of 26 cases (15%). In addition, increased LHß levels and/or a positive response of free LHß to TRH was observed in 3 patients with pure prolactinomas but in no patients with GH-secreting adenomas. Thus, using this very sensitive and specific IRMA, free LHß measurement is rarely helpful for determining the gonadotropic nature of NFPA.

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