Confounding factors in the interpretation of gonadotropin and gonadotropin-subunit release from cultured human pituitary adenomas

Abstract

Culture data of 31 human pituitary non-functioning adenomas and effects of cross-reactivity and in vitro culturing conditions on immunoreactivity of gonadotropins and subunits were investigated. Using immunoradiometric assays for FSH and LH and radioimmunoassays for α-subunit and LH β -subunit crossreactivities were reduced to a minimum. Repeated freezing and thawing had no effect on immunoreactivity of hormones and subunits tested. Incubation at 37°C did not affect the immunoreactivity of purified subunit preparations and no recombination of α-subunit and LHβ into intact LH could be demonstrated after coincubation of the subunits. FSH immunoreactivity in culture media from 3 pituitary tumors was not affected by incubation at 37°C. LH from a purified preparation and LH in culture media from 3 pituitary adenomas showed a rapid decrease of LH immunoreactivity when left at 37°C. Concomitant with decreasing LH levels at 37°C, a rise in the concentration of α-subunit occurred. A direct correlation between gain in α-subunit and loss of LH was found. LHβ levels remained stable while LH decreased. This observation may be attributed to an increase in LHβ levels which is compensated by the loss of LH, which has a relatively high crossreactivity in the LHβ immunoassay. LH, FSH, α-subunit, LHβ or a combination of these glycoproteins could be demonstrated in 26 out of 31 cultured tumours from patients operated upon because of a clinically non-functioning adenoma. In none of the media of 15 adenomas in which both α-subunit and LH were detected, could α-subunit levels have been caused by dissociation of LH at 37°C. In two cases, measured LH levels could have been caused by crossreactivity of α-subunit and FSH. It was concluded that: (1) in research of non-functioning pituitary adenomas data on gonadotropin and gonadotropin-subunit secretion may suffer from bias caused by crossreactivity; (2) that dissociation of LH into subunits at 37°C is relatively unimportant in in vitro research of non-functioning adenomas; (3) that virtually all non-functioning pituitary adenomas contain or release gonadotropins and/or subunits.