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

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 alpha-subunit and LH beta-subunit crossreactivities were reduced to a minimum. Repeated freezing and thawing had no effect on immunoreactivity of hormones and subunits tested. Incubation at 37 degrees C did not affect the immunoreactivity of purified subunit preparations and no recombination of alpha-subunit and LH beta 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 degrees 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 degrees C. Concomitant with decreasing LH levels at 37 degrees C, a rise in the concentration of alpha-subunit occurred. A direct correlation between gain in alpha-subunit and loss of LH was found. LH beta levels remained stable while LH decreased. This observation may be attributed to an increase in LH beta levels which is compensated by the loss of LH, which has a relatively high crossreactivity in the LH beta immunoassay. LH, FSH, alpha-subunit, LH beta 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 alpha-subunit and LH were detected, could alpha-subunit levels have been caused by dissociation of LH at 37 degrees C. In two cases, measured LH levels could have been caused by crossreactivity of alpha-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 degrees 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.