Identification of gonadotroph adenomas in men with clinically nonfunctioning adenomas by the luteinizing hormoneβ subunit response to thyrotropin-releasing hormone

Because of the recent finding that a majority of clinically nonfunctioning pituitary macroadenomas in women could be identified as of gonadotroph origin by their LHβ-subunit responses to TRH, we evaluated in this study the value of the LHβ-subunit response to TRH in identifying gonadotroph adenomas in men with clinically nonfunctioning macroadenomas. Thirty-eight consecutively studied men with clinically nonfunctioning macroadenomas were given TRH iv, and intact FSH and LH and LHβ- and α-subunits were measured every 15 min for 90 min before and 90 min after. TRH tests were also performed on 15 healthy, age-matched control men and on 12 men with adenomas secreting GH or PRL. Of the 38 men with clinically nonfunctioning macroadenomas, basal values were supranormal in 10 for FSH and in 6 each for α- and LHβ-subunits. Responses to TRH were elevated, compared to the healthy, age-matched controls, in 14 for LHβ-subunit and in 5 each for intact FSH and LH. None of the men with adenomas secreting GH or PRL exhibited supranormal responses to TRH. Of the 38 clinically nonfunctioning adenomas, 35 were established in dispersed cell culture and 29 secreted readily detectable amounts of intact FSH, LH, and LHβ-subunit, strongly suggesting that these adenomas were of gonadotroph cell origin. We conclude that the LHβ-subunit response to TRH can identify gonadotroph adenomas in men with clinically nonfunctioning adenomas better than can basal concentrations of intact FSH and α-subunit, alone or combined, but not as well as it can in women.