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

Abstract

Because of the recent finding that a majority of clinically nonfunctioning pituitary macroadenomas in women could be identified as of gonadotroph origin by their LH beta-subunit responses to TRH, we evaluated in this study the value of the LH beta-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 LH beta- and alpha-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 alpha- and LH beta-subunits. Responses to TRH were elevated, compared to the healthy, age-matched controls, in 14 for LH beta-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 LH beta-subunit, strongly suggesting that these adenomas were of gonadotroph cell origin. We conclude that the LH beta-subunit response to TRH can identify gonadotroph adenomas in men with clinically nonfunctioning adenomas better than can basal concentrations of intact FSH and alpha-subunit, alone or combined, but not as well as it can in women.