IMMUNOHISTOCHEMICAL DETECTION OF GLYCOPROTEIN HORMONE ALPHA-SUBUNIT IN SOMATOPROLACTINIC AND PURE SOMATOTROPH ADENOMAS

Glycoprotein hormone alpha subunit (alpha SU) is expressed in nearly a ll thyreotroph adenomas and most gonadotrophinomas, but is less well d ocumented in plurisecreting adenomas. We therefore examined the immuno histochemical (IHC) expression of alpha SU in a generally accepted mod el of plurisecreting adenomas (somatoprolactinic type) by comparison t o a series of pure monosecreting somatotroph tumors. Fifty patients (3 2 females, 18 males) aged 15 to 68 years with clinical and/or biologic al acromegaly requiring adenomectomy were studied. Forty-five had clin ical acromegaly and 5 had isolated amenorrhea and/or galactorrhea synd romes. Forty-eight of the 49 patients who had baseline assessments of plasma GH had a mean concentration of 5 ng/ml or more (normal value <5 ). Fifteen of the 46 patients who had baseline measurements of plasma PRL had a prolactinemia value greater than 20 ng/ml (normal value <20) but below 100 ng/ml, except for one patient. All the adenomas studied were positive by GH immunohistochemistry; 21 were immunostained by an antiPRL antibody and formed the ''somatoprolactinic'' (GH-PRL) group. Five of these 21 patients were male. The 12 female patients younger t han 50 years had amenorrhea or galactorrhea, and one male patient comp lained of impotence. Eleven patients (9 females, 2 males) in this GH-P RL group had hyperprolactinemia. Sixteen of these GH-PRL adenomas were immunolabeled by alpha SU antiserum. The remaining 29 adenomas, which were immunonegative with the PRL antibody and formed the ''somatotrop h adenoma'' (GH) group, were more frequent in male patients (13/29; 45 %) compared to GH-PRL group. Eight amenorrhea or galactorrhea syndrome s occurred among the 14 women younger than 50 years, 3 of whom had hyp erprolactinemia. Thirteen of these 29 adenomas (45%) were immunopositi ve with aSU antibody. Compared to the GH group, the GH-PRL group had a significant higher frequency of amenorrhea and/or galactorrhea syndro mes among women under 50 years (100% vs 57%; p<0.01), as well as hyper prolactinemia (55% vs 15%; p<0.01) and positive aSU immunoreactivity ( 76% vs 45%; p<0.05). The frequency of extrasellar macroadenomas was no t different according to PRL or alpha SU immunoreactivity. Thus, in th is series of somatoprolactinic adenomas, alpha SU immunopositivity was slightly more frequent than in a control group of pure somatotroph ad enomas. Moreover, hyperprolactinemia was more frequent in patients wit h GH-PRL adenomas, although the size of the pure and mixed adenomas wa s not different. These results suggest that hyperprolactinemia and/or alpha SU immunopositivity are more often associated with mixed GH-PRL adenomas. (J. Endocrinol. Invest. 21: 434-440, 1998) (C)1998, Editrice Kurtis