Expression of inhibin alpha, and beta A subunit and activin type II receptor mRNAs in various human pituitary adenomas.

Inhibin and activin are known to be involved in the pituitary hormone secretion as well as proliferation of the pituitary. We studied the expression of inhibin alpha, and beta A subunit and activin type II receptor (ACTR 2) mRNAs in human pituitary adenomas to determine the significance of inhibin and activin in pituitary hormone secretion. Tumor tissues were homogenized immediately after resection in guanidinium thiocyanate to extract total RNA. PCR was performed with reversely transcripted cDNA and respective amplification primers. DNA bands obtained for inhibin alpha, beta A and ACTR 2 by agarose gel-electrophoresis were 367, 285, and 389 bp, respectively. Messenger RNAs for inhibin beta A were demonstrated in all of the pituitary tissues studied, namely in 3 GH, 2 ACTH, 6 PRL and 1 FSH producing adenomas and 17 non-functioning adenomas. Inhibin alpha mRNAs were detected in 10 of 12 functioning adenomas and 15 of 17 non-functioning adenomas. ACTR 2 mRNAs were found in 11 out of 17 non-functioning adenomas, but only found in 3 out of 12 functioning adenomas. These results suggested local production of activin, a homodimer of beta-subunits, and inhibin, a heterodimer of alpha and beta subunits, in most of the pituitary adenomas regardless of their hormone secretion. On the other hand, a significantly higher incidence of ACTR 2 in non-functioning adenomas than in functioning adenomas suggested that activin had its main site of action in non-functioning adenomas, which could be potential gonadotropinomas.