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.