This study, carried out on 9 nonfunctioning
pituitary adenomas, was undertaken in order to evaluate the ability of these
tumors to synthesize and release
gonadotropins and/or free alpha-subunit (alpha-SU) of
glycoproteins. The morphological study included electron microscopy and immunofluorescence analysis while
hormone release was evaluated by the reverse hemolytic plaque assay (RHPA) and measurements in
culture media. By electron microscopy in all
tumors (6 null cell
adenomas and 3 oncocytomas), it was possible to identify rough endoplasmic reticulum, Golgi apparatus and secretory granules. By immunofluorescence, 5 of 6
tumors were immunoreactive for one or more
gonadotropin subunits; in particular, 5
adenomas were positive for alpha-SU and
LH-beta, and 3 for
FSH-beta. By the RHPA, about 1% of cells obtained from one single
tumor formed plaques for
LH-beta and alpha-SU while the remaining
tumors were negative. Similarly, the study of media concentrations of LH, FSH and alpha-SU in 2 h culture revealed very low amounts of released
hormones. In these experimental conditions no modification was observed after the addition of stimulatory agents such as TRH,
GnRH and VIP. The present study clearly indicates that although the large majority of nonfunctioning
tumors are positive for
gonadotropins their secretory capacity is very low in both basal and stimulated conditions.