Structure-function correlations of growth hormone or/and
prolactin-producing pituitary adenomas: An in vitro study with the
reverse hemolytic plaque assay
The purpose of this study was to detect in vitro growth hormone (GH) and
prolactin (PRL) secretion from adenomas clinically associated with GH or
PRL hypersecretion. The reverse hemolytic plaque assay (RHPA) was
applied in order to reveal possible differences among various
morphologic adenoma types, and to examine the inhibitory effects of
octreotide on GH release as well. The 20 surgically resected pituitary
adenomas studied included 15 from acromegalic patients and 5 from
patients with hyperprolactinemia. All adenomas were diagnosed by
histology, immunocytochemistry and electron microscopy. Among tumors
associated with acromegaly, 5 were densely granulated (DG), 5 were
sparsely granulated (SG) somatotroph (SM) adenomas, 2 were
mammosomatotroph (MSM) and 3 mixed somatotroph-lactotroph cell (mixed
SM-LT) adenomas; tumors causing hyperprolactinemia included 4 lactotroph
(LT) adenomas and 1 mixed SM-LT adenoma. GH release assessed by the RHPA
corresponded to in vivo hormone secretion and to tissue
immunoreactivity. Statistical analysis showed significant differences
among all morphologic types of SM adenomas, exclusive of SG-SM adenomas
compared to mixed SM-LT adenomas. The mean plaque size in DG-SM and MSM
adenomas was significantly greater than that of SG-SM and mixed SM-LT
adenomas, indicating higher GH secretion by the former two types during
the same incubation time. PRL secretion was documented in 2 mixed SM-LT
adenomas. Plaques for PRL, but not for GH were formed in all LT
adenomas. In all SM and LT adenomas, cells producing large plaques
represented a minority of the plaque-forming cell population, however,
they accounted for the largest part of the total plaque area, thus the
largest part of hormone secretion. Octreotide effects on GH release were
studied in 6 adenomas by the RHPA. Octreotide treatment induced a rapid
and significant reduction in GH secretion by SM cells in vitro, with a
selective effect on high-secreting cells