Human mixed somatotrophic and lactotrophic pituitary adenomas

Six patients with acromegaly at examination were found to have pituitary adenomas composed of cells that secreted GH and PRL. This was demonstrated by the elevated serum hormone concentrations, by immunoperoxidase staining of 5 specimens, and by electron microscopic examination of 4. Ultrastructural characteristics, described in detail, suggest that these adenomas were mixed adenomas consisting of 2 well-defined, distinct cell types, each secreting one hormone. By immunoperoxidase staining some cells were found to contain immunoreactive growth hormone, other cells immunoreactive prolactin. No cells were detected exhibiting immunostaining for both growth hormone and prolactin. Eelctron microscopy, consistent with the results of immunostaining, revealed the presence of two distinct cell types, distinguishable from each other by their characteristic fine structural features. No intermediate forms were noted. Thus there was no evidence to suggest that one cell type might transform to the other. Present findings seem to indicate that mixed adenomas secreting growth hormone as well as prolactin and consisting of somatotrophs as well as lactotrophs do occur in the human pituitary gland. Although all the results obtained so far suggest that these tumors are composed of two distinct cell types and thus can be interpreted as representing real mixed adenomas, further work is required to establish whether or not they derive from one common progenitor.