Morphologic Aspects of Paracrine Interactions Between Endocrine and Folliculostellate Cells in the Rat Adenohypophysis

The histologic association of pituitary endocrine and folliculostellate (FS) cells could be accompanied by complex paracrine interactions. We analyzed the more frequently occurring connections between pituitary endocrine and FS cells by double-immunolabeling histochemistry, by using a streptavidin-biotin-alkaline phosphatase system and electron microscopy. We documented the following cytologic relationships (with 100% representing, in each of the comparisons, the total number of the first cell type mentioned): (a) juxtaposition of somatotrophs with corticotrophs (46%), and contact between thyrotrophs (18%), lactotrophs (17%), and FS cells (19%); (b) connections between lactotrophs and gonadotrophs (58%), somatotrophs (19%), and FS cells (23%); (c) interlinking between thyrotrophs and somatotrophs (35%), FS cells (34%), and other cell types (31%); and (d) interactions between gonadotrophs and lactotrophs (57%), corticotrophs (14%), and FS cells (29%). The immunohistochemical reaction of gonadotrophs was against luteinizing hormone (LH) and follicle-stimulating hormone (FSH) in combination (78%) or individually (11% for each antiserum); (e) short cellular projections from numerous corticotrophs surrounding somatotrophs (58%), gonadotrophs (18%), and FS cells (24%); and (f) FS cells contacting capillaries, gonadotrophs (32%), lactotrophs (21%), corticotrophs (18%), somatotrophs (16%), and thyrotrophs (13%). Electron microscopy revealed long branching processes between hormone-secreting cells and intercellular junctions, such as desmosomes, hemidesmosomes, and zonulae adherentes, in granular and FS cells. Union complexes occluding the follicular lumen can join two endocrine cells, two FS cells, or both types. Gap junctions occur between adjacent FS cells. In the pituitary there thus exist topographic spatial associations along with various interconnections between endocrine and FS cells. These findings may help to clarify the autocrine, juxtacrine, and paracrine mechanisms involved in the hormone-secretory activity of the pituitary gland.