Ultrastructural immunocytochemical characterization of the thyrotroph in rat and human pituitaries

The beta chain of thyroid stimulating hormone (TSH) was localized in normal rat and human pituitaries with the unlabeled antibody--peroxidase-antiperoxidase complex technique and antisera to rat or bovine TSH beta. Araldite embedded tissues, immunoreactivity of TSH was best preserved after fixation with 1% glutaraldehyde or picric acid formaldehyde. In the TSH cells, the immunocytochemical stain was located on granules. However, there was a variation in staining of individual granules, and among the population of granules. Rat TSH cells were ovoid or angular to stellate, and contained granules ranging in size from 60-175 nm. The human TSH cell was polyhedral, and contained scattered granules of 150-300 nm diameter. In both species, granule distribution was either in 1-2 rows at the periphery, or scattered throughout the cytoplasm with some concentration in cytoplasmic processes. TSH cells in female rats in estrous contained more granules than those of other stages. TSH cells were distinguished from adrenocorticotropic hormone cells and luteinizing hormone cells on the basis of granule size and distribution, and cell shape.