The thyrotropic cell of the rat hypophysis as studied with peroxidase‐labeled antibody

Utilizing the peroxidase‐labeled antibody procedure with anti‐serum to human thyrotropin (anti‐TSH), the thyrotropic cell was studied in the rat hypophysis with respect to its cytology, distribution, and reactivity to histochemical stains. The presumptive thyrotropic cells were polygonal and stained with aldehyde fuchsin and the periodic acid‐Schiff procedure. They were usually located centrally in cell cords. In the pars distalis thyrotropic cells were most numerous in the centromedian area of the lateral lobes and beneath the pars intermedia, while being rare in the dorsocephalic region. Several steps were taken to verify the specificity of the immunochemical procedure. After absorption with either human or bovine thyrotropin, anti‐TSH was completely ineffective; staining was almost completely prevented by prior absorption with either sheep or rat thyrotropin. Cytological alterations in thyrotropic cells generally paralleled the differences in pituitary thyrotropic content associated with sex, thyroid deficiency, thyroxine administration, and with rebound after cessation of treatment with propylthiouracil. Thyrotropic cells were differentiated from growth hormone, prolactin and corticotropic cells, as well as from presumptive luteinizing hormone cells, on the basis of shape, cytology, intraglandular distribution, and by immunochemical double‐staining. In this study they were not distinguished from follicle‐stimulating hormone cells which remain unidentified in this laboratory. Our observations confirm those of earlier investigators, who used histochemical methods for identification of the thyrotropic cell, with regard to its cytological features, intraglandular distribution and responsivity to altered levels of circulating thyroid hormone.