Immunohistochemical Identification of Cell Types in the Pars Distalis of Harp Seals, Phoca groenlandica

Abstract

The distribution of pars distalis mammotropic, somatotropic, luteotropic, folliculotropic, thyrotropic and corticotropic cells was examined in neonate, juvenile and adult harp seals (Phoca groenlandica) by means of immunohistochemistry, employing antisera to hormones of human or rat origin. All the cell types were evident in one day‐old animals, except for immunoreactive folliculotropic cells which were first apparent in five day‐old animals. Mammotropic cells were small and relatively inactive in neonatal animals compared with the juvenile and adults. Somatotrops increased in apparent activity between one and five days postpartum, were most active in the juveniles, and less so in the adults. The corticotrops, found predominantly in the anterior regions of the pars distalis, appeared to increase in number and activity in adult seals. The gonadotrops increased in numbers as the animals aged, but the cells tended to be smaller in the juvenile and adult animals. The thyrotrops were small cells found only in the central regions of the pars distalis. The distribution of immunostained cell types is compared with cell type characterization of the same pituitaries based on light and electron microscopic evidence alone.