The identification of a hoemone secreted by the pars tuberalis cells

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The hypophyseal parts tuberalis covers both the infundibular stalk and median eminence as thin cell layers. Despite of its occurrence in large numbers of animal species, the functional significance of the pars tuberalis remains obscure. A majority of the pars tuberalis consist of secretory cells specific to this portion of the pituitary. In contrast to the cells of mammalian species that contain only a few small secretory granules, the specific cells of the chicken pars tuberalis are characterized by the presence of many secretory granules ranging from 90 to 4O0nm in diameter. Almost all cells throughout the pars tuberalis of chickens were immunoreactive for luteinizing hormone (LH) and chromogranin A.Furthermore, immunoelectron microscopy using post-embedding immunogold labeling showed that gold particles representing immunoreactivily for LH were located in all secretory granules of the pars tuberalis cells. Double immunogold labeling confirmed that LH and chromogranin A were colocali … More zed on the same secretory granules. Concerning the ontogeny of the chicken pars tuberalis, the primordium of the pars tuberalis located close to the median eminence was first formed at the lateral-apical end of the pars distalis at 8 days of incubation. The primordium expressed intense signal for common a-subunit mRNA of glycoprotein hormones. In addition, it was immunoreactive for LH and chromogranin A.The pars tuberalis primordium progressively extended along the median eminence with age and reached to the rostoral end at 14 days of incubation. It was confirmed by in situ hybridization that the pars tuberalis cells expressed intense signal for a-subunit mRNA for life. High concentrations of melatonin-binding sites have been observed in the pars tuberalis of various animal species. Under long photo periods (24 his light) for I month, the specific cells of the chicken pars tuberalis were filled with enlarged secretory granules. On the other hand, under short photo periods (22 his dark) for I months, the cytoplasm of the pars tuberalis-specific cells were enlarged in size and revealed only a few small secretory granules. Furthermore, the cells contained numerous niitochondria, increased rough endoplasmic reticulum and Golgi complexes, showing increased cell activity. Northern blot analysis with 32P-labeled a-subunit cDNA exhibited that the amounts of a-subunit mRNA in the chicken pars tuberalis were conspicuously affected by the alterations of circadian rhythms. Less