LOCALIZATION AND DEVELOPMENT OF CHROMOGRANIN-A AND LUTEINIZING-HORMONE IMMUNOREACTIVITIES IN THE SECRETORY-SPECIFIC CELLS OF THE HYPOPHYSEAL PARS TUBERALIS OF THE CHICKEN

The pars tuberalis mainly consists of the secretory cells specific to this portion of the pituitary. We examined the localization and develo pment of luteinizing hormone (LH) and chromogranin A in the chicken pa rs tuberalis by immunohistochemistry. The vast majority of the chicken pars tuberalis was occupied by cells immunoreactive for both LH and c hromogranin A. Furthermore, immunoblot analysis of chicken pars tubera lis extracts with LH antiserum demonstrated that two bands, the large a-subunit and small beta-subunit of the LH molecule, were expressed in this tissue as well as in the pars distalis. A band for chromogranin A was also detected in pars tuberalis extracts with chromogranin A ant iserum. In contrast to the cells of mammalian species that contain onl y a few small secretory granules, the specific cells of the chicken pa rs tuberalis were characterized by the presence of many secretory gran ules ranging from 90 to 400 nm in diameter. Postembedding immunogold l abeling being showed that gold particles representing immunoreactivity for LH were densely located on all secretory granules of the secretor y-specific cells. Many secretory granules, especially the large ones, of the cells were also loaded with immunogold particles for chromogran in A. Double immunogold labeling confirmed that LH and chromogranin A were colocalized on the same secretory granules. During embryonic deve lopment, the primordium of the pars tuberalis was first detected at 8 days of incubation as a small group of cells containing LH- and chromo granin-immunoreactive cells. In the pars distalis, the onset of LH and chromogranin expression occurred earlier, at 6 days of incubation. At 10 days of incubation, the pars tuberalis primordium became large cel l masses consisting of LH-and chromogranin-immunoreactive cells, which were located close to the median eminence. Subsequently, the primordi um extended along the median eminence progressively with age. At 14 da ys of incubation, it reached to the rostral end and surrounded the med ian eminence as slender cell cords. These results indicate that specif ic cells of the chicken pars tuberalis synthesize a glycoprotein hormo ne related to the LH molecule, which is stored in the secretory granul es together with chromogranin A. The pars tuberalis may be involved in the regulation of gonadal function in a different way from that of th e pars distalis.