Growth hormone- and prolactin-producing cells in the pituitary gland of striped bass (Morone saxatilis): Immunocytochemical characterization at different life stages

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The striped bass (Morone saxatilis) is a seasonally breeding, long-lived, anadromous fish of growing economic importance. To describe the apparent activities of growth hormone (GH)- and prolactin (PRL)-producing cells, pituitaries were collected from captive juveniles and from wild adult fish in late spring off the Rhode Island coast during their coastal migration and in the Hudson River during the spawning migration. GH and PRL were separated by reversed-phase HPLC of pituitary extracts from captive adults and characterized as having apparent molecular masses of 23 kDa (GH) and 26 kDa (PRL) by SDS-polyacrylamide gel electrophoresis. Antisera generated in rabbits against synthetic fragments of GH and PRL188 from tilapia were shown by Western blot analysis of reversed-phase HPLC-purified striped bass GH and PRL and of striped bass pituitary extract to be specific for the appropriate hormone and were used to localize GH and PRL cells. GH cells and PRL cells lie in the proximal pars distalis and the rostral pars distalis, respectively. Small clusters of GH- and PRL-immunoreactive cells were found at ectopic sites within the pituitary. There were many intensely labeled GH cells in the pituitaries of juvenile and adult striped bass, whereas the immunoreactivity of GH cells in the pituitaries of spawning fish decreased. PRL cells in juvenile fish kept in fresh water had big, round-nuclei, and were heavily labeled, indicating that they were active. PRL cells in adult fish from seawater were also intensely labeled, but had kidney-shaped nuclei, indicating inactivity. PRL cells in fish from the spawning ground had polymorphic nuclei, appearing as round, indented or kidney-shaped forms, and they were unevenly and lightly labeled, suggesting highly variable stages of activity. No difference was found between males and females. The apparent activities of GH- and PRL-producing cells differ among these life stages, suggesting changing roles for the hormones. © 1994 by Academic Press, Inc.

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General and Comparative Endocrinology