Immunohistochemical Study of Growth Hormone and Prolactin Cells in the Pituitaries of Anguilliform Leptocephali Captured in the Atlantic Sargasso Sea.

Abstract

Growth hormone (GH) and prolactin (PRL), which are secreted by the pituitary gland, are considered to have important roles in the development and growth of fish as well as other vertebrates. We therefore studied ontogeny of GH and PRL immunoreactive (ir) cells in the pituitaries of anguil-liform leptocephali, the total length (TL) of which varied from 17 to 51mm. GH-ir cells were mainly located as a small cell mass in the dorsal part of the proximal pars distalis (PPD). A small number of GH-ir cells were also found in the rostral pars distalis (RPD) where PRL-ir cells were dominant, indicating that some GH cells were scattered among the PRL cells in the leptocephalus pituitary. PRL-ir cells were distributed within but throughout the RPD. Although no significant changes were found in the number of either GH-ir or PRL-ir cells, the staining intensity and cell sizes for these cells apparently increased during growth. These results indicate that leptocephalus GH and PRL cells may not actively secrete, but gradually store up hormones before metamorphosis.