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Title: HORMONE RELEASE IS TIED TO CHANGES IN CELL SIZE IN THE OSMORECEPTIVE PROLACTIN CELL OF A EURYHALINE TELEOST FISH, THE TILAPIA, OREOCHROMIS MOSSAMBICUS

Author
item Weber, Gregory - Greg
item SEARLE, ANDRE - HIMB, UNI OF HAWAII
item RICHMAN, N. HAROLD - HIMB, UNI OF HAWAII
item STETSON, M - UNIV. OF DELAWARE
item HIRANO, TETSUYA - HIMB, UNI OF HAWAII
item GRAU, E. GORDON - HIMB, UNI OF HAWAII

Submitted to: General and Comparative Endocrinology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/22/2004
Publication Date: 5/28/2004
Citation: Weber, G.M., Searle, A.P., Richman, N., Stetson, M.H., Hirano, T., Grau, E. 2004. Hormone release is tied to changes in cell size in the osmoreceptive prolactin cell of a euryhaline teleost fish, the tilapia, oreochromis mossambicus. General and Comparative Endocrinology.

Interpretive Summary: Prolactin (PRL) is a hormone released from the pituitary gland that acts in enabling the tilapia to live in freshwater. PRL is released into the blood when a tilapia is moved from high to low salinity water. A similar response to extracellular omolality occurs when PRL cells are incubated in vitro. We found the PRL cell increases PRL release in vitro within 5 minutes of the osmolality of the incubation medium being reduced. An increase in cell size precedes this rise. Cell size and PRL release also increase, albeit more slowly, following the partial replacement of medium NaCl with an equivalent concentration of urea, a membrane-permeant molecule. Similar replacement using mannitol, which is membrane-impermeant, elicits no response. These findings suggest that osmoreception is linked to changes in cell volume rather than to extracellular osmolality per se.

Technical Abstract: PRL cells from a teleost fish, the tilapia, Oreochromis mossambicus, facilitate the direct study of osmoreception. The release of PRL, which acts in freshwater osmoregulation in teleost fish, rises in vitro within 5 minutes after extracellular osmolality falls. An increase in cell size precedes this rise. Cell size and PRL release also increase, albeit more slowly, following the partial replacement of medium NaCl (55 mOsmolal) with an equivalent concentration of urea, a membrane-permeant molecule. Similar replacement using mannitol, which is membrane-impermeant, elicits no response. These findings suggest that osmoreception is linked to changes in cell volume rather than to extracellular osmolality per se.