Mechanisms mediating the prolactin cell response to changes in osmolality in the tilapia, Oreochromis mossambicus

The prolactin (PRL) cell of a euryhaline teleost, the tilapia (Oreochromis mossambicus) is osmosensitive. The release of its two hormones, PRL177 and PRL188. increases as extracellular osmolality is reduced. Taurine, a major intracellular osmolyte, is released from a variety of vertebrate cell types in response to a decline in extracellular osmolality. Our findings, although preliminary in nature, suggest that taurine concentrations less than or equal to I mh? inhibit while those above 1 mM stimulate the release of PRL177 and PRL188 in vitro. These findings suggest that taurine, which is released under hyposmotic conditions, may be an important regulator of PRL release. Overall, present evidence indicates that the osmosensitivity of the tilapia PRL cell involves a change in cell volume that is linked to intracellular free-[Ca++] through putative stretch-sensitive Ca++ channels and now possibly a sensitivity to taurine.