Hypothalamic control of prolactin release in the rainbow trout,Salmo gairdneri: in vitro studies

摘要

Hypothalamic control of prolactin (PRL) release in immature rainbow trout Salmo gairdneri was investigatedusing an in vitro perifusion system of the rostral pars distalis. Hypothalamic extract of trout induced a dose dependent stimulation of PRL release. A similar effect was observed when infusing the medium from a 24hstatic incubation of the hypothalamus. Extracts from different control tissues (muscle, liver, gut) did notchange in vitro release, thus confirming the specificity of this stimulatory effect. Hypothalamic extract fromadult male rat, known to contain PRL release inhibiting factors, stimulated in vitro PRL secretion in rainbowtrout. This suggests that PRL cells are predominantly influenced by PRL releasing factors. Measurementof TRH and serotonin content in trout hypothalamus indicated consistent physiological levels of thesetwo factors. HPLC studies of hypothalamic extract showed that immunoreactive - TRH eluted at the sameplace as labelled TRH standard. Moreover, pizotifen, a serotonin antagonist, partially inhibited the stimulationobserved with trout hypothalamic extract. These results suggest that, in immature rainbow trout, PRLrelease is under stimulatory hypothalamic control and that serotonin and probably TRH play a major rolein this control.