The effects of lons and hypothalamic factors on the in vitro activity of rainbow trout prolactin cells

Abstract

The influence of various ions and of dopamine and somatostatin on the in vitro activity of rainbow trout prolactin (PRL) cells was investigated. There was a positive correlation between medium Ca 2+ concentration and both PRL synthesis and release up to 1.8 m M Ca 2+, above which no further increase occurred. Even with no Ca 2+ in the medium, there was still PRL secretion during the incubation. Replacement of Ca 2+ with Ba 2+ in the medium did not elevate either total PRL levels or PRL release above that in Ca 2+-free medium. Neither elevated Mg 2+ nor increased medium K + had any effect on PRL synthesis or release. Dopamine inhibited PRL release but not synthesis, as did the D 2 receptor agonist, apomorphine. However, the D 2 receptor antagonist, (+)-butaclamol was unable to prevent the action of dopamine on PRL release. Somatostatin inhibited both PRL synthesis and release in normal Ca 2+ medium, but release only in reduced Ca 2+ medium. Thus, Ca 2+, dopamine, and somatostatin may all have roles in regulating prolactin secretion in this fish. In addition, oPRL reduced trout PRL release, indicating a possible negative feedback mechanism for trout PRL secretion.