Urotensin II inhibits arginine vasotocin and stimulates isotocin release from nerve endings in the pituitary of gilthead sea bream (Sparus aurata).

The aim of this in vitro study was to determine whether arginine vasotocin (AVT) and isotocin (IT) release from nerve endings is affected by urotensin II (UII) in gilthead sea bream pituitary. Primary cultures of pituitary cells were exposed to 10(-12), 10(-10), and 10(-8) M UII for 6, 24, and 48 hr. AVT and IT contents were determined in the culture media by high performance liquid chromatography (HPLC). UII at all doses decreased AVT release after 6, 24, and 48 hr of incubation. IT release was increased by UII only after 24 hr of incubation. This study, for the first time, indicates that UII affects AVT and IT release from nerve endings in the pituitary of Sparus aurata. It is presumed that UII together with AVT and IT may control response to different salinities in fishes.