RESPONSE OF CIRCULATING ARGININE VASOTOCIN AND ISOTOCIN TO RAPID OSMOTIC CHALLENGE IN RAINBOW-TROUT

The plasma levels of arginine vasotocin (AVT) and isotocin (IT) in rai nbow trout (Oncorhynchus mykiss) were studied to demonstrate changes i n neurohypophysial nonapeptides following rapid osmotic challenge. Fre shwater-adapted fish were transferred to brackish Baltic water (BW) an d brackishwater-adapted fish were transferred to fresh water (FW). In both experiments blood samples for AVT, IT and osmolality were taken 3 0 min, 1, 2, 24 hr, and 10 days after transfer. Hormones were determin ed by gradient high-performance liquid chromatography preceded by soli d phase extraction. The pattern of AVT and IT response to external sal inity changes was similar during the first hours and showed transient increase or decrease after transfer to brackish or fresh water, respec tively. The AVT plasma concentration after 10 days in FW was significa ntly higher than that in BW, whereas the IT plasma concentrations in b oth salinities did not differ. These data suggest that the synthesis a nd or release of AVT and IT are controlled independently, and the role s of hormones in long-term osmotic adaptation are different. (C) 1997 Elsevier Science Inc.