Objectives: 

Hydrostatic pressure is an important physical parameter in the acclimatization of numerous fish species to the aquatic conditions, which affects their distribution in the water column. The adaptation process to hydrostatic pressure involves changes in endocrine and biochemical functions, and the peptidergic hormone arginine vasotocin (AVT) may have an important role. In order to isolate possible physiological effects not influenced by genomic adaptation, in this study we use a non-high pressure adapted fish like the rainbow trout to evaluate changes in the AVT system induced by the exposure to different hydrostatic pressures.

Materials: 

Groups (n=6) of trout acclimated to 51 bars for 1, 3 and 15 days and their respective control groups were sacrificed, and samples of the hypothalamus, pituitary and plasma were collected. The hypothalamic pro-vasotocin mRNA levels were measured by Q-PCR, whereas gradient HPLC was used to assess the pituitary and plasma vasotocin content.

Results: 

The results obtained showed that exposure to high hydrostatic pressure stimulates at short time (1-3 days) the plasma and pituitary AVT levels in trout, which returned to the basal status after 15 days.

Conclusions: 

These changes suggest that increased hydrostatic pressure stimulates the neurohypophyseal secretion of AVT at short time, which might mediate antidiuretic effects related to the adaptation to the new environment. Changes operating at long-term could involve alterations in AVT receptors of the different central and peripheral target tissues in order to enhance AVT-response.