Corticosteroids control inter alia, metabolism, immunology, osmoregulation, and stress responses. In the present work, we examined the different physiological and molecular responses evoked in the gilthead seabream acclimated to seawater (SW, 38 ppt) after chronic oral administration for 30 days of cortisol (F; 400 mg/kg fish feed) and the synthetic glucocorticoid dexamethasone (DEX; 300 mg/kg fish feed), prior- and post-hypersaline seawater (HSW, 60 ppt) direct transfer for 3 days. After the feeding trial, plasma cortisol levels showed the following pattern: CT > F > DEX. HSW transfer significantly enhanced plasma cortisol levels in the CT group, whereas F and DEX groups showed about half of these values. Na+/K+-ATPase (NKA) activity increased dramatically in the DEX group prior to HSW transfer. Surprisingly gill NKA activity levels in this tissue were recovered to the initial lowest levels for all the groups. Plasma and intestinal fluid osmolalities enhanced significantly after HSW transfer in the DEX group. Intestinal short circuit-current (Isc) showed a more anion absorptive capacity in the posterior intestine (PI) than the anterior. Moreover, F treatment significantly increased this anion absorptive capacity in the PI after HSW transference. Surprisingly HSW significantly decreased the anion absorptive capacity in all intestinal regions, specifically in the PI, indicating the appearance and/ or switch to secretory mechanisms in the intestine to counteract hypersalinity. Furthermore, molecular hypophyseal markers such as the pomcb and the gh were significantly altered/modulated by both pharmacological treatments and HSW challenge.

This work was funded by Agencia Estatal de Investigación (Ministerio de Ciencia e Investigación, Spanish Government) (PID2020-117557RB-C22). A. Barany was supported by the University of Cadiz Ph.D. scholarship (UCA/REC01VI/2017).

Trabajo presentado en el XIII Congreso de la Asociación Ibérica de Endocrinología Comparada, celebrado los días 16 y 17 de septiembre de 2021