Osmoregulatory role of vasotocinergic and isotocinergic systems in the gilthead sea bream (Sparus aurata L)

Abstract

Gilthead sea bream, Sparus aurata L., is an important fish species for the Mediterranean aquaculture and is considered a good model for studying the osmoregulatory process, due to its capacity to cope with great changes in environmental salinity (5-60‰). Our group studied the osmoregulatory role of different endocrine systems in this species, focusing on the vasotocinergic and isotocinergic systems over several years. For this purpose, the cDNAs coding for pro-vasotocin (pro-vt), pro-isotocin (pro-it), two arginine vasotocin (AVT) receptors (avtr v1a2- and v2-types) and one IT receptor (itr) were cloned. Acclimation to different environmental salinities induced a direct lineal relationship between plasma AVT levels and salinity, with no changes in plasma IT values. In addition, higher values in vasotocinergic, isotocinergic and stress pathways (pro-vt and pro-it gene expression, AVT and IT storage and plasma cortisol levels) in both hypo- and/or hyper-osmotic transfers, suggest an interaction between cortisol and AVT/IT pathways. Moreover, gene expression of specific receptors, as well as the use of different in vitro techniques, demonstrated an important osmoregulatory orchestration in different organs. In addition, individuals intraperitoneally injected with AVT and transferred to different environmental salinities enhanced plasma cortisol levels and/or gill Na, K-ATPase activity. These effects could be related to the energy repartitioning process occurring during osmotic adaptation of S. aurata to extreme environmental salinities, which could be mediated not only by plasma cortisol but also by AVT. Finally, our results indicated a very important role of the vasotocinergic and/or isotocinergic systems in both osmoregulatory and non-osmoregulatory organs.

The vertebrate Aqp14 water channel is a neuropeptide-regulated polytransporter

“…In teleosts, osmoregulatory adaptations are regulated by the pituitary neurohormones vasotocin (AVT) and isotocin (IT), which evolutionarily, are amongst the most primitive molecules involved in vertebrate osmoregulation 35 . AVT and IT are orthologs of mammalian arginine vasopressin and oxytocin, respectively, which act on target tissues through specific AVT1a and AVT2 receptors (AVT1aR and AVT2R), preferentially coupled to PKC- or PKA-mediated pathways, respectively, or the IT receptor (ITR) that also acts via PKC 36–38 . We therefore investigated the possible control of seabream Aqp14 intracellular transport by AVT and IT, and whether this regulation involves the same C-terminal Thr and Ser residues identified above.…”

Impact of Air Exposure on Vasotocinergic and Isotocinergic Systems in Gilthead Sea Bream (Sparus aurata): New Insights on Fish Stress Response

“…In addition to the clasical point of view of HSC and HPI axes as the main endocrine cascades to face the stress response caused after a large variety of challenges, the role of Avt in the activation of teleostean stress system at central level has been proposed in several studies (Kulczykowska, 2001 ; Balment et al, 2006 ; Mancera et al, 2018 ). This role was based on the finding than hypothalamic neurons responsible for the synthesis and release of this neuropeptide innervate adenohypophyseal cells (Moons et al, 1989 ).…”

“…In spite of the role of catecholamines and cortisol in the stress response of teleosts, the stress axis orchestration requires the dominant positive feed-forward signals of corticotropin-releasing hormone (Crh), together with others hypothalamic and hypophysiotropic factors (Bernier et al, 2009 ; Cerdá-Reverter and Canosa, 2009 ; Gorissen and Flik, 2016 ). In fact, arginine vasotocin (Avt) and isotocin (It) hormones have been reported to be important players in this endocrine cascade, and they have been pointed out as good indicators of fish welfare (Kulczykowska et al, 2009 ; Skrzynska et al, 2017 ; Mancera et al, 2018 ). Avt and It, which are known as homologs of arginine vasopressin (AVP) and oxytocin (OXY) in mammals (Acher, 1993 ), are both neuromodulators in central nervous system (Goodson and Bass, 2000 ).…”

The effect of starvation and re-feeding on vasotocinergic and isotocinergic pathways in immature gilthead sea bream (Sparus aurata)

“…Moreover, the corticotrope cells are innervated by hypothalamic neurons that produce AVT (Batten et al, 1990), indicating a role for AVT in the activation of the stress response system in fish (Bernier et al, 2009). Vasotocinergic and isotocinergic systems have a wide range of physiological functions that depend on many internal and external factors that control various processes at the neuronal level, such as pro-vt and pro-it mRNA expression, peptide synthesis, transport, maturation and storage, and the release of mature nonapeptides into the circulation (Mancera et al, 2017). The plasma levels of active AVT and IT could be reduced by: i) inhibition during the production of the pro-peptides at the level of the hypothalamus and/or during processes related to peptide maturation, ii) inhibition of the release of mature nonapeptides in the neurohypophysis, iii) renal clearance, and iv) inactivation of nonapeptides by plasma or tissue peptidases.…”