Neurohypophysial hormone receptors and second messengers in trout hepatocytes

Abstract

Neurohypophysial hormone receptors and second messengers were studied in trout (Oncorhynchus mykiss) hepatocytes. Arginine vasotocin (AVT) and isotocin (IT) elicited a concentration-dependent inhibition of cAMP accumulation in the presence of 5 10 -8 M glucagon (maximal effect for 4·5 10 -7 M and 1·4 10 -7 M, half-maximal effect for 2·1 10 -8 M and 0·7 10 -8 M, AVT and IT respectively). The effect of glucagon was inhibited up to 90% by AVT and 80% by IT. While AVT inhibited (up to 50%) the basal cAMP production, IT had no such action.Specific V 1 or V 2 analogues (with reference to vasopressin in mammals) were used for pharmacological characterization of the type of neurohypophysial hormone receptor involved in this inhibition. The ]-vasopressin had no such effect. In this particular case, maximal and half-maximal effects of the V 1 antagonist were obtained for 2·3 10 -6 M and 1·2 10 -6 M respectively.Changes in intracellular calcium content were measured using the fluorescent probe FURA-2/AM. AVT and IT elicited a concentration-dependent increase in Ca 2+ accumulation. The comparison of the effect of 10 -8 M agonists versus AVT showed the following order of potency: AVT=IT>V 1 agonist>V 2 agonist. The V 1 antagonist reversed the AVT-induced Ca 2+ accumulation whereas the V 2 antagonist had no such effect.These results are taken as evidence for the presence in trout hepatocytes of neurohypophysial hormone receptors functionally close to the V 1a -type linked to cAMP production and Ca 2+ mobilization.

Regulation of Cl− secretion in seawater fish (Dicentrarchus labrax) gill respiratory cells in primary culture

“…Activation of either pathway may lead to the phosphorylation and activation of the apical chloride channels. However, it has been suggested that AVT inhibits adenylate cyclase activity in trout and eel gill cells in suspension (Guibbolini & Lahlou, 1987 b ; Guibbolini et al 1988; Sainsbury & Balment, 1991) via the G i protein (Guibbolini & Lahlou, 1992) and in lamprey kidney tubules and trout hepatocytes (Lahlou et al 1988; Guibbolini et al 1994). Therefore, the present AVT stimulatory effect on I sc is unlikely to be mediated by an AVT‐dependent cAMP increase via V 2 receptors.…”

Neurohypophysial hormone regulation of Cl- secretion: physiological evidence for V1-type receptors in sea bass gill respiratory cells in culture

“…Several investigators have utilized this approach in amphibians (Larcher et al 1992, Butlen et al 1993) and fishes (Pang & Furspan 1984, Guibbolini & Lahlou 1990, Uchiyama & Murakami 1994, Pierson et al 1996, Guibbolini et al 2000. The present study is the first attempt to characterize pharmacologically the neurohypophysial peptide receptors in the gill respiratory cells of a marine fish.…”

Cortisol modulates vasotocinergic and isotocinergic pathways in the gilthead sea bream (Sparus aurata, Linnaeus 1758)

“…The presence of these receptors in a variety of tissues, such as the brain, liver, gills and head kidney, has previously been demonstrated while assessing the effects of AVT and IT administration or even analysing its mRNA expression (e.g. Motais and Maetz, 1967;Henderson and Wales, 1974;Guibbolini et al, 1988;Guibbolini et al, 2000;Amer and Brown, 1995;Conklin et al, 1996;Konno et al, 2009;Konno et al, 2010;Lema, 2010;Martos-Sitcha et al, 2014a), suggesting that physiological processes within these tissues are regulated by the vasotocinergic and/or isotocinergic systems. Interestingly, our results …”