Inhibitory effect of neurohypophysial peptides on cyclic AMP accumulation by isolated hepatocytes of the trout

Abstract

Cyclic AMP levels were measured in freshly isolated hepatocytes of the rainbow trout. Compared with basal values, the average levels were increased up to 60 times in a dose-dependent manner either by mammalian glucagon (concentration range 1 nmol-1 mumol/l; dose giving half maximum response (EC50) 0.18 mumol/l) or by forskolin (concentration range 0.1-100 mumol/l; EC50 about 10 mumol/l). These stimulatory effects were partially inhibited by fish or mammalian neurohypophysial hormones used at relatively high concentrations (1-5 mumol/l). It is suggested that these results are evidence for the presence of V1-type receptors in fish hepatocytes. Together with previous results obtained with gills on the hormonal inhibition of adenylate cyclase activity, they suggest that teleost fish may possess only V1-type receptors (or two V1-related types), while the V2 receptors have evolved (or have become functional) in higher vertebrates.

Neurohypophyseal peptide inhibition of adenylate cyclase activity in fish gills The effect of environmental salinity

“…rat hepatocytes [ 151, rat brain [ 161, rat cultured aortic smooth muscle [ 171, and human platelets [9]. It has also been shown in our laboratory [18] However, circumstantial evidence suggests that the VI receptors may comprise 2 subtypes or more [25] and that a third class (V3) of receptor may exist [16,26,27]. In addition, Morgan [15] Another outcome of the present work is that the stability to which fish were acclimated had a large effect on the basal and hormone-sensitive enzyme activity.…”

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 receptors and second messengers in trout hepatocytes

“…However, the concentrations of AVT used in their study were relatively high (10 -7 to 10 -5 M). In contrast, Lahlou et al (1988) showed in the trout that neurohypophysial peptides at concentrations of 5 10 -7 to 5 10 -6 M (concentrations also relatively high) inhibited the cAMP accumulation stimulated by 4 10 -8 M glucagon . Taken together, these data led us to investigate further the mechanism of action of neurohypophysial peptides in trout hepatocytes.…”

“…The basic technique has been described previously by Lahlou et al (1988). Routinely, the typical incubation medium contained 10 mM theophylline and 5‰ (w/v) BSA in HMEM, pH 7·4.…”