Pronatriuretic peptide is a sensitive marker of the endocrine function of teleost heart

Characterization of promoter elements required for cardiac chamber-specific expression

Salmon cardiac natriuretic peptide (sCP, an A-type natriuretic peptide) is an excellent model for the study of cardiac chamber-specific gene expression because it is uniquely specific to the heart and its promoter drives gene expression effectively in mammalian cardiac atrial but not in ventricular cells. We have now prepared hybrid luciferase constructs containing specific sequences from both sCP and BNP 5' promoters. According to our results the simple addition of a short rat BNP proximal promoter fragment to the inert 846 nucleotide sCP proximal promoter increases 100 times the basal activity of the sCP promoter in rat ventricular cardiomyocytes, and also conveys inducibility by mechanical load and endothelin-1. Thus, a small rBNP promoter fragment can transform the prototypical A-type natriuretic peptide regulation of sCP to B-type regulation, a result which argues against a major role of repressors causing the low expression level of A-type peptides in ventricular cardiomyocytes.

Synergistic activation of salmon cardiac function by endothelin and beta-adrenergic stimulation

The aim was to find out the effects of endothelin-1 (ET-1) in salmon (Salmo salar) cardiac contractile and endocrine function and its possible interaction with beta-adrenergic regulation. We found that ET-1 has a positive inotropic effect in salmon heart. ET-1 (30 nM) increased the contraction amplitude 17+/-4.7% compared with the basal level. beta-Adrenergic activation (isoprenaline, 100 nM) increased contraction amplitude 30+/-13.1%, but it did not affect the contractile response to ET-1. ET-1 (10 nM) stimulated the secretion of salmon cardiac natriuretic peptide (sCP) from isolated salmon ventricle (3.3+/-0.14-fold compared with control) but did not have any effect on ventricular sCP mRNA. Isoprenaline alone (0.1-1,000 nM) did not stimulate sCP release, but ET-1 (10 nM) together with isoprenaline (0.1 nM) caused a significantly greater increase of sCP release than ET-1 alone (5.4+/-0.07 vs. 3.3+/-0.14 times increase compared with control). The effects on the contractile and secretory function could be inhibited by a selective ETA-receptor antagonist BQ-610 (1 microM), whereas ETB-receptor blockage (by 100 nM BQ-788) enhanced the secretory response. Thus ET-1 is a phylogenetically conserved regulator of cardiac function, which has synergistic action with beta-adrenergic stimulation. The modulatory effects of ET-1 may therefore be especially important in situations with high beta-adrenergic tone.

Salmon cardiac natriuretic peptide is a volume-regulating hormone

The present study tested the hypothesis that salmon cardiac peptide (sCP), a new member of the family of natriuretic peptides, has an important role in the regulation of fluid balance and cardiovascular function. Intra-arterial administration of sCP increased urine output in salmon. It had a diuretic effect in rat as well, but the potency was lower. sCP increased the sodium excretion in proportion to the increased urine flow. Blood pressure was not affected by sCP in either species. Acute volume expansion elevated the plasma level of sCP in salmon, and an acute transfer of salmon from fresh to sea water decreased the circulating sCP level. Cardiac immunoreactive sCP or sCP mRNA levels were not affected by transfer to sea water. These results indicate that sCP has an important physiological role in defending salmon against volume overload but that it does not appear to contribute to the short-term regulation of blood pressure. sCP provides an excellent model of the general mechanisms of regulation of the A-type (atrial) natriuretic peptide system.