Renal effects of high-dose natriuretic peptide receptor blockade in rats with congestive heart failure

Gene expression of (pro)renin receptor is upregulated in hearts and kidneys of rats with congestive heart failure

Recent studies have revealed that (pro)renin receptor ((P)RR), a newly identified member of the renin-angiotensin system, was associated with organ damage in the kidney. However, there has been little information for (P)RR in hearts. To investigate the regulation of (P)RR in heart failure, we examined the expression of (P)RR in hearts and kidneys of rats with congestive heart failure (CHF) due to coronary ligation by quantitative RT-PCR and immunohistochemistry. Significantly increased levels of (P)RR mRNA were found in the atrium, right ventricle, non-infarcted part of left ventricle, infarcted part of left ventricle and kidney of CHF rats, when compared with sham operated rats (about 1.6-fold, 1.4-fold, 1.6-fold, 1.7-fold and 1.5-fold, respectively). Expression levels of mRNAs encoding renin and angiotensinogen in these heart and kidney tissues were also increased in the CHF rats. Immunohistochemistry showed positive (P)RR immunostaining in the myocardium, the renal tubular cells, and vascular smooth muscle and endothelial cells in the heart and the kidney. The renal tubular cells were more intensely immunostained in CHF rats than in sham operated rats. These findings suggest that the expression of (P)RR is increased in the hearts and kidneys of rats with heart failure, and that (P)RR may contribute to heart failure.

Natriuretic peptides increase beta1-adrenoceptor signalling in failing hearts through phosphodiesterase 3 inhibition

AIMS

Whereas natriuretic peptides increase cGMP levels with beneficial cardiovascular effects through protein kinase G, we found an unexpected cardio-excitatory effect of C-type natriuretic peptide (CNP) through natriuretic peptide receptor B (NPR-B) stimulation in failing cardiac muscle and explored the mechanism.

METHODS AND RESULTS

Heart failure was induced in male Wistar rats by coronary artery ligation. Contraction studies were performed in left ventricular muscle strips. Cyclic nucleotides were measured by radio- and enzyme immunoassay. Apoptosis was determined in isolated cardiomyocytes by Annexin-V/propidium iodide staining and phosphorylation of phospholamban (PLB) and troponin I was measured by western blotting. Stimulation of NPR-B enhanced beta1-adrenoceptor (beta1-AR)-evoked contractile responses through cGMP-mediated inhibition of phosphodiesterase 3 (PDE3). CNP enhanced beta1-AR-mediated increase of cAMP levels to the same extent as the selective PDE3 inhibitor cilostamide and increased beta1-AR-stimulated protein kinase A activity, as demonstrated by increased PLB and troponin I phosphorylation. CNP promoted cardiomyocyte apoptosis similar to inhibition of PDE3 by cilostamide, indicative of adverse effects of NPR-B signalling in failing hearts.

CONCLUSION

An NPR-B-cGMP-PDE3 inhibitory pathway enhances beta(1)-AR-mediated responses and may in the long term be detrimental to the failing heart through mechanisms similar to those operating during treatment with PDE3 inhibitors or during chronic beta-adrenergic stimulation.

Increased gene expression of urotensin II-related peptide in the hearts of rats with congestive heart failure

Urotensin II-related peptide (URP) is a novel endogenous ligand for urotensin II receptor (UT-R). To investigate the pathophysiological role of URP in heart failure, we examined URP, UII and UT-R expression in hearts and kidneys of rats with congestive heart failure due to coronary ligation by quantitative RT-PCR and immunocytochemistry. Significantly increased expression levels of URP mRNA were found in the atrium, the right ventricle and the infarcted part of left ventricle of heart failure rats, when compared with sham-operated rats (about 2.2-fold, 2.7-fold and 3.9-fold, respectively). Expression levels of UII mRNA in the heart were about 10% of URP mRNA, and were slightly increased only in the infarcted part of left ventricle of heart failure rats, when compared with sham-operated rats. The expression levels of UT-R mRNA were increased in the atrium of heart failure rats. There was no significant change of URP, UII and UT-R mRNA expression levels in the kidney between heart failure and sham-operated rats. The myocardium was diffusely immunostained with URP in both rats. The blood vessels in the heart were positively immunostained with URP in heart failure rats, but not in sham-operated rats, whereas they were positively immunostained with UT-R in both rats. These findings suggest that the expression of URP, UII and UT-R is enhanced in failing heart, and the UII/URP/UT-R system has important pathophysiological roles in the progression of heart failure.

Vitamin D activates type A natriuretic peptide receptor gene transcription in inner medullary collecting duct cells

Many clinical and animal studies suggest that vitamin D and its metabolites have beneficial effects in the cardiovascular and renal systems. Using immunologic and enzymatic assays, vitamin D receptor and 25 hydroxyvitamin D3 1alpha-hydroxylase activity were found in inner medullary collecting duct (IMCD) cells suggesting an autocrine/paracrine role in this nephron segment. In this study, we examined the ability of 1,25 dihydroxyvitamin D3 (1,25(OH)(2)D3) to regulate the expression of the vasculoprotective natriuretic peptide receptor-A gene in these cells in culture. Treatment of the cells with 1,25(OH)(2)D3 caused a doubling of natriuretic peptide-dependent cyclic guanosine monophosphate production and a significant increase in natriuretic peptide receptor-A protein expression. This was accompanied by significant increases in receptor mRNA levels and gene-promoter activity. Mutation of a vitamin D response element, positioned upstream from the gene start site, resulted in a complete loss of 1,25(OH)(2)D3-dependent induction but not the induction by hypertonic stimuli. Introduction of small interfering RNA directed against the vitamin D receptor into the IMCD cells resulted in decreased natriuretic peptide receptor-A gene promoter activity and protein. The increase in this receptor expression may account for some of the reported beneficial effect of 1,25(OH)(2)D3 on the cardiovascular system and kidney.

Mechanism of relaxations to dendroaspis natriuretic peptide in canine coronary arteries

Experiments were designed to determine mechanisms by which Dendroaspis natriuretic peptide (DNP) causes relaxations in coronary arteries. Rings of canine left circumflex artery with and without endothelium were suspended in organ chambers filled with Krebs-Ringer bicarbonate solution (37 degrees C, bubbled with 95% O2/5% CO2). Concentration-response curves to DNP (10(-10) to 3 x 10(-7) M) were obtained in arteries contracted with prostaglandin (PGF(2alpha), 2 x 10(-6) M), either in the absence or the presence of C-ANP (10(-6) M) to inhibit natriuretic clearance receptors; indomethacin to inhibit cyclooxygenase (INDO, 10(-5) M), N(G)-monomethyl-L-arginine to inhibit production of nitric oxide (L-NMMA; 10(-4) M), HS-142-1 to inhibit particulate guanylate cyclase (10(-5) M); 1H-[1,2,4]oxadiazolo-[4,3-alpha]quinoxalin-1-one to inhibit soluble guanylate cyclase (ODQ; 10(-5) M), or tetraethylammonium to inhibit potassium channels (TEA; 10(-3) or 10(-2) M). Relaxations to DNP were greater in rings with than in those without endothelium. C-ANP significantly attenuated relaxations to DNP only in rings with endothelium. HS-146-1 but not INDO, L-NMMA, ODQ, and TEA significantly reduced relaxations to DNP in rings with and without endothelium contracted with PGF(2alpha). These results suggest that the endothelium augments inhibitory effects of DNP and that natriuretic clearance receptors mediate this component of the response to DNP in canine coronary arteries. In addition, relaxations to DNP in canine arterial smooth muscle involve activation of particulate guanylate cyclase but not hyperpolarization.

Renal function in high-output heart failure in rats: role of endogenous natriuretic peptides

The physiologic and pathophysiologic importance of natriuretic peptides (NP) has been imperfectly defined. The diminished renal responses to exogenous atrial NP in heart failure have led to the perception that the endogenous NP system might be less effective and thus contribute to renal sodium retention in heart failure. This study tests the hypothesis that in experimental heart failure, the renal responses to an acute volume load are still dependent on the NP system. The specific antagonist HS-142-1 was used to block the effects of NP in a model of high-output heart failure induced by an aortocaval shunt. Plasma cGMP levels and renal cGMP excretion were significantly lower in shunted and sham-operated rats receiving HS-142-1, compared with vehicle-treated controls, indicating effective blockade of guanylate cyclase-coupled receptors. Baseline sodium excretion and urine flow rate were lower in HS-142-1-treated sham-operated rats (15.2+/-1.1 microl/min versus 27.5+/-3.1 microl/min with vehicle, P < 0.001) and in HS-142-1-treated shunted rats (8.1+/-1.3 microl/min versus 19.9+/-2.3 microl/min with vehicle, P < 0.001). After an acute volume load, the diuretic and natriuretic responses were attenuated by HS-142-1 in control and shunted rats. The renal responses were reduced by HS-142-1 to a significantly greater extent in shunted rats than in control rats. HS-142-1 did not induce any significant systemic hemodynamic changes in either group, nor did it alter renal blood flow. However, the GFR in HS-142-1-treated shunted rats was lower than that in vehicle-treated shunted rats, both at baseline (0.6+/-0.3 ml/min versus 2.1+/-0.4 ml/min with vehicle, P < 0.05) and after an acute volume load (1.2+/-0.4 ml/min versus 2.6+/-0.4 ml/min with vehicle, P = 0.01), whereas no such effect was observed in control rats. These data indicate that the maintenance of basal renal function and the responses to acute volume loading are dependent on the NP system. The NP seem to be of particular importance for the maintenance of GFR in this model of experimental heart failure. These observations provide new insights into the importance of the renal NP system in heart failure.

Short-term and long-term inhibition of endogenous atrial natriuretic peptide in dogs with early-stage heart failure

Early-stage heart failure (HF) is characterized by an increase in circulating atrial natriuretic peptide (ANP) without activation of the renin-angiotensin-aldosterone system (RAAS) or body fluid retention. To test the hypothesis that elevated endogenous ANP suppresses the RAAS, maintains body fluid balance, and regulates vascular tone in early-stage HF, we assessed the effects of short-term and long-term inhibition of ANP on cardiorenal and neurohormonal functions. Short-term antagonism was produced by bolus administration (3 mg/kg) of HS-142-1, an antagonist of guanylate-cyclase coupled ANP receptors, and long-term antagonism was produced by continuous infusion (1 mg/kg per h) of HS-142-1 for 8 h to dogs with early-stage HF induced by rapid ventricular pacing (270 beats/min, 8 days). In this experimentally produced HF, plasma ANP was significantly increased relative to the pre-pacing value, but not plasma renin activity (PRA) or plasma aldosterone level. HS-142-1 significantly suppressed plasma and urinary guanosine 3',5'-cyclic monophosphate (cGMP) levels, markers of endogenous ANP activity, in both experiments. Although mean arterial pressure and cardiac output did not change significantly, pulmonary capillary wedge pressure and right atrial pressure were elevated in both experiments. While short-term inhibition of ANP did not change PRA and aldosterone levels, long-term inhibition significantly increased these hormonal levels, resulting in decreases in urine flow rate, urinary sodium excretion rate, glomerular filtration rate, and renal plasma flow. These findings suggest that endogenous ANP plays a critical role in regulating venovascular tone, inhibiting activation of RAAS, and maintaining renal functions in early-stage HF.

Coronary arterial hyperreactivity and mesenteric arterial hyporeactivity after myocardial infarction in the rat

After myocardial infarction, several neurohumoral systems become activated to maintain systemic perfusion pressure. We evaluated whether this leads to alterations of wall structure and contractile reactivity in the thoracic aorta, coronary septal artery, and mesenteric resistance arteries. In male Wistar rats, myocardial infarction (MI) was induced by permanent ligation of the left coronary artery. At 5 weeks after MI or sham operation, vessel segments were isolated, chemically sympathectomized, and mounted in a myograph for recording of isometric force development. Contractile reactivity to high potassium, norepinephrine, phenylephrine, serotonin, and Arg-vasopressin was determined. At the end of the experiments, vessels were fixed for morphometric analysis (cross-sectional area, media thickness, radius, and wall-to-lumen ratio). At 5 weeks after myocardial infarction, no alterations of contractile reactivity or wall structure were observed in the thoracic aorta of MI rats. In mesenteric resistance arteries, a nonselective reduction of maximal active wall tension and of active wall stress in response to vasoconstrictors was observed, whereas vessel wall structure and sensitivity to stimuli were not modified. On the other hand, coronary septal arteries displayed hyperreactivity to all strong contractile stimuli. These observations demonstrate a heterogeneity of arterial reactivity changes at 5 weeks after MI in the rat: (a) no alterations in thoracic aorta, (b) hyporeactivity of mesenteric resistance arteries despite maintenance of media mass, and (c) hyperreactivity of coronary vessels obtained from the hypertrophic remnant myocardium. This could result from the complex regional hemodynamic and neurohumoral changes associated with heart failure and may contribute to the further deterioration of cardiovascular function in this setting.