Low-dose L-NAME induces salt sensitivity associated with sustained increased blood volume and sodium-chloride cotransporter activity in rodents

To investigate the cause of salt sensitivity in a normotensive animal model, we treated rats with a low-dose of the nitric oxide synthase inhibitor, L-NAME, that does not elevate blood pressure per se or induce kidney fibrosis. A high salt diet increased the circulating blood volume both in L-NAME-treated and nontreated animals for the first 24 hours. Thereafter, the blood volume increase persisted only in the L-NAME-treated rats. Blood pressure was higher in the L-NAME-treated group from the start of high salt diet exposure. Within the first 24 hours of salt loading, the L-NAME treated animals failed to show vasodilation and maintained high systemic vascular resistance in response to blood volume expansion. After four weeks on the high salt diet, the slope of the pressure-natriuresis curve was blunted in the L-NAME-treated group. An increase in natriuresis was observed after treatment with hydrochlorothiazide, but not amiloride, a change observed in parallel with increased phosphorylated sodium-chloride cotransporter (NCC). In contrast, a change in blood pressure was not observed in L-NAME-treated NCC-deficient mice fed a high salt diet. Moreover, direct L-NAME-induced NCC activation was demonstrated in cells of the mouse distal convoluted tubule. The vasodilatator, sodium nitroprusside, downregulated phosphorylated NCC expression. The effect of L-NAME on phosphorylated NCC was blocked by both the SPAK inhibitor STOCK2S-26016 and the superoxide dismutase mimetic TEMPO which also attenuated salt-induced hypertension. These results suggest that the initiation of salt sensitivity in normotensive rodents could be due to hyporeactivity of the vasculature and that maintaining blood pressure could result in a high circulating volume due to inappropriate NCC activity in the low-dose L-NAME model. Thus, even slightly impaired nitric oxide production may be important in salt sensitivity regulation in healthy rodents.

Abstract P164: Inflammatory Cell Populations in a Mouse Model of Cardiorenal Syndrome

Objective: Renal dysfunction frequently coexists with heart disease, manifesting in a condition called cardiorenal syndrome (CRS). CRS results in accelerated failure of the heart and kidney via a complex combination of hemodynamic, neurohormonal, immunological and biochemical feedback pathways. Preliminary evidence suggests that inflammatory cells such as monocytes and macrophages may contribute to the pathogenesis of CRS. However, animal models of CRS remain limited and the roles of specific inflammatory cell subsets in CRS remains unclear. Here, we describe the establishment of a mouse model of CRS.

Methods: Three-week-old C57BL/6J mice were subjected to sham uninephrectomy and normal-salt (SHAM/NS) diet or left uninephrectomy and high-salt (UNIX/HS) diet. After 4, 6 or 8 weeks, urine was collected for salt and protein analyses. The heart and kidney were collected for histochemical staining and analyses of inflammatory cell distribution by flow cytometry.

Results: UNIX/HS mice had a higher kidney weight/body weight ratio and higher water intake than that of SHAM/NS mice. As early as 4 weeks post-surgery, UNIX/HS mice had higher urine creatinine levels (0.22 ± 0.02 mg/day c.f. 0.13 ± 0.02 mg/day) and higher proteinuria (0.46 ± 0.18 mg/day c.f. 5.37 ± 1.19 mg/day) than SHAM/NS mice. These results suggest the development of kidney dysfunction. Histological analysis revealed increased fibrosis in the heart and kidney at 8 weeks after UNIX/HS. Using flow cytometry, we characterized changes in the inflammatory cell populations in the heart and kidney that occur as CRS progresses. A significant increase in Ly6C hi monocyte (0.29 ± 0.06% c.f. 0.15 ± 0.02% of mean 1.0 x 10 6 total live cells) and neutrophil (1.00 ± 0.27% c.f. 0.41 ± 0.09%) proportions in the heart was observed 8 weeks after UNIX/HS.

Conclusion: Therapeutic strategies targeting inflammatory signaling pathways and modulating specific inflammatory cell populations may reduce organ damage and improve prognosis in patients with CRS.

Aliskiren reduces myocardial ischemia-reperfusion injury by a bradykinin B2 receptor- and angiotensin AT2 receptor-mediated mechanism

Angiotensin-converting enzyme inhibitors and angiotensin AT1 receptor blockers reduce myocardial ischemia-reperfusion injury via bradykinin B2 receptor- and angiotensin AT2 receptor-mediated mechanisms. The renin inhibitor aliskiren increases cardiac tissue kallikrein and bradykinin levels. In the present study, we investigated the effect of aliskiren on myocardial ischemia-reperfusion injury and the roles of B2 and AT2 receptors in this effect. Female Sprague-Dawley rats were treated with aliskiren (10 mg/kg per day) and valsartan (30 mg/kg per day), alone or in combination, together with the B2 receptor antagonist icatibant (0.5 mg/kg per day) or the AT2 receptor antagonist PD123319 (30 mg/kg per day), for 4 weeks before myocardial ischemia-reperfusion injury. Aliskiren increased cardiac bradykinin levels and attenuated valsartan-induced increases in plasma angiotensin II levels. In vehicle-treated rats, myocardial infarct size (% area at risk, mean±SEM, n=7-13) was 43±3%. This was reduced to a similar extent by aliskiren, valsartan, and their combination to 24±3%, 25±3%, and 22±2%, respectively. Icatibant reversed the cardioprotective effects of aliskiren and the combination of aliskiren plus valsartan, but not valsartan alone, indicating that valsartan-induced cardioprotection was not mediated by the B2 receptor. PD123319 reversed the cardioprotective effects of aliskiren, valsartan, and the combination of aliskiren plus valsartan. Aliskiren protects the heart from myocardial ischemia-reperfusion injury via a B2 receptor- and AT2 receptor-mediated mechanism, whereas cardioprotection by valsartan is mediated via the AT2 receptor. In addition, aliskiren attenuates valsartan-induced increases in angiotensin II levels, thus preventing AT2 receptor-mediated cardioprotection by valsartan.