Sodium transport antagonism reduces thrombotic microangiopathy in stroke-prone spontaneously hypertensive rats

Abstract

We examined whether amiloride, an agent that possesses epithelial sodium channel (ENaC)- and sodium/hydrogen exchange (NHE)-inhibitory activities, would exhibit renal vascular protection in saline-drinking, stroke-prone spontaneously hypertensive rats (SHRSP). SHRSP received amiloride (1.0 mg.kg(-1).day(-1), n = 6) or deionized water (3 mg.kg(-1).day(-1), n = 6) for 5 wk starting at 61 days of age. Systolic blood pressure (SBP) did not differ among the groups, and there was no difference in the average daily urine output, sodium excretion, or potassium excretion. Terminal urinary protein excretion, blood urea nitrogen, and renal thrombotic microangiopathic lesions were markedly reduced in the amiloride group with no difference in plasma renin activity (PRA). In a survival protocol, SHRSP infused subcutaneously with benzamil (0.7 mg.kg(-1).day(-1), n = 8), a selective ENaC inhibitor, dimethylamiloride (0.7 mg.kg(-1).day(-1), n = 8), a selective NHE inhibitor, or vehicle (n = 7) had comparable SBP. Dimethylamiloride nonetheless prolonged survival of SHRSP (P < 0.005 vs. vehicle), and benzamil-treated SHRSP lived even longer (P < 0.0001 vs. vehicle; P < 0.05 vs. dimethylamiloride). In a separate series, plasma potassium concentration was elevated by dimethylamiloride (3.4 +/- 0.1 meq/l, n = 8) and benzamil (3.3 +/- 0.1 meq/l, n = 8) relative to vehicle (3.0 +/- 0.1 meq/l, n = 8) at 4 but not at 24 h after dosing. These findings suggest the involvement of a sodium transport mechanism in the development of thrombotic microangiopathy in SHRSP, unrelated to marked changes in arterial pressure, PRA, plasma potassium, or urinary water and electrolyte excretion.

Trafficking of ENaC subunits in response to acute insulin in mouse kidney

“…In the first experiment, mice (same age, sex, and strain as above) were injected with insulin and 25% dextrose or vehicle (n ϭ 6/treatment) and urine was collected in metabolic cages (Hatteras Instruments, Cary, NC) for 2.5 h. Three days later, all the mice in the above set were administered benzamil (1.4 mg/kg body wt ip; Sigma, St. Louis, MO), a specific antagonist of ENaC, 30 min following insulin-plus-dextrose or vehicle injections, as above, and then urine was collected for 2.5 h. The 30-min lag period was instituted to allow time for ENaC to be upregulated by insulin before antagonizing its actions. The antinatriuretic response to benzamil has been used as an index of relative ENaC activity (22) and was dosed based on a previously published therapeutic dose (40).…”

Regulation of blood pressure, the epithelial sodium channel (ENaC), and other key renal sodium transporters by chronic insulin infusion in rats

“…This test was performed after 7 days on the study. After a 24-h baseline collection of urine in Nalgene metabolic cages (Harvard Apparatus, Holliston, MA), benzamil (0.7 mg/kg body wt) was administered intraperitoneally (ip) in a single injection based on a previously published therapeutic dose (44). Urine was then collected in the following time increments after the injection: 0 -3, 3-6, and 6 -24 h. Urinary sodium was measured by an ionselective electrode system (EL-ISE Electrolyte System, Beckman Instruments, Brea, CA).…”

Pharmacological manipulation of arachidonic acid-epoxygenase results in divergent effects on renal damage

“…Previous studies in SHRSP using agents that interfere with the renin–angiotensin–aldosterone system have shown a dissociation between BP lowering and protection against salt-sensitive end-organ damage (Stier et al, 1991; Rocha et al, 1998) and have specifically implicated aldosterone as a major factor in the etiology of salt-sensitive kidney damage (Chander et al, 2003). Consistent with a pivotal pathophysiological role of aldosterone in the saline-drinking SHRSP and the ability of aldosterone to stimulate the epithelial sodium channel (ENaC), Sepehrdad et al (2003, 2004) found that amiloride and other agents that inhibit ENaC function offer protective effects against the development of proteinuria and renal microvascular damage. Interestingly, epoxyeicosatrienoic acids (EETs), cytochrome P450 (CYP) epoxygenase metabolites of arachidonic acid, have been shown to directly inhibit ENaC activity (Wei et al, 2004).…”