Rawi Ramadan

Mechanisms of big endothelin-1-induced diuresis and natriuresis : role of ET(B) receptors.

Endothelin-1 (ET-1) at high concentrations has marked antidiuretic and antinatriuretic activities, whereas its precursor, big endothelin-1 (big ET-1), has surprisingly potent diuretic and natriuretic actions. The mechanisms underlying the excretory effects of big ET-1 have not been fully elucidated. To explore these mechanisms, we examined the effects of a highly selective ET(B) antagonist (A-192621.1), a calcium channel blocker (verapamil), a nitric oxide synthase inhibitor (N-nitro-L-arginine methyl ester [L-NAME]), and a cyclooxygenase inhibitor (indomethacin) on the systemic and renal actions of big ET-1 in anesthetized rats. An intravenous bolus injection of incremental doses of big ET-1 (0.3, 1. 0, and 3.0 nmol/kg) produced a significant hypertensive effect that was dose dependent and prolonged (from 113+/-7 mm Hg to a maximum of 148+/-6 mm Hg). The administration of big ET-1 induced marked diuretic and natriuretic responses (urinary flow rate increased from 8.5+/-1 to 110+/-14 microL/min, and fractional excretion of sodium increased from 0.38+/-0.13% to 7.51+/-1.24%). Glomerular filtration rate and renal plasma flow significantly decreased only at the highest dose of big ET-1. Pretreatment with A-192621.1 (3 mg/kg plus 3 mg. kg(-1). h(-1)) significantly abolished the diuretic (17+/-5 microL/min to a maximum of 19+/-3 microL/min) and natriuretic (0. 29+/-0.1% to a maximum of 1.93+/-0.37%) responses induced by big ET-1. Moreover, A-192621.1 potentiated the decline in glomerular filtration rate and renal plasma flow and the increase in mean arterial blood pressure produced by the low doses of big ET-1. Similar to A-192621.1, pretreatment with a nitric oxide synthase inhibitor (L-NAME, 10 mg/kg plus 5 mg. kg(-1). h(-1)) significantly and comparably reduced the diuretic and natriuretic actions of big ET-1 and augmented the hypoperfusion/hypofiltration and systemic vasoconstriction induced by high doses of the peptide. Pretreatment with verapamil (2 mg. kg(-1). h(-1)) slightly inhibited the diuretic/natriuretic effects of the high-dose big ET-1 and completely prevented the increase in mean arterial blood pressure provoked by the peptide. Unlike verapamil and L-NAME, only indomethacin administration was associated with significant natriuretic/diuretic responses and did not influence the pressor effect and renal actions of big ET-1. Taken together, these results suggest that big ET-1-induced diuretic and natriuretic responses are mediated mainly by stimulation of nitric oxide production coupled to ET(B) receptor subtype activation.

Effects of A-192621.1, a specific endothelin-B antagonist, on intrarenal hemodynamic responses to endothelin-1

The present study examined the effects of A-192621.1, a highly selective endothelin-B- (ETB) receptor antagonist, on the renal hemodynamic and systemic actions of endothelin-1 (ET-1). Intravenous injection of ET-1 (1.0 nmol/kg) into anesthetized rats produced a sustained decrease in renal blood flow (assessed by ultrasonic flowmeter) and a significant increase in renal vascular resistance, as well as an increase in mean arterial pressure. These changes were significantly augmented by pretreatment with A-192621.1 (3.0 mg/kg/h). Analysis of intrarenal blood flow by laser-Doppler flowmeter revealed that ET-1 caused a marked and sustained decrease in cortical blood flow, associated with a transient increase in medullary blood flow. The reduction in cortical blood flow in response to ET-1 was further enhanced by pretreatment with A-192621.1, whereas the ET-1-induced medullary vasodilatation was completely abolished and reversed into a vasoconstrictor response. These findings suggest that the ETB-receptors mediate the systemic and renal vasodilatory actions of ET-1 in the rat, and that their activation may serve as a physiological counterbalance that modulates ET-1-induced vasoconstriction.

Pneumoperitoneum Aggravates Renal Function in Cases of Decompensated But Not Compensated Experimental Congestive Heart Failure: Role of Nitric Oxide

PURPOSE Congestive heart failure is associated with impaired renal function. Previously we noted that increased intra-abdominal pressure (pneumoperitoneum) in normal rats induced renal dysfunction. In this study we investigated the renal effects of pneumoperitoneum in rats with compensated (urinary Na(+) excretion greater than 1,200 μEq per 24 hours) and decompensated (urinary Na(+) excretion less than 200 μEq per 24 hours) congestive heart failure, and the possible involvement of nitric oxide in these effects. MATERIALS AND METHODS After a baseline period rats with congestive heart failure induced by aorto-caval fistula and sham operated controls underwent consecutive intra-abdominal pressures of 7, 10 or 14 mm Hg for 45 minutes each. Urinary flow, urinary Na(+) excretion, glomerular filtration rate, renal plasma flow and urinary nitric oxide metabolites were determined. RESULTS There were no changes in urinary flow, urinary Na(+) excretion, glomerular filtration rate or renal plasma flow during 7 mm Hg insufflation in controls. However, significant decreases in these parameters were observed during 10 and 14 mm Hg in correlation with intra-abdominal pressure. Baseline renal function and hemodynamics were lower in rats with congestive heart failure in correlation with disease severity. Rats with decompensated congestive heart failure that underwent 10 and 14 mm Hg showed aggravated decreases in urinary flow, urinary Na(+) excretion, glomerular filtration rate and renal plasma flow. In contrast, no adverse renal effects were observed in rats with compensated congestive heart failure under identical intra-abdominal pressure conditions. Despite unaltered baseline urinary nitric oxide metabolites in the 2 congestive heart failure subgroups, the decompensated group showed decreased urinary nitric oxide metabolites after 14 mm Hg. Finally, rats with compensated congestive heart failure pretreated with the nitric oxide synthase inhibitor L-NAME showed worse renal function in response to pneumoperitoneum. CONCLUSIONS Decompensated congestive heart failure renders rats susceptible to the adverse renal effects of pneumoperitoneum, a phenomenon that may involve alterations in the renal nitric oxide system.

Early treatment with everolimus exerts nephroprotective effect in rats with adriamycin-induced nephrotic syndrome

BACKGROUND Nephrotic syndrome (NS) is a clinical state characterized by massive proteinuria and excessive fluid retention. The effects of early versus late treatment with low or high doses of oral everolimus, a mammalian target of rapamycin inhibitor, on proteinuria in NS have not been previously described. METHODS The effects of early treatment (2 days prior to NS induction) versus late treatment (beginning 2 weeks following the establishment of NS) with a low (20 mg/L) or high (100 mg/L) dose of everolimus for 5-7 weeks on proteinuria and nephrin/podocin abundance were assessed in male adult SD rats with adriamycin-induced NS. RESULTS Adriamycin caused a significant increase in daily and cumulative proteinuria throughout the experimental period. Early, and to a lesser extent late treatment, with a low dose of everolimus, significantly decreased both daily and cumulative proteinuria and improved renal function. The anti-proteinuric effects of low-dose everolimus were associated with restoration of the disruptive glomerular nephrin/podocin abundance. In contrast, administration of a high dose of everolimus resulted in a decrease in proteinuria in NS rats, subsequently to deterioration of renal function. CONCLUSIONS Early, and to a lesser extent late treatment, with a low but not a high dose of everolimus is effective in reducing proteinuria in nephrotic rats. The mechanism may be via nephrin/podocin protection.

Urinary Excretion of Endothelin Receptors ETA and ETB in Hypertensive Patients and Normotensive Subjects

Background/Aims: Endothelin (ET)-1 is produced by most renal cell types. Renal tubular and vascular cells express both the ET receptors ETA and ETB. Since significant amounts of ET-1 of renal origin were detected in human urine, urinary ET-1 has been used as an index for the capacity of renal ET-1 production. Here, we determine the existence of additional components of the intrarenal ET system, namely the ETA and ETB receptor subtypes, in the urine of normal and hypertensive subjects. Methods: ETA and ETB receptors were detected in urine samples that were concentrated by TCA precipitation, Speedvac or ProteoSpin™. Results: Analysis of the human urine extracts revealed the existence of approximately 50 and 55 kDa of immunoreactive proteins, corresponding to ETB and ETA, respectively, indicating that intact ETA and ETB are excreted in the urine of healthy subjects and hypertensive patients. Normotensive and hypertensive subjects had statistically comparable ETB excretion normalized to creatinine (0.58 ± 0.16 vs. 0.83 ± 0.17 μg/mg creatinine, respectively; p = 0.304). In contrast, ETA excretion was higher among hypertensive subjects (0.05 ± 0.01 vs. 0.11 ± 0.02 μg/mg creatinine; p = 0.0451). Immunostaining of ETA and ETB in the human urinary system revealed expression of both receptors, principally in tubular cells (mainly in medullary collecting ducts) and in the bladder urothelium, and ETA expression in the peritubular capillaries and arterioles. Urinary ET receptors closely and inversely correlated with indices of urine concentration, suggesting that their shedding is principally affected by urine flow. Conclusion: ET receptors are present in human urine, conceivably originating within the urinary system. Their excretion is principally affected by urinary concentration. It remains to be determined whether urinary ETA/ETB is of physiological/pathophysiological relevance.

Renal and Systemic Effects of Endothelin-1 in Diabetic-Hypertensive Rats

Abstract The Cohen-Rosenthal Diabetic Hypertensive rat (CRDH) is a unique animal model in which genetic hypertension and diabetes developed after crossbreeding of Cohen diabetic rats sensitive substrain (CDR) and spontaneously hypertensive rats (SHR). The present study examined: 1) The acute effects of ET-1 on the systemic and renal hemodynamics in CRDH rats, CDR, and SHR; 2) The expression of ET-1 and its receptors in the renal tissue of CRDH rats. Intravenous injection of ET-1 (1.0 nmol/kg) into anesthetized SHR rats resulted in a significant immediate depressor response (mean arterial pressure (MAP) decreased from 165 ± 3 to 124 ± 12 mmHg, p < 0.0001) followed by a minor hypertensive phase (MAP increased to 170 ± 2 mmHg). Simultaneously, the administration of ET-1 caused a significant decrease in renal blood flow (RBF) from 5.8 ± 0.9 ml/min to 3.2 ± 0.5 ml/min (p = 0.026). These responses were blunted in CRDH rats and CDR. Analysis of intra-renal blood flow by laser-Doppler in CRDH rats revealed that ET-1 injection caused a decrease in cortical blood flow (Δ = −12 ± 2.9%). However, in contrast to its well-known renal medullary vasodilatory effect, ET-1 produced a significant decline in the medulla blood flow (Δ = −17.5 ± 3.4%) (p = 0.0125). These findings suggest that CDR and CRDH rats have reduced sensitivity to vascular and renal action of ET-1. Furthermore, in the CRDH rats, the expected ET-1-induced medullary vasodilatation was abolished and even reversed into prolonged vasoconstriction.