Regulation of fluid reabsorption in rat or mouse proximal renal tubules by asymmetric dimethylarginine and dimethylarginine dimethylaminohydrolase 1.

Nitric oxide prevents hypertension yet enhances proximal tubule Na+ reabsorption. Nitric oxide synthase is inhibited by asymmetric dimethylarginine (ADMA) that is metabolized by dimethylarginine dimethylaminohydrolase (DDAH) whose type 1 isoform is expressed abundantly in the proximal tubule (PT). We hypothesize that ADMA metabolized by DDAH-1 inhibits fluid reabsorbtion (Jv) by the proximal tubule. S2 segments of the PT were microperfused between blocks in vivo to assess Jv in anesthetized rats. Compared with vehicle, microperfusion of ADMA or Nω-nitro-l-arginine methyl ester (l-NAME) in the proximal tubule reduced Jv dose dependently. At 10-4 mol/l both reduced Jv by ~40% (vehicle: 3.2 ± 0.7 vs. ADMA: 2.1 ± 0.5, P < 0.01 vs. l-NAME: 1.9 ± 0.4 nl·min-1·mm-1, P < 0.01; n = 10). Selective inhibition of DDAH-1 in rats with intravenous L-257 (60 mg/kg) given 2 h before and L-257 (10-5 mol/l) perfused in the proximal tubule for 5 min reduced Jv by 32 ± 4% (vehicle: 3.2 ± 0.5 vs. L-257: 2.2 ± 0.5 nl·min-1·mm-1; P < 0.01) and increased plasma ADMA by ≈50% (vehicle: 0.46 ± 0.03 vs. L-257: 0.67 ± 0.03 µmol/l, P < 0.0001) without changing plasma symmetric dimethylarginine. Compared with nontargeted control small-interference RNA, knock down of DDAH-1 in mice by 60% with targeted small-interference RNAs (siRNA) reduced Jv by 29 ± 5% (nontargeted siRNA: 2.8 ± 0.20 vs. DDAH-1 knockdown: 1.9 ± 0.31 nl·min-1·mm-1, P < 0.05). In conclusion, fluid reabsorption in the proximal tubule is reduced by tubular ADMA or by blocking its metabolism by DDAH-1. L-257 is a novel regulator of proximal tubule fluid reabsorption.

A quality improvement initiative for delayed umbilical cord clamping in very low-birthweight infants.

BACKGROUND: Due to clinical benefits, delayed cord clamping (DCC) is recommended in infants born before 37 weeks gestational age. The objective was to institute a delayed cord clamping program and to evaluate clinical outcomes one year after initiation. METHODS: This study occured at Christiana Care Health System, a tertiary care facility with a 52 bed level 3 Neonatal Intensive Care Unit (NICU). A multidisciplinary team created a departmental policy, a DCC protocol and educational programs to support the development of a DCC program. A year after initiation of DCC, we evaluated two cohorts of very low birth weight (VLBW) infants (<1500 g) prior to (Cohort 1) and after initiation (Cohort 2) of DCC (n = 136 and n = 142 respectively). Chart review was conducted to evaluate demographic data and clinical outcomes. Analysis was completed with a retrospective, cohort analysis on an intention-to-treat basis. RESULTS: There were no differences in demographic factors between the two cohorts. We demonstrated a 73 % compliance rate with the delayed cord clamping protocol and a decrease in the percentage of VLBW infants requiring red blood cell transfusion from 53.7 to 35.9 % (p = 0.003). We also found a decreased need for respiratory support in the second cohort with no increases in the balancing measures of admission hypothermia and jaundice requiring phototherapy. During the Control Phase ongoing monitoring and education has led to a 93.7 % compliance rate. CONCLUSIONS: A multidisciplinary team including key leadership from the obstetric and pediatric departments allowed for the rapid and safe implementation of DCC.

Adenosine A1-receptor knockout mice have a decreased blood pressure response to low-dose ANG II infusion.

Adenosine, acting on A(1)-receptors (A(1)-AR) in the nephron, increases sodium reabsorption, and also increases renal vascular resistance (RVR), via A(1)-ARs in the afferent arteriole. ANG II increases blood pressure and RVR, and it stimulates adenosine release in the kidney. We tested the hypothesis that ANG II-infused hypertension is potentiated by A(1)-ARs' influence on Na(+) reabsorption. Mean arterial pressure (MAP) was measured by radiotelemetry in A(1)-AR knockout mice (KO) and their wild-type (WT) controls, before and during ANG II (400 ng·kg(-1)·min(-1)) infusion. Baseline MAP was not different between groups. ANG II increased MAP in both groups, but on day 12, MAP was lower in A(1)-AR KO mice (KO: 128 ± 3 vs. 139 ± 3 mmHg, P < 0.01). Heart rates were significantly different during days 11-14 of ANG II. Basal sodium excretion was not different (KO: 0.15 ± 0.03 vs. WT: 0.13 ± 0.04 mmol/day, not significant) but was higher in KO mice 12 days after ANG II despite a lower MAP (KO: 0.22 ± 0.03 vs. WT: 0.11 ± 0.02 mmol/day, P < 0.05). Phosphate excretion was also higher in A(1)-AR KO mice on day 12. Renal expression of the sodium-dependent phosphate transporter and the Na(+)/glucose cotransporter were lower in the KO mice during ANG II treatment, but the expression of the sodium hydrogen exchanger isoform 3 was not different. These results indicate that the increase in blood pressure seen in A(1)-AR KO mice is lower than that seen in WT mice but was increased by ANG II nonetheless. The presence of A(1)-ARs during a low dose of ANG II-infusion limits Na(+) and phosphate excretion. This study suggests that A(1)-AR antagonists might be an effective antihypertensive agent during ANG II and volume-dependent hypertension.

Glomerular tubular balance is suppressed in adenosine type 1 receptor-deficient mice.

Glomerular tubular balance maintains a stable fractional solute and fluid reabsorption in the proximal tubule over a range of glomerular filtration rates. The mediators of this process are unknown. We tested the hypothesis that adenosine, produced in proximal tubule cells acting on adenosine type 1 receptors (A(1)-AR) promotes Na(+) and fluid uptake and mediates glomerular tubular balance. Absolute proximal fluid reabsorption (J(v)) was measured by in vivo microperfusion in A(1)-AR knockout and wild-type mice during perfusion of the closed proximal tubule at 2-10 nl/min. J(v) increased with perfusate flow from 2-4 nl/min in both strains, but the fractional increase was lower in A(1)-AR(-/-) mice (A(1)-AR(+/+): 114% vs. A(1)-AR(-/-): 38%; P < 0.001), suggesting reduced glomerular tubular balance (GTB). At higher perfusion rates, J(v) increased modestly in both strains, indicating less GTB at higher flow. The physiological effects of reduced GTB in A(1)-AR(-/-) mice were assessed from the response to an acute volume load (1 ml/2 min). Na(+) excretion and urine flow increased 76 and 73% more in A(1)-AR(-/-) mice than A(1)-AR(+/+) over the following 30 min, accompanied by a higher proximal tubule flow (A(1)-AR(-/-): 6.9 ± 0.9 vs. A(1)-AR(+/+): 5.2 ± 0.6 nl/min; P < 0.05). The expression of the sodium-hydrogen exchanger 3 and sodium phosphate cotransporter-2 were similar between strains. In conclusion, GTB is dependent on adenosine acting on type 1 receptors in the proximal tubule. This may contribute to acute changes in Na(+) and fluid reabsorption.

Regulation of renal arteriolar tone by adenosine: novel role for type 2 receptors.

Tubuloglomerular feedback regulation of glomerular filtration rate (GFR) is mediated by adenosine, which acts on type 1 receptors in the afferent arteriole to increase resistance. However, new findings in isolated mouse tissue suggest that adenosine also dilates the efferent arteriole, which would reinforce the ability of adenosine to reduce GFR. This new information extends the concept that adenosine acts as a paracrine agent on both afferent and efferent arterioles.

Blood pressure early in diabetes depends on a balance between glomerular filtration rate and the renin-angiotensin system.

Onset of diabetes increases plasma renin activity (PRA) and glomerular filtration rate (GFR), but blood pressure (BP) is normal. In this study, a 70% surgical reduction in kidney mass (RK) was used to decrease baseline GFR and to prevent hyperfiltration during diabetes, and angiotensin converting enzyme inhibitors (ACEI) were used to inhibit angiotensin II (AngII) production, to test the hypothesis that a balance between GFR and AngII is required for normal BP early in diabetes. Diabetes was induced with streptozotocin (STZ) (35 mg/kg intravenously); and after 7 days of hyperglycemia (range: 408 to 486 mg/dL), insulin was intravenously infused continuously for a 4-day normoglycemic recovery period. In normal kidney (NK) rats, diabetes increased PRA (2.4 +/- 0.6 to 4.6 +/- 0.5 ngAI/mL/h) and GFR (2.9 +/- 0.1 to 3.5 +/- 0.2 mL/min), and there was no change in mean arterial pressure (MAP) (89 +/- 1 v 91 +/- 1 mm Hg, measured 18 h/day). There was no change in either GFR or AngII during diabetes in RK+ACEI rats, and their MAP also did not change. Thus, the maintenance of normal MAP was accompanied by a balance between GFR and AngII in both of those groups. In NK+ACEI rats, however, GFR increased significantly with no change in AngII, and MAP decreased significantly during diabetes by approximately 8 mm Hg. In RK rats, PRA increased (0.5 +/- 0.1 to 2.6 +/- 0.5) but GFR did not increase, and MAP increased significantly by approximately 16 mm Hg. All rats were in sodium balance by day 4 of diabetes. These data support the hypothesis that normotension early in diabetes requires a balance between the increased AngII and GFR, and that BP will increase if AngII increases but GFR does not.

Phase I Safety, Pharmacokinetic, and Pharmacodynamic Study of the Poly(ADP-ribose) Polymerase (PARP) Inhibitor Veliparib (ABT-888) in Combination with Irinotecan in Patients with Advanced Solid Tumors.

PURPOSE: PARP is essential for recognition and repair of DNA damage. In preclinical models, PARP inhibitors modulate topoisomerase I inhibitor-mediated DNA damage. This phase I study determined the MTD, dose-limiting toxicities (DLT), pharmacokinetics (PK), and pharmacodynamics (PD) of veliparib, an orally bioavailable PARP1/2 inhibitor, in combination with irinotecan. EXPERIMENTAL DESIGN: Patients with advanced solid tumors were treated with 100 mg/m(2) irinotecan on days 1 and 8 of a 21-day cycle. Twice-daily oral dosing of veliparib (10-50 mg) occurred on days 3 to 14 (cycle 1) and days -1 to 14 (subsequent cycles) followed by a 6-day rest. PK studies were conducted with both agents alone and in combination. Paired tumor biopsies were obtained after irinotecan alone and veliparib/irinotecan to evaluate PARP1/2 inhibition and explore DNA damage signals (nuclear γ-H2AX and pNBS1). RESULTS: Thirty-five patients were treated. DLTs included fatigue, diarrhea, febrile neutropenia, and neutropenia. The MTD was 100 mg/m(2) irinotecan (days 1 and 8) combined with veliparib 40 mg twice daily (days -1-14) on a 21-day cycle. Of 31 response-evaluable patients, there were six (19%) partial responses. Veliparib exhibited linear PK, and there were no apparent PK interactions between veliparib and irinotecan. At all dose levels, veliparib reduced tumor poly(ADP-ribose) (PAR) content in the presence of irinotecan. Several samples showed increases in γ-H2AX and pNBS1 after veliparib/irinotecan compared with irinotecan alone. CONCLUSIONS: Veliparib can be safely combined with irinotecan at doses that inhibit PARP catalytic activity. Preliminary antitumor activity justifies further evaluation of the combination. Clin Cancer Res; 22(13); 3227-37. ©2016 AACR.

Chronic glucose infusion causes sustained increases in tubular sodium reabsorption and renal blood flow in dogs.

This study tested the hypothesis that inducing hyperinsulinemia and hyperglycemia in dogs, by infusing glucose chronically intravenously, would increase tubular sodium reabsorption and cause hypertension. Glucose was infused for 6 days (14 mg.kg(-1).min(-1) iv) in five uninephrectomized (UNX) dogs. Mean arterial pressure (MAP) and renal blood flow (RBF) were measured 18 h/day using DSI pressure units and Transonic flow probes, respectively. Urinary sodium excretion (UNaV) decreased significantly on day 1 and remained decreased over the 6 days, coupled with a significant, sustained increase in RBF, averaging approximately 20% above control on day 6. Glomerular filtration rate and plasma renin activity (PRA) also increased. However, although MAP tended to increase, this was not statistically significant. Therefore, the glucose infusion was repeated in six dogs with 70% surgical reduction in kidney mass (RKM) and high salt intake. Blood glucose and plasma insulin increased similar to the UNX dogs, and there was significant sodium retention, but MAP still did not increase. Interestingly, the increases in PRA and RBF were prevented in the RKM dogs. The decrease in UNaV, increased RBF, and slightly elevated MAP show that glucose infusion in dogs caused a sustained increase in tubular sodium reabsorption by a mechanism independent of pressure natriuresis. The accompanying increase in PRA, together with the failure of either RBF or PRA to increase in the RKM dogs, suggests the site of tubular reabsorption was before the macula densa. However, the volume retention and peripheral edema suggest that systemic vasodilation offsets any potential renal actions to increase MAP in this experimental model in dogs.

Continuously measured renal blood flow does not increase in diabetes if nitric oxide synthesis is blocked.

This study used 16 h/day measurement of renal blood flow (RBF) and arterial pressure (AP) to determine the role of nitric oxide (NO) in mediating the renal vasodilation caused by onset of type 1 diabetes. The AP and RBF power spectra were used to determine the autoregulatory efficiency of the renal vasculature. Rats were instrumented with artery and vein catheters and a Transonic flow probe on the left renal artery and were divided randomly into four groups: control (C), diabetes (D), control plus nitro-L-arginine methyl ester (L-NAME; CL), and diabetes plus L-NAME (DL). Mean AP averaged 90 +/- 1 and 121 +/- 1 mmHg in the D and DL groups, respectively, during the control period, and RBF averaged 5.9 +/- 1.2 and 5.7 +/- 0.7 ml/min, respectively. Respective C and CL groups were not different. Onset of diabetes (streptozotocin 40 mg/kg iv) in D rats increased RBF gradually, but it averaged 55% above control by day 14. In DL rats, on the other hand, RBF remained essentially constant, tracking with RBF in the nondiabetic C and CL groups for the 2-wk period. Diabetes did not change mean AP in any group. Transfer function analysis revealed impaired dynamic autoregulation of RBF overall, including the frequency range of tubuloglomerular feedback (TGF), and L-NAME completely prevented those changes as well. These data strongly support a role for NO in causing renal vasodilation in diabetes and suggest that an effect of NO to blunt RBF autoregulation may play an important role.

Lack of blood pressure salt-sensitivity supports a preglomerular site of action of nitric oxide in Type I diabetic rats.

1. The relationship between sodium intake and blood pressure is affected differently by changes in angiotensin (Ang) II and preglomerular resistance, and this study measured that relationship to evaluate the link between nitric oxide and blood pressure early in diabetes. 2. Rats were chronically instrumented, placed on high-sodium (HS = 12 mEq/d) or low-sodium (LS = 0.07 mEq/d) intake diets and assigned to either vehicle- (V) or Nomega-nitro-L-arginine methyl ester- (L-NAME; L) treated groups. Mean arterial pressure (MAP) was measured 18 h/day for a 6-day control and 14-day streptozotocin diabetic period in each animal. 3. The MAP of the control period averaged 95 +/- 1 and 94 +/- 1 mmHg in the LSV and HSV rats and 116 +/- 2 and 124 +/- 1 mmHg in the LSL and HSL rats, respectively (LSL vs HSL was significant at P < 0.05). Diabetes increased MAP only in the LSL and HSL rats to 141 +/- 2 mmHg and 152 +/- 2, respectively, similar to our previous reports, and those respective 25 and 28 mmHg increases were a parallel shift in the pressure natriuresis relationship. However, the apparent difference between the LSL and HSL groups when compared was a parallel of the control MAP difference. Plasma renin activity (PRA) in the control period averaged 1.5 +/- 0.5 and 8.1 +/- 1.8 ng AI/mL per h in the HSV and LSV rats, and 0.8 +/- 0.2 and 2.8 +/- 0.5 ng AI/mL per h in the HSL and LSL rats, respectively, and increased similarly by 4.6-fold in the HSL and 4.8-fold in the LSL rats during diabetes. Glomerular filtration rate (GFR) increased in the vehicle but not the L-NAME-treated groups, consistent with our previous reports. 4. Thus, the hypertension caused by the onset of diabetes in L-NAME-treated rats was not salt-sensitive. The normal modulation of PRA by salt intake and the failure of GFR to increase are consistent with our hypothesis that nitric oxide may protect against hypertension early in diabetes by preventing preglomerular vasoconstriction by AngII.

Mechanisms for renal blood flow control early in diabetes as revealed by chronic flow measurement and transfer function analysis.

The purpose of this study was to establish the roles of the myogenic response and the TGF mechanism in renal blood flow (RBF) control at the very earliest stages of diabetes. Mean arterial pressure (MAP) and RBF were measured continuously, 18 h/d, in uninephrectomized control and diabetic rats, and transfer function analysis was used to determine the dynamic autoregulatory efficiency of the renal vasculature. During the control period, MAP averaged 91 +/- 0.5 and 89 +/- 0.4 mmHg, and RBF averaged 8.0 +/- 0.1 and 7.8 +/- 0.1 ml/min in the control and diabetic groups, respectively. Induction of diabetes with streptozotocin caused a marked and progressive increase in RBF in the diabetic rats, averaging 10 +/- 6% above control on day 1 of diabetes and 22 +/- 3 and 34 +/- 1% above control by the end of diabetes weeks 1 and 2. MAP increased approximately 9 mmHg during the 2 wk in the diabetic rats, and renal vascular resistance decreased. Transfer function analysis revealed significant increases in gain to positive values over the frequency ranges of both the TGF and myogenic mechanisms, beginning on day 1 of diabetes and continuing through day 14. These very rapid increases in RBF and transfer function gain suggest that autoregulation is impaired at the very onset of hyperglycemia in streptozotocin-induced type 1 diabetes and may play an important role in the increase in RBF and GFR in diabetes. Together with previous reports of decreases in chronically measured cardiac output and hindquarter blood flow, this suggests that there may be differential effects of diabetes on RBF versus nonrenal BF control.

Nitric oxide may prevent hypertension early in diabetes by counteracting renal actions of superoxide.

The dependence of blood pressure on a balance between superoxide and nitric oxide may be amplified in diabetes. We have shown that the first occurrence of sustained hyperglycemia in type I diabetes causes hypertension when induced in rats that have had nitric oxide synthesis blocked chronically (L-NAME, 10 microg/kg per minute IV). This study used tempol (18 micromol/kg per hour IV) to test the hypothesis that superoxide mediates that hypertensive response. Induction of diabetes in untreated rats had no significant effect on mean arterial pressure (MAP, measured 18 h/d), and glomerular filtration rate (GFR) increased significantly during the 2 weeks of diabetes. Chronic infusion of L-NAME in a separate group of rats increased baseline MAP from approximately 90 mm Hg to a stable level of approximately 120 mm Hg after 6 days of infusion, and induction of diabetes (streptozotocin, 40 mg/kg IV) in those rats caused a rapid, progressive increase in MAP that averaged 156+/-5 mm Hg by day 14 of diabetes that was associated with a decrease in GFR and 4-fold increase in isoprostane excretion. Tempol infusion was begun on day 2 of diabetes in a subgroup of those rats, and the progressive hypertensive response was prevented, with MAP averaging 134+/-10 mm Hg by day 14. In addition, the normal renal hyperfiltration response was restored by tempol and the increase in isoprostane did not occur. Thus, the hypertension and decrease in GFR caused by onset of diabetes in rats without a functioning nitric oxide system was prevented by chronic administration of the superoxide dismutase mimetic tempol.