Acute Saline Volume Expansion Research Articles

Cardiac Versus Renal Response to Volume Expansion in Preclinical Systolic Dysfunction With PDEV Inhibition and BNP

Impaired cardiorenal response to acute saline volume expansion in preclinical systolic dysfunction (PSD) may lead to symptomatic heart failure. The objective was to determine if combination phosphodiesterase-V inhibition and exogenous B-type natriuretic peptide (BNP) administration may enhance cardiorenal response. A randomized double-blinded, placebo-controlled study was conducted in 21 subjects with PSD and renal dysfunction. Pre-treatment with tadalafil and subcutaneous BNP resulted in improved cardiac function, as evidenced by improvement in ejection fraction, left atrial volume index, and left ventricular end-diastolic volume. However, there was reduced renal response with reduction in renal plasma flow, glomerular filtration rate, and urine flow. (Tadalafil and Nesiritide as Therapy in Pre-clinical HeartFailure; NCT01544998).

Abstract P381: Deletion of Na + /H + Exchanger 3 Selectively in the Proximal Tubule of the Kidney Augments Acute and Chronic Natriuretic Responses to Saline Volume Expansion in Mice

The Na + /H + exchanger 3 (NHE3), a ~85 kDa protein encoded by the SLC9A3 gene, plays a key role in mediating Na + reabsorption in the proximal tubule of the kidney and in maintaining blood pressure homeostasis. In the present study, we tested the hypothesis that deletion of NHE3 selectively in the proximal tubule of the kidney, but not globally, augments acute and chronic natriuretic responses to saline volume expansion in mice. Adult male wildtype ( Nhe3 +/+ ), global NHE3 knockout ( Nhe3 -/- ) and proximal tubule-specific NHE3 knockout mice (PT- Nhe3 -/- ) (n=8-13/group) were subject to acute saline administration of 10% body wt., i.p., or a 2% high salt diet for 2 weeks to determine and compare acute or chronic natriuretic responses. In response to 10% acute saline volume expansion, urinary Na + excretion increased 6.5 fold from basal 18.9 ± 5.0 μmol/3h to 122.2 ± 7.7 μmol/3h in wildtype mice ( p <0.01). By comparison, urinary Na + excretion increased 8.4 fold from basal 26.2 ± 3.9 μmol/3h to 206.5 ± 5.7 μmol/3h in PT- Nhe3 -/- mice ( p <0.01), whereas the natriuretic response increased 4.8 fold in Nhe3 -/- mice ( p <0.01). The differences in the natriuretic responses to acute saline expansion between Nhe3 +/+ , Nhe3 -/- and PT- Nhe3 -/- mice were statistically significant ( p <0.01). However, the diuretic response to acute water volume expansion (10% of body wt., i.p.) was not different between Nhe3 +/+ and PT- Nhe3 -/- mice ( n.s. ). In response to 2% NaCl diet for 2 weeks, 24 h urinary Na + excretion increased 19% in Nhe3 +/+ mice ( n.s. ), whereas the natriuretic response increased 43% in PT- Nhe3 -/- mice ( p <0.01). Interestingly, the natriuretic responses to 2% high salt diet were greater in adult female wildtype (Δ66%, p <0.01) and PT- Nhe3 -/- mice (Δ62%, p <0.01), respectively. By contrast, the natriuretic response to 2% high salt diet was significantly attenuated in global Nhe3 -/- mice ( p <0.01). These data suggest that the deletion of NHE3 selectively in the proximal tubule of the kidney, but not globally, augments the natriuretic responses to acute or chronic saline volume expansion in PT- Nhe3 -/- mice.

ANP antibody attenuates RIHP amplification during acute Saline Volume Expansion in rats

The role of Atrial Natriuretic Peptide (ANP) on renal interstitial hydrostatic pressure (RIHP), urinary excretion of sodium (UNaV) and water (V) amplification responses during saline volume expansion (SVE, 5% bw, ~30 min, 0.9%), and immediately after (maintained SVE, 10 min) was studied in male adult wistar rats 24 h after antiseptic intra‐arterial infusion of polyglonal IgG anti‐Atrial Natriuretic Factor (ANF) antibody (AbANP, 18 μg, wich theoretically blocked all ANP secretion, n=8) versus control (CTR, gluc5%, n=10). The day of the acute experiment, variables were continously measured in anesthetized animals with hormonal clamp (without ANP), kidney denervation (chemical and mechanical) and renal perfusion pressure control at 100 mmHg during hydropenia (H), SVE, and maintained SVE(mSVE).The results are shown in table 1. For Ht and plasmatic protein, there were no differences between groups during H period and the hemodilution response was similar between groups. For RIHP, an attenuation in the amplification response was obtained, from 3 times in CTR vs H to 1 time in abANP group (MANOVA test, p<0.05 between groups, SVE and mSVE., t‐student test vs H each group p<0.05). For V and UNaV responses, there were no differences between groups or periods, achieving the amplification response in the same magnitude for both groups. Finally, an increase in UGMPcV and UNOxV during SVE and mSVE were similar in both groups.Conclusionsin rats, the acute increase in plasmatic ANP is necessary for the complete RIHP amplification during acute SVE, probably involving an independent nitric‐oxide mechanism. Also, a dissociation between RIHP and natriuretic response was observed.Support or Funding InformationSupported by IPL's financial resourcesThis abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Knockdown of parathyroid hormone related protein in smooth muscle cells alters renal hemodynamics but not blood pressure

Parathyroid hormone-related protein (PTHrP) belongs to vasoactive factors that regulate blood pressure and renal hemodynamics both by reducing vascular tone and raising renin release. PTHrP is expressed in systemic and renal vasculature. Here, we wanted to assess the contribution of vascular smooth muscle cell endogenous PTHrP to the regulation of cardiovascular and renal functions. We generated a mouse strain (SMA-CreERT2/PTHrPL2/L2 or premutant PTHrPSM-/-), which allows temporally controlled, smooth muscle-targeted PTHrP knockdown in adult mice. Tamoxifen treatment induced efficient recombination of PTHrP-floxed alleles and decreased PTHrP expression in vascular and visceral smooth muscle cells of PTHrPSM-/- mice. Blood pressure remained unchanged in PTHrPSM-/- mice, but plasma renin concentration and creatinine clearance were reduced. Renal hemodynamics were further analyzed during clearance measurements in anesthetized mice. Conditional knockdown of PTHrP decreased renal plasma flow and glomerular filtration rate with concomitant reduction in filtration fraction. Similar measurements were repeated during acute saline volume expansion. Saline volume expansion induced a rise in renal plasma flow and reduced filtration fraction; both were blunted in PTHrPSM-/- mice leading to impaired diuresis. These findings show that endogenous vascular smooth muscle PTHrP controls renal hemodynamics under basal conditions, and it is an essential factor in renal vasodilation elicited by saline volume expansion.

Acute saline expansion increases nephron filtration and distal flow rate but maintains tubuloglomerular feedback responsiveness: role of adenosine A1 receptors

Temporal adaptation of tubuloglomerular feedback (TGF) permits readjustment of the relationship of nephron filtration rate [single nephron glomerular filtration rate (SNGFR)] and early distal tubular flow rate (V(ED)) while maintaining TGF responsiveness. We used closed-loop assessment of TGF in hydropenia and after acute saline volume expansion (SE; 10% body wt over 1 h) to determine whether 1) temporal adaptation of TGF occurs, 2) adenosine A(1) receptors (A(1)R) mediate TGF responsiveness, and 3) inhibition of TGF affects SNGFR, V(ED), or urinary excretion under these conditions. SNGFR was evaluated in Fromter-Wistar rats by micropuncture in 1) early distal tubules (ambient flow at macula densa), 2) recollected from early distal tubules while 12 nl/min isotonic fluid was added to late proximal tubule (increased flow to macula densa), and 3) from proximal tubules of same nephrons (zero flow to macula densa). SE increased both ambient SNGFR and V(ED) compared with hydropenia, whereas TGF responsiveness (proximal-distal difference in SNGFR, distal SNGFR response to adding fluid to proximal tubule) was maintained, demonstrating TGF adaptation. A(1)R blockade completely inhibited TGF responsiveness during SE and made V(ED) more susceptible to perturbation in proximal tubular flow, but did not alter ambient SNGFR or V(ED). Greater urinary excretion of fluid and Na(+) with A(1)R blockade may reflect additional effects on the distal nephron in hydropenia and SE. In conclusion, A(1)R-independent mechanisms adjust SNGFR and V(ED) to higher values after SE, which facilitates fluid and Na(+) excretion. Concurrently, TGF adapts and stabilizes early distal delivery at the new setpoint in an A(1)R-dependent mechanism.

Enalapril treatment restores the decreased proximal tubule reabsorption in response to acute volume expansion in diabetic rats

The renin–angiotensin system (RAS) plays an important role in the regulation of blood pressure, fluid and electrolyte homeostasis. The RAS is activated and renal interstitial hydrostatic pressure (RIHP) is decreased in diabetic rats. The objective of this study was to evaluate the roles of proximal tubule reabsorption and RAS in the decreased RIHP and blunted natriuretic and diuretic responses to acute saline volume expansion (VE) in diabetic rats. Enalapril was utilized to inhibit angiotensin II (AII) formation. Diabetes mellitus (DM) was induced by a single intraperitoneal (i.p.) injection of streptozotocin (STZ, 65 mg/kg). RIHP was measured by a polyethylene (PE) matrix that was chronically implanted in the left kidney. Fractional excretion of phosphate (FE Pi) and fractional excretion of lithium (FE Li) were used as indexes for proximal tubule reabsorption. VE significantly increased both FE Li and FE Pi in all groups of rats studied. However, the increase in FE Li (ΔFE Li = 17.26 ± 3.83%) and FE Pi (ΔFE Pi = 7.38 ± 2.37%) in diabetic rats (DC, n = 12) were significantly lower as compared with those in nondiabetic control rats (NC, n = 8; ΔFE Li = 32.15 ± 4.71% and ΔFE Pi = 20.62 ± 3.27%). The blunted increases in FE Li and FE Pi were associated with an attenuated increase in RIHP (ΔRIHP) in DC (1.8 ± 0.4 mm Hg) compared with NC rats (4.3 ± 0.3 mm Hg). Enalapril treatment (25 mg/kg/day in drinking water) had no effect on nondiabetic rats (NE, n = 8) as compared with untreated NC rats, but significantly improved RIHP response (ΔRIHP) to VE in diabetic rats (DE, n = 9; 2.8 ± 0.5 mm Hg). Both ΔFE Li and ΔFE Pi were restored by enalapril treatment in diabetic rats and no significant differences were found in ΔFE Li and ΔFE Pi between DE (ΔFE Li = 26.81 ± 4.94% and ΔFE Pi = 10.45 ± 4.67%) and NC groups of rats in response to VE. These data suggest that the activated RAS and the decrease in RIHP may play an important role in the increased proximal tubule reabsorption, and the attenuated natriuretic and diuretic responses to acute volume expansion in diabetic rats.

Enalapril Treatment Restores the Attenuated Proximal Tubule Reabsorption in Response to Acute Volume Expansion (VE) in Diabetic Rats

The natriuretic and diuretic responses to an acutely administered saline load are reduced in diabetes mellitus and these altered responses are associated with sodium retention. Inhibition of the renin-angiotensin-system (RAS) has renoprotective and cardiovascular protective effects. The objective of this study was to determine the roles of proximal tubule reabsorption and the RAS in the attenuated natriuretic and diuretic responses to VE in diabetic rats (DC, n=12). Fractional excretions of phosphate (FEPi) and lithium (FELi) were utilized as indexes for proximal tubule reabsorption. VE significantly increased both FELi and FEPi in all groups of rats. However, the increased FELi and FEPi in DC rats (ΔFELi=17.26±4.69% and ΔFEPi=7.38±2.9%) were significantly lower as compared with those in nondiabetic control rats (NC, n=8; Δ FELi=32.15±5.03% and ΔFEPi=20.62±3.5%). The lower increases in FELi and FEPi are associated with an attenuated increase in renal interstitial hydrostatic pressure (ΔRIHP) in DC (1.8±0.5 mmHg) compared with NC rats (4.3±0.4 mmHg). Enalapril treatment (25 mg/kg/day in drinking water) had no effect on nondiabetic rats (NE, n=8) as compared with untreated NC rats, but significantly improved RIHP response (ΔRIHP) to VE in diabetic rats (DE, 2.8± 0.6 mmHg). Both ΔFELi and FEPi were restored by enalapril treatment in diabetic rats and no significant differences were found in ΔFELi and ΔFEPi between DE (ΔFELi=26.81±5.24% and ΔFEPi=10.45±4.95%) and NC groups of rats in response to VE. These data suggest that RAS and RIHP may play an important role in the attenuated inhibition of proximal tubule reabsorption in response to acute saline volume expansion in diabetic rats.

Natriuretic Response to Direct Renal Interstitial Volume Expansion (DRIVE) in Pregnant Rats

Basal renal interstitial hydrostatic pressure (RIHP) is lower in pregnant rats, suggesting an increase in renal interstitial compliance during pregnancy. The RIHP responses to increases in renal perfusion pressure (RPP) and acute saline volume expansion (VE) are attenuated in pregnant rats. Pressure natriuresis and diuresis responses are significantly attenuated during normal pregnancy, whereas the natriuretic and diuretic responses to VE remain intact. The objectives of this study were to use direct renal interstitial volume expansion (DRIVE) to selectively increase RIHP and determine the renal interstitial compliance and the relationship between RIHP, natriuretic, and diuretic responses in nonpregnant (NP; n = 8), midterm pregnant (MP; n = 8), and late-term pregnant (LP; n = 8) Sprague-Dawley (SD) rats. DRIVE resulted in significant increases in RIHP, fractional excretion of sodium (FE(Na)), and urine flow rate (V) in all groups of rats. The increase in RIHP (DeltaIHP) was greatest for NP (3.3 +/- 0.2 mm Hg) as compared to MP (1.3 +/- 0.1 mm Hg; P < .05 v NP) and LP (1.4 +/- 0.2 mm Hg; P < .05 v NP) in response to DRIVE showing that renal interstitial compliance was greater in MP and LP as compared to the NP group of rats. The increase in fractional excretion of sodium (DeltaFE(Na)) was similar in NP (3.1% +/- 0.3%) and LP (3.6% +/- 0.8%), but was significantly lower in MP (1.5% +/- 0.4%; P < .05 v NP and LP) in response to DRIVE. These data suggest that the blunted increase in RIHP and natriuresis in response to DRIVE in midterm pregnant rats may play an important role in the gradual plasma volume expansion that is occurring during this stage of pregnancy.

Natriuretic and antialdosterone actions of chronic oral NEP inhibition during progressive congestive heart failure

Neutral endopeptidase (NEP) degrades atrial natriuretic peptide (ANP) that via cyclic guanosine monophosphate (cGMP) is natriuretic and aldosterone-inhibiting. We hypothesized that chronic oral NEP inhibition (NEPI), initiated in early experimental congestive heart failure (CHF), would delay onset of decreases in sodium excretion during the progression of CHF and, in the severe phase, suppress aldosterone activation and reduce the magnitude of sodium retention. We also hypothesized that chronic NEPI during progressive CHF (PCHF) would improve the natriuretic response to acute volume expansion. In a novel canine model that progresses over 38 days from early to moderate and finally severe CHF, we defined the actions of chronic NEPI (candoxatril, 10 mg/kg, orally, twice a day) upon cardiorenal and neurohumoral function as well as the clinical well being of treated and untreated dogs in CHF. From baseline through the moderate phase of CHF, NEPI maintained sodium excretion. In contrast, in moderate CHF, sodium excretion was reduced compared to the early phase in the controls. In severe CHF, sodium excretion was higher with NEPI compared to control. Chronic NEPI also resulted in lower plasma aldosterone as compared to controls. In severe CHF, the natriuretic response to acute saline volume expansion was enhanced with oral NEPI as compared to control. This study supports the conclusion that chronic oral NEPI delays the onset of reduction in sodium excretion during the transition from early to severe CHF in this model of PCHF. This therapeutic strategy also improved the natriuretic response to acute volume expansion in severe CHF while enhancing ANP and suppressing aldosterone activation. Thus, these studies demonstrated a selective renal and adrenal action of chronic NEPI in heart failure indicating a therapeutic potential.

Cardiovascular and renal characteristics, and responses to acute volume expansion of a rat model of diabetic pregnancy

The objective of this study was to characterize the cardiovascular and renal alterations that occur during diabetic pregnancy, and to evaluate the effect of insulin treatment in 12–14 days pregnant diabetic rats. Four groups of female Sprague Dawley rats were studied: virgin control group (NP), pregnant control group (CP), diabetic pregnant group (DP), and diabetic pregnant group with insulin treatment (DPI). Systolic arterial pressure (SAP) was increased on day 12, whereas heart rate (HR) decreased starting with day 3 in DP group of rats. DP rats exhibited marked renal hypertrophy with greater kidney weight (wt) and kidney wt/body wt ratio. Insulin treatment normalized blood glucose (BG) concentration, SAP and HR, and prevented the increase in kidney wt/body wt ratio in DPI rats. At the time of the terminal acute experiment, acute saline volume expansion (VE, 5% body wt/30 min) significantly increased renal interstitial hydrostatic pressure (RIHP), urinary sodium excretion (U NaV) and urine flow rate (V) in all groups, but the increases (Δ) were significantly attenuated in both CP (1.7 ± 0.2mmHg, 12.0 ± 1.5 μEq.min −1.g kidney wt −1 and 76.2 ± 10.9 μl.min −1.g kidney wt −1 for ΔRIHP, ΔU NaV and ΔV respectively) and DP (1.3 ± 0.1 mmHg, 6.8 ± 1.8 μEq.min −1.g kidney wt −1 and 32.3 ± 9.3 μl.min −1.g kidney wt −1 for ΔRIHP, ΔU NaV and ΔV respectively) group of rats as compared to NP (4.0 ± 0.6 mmHg, 21.6 ± 1.4 μEq.min −1.g kidney wt −1and 136.8 ± 10.5 μl.min −1.g kidney wt −1 for ΔRIHP, ΔU NaV and ΔV respectively) group of rats. Although RIHP response to VE was similar in DP and CP group of rats, the natriuretic and diuretic responses to VE were significantly lower in DP as compared to CP group of rats. Insulin treatment had no effect on RIHP response (ΔRIHP = 1.5 ± 0.3 mmHg), but restored most of the natriuretic (ΔU NaV = 15.7 ± 2.9 μEq.min −1.g kidney wt −1) and diuretic (ΔV = 100.2 ± 19.3 μl.min −1.g kidney wt −1) responses to VE in DPI as compared with CP group of rats. These data suggest that with VE, the restoration of the increase in U NaV and V with insulin treatment in diabetic pregnant rats is not mediated by changes in RIHP.

Effects of insulin on renal interstitial hydrostatic pressure and natriuretic response to volume expansion in diabetic rats

Diabetes mellitus (DM) is characterized by alterations in fluid balance and blood volume homeostasis. Renal interstitial hydrostatic pressure (RIHP) has been shown to play a critical role in mediating sodium and water excretion under various conditions. The objective of this study was to determine the effects of immediate and delayed initiation of insulin treatment on the restoration of the relationship between RIHP, natriuretic, and diuretic responses to acute saline volume expansion (VE) in diabetic rats. Diabetes was induced by an intraperitoneal injection of streptozotocin (STZ; 65 mg/kg body wt). Four groups of female Sprague-Dawley rats were studied: normal control group (C), untreated diabetic group (D), immediate insulin-treated diabetic group (DI; treatment with insulin for 2 wk was initiated immediately when diabetes was confirmed, which was 2 days after STZ injection), and delayed insulin-treated diabetic group (DDI; treatment with insulin for 2 wk was initiated 2 wk after STZ injection). RIHP and sodium and water excretions were measured before and during VE (5% body wt/30 min) in the four groups of anesthetized rats. VE significantly increased RIHP, fractional excretion of sodium (FE(Na)), and urine flow rate (V) in all groups of rats. Basal RIHP, RIHP response to VE (Delta RIHP), and FE(Na) and V responses to VE (Delta FE(Na) and Delta V) were significantly lower in the D group compared with the C group of rats. Delta RIHP was significantly higher in both DI and DDI groups compared with D group but was similar to that of the C group of rats. While in the DI group the Delta FE(Na) response to VE was restored, Delta FE(Na) was significantly increased in DDI compared with D group, but it remained lower than that of the C group. In conclusion, insulin treatment initiated immediately after the onset of diabetes restores basal RIHP and RIHP, natriuretic, and diuretic responses to VE; however, delayed insulin treatment restores the basal RIHP and RIHP response to VE but does not fully restore the natriuretic response to VE.

Role of nitric oxide in the natriuretic and diuretic responses in pregnant rats.

Normal pregnancy is characterized by sodium conservation and increase in plasma volume, yet the natriuretic response to acute saline volume expansion (VE) is intact in pregnant rats. Nitric oxide (NO) has been suggested to play a role in renal and cardiovascular adaptations to normal pregnancy. The objective of this study was to determine the role of NO in the natriuretic and diuretic responses to VE during pregnancy. Infusion of NG-monomethyl-l-arginine (l-NMMA) was used to inhibit NO synthesis. Nine groups of Sprague-Dawley (SD) rats were studied: nonpregnant (NP-VE, n = 7), midterm pregnant (MP-VE, n = 8), and late-term pregnant (LP-VE, n = 7) SD groups that underwent VE alone after a control period; NP-l-NMMA (n = 7), MP-l-NMMA (n = 8), and LP-l-NMMA (n = 7) SD groups that were infused with l-NMMA after a control period; and another three groups of SD rats (NP-VE-l-NMMA, n = 8; MP-VE-l-NMMA, n = 7; and LP-VE-l-NMMA, n = 12) that underwent simultaneous VE and l-NMMA infusion after a control period. The change in fractional excretion of sodium was 7.22 +/- 1.03% for NPVE, 9.89 +/- 1.85% for NP-l-NMMA, and 17.66 +/- 1.85% for NP-VE-l-NMMA (P < 0.05 vs. NP-VE and NP-l-NMMA); 6.61 +/- 1.07% for MP-VE, 7.99 +/- 1.92% for MP-l-NMMA, and 10.24 +/- 1.91% for MP-VE-l-NMMA [not significant (NS) vs. MP-VE and MP-l-NMMA]; 8.20 +/- 1.92% for LP-VE, 8.09 +/- 0.70% for LP-l-NMMA, and 7.57 +/- 1.11% for LP-VE-l-NMMA (both NS vs. LP-VE and LP-l-NMMA). The increase in renal interstitial hydrostatic pressure was significantly greater in all NP compared with pregnant groups with similar experimental intervention (i.e., VE, l-NMMA, or VE-l-NMMA). In conclusion, the natriuretic and diuretic responses to VE and l-NMMA infusion were additive in NP but not in pregnant rats, indicating a possible lower ability of pregnant rats to respond to combined significant natriuretic and diuretic stimuli.

Altered renal hemodynamics in mice overexpressing the parathyroid hormone (PTH)/PTH-related peptide type 1 receptor in smooth muscle.

PTH-related protein (PTHrP) is an autocrine/paracrine peptide expressed in renal tubules and vasculature and may play an important role in regulating overall renal function. To evaluate the potential role of endogenous PTHrP in the control of renal hemodynamics, we performed clearance measurements in transgenic (TG) mice in which the SMP8 alpha-actin promoter was used to drive overexpression of the PTH/PTHrP type 1 receptor in smooth muscle. In protocol I, responses to acute saline volume expansion (SVE, 0.75 microl/min.g body weight) were measured in TG and nontransgenic (NTG) mice. Mean arterial pressure was significantly lower in TG mice throughout the experiment, and it decreased comparably in both groups in response to SVE. SVE significantly increased effective renal plasma flow in both groups of mice, but the increase was greater in TG than in NTG. Glomerular filtration rate decreased in response to SVE in NTG but did not change in TG animals. In protocol II, renal responses to angiotensin II (ANG II) infusion were determined (0.5 ng/min.g body weight). Baseline arterial pressure was again significantly lower in TG, compared with NTG mice, and TG mice had a blunted pressor response to ANG II. Also, ANG II decreased effective renal plasma flow and glomerular filtration rate in both groups of animals, but the reductions were less in TG than in NTG mice. Our findings indicate that smooth-muscle-specific overexpression of the PTH/PTHrP type 1 receptor resulted in augmentation of the vasodilatory response to SVE and attenuation of the vasoconstrictor response to ANG II. We conclude that endogenous PTHrP can act as an endogenous vasorelaxant factor to modulate renal responses to vasoactive stimuli.

Renal interstitial hydrostatic pressure and natriuretic responses to volume expansion in pregnant rats.

During normal pregnancy, a gradual plasma volume expansion (VE) occurs and reaches a maximum level at late term. Pressure natriuresis and renal interstitial hydrostatic pressure (RIHP) responses are attenuated in pregnant rats. Also, basal RIHP is lower in pregnant rats, suggesting an increase in renal interstitial compliance during pregnancy. This adaptation may contribute to the increase in plasma volume that is required for a normal pregnancy, because increases in RIHP have been consistently shown to produce natriuresis and diuresis. Acute saline VE (5% body wt/30 min) has been shown to increase RIHP in normal nonpregnant rats. Therefore, the objective of this study was to determine RIHP, natriuretic, and diuretic responses to VE in nonpregnant (n = 7), midterm pregnant (n = 8), and late-term pregnant (n = 8) Sprague-Dawley rats. Although VE significantly increased RIHP, fractional excretion of sodium (FE(Na)), and urine flow rate (V) in all groups, DeltaRIHP was highest for nonpregnant (3.0 +/- 0.3 mmHg) compared with midterm pregnant (1.6 +/- 0.1 mmHg; P < 0.05 vs. nonpregnant) and late-term pregnant rats (1.2 +/- 0.1 mmHg; P < 0.05 vs. both midterm pregnant and nonpregnant rats). DeltaFE(Na) and DeltaV were similar in all groups: 5.8 +/- 1.0% and 231 +/- 27 microl/min for nonpregnant, 6.8 +/- 1.3% and 173 +/- 16 microl/min for midterm pregnant, and 7.6 +/- 1.2% and 203 +/- 10 microl/min for late-term pregnant rats, respectively. In conclusion, basal RIHP and the increase in RIHP during VE were attenuated during pregnancy; however, the natriuretic and diuretic responses to VE remain intact during the course of pregnancy.

Interactions between nitric oxide and renal nerves in the excretion of a saline load in obese Zucker rats

The present study investigated the potential role of nitric oxide (NO) and its interaction with renal sympathetic nerves in modulating the excretory responses to an acute saline volume expansion (VE), of 10% of body weight, in the innervated and denervated kidneys of both lean and obese Zucker rats. This was done using the NO synthase inhibitors N(G)-nitro-L-arginine methyl ester (L-NAME), 7-nitroindazole and aminoguanidine. In lean rats, cumulative urinary sodium excretion (cuU(Na)V) after 40 min of VE in the innervated kidney was enhanced by 48% in L-NAME-treated rats compared with that in untreated rats, but this was not the case for the denervated kidney. VE in untreated obese rats raised cuU(Na)V to a lesser extent than in the untreated lean rats, by 36% and 46% in the denervated and innervated kidneys respectively (both P<0.001). L-NAME treatment of obese rats increased cuU(Na)V after VE compared with that in untreated obese rats, by 48% in the denervated kidney and by 136% in the innervated kidney (both P<0.001). The magnitude of cuU(Na)V after VE in both kidneys of 7-nitroindazole-treated obese rats was not different from that in untreated obese rats. However, cuU(Na)V was raised (P<0.01) by 56% in the innervated, but not the denervated, kidney of aminoguanidine-treated obese rats. These data show that NO is partially involved in mediating the reflex renal responses to VE in Zucker rat strains. NO, possibly generated by endothelial NO synthase, exerts its effects in obese rats through a renal-nerve-independent mechanism, while the effect of NO generated by inducible NO synthase requires intact renal innervation.

Effect of acute saline volume expansion in the anaesthetised DeltaF508 cystic fibrosis mouse.

It has been suggested that CFTR Cl(-) channels in the renal inner medullary collecting duct may be involved in mediating increased renal salt excretion during extracellular fluid volume expansion. To investigate this hypothesis, in-vivo clearance experiments were performed comparing wild-type (WT) and DeltaF508-CFTR transgenic mice (cftr (tm2Cam)). Control animals were given a 0.1-ml bolus of 0.9% saline, followed by I.V. infusion at 0.3 ml x h(-1). Volume expansion was applied by infusing a 1-ml bolus of 0.9% saline followed by infusion at 0.6 ml x h(-1). No significant differences in renal NaCl handling between WT mice ( C(Na)=1.2 +/- 0.3 microl x min(-1), C(Cl)=4.0 +/- 0.5 microl x min(-1)) and DeltaF508-CFTR mice ( C(Na)=1.7 +/- 0.5 microl x min(-1), C(Cl)=4.1 +/- 0.8 microl x min(-1)) were observed under control conditions. Volume expansion resulted in large significant increases in NaCl clearance in both WT mice ( C(Na)=7.0 +/- 0.9 microl x min(-1), C(Cl)=12.0 +/- 0.6 microl x min(-1)) and DeltaF508-CFTR mice ( C(Na)=7.2 +/- 1.6 microl x min(-1), C(Cl)=11.0 +/- 2.2 microl x min(-1)). However, there was no significant difference between WT and DeltaF508-CFTR mice. In conclusion, renal NaCl excretion is not significantly different under basal conditions and during saline volume expansion in DeltaF508-CFTR mice. The data suggest that CFTR is not a physiologically important mediator of volume natriuresis.

Role of nitric oxide and renal nerves in the renal responses to acute volume expansion in anaesthetized rats.

An investigation was undertaken into the potential role of nitric oxide (NO) and its interaction with renal sympathetic nerves in mediating renal responses to acute saline volume expansion (VE). Groups of anaesthetized Wistar rats with innervated and denervated kidneys were subjected to VE, 0.25 % body wt min-1 for 40 min, in the presence and absence of nitric oxide synthase (NOS) inhibitors, NG-nitro-L-arginine-methyl-ester (L-NAME, non-selective), aminoguanidine (AG, relatively selective for inducible NOS (iNOS)), and 7-nitroindazole (7-NI, relatively selective for neuronal NOS (nNOS)). Pretreatment with L-NAME or AG enhanced the cumulative sodium excretion (CuU(Na)V) after 40 min VE in the innervated kidneys by 27 and 23 % (both P < 0.001), respectively, compared to the untreated control group, whereas they were without effect in the denervated kidneys. Cumulative urine flow (CuUV) after VE in L-NAME- and AG-treated groups was enhanced in both kidneys, by some 17-21 % in the denervated (P < 0.01) and 37-39 % in the innervated kidneys (P < 0.001) by comparison with the corresponding untreated controls. 7-NI had no effect on CuUV, but reduced CuU(Na)V in the denervated kidneys by 25 % (P < 0.01) when compared to the control group. The results suggested that NO, possibly generated by endothelial NOS (eNOS) and iNOS, was a contributory factor in mediating the renal response to VE. There appeared to be a tonic inhibitory action of NO on water excretion which was renal nerve independent, whereas its impact on sodium handling appeared to be dependent upon a background level of renal nerve activity. Experimental Physiology (2001) 86.1, 47-54.

Gender differences in renal growth and function after uninephrectomy in adult rats

It is known that compensatory renal growth (CRG) following unilateral nephrectomy (UNX) increases both the size of the kidney and its functional capacity; however, few studies have investigated whether differences in CRG exist between the sexes. Our study examined the sex-related differences in remnant kidney growth and function two months following UNX. Adult male and female Wistar rats underwent either left UNX or sham operation and recovered for 8 to 10 weeks. Another group of female rats underwent ovariectomy (Ox), with vehicle, estrogen, or testosterone replacement: two-weeks postsurgery animals underwent UNX and recovered for 8 to 10 weeks. Metabolic studies, acute renal function studies [response to acute saline volume expansion (2 to 4% of body wt) or phosphate (Pi) infusions in thyroparathyroidectomized rats (to determine the transport maximum (TmPi)], and renal morphology were assessed at the end of the experimental period. Two months post-UNX, male remnant kidneys grew 114+/-7% of their excised kidney weight (KW), whereas female remnant kidneys grew only 57+/-4% (P<0.05). There was a significant increase in the glomerular volume of male remnant kidneys (126.2+/-13.4%, P<0.001) compared with control kidney volume, whereas there was no change in glomerular volume in female remnant kidneys (20.2+/-16.1%, P = NS). There was also glomerular and tubular damage in the male remnant kidneys, whereas female remnant kidneys were intact. Studies in Ox female rats supplemented with gonadal steroids determined that testosterone is the driving force for the enhanced remnant kidney growth and glomerular hypertrophy. Renal function studies determined that UNX males had significantly higher glomerular filtration rates (GFRs) than UNX females, although the GFR/single KW was not different between the sexes, indicating a proportional increase in GFR. Basal urinary sodium excretion and urine flow rates were significantly higher in anesthetized UNX rats than their sham-operated controls, and urinary sodium excretion and urine flow rates in UNX males were significantly higher than in UNX females. Both male and female UNX rats responded to volume expansion with an exaggerated initial sodium and urine excretion compared with their controls. Phosphate handling was not altered in UNX male rats; however, UNX female rats had increases in fractional Pi excretion that were associated with significant reductions in the maximum capacity for Pi reabsorption (2.10+/-0.07 vs. 3.43+/-0.24 micromol/ml GFR in female controls, P<0.0001). This difference was also observed in Ox rats treated with estrogen and testosterone (2.31+/-0.07 vs. 3.12+/-0.11 micromol/ml GFR, P<0.0007). These findings indicate that sexual dimorphism exists in remnant kidney growth and function two months following UNX. Indeed, morphological abnormalities and impairment in renal phosphate handling are affected by gonadal steroids by two-months post-UNX. The fact that renal Pi transport was reduced in female but not male UNX rats may also have important implications during periods of high metabolic demand for phosphate in the female.

Effect of acute saline volume loading on renal sympathetic nerve activity in anaesthetised fructose-fed and fat-fed rats

Experiments were conducted to investigate the effects of activation of cardiopulmonary vagal afferent nerve endings by acute saline volume expansion on sympathetic efferent renal nerve activity in anaesthetised fat-fed and fructose-fed Wistar rats. Four weeks of fat feeding caused obesity in the Wistar rats which was associated with a mild elevation in blood pressure (118±4 mmHg vs. 105±1 mmHg in the lean control rats, P<0.05). Fructose feeding in Wistar rats for 4 weeks also elicited an elevation of blood pressure (113±4 mmHg, P<0.05) and plasma glucose levels (6.3±0.3 mmol/l vs. 4.0±0.3 mmol/l lean control rats, P<0.01). The fat-fed rats displayed a higher basal renal sympathetic nerve activity (RSNA) value when compared with the lean rats (3.9±0.4 mV/s vs. 2.8±0.4 mV/s, P<0.05) whereas the RSNA levels were similar in all the other rat groups. The power spectral analysis of RSNA showed the basal values of percentage power at heart rate frequency were significantly higher in Wistars fed ad lib ( P<0.01), rats fed on fructose for 2 or 4 weeks ( P<0.01 and P<0.05, respectively) and fat-fed rats ( P<0.01) when compared to the lean diet-controlled rats. Acute volume expansion (10% body wt) over 40 min caused efferent renal sympatho-inhibition in all the animal groups. The pattern and magnitude of response in MAP, RSNA, and power spectral analysis parameters to the volume expansion were similar in the lean control rats, the Wistar and fructose fed rats but was greater in the fat-fed rats ( P<0.05) as compared to the lean control rat. The profile of the reduction in percentage power at heart rate frequency to volume expansion was greater ( P<0.05) in the fat-fed rat than in the lean control rats. The present data demonstrates that the reflex efferent renal sympatho-inhibition to volume expansion was impaired in the diet-induced obese rat but not in the fructose fed rats. This suggests that a defect in the neuro-humoral regulation of kidney control of extracellular fluid volume is present which may contribute to the mild hypertension in the obese rat.

A004 Adrenomedullin inhibited by acute saline volume expansion in rats

A004 Adrenomedullin inhibited by acute saline volume expansion in rats