Effect of atrial natriuretic peptide on arterial pressure and renal function in cirrhotic rats with ascites

Glomerular filtration rate, urine volume, sodium excretion and mean arterial pressure were measured in 10 rats with Cl4C induced cirrhosis presenting sodium retention and ascites, and in 10 control rats before and during the iv administration of the 28 aminoacid rat alpha-Atrial Natriuretic Peptide (alpha-ANP) (a bolus of 1 microgram followed by a constant infusion of 33 ng/min). alpha-ANP induced a similar increase in glomerular filtration rate and filtered sodium load in both groups of rats. In contrast, the increase in urine volume and sodium excretion produced by alpha-ANP was significantly lower in cirrhotic rats (from 13.8 +/- 1.9 to 37.9 +/- 9.1 microliters/min., and from 0.5 +/- 0.1 to 3.3 +/- 1.0 microEq/min) than in control animals (from 14.6 +/- 1.3 to 102.5 +/- 17.7 microliters/min., p less than 0.005; and from 1.0 +/- 0.3 to 14.1 +/- 3.2 microEq/min., p less than 0.001). The results indicate that in rats with experimental cirrhosis and ascites there are blunted diuretic and natriuretic responses to alpha-ANP, probably as a consequence of the exaggerated tubular sodium reabsorption present in these animals.     

Antioxidants attenuate endotoxin-induced microvascular leakage of macromolecules in vivo.

The purpose of this study was to examine whether antioxidants attenuate endotoxin-induced microvascular hyper-permeability for macromolecules in the hamster cheek pouch. Twenty-two adult male Syrian hamsters were anesthetized, and a removable plastic chamber was placed in the cheek pouch to observe and collect suffusate from the microvasculature. Fluorescent-labeled dextran (FITC-D; mol wt 150,000) was injected intravenously, and changes in the number of microvascular leaky sites and microvascular clearance of FITC-D were measured in five groups: saline control (group 1, n = 4), endotoxin (0.1 mg/ml) suffusion for 120 min (group 2, n = 6), endotoxin plus dimethyl sulfoxide (1.0 g/kg iv; group 3, n = 4), endotoxin plus allopurinol (30 mg/kg ip; group 4, n = 4), and endotoxin plus dimethyl sulfoxide and allopurinol (group 5, n = 4). The number of leaky sites and the FITC-D clearance were significantly higher in group 2 [45 +/- 18 (SD) sites/cm2 and 20 +/- 6 X 10(-6) ml/min, respectively; P less than 0.01] than in group 1 (7 +/- 6 sites/cm2 and 7 +/- 5 X 10(-6) ml/min), group 3 (9 +/- 5 sites/cm2 and 8 +/- 2 X 10(-6) ml/min), group 4 (11 +/- 7 sites/cm2 and 9 +/- 4 X 10(-6) ml/min), and group 5 (11 +/- 6 sites/cm2 and 7 +/- 1 x 10(-6) ml/min). The leaky sites appeared predominantly in postcapillary venules. There was a positive and significant correlation between the number of leaky sites and FITC-D clearance.(ABSTRACT TRUNCATED AT 250 WORDS)     

Role of neutrophils in endotoxin-mediated microvascular injury in hamsters.

The purpose of this study was to examine the role of circulating neutrophils in endotoxin-induced increase in microvascular permeability in vivo. Fifteen hamsters were anesthetized, and a plastic chamber was placed in each cheek pouch to observe the microvasculature. Fluorescein-labeled dextran (FITC-D, 150 kDa) was injected intravenously, and changes in leaky sites and FITC-D clearance were measured in three groups: control (saline, n = 4), endotoxin suffusion (n = 6), and endotoxin suffusion after neutropenia induction (n = 5). We found a significant increase in leaky sites and FITC-D clearance with endotoxin (45 +/- 18/cm2 and 20 +/- 6 x 10(-6) ml/min, respectively; mean +/- SD, P less than 0.05) in comparison to control (7 +/- 6/cm2 and 7 +/- 5 x 10(-6) ml/min) and endotoxin suffusion in neutropenic animals (19 +/- 11/cm2 and 12 +/- 4 x 10(-6) ml/min). There was a significant correlation between the number of leaky sites and FITC-D clearance (r = 0.91, P less than 0.01) and between the number of circulating neutrophils and FITC-D clearance (r = 0.87, P less than 0.01). We conclude that endotoxin-mediated increase in microvascular permeability in the peripheral circulation is dependent in part on circulating neutrophils.     

Hog barn dust extract increases macromolecular efflux from the hamster cheek pouch.

The purpose of this study was to determine whether short-term exposure to an aqueous extract of hog barn dust increases macromolecular efflux from the intact hamster cheek pouch and, if so, to begin to determine the mechanism(s) underlying this response. By using intravital microscopy, we found that suffusion of hog barn dust extract onto the intact hamster cheek pouch for 60 min elicited a significant, concentration-dependent leaky site formation and increase in clearance of FITC-labeled dextran (molecular mass, 70 kDa). This response was significantly attenuated by suffusion of catalase (60 U/ml), but not by heat-inactivated catalase, and by pretreatment with dexamethasone (10 mg/kg iv) (P < 0.05). Catalase had no significant effects on adenosine-induced increase in macromolecular efflux from the cheek pouch. Suffusion of hog barn dust extract had no significant effects on arteriolar diameter in the cheek pouch. Taken together, these data indicate that hog barn dust extract increases macromolecular efflux from the in situ hamster cheek pouch, in part, through local elaboration of reactive oxygen species that are inactivated by catalase. This response is specific and attenuated by corticosteroids. We suggest that plasma exudation plays an important role in the genesis of upper airway dysfunction evoked by short-term exposure to hog barn dust.     

Dexamethasone attenuates grain sorghum dust extract-induced increase in macromolecular efflux in vivo.

The purpose of this study was to determine whether dexamethasone attenuates grain sorghum dust extract-induced increase in macromolecular efflux from the in situ hamster cheek pouch and, if so, whether this response is specific. By using intravital microscopy, we found that an aqueous extract of grain sorghum dust elicited significant, concentration-dependent leaky site formation and increase in clearance of FITC-labeled dextran (FITC-dextran; mol mass, 70 kDa) from the in situ hamster cheek pouch (P < 0.05). This response was significantly attenuated by dexamethasone (10 mg/kg iv). Dexamethasone also attenuated substance P-induced leaky site formation and increase in clearance of FITC-dextran from the cheek pouch but had no significant effects on adenosine-induced responses. Dexamethasone had no significant effects on arteriolar diameter in the cheek pouch. On balance, these data indicate that dexamethasone attenuates grain sorghum dust extract- and substance P-induced increases in macromolecular efflux from the in situ hamster cheek pouch in a specific fashion.     

Atrial natriuretic peptides cleaved by endopeptidase are inactive in conscious spontaneously hypertensive rats

The dose-related natriuretic and depressor responses to atrial natriuretic peptides (ANP) 99-126, 103-126 and 103-123 were determined in unanesthetized spontaneously hypertensive rats (SHR) and were compared to the activities of their Cys105-Phe106 ring-opened metabolites. These metabolites were previously identified as the major initial products formed by incubation of the intact peptides with neutral endopeptidase (NEP). The areas over the curves (AOC) of the depressor responses to the intact peptides were dose-related and, at 30 nmole/kg, iv were greatest for ANP 99-126 and 103-126 (833 +/- 241 and 1157 +/- 221 mm Hg x min). Thirty nmole/kg of ANP 103-123, a possible product of NEP cleavage of ANP 103-126, produced a lesser AOC (442 +/- 152 mm Hg x min) than did either of the longer peptides. The AOC responses to 100 nmole/kg of the ring-opened metabolites of ANP 99-126, 103-126 and 103-123 (105 +/- 80, 153 +/- 43 and 148 +/- 64 mm Hg x min) were not significantly different from the effect of vehicle treatment (84 +/- 23 mm Hg x min). Although the natriuretic responses to increasing doses of the intact peptides did not occur in a linear fashion, sodium excretion was maximally elevated by 24 +/- 4, 16 +/- 3 and 10 +/- 3 microEq/kg/min by 3 nmole/kg of ANP 99-126, 30 nmole/kg of ANP 103-126 and 10 nmole/kg of ANP 103-123, respectively. In contrast, the natriuretic responses to 100 nmole/kg of the ring-opened metabolites of ANP 99-126, 103-126 and 103-123 (1 +/- 0, 5 +/- 2 and 2 +/- 1 microEq/kg/min, respectively) were not significantly different from the response to vehicle treatment (3 +/- 1 microEq/kg/min). In conclusion, three ring-opened products of NEP cleavage of ANP 99-126, 103-126 and 103-123 were inactive in conscious SHR.     

In vivo assessment of microvascular nitric oxide production and its relation with blood flow

To assess the hypothesis that microvascular nitric oxide (NO) is critical to maintain blood flow and solute exchange, we quantified NO production in the hamster cheek pouch in vivo, correlating it with vascular dynamics. Hamsters (100-120 g) were anesthetized and prepared for measurement of microvessel diameters by intravital microscopy, of plasma flow by isotopic sodium clearance, and of NO production by chemiluminescence. Analysis of endothelial NO synthase (eNOS) location by immunocytochemistry and subcellular fractionation revealed that eNOS was present in arterioles and venules and was 67 +/- 7% membrane bound. Basal NO release was 60.1 +/- 5.1 pM/min (n = 35), and plasma flow was 2.95 +/- 0.27 microl/min (n = 29). Local NO synthase inhibition with 30 microM N(omega)-nitro-L-arginine reduced NO production to 8.6 +/- 2.6 pmol/min (-83 +/- 5%, n = 9) and plasma flow to 1.95 +/- 0.15 microl/min (-28 +/- 12%, n = 17) within 30-45 min, in parallel with constriction of arterioles (9-14%) and venules (19-25%). The effects of N(omega)-nitro-L-arginine (10-30 microM) were proportional to basal microvascular conductance (r = 0.7, P < 0.05) and fully prevented by 1 mM L-arginine. We conclude that in this tissue, NO production contributes to 35-50% of resting microvascular conductance and plasma-tissue exchange.     

The effect of atrial natriuretic peptide on intestinal electrolyte transport.

The effect of atrial natriuretic peptide (ANP) on rat small intestinal electrolyte transport was examined. In vivo, intravenous administration of rat ANP(99-126) induced diuresis and natriuresis in conjunction with a significant decrease in intestinal water (basal, 37.1 +/- 5.7 versus ANP 28.5 +/- 6.0 microliters/cm per 20 min, P less than 0.05) and Na+ (4.0 +/- 0.7 versus 2.8 +/- 0.9 mumol/cm per 20 min, P less than 0.05) absorption (n = 9). In vitro, in Ussing chambers, in both jejunum and ileum, addition of 1.0 microM ANP to short circuited, stripped tissue produced a maximal increase in short circuit current and stimulated net Cl- secretion due to a significant increase in the unidirectional serosal to mucosal flux (JCl-sm: jejunum 17.4 +/- 1.3 versus 19.8 +/- 1.3 microEq/cm2 per h, P less than 0.01, n = 6; ileum 13.4 +/- 0.5 versus 17.2 +/- 0.6, P less than 0.01, n = 6) which was inhibited by the calcium channel antagonist verapamil (82 +/- 26%, P less than 0.05) and by the 5-HT2 receptor antagonist cinanserin (72 +/- 44%, P less than 0.05). Guanylate cyclase activity was stimulated by ANP in intact epithelium, but not in isolated crypt and villus enterocytes.     

The effect of propranolol on renal sodium handling in patients with cirrhosis

Beta-adrenergic blockade by oral propanolol in five cirrhotic patients caused changes in the handling of an acute sodium load. Fractional sodium excretion following an acute saline load increased from 0.69% +/- 0.29 to 1.49% +/- 0.11 (103 microEq/min +/- 7.5 to 129 microEq/min +/- 18) before propranolol administration. After 3 days of oral propanolol 1 mg/kg day, the fractional excretion of sodium by saline loading increased from 0.52% +/- 0.19 to 2.17 +/- 0.19 (109 microEq/min +/- 9 to 178 microEq/min +/- 11). This change was not accompanied by changes in GFR, RPF or in the renin-aldosterone system. The possibility that these changes are caused by a change in the sodium transport at the tubular cell level induced by the beta-adrenergic blockade, is entertained.     

Dexamethasone attenuates acute macromolecular efflux increase evoked by smokeless tobacco extract.

The purpose of this study was to determine whether dexamethasone attenuates the acute increase in macromolecular efflux from the oral mucosa elicited by an aqueous extract of smokeless tobacco (STE) in vivo, and, if so, whether this response is specific. Using intravital microscopy, we found that 20-min suffusion of STE elicited significant, concentration-related leaky site formation and an increase in clearance of fluorescein isothiocyanate-labeled dextran (FITC-dextran; mol mass 70 kDa) from the in situ hamster cheek pouch (P < 0.05). This response was significantly attenuated by dexamethasone (10 mg/kg iv). Dexamethasone also attenuated the bradykinin-induced leaky site formation and the increase in clearance of FITC-dextran from the cheek pouch. However, it had no significant effects on adenosine-induced responses. Dexamethasone had no significant effects on baseline arteriolar diameter and on bradykinin-induced vasodilation in the cheek pouch. Collectively, these data indicate that dexamethasone attenuates, in a specific fashion, the acute increase in macromolecular efflux from the in situ oral mucosa evoked by short-term suffusion of STE. We suggest that corticosteroids mitigate acute oral mucosa inflammation elicited by smokeless tobacco.     

Albumin transport across pulmonary capillary-interstitial barrier in anesthetized dogs

To evaluate albumin transport across the pulmonary capillary endothelial and interstitial barriers, we simultaneously measured blood-to-tissue (QA,t) and blood-to-lymph (QA,l) clearances of 125I-radiolabeled albumin as well as endogenous albumin clearance (Qa,l) in the canine lung in vivo (n = 10). Steady-state prenodal lung lymph flows (Qw,l) and protein clearances were measured over a 2-h period at a constant capillary pressure (Pc, 13-33 cmH2O). Comparison between QA,t and QA,l as a function of Pc suggests that little of the albumin that crossed the capillary wall remained in the lung tissue, with most leaving in the lymph. Qw,l increased significantly as Pc increased, but lung tissue water was minimally affected. From the ratio of the clearance-Pc slopes for albumin and water, the albumin reflection coefficient was estimated to be 0.81 using QA,l and Qw,l and 0.56 using Qa,l and Qw,l. The permeability surface area product for the sum of blood-to-tissue and blood-to-lymph fluxes of labeled albumin (QA,t + QA,l) was 31 +/- 9 microliters/min, whereas that calculated from the blood-to-lymph flux of endogenous albumin (Qa,l) was 97 +/- 22 microliters/min. These data suggest that 1) both tissue and lymph accumulations of albumin must be considered when microvascular permeability is evaluated using protein tracers; 2) lymph clearance, but not tissue accumulation of albumin, was filtration dependent; and 3) lymph flow was an important contributor to the safety factor against edema formation over a moderate range of capillary pressures.     

Natriuretic effect of atrial natriuretic peptide in diabetes insipidus rats

Washout of the solute concentration gradient in the renal medullary interstitium has been suggested to play a role in mediating the natriuretic response to atrial natriuretic peptide (ANP). The purpose of this study was to determine the effects of ANP 8-33 on sodium excretion in Brattleboro diabetes insipidus (DI) rats, in which medullary tonicity is known to be decreased as compared to Long-Evans (LE) control rats. Basal urine osmolality (Uosm) was significantly lower in DI rats as compared to LE rats (123 +/- 6 vs 673 +/- 38 mOsm/kg). Infusion of ANP 8-33 at a rate of 4 micrograms/kg/hr for 60 min resulted in a significantly greater increase in UnaV (delta 6.1 +/- 1.2 vs delta 2.9 +/- 0.7 microEq/min) and urine flow (delta 40 +/- 12 vs delta 8 +/- 7 microliter/min) in the LE rats than in the DI rats. The greater natriuresis occurred in the LE rats despite no significant change in Uosm. Fractional lithium reabsorption (an indicator of proximal sodium reabsorption) decreased similarly in both groups. Infusion of ANP had no effect on mean arterial pressure in LE and DI groups. In summary, infusion of ANP in the DI rat resulted in a significant natriuresis, albeit less than in LE rats. The natriuresis in the LE rats occurred despite no significant change in Uosm. These data suggest that mechanisms other than medullary washout are responsible for the natriuretic effects of ANP.     

Adenosine A(1) receptors mediate plasma exudation from the oral mucosa.

The purpose of this study was to pharmacologically characterize the adenosine receptor subtype(s) that mediates adenosine-induced increases in macromolecular efflux from the intact hamster cheek pouch. Using intravital microscopy, we found that 1,3-dipropyl-8-(2-amino-4-chlorophenyl)-xanthine (PACPX), a selective adenosine receptor-1 antagonist, but not 3,7-dimethyl-1-propargylxanthine (DMPX), a selective adenosine receptor-2 antagonist, significantly attenuated adenosine-induced leaky site formation and increased clearance of fluorescein isothiocyanate-labeled dextran (molecular mass, 70 kDa) from the intact hamster cheek pouch (P < 0.05). Both compounds had no significant effects on bradykinin-induced responses. Nanomolar concentrations of R(-)-N(6)-(2-phenylisopropyl)-adenosine [R(-)-PIA], a selective adenosine A(1) agonist, evoked significant, concentration-dependent increases in macromolecular efflux. This response was significantly attenuated by PACPX but not by DMPX. In contrast, CGS-21680, a selective adenosine A(2) agonist, increased macromolecular efflux but only at micromolar concentrations. This response was significantly attenuated by DMPX but not by PACPX. Suffusion of nitroglycerin had no significant effects on R(-)-PIA- and CGS-21680-induced responses. In addition, suffusion of N(G)-nitro-L-arginine methyl ester, a nitric oxide synthase inhibitor, had no significant effects on adenosine-induced responses. Indomethacin had no significant effects on adenosine-, R(-)-PIA-, and CGS-21680-induced increases in macromolecular efflux. Collectively, these data indicate that adenosine increases macromolecular efflux from the intact hamster cheek pouch by stimulating high-affinity adenosine A(1) receptors in a specific, nitric oxide- and prostaglandin-independent fashion.     

The effects of atrial natriuretic peptide on whole-kidney and proximal straight tubular function in the rabbit

The mechanisms by which atrial natriuretic peptide (ANP) produces a diuresis and natriuresis remain unclear. It has been suggested that the major if not sole mediator of ANP's renal effects is a hemodynamically induced increase in glomerular filtration rate (GFR). Data from clearance studies in anesthetized rabbits demonstrate that ANP administration can produce a significant increase in absolute and percentage sodium excretion (42.0 +/- 5.9----64.6 +/- 10.2 mu eq/min, P less than 0.01, and 1.97 +/- 0.28----3.12 +/- 0.35%, P less than 0.001, respectively) without increasing GFR (16.8 +/- 2.1----16.1 +/- 2.5 cc/min, P greater than 0.30). The natriuresis occurred despite a fall in renal plasma flow (RPF) (56.7 +/- 7.0----44.5 +/- 9.4 cc/min, P less than 0.01), a rise in filtration fraction (0.33 +/- 0.01----0.46 +/- 0.05, P less than 0.01), and an unchanged filtered load of sodium (2.28 +/- 0.27----2.16 +/- 0.32 mu eq/min, P greater than 0.10). Isolated tubular microperfusion studies demonstrated that ANP, present as a 10(-9) M concentration in the solution bathing perfused proximal straight tubules (PST), did not affect fluid flux (Jv) (0.38 +/- 0.07----0.41 +/- 0.07 nl/mm/min, P greater than 0.30) or phosphate reabsorption (Jp) (1.50 +/- 0.5----1.38 +/- 0.36 pmole/mm/min, P greater than 0.50). When ANP was infused into rabbits prior to harvesting the PSTs for isolated tubular microperfusion and the results were compared to tubules taken from control animals, there was again no effect on Jv (0.37 +/- 0.05 vs 0.42 +/- 0.05 nl/mm/min, P greater than 0.50) or Jp (2.41 +/- 0.27 vs 2.42 +/- 0.44 pmole/mm/min, P greater than 0.90). These findings suggest that ANP can inhibit sodium transport without increasing whole-kidney GFR or RPF, but does not directly inhibit transport in the proximal straight tubule.     

Effects of albumin, dextran, and hyaluronidase on pulmonary interstitial conductivity

The fluid conductivity of albumin solutions of various concentrations relative to that of saline was measured in the interstitium surrounding a short segment of a large (1.5- to 3-mm-diam) blood vessel of an isolated rabbit lung of which air spaces and vasculature were filled with silicon rubber. At a constant driving pressure, the flow of the following solutions was measured sequentially: normal saline and albumin solution (3, 5.5, 8, or 15 g/100 ml saline), hyaluronidase solution (0.02 g/100 ml), and albumin solution (same concentration used before hyaluronidase solution). The albumin-to-saline flow ratios averaged 1.00 +/- 0.23 (SD), 1.01 +/- 0.21, 1.32 +/- 0.63, and 1.54 +/- 0.36 for albumin concentrations of 3, 5.5, 8, and 15 g/100 ml, respectively. These ratios were higher than the corresponding values of 0.88, 0.78, 0.72, and 0.5 expected if the flow of albumin solution were to depend only on fluid viscosity. The flow of dextran and hyaluronan solutions was more viscosity dependent than the flow of albumin solutions. The increased flow of albumin solution could be the result of a reduced excluded volume of albumin caused by collagen and glycosaminoglycans with an increased albumin concentration. The flow of hyaluronidase solution was 24 +/- 22 (SD)-fold (n = 36) larger than the flow of albumin solution. Thus hyaluronan was responsible for most of the hydraulic resistance of the interstitium to bulk flow. After its degradation, the flow of albumin solution became more viscosity dependent. The interaction between plasma proteins and glycosaminoglycans in the pulmonary interstitium could serve to enhance clearance of microvascular filtrate, particularly under conditions of large protein leaks.     

Role of increased glomerular filtration rate in atrial natriuretic factor-induced natriuresis in the rat

One of the major renal hemodynamic actions of atrial natriuretic factor (ANF) is to increase glomerular filtration rate (GFR). To assess the role of this effect on ANF-induced natriuresis (UNaV), diuresis (V) and kaliuresis (UKV) we performed late clamp experiments in six rats. After control periods (C), synthetic ANF (auriculin A) was infused i.v. (2 micrograms X min-1/kg body wt) throughout the experiment (150 min). After pre-clamp periods, the perfusion pressure of the left kidney (LK) was reduced to 75-80 mmHg. The right kidney (RK) served as a time control. In LK, before the late clamp, ANF increased (p less than 0.01) GFR from 1.5 +/- 0.1 to 1.8 +/- 0.1 ml/min, V from 17 +/- 5 to 53 +/- 5 microliters/min, and UNaV from 2.1 +/- 0.6 to 10.0 +/- 0.9 microEq/min. Almost identical increases occurred in the RK. The late clamp returned all parameters in LK to C values (p greater than 0.05): GFR to 1.4 +/- 0.1 ml/min, V to 6.3 +/- 1.2 microliter/min, and UNaV to 1.0 +/- 0.3 microEq/min. The late clamp also reversed the ANF-induced increase in UKV. In the RK, GFR (1.8 +/- 0.1 ml/min), V (38 +/- 4 microliter/min) and UNaV (7.8 +/- 0.8 microEq/min) remained elevated (p less than 0.01 vs. C) to the end of the experiment. These data demonstrate that upon return of GFR to control levels, the ANF-induced diuresis, natriuresis and kaliuresis is abolished. The results support our previous view that the increase in GFR together with a decrease in inner-medullary hypertonicity account wholly or in great part for the natriuretic action of ANF.     

Hypotension and bradycardia during caloric restriction in mice are independent of salt balance and do not require ANP receptor

We hypothesized that caloric restriction (CR)-induced hypotension would correlate with increased sodium excretion through an atrial natriuretic peptide (ANP)-dependent mechanism. To test this hypothesis, the cardiovascular parameters of c57/Bl mice were measured with radiotelemetry while urine was collected. The 23-h mean blood pressure (BP) dropped from 108.6 +/- 1.8 to 92.7 +/- 2.4 mmHg, and 23-h heart rate dropped from 624 +/- 5 to 426 +/- 13 beats/min over 7 days of CR at 29 degrees C. Contrary to our hypothesis, urine sodium excretion decreased by 55% by day 7 of CR. Consistent with decreased sodium excretion was the drop in plasma ANP (from 82.4 +/- 4.3 to 68.0 +/- 5.8 pg/ml). To explore the possibility that CR lowers BP through an ANP receptor-dependent mechanism that is independent of its effect on sodium retention, we measured the cardiovascular parameters of mice deficient in the ANP receptor (NPR1(-/-)) or the ANP clearance receptor (NPR3(-/-)). Mean BP fell from 117.1 +/- 3.9 to 108.0 +/- 4.7 mmHg in the NPR1(-/-) mice and from 87.0 +/- 2.4 to 78.4 +/- 1.7 mmHg in the NPR3(-/-) mice during CR. These data indicate that the hypotension induced by CR does not depend on increased sodium excretion. Rather, it appears that the mouse responds to the low BP induced by CR with an increase in sodium reabsorption. Furthermore, circulating ANP levels and data from NPR1(-/-) and NPR3(-/-) mice suggest that the ANP pathway may not be involved in the cardiovascular response to CR.     

Anti-DNA antibodies bind directly to renal antigens and induce kidney dysfunction in the isolated perfused rat kidney

The pathogenesis of SLE is commonly attributed to the deposition of circulating immune complexes consisting of DNA and anti-DNA autoantibodies. However, recent work has shown multiple cross-reactions between anti-DNA antibodies and a variety of cellular and extracellular Ag. To test the possibility that these antibodies interact directly with glomerular Ag and induce kidney dysfunction, we applied mouse and human anti-DNA IgG to the isolated perfused rat kidney. The NZB/NZW mouse monoclonal anti-DNA bound to glomerular Ag with a concomitant induction of proteinuria and a decrease in inulin clearance. The albumin excretion was 2301 +/- 734 micrograms/min at 160 min of perfusion, as compared with 85 +/- 21 micrograms/min in controls (p less than 0.001). The inulin clearance was reduced to 0.17 +/- 0.02 ml/min as compared with 0.28 +/- 0.09 ml/min in controls (p less than 0.05). Polyclonal anti-DNA IgG obtained from patients with lupus nephritis bound to rat glomeruli and induced albumin excretion of 542 +/- 217 micrograms/min at 160 min of perfusion, as compared with 163 +/- 77 micrograms/min in controls (p = NS). The addition of plasma as a source of C to the human IgG increased the proteinuria markedly (albumin excretion of 1115 +/- 195 micrograms/min at 160 min of perfusion, p less than 0.02), probably due to C activation. Preincubation of the reactive mouse and human IgG with DNA completely abolished their binding to renal tissue and its physiologic consequences. These results suggest that direct binding of anti-DNA antibodies to renal Ag may play an important role in the induction of lupus nephritis.     

Reduced natriuresis after oral sodium load in cholestatic rats: role of compartment volumes and ANP

The purpose of this study was to assess the participation of the atrial natriuretic peptide (ANP)-cGMP system in electrolyte and volume handling of cholestatic rats submitted to an acute oral sodium load. Cholestasis was induced by ligation and section of the common bile duct (n = 51). Control rats were sham operated (n = 56). Three weeks after surgery, 24-hr urinary volume, sodium, potassium, cGMP and creatinine excretion were measured. Three days later, animals received 10 mmol/kg NaCl (1 M) by gavage, and urinary excretion was measured for 6 hr. In parallel groups of rats, plasma volume, electrolytes and ANP concentration, extracellular fluid volume (ECFV), and renal medullary ANP-induced cGMP production were determined in basal conditions or 1 hr after oral sodium overload. As compared with controls, cholestatic rats had a larger ECFV and higher plasma ANP (67.2 +/- 5.2 vs 39.7 +/- 3.5 pg/ml), but lower hematocrit and blood volume, and were hyponatremic. Cholestatic rats showed higher basal excretion of sodium, potassium, and volume than controls, but equal urinary cGMP. After the NaCl overload, cholestatic rats showed a reduced sodium excretion but equal urinary cGMP. One hr after sodium overload, both groups showed hypernatremia, but whereas in control rats ECFV and ANP increased (50.7 +/- 4.1 pg/ml), in cholestatic rats ECFV was unchanged, and plasma volume and ANP were reduced (37.5 +/- 5.8 pg/ml). ANP-induced cGMP production in renal medulla was similar in cholestatic and control nonloaded rats (14.2 +/- 5.2 vs 13.4 +/- 2.6 fmol/min/mg). One hr after the load, medullary cGMP production rose significantly in both groups, without difference between them (20.6 +/- 3.1 vs 22.7 +/- 1. 7 fmol/min/mg). We conclude that the blunted excretion of an acute oral sodium load in cholestatic rats is associated with lower plasma ANP due to differences in body fluid distribution and cannot be explained by renal refractoriness to ANP.     

Evans blue dye as a marker of albumin clearance in cultured endothelial monolayer and isolated lung.

Determination of protein transfer across the endothelial barrier or the entire alveolar capillary membrane is critical for investigation of mechanisms leading to pulmonary edema. The purpose of this study was to evaluate Evans blue dye for determination of protein clearance across cultured bovine pulmonary artery endothelial cell monolayers and as a quantitative marker for albumin leakage to the air spaces in isolated perfused rat lungs. Evans blue dye bound tightly to albumin (EBA) as determined by lack of transfer through dialysis membranes and specific elution with albumin from a molecular exclusion column. EBA was equivalent to 125I-labeled albumin for calculation of albumin clearance rates (Calb) across intact and challenged monolayers [Calb (+ vehicle) = 0.12 microliters/min; Calb (+10 nM alpha-thrombin) = 0.47 microliters/min; Calb (+5 mg/ml trypsin) = 1.29 microliters/min]. Transfer of EBA was linear with time in both the endothelial cell monolayer model and the perfused lung. EBA was a sensitive marker for early edema in the perfused lung (before detectable weight gain) as well as for severe edema in the oxidant-injured lung (marked EBA accumulation in lavage fluid) and was a more specific marker for protein transfer than lavage fluid protein. EBA transfer is a convenient, reproducible, and accurate means to assess alterations in vascular permeability.