Effects of renal nerves and plasma epoxyeicosatrienoic acids on blood pressure, renal hemodynamics and excretion in spontaneously hypertensive rats

Spontaneously hypertensive rats (SHR) display deficiency of epoxyeicosatrienoic acids (EETs). Their possible interaction with renal sympathetic nerves remains unexplored; synthesis of EET-A [disodium (S)-2-(13-(3-pentyl)ureido)-tridec-8(Z)-enamido)succinate], a stable 14,15-EET analog, helps clarify the issue. In anesthetized SHR, untreated or pretreated with EET-A, we assessed early responses of blood pressure (MAP), renal hemodynamics and excretion, and indices of nitric oxide (NO) activity, to bilateral noninvasive renal denervation (DNX). DNX significantly decreased MAP, with or without EET-A pretreatment. Renal perfusion decreased in EET-A treated but not in control rats. After EET-A pretreatment DNX decreased renal excretion of sodium and total solutes, compared to increasing tendency in untreated rats. In EET-A treated but not in untreated SHR denervation reduced the excretion of NO metabolites. Antihypertensive action of EET-A in anesthetized SHR was not clearly dependent on renal nerve activity. On the other hand, DNX unmasked the unexpected effect of EET-A to lower renal perfusion. The mechanism of this novel finding is unclear, as is also the simultaneous post-denervation decrease in renal excretion, again, observed only under EET-A treatment. Possibly, the decrease was secondary to falling MAP and renal perfusion. Increased renal excretion of nitric oxide metabolites under EETs elevation strongly suggests facilitation of NO release; the effect that was observed only with intact renal nerve activity.

P3513Sex-related differences in the outcome of congestive heart failure: study on rats treated with ACEi alone or combined with soluble epoxide hydrolase inhibitor

Introduction

In search for new therapeutic measures of congestive heart failure (CHF) attention focused on the role of epoxyeicosatrienoic acids (EETs), cytochrome P450-dependent epoxygenase pathway metabolites of arachidonic acid, with antihypertensive and organ-protective actions. The EETs are rapidly broken-down by soluble epoxide hydrolase (sEH). Blocking sEH and increasing tissue EETs bioavailability had antihypertensive and cardio- and renoprotective effects. The studies of the biological mechanisms underlying the sex-related differences in the CHF and in the responses to new pharmacological measures are missing. The rat model in which CHF is induced by volume overload by creation of the aorto-caval fistula (ACF) is recommended for preclinical studies by American Heart Association. It has been noticed that the hypertensive rat transgenic for the mouse Ren-2 renin gene (TGR) presents a unique angiotensin II-dependent model of hypertension. We found that male ACF TGR displayed tissue deficiency of EETs, and increasing intrarenal EETs levels by pharmacological blockade of sEH attenuated the progression of CHF in male ACF TGR. However, we did not examine if this effect occurs also in female ACF TGR.

Purpose

The aim was to establish if sex-related differences, if present, are demonstrable with standard treatment with ACEi alone and with the combined treatment with ACEi and sEHi.

Methods

Male and female TGR rats were randomly assigned either to ACF procedure or to sham-operation. One week after the procedure rats were divided into the 8 experimental groups (sham-operated male TGR + placebo, ACF male TGR + placebo, ACF male TGR + ACEi, ACF male TGR + ACEi + sEHi, sham-operated female TGR + placebo, ACF female TGR + placebo, ACF female TGR + ACEi, ACF female TGR + ACEi + sEHi). C-AUCB was used as an sEHi and trandolapril as ACEi, both in drinking water in doses previously tested. The follow-up period was 50 weeks and the primary end-point was death from any cause.

Results

All sham-operated male and female TGR survived until the end of experiment. All untreated male ACF TGR animals died by week 20. In contrast, untreated female ACF survived in the rate of 32%. The treatment with ACEi improved survival rate similary in male as well as female ACF TGR (74% and 65%). The combined treatment with ACEi and sEHi worsened the survival in male ACF TGR as compared with ACF TGR + ACEi (38%). In contrast, the combined treatment with ACEi and sEHi in female ACF TGR significantly improved the course and the final survival rate (84%) as compared with female ACF TGR + ACEi alone.

Picture 1

Conclusions

The study suggests that in CHF individuals in whom hypertension and increased RAS activity run in parallel, the patients' sex is the co-determinant of CHF progression. In particular it can influence the effectiveness of the therapeutic measures applied to slow it down. Therefore, in pre- and clinical studies the sex-related differences should be seriously considered.

Acknowledgement/Funding

Ministry of Health of the Czech Republic grant no. 17- 28220A; Grant Agency of Charles University, project number 32218

Ventricular assist devices in heart failure: how to support the heart but prevent atrophy?

Ventricular assist devices (VAD) have recently established themselves as an irreplaceable therapeutic modality of terminal heart failure. Because of the worldwide shortage of donors, ventricular assist devices play a key role in modern heart failure therapy. Some clinical data have revealed the possibility of cardiac recovery during VAD application. On the other hand, both clinical and experimental studies indicate the risk of the cardiac atrophy development, especially after prolonged mechanical unloading. Little is known about the specific mechanisms governing the unloading-induced cardiac atrophy and about the exact ultrastructural changes in cardiomyocytes, and even less is known about the ways in which possible therapeutical interventions may affect heart atrophy. One aim of this review was to present important aspects of the development of VAD-related cardiac atrophy in humans and we also review the most significant observations linking clinical data and those derived from studies using experimental models. The focus of this article was to review current methods applied to alleviate cardiac atrophy which follows mechanical unloading of the heart. Out of many pharmacological agents studied, only the selective beta2 agonist clenbuterol has been proved to have a significantly beneficial effect on unloading-induced atrophy. Mechanical means of atrophy alleviation also seem to be effective and promising.

Moisture sorption isotherms and glass transition temperature of elecampe (Inula helenium L.) and burdock (Arctium lappa L.) roots at 25°C

Sorption isotherms of elecampe (Inula helenium L.) and burdock (Arctium lappa L.) root samples were obtained at 25 °C. Elecampe exhibited hysteresis loop in the range of 0.35-0.90 a(w) , whereas burdock roots showed significant differences between adsorption and desorption isotherms from 0.65 to 0.80 a(w) . Blahovec-Yanniotis was considered to give the best fit over the whole range of a(w) tested. Various parameters describing the properties of sorbed water derived from GAB, Henderson and Blahovec-Yanniotis models have been discussed. Differential scanning calorimetric method was used to measure the glass transition temperature (T (g)) of root samples in relation to water activity. The safe moisture content was determined in 12.01 and 14.96 g/100 g d. b. for burdock and elecampe root samples at 25 °C, respectively. Combining the T (g) line with sorption isotherm in one plot, it was found that the glass transition temperature concept overestimated the temperature stability for both root samples.

Despite similar reduction of blood pressure and renal ANG II and ET-1 levels aliskiren but not losartan normalizes albuminuria in hypertensive Ren-2 rats

The relationship between angiotensin II (ANG II) and endothelin-1 (ET-1) is known to be complex; both peptides can initiate and potentiate the gene expression of each other. This pilot study investigated the effects of the AT(1) receptor blocker losartan or the direct renin inhibitor aliskiren on mean arterial pressure (MAP) and albuminuria and the renal ANG II and ET-1 levels. 3-month-old male Ren-2 transgenic rats (TGR) were treated either with losartan (5 mg kg(-1) day(-1)) or aliskiren (10 mg kg(-1) day(-1)) for 10 weeks. At the end of the experiment, rats were decapitated and cortical and papillary parts of kidneys were separated. Plasma and tissue ANG II levels were measured by RIA and tissue ET-1 concentrations by ELISA. In all four groups of animals ET-1 levels were lowest in renal cortex and more than 100-fold higher in the papilla. Cortical and papillary ET-1 concentrations in untreated TGR significantly exceeded those of control HanSD rats and were significantly depressed by both drugs. In both strains, papillary ANG II concentrations were moderately but significantly higher than cortical ANG II, TGR exhibited higher ANG II levels both in cortex and papilla as compared to control HanSD rats. Aliskiren and losartan at the doses used depressed similarly the levels of ANG II in cortex and papilla and reduced ET-1 significantly in the renal cortex and papilla below control levels in HanSD rats. Albuminuria, which was more than twice as high in TGR as in HanSD rats, was normalized with aliskiren and reduced by 28% with losartan, although MAP was reduced to a similar degree by both drugs. Despite similar reductions of MAP and renal ET-1 and ANG II levels aliskiren appears to be more effective than losartan, at the doses used, in reducing albuminuria in heterozygous hypertensive Ren-2 rats.

Renal interactions of renin-angiotensin system, nitric oxide and superoxide anion: implications in the pathophysiology of salt-sensitivity and hypertension

Renin-angiotensin system (RAS) plays a key role in the regulation of renal function, volume of extracellular fluid and blood pressure. The activation of RAS also induces oxidative stress, particularly superoxide anion (O(2)(-)) formation. Although the involvement of O(2)(-) production in the pathology of many diseases is known for long, recent studies also strongly suggest its physiological regulatory function of many organs including the kidney. However, a marked accumulation of O(2)(-) in the kidney alters normal regulation of renal function and thus may contribute to the development of salt-sensitivity and hypertension. In the kidney, O(2)(-) acts as vasoconstrictor and enhances tubular sodium reabsorption. Nitric oxide (NO), another important radical that exhibits opposite effects than O(2)(-), is also involved in the regulation of kidney function. O(2)(-) rapidly interacts with NO and thus, when O(2)(-) production increases, it diminishes the bioavailability of NO leading to the impairment of organ function. As the activation of RAS, particularly the enhanced production of angiotensin II, can induce both O(2)(-) and NO generation, it has been suggested that physiological interactions of RAS, NO and O(2)(-) provide a coordinated regulation of kidney function. The imbalance of these interactions is critically linked to the pathophysiology of salt-sensitivity and hypertension.

End-organ damage in hypertensive transgenic Ren-2 rats: influence of early and late endothelin receptor blockade

The rat strain transgenic for the murine Ren-2 renin gene (TGR) is defined as a monogenic model of angiotensin II-dependent hypertension with endogenous activation of the renin-angiotensin system. Homozygous males TGR develop malignant hypertension with a strong salt-sensitive component. These animals show severe hypertension, proteinuria and high mortality. Morphological changes of renal parenchyma correspond to chronic ischemic glomerular changes. Heterozygous TGR develop only mild hypertension and thus provide a more suitable model of hypertension regarding to clinical studies. Within the renal parenchyma, secondary focal segmental glomerulosclerosis (FSGS) predominates. High-salt diet in heterozygous animals induces transition from benign to malignant phase of hypertension. In this case, ischemic glomerular changes are superimposed on preexisting secondary FSGS. In the regression model of hypertension (late-onset treatment) the effect of salt intake is attenuated. In homozygous TGR, early selective ET(A) receptor blockade decreased blood pressure and ameliorated end-organ damage. Late selective ET(A) receptor blockade reduced podocyte injury despite final severe hypertension. Survival rate was markedly improved in both regimens with ET(A) selective blockade, while there was only partial improvement with early non-selective blockade. Both bosentan and atrasentan decreased ET-1 levels in both regimens. In heterozygous TGR, early and late ET(A) treatment substantially while ET(A)/ET(B) treatment partially improved survival rate. Significant effect on BP was found with early and late ET(A) blockade, while ET(A)/ET(B) blockade had no effect. Bosentan and atrasentan similarly decreased ET-1 levels on both regimens. In conclusion, selective ET(A) receptor blockade is superior to nonselective ET(A)/ET(B) receptor blockade in attenuating hypertension and end-organ damage. Its effect is more pronounced when applied early in the life.

The effect of acetic acid, citric acid, and trisodium citrate in combination with different levels of water activity on the growth ofArcobacter butzleri in culture

The influence of weak organic acids and trisodium citrate in combination with a high or a reduced water activity (aw) was investigated when a population of Arcobacter butzleri was exposed to a low concentration of acetic or citric acid, and trisodium citrate combined with high (0.993) and reduced (0.977) aw in culture broth at 30 degrees C. Regardless of water activity, acetic and citric acid (> 0.2%) inhibited the growth of A. butzleri with no viable cells detected after 4-5 h of incubation. Enhanced survival was found at reduced aw with addition of acetic acid. In contrast, after exposure to citric acid in combination with reduced aw inactivation was more rapid than that after being exposed to high water activity. Incorporation of trisodium citrate in combination with reduced aw (0.977) would probably not confer any extra protection. Concentrations of organic acid widely used in meat decontamination processing represent feasible tools for reducing A. butzleri contamination and hence the risk of Arcobacter infection.

Detection of aflatoxigenic fungi in feeds using the PCR method

The possibility of using the polymerase chain reaction (PCR) to speed up and specify the detection of aflatoxigenic fungi isolated from feed was investigated. The method, applied to 2 genes encoding the biosynthesis of aflatoxins (apa-2 and ver-1), was optimized on two collection cultures (Aspergillus flavus CCM F-108 and A. parasiticus CCM F-550). The specificity of the optimized PCR method was proved on collection cultures of different kinds of fungi. Fifty feed samples out of which 18 showed positive findings of aflatoxigenic fungi on an Aspergillus Flavus and Parasiticus Agar (AFPA) medium were tested. Isolated strains of Aspergillus strains were verified using the PCR method; its reaction products were detected in 1% agarose gel by electrophoresis. The results almost exclusively matched those gained from the AFPA medium.

Role of nNOS in regulation of renal function in hypertensive Ren-2 transgenic rats

The present study was performed to evaluate the role of neuronal nitric oxide synthase (nNOS)-derived nitric oxide (NO) during the developmental phase of hypertension in transgenic rats harboring the mouse Ren-2 renin gene (TGR). The first aim of the present study was to examine nNOS mRNA expression in the renal cortex and to assess the renal functional responses to intrarenal nNOS inhibition by S-methyl-L-thiocitrulline (L-SMTC) in heterozygous TGR and in age-matched transgene-negative Hannover Sprague-Dawley rats (HanSD). The second aim was to evaluate the role of the renal sympathetic nerves in mediating the renal functional responses to intrarenal nNOS inhibition. Thus, we also evaluated the effects of intrarenal L-SMTC administration in acutely denervated TGR and HanSD. Expression of nNOS mRNA in the renal cortex was significantly increased in TGR compared with HanSD. Intrarenal administration of L-SMTC decreased the glomerular filtration rate (GFR), renal plasma flow (RPF) and sodium excretion and increased renal vascular resistance (RVR) in HanSD. In contrast, intrarenal inhibition of nNOS by L-SMTC did not alter GFR, RPF or RVR and elicited a marked increase in sodium excretion in TGR. This effect of intrarenal L-SMTC was not observed in acutely denervated TGR. These results suggest that during the developmental phase of hypertension TGR exhibit an impaired renal vascular responsiveness to nNOS derived NO or an impaired ability to release NO by nNOS despite enhanced expression of nNOS mRNA in the renal cortex. In addition, the data indicate that nNOS-derived NO increases tubular sodium reabsorption in TGR and that the renal nerves play an important modulatory role in this process.

Role of nNOS in regulation of renal function in angiotensin II-induced hypertension

Previous studies have indicated that in normotensive rats, NO produced by neuronal NO synthase (nNOS) plays an important role in modulating tubuloglomerular feedback (TGF)-mediated afferent arteriolar constriction. It has also been shown that in angiotensin (Ang) II-infused hypertensive rats, there is a reduced ability of nNOS-derived NO to counteract this vasoconstriction. The present study was performed to (1) assess in vivo renal functional responses to intrarenal nNOS inhibition in control and Ang II-infused rats and (2) determine whether changes in renal function following nNOS inhibition are mediated by unopposed stimulation of Ang II receptor subtype 1 (AT(1)). Wistar rats were infused with either saline (SAL) or Ang II (80 ng/min) by osmotic minipumps implanted subcutaneously. Mean arterial blood pressure of SAL- and Ang II-infused rats on day 13 after implantation averaged 121+/-4 (n=28) and 151+/-5 (n=30), respectively (P<0.05). There were no differences in glomerular filtration rate (GFR) (0.68+/-0.09 versus 0.59+/-0.09 mL. min(-1). g(-1)), renal plasma flow (RPF) (2.66+/-0.31 versus 2.34+/-0.39 mL. min(-1). g(-1)), and absolute sodium excretion (0.37+/-0.07 versus 0.42+/-0.09 micromol. min(-1). g(-1)). Intrarenal infusion of SAL did not change GFR, RPF, and sodium excretion in either SAL-infused (n=7) or Ang II-infused rats (n=8). Acute intrarenal administration of the nNOS inhibitor S-methyl-L-thiocitrulline (L-SMTC; 0.3 mg/h) decreased GFR, RPF, and sodium excretion in SAL-infused rats (n=9) by 29+/-4%, 38+/-4%, and 70+/-4% compared with control values (P<0.05). The pretreatment by the AT(1) receptor antagonist candesartan (750 ng IR) in SAL-infused rats (n=7) effectively prevented the decrease in RPF (-3+/-3%) elicited by nNOS inhibition and resulted in an increase in GFR (+25+/-12, P<0.05) and a concomitant greater increase in sodium excretion (84+/-12%, P<0.05) compared with control values. In contrast, in Ang II-infused rats (n=10) intrarenal inhibition of nNOS by L-SMTC did not cause significant decreases in GFR, RPF and sodium excretion (-2+/-2%, -15+/-10%, and -14+/-10%, respectively). These results suggest that in normotensive rats nNOS-derived NO counteracts Ang II-mediated vasoconstriction in the pre- and postglomerular microcirculation. Furthermore, Ang II-infused rats exhibit an impaired ability to release NO by nNOS. Decreased nNOS activity is likely to account at least partially for the enhanced TGF responsiveness in Ang II-infused rats and thus may contribute to the maintenance of hypertension in this model.

Angiotensin II-induced hypertension in bradykinin B2 receptor knockout mice

The present study was performed to examine the role of endogenous bradykinin (BK) in the development of angiotensin II (Ang II)-induced hypertension in mice. BK B2receptor knockout (B2R-/-) and wild-type (B2R+/+) mice (22to 26 g) were infused with either saline (SAL) or Ang II (40ng/min) via an osmotic minipump implanted intraperitoneally. On day 12after implantation, there was no difference in systolic blood pressure (SBP, tail-cuff plethysmography) between SAL/B2R+/+ and SAL/B2R-/- mice(128+/-5 versus 133+/-6 mm Hg, n=24/group). In contrast, SBP was higher on day 12 of infusion in Ang II/B2R-/- than in Ang II/B2R+/+ mice (173+/-6versus 156+/-5 mm Hg; P<0.05, n=27 and 28). Mean arterial pressure (MAP)was also higher in anesthetized Ang II/B2R-/- mice than in Ang II/B2R+/+mice (139+/-3 versus 124+/-3 mm Hg; P<0.05, n=16 and 14). Unlike Ang II, long-term norepinephrine (NE) infusion via an osmotic minipump (45ng/min) caused equivalent increases in SBP in B2R+/+ and B2R-/- mice measured on day 12 after implantation (151+/-4 versus 149+/-5 mm Hg, n=9and 8). MAP also did not differ on day 13 after implantation between NE/B2R+/+ and NE/B2R-/- mice (120+/-6 versus 122+/-4 mm Hg, n=9 and 8). There were no differences in glomerular filtration rate and urinary sodium excretion among the groups. However, renal plasma flow (RPF) was lower in Ang II/B2R-/- mice than in Ang II/B2R+/+ mice (2.34+/-0.06 versus 4.33+/-0.19 mL x min-1 x g-1; P<0.05). Acute inhibition of NO synthase (NOS)with nitro-L-arginine-methyl ester (0.5 microg x g-1 x min-1) in SAL/B2+/+ and SAL/B2-/- mice caused equal increases in MAP (142+/-1 versus 145+/-1 mmHg) and decreases in RPF (2.06+/-0.06 versus 2.12+/-0.15 mL x min-1 x g-1).However, short-term NOS inhibition caused a greater increase in MAP of Ang II/B2R+/+ mice than of Ang II/B2R-/- mice, such that MAP after NOS inhibition in Ang II/B2R+/+ approached that of Ang II/B2R-/- mice (156+/-2versus 159+/-2 mm Hg). These changes were associated with a decrease in RPF in Ang II/B2R+/+ mice to values similar to those of Ang II/B2R-/- mice before NOS inhibition (2.12+/-0.09 versus 2.34+/-0.06 mL x min-1 x g-1). These results demonstrate that the kallikrein-kinin system selectively buffers the vasoconstrictor activity of Ang II. Furthermore, the enhanced susceptibility of B2R-/- mice to Ang II-induced hypertension and renal vasoconstriction is likely due to an impaired ability to release NO by endogenous kinins.

[Experimental ischemic renal injury--effect of surgical technique and the protective effect of a nonpeptide angiotensin II antagonist (losartan)]

Experimental renal ischaemic injuries are typically produced by temporary closure of the renal artery. In rats, two different methods of such temporary closure of the renal artery were compared: snaring of the artery by tourniquet, and clamping by a microsurgical bulldog clamp. The consequences of ischaemic periods 60, 90 and 120 minutes were evaluated. In different experimental series, the potential protective effect of non-peptic AT1 angiotensin II receptor antagonist losartan on postischaemic renal injury was evaluated. The seven-day survival and the degree of functional renal damage (according to the plasma levels of creatinine and urea) were analyzed 24 hours and 7 days after experimental renal ischaemia. Ischaemia, produced by the tourniquet led to a more significant renal damage than ischaemia caused by clamping of the renal artery by a microclamp (higher 7-day mortality rate, higher postischaemic plasma levels of creatinine and urea). Losartan decreased the consequences of renal ischaemia caused by the tourniquet, but did not change the outcome of renal ischaemia produced by microsurgical bulldog clamps. We found, that not only the duration of ischaemia and pharmacology, but even the surgical technique of producing renal ischaemia are important factors in experimental studies evaluating ischaemic renal damage. These findings provide evidence of the role of angiotensin II in postischaemic renal injury by a renal tourniquet. This particular mechanism is probably not involved, when renal artery is gently temporarily closed by a bulldog microclamp.

[Role of the kidney in long-term regulation of blood pressure and the development of hypertension]

Evidence about the crucial role of the kidney in the development and maintenance of the "essential" hypertension (i.e. hypertension which is accompanied with the absence of any pathological change in any of body organs) and in the regulation of "normal" blood pressure level (BP) has been accumulated. Blood pressure is expressed as a product of cardiac output (CO) and total peripheral resistance (TPR). TPR almost entirely depends on the volume of the extracellular fluid (ECFV): With increasing volume BP rises and vice versa. ECFV--due to intensive maintenance of the osmolality--almost entirely depends on the total amount of sodium in the organism. This amount is not determined by the intake of salt, which is in every civilized population always higher than necessary. Sodium balance is therefore critically determined by the output of sodium, which is carried out almost entirely by the kidney. The output depends on the quantity of the glomerular filtration and on the tubular reabsorption. Under normal circumstances, the increased sodium intake is accompanied by an increased excretion via the mechanism called "pressure natriuresis". It is based on the prompt increase of sodium excretion after an increase of BP, resulting from the increased sodium intake. Mechanism of such elevated excretion is not clear; lot of evidence has been accumulated for the existence of a humoral principle produced within the kidney. Such assumption is supported by experiments in which a kidney is transplanted from a hypertonic donor to a normotensive recipient: hypertension in the recipient develops. Similarly, kidney grafting from a normotensive animal corrects the hypertension in an originally hypertensive recipient. Important role of the renin-angiotensin (RAS) and nitric oxide (NO) systems is often stressed in this context. If kidney is unable to excrete the ingested amount of sodium at the normal BP, blood pressure must rise and the shift of the pressure-natriuresis curve to the right is the necessary consequence. If these conditions are long lasting, hypertension develops soon and becomes "fixed" by rebuilding the resistance arteries architecture.

Effect of intrarenal infusion of angiotensin-(1-7) in the dog

Angiotensin-(1-7), (Ang-(1-7)), a metabolite of Ang II and /or Ang I, was infused into the renal artery (i.r.a) of anesthetized dogs in order to demonstrate its possible direct renal action. The dose administered, 15 Ig/kg BW/min in isotonic saline (0.072 ml/kg BW/min) throughout the experiment, did not influence the systemic arterial pressure and water and sodium excretion from the contralateral noninfused kidney. Renal blood flow (RBF) was measured by an electromagnetic flowmeter, glomerular filtration rate (GFR) by (exogenous) creatinine clearance. In other groups of animals, either EXP 3174, an AT-1 receptor antagonist alone (30 Ig/kg BW/ min) or together with Ang-(1-7) (15 Ig/kg BW/min), were infused. In the last group, the AT-2 receptor antagonist PD 123319, 10 Ig/kg BW/min, was added to the infusion of Ang-(1-7). A small but significant decrease of RBF from 4.51+/-0.32 to 3.8+/-0.29 ml/g BW/min occurred after Ang-(1-7); this decrease was very similar when PD 123319 was added. However, an increase to 4.98+/-0.34 ml/g BW/min was seen after the addition of EXP 3174 to the i.r.a. infusion of Ang-(1-7); this increase was similar to the increase observed after EXP 3174 alone (5.21+/-0.33; p<0.02 in both cases). A very small but significant increase in GFR was seen after Ang-(1-7) + EXP 3174 or after the AT-1 blocker alone (0.64+/-0.049 and 0.62+/-0.05 vs. 0.6+/-0.05 ml/g BW/min in the Time Control Group, p<0.01 and 0.05, respectively). Water, sodium and urea excretion rates were increased in all groups infused with Ang-(1-7); after the combination of Ang-(1-7) + EXP 3174, all increases were higher than after every substance alone; however, statistical significance (p<0.05) was reached in sodium excretion values only. Potassium excretion rates were increased just in those groups in which EXP 3174 was present in the infusion fluid. In summary, Ang-(1-7) i.r.a. infusion in the dog is followed by increases in water, sodium and urea (but not potassium) excretion rates, highly probably of tubular origin. This effect is not completely blocked by the AT-1 - and not at all by the AT-2 receptor antagonist - thus indirectly suggesting another receptor could play a role. A small decrease in RBF disappears after EXP 3174, thus indicating an AT-1 receptor action.

Renal responses to AT1 receptor blockade

Because of the importance of the renin-angiotensin system in the pathophysiology of hypertension and in mediating associated alterations in renal function, angiotensin II (Ang II) AT1 receptor blockers provide a direct means of protecting against influences of excessive Ang II levels. The kidney is an important site of action of Ang II AT1 receptor blockers because intrarenal Ang II not only vasoconstricts the renal vasculature but also reduces sodium excretion and suppresses the pressure natriuresis relationship. Even in normal conditions, intrarenal Ang II content is greater than can be explained on the basis of circulating Ang II and is compartmentalized with proximal tubule concentrations of Ang I and Ang II being several times higher than plasma concentrations. The localization of angiotensinogen in proximal tubule cells further supports the concept that the proximal tubule secretes Ang II or precursors of Ang II into the tubular fluid to activate luminal Ang II receptors. Recent immunohistochemical studies have demonstrated an abundance of AT1 receptors on the luminal surface of proximal and distal tubule cells as well as on vascular smooth muscle cells of afferent and efferent arterioles and on glomerular mesangial cells. Activation of luminal AT1 receptors stimulates the sodium hydrogen exchanger and increases reabsorption rate. The prominence of AT1 receptors in vascular and epithelial tissues in the kidney provides the basis for the powerful effects of AT1 receptor blockers on renal function especially in hypertensive conditions. In the two-kidney, one-clip (2K1C) Goldblatt hypertensive rat model, the nonclipped kidney is renin depleted but the intrarenal Ang II levels are not suppressed and Ang II concentrations in proximal tubular fluid remain high (10(-8) mol/L). AT1 receptor blockers such as candesartan have been shown to cause significant increases in glomerular filtration rate, renal blood flow and proportionately much greater increases in sodium excretion and fractional sodium excretion. Ang II blockade also markedly increases the slope of the pressure natriuresis relationship. The collective actions of Ang II blockers on tubular transport and renal hemodynamics provide long-term effects to regulate sodium balance, which contributes to the long-term control of hypertension.

Renal function in mice: effects of volume expansion and angiotensin II

The present study was performed to validate a simple means for assessing renal function in anesthetized mice and to characterize the renal hemodynamic responses to acute volume expansion and how these responses are altered by concurrent angiotensin II (AngII) infusions. Inulin and para-aminohippurate clearances were used to assess GFR and renal plasma flow (RPF) in three groups of male C57Bl/6 mice anesthetized with inactin (100 mg/kg, intraperitoneally) and ketamine (10 mg/kg). To avoid the hypotension associated with repeated blood sampling, a single blood sample was taken after three timed urine collections. Renal function and mean arterial pressure (MAP) were measured under euvolemic conditions (2.5 microl/min, intravenously, n = 7) during isotonic saline volume expansion (12.5 microl/min, intravenously, n = 5) and during volume expansion with concurrent AngII infusion (5 ng/min x g, n = 5). MAP in the control group was 77 +/- 2 mmHg; volume expansion alone did not change MAP significantly (83 +/- 2 mmHg), but led to significantly greater values in both GFR and RPF (1.35 +/- 0.14 versus 1.01 +/- 0.1 ml/min x g and 11.26 +/- 1.39 versus 6.29 +/- 0.5 ml/min x g, respectively). Infusion of AngII during volume expansion led to significant elevations of MAP (100 +/- 3 mmHg, P < 0.05) and prevented the increases in GFR and RPF elicited by volume expansion (0.77 +/- 0.08 and 5.35 +/- 0.48 ml/min x g, respectively). Volume expansion also elicited marked increases in absolute and fractional sodium excretion (6.1 +/- 1.0 versus 0.62 +/- 0.2 microEq/min x g and 3.1 +/- 0.7 versus 0.4 +/- 0.1%, respectively). AngII infusion attenuated the absolute and fractional sodium excretion responses to volume expansion (3.4 +/- 1.2 microEq/min x g and 2.5 +/- 0.5%, respectively). The present findings demonstrate that anesthetized mice exhibit marked renal hemodynamic and excretory responses to isotonic saline volume expansion. Concomitant AngII infusion attenuates these responses in spite of greater increases in arterial pressure.

Renal function in the AT1A receptor knockout mouse during normal and volume-expanded conditions

BACKGROUND

Genetically altered mice lacking the AT1A angiotensin II (Ang II) receptor were used to examine the role of AT1A receptors in regulating renal hemodynamics, sodium excretion, glomerulotubular balance, and Ang II levels in plasma and kidney during normal and volume-expanded conditions.

METHODS

AT1A receptor-deficient mice and their wild-type controls were anesthetized with inactin and ketamine, and were prepared to allow intravenous infusions of solutions and measurements of aortic pressure and urine collections. Inulin and para-aminohippurate (PAH) solutions were infused intravenously for clearance determinations under conditions of euvolemia (2.5 microliter/min infusion of isotonic saline) or volume-expansion conditions (12.5 microliter/min). After three 30-minute urine collections, blood samples were collected, and kidneys were harvested. Plasma and kidney Ang II measurements were made by radioimmunoassay.

RESULTS

In the euvolemic state, mean arterial pressures (MAPs) were significantly lower in the AT1A receptor-deficient mice (68 +/- 4 mm Hg) compared with wild-type controls (89 +/- 3 mm Hg). Despite the lower MAP, the glomerular filtration rate (GFR), renal plasma flow (RPF), absolute sodium excretion, and fractional sodium excretion were not significantly different between wild-type and AT1A-/- mice. Volume expansion did not alter MAP in wild-type mice, but significantly increased MAP in the AT1A-/- mice (68 +/- 4 to 83 +/- 5 mm Hg). Similar increases in GFR, RPF, absolute sodium excretion, and fractional sodium excretion in AT1A+/+ and AT1A-/- mice were observed. Glomerulotubular balance was not disrupted by the absence of AT1A receptors. During euvolemia, plasma Ang II concentrations were significantly higher in the AT1A-/- mice compared with wild-type mice (536 +/- 172 vs. 198 +/- 36 fmol/ml). Although volume expansion had no effect on plasma Ang II levels in the AT1A+/+ group, plasma Ang II concentrations were markedly suppressed in the AT1A-/- mice to levels that were not different from those in wild-type mice. In contrast, kidney tissue Ang II contents were reduced in the AT1A-/- mice and were not significantly altered during volume expansion in either the AT1A-/- or the AT1A+/+ mice.

CONCLUSIONS

The absence of AT1A receptors does not impair chronic regulation of renal blood flow, GFR, or glomerulotubular balance. The prompt restoration of MAP following volume expansion suggests that low blood pressure in the AT1A receptor-deficient mice is primarily due to reduced effective plasma and extracellular fluid volume. Normalization of plasma Ang II levels with volume expansion demonstrates a dominant effect of extracellular fluid volume and blood pressure over AT1A receptor-mediated short-loop feedback in the regulation of plasma Ang II levels.

Early onset salt-sensitive hypertension in bradykinin B(2) receptor null mice

Kinins have been implicated in the hemodynamic adaptation to postnatal life. The present study examined the impact of bradykinin B(2) receptor (B(2)R) gene disruption on the postnatal changes in blood pressure (BP) and the susceptibility to early onset salt-sensitive hypertension in mice. B(2)R null (-/-) and wild-type (+/+) mice were fed normal (NS, 1% NaCl) or high (HS, 5% NaCl) salt diets during pregnancy. After birth, the pups remained with their mothers until they were weaned and were subsequently continued on the respective maternal salt intake until 4 months of age. The age-related changes at 3 and 4 months in tail-cuff BP and anesthetized mean arterial pressure at 4 months were not different in NS/B(2)R(-/-) and NS/B(2)R(+/+) mice. However, there was a mild increase in BP in NS/B(2)R(-/-) at 2 months versus NS/B(2)R(+/+). In contrast, HS/B(2)R(-/-) mice manifested early onset and persistent elevations of tail-cuff BP (P<0.05) at 2, 3, and 4 months versus other groups. MAP was also higher in HS/B(2)R(-/-) than HS/B(2)R(+/+), NS/B(2)R(-/-), and NS/B(2)R(+/+) (91+/-3 versus 75+/-5, 74+/-2, and 70+/-2 mm Hg, respectively; P<0.05). Kidney renin and angiotensin type 1 receptor mRNA levels were not different. Additional studies showed that a delay in the initiation of HS until after birth was accompanied by later development of hypertension, although postnatal discontinuation of HS resulted in a gradual return of BP to normal values by 4 months of age. The results demonstrate that (1) kinins protect the developing animal from salt-sensitive hypertension, (2) lack of B(2)R from early development does not alter the maturation of BP under conditions of normal sodium intake, and (3) exposure to a HS diet during fetal life is not sufficient in itself to induce long-term hypertension in either wild-type or B(2)R null mice.

Intrarenal angiotensin II generation and renal effects of AT1 receptor blockade

The intrarenal renin-angiotensin system plays a critical role in the paracrine regulation of renal function and the pathophysiology of hypertension. Angiotensin II (AngII) is formed intrarenally from systemically delivered angiotensin I (AngI) and intrarenally formed AngI. Intrarenal AngII content, which is greater than can be explained by the circulating AngII concentrations, is compartmentalized such that proximal tubule concentrations of AngI and AngII greatly exceed plasma concentrations. Proximal tubule cells are thought to secrete AngII or precursors of AngII into the tubular fluid to activate luminal AngII receptors. Recent immunohistochemical studies have demonstrated an abundance of AT1 receptors on the luminal surface of proximal and distal tubule cells and on afferent and efferent arteriolar vascular smooth muscle cells and mesangial cells of glomeruli. Activation of luminal AT1 receptors stimulates tubular sodium reabsorption rate. To evaluate the direct effects of AT1 receptor blockade on renal function in AngII-dependent hypertension, experiments were performed on two-kidney, one-clip (2K1C) Goldblatt hypertensive rats. Although the nonclipped kidney is renin-depleted, the intrarenal AngII levels are not suppressed, and AngII concentrations in proximal tubular fluid remain high (10(-8) M). Candesartan was administered into the renal artery of nonclipped kidneys to avoid the confounding consequences of decreases in arterial pressure. Blockade of intrarenal AT1 receptors elicited significant increases in GFR, renal blood flow, sodium excretion, and fractional sodium excretion, suggesting synergistic actions on tubular transport and vascular smooth muscle cells.

Renal responses of the nonclipped kidney of two-kidney/one-clip Goldblatt hypertensive rats to type 1 angiotensin II receptor blockade with candesartan

Recent studies with normal rats indicated that systemic administration of the angiotensin II (AngII) type 1 (AT1) receptor blocker candesartan elicited divergent renal hemodynamic and excretory responses depending on the magnitude of associated decreases in mean arterial pressure. To evaluate the responses to candesartan in hypertensive rats, experiments were performed 25 d after unilateral renal arterial constriction with a 0.25-mm clip. The rats were anesthetized and prepared for acute clearance experiments. Control arterial pressure responses to a bolus AngII dose (50 ng) averaged 35+/-7 mmHg; the control decreases in cortical renal blood flow (RBF), measured with laser Doppler flowmetry, were 58+/-9%. The vasoconstrictor responses to AngII were abolished by candesartan doses of 1 and 0.1 mg/kg. Treatment with 0.01 mg/kg candesartan attenuated the arterial pressure responses but did not prevent the cortical RBF decreases. The highest dose of candesartan (1 mg/kg) elicited rapid reductions in arterial pressure (from 154+/-5 to 122+/-9 mmHg), leading to associated decreases in RBF (from 5.5+/-0.2 to 4.6+/-0.4 ml/min x g) and sodium excretion (from 0.4+/-0.1 to 0.2+/-0.1 microEq/min x g). The 0.1 mg/kg dose of candesartan led to gradual reductions in arterial pressure (from 155+/-5 to 140+/-5 mmHg), and there were significant increases in RBF (from 5.4+/-0.2 to 6.8+/-0.4 ml/min x g) and decreases in renal vascular resistance. However, this dose still decreased urine flow and sodium excretion. In contrast, when candesartan was administered at 0.01 mg/kg, a dose that did not significantly decrease arterial pressure, there were significant increases in RBF (26+/-11%) and urine flow (43+/-19%) and proportionately greater increases in sodium excretion (284+/-89%) and fractional sodium excretion (351+/-99%). These data demonstrate the divergent renal hemodynamic and sodium excretory responses to AT1 receptor blockade in hypertensive rats, depending on the magnitude of decreases in arterial pressure. The lower candesartan dose, which did not cause hypotension, elicited substantial increases in RBF and proportionally much greater increases in sodium excretion, revealing the direct renal vasodilation and natriuretic effects of AT1 receptor blockade.

Proximal tubular angiotensin II levels and renal functional responses to AT1 receptor blockade in nonclipped kidneys of Goldblatt hypertensive rats

-Previous studies have shown that whereas the nonclipped kidney in two-kidney, one clip (2K1C) rats undergoes marked depletion of renin content and renin mRNA, intrarenal angiotensin II (Ang II) levels are not suppressed; however, the distribution and functional consequences of intrarenal Ang II remain unclear. The present study was performed to assess the plasma, kidney, and proximal tubular fluid levels of Ang II and the renal responses to intrarenal Ang II blockade in the nonclipped kidneys of rats clipped for 3 weeks. The Ang II concentrations in proximal tubular fluid averaged 9.19+/-1.06 pmol/mL, whereas plasma Ang II levels averaged 483+/-55 fmol/mL and kidney Ang II content averaged 650+/-66 fmol/g. Thus, as found in kidneys from normal rats with normal renin levels, proximal tubular fluid concentrations of Ang II are in the nanomolar range. To avoid the confounding effects of decreases in mean arterial pressure (MAP), we administered the nonsurmountable AT1 receptor antagonist candesartan directly into the renal artery of nonclipped kidneys (n=10). The dose of candesartan (0.5 microg) did not significantly decrease MAP in 2K1C rats (152+/-3 versus 148+/-3 mm Hg), but effectively prevented the renal vasoconstriction elicited by an intra-arterial bolus of Ang II (2 ng). Candesartan elicited significant increases in glomerular filtration rate (GFR) (0.65+/-0. 06 to 0.83+/-0.11 mL. min-1. g-1) and renal blood flow (6.3+/-0.7 to 7.3+/-0.9 mL. min-1. g-1), and proportionately greater increases in absolute sodium excretion (0.23+/-0.07 to 1.13+/-0.34 micromol. min-1. g-1) and fractional sodium excretion (0.38+/-0.1% to 1.22+/-0. 35%) in 2K1C hypertensive rats. These results show that proximal tubular fluid concentrations of Ang II are in the nanomolar range and are much higher than can be explained on the basis of plasma levels. Further, the data show that the intratubular levels of Ang II in the nonclipped kidneys of 2K1C rats remain at levels found in kidneys with normal renin content and could be exerting effects to suppress renal hemodynamic and glomerular function and to enhance tubular reabsorption rate.

Concentrations and actions of intraluminal angiotensin II

Although the presence of angiotensin II (AngII) receptors on the luminal membranes of proximal tubule cells has been recognized for many years, recent immunohistochemical studies using polyclonal and monoclonal antibodies to the AngII type 1 (AT1) receptor have demonstrated an abundance of the AT1 receptor not only on the luminal surface of proximal tubule cells but also on the luminal surfaces of distal nephron segments. An important role for these receptors in the regulation of tubular transport mechanisms was indicated by the recent findings of remarkably high proximal intratubular concentrations of AngII (in the range of 10(-9) to 10(-8) M). The high intratubular concentrations of AngII, as well as angiotensin I and angiotensinogen, are much greater than can be explained on the basis of delivery via glomerular filtration. When coupled with the findings demonstrating the presence of angiotensinogen and angiotensinogen mRNA in proximal tubule cells, the data indicate that AngII or precursors of AngII are secreted directly into the proximal tubule lumen by the epithelial cells. Although the mechanisms responsible for the regulation of intratubular AngII concentrations remain to be determined, micropuncture studies have provided direct evidence that activation of intraluminal AT1 receptors by AngII exerts a substantial stimulatory influence on sodium and bicarbonate transport by both proximal and distal tubules. Collectively, these data provide support for the hypothesis that activation of luminal AT1 receptors by AngII present in the tubular fluid contributes importantly to regulation of the tubular reabsorption rate.

Effects of acute AT1 receptor blockade by candesartan on arterial pressure and renal function in rats

Experiments were performed on normal anesthetized rats to determine the effects of candesartan, a novel AT1 receptor antagonist, on the arterial pressure and renal hemodynamic responses to bolus doses of angiotensin II (ANG II) and on renal hemodynamics and sodium excretion. Control arterial pressure responses to bolus ANG II doses of 10, 50, 100 and 1,000 ng were 26 +/- 6, 54 +/- 7, 57 +/- 7, and 79 +/- 7 mmHg; the decreases in cortical renal blood flow (CRBF), measured with laser-Doppler flowmetry, were 47 +/- 9, 64 +/- 8, 71 +/- 6, and 82 +/- 6%. The vasoconstrictor responses to ANG II up to 1,000 ng were completely blocked by candesartan doses of 1 and 0.1 mg/kg, whereas treatment with 0.01 mg/kg candesartan attenuated the arterial pressure and CRBF responses. The higher doses of candesartan (1 and 0.1 mg/kg) elicited rapid decreases in arterial pressure, leading to associated decreases in sodium excretion. Renal blood flow (RBF), glomerular filtration rate (GFR), and urine flow also decreased following treatment with candesartan at 1 mg/kg. In contrast, when candesartan was given at 0.01 mg/kg, which did not decrease arterial pressure significantly, there were significant increases in GFR (16 +/- 4), RBF (9 +/- 2), urine flow (11 +/- 2), sodium excretion (35 +/- 7), and fractional sodium excretion (39 +/- 8%). The inability to overcome blockade, even with very high ANG II doses, indicates that candesartan is a potent noncompetitive blocker of ANG II pressor and renal vasoconstrictor effects. The lower candesartan dose that did not cause significant hypotension elicited substantial increases in RBF, GFR, and sodium excretion, revealing the direct renal vasodilator and natriuretic effects of AT1 receptor blockade.

Losartan protects the rat kidney from ischemic injury

Administration of losartan (L), an angiotensin II receptor antagonist, at a daily dose of 3 mg/kg body wt, lowered systolic blood pressure (SBP) in both the Prague hypertensive rat and the Prague normotensive rat (PNR). Proteinuria was markedly reduced in both strains by L. Seven days after kidney ischemia due to bilateral clamping of both renal arteries for 45 minutes, the renal function (endogenous creatinine clearance, sodium, potassium, and urea excretion rates) was completely normal in L-treated PHR and PNR, whereas distinct deterioration was observed in untreated animals. The survival rate after kidney ischemia was significantly improved by L in both PHR and PNR. Thus, L had a significant blood pressure-lowering action in both strains and exerted a distinct renal protective effect from kidney ischemia.

[Comparison of the effects of a low protein diet and angiotensin converting enzyme inhibitors on renal insufficiency in hypertensive rats]

BACKGROUND

It is known that hypertension to aggravate the course of chronic renal insufficiency (CRI). It is too know the beneficial effect of the angiotensin-converting enzyme inhibitors (ACEI) and the low-protein diet. In this study, the effect of a low protein diet on the course of CRI was compared with that of administration of enalapril (ENA), an ACEI.

METHODS AND RESULTS

A new model of genetic hypertension, the Prague Hypertensive Rat (PHR) was used. In rats just after weaning, 5/6 of renal parenchyma were removed surgically (5/6NX). The rats were observed for 8 weeks after 5/6NX. The animals were fed either a normal rat chow containing 23% of protein, or a low-protein diet containing only 6% protein. Control groups drank tap water, experimental groups received water containing ENA at a dose of 5 mg/kg BW. The rats on normal diet drinking water had the highest levels of blood pressure (200 +/- 4.3 mm Hg), proteinuria (56.2 +/- 14.6 mg/24 hours) and heaviest kidney remnants i.e. highest compensatory hypertrophy (2352 +/- 239.4 mg). Both ENA and low-protein diet significantly improved these functions to the same extent. However, a combination of low-protein diet with ENA had no further beneficial effect as against any of these manoeuvres alone.

CONCLUSIONS

We assume every manoeuvre (low-protein diet and enalapril) exerts a maximal beneficial effect per se: the mechanism of this effect is highly speculative: inhibition of growth factors seems to be the most logical explanation. ACEIs are known to inhibit the production of angiotensin II, low-protein diet should inhibit transforming growth factor beta.

[The effect of electrostimulation with the Rebox apparatus on ischemic renal injury in rats]

BACKGROUND

With developing transplantation programmes the problem of protection against ischaemic renal damage had become important. The results of experimental pharmacological protection of the kidneys are not quite conclusive. The objective of the presented paper was to assess the effect of electrostimulation by means of a Rebox apparatus (generator of direct rectangular impulses at a frequency of 1 to 10 kHz), on the development of ischaemic damage of the renal parenchyma induced experimentally in rats.

METHODS AND RESULTS

The experiments were made on Wistar strains rats (n = 15) which were subjected to dextrolateral nephrectomy and the left renal artery was closed by a clamp which was released in the tested and the control group after 30 minutes. In the rebox group electrostimulation with the Rebox apparatus was implemented immediately after release of the clamp. In rats which were in metabolic cages the following parameters were assessed: diuresis, period of survival, endogenous creatinine clearance, plasma creatinine level, urea level and excretion, as well as sodium and potassium urinary excretion. No significant difference in the survival time of the rats was found nor in the plasma levels of creatinine, urea and urinary excretion of potassium and urea between the control and the Rebox group. In the Rebox group, as compared with the control group, a significantly higher diuresis was found 22.8 vs 5.6 (p < 0.001) and natriuresis 0.44 vs 0.11 (p < 0.01).

CONCLUSIONS

Electrostimulation by rebox currents in rats increases significantly the diuresis and natriuresis of the solitary kidney exposed to 30-minute ischaemia but has no impact on other parameters. The mechanism of action is not quite clear, apparently the reabsorption of sodium in the proximal tubule is inhibited.

Comparison of the effects of a low-protein diet with the effects of a converting enzyme inhibitor on the progression of renal insufficiency in hypertensive rats

The beneficial effects of a low-protein diet vs. angiotensin-converting enzyme inhibitor (ACEI, enalapril) on the course of ablation nephropathy (5/6 nephrectomy, 5/6NX) were compared in a new strain of genetic hypertensive rats, the Prague hypertensive rat (PHR). Both maneuvers were followed by a significant drop in proteinuria (1.27 and 8.8 vs. 56.2 mg/24 hod, p < 0.001, low-protein diet vs. ACEI vs. untreated), plasma levels of creatinine (175.3 and 177.1 vs. 245.3 mumol/L, p < 0.001) and urea (7.95 and 13.51 vs. 37.6 mmol/L, p < 0.001). Endogenous creatinine clearance was higher after both low-protein diet and ACEI than without them (134.6 and 127.8 vs. 56.7 microL/min/100 g BW, p < 0.001). Both maneuvers had a similar beneficial effect: no additional amelioration was observed with a combination of both low-protein diet and ACEI. Compared to normotensive Wistar rats, the results were quite similar in PHR except the blood pressure values; hypertension had no substantial effect on the course of 5/6NX or on the beneficial action of both low-protein diet and ACEI.

Lack of a beneficial effect of PD123319, an AT2-angiotensin receptor antagonist, on the course of ablation nephropathy in the rat

Since angiotensin II (ANGII) AT1-receptor antagonists have been shown to possess a beneficial effect on the course of ablation nephropathy, and since the possibility that AT2-receptors are also involved could not be ruled out, the effect of the AT1 antagonist, losartan (L), on the course of ablation nephropathy was compared wit that of PD123319 (PD), an AT2 antagonist. Wistar rats underwent surgical ablation of 5/6 of their renal parenchyma (5/6NX) and for the next 8 weeks were treated with either L alone (5 mg/kg/day), or with L + PD (10 mg/kg/day) or with PD alone. The drugs were administered in drinking water and rats drinking pure water served as controls. Whereas in both groups drinking L the survival rate was 100%, it was only 60% in controls and 66.6% in PD (no significant difference). The rats drinking L have a lower blood pressure, proteinuria and glomerulosclerosis score, and higher creatinine clearance than control and PD rats, again with no difference between these two. Cardiac and kidney remnant hypertrophy was completely abolished in both L groups, whereas it was distinctly present in the other 2 groups without a difference between them. Plasma renin activity was elevated only in both L groups. In conclusion, the beneficial effect of the AT1-receptor blocker L was again confirmed. AT2 receptors are obviously not involved in the detrimental effect of ANGII on the course of ablation nephropathy.

[Ineffectiveness of ACE inhibitors (enalapril) on glomerular damage in rats after a 5/6 nephrectomy and a high-salt diet]

Wistar rats with surgically removed 5/6 of renal parenchyma were fed either standard (0.35% salt content) or a high-salt (2%) diet. Half of the animals of each group drunk plain water while the other half was provided water enriched with the angiotensin-converting enzyme inhibitor enalapril (ENA) at a dose of 5 mg/kg/day. In rats receiving standard diet, ENA had a significant inhibitory effect on the consequences of ablation: the rats had normal blood pressure, low proteinuria, and high endogenous creatinine clearance compared to water-drinking controls. The high-salt diet significantly enhanced the sequelae of ablation: a high blood pressure and proteinuria, low clearance, which ENA was unable to prevent in these animals. No plausible explanation for the absence of ENA's beneficial effect is available: one can speculate that, under conditions of high-salt intake, the activity of the renin-angiotensin system is suppressed leaving no place for ENA to exert its effect. We also believe that the highly adverse effect of a high-salt diet in chronic renal failure is due to growth factors other than angiotensin II.

[The effect of Tenziomin on function, morphology and lectin binding in rat kidney remnants after experimental subtotal nephrectomy]

Captopril (Tenziomin) treated rats after subtotal (5/6) nephrectomy showed conspicuously better function of kidney tissue remnants than untreated animals. Histology was the same in both groups--focal glomerulosclerosis, anisocytosis and anisokaryosis of tubular epithelial cells, hyperplasia of proximal tubuli. Proteinuria was substantially lower in treated animals. Lectin histochemistry showed differences between superficial and juxtamedullary nephrons in glycoprotein contents and function. An important finding was selective binding of WGA lectin in brush border of proximal convoluted tubuli of juxtamedullary nephrons. Differences in lectin binding between nephrectomized and intact control animals were rather quantitative than qualitative.

A comparison of the effect of feeding a low-protein diet and of pharmacological intervention on the course of ablation nephropathy in the rat

In Wistar rats just after weaning, 5/6 of renal parenchyma were removed surgically. Thereafter, the rats were fed either a "high-protein" (21%) or two types of a "low-protein" (6%) diet; in one of the latter the lack of protein was substituted by saccharide, in the other by fat, making the substitution "isocaloric" in either case. In all three diet groups, subgroups were formed drinking either tap water or water containing either the ACE inhibitor enalapril (Ena) or the calcium antagonist diltiazem (Dil), or both (Ena + Dil). In the high-protein diet group, increases in the weight of kidney remnants, in proteinuria and in systolic blood pressure (SBP) were seen. This was prevented by feeding either type of the low-protein diet but also by Ena and Ena + Dil. Ena and Ena + Dil not only prevented the increase in SBP but actually lowered it significantly. Dil alone also had a SBP-lowering action but offered no protection from kidney hypertrophy and proteinuria. No additive protective action of Ena + Dil or Ena + low protein or Ena + Dil + low protein was seen, suggesting that a bottom limit of these protective action was reached by the low-protein diet alone. There was no substantial difference between either type of the low-protein diet except a small and transient decrease in body weight in the first week of fat-rich diet administration.

[The effect of a low-protein diet and certain pharmaceutical agents on the course of ablation nephropathy in rats]

BACKGROUND

The beneficial effect of a low-protein diet on the course of renal failure after ablation nephropathy in the rat is known; also calcium channel antagonists (CaA) and angiotensin I converting enzyme inhibitors (ACEI) have a protective effect. Because even simple energy restriction retards the development of spontaneous or ablation-induced glomerulosclerosis the authors decided to replace the lacking dietary protein in the low protein diet by starch (disaccharide) and by fat (cereal oil) and compare these two low-protein diets as to their effect on the development of chronic renal failure (CRI) caused by surgical removal of 5/6 of renal parenchyma (5/6 NX).

METHODS AND RESULTS

In Wistar rats just after weaning, 5/6 of renal parenchyma were removed surgically. Thereafter, the rats were fed either a "high-protein" (21%) or two types of a "low-protein" (6%) diet, in one of the latter, the lack of protein was substituted by saccharide, in the other by fat making the substitution "isocaloric" in either case. In all three diet groups, subgroups drinking either tap water or water containing either the ACE-inhibitor enalapril (ena) or the calcium antagonist diltiazem (dil) or both (ena+dil) were formed. On the high-protein diet, an increase in the weight of kidney remnants, in proteinuria and in systolic blood pressure (SBP) was seen. This was prevented by feeding either type of the low-protein diet but also by ena and ena+dil. Ena and ena+dil not only prevented the increase in SBP but actually lowered it significantly. Dil alone also had a SBP-lowering action but offered no protection from kidney hypertrophy and it significantly. Dil alone also had a SBP-lowering action but offered no protection from kidney hypertrophy and proteinuria. No additive protective action of ena+dil or ena+low-protein or ena+dil+low-protein was seen suggesting that the lower limit of these protective actions was reached by the low-protein diet alone. There was no substantial difference between either type of low-protein diet except a small and transient decrease in body weight in the first week on a fat-rich diet.

CONCLUSIONS

In the described experiments and with the set-up used the low-protein diet had no effect on the plasma creatinine and urea levels nor on creatinine clearance. The weight of the kidney remnants and proteinuria were significantly higher in animals on a high-protein diet who drank water or water with diltiazem. These changes were suppressed by administration of angiotensin converting enzyme inhibitors either alone or combined with diltiazem. A low- protein diet (both types tested) as well as angiotensin converting enzyme inhibitors improve the course of chronic renal failure in ablation nephropathy in the rat; the authors did not prove an additive effect of the combination of this diet with angiotensin converting enzyme inhibitors.