Adrenomedullin and its receptor complexes in remnant kidneys of rats with renal mass ablation: decreased expression of calcitonin receptor-like receptor and receptor-activity modifying protein-3

Adrenomedullin (AM) has vasodilator and diuretic actions, similarly to natriuretic peptides. AM receptor complexes are composed of calcitonin receptor-like receptor (CRLR) and receptor-activity modifying protein-2 (RAMP2), or CRLR and RAMP3. We aimed to know whether gene expression of AM and AM receptor complexes are regulated in kidneys under pathophysiological conditions. Expression of AM, RAMP2, RAMP3 and CRLR mRNA was studied in the remnant kidney of rats with renal mass ablation using competitive quantitative RT-PCR techniques. Partial cloning was performed to determine the rat RAMP3 nucleotide sequence. In normal rat kidneys, expression levels of RAMP2, RAMP3, CRLR and AM mRNAs were 26.5 +/- 1.9 mmol/mole of GAPDH, 7.7 +/- 0.9 mmol/mole of GAPDH, 3.6 +/- 0.2 mmol/mole of GAPDH and 0.57 +/- 0.03 mmol/mole of GAPDH (mean +/- SE, n = 6), respectively. RAMP3 mRNA levels decreased significantly to about 50% and about 70% of control (sham-operated rats) 4 days and 14 days after 5/6 nephrectomy, respectively. CRLR mRNA levels also decreased significantly to about 30% and about 43% of control. Sodium intake restriction had no significant effects on the RAMP3 and CRLR gene expression. On the other hand, RAMP2 mRNA expression in the kidney was suppressed by sodium intake restriction regardless of nephrectomy, while RAMP2 levels in the remnant kidney were not significantly changed by 5/6 nephrectomy. Neither 5/6 nephrectomy or sodium intake restriction had any significant effects on the AM gene expression in the kidney. The present study showed that expression of mRNAs encoding AM, RAMP2, RAMP3 and CRLR were differentially regulated in remnant kidneys of rats with renal mass ablation.

Mechanisms underlying renoprotection during renin-angiotensin system blockade

Potential determinants of chronic renal disease (CRD) progression were studied in male Munich-Wistar rats subjected to 5/6 nephrectomy and treated with candesartan (Csn; n = 30) or enalapril (Ena; n = 27) from 5 wk postsurgery. Despite control of systolic blood pressure (SBP; 24 wk: Csn = 143 +/- 9; Ena = 148 +/- 8 mmHg), urinary protein excretion rates (U(pr)V) increased over 24 wk (Csn = 92 +/- 10; Ena = 99 +/- 8mg/day). Glomerulosclerosis scores (GS) at 24 wk were similar for Csn (42 +/- 7%) vs. Ena (42 +/- 4%), values close to those of untreated controls at 12 wk (43 +/- 4%). At 24 wk, SBP and UprV correlated strongly with GS, together accounting for 72% of the variance in GS. Renal cortex mRNA levels (determined by competitive RT-PCR) for transforming growth factor (TGF)-beta1 and monocyte chemoattractant protein (MCP)-1 were elevated in Csn and Ena at 12 wk and remained higher at 24 wk vs. sham. Strong correlations were evident among TGF-beta1, MCP-1, and interleukin-1beta and renal injury at 24 wk. Cns and Ena are thus equally effective renoprotective agents in this model. During renin-angiotensin system inhibition, renoprotection is dependent on control of both SBP and UprV. Incomplete suppression of renal cytokine gene expression may also contribute to CRD progression.

Increased gene expression of adrenomedullin and adrenomedullin-receptor complexes, receptor-activity modifying protein (RAMP)2 and calcitonin-receptor-like receptor (CRLR) in the hearts of rats with congestive heart failure

Adrenomedullin is a vasodilator peptide produced in various organs, including heart and kidney. A novel adrenomedullin receptor complex has recently been identified, namely the calcitonin receptor-like receptor (CRLR) and receptor-activity modifying protein (RAMP) 2. In the present study, we have examined gene expression of RAMP2, CRLR and adrenomedullin in hearts and kidneys of rats with congestive heart failure caused by coronary artery ligation. Partial cloning was performed to determine the rat RAMP2 nucleotide sequence. Messenger RNA levels were then determined using competitive, quantitative reverse transcription-PCR techniques. Significantly increased expression levels (means+/-S.E.) of RAMP2, CRLR and adrenomedullin mRNA were found in the atrium (1.8+/-0.2-fold, 1. 8+/-0.2-fold and 2.1+/-0.1-fold, respectively, compared with sham operated rats) and in the ventricle (1.4+/-0.1-fold, 1.3+/-0.03-fold and 3.0+/-0.5-fold respectively). On the other hand, expression levels of RAMP2, CRLR and adrenomedullin mRNAs were not significantly changed in the kidney. These findings suggest potential roles of locally-produced and locally-acting adrenomedullin in the failing heart.

Cellular and molecular mediators in common pathway mechanisms of chronic renal disease progression

Injury mechanisms activated by the hemodynamic adaptations to nephron loss are considered to represent a final common pathway that underlies the progressive nature of chronic renal disease. In this article, we review experimental evidence that the induction of cell adhesion molecule, cytokine and profibrotic growth factor gene expression and the resultant renal infiltration by inflammatory cells, especially macrophages, are important components of these common pathway mechanisms. Interventions aimed at inhibiting these mechanisms may offer new treatments for slowing or arresting the progression of chronic renal disease.

IHG-2, a mesangial cell gene induced by high glucose, is human gremlin. Regulation by extracellular glucose concentration, cyclic mechanical strain, and transforming growth factor-beta1

We used cloning in silico coupled with polymerase chain reaction to demonstrate that IHG-2 is part of the 3'-untranslated region of gremlin, a member of the DAN family of secreted proteins that antagonize the bioactivities of members of the transforming growth factor (TGF)-beta superfamily. Mesangial cell gremlin mRNA levels were induced by high glucose, cyclic mechanical strain, and TGF-beta1 in vitro, and gremlin mRNA levels were elevated in the renal cortex of rats with streptozotocin-induced diabetic nephropathy in vivo. gremlin expression was observed in parallel with induction of bone morphogenetic protein-2 (BMP-2), a target for gremlin in models of cell differentiation. Together these data indicate that (a) IHG-2 is gremlin, (b) gremlin is expressed in diabetic nephropathy in vivo, (c) both glycemic and mechanical strain stimulate mesangial cell gremlin expression in vitro, (d) high glucose induces gremlin, in part, through TGFbeta-mediated pathways, and (e) Gremlin is a potential endogenous antagonist of BMPs within a diabetic glomerular milieu.

Long-term regulation of urea transporter expression by vasopressin in Brattleboro rats

Regulation of urea concentration in the renal medullary interstitium is important for maintenance of hypertonicity and therefore the osmotic driving force for water reabsorption. Studies in Sprague-Dawley rats showed that restriction of water intake for 3 days results in upregulation of urea transporter (UT) mRNA in the inner stripe of outer medulla of the kidney (2.9-kb UT2) but not in the inner medulla (4.0-kb UT1). The present study was performed to investigate the role of vasopressin in long-term regulation of UT1 and UT2 in neurogenic diabetes insipidus (Brattleboro) rats treated with a 7-day continuous infusion of [Arg(8)]-vasopressin (AVP), [deamino-Cys(1), D-Arg(8)]-vasopressin (dDAVP) or vehicle. Northern analysis showed that water restriction alone had no effect on the level of UT2 mRNA in vehicle-treated Brattleboro rats but UT2 mRNA markedly increased and UT1 mRNA modestly decreased after treatment with dDAVP. In situ hybridization further demonstrated that the UT2 signal is upregulated and spread along the descending thin limbs of loops of Henle and that UT1 signal is downregulated in the inner medullary collecting ducts in vasopressin-treated rats, with a greater response for dDAVP compared with the AVP-treated group. Immunocytochemistry studies revealed that the UT1 and UT2 proteins are also modified in the same pattern as the transcript changes. Our studies reveal the role of vasopressin in long-term regulation of UT1 and UT2 expression during water restriction.

Activation of inflammatory mediators in rat renal isografts by donor brain death

BACKGROUND

Brain death (BD) has been thought to influence the early course of transplanted organs by triggering a series of nonspecific inflammatory events that in turn may increase the kinetics and intensity of the immunological host responses. In this study early nonspecific, cellular, and molecular changes occurring in kidney isografts from BD donors are compared with those from normal anesthetized, ventilated controls.

METHODS

After induction of brain death, the animals were mechanically ventilated for 6 hr before organ removal. Only rats with stable blood pressure (mean arterial pressure >80 mmHg) were included. Serum creatinines were measured daily. Representative grafts were harvested 6 hr after brain death and between 1 hr and 5 days after engraftment for morphology, immunohistology, and reverse transcriptase-polymerase chain reaction. The presence of serum cytokines was assessed by enzyme linked immunoabsorbant assay.

RESULTS

Serum creatinine levels rose slightly in recipients from BD donors. Serum interleukin-1beta levels increased within 6 hr versus controls (P<0.05). mRNA levels of interleukin-1beta and macrophage inhibitory protein-1 in the kidneys were up-regulated transiently before engraftment (6 hr after BD) and 1 hr after revascularization (P<0.05). By immunohistology, numbers of infiltrating polymorphonuclear leukocytes peaked at 24 hr in parallel with intragraft induction of P- and E-selectin, complement, and other proinflammatory chemokines and cytokines. At 5 days, the isografts from BD donors were highly infiltrated by host leukocyte populations associated with intense up-regulation of their products. In contrast, those from control donors remained relatively normal through this initial follow-up period.

CONCLUSIONS

The intense nonimmune inflammation produced in isografts after donor BD may represent the initial stages of a continuum between an initial nonspecific and later immune reactivity, when placed in the context of allotransplantation.

Angiotensin receptor blockers in chronic renal disease: the promise of a bright clinical future

Pharmacologic interruption of the renin-angiotensin system (RAS) with angiotensin-converting enzyme inhibitors (ACEI) is considered a standard therapeutic intervention for patients with chronic renal disease, regardless of whether systemic hypertension is present. The advent of orally active angiotensin receptor blockers (ARB) increases the number of therapeutic options for inhibiting the RAS in patients with chronic renal diseases. Clinical studies of ARB that can be compared with large-scale ACEI clinical trials have yet to be completed. More than a dozen experimental studies comparing ARB with ACEI suggest that the two classes of drugs share similar renoprotective properties. Like ACEI, ARB are effective antihypertensive and antiproteinuric agents, which greatly reduce glomerular and tubulointerstitial scarring. Although both reduce stimulation of the AT1 receptor, ARB lack the kinin-potentiating effects of ACEI. ARB may exert antifibrotic actions via the AT2 receptor, through increased levels of angiotensin II resulting from AT1 receptor blockade. Despite these pharmacologic distinctions, recent studies have not detected differences in renoprotection between ARB and ACEI. In the context of RAS inhibition, the magnitude of antihypertensive and antiproteinuric effects achieved appears to be the major determinant of renoprotection, not the class of drug used. Thus, experimental data suggest that ARB will fulfill their promise as effective agents to be used as mainstays in multifaceted clinical strategies designed to slow or arrest the progression of chronic renal disease. Confirmation of this view awaits the results of clinical trials.

Renal function in high-output heart failure in rats: role of endogenous natriuretic peptides

The physiologic and pathophysiologic importance of natriuretic peptides (NP) has been imperfectly defined. The diminished renal responses to exogenous atrial NP in heart failure have led to the perception that the endogenous NP system might be less effective and thus contribute to renal sodium retention in heart failure. This study tests the hypothesis that in experimental heart failure, the renal responses to an acute volume load are still dependent on the NP system. The specific antagonist HS-142-1 was used to block the effects of NP in a model of high-output heart failure induced by an aortocaval shunt. Plasma cGMP levels and renal cGMP excretion were significantly lower in shunted and sham-operated rats receiving HS-142-1, compared with vehicle-treated controls, indicating effective blockade of guanylate cyclase-coupled receptors. Baseline sodium excretion and urine flow rate were lower in HS-142-1-treated sham-operated rats (15.2+/-1.1 microl/min versus 27.5+/-3.1 microl/min with vehicle, P < 0.001) and in HS-142-1-treated shunted rats (8.1+/-1.3 microl/min versus 19.9+/-2.3 microl/min with vehicle, P < 0.001). After an acute volume load, the diuretic and natriuretic responses were attenuated by HS-142-1 in control and shunted rats. The renal responses were reduced by HS-142-1 to a significantly greater extent in shunted rats than in control rats. HS-142-1 did not induce any significant systemic hemodynamic changes in either group, nor did it alter renal blood flow. However, the GFR in HS-142-1-treated shunted rats was lower than that in vehicle-treated shunted rats, both at baseline (0.6+/-0.3 ml/min versus 2.1+/-0.4 ml/min with vehicle, P < 0.05) and after an acute volume load (1.2+/-0.4 ml/min versus 2.6+/-0.4 ml/min with vehicle, P = 0.01), whereas no such effect was observed in control rats. These data indicate that the maintenance of basal renal function and the responses to acute volume loading are dependent on the NP system. The NP seem to be of particular importance for the maintenance of GFR in this model of experimental heart failure. These observations provide new insights into the importance of the renal NP system in heart failure.

Suppression subtractive hybridization identifies high glucose levels as a stimulus for expression of connective tissue growth factor and other genes in human mesangial cells

Accumulation of mesangial matrix is a pivotal event in the pathophysiology of diabetic nephropathy. The molecular triggers for matrix production are still being defined. Here, suppression subtractive hybridization identified 15 genes differentially induced when primary human mesangial cells are exposed to high glucose (30 mM versus 5 mM) in vitro. These genes included (a) known regulators of mesangial cell activation in diabetic nephropathy (fibronectin, caldesmon, thrombospondin, and plasminogen activator inhibitor-1), (b) novel genes, and (c) known genes whose induction by high glucose has not been reported. Prominent among the latter were genes encoding cytoskeleton-associated proteins and connective tissue growth factor (CTGF), a modulator of fibroblast matrix production. In parallel experiments, elevated CTGF mRNA levels were demonstrated in glomeruli of rats with streptozotocin-induced diabetic nephropathy. Mannitol provoked less mesangial cell CTGF expression in vitro than high glucose, excluding hyperosmolality as the key stimulus. The addition of recombinant CTGF to cultured mesangial cells enhanced expression of extracellular matrix proteins. High glucose stimulated expression of transforming growth factor beta1 (TGF-beta1), and addition of TGF-beta1 to mesangial cells triggered CTGF expression. CTGF expression induced by high glucose was partially suppressed by anti-TGF-beta1 antibody and by the protein kinase C inhibitor GF 109203X. Together, these data suggest that 1) high glucose stimulates mesangial CTGF expression by TGFbeta1-dependent and protein kinase C dependent pathways, and 2) CTGF may be a mediator of TGFbeta1-driven matrix production within a diabetic milieu.

Upregulation of atrial natriuretic peptide gene expression in remnant kidney of rats with reduced renal mass

Atrial natriuretic peptide (ANP) is synthesized in the kidney but its physiologic significance there is unclear. To determine whether renal expression of the ANP gene is regulated, renal ANP mRNA expression was assessed in remnant kidneys after 5/6 nephrectomy in Munich-Wistar rats. In normal sodium intake groups, ANP mRNA expression in the remnant kidney was significantly increased by 5.0 +/- 0.8-fold (n = 7, mean +/- SEM) at 4 d when compared with sham-operated controls (n = 6, all sham-operated groups) (*P < 0.001 by Scheffe's test) and by 28.3 +/- 5.1-fold at 14 d. This latter response was markedly diminished to 7.6 +/- 2.1-fold (n = 7, versus sham) in rats maintained on a low sodium diet. At 4 d, on the other hand, no significant downregulation was observed with dietary sodium restriction. Because natriuretic peptides have previously been shown by us to play a major role in the adaptive responses of remnant nephrons to renal mass ablation, these data suggest that ANP of renal origin may contribute to the overall mechanism for enhancing sodium excretion in the face of declining nephron number.

Effects of explosive brain death on cytokine activation of peripheral organs in the rat

BACKGROUND

The success rate of transplanted organs from brain-dead cadaver donors is consistently inferior to that of living sources. As cadaver and living unrelated donors are equally genetically disparate with a given recipient, the difference must lie within the donor himself and/or the effects of organ preservation and storage. We have hypothesized that irreversible central nervous system injury may up-regulate proinflammatory mediators and cell surface molecules in peripheral organs to be engrafted, making them more prone to host inflammatory and immunological responses.

METHODS

Rats undergoing surgically induced acutely increased intracranial pressure (explosive brain death) were followed for 6 hr. Their peripheral tissues were examined by reverse transcriptase polymerase chain reaction and immunohistology, serum factors were assessed by enzyme-linked immunosorbent assay, and the influence of inflammatory molecules in the blood stream was determined by cross-circulation experiments with normal animals.

RESULTS

mRNA expression of both lymphocyte- and macrophage-associated products increased dramatically in all tissues. Similar factors in serum were coincidentally increased; these were shown to be active in vivo by cross-circulation with normal animals. The organs of all control groups, including animals with important ischemic injury and with hemorrhagic shock, were negative. Up-regulation of MHC class I and II antigens and the co-stimulatory molecule B7 suggests increased immunogenicity of the peripheral organs. These changes could be inhibited by: (i) administration of a recombinant soluble P-selectin glycoprotein ligand-Ig, a P- and E-selectin antagonist; and (ii) a fusion protein, cytotoxic T lymphocyte antigen 4-Ig, which blocks B7-mediated T-cell co-stimulation.

CONCLUSIONS

Activation of peripheral organs following explosive brain death may be caused by various interrelated events, including the effects of massive acute central injury, hypotension, and circulating factors. Almost complete suppression of these changes could be produced by biological agents. Such interventions, if reproducible in humans, could improve the quality of organs from "marginal" donors, broadening the criteria for donor acceptance.

Apoptosis of endothelial cells is associated with paracrine induction of adhesion molecules: evidence for an interleukin-1beta-dependent paracrine loop

Monocytic infiltration of the vessel wall is a hallmark of injury in a variety of vascular diseases. In the present study, we explored the relationship between endothelial apoptosis and hyperadhesiveness for monocytic cells. Apoptosis of human umbilical vein endothelial cells (HUVECs) was induced by either growth factor deprivation (GFD) for 24 hours or by incubation with mitomycin C (MMC) at 0.01 mg/ml for 24 hours and confirmed by light microscopy and DNA laddering. In parallel assessments of cell-cell adhesion, GFD and MMC induced hyperadhesiveness of HUVECs for the THP-1 monocytic cell line. Hyperadhesiveness developed in association with induction of intercellular adhesion molecule (ICAM)-1 and vascular cell adhesion molecule (VCAM)-1 on HUVECs and was attenuated by monoclonal antibodies directed against these ligands. Culture medium conditioned by apoptotic HUVECs up-regulated the expression of adhesion molecules on normal HUVECs, suggesting that paracrine factors in the apoptotic milieu led to induction of adhesion molecules. Interleukin (IL)-1beta was implicated as a putative mediator in this setting because 1) exogenous IL-1beta up-regulates ICAM-1 and VCAM-1 with kinetics similar to those noted during endothelial cell apoptosis, 2) endothelial apoptosis was associated with increased expression of IL-1beta converting enzyme, and 3) the adhesion-promoting actions of GFD and MMC were attenuated by an anti-IL-1beta antibody.

Effects of combination therapy with enalapril and losartan on the rate of progression of renal injury in rats with 5/6 renal mass ablation

Angiotensin-converting enzyme inhibitors (ACEI) and angiotensin II receptor antagonists (AT1RA) slow the rate of progression of experimental renal disease. Although the end result of both classes of drugs is to block the renin-angiotensin system (RAS), ACEI and AT1RA act at different sites in the RAS cascade. The aim of this study was to compare the effects of an ACEI (enalapril) and AT1RA (losartan), alone or in combination, in slowing the progression of experimental renal disease in a model of reduced renal mass. Two weeks after 5/6 renal ablation, rats were divided into five groups matched for body weight, systolic BP (SBP), and urinary protein excretion rate (UprotV). The effects on SBP and UprotV of treatment with 25 and 40 mg/L enalapril (groups I and II; both n = 7), 180 mg/L losartan (group III, n = 8), or a combination of enalapril (25 mg/L) + losartan (180 mg/L) (group IV, n = 9) versus vehicle (group V, n = 9) were studied for 12 wk. Remnant kidneys were then assessed histologically for evidence of focal and segmental glomerulosclerosis and hyalinosis (FSGS), and interstitial fibrosis. There were no significant differences (NSD) in body weight among the groups at any time. Combination therapy reduced SBP (122 +/- 8 mmHg) significantly at 12 wk to levels similar to losartan (127 +/- 3 mmHg) or enalapril (40 mg/L) alone (124 +/- 5 mmHg) (P < 0.05 versus vehicle controls). With equivalent antihypertensive effects, no differences in frequency of FSGS were discerned among the treatment groups (groups II through IV; F = 1.7, NSD). Tubulointerstitial injury scores followed a similar pattern. BP was highly correlated with the extent of FSGS, both among individual rats (r = 0.68, P = 0.05) and the group means (r = 0.99, P = 0.001). We conclude that the renoprotective effects of enalapril, losartan, or combination therapy are similar in this model over the 12 wk of the study, and are closely related to the magnitude of their antihypertensive effects.

Current strategies for retarding progression of renal disease

Physiological insights gained in the 1980s into mechanisms of disease progression in experimental chronic nephropathies established the basis for therapeutic interventions to retard the progression of chronic renal disease in humans. In the 1990s, several large-scale clinical trials have confirmed the renoprotective effects of angiotensin-converting enzyme inhibitors in diabetic and nondiabetic nephropathies. Other studies have afforded strong support for the efficacy of dietary protein restriction in certain settings and underscored the importance of blood pressure control in proteinuric individuals. These interventions form the core of current strategies designed to preserve kidney function in patients with chronic renal disease.

Angiotensin receptor antagonists in experimental models of chronic renal failure

The efficacy of angiotensin converting enzyme inhibitors (ACEI) in slowing the advancement of chronic renal disease attests to the importance of angiotensin II (Ang II) in the pathophysiological mechanisms underlying disease progression. It is apparent from studies of the effects of orally-active AT1 receptor antagonists (AT1RA) in experimental models of chronic progressive renal disease, that AT1RA have broadly similar effects to those of ACEI, implying that the favorable effects of ACEI on systemic and renal hemodynamics and indices of glomerular injury are mediated, in large part, by reducing the action of Ang II at AT1 receptors. The possibility remains, however, that differences in the modes of action of ACEI and AT1RA are significant in terms of renal protection and that the two classes of drugs are not therapeutically equivalent. Thus far, however, virtually all experimental studies comparing the renal protective effects of ACEI versus AT1RA have failed to show any convincing differences between the two classes of drug that cannot be attributed to discrepancies in the levels of blood pressure control achieved. As many rodent studies have adopted protocols originally designed to distinguish between the effects of treatment versus no treatment, however, it may be premature to conclude that ACEI and AT1RA are, essentially, therapeutically equivalent. Since both classes of drug have such potent renoprotective effects, the extent of injury that develops in treated rats may be so slight as to compromise the sensitivity of the experimental comparison. Fresh experimental approaches may be required to overcome this issue and resolve any outstanding questions concerning the therapeutic equivalence of AT1RA and ACEI in slowing the progression of renal disease.

Nephron mass as a risk factor for progression of renal disease

Partial ablation of renal mass initiates a cycle of progressive glomerular injury in the remnant. This process is associated with glomerular hypertrophy, hyperfiltration and systemic hypertension. Congenital deficits in nephron number are also associated with adverse effects on the kidney. Since intrauterine growth retardation is associated with formation of fewer nephrons, the recent observation that low birth weight is associated with increased risk of hypertension in later life raises the possibility that even modest reductions in nephron complement may also predispose to renal injury. Likewise, the numbers of viable nephrons supplied to renal, allograft recipients may be critical determinants of late allograft success or failure, since subsequent acute ischemia and rejection combine to lower the nephron complement to levels akin to the more extensive reductions in renal mass seen in patients with surgical reduction of a solitary kidney, in whom predisposition to hypertension and glomerulosclerosis is evident. This article summarizes recent findings suggesting that congenital nephron endowment is a significant factor in the pathogenesis of chronic renal disease and hypertension.

Candesartan cilexetil reduces chronic renal allograft injury in Fisher-->Lewis rats

OBJECTIVES

To determine the effects of the angiotensin II receptor antagonist, candesartan cilexetil, on glomerular and systemic blood pressures and the development of renal injury in Lewis rat recipients of a single Fisher kidney (F334--> LEW transplantation), an established rat model of chronic renal allograft failure.

DESIGN

Recent studies have shown that chronic injury of renal allografts in F334-->LEW rats may be virtually abrogated by supplying the Lewis recipients with two Fisher kidneys or, alternatively, by retaining a native kidney. These findings imply a major contribution from processes associated with nephron loss to the pathogenesis of chronic renal allograft failure, a notion supported by the observation that transplanting two kidneys also normalizes glomerular capillary pressure (PGC) in F344-->LEW rats. Thus, a pharmacological reduction in PGC, by blocking the effects of angiotensin II, should also lessen renal injury in F344-->LEW rats.

MATERIALS AND METHODS

Bilaterally nephrectomized F344--> LEW rats were treated with the angiotensin II receptor blocker candesartan cilexetil (TCV-116) at 40 mg/l or with vehicle, administered in drinking water. Proteinuria and systolic blood pressure were assessed monthly, and histological studies were carried out after 24 weeks. The glomerular filtration rate and glomerular pressures were determined after 10 weeks in additional rats by clearance and micropuncture studies.

RESULTS

Treatment with candesartan cilexetil lowered systemic blood pressure, normalized PGC at 10 weeks and greatly reduced proteinuria and allograft glomerulosclerosis at 24 weeks.

CONCLUSIONS

These data indicate that the development of renal injury in F344-->LEW renal allografts can be prevented by the pharmacological blockade of angiotensin II receptors using candesartan cilexetil. This suggests that angiotensin-dependent processes contribute significantly to chronic injury in this model of late renal allograft failure.

Cellular and molecular predictors of chronic renal dysfunction after initial ischemia/reperfusion injury of a single kidney

BACKGROUND

Initial ischemia/reperfusion injury occurring secondary to organ retrieval, storage, and transplantation has been associated with late renal allograft deterioration and failure. In addition, there is an apparent synergy, reported in several clinical series, between the initial injuries of ischemia/reperfusion and acute rejection; the long-term results of graft survival are significantly deceased after both events in combination as compared with either alone or if no such episodes occur.

METHODS

In the present study, we examined patterns of proteinuria, cellular infiltration, cytokine expression, and glomerulosclerosis over time in Lewis and Fischer 344 rats after 45 min of warm ischemia of a single kidney and with or without contralateral nephrectomy. Both early (4 hr to 7 days) and late (2-52 weeks) events were studied serially in the affected kidneys morphologically, by immunohistology and by reverse transcriptase polymerase chain reaction.

RESULTS

Intercellular adhesion molecule 1, endothelin, and major histocompatibility complex class II expression were up-regulated within 2 to 5 days after injury; T cells and macrophages increased transiently. Proteinuria developed after approximately 8 weeks only in animals bearing a single injured kidney, and not in those with a retained native organ. Progressive morphological changes occurred after 16 weeks, including glomerulosclerosis, arterial obliteration, and interstitial fibrosis. After a period of relative quiescence, expression of intercellular adhesion molecule 1 again increased in relation to progressive macrophage infiltration and their associated products, particularly, interleukin 1, tumor necrosis factor-alpha, transforming growth factor-beta, and inducible nitric oxide synthase. Monocyte chemotactic protein 1 was intensely up-regulated by 24 weeks, coincident with a dramatic rise in this infiltrating population. These changes remained virtually at baseline in animals with a retained native kidney.

CONCLUSIONS

These data imply that chronic injury after significant initial ischemia and reperfusion occurs when there is already a 50% renal mass reduction, but not when two kidneys remain in place. Permanent nephron loss resulting from such an insult could account for this phenomenon. Early ischemia and reperfusion, if severe enough in a single kidney, may be an important antigen-independent risk factor for later renal deterioration and failure. In the context of a renal allograft, it may contribute to chronic rejection.

Nephron mass modulates the hemodynamic, cellular, and molecular response of the rat renal allograft

Functioning nephron mass has recently been implicated as a risk factor for development of chronic "rejection" of kidney allografts. Reductions in nephron number below 50% may induce glomerular hypertension and hyperfiltration in surviving units, which in turn lead to graft injury. In the present study, which extends and amplifies our previous investigations, cellular and molecular characteristics of single allografts from F344 donors in bilaterally nephrectomized LEW recipients, our standard experimental model of chronic renal allograft dysfunction, were compared with allografts from recipients where total renal mass was reduced (by ligating branches of the graft renal artery) or restored to normal levels by transplanting or retaining a second kidney. Our findings in this study confirm that progressive proteinuria and structural injury in recipients of single allografts were accentuated in grafts with reduced mass but virtually absent in rats with increased kidney mass. A striking observation was that patterns of cell surface molecule expression, cellular infiltration, and expression of all T cell- and macrophage-associated products studied were all markedly modulated by changes in renal mass. Moreover, several molecules that are up-regulated before evidence of graft injury are down-regulated by providing increased renal mass. These data show that the quantity of functioning renal mass is not only an important independent determinant of the tempo and intensity of chronic renal allograft failure, but also a potent modulator of fundamental cellular and molecular components of a complex process. This phenomenon involves antigen-dependent and antigen-independent elements that ultimately result in chronic allograft failure.

Antigen-independent determinants of cadaveric kidney transplant failure

OBJECTIVE

To determine the association of various antigen-independent factors with long-term cadaveric kidney transplant failure.

DESIGN

Cohort analytic study.

SETTING

Kidney transplant centers (N=131) in the United States.

PATIENTS

A total of 31 515 patients who received cadaveric kidney transplants between October 1987 and December 1991. Patients with unknown or uninterpretable vital status or graft survival time (n=264 [0.8%]) were excluded.

MAIN OUTCOME MEASURE

Graft failure, estimated at 2 extremes, depending on whether the death of a patient with a functioning graft was censored ("censored graft failure") or not ("uncensored graft failure").

RESULTS

During the 62-month study period, 5883 patients required the reinstitution of dialysis because of graft failure, 2404 patients died with graft failure, and 2041 patients died with a functioning graft. The relative risks of censored and uncensored graft failure were significantly associated with donor age, sex, and race and recipient body surface area, after adjusting for recipient age, sex, race, diabetes, cold ischemia time, panel cross-reactivity, pretransplant blood transfusions, previous renal transplantation, functional status, and HLA antigen mismatch.

CONCLUSIONS

In cadaveric kidney transplantation, selected demographic and anthropometric factors are significantly related to long-term graft outcomes, even after adjusting for well-known antigen-dependent risk factors. These results support the hypothesis that the supply of viable donor nephrons and the physiologic demands of the transplant recipient are important determinants of long-term graft failure. Antigen-independent factors such as donor age should be incorporated into organ allocation algorithms to optimize equity and efficiency.

The angiotensin receptor antagonist, irbesartan, reduces renal injury in experimental chronic renal failure

The effects of chronic treatment with the specific AT1 angiotensin receptor antagonist, irbesartan, or the angiotensin converting enzyme inhibitor, enalapril, were assessed in uninephrectomized fawn-hooded hypertensive rats (FHH) and compared with vehicle treatment. Three days after uninephrectomy, irbesartan (240 mg/liter), enalapril (80 mg/liter) or vehicle were administered via the drinking water. Systolic blood pressure (SBP) and protein excretion rates (UprotV) were determined monthly. In rats receiving irbesartan (N = 7) and enalapril (N = 6) SBP (132 +/- 3 mm Hg and 133 +/- 6, respectively) was essentially normalized at 12 weeks when compared with vehicle (169 +/- 6 mm Hg (N = 6); all comparisons were P < 0.05 by ANOVA). Similarly, proteinuria was lower in irbesartan (44 +/- 12 mg/day) and enalapril (19 +/- 2) groups versus vehicle (123 +/- 10 mg/day). Treatment with both drugs was associated with marked reduction in glomerulosclerosis at 12 weeks (both < 5% vs. vehicle, 43 +/- 9%) without effect on glomerular volume. In identically prepared rats, glomerular capillary hydraulic pressure (PGC, estimated from stop-flow pressure, Psf) was lower in FHH receiving irbesartan (58 +/- 1 mm Hg, N = 6) or enalapril (54 +/- 2, N = 6) than in vehicle-treated rats, in whom PGC was greatly elevated (68 +/- 2 mm Hg; N = 7). Despite this, GFR and single nephron GFR were well maintained. These data support a critical role for AT1 receptor-mediated, angiotensin-dependent processes in the pathogenesis of hypertension in FHH, and further implicate elevated PGC as a major determinant of glomerular injury in this model.

Congenital oligonephropathy: The fetal flaw in essential hypertension?

In 1988, Brenner, Garcia and Anderson advanced the hypothesis that the nephron endowment at birth is inversely related to the risk of developing essential hypertension in later life. This novel perspective on the origins of essential hypertension was taken from the viewpoint that the development and maintenance of hypertension must involve a renal factor favoring sodium retention, thereby preventing pressure-induced natriuresis from restoring blood pressure toward normal levels. Since nephron numbers in the normal population range from 300,000 to 1,100,000 or more, it was reasoned that a congenital shortfall in nephron endowment itself could be the renal risk factor for hypertension: demographic groups in whom hypertension is unusually prevalent tend to have smaller kidneys, implying fewer nephrons, and some inbred hypertensive rat strains have, on average, fewer nephrons than their respective normotensive counterparts. Recent independent observations in humans, relating low birth weight to both increased risk of hypertension in later life and the formation of fewer nephrons at birth, lend support to this nephron number hypothesis. Moreover, independent experimental studies in rodents suggest that maternal protein intake during gestation is directly related to the numbers of nephrons formed, and when protein intake is restricted, the offspring develop hypertension in maturity. The concept that nephron numbers may be programmed during gestation, as these observations imply, is discussed in relation to the potential advantages and disadvantages of such a mechanism for the next generation. Parallels are drawn with the relationship of low birth weight to pancreatic beta cell development and maturity-onset diabetes. We suggest that the programming of fewer nephrons at birth may provide a fitting and overlooked explanation for the eventual development of hypertension in those of low birth weight.

The hyperfiltration theory: a paradigm shift in nephrology

Experimental studies incriminate glomerular hypertension in mediating progressive renal damage after any of a variety of initiating injuries. Prevention of glomerular hypertension by dietary protein restriction or antihypertensive therapy lessens progressive glomerular damage in several experimental models of chronic renal disease. Glomerular hypertension and hyperfiltration also occur in humans with diabetes mellitus, solitary or remnant kidneys, and various forms of acquired renal disease. Clinical studies indicate that dietary protein restriction and antihypertensive therapy also slow progression in many of these disorders. Large multicenter trials confirm the beneficial effects of these therapeutic maneuvers on the rate of progression of chronic renal disease.

Augmenting kidney mass at transplantation abrogates chronic renal allograft injury in rats

Conventional renal transplantation, which substitutes a single allograft for two native kidneys, imposes an imbalance between nephron supply and the metabolic and excretory demands of the recipient. This discrepancy, which stimulates hyperfunction and hypertrophy of viable allograft nephrons, may be intensified by nephron loss through ischemia-reperfusion injury or acute rejection episodes occurring soon after transplantation. In other settings where less than 50% of the total renal mass remains, progressive glomerular injury develops through mechanisms associated with compensatory nephron hyperfiltration and hypertrophy. To determine whether responses to nephron loss contribute to chronic injury in renal allografts, nephron supply was restored to near-normal levels by transplanting Lewis recipients with two Fisher 344 kidneys (group 2A) compared with the standard single allograft F344 --> LEW rat model of late renal allograft failure (group 1A). At 20 weeks, indices of injury were observed in 1A but not 2A rats. These indices included proteinuria (1A: 45 +/- 13; 2A: 4.0 +/- 0.29 mg/day) and glomerulosclerosis (1A: 23 +/- 4.9%, 2A: 0.7 +/- 0.3%) (p < .05). Double-allograft recipients maintained near normal renal structure and function, whereas 1A rats showed evidence of compensatory hyperfiltration (single-nephron glomerular filtration rate of 63 +/- 10 versus 44 +/- 2.0 nl/min in 2A rats) and hypertrophy (mean glomerular volume of 2.64 +/- 0.15 versus 1.52 +/- 0.05 microns3 x 10(6) in 2A rats) (p < .05). Thus, we conclude that a major component of late allograft injury is attributable to processes associated with inadequate transplanted renal mass, a finding that has major implications for kidney transplantation biology and policy.

Renal mass as a determinant of late allograft outcome: insights from experimental studies in rats

Experimental studies of renal mass augmentation were conducted in the Fisher-->Lewis rat model of late renal allograft failure to assess the injury attributable to inadequate nephron supply in single allografts. Marked proteinuria, glomerulosclerosis and cellular infiltration developed in bilaterally nephrectomized recipients of single allografts at 16 to 20 weeks. By contrast, recipients with two kidney showed markedly reduced indices of allograft injury, irrespective of whether the second kidney was native or transplanted. Micropuncture whether the second kidney was native or transplanted. Micropuncture study of solitary allografts revealed glomerular hyperfiltration and elevated glomerular capillary pressure with marked inter-nephron variation despite normal systemic arterial pressure. In the two-kidney groups, single-nephron GFR and glomerular capillary pressures were essentially normal. These findings provide unambiguous evidence that the cycle of progressive nephron loss characteristic of extensive renal mass ablation operates in single allografts and contributes significantly to injury. The magnitude of allograft protection obtained by augmenting renal mass attests to the importance of nephron supply as a determinant of injury in this model. We conclude that mass-related injury processes may play a potentially major and underappreciated role in the pathogenesis of late renal allograft failure.

Non-immunologic predictors of chronic renal allograft failure: data from the United Network of Organ Sharing

Experimental evidence and clinical experience suggest that non-immunologic factors are important predictors of long-term renal allograft survival. It has been suggested that chronic allograft failure may in some cases by mediated by non-immunologic factors implicated in the pathobiology of other forms of progressive renal disease. Donor age, sex, and race may influence the "dose" of nephrons delivered in cadaveric renal transplantation. The United Network of Organ Sharing 1994 Public Use Data Tape was used to evaluate these and other risk factors in more than 31,000 recipients of cadaver allografts followed between 1987 and 1992. Female sex and African American race of the donor were important predictors of allograft failure. There was a markedly increased risk of allograft failure at both extremes of donor age. Recipients of large body size had accelerated graft loss. Stratified analyses suggested an interaction between donor and recipient race; nevertheless, all non-immunologic factors examined expressed independent associations with allograft survival. In sum, antigen-independent factors appear to be important determinants of allograft performance. Additional multivariable analyses are required to assess the relative importance of these factors compared with other known immunologic factors, such as HLA antigen mismatch. These findings may have important biomedical and health care policy implications.

Renal effects of high-dose natriuretic peptide receptor blockade in rats with congestive heart failure

Previous studies suggest that elevated plasma atrial natriuretic peptide (ANP) levels participate in regulating renal excretory function in rats with congestive heart failure (CHF). To define the role of natriuretic peptides (NPs) in the regulation of renal function in CHF, the renal responses to HS-142-1 (HS), a potent NP receptor antagonist, were studied in anesthetized rats subjected to coronary ligation that developed left ventricular infarction and CHF or in sham-operated (SO) control rats. Plasma ANP levels averaged > 14-fold higher in rats with CHF than in SO rats. In response to HS (20 mg/kg IV bolus), both mean arterial pressure and renal vascular resistance increased in rats with CHF but not in SO rats; glomerular filtration rate (GFR, 1.26 +/- 0.04 versus 0.76 +/- 0.11 mL/min) and renal plasma flow rate (RPF, 3.52 +/- 0.27 versus 2.70 +/- 0.32 mL/min) were significantly reduced in rats with CHF; and in SO rats, GFR (1.26 +/- 0.06 versus 1.20 +/- 0.07 mL/min) and RPF (3.98 +/- 0.21 versus 3.99 +/- 0.18 mL/min) were not significantly affected by HS. The sodium excretion rate (0.18 +/- 0.04 to 0.06 +/- 0.01 muEq/min) and fractional sodium excretion (0.01 +/- 0.02% to 0.04 +/- 0.01%) also fell markedly after HS administration in rats with CHF, but these parameters were unchanged in SO rats. These data indicate that NPs play a critical role in maintaining renal hemodynamic function and inhibiting tubule sodium reabsorption in rats with CHF, thus opposing sodium retention and preserving sodium balance in this model.

Fewer nephrons at birth: a missing link in the etiology of essential hypertension?

In 1988, Brenner et al advanced the hypothesis that the nephron endowment at birth is inversely related to the risk of developing essential hypertension in later life (Am J Hypertens 1:335-347, 1988). This novel perspective on the origins of essential hypertension was taken from the viewpoint that the development and maintenance of hypertension must involve a renal factor favoring sodium retention, thereby preventing pressure-induced natriuresis from restoring blood pressure toward normal levels. Since nephron numbers in the normal population range from 300,000 to 1,100,000 or more, it was reasoned that a congenital deficit in nephron endowment itself could be the renal risk factor for hypertension: demographic groups in whom hypertension is unusually prevalent tend to have smaller kidneys, implying fewer nephrons, and some inbred hypertensive rat strains have, on average, fewer nephrons than their respective normotensive controls. We argue that recent independent observations in humans relating low birth weight to both increased risk of hypertension in later life and the formation of fewer nephrons at birth lend strong support to the nephron number hypothesis. Moreover, independent experimental studies in rodents suggest that maternal protein intake during gestation is directly related to he numbers of nephrons formed and that when protein intake is restricted, the offspring develop hypertension in maturity. The concept that nephron numbers may be programmed during gestation, as these observations imply, is discussed in relation to the potential advantages and disadvantages of such a mechanism for the next generation; parallels are drawn with the relationship of low birth weight to pancreatic beta cell development and maturity-onset diabetes.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of chronic treatment with angiotensin converting enzyme inhibitor or an angiotensin receptor antagonist in two-kidney, one-clip hypertensive rats

The effects of chronic angiotensin II (Ang II) receptor blockade (losartan) or converting enzyme inhibition (enalapril) on blood pressure (BP), urinary albumin excretion (Ualb V), renal histology and the hemodynamic and excretory function of the clipped and nonclipped kidneys were studied in two-kidney, one-clip (2-K 1-C) rats. One day after clipping the right renal artery, male Wistar rats were divided into three groups receiving: (1) losartan, 20 mg/kg/day (N = 7), (2) enalapril, 20 mg/kg/day (N = 8), or (3) no treatment (controls, N = 9) for three weeks. Both losartan and enalapril treatments maintained conscious BP at comparably lowered levels compared to control animals (116 +/- 6 mm Hg and 113 +/- 2 mm Hg vs. 188 +/- 11 mm Hg, respectively, P < 0.01). Treatment also prevented the increase in Ualb V, observed for the untreated group, three weeks after clipping (1.7 +/- 0.5 and 0.7 +/- 0.1 mg/24 hr vs. 17.8 +/- 7 mg/24 hr, respectively, P < 0.01). After three weeks of treatment, acute study of renal function during pentobarbital anesthesia revealed higher values of GFR and RPF and lowered vascular resistance for nonclipped kidneys from the losartan and enalapril groups compared to the corresponding kidneys from control animals. Despite the lower BP of both treated groups, clipped kidney GFR and RPF were unchanged compared to the control group. Ualb V for nonclipped kidneys from untreated rats was approximately 5- to 10-fold higher than in the nonclipped kidneys from the treated groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Nephron supply is a major determinant of long-term renal allograft outcome in rats

The effects of augmenting the nephron supply on indices of allograft injury were assessed in a rat model of "chronic rejection." Orthotopic renal allotransplantation into unine-phrectomized rats was followed by excision (allograft-alone group) or preservation of the remaining native kidney (allograft+native kidney group) such that the total kidney complement was either the allograft alone, or the allograft plus one retained native kidney. After 18 wk, values for GFR (1.85 +/- 0.3 ml/min) and kidney weights (2.3 +/- 0.2 g) in allograft-alone rats were far in excess of corresponding values in the allograft of allograft+native kidney rats (0.88 +/- 0.1 ml/min and 1.1 +/- 0.5 g, respectively). Proteinuria (35 +/- 2 mg/d) and allograft glomerulosclerosis (24 +/- 8%) also characterized allograft-alone but not allograft+native kidney rats, in whom glomerular structure (allograft glomerulosclerosis, 4 +/- 1%; native kidney glomerulosclerosis, 0%) and glomerular functional integrity (proteinuria 7 +/- 0.7 mg/d) were well preserved. Thus, the observed allograft protection derived from the presence of a retained recipient native kidney supports the hypothesis that a single renal allograft contains insufficient nephrons to prevent progressive renal injury, implicating nephron supply as a major determinant of long-term allograft outcome.

TCV 116 prevents progressive renal injury in rats with extensive renal mass ablation

OBJECTIVE

The objective of this study was to determine the renal protective effects of TCV 116, a novel, non-competitive, angiotensin II type 1 (AT1) receptor antagonist, in rats with 5/6 renal mass ablation.

DESIGN

Adult male Wistar rats were subjected to 5/6 nephrectomy and treated continuously with either TCV 116 (group I, n = 8; group III, n = 9) or vehicle (group II, n = 8; group IV, n = 8). The development of elevated systolic blood pressure, 24-h urinary protein excretion, glomerular hemodynamics and glomerular morphology were compared among groups.

RESULTS

Systolic blood pressure rapidly reached hypertensive levels in group II, increasing from 175 +/- 8 mmHg after 3 weeks to 221 +/- 15 mmHg after 12 weeks, whereas group I rats remained normotensive (101 +/- 8 to 112 +/- 6 mmHg). Similarly, urinary protein excretion increased from 45 +/- 11 to 104 +/- 18 mg/day in group II, but remained low (6.9 +/- 1 to 19 +/- 4 mg/day) in group I. After 12 weeks, there was an average of 42 +/- 6% glomerulosclerosis in group II, but only 1.6 +/- 0.5% in group I. After 4-6 weeks, a markedly elevated glomerular capillary pressure (62 +/- 1.2 mmHg) was observed in group IV, but the pressure was normal in group III (50 +/- 1.1 mmHg).

CONCLUSIONS

These data show that TCV 116 prevents the development of systemic hypertension, glomerular capillary hypertension, proteinuria and glomerulosclerosis in rats with reduced renal mass. We therefore conclude that the renal protection associated with angiotensin I converting enzyme inhibitors and other pharmacologic blockers of the renin-angiotensin system arises chiefly from blockade of AT1 receptor-mediated hemodynamic effects.

HS-142-1, a potent antagonist of natriuretic peptides in vitro and in vivo

To determine whether HS-142-1 (HS), a potent atrial natriuretic peptide (ANP) receptor antagonist, also inhibits the effects of brain natriuretic peptide (BNP), urodilatin (URO), and C-type natriuretic peptide, in vitro studies were carried out, demonstrating that HS inhibited production of cGMP by rat fetal lung fibroblast cells induced by ANP, BNP, URO, and C-type natriuretic peptide. Acute clearance studies were conducted in euvolemic Munich-Wistar rats under inactin anesthesia to characterize the effects of HS in vivo. In response to ANP, BNP, or URO (4 micrograms/kg priming dose plus 0.5 micrograms/kg per minute for 20 min), urine flow, absolute sodium excretion rates, and fractional sodium excretion exhibited similar increases (four- to fivefold) in vehicle-treated rats; these responses were, however, completely abolished by prior HS treatment. The tendency for GFR to rise during the infusion of natriuretic peptides (NP) was also blocked after HS. By contrast, HS did not block the renal effects of L-arginine, a precursor of nitric oxide, or of furosemide. Furthermore, the inhibition of endogenous NP by HS was associated with small but significant reductions in GFR and absolute and fractional sodium excretion in normal rats under euvolemic but not hydropenic conditions. These studies provide evidence that the observed effects of HS in vivo and in vitro are mediated exclusively by receptors of NP. Together, these data support the view that HS is a highly specific ligand for NP receptors, capable of antagonizing the renal effects not only of exogenous ANP, but also those of BNP and URO.

Renal effects of natriuretic peptide receptor blockade in cirrhotic rats with ascites

The aim of this study was to assess the effect of HS-142-1, a recently discovered specific antagonist of endogenous natriuretic peptides, on systemic hemodynamics, renal function, and the renin-aldosterone system in rats with cirrhosis and ascites. The study consisted of three protocols, each including 10 conscious control rats and 10 conscious rats with carbon-tetrachloride-induced cirrhosis with ascites. In protocol 1, HS-142-1 administration (by intravenous bolus of 20 mg.kg-1.body weight in all protocols) was not associated with significant changes in mean arterial pressure, heart rate, cardiac output or total peripheral resistance in the two groups of animals. In protocol 2, HS-142-1 induced a significant reduction in glomerular filtration rate (from 4.2 +/- 0.5 to 2.6 +/- 0.3 ml/min, p < 0.025) in control animals. A decrease in renal plasma flow and an increase in renal vascular resistance also occurred, but these changes were not statistically significant. In cirrhotic rats, HS-142-1 resulted in a significant decrease in renal plasma flow (from 10.9 +/- 0.7 to 4.3 +/- 0.6 ml/min, p < 0.001) and a significant increase in renal vascular resistance (from 6.0 +/- 0.6 to 16.3 +/- 2.7 mm Hg.min.ml-1, p < 0.025). Glomerular filtration rate decreased more in cirrhotic rats with ascites than in control rats (from 3.8 +/- 0.3 to 1.3 +/- 0.2 ml/min, p < 0.001). Changes in urine flow rate and urinary sodium excretion rate paralleled those of glomerular filtration rate in both groups of animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of natriuretic peptide receptor inhibition on remnant kidney function in rats

To identify the contribution of natriuretic peptide (NP) activity to the adaptative increases in glomerular filtration rate (GFR), effective renal plasma flow rate (ERPF) and fractional sodium excretion (FENa) observed in the remnant kidney, we investigated the acute effects of administering HS-142-1 (HS), a potent NP receptor antagonist, in 5/6th nephrectomized (NPX) rats. In addition to normal sodium intake, high or low sodium intakes were used to stimulate or suppress, respectively, endogenous NP activity in NPX rats. In rats three days after NPX on high sodium, HS (20 mg/kg bolus i.v.) reduced GFR from 0.55 +/- 0.05 to 0.35 +/- 0.04 ml/min; ERPF from 1.83 +/- 0.19 to 1.53 +/- 0.16 ml/min; and FENa from 7.1 +/- 1.1 to 1.6 +/- 0.4%, without affecting MAP. Similar changes of lesser magnitude were observed in NPX rats on normal sodium intake. By contrast, GFR, ERPF, FENa and MAP were unchanged following HS in NPX rats on low sodium intake, suggesting that the magnitude of responses to HS is dependent upon the expected levels of activity of NP. We conclude that in anesthetized rats, natriuretic peptides contribute to the compensatory increases in GFR, ERPF and FENa observed in the remnant kidney under normal and salt-replete conditions.

Effects of an atrial natriuretic peptide receptor antagonist on glomerular hyperfiltration in diabetic rats

Previous studies from this laboratory implicated atrial natriuretic peptide (ANP) as a possible mediator of glomerular hyperfiltration in diabetic rats. In this study, the potential of HS-142-1 (HS), a novel polysaccharide compound with ANP receptor antagonist properties, to ameliorate glomerular hyperfiltration in diabetic rats was assessed. Initially, it was confirmed that a bolus iv injection of HS blocked both diuretic and natriuretic responses to exogenous ANP in normal Munich-Wistar rats. The acute effects of HS in moderately hyperglycemic diabetic rats with glomerular hyperfiltration and hyperperfusion were then determined. In diabetic rats, HS (20 mg/kg bolus iv) lowered GFR by approximately 46% from hyperfiltering (1.86 +/- 0.06 mL/min) to normal (1.13 +/- 0.13 mL/min) levels, whereas GFR in vehicle-treated diabetic rats remained unchanged (1.92 +/- 0.08 mL/min to 1.77 +/- 0.09 mL/min). In nondiabetic euvolemic rats, GFR was reduced by 20% after HS, whereas GFR in vehicle-treated controls was unchanged. In contrast, HS had no effect on GFR in hydropenic rats. Effective RPF was not significantly reduced in either diabetic or normal euvolemic rats in response to HS; consequently, significant reductions in filtration fraction were observed in both groups. Urine flow and sodium excretion rates were significantly reduced after HS in both diabetic and nondiabetic groups but not in hydropenic or vehicle-treated groups. These data show that HS ameliorates glomerular hyperfiltration in diabetic rats, further supporting the hypothesis that intrarenal actions of natriuretic peptides contribute significantly to glomerular hyperfiltration in experimental diabetes mellitus.

Dye lasers using tapered optical fibers

A new type of dye laser operating in a single-mode optical fiber has been studied. The gain is produced by surrounding a tapered section of the fiber with laser dye. Interaction of the light in the fiber with the laser dye is achieved through the exposed evanescent field at the taper waist. Low lasing thresholds (25-65 mW) are obtained as a result of the high intensities at the taper waist. These tapered fiber dye lasers combine the advantages of a laser in fiber form with the wide spectral tuning ranges provided by laser dyes. Three experiments, demonstrating low-threshold operation of a grating tuned laser, an all-fiber ring laser, and cw lasing in tapered fiber dye devices, are presented.

Tubuloglomerular feedback in one-kidney, one-clip hypertensive rats

Previous studies have shown that hydropenic one-kidney, one-clip (1-K, 1-C) hypertensive HT rats exhibit impaired autoregulation of glomerular filtration rate (GFR) in response to reduced arterial perfusion pressure. We investigated the possible role of altered tubuloglomerular feedback (TGF) activity in this phenomenon. Uninephrectomized Wistar rats were studied acutely 3 weeks after placing silver clips (0.2 mm) on the renal artery. Experiments were performed in 1-K,1-C HT rats and in uninephrectomized control animals. TGF activity was assessed as changes in proximal tubule stop-flow pressure (SFP) in response to orthograde microperfusion from 0 to 80 nl/min into late proximal tubule segments. Only the highest perfusion rates (approximately 40 nl/min) into late proximal tubule segments resulted in maximal decreases in SFP, indicating a marked rightward shift of overall TGF activity in 1-K,1-C HT rats. Similar responses were observed in the uninephrectomized animals. In contrast, changes of SFP were observed at lower perfusion rates in normal animals and maximal responses were observed at perfusion rates of approximately 20 nl/min. These observations are consistent with the possibility that altered TGF activity contributes to impaired autoregulation of GFR in 1-K,1-C HT rats in response to reduced renal perfusion pressure. In response to treatment with i.v. captopril, the 1-K,1-C HT rats exhibited marked decreases in systemic arterial pressure associated with decreases in SFP and virtually complete inhibition of TGF activity. It is attractive to hypothesize that these alterations in TGF characteristics in the 1-K,1-C HT rats play a significant pathophysiologic role in the acute renal dysfunction observed in response to acute decreases of blood pressure during conditions of augmented angiotensin activity. Additional future studies will allow us to address the precise role for intrarenal angiotensin in these phenomena.

Pressure dependence of exaggerated natriuresis in two-kidney, one clip Goldblatt hypertensive rats

This study evaluated the responses of each kidney of two-kidney, one clip Goldblatt hypertensive rats to acute volume loading to delineate the contribution of elevated perfusion pressure to the mechanisms of the exaggerated natriuresis in this model of hypertension. Eleven Goldblatt animals (0.2 mm clip 3 weeks prior to study) were studied at spontaneous blood pressure for each kidney's response to volume loading. In 11 other Goldblatt animals an aortic clamp between the renal arteries allowed reduction of perfusion pressure for the left, nonclipped kidney to normal levels. Ten normal rats served as controls. Renal function was examined during control periods and following the infusion of 3.5% body wt of 154 mM X liter-1 NaCl at 22.5 ml X hr-1. An exaggerated natriuresis was observed for the left, nonclipped kidney of the hypertensive Goldblatt rats, while the clipped kidney exhibited an attenuated natriuresis compared to either kidney of normal control rats. Reduction of perfusion pressure to the nonclipped kidney of Goldblatt animals to normal levels resulted in reduced clearance and excretory function before volume loading and attenuated its natriuretic response to levels less than those for the Goldblatt group at spontaneous, hypertensive blood pressure. The exaggerated natriuresis observed at hypertensive blood pressure was attributable to increases of filtered load of Na+ and reduced fractional absorption. These observations indicate that an exaggerated natriuresis occurs in the two-kidney, one clip Goldblatt hypertensive rat and that this phenomenon depends on the elevated renal perfusion pressure to the nonclipped kidney.