Dilemmas in human and rat pregnancy: proposed mechanisms relating to arterial vasodilation.

There are several mysteries about the normal physiology of pregnancy (1). Renal sodium and water reabsorption occurs despite an increase in total blood volume. Moreover, the renin-angiotensin-aldosterone system (RAAS) is also stimulated in normal pregnancy, even though an increase in total blood volume normally suppresses the RAAS and increases sodium excretion in the nonpregnant state. Water retention also occurs and leads to hypoosmolality in normal pregnancy, even though total blood volume is expanded. On rare occasions, an extreme polyuria occurs in pregnancy that is unresponsive to arginine vasopressin (AVP). The receptors whereby AVP and oxytocin stimulate the principal cell of the collecting duct, vascular smooth muscle, glomerular mesangial and endometrial cells are in need of clarification. The present study proposes potential mechanisms relating to systemic arterial vasodilation to explain some of the apparent dilemmas of pregnancy.

VEGF receptor inhibition slows the progression of polycystic kidney disease.

Although the receptors for vascular endothelial growth factor (VEGF) exert their effects on vasculogenesis and angiogenesis through receptors located on endothelial cells, recent studies have shown that these receptors are also present on renal tubular epithelial cells. We investigated the role of VEGF on increased tubule cell proliferation in the Han:SPRD heterozygous (Cy/+) rat model of polycystic kidney disease. The levels of VEGF in the kidneys and the serum, and the expression of the two receptors on tubules were increased in Cy/+ rats. These rats were given ribozymes that specifically inhibited VEGFR1 and VEGFR2 mRNA expression. Tubule cell proliferation within the cysts was significantly decreased in the ribozyme-treated animals leading to decreased cystogenesis, blunted renal enlargement, and prevented the loss of renal function. Our studies show that inhibition of VEGF function may be an important therapeutic option to delay the progression of polycystic kidney disease.

Polyuria of thyrotoxicosis: downregulation of aquaporin water channels and increased solute excretion.

Thyrotoxicosis is a common disorder causing cardiovascular and renal irregularities. In this study, thyrotoxicosis was produced in rats by 14 days of daily thyroxine injection. This was associated with an increase in cardiac index, mean arterial pressure, and renal blood flow compared with euthyroid controls. Food and water intake along with urine output were significantly increased in the thyrotoxic rats compared with control animals associated with a significant increase in solute excretion. Polyuria and increased solute excretion still occurred even when food and water intake was equivalent. These renal responses were associated with significant decreases in AQP1 and AQP2 water channel expression in both the ad lib and paired intake studies in the cortex and inner medulla. The downregulation of AQP2 protein occurred in spite of equivalent plasma arginine vasopressin (AVP) in the ad lib and increased AVP in the paired feeding studies. Solute-free water reabsorption was greater in both the ad lib and paired thyrotoxic than euthyroid rats and was associated with increased Na-K-2Cl cotransporter expression. We propose that the AVP-independent downregulation of AQP2, the observed increase in renal arterial pressure, and decrease in filtration fraction contribute to polyuria the increased solute excretion in spite of enhanced ion transporters in thyrotoxicosis.

Oral V2 receptor antagonist (RWJ-351647) in patients with cirrhosis and ascites: a randomized, double-blind, placebo-controlled, single ascending dose study.

BACKGROUND: RWJ-351647 is a selective V2 receptor antagonist that inhibits vasopressin-induced water reabsorption in the kidney. AIM: To investigate the safety and tolerability of RWJ-351647 compared with placebo after single oral dose administration to patients with cirrhosis and ascites, on a stable treatment with furosemide and spironolactone. METHODS: Single oral doses of 1, 2 and 5 mg of RWJ-351647 were administered to 24 patients with ascites on stable concomitant diuretic treatment. RESULTS: RWJ-351647 had a tmax of 1 to 1.1 h and mean half-life of 10.4-17.4 h. There was no affect on the pharmacokinetics of concomitant diuretics. Increases in cumulative urine volume and free water excretion, and a decrease in urine osmolality were noted in a dose-dependent manner reaching the statistical significance at the 5-mg dose. Four patients exhibited a decrease of > 2 kg in weight in the 24 h after dosing. RWJ-351647 was well tolerated, with no evidence of a dose-related increase in adverse events when compared with placebo. No changes in either serum chemistry or plasma AVP (arginine vasopressin) and renin levels were observed despite the observed aquaresis. CONCLUSION: RWJ-351647 is an effective aquaretic causing dose-dependent increases in urine output and free water clearance, when co-administered with conventional diuretics in patients with cirrhosis and ascites.

Impaired fibrinolytic activity in type II diabetes: correlation with urinary albumin excretion and progression of renal disease.

Progression of renal disease and cardiovascular complications in type II diabetes mellitus have been shown to correlate with control of blood glucose, lipids, blood pressure, and smoking. These factors, however, do not appear to totally explain these diabetic complications. Renal disease and cardiovascular complications in type II diabetes are associated with vascular abnormalities and fibrosis, both of which may occur with impaired fibrinolysis. A cross-sectional study was therefore performed in 107 type II diabetic patients recruited from the Denver Metropolitan Area to examine the effect of impaired fibrinolysis, as assessed by the ratio of plasminogen activator inhibitor (PAI-1) to tissue-type plasminogen activator (t-PA). With urinary albumin excretion (UAE) as a risk factor for both renal disease progression and cardiovascular complications, the patients were analyzed with respect to UAE less than and greater than 1 gm/day. The age, blood glucose, hemoglobin A1C, duration of diabetes, lipids, body mass index, and smoking were no different between the groups. As expected, the group with greater UAE had worse renal function, the serum creatinine (1.98 +/- 0.24 vs 1.21 +/- 0.05 mg/dl, P < 0.001) and creatinine clearance (55.5 +/- 6.0 vs 76.8 +/- 2.7 ml/min, P < 0.001) were significantly different. The type II diabetic patients with greater UAE exhibited significantly higher PAI-1/t-PA (2.43 +/- 0.26 vs 1.85 +/- 0.07, P < 0.03). The past history of cardiac complications was also higher (87.5 vs 72.3%, P < 0.07) in the diabetic patients with more impaired fibrinolysis and greater UAE. Thus a prospective, randomized clinical trial in type II diabetes with PAI-1 inhibitors is needed.

From finch to fish to man: role of aquaporins in body fluid and brain water regulation.

Charles Darwin, in his Origin of the Species, noted that different species of finches on the Galapagos Islands had adapted their beak size based on where they sought their food. Homer Smith, in his book From Fish to Philosopher, discussed the evolution of the nephron from a single conduit in salt water vertebrates, to nephrons with large glomerular capillaries and proximal and distal tubules in fresh water vertebrates, to smaller glomerular capillaries in amphibians, to nephrons with loops of Henle to allow for urinary concentration and dilution in mammals. The kidney with its million nephrons has emerged as the vital organ for regulating body fluid composition and volume. With the recent discovery of aquaporin water channels, our understanding of volume regulation has been greatly enhanced. This article reviews current knowledge regarding: 1) the unifying hypothesis of body fluid volume regulation; 2) brain aquaporins and their role in pathophysiologic states; and 3) function and regulation of renal aquaporins in the syndrome of inappropriate antidiuretic hormone secretion (SIADH).

Role of glucocorticoid hormones in arginine vasopressin gene regulation.

The mechanism underlying increased AVP synthesis and release in glucocorticoid deficiency is not known. Therefore, the present study was undertaken to investigate whether the mechanism was at the level of AVP gene transcription. The AVP gene promoter contains a consensus GRE, a CRE, and four AP2 sites. To assess the functional importance of these sites, 5' deletions of the AVP promoter were created and transient transfections were performed. Promoter activity in hypothalamic cells transfected with deletions lacking the GRE or both the GRE and CRE exhibited higher activity when compared to longer constructs containing both sites. In neuroblastoma cells, only the deletion lacking the GRE exhibited increased AVP promoter activity over the longer construct. These results are consistent with the idea that glucocorticoids suppress AVP gene expression by acting on a GRE in the AVP promoter region. Further, dexamethasone inhibited AVP promoter activity by >50% in hypothalamic cells transfected with the GRE-containing construct. In conclusion, the data presented here support a central mechanism to explain, at least in part, the nonosmotic increase in AVP with glucocorticoid deficiency.

Gibbs memorial lecture. Unifying hypothesis of body fluid volume regulation: implications for cardiac failure and cirrhosis.

Body fluid volume regulation is critically important in maintaining life. In this paper, we review our unifying hypothesis of body fluid volume regulation, which maintains arterial circulatory integrity in health and disease. The integrity of the arterial circulation, as determined by cardiac output and peripheral vascular resistance, is the predominant determinant of renal sodium and water retention. Arterial circulatory integrity can be disturbed either by a decrease in cardiac output, as in low-output cardiac failure, or by a decrease in peripheral vascular resistance, as in high-output states such as high-output cardiac failure and cirrhosis. The resulting arterial underfilling is sensed by baroreceptors that are located in the left ventricle, the aortic arch, the carotid sinus and the renal afferent arterioles. Decreased activation of these receptors during arterial underfilling leads to neurohumoral compensatory responses, which include the stimulation of the sympathetic nervous system, activation of the renin-angiotensin-aldosterone system (RAAS) and the non-osmotic release of vasopressin. These compensatory responses maintain arterial circulatory integrity by increasing peripheral and renal arterial vascular resistance together with renal sodium and water retention. However, over the long term, these adaptive responses may have detrimental effects, such as pulmonary congestion, increased myocardial demand, increased cardiac afterload, ascites and hyponatremia. The intensity of the neurohumoral responses correlates with the progression and severity of both cardiac failure and cirrhosis. The understanding of the pathogenesis of sodium and water retention in cardiac failure and cirrhosis has led to therapies that favorably affect the morbidity and mortality of these patients.

Treating hypertension in the elderly.

Hypertension is highly prevalent in elderly individuals, the most rapidly growing segment of the US population. Epidemiologic studies have established that increased risk of cardiovascular disease is associated with elevated blood pressure. Treatment of hypertension in elderly patients significantly reduces their cardiovascular morbidity and mortality. However, antihypertensive therapy is often challenging in this patient population because of potential metabolic and physiologic alterations, multiple comorbidities, polypharmacy, and biologic variability. Drugs with a convenient dosing schedule, minimal side effects, and the ability to impact comorbid conditions are important considerations in the treatment of hypertension in the elderly.

Increasing homocysteine levels and diabetic autonomic neuropathy.

OBJECTIVE: To determine if hyperhomocysteinemia is a risk factor for the development of diabetic sensorimotor peripheral neuropathy (DSPN) and diabetic autonomic neuropathy (DAN). BACKGROUND: Hyperhomocysteinemia and non-insulin-dependent diabetes mellitus (NIDDM) are both associated with premature vascular disease. Microvascular ischemia may be a risk factor for DSPN and DAN; therefore, the relationship of hyperhomocysteinemia to DSPN and DAN was investigated. METHODS: Baseline neurological tests and homocysteine levels were determined in patients from a large prospective study of diabetic complications, the Appropriate Blood Pressure Control in Diabetes (ABCD) Trial. RESULTS: Total homocysteine (tHcy) was independently associated with DAN; for each 1 micromol/l increase in tHcy, there was a 7.1% increased risk of developing DAN (P<0.05). There was no association between tHcy and DSPN. CONCLUSIONS: Hyperhomocysteinemia may be a risk factor for DAN but not for DSPN. This relationship may be related to differential small fiber injury. Further studies are needed to investigate this relationship between tHcy and DAN. specifically whether treatment of hyperhomocysteinemia may modify DAN.

Effects of nitric oxide and peroxynitrite on endotoxin-induced leukocyte adhesion to endothelium.

Leukocyte accumulation has been shown to be increased in sepsis. Moreover, in inducible nitric oxide synthase (iNOS) knockout mice, a further increase in leukocyte accumulation has been observed during sepsis, suggesting that nitric oxide (NO) may affect leukocyte/endothelial interaction. Accelerated peroxynitrite formation also occurs during sepsis. In the present study, the effect of peroxynitrite or NO on leukocyte adhesion to nitric oxide synthase (NOS)-inhibited or endotoxin-treated endothelium was examined. Bovine aortic endothelial cells were treated with either L-NAME or lipopolysaccharide (LPS) and interferon-gamma for 4 hr and subsequent leukocyte adhesion was measured. Both L-NAME and LPS treatment resulted in increased leukocyte adhesion compared with control. Neither a peroxynitrite donor, SIN-1, nor a direct NO donor, DETA-NO, had any effect on leukocyte adhesion to untreated endothelium. However, when the L-NAME or LPS-treated endothelial cells were treated simultaneously with either SIN-1 or DETA-NO, there was a significant reduction in leukocyte adhesion. Moreover, at the concentrations used in the present study, neither peroxynitrite nor NO showed harmful effects on normal cultured endothelial cells. These data demonstrating inhibition of leukocyte adhesion to endotoxin-treated endothelium suggest that peroxynitrite or NO may exert a beneficial effect during sepsis.

Diuretics versus angiotensin-converting enzyme inhibitors in autosomal dominant polycystic kidney disease.

Hypertension, which occurs commonly and early in autosomal dominant polycystic kidney disease (ADPKD), affects both renal and patient outcome. However, there is no consensus about the type of antihypertensive therapy that is most appropriate for patients with ADPKD. This historical prospective, nonrandomized study was designed to investigate the effect on renal function of diuretics versus angiotensin-converting enzyme (ACE) inhibitors in hypertensive patients with ADPKD who entered the study with comparable renal function. Among hypertensive ADPKD patients followed in our center, patients taking diuretics without any ACE inhibitors were included in the diuretic group (n = 14, male/female ratio 5/9, mean age 47 years), whereas patients taking ACE inhibitors but no diuretics were included in the ACE inhibitor (ACEI) group (n = 19, male/female ratio 11/8, mean age 41 years). For comparable blood pressure control, 21% of the ACEI group and 64% of the diuretic group (p < 0.05) needed additional antihypertensive medications. After an average follow-up period of 5.2 years, the creatinine clearance decreased significantly in the diuretic group (74 vs. 46 ml/min/1.73 m2, p < 0.0001) and in the ACEI group (83 vs. 71 ml/min/1.73 m2, p = 0.0005). The decrement in creatinine clearance was significantly larger in the diuretic group than the ACEI group (p < 0.05). The annual decrease in creatinine clearance was 5.3 ml/min/1.73 m2 in the diuretic group and 2.7 ml/min/1.73 m2 in the ACEI group (p < 0.05). A significant increase in urinary protein excretion occurred in the diuretic but not in the ACEI group. Hypertensive ADPKD patients treated with diuretics had a faster loss of renal function as compared with patients treated with ACE inhibitors, despite similar blood pressure control. This result will need to be further examined in a randomized study.

Impaired IL-18 processing protects caspase-1-deficient mice from ischemic acute renal failure.

We sought to determine whether mice deficient in the proinflammatory caspase-1, which cleaves precursors of IL-1 beta and IL-18, were protected against ischemic acute renal failure (ARF). Caspase-1(-/-) mice developed less ischemic ARF as judged by renal function and renal histology. These animals had significantly reduced blood urea nitrogen and serum creatinine levels and a lower morphological tubular necrosis score than did wild-type mice with ischemic ARF. Since caspase-1 activates IL-18, lack of mature IL-18 might protect these caspase-1(-/-) mice from ARF. In wild-type animals, we found that ARF causes kidney IL-18 levels to more than double and induces the conversion of the IL-18 precursor to the mature form. This conversion is not observed in caspase-1(-/-) ARF mice or sham-operated controls. We then injected wild-type mice with IL-18-neutralizing antiserum before the ischemic insult and found a similar degree of protection from ARF as seen in caspase-1(-/-) mice. In addition, we observed a fivefold increase in myeloperoxidase activity in control mice with ARF, but no such increase in caspase-1(-/-) or IL-18 antiserum-treated mice. Finally, we confirmed histologically that caspase-1(-/-) mice show decreased neutrophil infiltration, indicating that the deleterious role of IL-18 in ischemic ARF may be due to increased neutrophil infiltration.

Endotoxemic renal failure in mice: Role of tumor necrosis factor independent of inducible nitric oxide synthase.

BACKGROUND: Renal failure is a frequent complication of sepsis with a high mortality. Tumor necrosis factor (TNF) has been suggested to be a factor in the acute renal failure in sepsis or endotoxemia. Recent studies also suggest involvement of nitric oxide (NO), generated by inducible NO synthase (iNOS), in the pathogenesis of endotoxin-induced renal failure. The present study tested the hypothesis that the role of TNF in endotoxic renal failure is mediated by iNOS-derived NO. METHODS: Renal function was evaluated in endotoxemic [Escherichia coli lipopolysaccharide (LPS), 5 mg/kg IP] wild-type and iNOS knockout mice. The effect of TNF neutralization on renal function during endotoxemia in mice was assessed by a TNF-soluble receptor (TNFsRp55). RESULTS: An injection of LPS to wild-type mice resulted in a 70% decrease in glomerular filtration rate (GFR) and in a 40% reduction in renal plasma flow (RPF) 16 hours after the injection. The results occurred independent of hypotension, morphological changes, apoptosis, and leukocyte accumulation. In mice pretreated with TNFsRp55, only a 30% decrease in GFR without a significant change in RPF in response to LPS, as compared with vehicle-treated mice, was observed. Also, the serum NO concentration was significantly lower in endotoxemic wild-type mice pretreated with TNFsRp55, as compared with untreated endotoxemic wild-type mice (260 +/- 52 vs. 673 +/- 112 micromol/L, P < 0.01). In LPS-injected iNOS knockout mice and wild-type mice treated with a selective iNOS inhibitor, 1400W, the development of renal failure was similar to that in wild-type mice. As in wild-type mice, TNFsRp55 significantly attenuated the decrease in GFR (a 33% decline, as compared with 75% without TNFsRp55) without a significant change in RPF in iNOS knockout mice given LPS. CONCLUSIONS: These results demonstrate a role of TNF in the early renal dysfunction (16 h) in a septic mouse model independent of iNOS, hypotension, apoptosis, leukocyte accumulation, and morphological alterations, thus suggesting renal hypoperfusion secondary to an imbalance between, as yet to be defined, renal vasoconstrictors and vasodilators.

Chronic NOS inhibition reverses systemic vasodilation and glomerular hyperfiltration in pregnancy.

The chronic role of nitric oxide (NO), independent of prostaglandin synthesis, in the primary peripheral vasodilation, increased glomerular filtration rate (GFR), and renal plasma flow (RPF) in normal pregnancy remains to be defined. The purpose of the present study was to chronically inhibit NOS to return systemic vascular resistance (SVR), cardiac output (CO), GFR, and RPF to nonpregnant values. Pregnant rats received the nitric oxide synthase (NOS) inhibitor, nitro-L-arginine methyl ester (L-NAME), orally from gestational days 7 through 14. Results were compared with nonpregnant and untreated pregnant rats. At 14 days gestation, CO significantly increased in pregnant vs. nonpregnant rats (187 +/- 17 vs. 125 +/- 10 ml/min, P < 0.05) as SVR decreased (0.64 +/- 0.08 vs. 1.08 +/- 0.08 mmHg. ml(-1). min, P < 0.05) and mean arterial pressure was unchanged (117 +/- 5 vs. 125 +/- 2 mmHg, not significant). Pregnant rats also demonstrated increased GFR (3,015 +/- 33 vs. 2,165 +/- 136 microl/min, P < 0.01) and RPF (7,869 +/- 967 vs. 5,507 +/- 290 microl/min, P < 0.05) vs. nonpregnant rats. L-NAME-treated pregnant rats had values for CO (118 +/- 7 ml/min), SVR (1.09 +/- 0.07 mmHg. ml(-1). min), GFR (2,264 +/- 150 microl/min), and RPF (5,777 +/- 498 microl/min), which were no different than nonpregnant animals. In summary, similar to human pregnancy, primary peripheral vasodilation occurs early in rat pregnancy. Furthermore, the hyperdynamic circulation and glomerular hyperfiltration of normal rat midterm pregnancy can be chronically reversed by NOS inhibition. These findings suggest a role for endothelial damage and decreased NO in the pathogenesis of preeclampsia.

Role of polymeric Tamm-Horsfall protein in cast formation: oligosaccharide and tubular fluid ions.

BACKGROUND: In acute tubular necrosis (ATN), distal tubules are obstructed by casts formed by tubular debris, cells, and Tamm-Horsfall protein (THP). Since there are Arginine-Glycine-Aspartate (RGD) and Leucine-Aspartate-Valine (LDV) adhesive sequences in human THP, there may be direct integrin-mediated binding of tubular cells to THP. Alternatively, polymerization of THP may result in entrapment of the cells in its gel. METHODS: Adhesion of LLC-PK(1) cells to THP-coated wells was directly measured. THP concentrate was dissolved in solutions which mimic urine from ATN (ATN-S), distal convoluted tubule (DCT-S), collecting duct (CD-S), and monomeric buffer (M buffer). THP was also denatured by either boiling or N-glycanase digestion. Gel formation of THP was then measured. Inhibition of LLC-PK(1) cell adhesion to collagen type I was measured with each solution, as well as after the collagen was pretreated with either monomeric (mTHP) or polymeric (pTHP) THP. The effect of pTHP on the settling rate of LLC-PK(1) cells in suspension was also measured. RESULTS: LLC-PK(1) cells did not directly adhere to THP, a finding against integrin-mediated binding as a mechanism for in vivo tubular cell/THP cast formation. The high electrolyte concentration of ATN-S and CD-S, however, was associated with pTHP gel formation. Moreover, cells suspended in pTHP remained in suspension. In cell adhesion studies, mTHP attenuated cell adhesion by binding to the matrix, whereas pTHP attenuated cell adhesion by trapping cells in its gel. An active process was involved since both pTHP gel formation and attenuation of cell adhesion were abolished by boiling or oligosaccharide removal with N-glycanase digestion. CONCLUSIONS: With renal ischemia and proximal tubule cell shedding, ATN and collecting duct fluid composition enhance THP gel formation and thus favor tubular cast formation and obstruction. The present in vitro results indicate the importance of oligosaccharide residues in mediating the effect of the THP on gel formation and potential cast formation in ATN.

Pathogenesis and management of sodium and water retention in cardiac failure and cirrhosis.

The kidneys play the crucial role in the maintenance of the body fluid volume homeostasis. Several hypotheses have been introduced to explain sodium and water retention leading to edematous states in such pathologic conditions as congestive heart failure (CHF) and cirrhosis. We have suggested a unifying arterial underfilling hypothesis, explaining the development of edema in these conditions. Arterial underfilling, caused by decreased cardiac output or peripheral arterial vasodilation, leads to activation of the sympathetic nervous system, renin-angiotensin-aldosterone system, and nonosmotic vasopressin release. This review discusses the pathophysiologic mechanisms resulting in renal sodium and water retention, impaired mineralocorticoid escape, and resistance to atrial natriuretic peptide in patients with CHF and cirrhosis. Furthermore, the basis of current therapies in these disorders is discussed, including beta-blockers, angiotensin-converting enzyme inhibitors, angiotensin-receptor blockers, aldosterone antagonists, and diuretics in CHF and cirrhosis, as well as new approaches to treatment of water retention with vasopressin V(2) receptor antagonists.