Prostaglandin synthesis by rat glomerular mesangial cells in culture. Effects of angiotensin II and arginine vasopressin

Calcium channel blockade and renal function

Since calcium channel blocking agents were introduced into the treatment of hypertension their influence on renal function has become an important issue. In animal experiments calcium channel blocking agents have been shown to increase renal blood flow and glomerular filtration rate and to augment urine flow and electrolyte excretion. In human acute studies the administration of calcium channel blocking agents have elicited similar renal hemodynamic and diuretic effects. Clinical studies on the renal effects of long-term treatment are however still lacking. Studies on the effect on renin release have given divergent results. In acute experiments renin release is increased by calcium channel blocking agents. In long-term treatment, however, no change in peripheral plasma levels of renin has been demonstrated. The influence of decreased renal function on the pharmacokinetics of calcium channel blocking agents has been studied in patients with renal disease. For verapamil the volume of distribution is smaller in uremic patients than in normals and both metabolic and renal clearances are decreased. For nifedipine, on the other hand, similar plasma levels, plasma half life and total plasma clearance are found in uremic patients and normal subjects.

Effects of YM218, a nonpeptide vasopressin V1A receptor-selective antagonist, on vasopressin-induced growth responses in human mesangial cells

Mesangial cells are centrally-located glomerular pericytes with contractile, endocrine, and immunity-regulating functions. These cells are thought to maintain normal glomerular function, since mesangial cell proliferation and extracellular matrix formation are hallmarks of chronic glomerular disease. Vasopressin causes mesangial cell contraction, proliferation and hypertrophy. Consequently, the effects of YM218, a potent, nonpeptide vasopressin V(1A) receptor-selective antagonist, on the growth responses of human mesangial cells to vasopressin were investigated. YM218 showed high affinity for vasopressin V(1A) receptors, exhibiting a K(i) value of 0.18 nM. Vasopressin concentration-dependently increased intracellular Ca(2+) levels and induced hyperplasia and hypertrophy in cultured mesangial cells, YM218 potently inhibited these vasopressin-induced responses. These results clearly show that YM218 has both strong affinity for human mesangial cell vasopressin V(1A) receptors and great potency in inhibiting the vasopressin-induced growth responses of mesangial cells controlled by the vasopressin V(1A) receptors. The hyperplasia and hypertrophy of mesangial cells in vitro caused by vasopressin indicate its possible in vivo role in glomerular disease pathogenesis. Therefore, YM218 is a potent pharmacologic probe to investigate the physiologic and pathophysiologic roles of vasopressin in the development of renal disease.

Efficacy of COX-2 inhibitors in a case of congenital nephrogenic diabetes insipidus

A 17-month-old boy presented with failure to thrive, polyuria, and vomiting. He had been diagnosed clinically with nephrogenic diabetes insipidus and treated by amiloride and hydrochlorothiazide combination without a satisfactory outcome at another center since 1 year of age. The diagnosis was confirmed by genetic analysis (AVPR2mutation), and the treatment was modified to include rofecoxib (a selective cyclooxygenase-2 inhibitor) in addition to hydrochlorothiazide and amiloride. This combination along with a low-salt diet resulted in a dramatic decrease in urinary free-water loss, while no side effect was noted. Because of prohibition of rofecoxib, it had to be substituted first by indomethacin and then by ibuprofen. However, both drugs were ineffective in controlling water diuresis. Thus, we had to replace these drugs by celecoxib (another selective cyclooxygenase-2 inhibitor). We conclude that the combination hydrochlorothiazide/amiloride/cyclooxygenase-2 inhibitor could be successfully used to treat congenital nephrogenic diabetes insipidus.

The clinical use of angiotensin-converting enzyme inhibitors

Through an integrative understanding of cardiovascular pathophysiologic characteristics at the multiorgan level, significant achievements in cardiovascular therapeutics have been achieved and enabled the rationale design and development of drugs such as the angiotensin-converting enzyme (ACE) inhibitors and angiotensin receptor blockers (ARBs). In this article, we present a detailed review of the physiologic features of the renin-angiotensin-aldosterone system (RAAS), ACE inhibitors and ARB clinical pharmacologic characteristics, and specific diseases in which they are considered to be the standard of the care as supported by important clinical trial data. It is envisioned that an updated and detailed understanding of ACE inhibitors and ARBs will facilitate their successful use in the treatment of heart failure, myocardial infarction, hypertension, renal failure, and diabetic nephropathy.

Characterization of the PGI2/IP system in cultured rat mesangial cells

Mesangial cells play an important role in glomerular function. They are an important source of cyclooxygenase (COX)-derived arachidonic acid metabolites, including prostaglandin E(2) and prostacyclin. Prostacyclin receptor (IP) mRNA was amplified from cultured mesangial cell total RNA by RT-PCR. While the prostaglandin E(2) receptor subtype EP(2) was not detected, EP(1,3,4) mRNA was amplified. Also, IP protein was noted in mesangial cells, proximal tubules, inner medullary collecting ducts, and the inner and outer medulla. But no protein was detected in whole cortex preparations. Prostacyclin analogues: cicaprost and iloprost, increased cAMP levels in mesangial cells. On the other hand, arginine-vasopressin and angiotensin II increased intracellular calcium in mesangial cells, but cicaprost, iloprost and prostaglandin E(2) had no effect. Moreover, a 50% inhibition of cicaprost- and iloprost-cAMP stimulation was observed upon mesangial cell exposure to 25 and 35 mM glucose for 5 days. But no change in IP mRNA was observed at any glucose concentration or time exposure. Although 25 mM glucose had no effect on COX-1 protein levels, COX-2 was increased up to 50%. In contrast, PGIS levels were reduced by 50%. Thus, we conclude that the prostacyclin/IP system is present in cultured rat mesangial cells, coupling to a cAMP stimulatory pathway. High glucose altered both enzymes in the PGI(2) synthesis pathway, increasing COX-2 but reducing PGIS. In addition, glucose diminished the cAMP response to prostacyclin analogues. Therefore, glucose attenuates the PGI(2)/IP system in cultured rat mesangial cells.

Proinflammatory cytokines enhance COX-1 gene expression in cultured rat glomerular mesangial cells

Glomerular mesangial cells (GMC) exert an essential maintaining effect on hemodynamic integrity and immune competence of the kidney through arachidonate metabolism. To clarify this, cultured rat GMC were measured for the expression and production of cyclooxygenase (COX) and excretion of prostaglandin (PG). The rat GMC spontaneously expressed type 1 cyclooxygenase (COX-1), but not COX-2. The PGE2 and thromboxane B2 (TXB2) were spontaneously produced by the cells. Interleukin (IL)-1beta (25 ng/ml), IL-8 (25 ng/ml), growth-related oncogene-alpha (GRO, 50 ng/ml) and tumor necrosis factor-alpha (TNF-alpha, 25 ng/ml) stimulated the COX-1 protein production as demonstrated by Western blot and enhanced PGE2 synthesis in GMC, beginning on 2 h of incubation, and steadily enhanced TXB2 synthesis over a 24-h period. Lipopolysaccharide (LPS, 100 ng/ml) enhanced both PGE2 and TXB2 syntheses from 2 h to at least 24 h of incubation. Collectively, the proinflammatory cytokines could enhance COX-1 but not COX-2 expression in GMC leading to increased PGE2 and TXB2 production. These biochemical events may be implicated in normal renal physiology as well as in pathogenesis of glomerular diseases.

Increased expression of cyclooxygenase-1 and -2 in the diabetic rat renal medulla

Alterations in renal prostaglandins (PGs) may contribute to some of the renal manifestations in diabetes leading to nephropathy. PG production is dependent on the activity of cyclooxygenases (COX-1 AND -2) and PG synthases. Our present study investigated levels of these enzymes in streptozotocin-diabetic rats at 2, 4, 6, and 8 wk of diabetes. Immunohistochemical analysis revealed an increase in COX signal in the inner and outer medulla of diabetic rats. This was confirmed by Western blotting, showing up to a fourfold increase in both COX isoforms at 4-6 wk of diabetes. Also, Western blot analysis revealed a sixfold increase in PGE2 synthase expression in the outer medullary region of 6-wk diabetic rats but no difference in the inner medulla. In cultured rat inner medullary collecting duct (IMCD), levels of COX were increased two- to threefold in cells exposed for 4 days to 37.5 mM glucose compared with control of 17.5 mM. While no change in PGE2 synthase levels was noted, PGE2 synthesis was increased. Furthermore, levels of EP1 and EP4 mRNA were increased, as well as a twofold increase in EP4 protein levels. Future studies will determine which COX isoform is contributing to the majority of PGE2 produced in the diabetic IMCD and the significance of these findings to disturbances in IMCD function and to the progression of diabetic nephropathy.

Differential effects of Sendai virus infection on mediator synthesis by mesangial cells from two mouse strains

BACKGROUND

Recently, we observed that the severity of glomerulonephritis in an experimental model of immunoglobulin A nephropathy (IgAN) induced by Sendai virus differs between C57BL/6 and BALB/c mouse strains. The determinants of differing renal insufficiency are not understood. In the present study, we examine the capacity for mesangial cells to support Sendai viral replication and assess the direct effects of Sendai virus on the production of selected cytokines, chemokines, and eicosanoids by mesangial cells, comparing C57BL/6 to BALB/c mouse strains.

METHODS

Sendai virus replication was measured by viral plaque assay using LLCMK2 cells. Production of cytokines [interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-alpha)], chemokines (JE and KC), and eicosanoids [prostaglandin E2 (PGE2) and thromboxane B2 (TxB2)] in culture medium was evaluated by sandwich enzyme-linked immunosorbent assay (ELISA) or competitive enzyme immunoassay (EIA) after 48 hours' incubation with infectious or inactivated Sendai virus.

RESULTS

Sendai virus replicates equally well in mesangial cells from both strains, and infection evokes increased IL-6, JE, KC, and PGE2 production in relation to viral dose. BALB/c mesangial cells produce significantly more IL-6 and JE than those from C57BL/6, and the dose response for KC is steeper in BALB/c mesangial cells than those from C57BL/6. Synthesis of PGE2 in BALB/c mesangial cells is higher than that of C57BL/6 mesangial cells, both under basal conditions and in response to infectious Sendai virus, again in a dose-dependent manner. There is no TNF-alpha or thromboxane response to viral stimulation.

CONCLUSION

We conclude that different mesangial cell responses to this common mucosal viral pathogen might influence the severity of IgAN in our model system.

Inflammation and angiotensin II

Angiotensin II (AngII), the major effector peptide of renin-angiotensin system (RAS), is now recognized as a growth factor that regulates cell growth and fibrosis, besides being a physiological mediator restoring circulatory integrity. In the last few years, a large number of experimental studies has further demonstrated that AngII is involved in key events of the inflammatory process. Here, we summarize the wide variety of AngII functions and discuss them in relation with the inflammatory cascade. AngII increases vascular permeability (via the release of prostaglandins and vascular endothelial cell growth factor or rearrangement of cytoskeletal proteins) that initiates the inflammatory process. AngII could contribute to the recruitment of inflammatory cells into the tissue through the regulation of adhesion molecules and chemokines by resident cells. Moreover, AngII could directly activate infiltrating immunocompetent cells, including chemotaxis, differentiation and proliferation. Recent data also suggest that RAS activation could play a certain role even in immunologically-induced inflammation. Transcriptional regulation, predominantly via nuclear factor-kappaB (NF-kappaB) and AP-1 activation, and second mediator systems, such as endothelin-1, the small G protein (Rho) and redox-pathways are shown to be involved in the molecular mechanism by which AngII exerts those functions. Finally, AngII participates in tissue repair and remodeling, through the regulation of cell growth and matrix synthesis. In summary, recent data support the hypothesis that RAS is key mediator of inflammation. Further understanding of the role of the RAS in this process may provide important opportunities for clinical research and treatment of inflammatory diseases.

Indomethacin protects permeability barrier from focal segmental glomerulosclerosis serum

BACKGROUND

Eicosanoids are believed to play a role in the pathophysiology of several models of glomerular disease. The cyclooxygenase inhibitor indomethacin reduces proteinuria in patients with focal segmental glomerulosclerosis (FSGS) or other glomerular diseases. We have shown that sera of some patients with FSGS significantly increase glomerular albumin permeability (Palb) in an in vitro assay.

METHODS

To determine the role of eicosanoids in the increased Palb caused by the FSGS factor, glomeruli were isolated from normal rats, preincubated with indomethacin, then incubated with FSGS serum or normal serum and Palb was calculated. To study the direct effect of individual eicosanoids on Palb, glomeruli were incubated with prostaglandin E2, prostaglandin F2alpha or a thromboxane A2 mimetic, and Palb was calculated. In the final set of experiments, normal glomeruli were preincubated with the thromboxane synthase inhibitor furegrelate, incubated with FSGS serum, and Palb was calculated.

RESULTS

Preincubation of isolated glomeruli with either the cyclooxygenase inhibitor indomethacin or the thromboxane synthase inhibitor furegrelate protected glomeruli from the increase in Palb caused by FSGS serum. Each of the three principal glomerular eicosanoids significantly increased Palb of isolated glomeruli.

CONCLUSIONS

These studies implicate a product of the cyclooxygenase pathway of arachidonic acid metabolism as mediating the increased Palb caused by FSGS serum in our in vitro assay and possibly the proteinuria seen in patients with FSGS.

Antiproliferative effect of nitric oxide on rat glomerular mesangial cells via inhibition of mitogen-activated protein kinase

The effect of nitric oxide (NO) donors and lipopolysaccharide (LPS) on the proliferation of rat glomerular mesangial cells was characterized. Exogenous application of a NO donor inhibited serum-induced proliferation in a time- and dose-dependent manner. S-Nitrosoglutathione (GSNO) also increased cGMP generation and arachidonic acid release, but it did not cause any measurable increase in the cytosolic Ca2+ concentration. Chelation of cytosolic Ca2+ or inhibition of mitogen-activated protein kinase (MAPK) kinase had an inhibitory effect on proliferation, but neither enhanced the antiproliferative effect of GSNO. In contrast, inhibition of guanylate cyclase or phospholipase A2 had no effect on proliferation, but partially reversed GSNO-induced antiproliferation by approximately 98 and 65%, respectively. GSNO did not cause cell death. Incubation of cells with LPS induced endogenous NO generation and had an antiproliferative effect. LPS-induced antiproliferation was reversed completely by inhibition of nitric oxide synthase and partially by inhibition of guanylate cyclase or phospholipase A2. GSNO or LPS inhibited serum-induced MAPK activation, and both effects were partially reversed by inhibition of guanylate cyclase or phospholipase A2. Inclusion of 8-bromo-cGMP or arachidonic acid in the growth medium resulted in a similar antiproliferative effect. In conclusion, in rat glomerular mesangial cells, MAPK inhibition and an antiproliferative effect could be induced by either an increase in the cellular concentration of NO or exposure of the cells to LPS. Part of the effect of NO was attributable to the increased cellular cGMP generation and arachidonic acid release.

Sodium-coupled glucose transporter as a functional glucose sensor of retinal microvascular circulation

To clarify the function of the Na(+)-coupled glucose transporter in the regulation of cellular tone of cultured retinal pericytes, we investigated the effects of extracellular glucose concentration on cell size. The surface area and diameter of cultured bovine retinal pericytes under different glucose concentrations were measured by using a light microscope with a digital camera. We also examined the effects of extracellular Na(+) and Ca(2+), inhibitors of the Na(+)-coupled glucose transporter and Na(+)-Ca(2+) exchanger, a Ca(2+) channel blocker, and nonmetabolizable sugars on cell size. The surface area and diameter of the cells changed according to extracellular glucose concentrations. alpha-Methyl glucoside, which enters the cell through the Na(+)-coupled glucose transporter, induced cellular contraction. However, the cells did not contract in response to 2-deoxyglucose, which enters the cell through a facilitated glucose transporter. Glucose-induced cellular contraction was abolished in the absence of extracellular Na(+) and Ca(2+). Moreover, phlorizin, an inhibitor of the Na(+)-coupled glucose transporter, and 2',4'-dichlorobenzamil-HCl, an inhibitor of the Na(+)-Ca(2+) exchanger, also abolished glucose-induced cellular contraction, whereas nicardipine, a Ca(2+) channel blocker, did not. Our results indicate that high extracellular glucose concentrations induce contraction of bovine retinal pericytes via Na(+) entry through a Na(+)-coupled glucose transporter, suggesting that the Na(+)-coupled glucose transporter may act as a functional glucose sensor of retinal microvascular circulation.>

Role of prostanoids and endothelins in the prevention of cyclosporine-induced nephrotoxicity

Cyclosporine A nephrotoxicity includes both functional toxicity and histological changes, whose seriousness is dependent upon the dose and the duration of the drug administration. Several vasoactive agents have been found to be implicated in cyclosporine induced nephrotoxicity, among which prostanoids and endothelins are the most important. In previous studies we were able to prevent the early stage (7 days) of cyclosporine (37.4 micromol [45 mg]/kg/day) induced nephrotoxicity in rats either by the administration, i) of OKY-046, a thromboxane A(2)synthase inhibitor, ii) of ketanserine, an antagonist of S(2)serotonergic, a(1)adrenergic, and H(1)histaminergic receptors and iii) of nifedipine, a calcium channel blocker, or by diet supplementation either with evening primrose oil or fish oil. All these protective agents elevated ratios of excreted renal prostanoid vasodilators (prostaglandins E(2), 6ketoF(1 alpha)) to vasoconstrictor (thromboxane B(2)), a ratio which was decreased by the administration of cyclosporine alone. Nifedipine averted the cyclosporine induced increase of urinary endothelin-1 release. All protections were associated with the reinstatement of glomerular filtration rate forwards normal levels whereas renal damage defence, consisting of a decrease of the cyclosporine induced vacuolizations, was variable. Ketanserine and evening primrose oil were the only agents which prevented the animal body weight loss. These data suggest that prostanoids and endothelin-1 may mediate functional toxicity while thromboxane A(2)is involved the morphological changes too, provoked in the early stage of cyclosporine treatment. However, other nephrotoxic factors and additional mechanisms could also be implicated in the cyclosporine induced nephrotoxicity.

Hydrogen peroxide increases extracellular matrix mRNA through TGF-beta in human mesangial cells

BACKGROUND

Reactive oxygen species (ROS) are excessively produced in pathologic states, including many renal diseases. Transforming growth factor-beta (TGF-beta) may mediate renal fibrotic injury, and ROS may act through the TGF-beta pathway to exert a profibrotic effect.

METHODS

The expression of TGF-beta1 and extracellular matrix (ECM) components were assessed in cultured human mesangial cells (HMCs) incubated with glucose oxidase (GO), an enzyme that continuously generates hydrogen peroxide from glucose. A neutralizing anti-TGF-beta antibody was added to test the hypothesis that hydrogen peroxide acts through activation of the TGF-beta pathway to stimulate ECM expression.

RESULTS

Northern blot analysis revealed significantly increased steady-state levels of TGF-beta1 and ECM proteins (collagen types I, III, and IV, and fibronectin) by approximately twofold. While no significant effect on mRNA stability after treatment with GO was observed, other studies employing promoter-reporter assays, competitive-quantitative reverse transcription-polymerase chain reaction, mink lung epithelial cell proliferation assay, and TGF-beta1 enzyme-linked immunosorbent assay all demonstrated significant stimulation by GO (>1.5-fold) of TGF-beta1 promoter activity, mRNA level, bioactivity, and protein production, respectively. Catalase pretreatment prevented the GO-induced stimulation of TGF-beta1 mRNA. When incubations were performed with a panselective neutralizing anti-TGF-beta antibody, the GO-stimulated expression of ECM molecules was prevented.

CONCLUSIONS

GO-induced hydrogen peroxide production induces TGF-beta1 synthesis and thereby increases ECM gene expression in cultured HMCs. These cellular responses may underlie the development and progression of renal diseases characterized by oxidative stress.

Indomethacin inhibits endothelial cell proliferation by suppressing cell cycle proteins and PRB phosphorylation: a key to its antiangiogenic action?

Nonsteroidal anti-inflammatory drugs (NSAIDs) inhibit angiogenesis in vivo and in vitro, but the mechanism of this action is unclear. Angiogenesis-formation of new capillary vessels-requires endothelial proliferation, migration, and tube formation. It is stimulated by basic fibroblast growth factor (bFGF) and vascular endothelial growth factor (VEGF). The cell cycle is regulated positively by cyclins and negatively by cyclin-dependent kinase inhibitors (CKI) and the retinoblastoma protein (pRb). Since the effects of NSAIDs on cell cycle-regulatory proteins in endothelial cells remain unknown, we examined the effect of indomethacin on bFGF-stimulated endothelial cell proliferation and on cell cycle regulatory proteins in rat primary aortic endothelial cells (RAEC). Indomethacin significantly inhibited basal and bFGF-stimulated endothelial cell proliferation. This inhibition correlated significantly with reduced cyclin D1 and increased p21 protein expression. Furthermore, indomethacin reduced pRb phosphorylation. These findings suggest that indomethacin arrests endothelial cell proliferation essential for angiogenesis by modulating cell cycle protein levels.

Inhibition of angiogenesis by nonsteroidal anti-inflammatory drugs: insight into mechanisms and implications for cancer growth and ulcer healing

Angiogenesis, the formation of new capillary blood vessels, is essential not only for the growth and metastasis of solid tumors, but also for wound and ulcer healing, because without the restoration of blood flow, oxygen and nutrients cannot be delivered to the healing site. Nonsteroidal anti-inflammatory drugs (NSAIDs) such as aspirin, indomethacin and ibuprofen are the most widely used drugs for pain, arthritis, cardiovascular diseases and, more recently, the prevention of colon cancer and Alzheimer disease. However, NSAIDs produce gastroduodenal ulcers in about 25% of users (often with bleeding and/or perforations) and delay ulcer healing, presumably by blocking prostaglandin synthesis from cyclooxygenase (COX)-1 and COX-2 (ref. 10). The hypothesis that the gastrointestinal side effects of NSAIDs result from inhibition of COX-1, but not COX-2 (ref. 11), prompted the development of NSAIDs that selectively inhibit only COX-2 (such as celecoxib and rofecoxib). Our study demonstrates that both selective and nonselective NSAIDs inhibit angiogenesis through direct effects on endothelial cells. We also show that this action involves inhibition of mitogen-activated protein (MAP) kinase (ERK2) activity, interference with ERK nuclear translocation, is independent of protein kinase C and has prostaglandin-dependent and prostaglandin-independent components. Finally, we show that both COX-1 and COX-2 are important for the regulation of angiogenesis. These findings challenge the premise that selective COX-2 inhibitors will not affect the gastrointestinal tract and ulcer/wound healing.

The concept of glomerular self-defense

The balance between local offense factors and defense machinery determines the fate of tissue injury: progression or resolution. In glomerular research, the most interest has been on the offensive side, for example, the roles of leukocytes, platelets, complement, cytokines, eicosanoids, and oxygen radical intermediates. There has been little focus on the defensive side, which is responsible for the attenuation and resolution of disease. The aim of this review is to address possible mechanisms of local defense that may be exerted during glomerular injury. Cytokine inhibitors, proteinase inhibitors, complement regulatory proteins, anti-inflammatory cytokines, anti-inflammatory eicosanoids, antithrombotic molecules, and extracellular matrix proteins can participate in the extracellular and/or cell surface defense. Heat shock proteins, antioxidants, protein phosphatases, and cyclin kinase inhibitors may contribute to the intracellular defense. This article outlines how the glomerulus, when faced with injurious cells or exposed to pathogenic mediators, defends itself via the intrinsic machinery that is brought into play in resident glomerular cells.

Cyclooxygenase inhibition reveals synergistic action of vasoconstrictors on mesangial cell growth

Since endogenous vasoconstrictors promote mesangial cell growth and increase the biosynthesis of antiproliferative prostaglandins, the effects of cyclooxygenase inhibition on mesangial cell proliferation should be strongly dependent on the prevailing levels of neuroendocrine vasoconstrictors. We compared the effects of indomethacin (10(-6) M), a cyclooxygenase inhibitor, on [3H]thymidine incorporation by cultured rat mesangial cells in the presence of various combinations of angiotensin II (10(-10) M), [Arg8]vasopressin (10(-11) M), (-)-norepinephrine (10(-8) M) and endothelin-1 (10(-11) M). Indomethacin did not enhance [3H]thymidine incorporation in cells treated with each individual vasoconstrictor, or in cells treated with two-way combinations with the exception of modestly increased [3H]thymidine incorporation in cells treated with angiotensin II + (-)-norepinephrine or [Arg8]vasopressin + (-)-norepinephrine. In contrast, in cells treated with any three-way or the four-way combination, indomethacin markedly increased [3H]thymidine incorporation. Importantly, a highly significant interaction (P<0.0001) was observed for thymidine incorporation between the number of vasoconstrictors present and indomethacin treatment, thus demonstrating that cyclooxygenase inhibition reveals a synergistic action of vasoconstrictors on the DNA synthesis in mesangial cells.

Desmopressin versus indomethacin treatment in primary nocturnal enuresis and the role of prostaglandins

OBJECTIVES

To compare the efficacy of desmopressin and indomethacin and also determine the prostaglandin E2 (PGE2) concentrations in the patient and control groups.

METHODS

Eighty-five children with primary nocturnal enuresis were followed up for a baseline period of 4 weeks, during which they recorded wet and dry nights. After this period, the patients were divided into three groups that used desmopressin, indomethacin, or placebo for 4 weeks. The dosage of desmopressin (group A, n = 31 ) was 20 microg/day and the dosage of indomethacin (group B, n = 29) was 100 mg/day. The placebo group (group C) consisted of 25 patients. We determined the serum PGE2 and urine PGE2 concentrations before and after treatment in the three groups and in a control group.

RESULTS

Treatment with desmopressin and indomethacin resulted in significantly more dry nights during the 4 weeks of observation than did placebo (P <0.005). The number of dry nights was also significantly different in the desmopressin group than in the indomethacin group (P <0.01). In the total patient group, the mean serum and urine PGE2 concentrations were significantly different from the control group's serum and urine PGE2 concentrations (P <0.001). There was a significant decrease in the serum and urine PGE2 concentrations in group A and group B after the treatment period (P <0.01).

CONCLUSIONS

Desmopressin and indomethacin were found to be more effective than placebo. We conclude that prostaglandins have an important role in the pathophysiology of primary nocturnal enuresis.

Ca2+ signaling induced by sphingosylphosphorylcholine and sphingosine 1-phosphate via distinct mechanisms in rat glomerular mesangial cells

BACKGROUND

To elucidate the molecular mechanism underlying sphingosine 1-phosphate (S1P) and sphingosylphosphorylcholine (SPC) mediated signaling, we compared their effects with those of adenosine triphosphate (ATP) and angiotensin II (Ang II) on the cytosolic free Ca2+ concentration ([Ca2+]i), inositol 1,4, 5-trisphosphate (IP3) generation and arachidonic acid release in rat glomerular mesangial cells.

METHODS

The fluorescent Ca2+ indicator, Fura-2, was used to measure the [Ca2+]i changes in cultured rat glomerular mesangial cells either in suspension or attached to the coverslips.

RESULTS

SPC 5 microM, S1P 5 microM, ATP 100 microM and Ang II 90 nM all induced increases in the [Ca2+]i, and the effect showed marked homologous desensitization, while heterologous desensitization was less. After the initial exposure of the cells to SPC, the increase in [Ca2+]i induced by subsequent addition of ATP or Ang II was only reduced by about 14.3% and 4.8%, respectively. After the initial exposure to S1P, a greater reduction was seen (42. 1% and 47.7%, respectively). Both arachidonic acid release and IP3 generation were activated by all four agonists with an identical rank order of effectiveness of SPC >> S1P > ATP = Ang II; both were pertussis toxin-sensitive and cholera toxin-resistant. The arachidonic acid release induced by all four agonists showed identical susceptibility to removal of extracellular Ca2+, whereas IP3 generation displayed differential extracellular Ca2+ dependence. Only SPC-induced IP3 generation was highly sensitive to extracellular Ca2+ level, and this Ca2+ dependence was abolished after pretreatment of cells with arachidonyl trifluoromethyl ketone (AACOCF3), a phospholipase A2 inhibitor. Furthermore, the Mn2+ influx was markedly greater in SPC-stimulated cells than in either control or other agonist-stimulated cells, and was decreased by prior exposure of cells to AACOCF3. After phospholipase A2 was inhibited or in the absence of extracellular Ca2+, SPC displayed identical effectiveness as S1P on desensitizing the action of ATP or Ang II on the increase in [Ca2+]i. Conclusions. Our results indicate that all four agents primarily activate phospholipase C through their receptor occupancies, but that SPC alone also induces further significant Mn2+ influx and IP3 generation attributable to its primary stimulatory effect on arachidonic acid release. Thus, the heterologous desensitization to ATP or Ang II induced by SPC was less profound than that induced by S1P, since SPC induced a Ca2+ influx.

Amelioration of polyuria in nephrogenic diabetes insipidus due to aquaporin-2 deficiency

OBJECTIVE

We have recently reported a large cluster of patients with nephrogenic diabetes insipidus (NDI) due to an autosomal recessive aquaporin-2 (AQP-2) early-stop codon. This paper describes the clinical manifestations and evaluation of therapeutic approaches to this new entity.

PATIENTS AND DESIGN

Nine patients with an AQP-2 mutation were studied. Urine osmolality was measured in five patients before and at 3 x 30 min intervals after desmopressin given in increasing doses of 5-100 micrograms. Urinary prostaglandins PGE2 and 6-keto PGF1 alpha, were extracted from 24-h urine samples and estimated by radioimmunoassays. Eight NDI patients were given a combination of a low-sodium diet and hydrochlorothiazide. Four to 11 weeks later, ibuprofen was added, and the patients were retested within the following 4-9 weeks.

RESULTS

Urine osmolality remained unchanged after supra-pharmacological doses of desmopressin, at 60-70 mOsm/kg. Urinary PGE2 in control subjects was 0.74 +/- 0.1 microgram/g creatinine (mean +/- SD) compared to 5.0 +/- 2.6 micrograms/g creatinine in AQP-2 deficient patients (P < 0.05). Urinary 6-keto PGF1 alpha, was 0.20 +/- 0.03 microgram/g creatinine in controls and 0.75 +/- 0.31 microgram/g creatinine in AQP-2 deficiency (P < 0.05). Urinary volumes decreased by a mean 31% on a low-salt diet and hydrochlorothiazide, and by a mean of 38% on the combination therapy. Plasma osmolality decreased by a mean 15 mOsm/kg on the low-salt diet and hydrochlorothiazide, and by 22 mOsm/kg on the combination therapy. Urinary osmolality increased from a mean 80 mOsm/kg to 96 mOsm/kg on the low-salt diet and hydrochlorothiazide, and to 146 mOsm/kg on the combination therapy.

CONCLUSION

AQP-2 deficiency in these patients with an early-stop codon is associated with complete unresponsiveness of the collecting duct to vasopressin, implying an indispensable role for AQP-2 in vasopressin antidiuresis. Urinary PGE2 and 6-keto PGF1 alpha are elevated, the former being extremely high, apparently due to the extreme vasopressin unresponsiveness. Combination therapy with a combination of a low-salt diet, thiazide and non-steroidal anti-inflammatory drug is partially effective.

Renoprotective effects of nitric oxide in angiotensin II-induced hypertension in the rat

Experiments were performed in anesthetized male Sprague-Dawley rats to determine whether increased nitric oxide (NO) activity during the development of hypertension exerts a protective effect on renal cortical blood flow (CBF) and medullary blood flow (MBF). The effects of acute NO synthase inhibition on renal function and on CBF and MBF, measured by laser-Doppler flow probes, were evaluated in control and ANG II-infused hypertensive rats, prepared by the infusion of ANG II at a rate of 65 ng/min via osmotic minipumps implanted subcutaneously for 13 days. In normotensive rats (n = 8), intravenous infusion of N omega-nitro-L-arginine (NLA; 20 micrograms.100 g-1.min-1) decreased CBF by 21 +/- 4% and MBF by 49 +/- 8% and increased blood pressure from 118 +/- 1 to 140 +/- 2 mmHg. In ANG II-infused rats (n = 7), CBF and MBF decreased by 46 +/- 5% and 25 +/- 6%, respectively, during infusion of NLA. Arterial pressure increased from 160 +/- 5 to 197 +/- 7 mmHg, which was a greater absolute increase than in normotensive controls. Basal renal blood flow (RBF), estimated from p-aminohippurate clearance and hematocrit, was similar in both the control (6.0 +/- 0.5 ml.min-1.g-1) and hypertensive (6.0 +/- 0.6 ml.min-1.g-1) rats. However, NLA-induced reductions in RBF averaged 60 +/- 5% in the hypertensive rats, compared with 31 +/- 9% observed in control rats. GFR in control (0.97 +/- 0.03 ml.min-1.g-1) and hypertensive rats (0.78 +/- 0.12 ml.min-1.g-1) decreased to a similar extent during the first 30-min period of NLA infusion. GFR returned toward control levels in control rats; in contrast, GFR remained significantly decreased in the ANG II-infused rats (0.58 +/- 0.11 ml.min-1.g-1). Basal urinary sodium excretion (0.2 +/- 0.08 mueq.min-1.g-1), fractional excretion of sodium (0.3 +/- 0.13%), and urine flow (4.9 +/- 0.39 microliters.min-1.g-1) in hypertensive rats did not increase significantly after NLA treatment as occurred in normotensive controls. These data suggest that a compensatory increase in nitric oxide activity partially counteracts the vasoconstrictor influence of elevated ANG II levels to regulate renal hemodynamics and maintain cortical perfusion in the renal circulation.

Arginine vasopressin stimulates phospholipid methylation in cultured rat mesangial cells: possible role for PGE2 production

Incorporation of [3H-methyl] groups into phospholipids and prostaglandin E2 (PGE2) production in cultured rat mesangial cells were examined in the presence and absence of arginine vasopressin (AVP). In cells stimulated with AVP, a rapid increase in the incorporation of [3H-methyl] group into phospholipids was observed within 1 min after stimulation. The [3H-methyl] group present in the phospholipids began to decline 2.5 min after stimulation. The production of PGE2 increased with AVP treatment, and the decline in methylated phospholipids paralleled the release of PGE2 in AVP-stimulated cells. The inhibition of phospholipid methylation by treatment with adenosyl-S-isobutyl mercaptan (SIBA) resulted in a marked decrease in AVP-stimulated PGE2 production. In order to determine the identity of the methylated phospholipids, [3H-methyl] incorporation into phosphatidylethanolamine derivatives was examined. In AVP-stimulated cells, an increase of [3H-methyl] labeled phosphatidylcholine and lysophosphatidylcholine was observed after stimulation with AVP, followed by an apparent increase of [3H-methyl] labeled lysophosphatidylcholine. These findings indicate that AVP stimulates phospholipid methylation in cultured rat mesangial cells and phosphatidylcholine, synthesized by a transmethylation pathway, may be a source for PGE2 production.

Cellular signaling and proliferative action of AVP in mesangium of SHR: effect of low density lipoprotein

The present study was undertaken to determine whether low density lipoprotein (LDL) modulates the cellular action of arginine vasopressin (AVP) in cultured glomerular mesangial cells of spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto rats (WKY). The AVP-induced cellular signal transduction, including inositol 1,4,5-trisphosphate (IP3) production, fura-2 intracellular calcium measurements and cellular alkalinization, was significantly greater in cells of SHR than those of WKY. This is based on an increase in AVP V1 receptor number in cells of the SHR. Also, the AVP activation of mitogen-activated protein (MAP) kinase and [3H]thymidine incorporation was significantly exaggerated in cells of SHR compared with those of WKY. LDL at a concentration of 10 micrograms/ml augmented the cellular signaling and proliferative action of AVP in cells of WKY, but not in those of SHR. Since [3H]AVP receptor binding was not affected by the LDL pretreatment, LDL modulates the signal transduction between a location distal to the AVP receptors and proximal from the production of IP3 and diacylglycerol. These results indicate that an increase in AVP receptor capacity has a profound effect on the AVP-induced cellular signaling and proliferation, and that LDL has a slight alteration on the action of AVP in glomerular mesangial cells of SHR.

Vasodilation induced by vasopressin V2 receptor stimulation in afferent arterioles

We have previously reported that vasopressin (AVP) V2 receptor stimulation increased renal blood flow in dogs anesthetized with pentobarbital. In this study, we examined the direct effects of AVP on afferent arterioles to clarify the role played by V2 receptors in regulating afferent arteriolar tone. We microdissected a superficial afferent arteriole with glomerulus from the kidney of a New Zealand White rabbit. Each afferent arteriole was cannulated with a pipette system and microperfused in vitro at 60 mm Hg. The effects of vasoactive substances were evaluated by changes in the lumen diameter of afferent arterioles. We found that AVP decreased the lumen diameter of microperfused afferent arterioles dose-dependently and that a V1 antagonist, OPC21268, inhibited the vasoconstrictor action of AVP. However, AVP 10(-8) M increased the lumen diameter of norepinephrine (NE)-constricted afferent arterioles pretreated with OPC21268 (OPC + NE, 8.2 +/- 0.7 microns; OPC + NE + AVP, 9.9 +/- 0.9 microns*; *P < 0.05, N = 13). This vasodilatory effect of AVP was abolished by pretreatment with a V2 antagonist, OPC31260. Desmopressin (dDAVP), a V2 agonist, increased the lumen diameter of the NE-constricted afferent arterioles (NE, 7.4 +/- 0.9 microns; NE + dDAVP, 10.1 +/- 0.7 microns*; *P < 0.05, N = 9). These results suggest that AVP V2 receptors are present in rabbit afferent arterioles and that V2 receptor stimulation induces vasodilation in rabbit afferent arterioles.

Escherichia coli verotoxin binding to human paediatric glomerular mesangial cells

Haemolytic uraemic syndrome (HUS) remains the leading cause of acute renal failure in children. Although an Escherichia coli-produced verotoxin (VT) has been implicated in the pathogenesis of HUS, the precise mechanisms of disease are not well defined. We hypothesise that the pathogenesis of renal failure in HUS includes the binding of E. coli VT to the glomerular mesangial cell, with consequent effects on renal function. Using human paediatric mesangial cells, we studied the binding and biological effects of the purified verotoxin VT-1. We isolated, purified and characterised paediatric glomerular mesangial cells. The mesangial cells were characterised by their immunoreactivity with both smooth muscle actin and vimentin antibodies, and lack of immunoreactivity with cytokeratin or factor VIII antibodies. Using an fluorescein isothiocyanate-conjugated VT (10(-7)-10(-8) M), we demonstrated specific binding to the mesangial cell membrane by immunofluorescence microscopy. We also demonstrated a dose-dependent inhibition of mesangial cell mitogenesis at concentrations from 10(-9) to 10(-17) M. Our data demonstrate that VT-1 binds to paediatric human glomerular mesangial cells and this binding results in specific biological actions, including an inhibition of cell mitogenesis.

Effects of lysophosphatidic acid, a novel lipid mediator, on cytosolic Ca2+ and contractility in cultured rat mesangial cells

Lysophosphatidic acid (LPA), the smallest and structurally simplest phospholipid, has the potential to modulate cellular signaling in diverse tissues and cell types, including fibroblasts. In the present study, we assessed the effects of LPA on cultured rat glomerular mesangial cells. Quantitative changes of [Ca2+]i in response to LPA were measured in monolayers of mesangial cells loaded with the fluorescent Ca2+ indicator fura 2. LPA (10 nmol/L to 100 mumol/L) increased [Ca2+]i in a dose-dependent manner and evoked inositol trisphosphate formation. LPA (1 mumol/L to 30 mumol/L) also elicited a marked, albeit transient, contractile response in mesangial cells cultured on collagen gel, as assessed by a decrease in cell surface area (CSA). The contraction persisted for 5 minutes (CSA decreased by 31%), whereupon the mesangial cells gradually relaxed with a consequent increase in CSA. Pretreatment of mesangial cells with isradipine (1 mumol/L), a dihydropyridine-sensitive Ca2+ channel blocker, completely blocked LPA-induced contraction. Isradipine also decreased resting [Ca2+]i levels as well as the peak and the subsequently sustained [Ca2+]i levels induced by LPA, suggesting that the contractile effects of LPA are dependent on Ca2+ entry through voltage-gated Ca2+ channels. Finally, LPA stimulated an increase in both prostaglandin E2 synthesis and cAMP accumulation, indicating that these mediators may modulate the contractile effects of LPA. Our study is the first demonstration that exogenous LPA induces mesangial cell contraction and suggests that the contraction is mediated by mobilization of intracellular Ca2+ by activation of the phosphoinositide cascade as well as by promotion of Ca2+ entry across the plasma membrane.

Inhibition of MAP kinase by prostaglandin E2 and forskolin in rat renal mesangial cells

Activation of the mitogen-activated protein (MAP) kinase pathway is believed to play a critical role in normal and pathophysiological proliferation of mesangial cells. Recent studies have shown that MAP kinase activation by growth factors in other cell types involves activation of the low-molecular-weight G protein Ras and the protooncogene serine kinase c-Raf-1. In this study, the role of this pathway in rat renal mesangial cells was assessed. Platelet-derived growth factor (PDGF), epidermal growth factor (EGF), as well as phorbol esters (PMA) rapidly activated MAP kinase three- to fourfold in these cells. PDGF and EGF, but not PMA, were able to activate c-Raf-1 and Ras activity. Stimulation of mesangial cells with the inflammatory mediator prostaglandin E2 (PGE2) or elevation of intracellular adenosine 3',5'-cyclic monophosphate (cAMP) by treatment with forskolin markedly blunted activation of MAP kinase induced by PDGF and EGF, but not by PMA. Consistent with this observation, PGE2 abolished growth factor-induced activation of c-Raf-1. However, Ras activation induced by growth factors was not affected by PGE2 and forskolin. These results suggest that MAP kinase activation can occur by at least two separate pathways in mesangial cells. Tyrosine kinase receptors activate MAP kinase through activation of Ras and Raf. This pathway can be blocked by PGE2 and elevation of cAMP, presumably by interfering with the ability of Ras to activate Raf. In addition, activation of protein kinase C by phorbol esters can activate MAP kinase in a Ras/Raf-independent manner.(ABSTRACT TRUNCATED AT 250 WORDS)

Rat kidney thromboxane receptor: molecular cloning, signal transduction, and intrarenal expression localization

Thromboxane (TX) plays important roles in control of renal hemodynamics and water and electrolyte metabolism, and is involved in the pathophysiology of many renal diseases. The aim of the present study is to isolate a rat kidney cDNA encoding functional TX receptor, and to reveal its intrarenal expression localization. A clone (rTXR2) was isolated from a rat kidney cDNA library by a homology screening approach. rTXR2 was shown to encode the amino acid sequence containing seven transmembrane spanning domains representing rat (r) TX receptor. The membrane from COS-7 cells transiently transfected with rTXR2 cDNA was shown to be specifically bound by a thromboxane receptor antagonist, SQ29548. Either in Xenopus oocyte expression or in transfected COS-7 cells, rTX receptor was shown to be linked with Ca2+ messenger system. TX receptor-mediated increase in cytosolic Ca2+ was also observed in cultured glomerular mesangial cells. In situ hybridization showed that rTX receptor mRNA was detected in renal glomeruli, smooth muscle cells in renal arterioles, and transitional cell epithelium of renal pelvis. Reverse transcription linked to PCR applied to microdissected nephron segments indicated the presence of rTX receptor mRNA exclusively in the glomerulus. In conclusion, we have cloned a functional rat kidney TX receptor, which is expressed specifically in renal glomerulus, arterial smooth muscle cells, and transitional cell epithelium of renal pelvis. The present study will provide important insights into the etiology and pathophysiology of renal diseases with relation to TX metabolism.

Thromboxane A2 and platelet-activating factor decrease in the platelet-mesangial cell interactions

To analyze the metabolisms of platelet-activating factor (PAF) and Thromboxane A2 (TxA2) when platelets and mesangial cells (MC) interact, immunoreactive thromboxane B2 (TxB2) and PAF were measured after incubation of cultured rat MC with platelets (P) and with platelet supernatants (PS). In both cases, TxB2 significantly decreased with respect to the P synthesis and to the PS content, suggesting an increased degradation of this metabolite or even the existence of a specific effect of MC upon platelet TxB2. When immunoreactive PAF was measured, results were comparable to those observed for TxB2. Moreover, when intrinsic mesangial cell synthesis of PAF was assessed by analyzing the [3H]-acetate incorporation by prelabeled MC in the HPLC fraction coeluting with cold PAF standards, it was possible to demonstrate that P or PS did not modify PAF synthesis in these cells. In summary, present results support the existence of a specific effect of mesangial cells upon platelet TxA2 and PAF.

Insulin nonattenuation of vasoactive agent-induced responses in mesangial cells from spontaneously hypertensive rats

We recently found that insulin attenuates intracellular calcium transients and cell contraction caused by vasoactive agents in cultured rat mesangial cells. Because altered glomerular function may be causally related to the evolution of hypertension, we examined in the present study the effects of insulin on the functions of mesangial cells derived from spontaneously hypertensive rats (SHR) of 4- and 8-weeks of age. Age-matched Wistar Kyoto rats (WKY) were used as controls. Intracellular calcium concentration ([Ca2+]i) was measured with Fura-2 method in suspended mesangial cells. Pretreatment of mesangial cells with 5 micrograms/ml insulin for 120 minutes did not affect basal [Ca2+]i in either WKY or SHR mesangial cells. However, insulin pretreatment significantly attenuated [Ca2+]i transients to vasoactive agents in WKY mesangial cells. In contrast, [Ca2+]i transients to these agents were not attenuated by insulin in SHR mesangial cells. Additionally, SHR mesangial cell contraction in response to angiotensin II (Ang II) was not altered by insulin, while WKY mesangial cell contraction to Ang II was, as in normal Wistar rats, significantly reduced by insulin. Since we previously showed the possibility that the attenuation of calcium signal by insulin is via insulin-like growth factor I (IGF-I) receptor, we also examined the effect of IGF-I. In contrast to WKY mesangial cells, IGF-I-induced attenuation of [Ca2+]i responses to platelet activating factor was absent in SHR mesangial cells. [125I]-IGF-I binding in SHR mesangial cells was not significantly different from that in WKY mesangial cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Prostaglandin F2 alpha modulates responses of single cultured mesangial cell to arginine vasopressin

The role of prostaglandin F2 alpha (PGF2 alpha) interaction with arginine vasopressin (AVP) in modulating intracellular Ca2+ homeostasis was studied. Examinations were done on single cultured mesangial cells loaded with fura-2. Pretreatment of cultured mesangial cells during 1 min with different concentrations of PGF2 alpha (10(-5)-10(-8) M) caused a significant prolongation of [Ca2+]i transients after subsequent AVP applications. The observed effect of a prolonged sustained phase was not influenced by the temporal sequence of AVP stimulation after preincubation with PGF2 alpha: the signal was modulated in nearly the same way after 5 min delay as after nearly simultaneous application of AVP and PGF2 alpha. Measurements in Ca(2+)-free medium showed that the prolonged sustained phase of [Ca2+]i transients after AVP applications in cells pretreated with PGF2 alpha was mostly due to Ca2+ release from intracellular store(s). Pretreatment of the cells with PGF2 alpha also greatly enhanced the % of AVP responsive cells. Even at concentrations of AVP as low as 10(-10) M about 30% of cells pretreated with PGF2 alpha responded with the fast [Ca2+]i rise. Thus, present studies showed that PGF2 alpha specifically modulates [Ca2+]i transients after AVP stimulation and enhances sensitivity of mesangial cells to AVP. The results help to identify PGF2 alpha participation in the cellular regulatory mechanisms of microcirculation and filtration in the kidney.

Insulin attenuates intracellular calcium responses and cell contraction caused by vasoactive agents

In the present study, we examined the effects of insulin and insulin-like growth factor I (IGF-I) on cultured rat mesangial cell responses to vasoactive agents. Intracellular calcium concentration ([Ca2+]i) was measured with the Fura-2 method in suspended mesangial cells. Pretreatment of mesangial cells with insulin (from 0.05 to 5 micrograms/ml) attenuated Ca2+ transients by platelet activating factor (PAF) in a dose dependent and a time dependent manner. Insulin also attenuated sustained elevation of [Ca2+]i elicited by PAF. Basal [Ca2+]i was not affected by insulin pretreatment. Since the effective dose of insulin (0.5 microgram/ml or higher) is much higher than the physiological concentration, the effects of insulin may be via IGF-I receptor. Indeed, IGF-I (50 ng/ml) similarly attenuated [Ca2+]i responses to PAF. Moreover, insulin pretreatment attenuated [Ca2+]i responses evoked by angiotensin II (Ang II) and endothelin-1. In addition, the pretreatment with insulin or IGF-I inhibited mesangial cell contraction in response to Ang II. The suppression of [Ca2+]i responses to vasoactive agents by insulin was abolished when extracellular Ca2+ was removed. These data suggest that insulin, probably via IGF-I receptor, attenuates [Ca2+]i responses and cell contraction of mesangial cells induced by vasoactive agents. It is likely that the change in Ca2+ influx from outside to inside the cell underlie the effect of insulin. The modification of mesangial cell function through IGF-I receptor may play a role in the regulation of glomerular hemodynamics.

Angiotensin II and renal prostaglandin release in the dog. Interactions in controlling renal blood flow and glomerular filtration rate

The relationship between angiotensin II and renal prostaglandins, and their interactions in controlling renal blood flow (RBF) and glomerular filtration rate (GFR) were investigated in 18 anaesthetized dogs with acutely denervated kidneys. Intrarenal angiotensin II infusion increased renal PGE2 release (veno-arterial concentration difference times renal plasma flow) from 1.7 +/- 0.9 to 9.1 +/- 0.4 and 6-keto-PGF1 alpha release from 0.1 +/- 0.1 to 5.3 +/- 2.1 pmol min-1. An angiotensin II induced reduction in RBF of 20% did not measurably change GFR whereas a 30% reduction reduced GFR by 18 +/- 8%. Blockade of prostaglandin synthesis approximately doubled the vasoconstrictory action of angiotensin II, and all reductions in RBF were accompanied by parallel reductions in GFR. When prostaglandin release was stimulated by infusion of arachidonic acid (46.8 +/- 13.3 and 15.9 +/- 5.4 pmol min-1 for PGE2, and 6-keto-PGF1 alpha, respectively), angiotensin II did not change prostaglandin release, but had similar effects on the relationship between RBF and GFR as during control. In an ureteral occlusion model with stopped glomerular filtration measurements of ureteral pressure and intrarenal venous pressure permitted calculations of afferent and efferent vascular resistances. Until RBF was reduced by 25-30% angiotensin II increased both afferent and efferent resistances almost equally, keeping the ureteral pressure constant. At greater reductions in RBF, afferent resistance increased more than the efferent leading to reductions in ureteral pressure. This pattern was not changed by blockade of prostaglandin synthesis indicating no influence of prostaglandins on the distribution of afferent and efferent vascular resistances during angiotensin II infusion. In this ureteral occlusion model glomerular effects of angiotensin II will not be detected, and it might well be that the shift from an effect predominantly on RBF to a combined effect on both RBF and GFR induced by inhibition of prostaglandin synthesis is located to the glomerulus. We therefore postulate that renal prostaglandins attenuate the effects of angiotensin II on glomerular surface area and the filtration barrier, and not on the afferent arterioles as previously suggested.

In vitro modulation of interleukin-1 beta secretion by cultured rat doxorubicin-stimulated whole glomeruli and dissociated mesangial glomerular cells

Doxorubicin-stimulated whole rat glomeruli and dissociated mesangial and resident glomerular macrophage cells produced the release of interleukin (IL)-1 beta cytokine. This activity increased after the addition of lipopolysaccharide (LPS) or LPS plus indomethacin to the cultures. In the presence of WEB2086 [platelet-activating factor (PAF)-acether antagonist], this activity showed a drastic reduction, without modification after sodium furegrelate (thromboxane synthetase inhibitor) was added to the cultures. Our results also demonstrate that this IL-1 beta activity is mainly produced by glomerular-resident macrophage cells. These findings support the important role by both IL-1 beta and PAF-acether mediator factors, at the cellular level, in the rat model of doxorubicin-induced nephrosis.

Effect of angiotensin II type 1 receptor antagonist on urinary prostaglandin E2 excretion following furosemide in rats

The present study was undertaken to examine an effect of an angiotensin II type 1 (AT1) receptor antagonist on urinary prostaglandin E2 (PGE2) excretion following furosemide, a loop diuretic, in rats. Furosemide (30 mg/kg) was given orally with or without pretreatment with derapril (30 mg/kg), an angiotensin converting enzyme inhibitor, TCV-116 (1 mg/kg), an AT1 receptor antagonist, or losartan (10 mg/kg), another AT1 receptor antagonist. The 6-hour urine was collected following furosemide, and the urinary excretion of PGE2 was determined. The urinary PGE2 increased significantly following furosemide alone. However, such a furosemide-induced increase was not observed with pretreatment with derapril, TCV-116 or losartan. These results suggest that the increased urinary excretion of PGE2 following furosemide is blunted by derapril, TCV-116 and losartan. As TCV-116 and losartan are selective AT1 receptor antagonists, the effect of furosemide on renal PGE2 production, as reflected by the urinary PGE2, might be mediated by an activation of AT1 receptors.

Glucose-induced protein kinase C activity regulates arachidonic acid release and eicosanoid production by cultured glomerular mesangial cells

Changes in glomerular eicosanoid production have been implicated in the development of diabetes-induced glomerular hyperfiltration and glomerular mesangial cells (GMC) are major eicosanoid-producing cells within the glomerulus. However, the mechanism for the effect of diabetes mellitus on glomerular mesangial eicosanoid production is unknown. The present study therefore examined whether elevated glucose concentrations activate protein kinase C (PKC) in GMC and whether this PKC activation mediates an effect of elevated glucose concentrations to increase the release of arachidonic acid and eicosanoid production by GMC. The percentage of [3H]arachidonic acid release per 30 min by preloaded GMC monolayers was significantly increased after 3-h exposure to high glucose (20 mM) medium (177% vs control medium) and this increase was sustained after 24-h exposure to high glucose concentrations. 3-h and 24-h exposure to high glucose medium also increased PGE2, 6-keto-PGF1 alpha, and thromboxane (TXB2) production by GMC. High glucose medium (20 mM) increased PKC activity in GMC at 3 and 24 h (168% vs control). In contrast, osmotic control media containing either L-glucose or mannitol did not increase arachidonic acid release, eicosanoid production, or PKC activity in GMC. Inhibiting glucose-induced PKC activation with either H-7 (50 microM) or staurosporine (1 microM) prevented glucose-induced increases in arachidonic acid release and eicosanoid production by GMC. These data demonstrate that elevated extracellular glucose concentrations directly increase the release of endogenous arachidonic acid and eicosanoids by GMC via mechanisms dependent on glucose-induced PKC activation.

Direct interactions between platelets and cultured rat mesangial cells

Platelets seem to be involved in the pathogenesis of some kidney diseases, but the exact relationships between platelets and the changes in renal function are incompletely known. Mesangial cells (MC) were incubated with platelet-supernatants (PS) and cellular surface area (CSA) and myosin light-chain phosphorylation (MLCP) were measured. CSA of PS-incubated MC (PS-MC) significantly diminished, as compared to control MC (70 +/- 6% vs. 100 +/- 5%). PS induced a significant increase in MLCP with respect to control cells (150 +/- 23% vs. 100 +/- 18%). When platelets were pretreated with indomethacin, the PS-dependent contraction was abolished. Pretreatment with sulotroban (SU) or BN-52021 (BN), a thromboxane A2 (TXA2) and a platelet-activating factor (PAF) receptor blocker respectively, also completely blocked the PS effects. In other experiments, platelets were activated with thrombin (T), adding the so obtained PS to MC. Moreover, cells were also preincubated with T and then added PS. No changes in CSA were observed in either case. It may be concluded that PS contracted cultured MC, and these changes could be related to the decreased glomerular filtration rate (GFR) observed in some diseases in which platelets seem to be involved. TXA2 and PAF may be responsible for this effect. In contrast, T incubation inhibited the effect of PS, perhaps through a direct relaxing effect of T in MC.

Effects of somatostatin and captopril on glomerular prostaglandin E2 production in normal and diabetic rats

Somatostatin (SRIH) has recently been shown to be effective in reversing many of the early changes of diabetic nephropathy. It is unknown whether SRIH exerts its protective effects via its ability to suppress growth hormone (GH) or via other direct renal effects. Since changes in glomerular prostaglandin (PG) E2 production are thought to be an important part of the underlying pathophysiology of diabetic nephropathy, we sought to determine if SRIH altered glomerular PG E2 production in the rat. Whole glomeruli isolated from streptozotocin-diabetic rats and from controls were incubated with either saline, captopril, or varying concentrations of SRIH, and PG E2 production was determined by direct radioimmunoassay of media. Incubation with captopril (10(-4) M) resulted in equivalent increases in PG E2 production in glomeruli from both control and diabetic rats (140.8 +/- 12.8% and 150.2 +/- 18.9% respectively). Incubation with high concentrations of SRIH (10(-6) M) also resulted in significant increases in glomerular PG E2 production in both diabetic and control rats. However, at low SRIH concentrations (10(-10) M), glomerular PG E2 production was increased only in the diabetic rats (167.0 +/- 11.4% vs 95.3 +/- 9.2% in normals). We conclude that SRIH increases glomerular PG E2 production, and that glomeruli from diabetic rats appear to be more sensitive to lower concentrations of SRIH when compared to normal rats. It is possible that this effect on PG E2 production may underlie the favorable effects of SRIH on the glomerulus in diabetes.

Thromboxane and prostacyclin differentially regulate murine extracellular matrix gene expression

Alterations in the arachidonic acid metabolites thromboxane and prostacyclin are known to contribute to hemodynamic changes observed in certain models of acute and chronic renal failure. We have previously shown that thromboxane may have an important role in mediating glomerulosclerosis by stimulating the expression of certain extracellular matrix proteins. In the present study, we compared the effects of thromboxane and prostacyclin on the expression of genes encoding basement membrane proteins using a murine teratocarcinoma cell line, that when differentiated to an endodermal phenotype synthesizes abundant extracellular matrix. Incubation of these cells with stable analogs of thromboxane and prostacyclin for four hours resulted in changes in basement membrane gene expression. Thromboxane increased steady-state mRNA levels for all three laminin chains, type IV collagen, and fibronectin, but decreased the level of mRNA for heparan sulfate proteoglycan. In contrast, incubation with carbo-prostacyclin, a stable analog of prostacyclin, decreased the steady-state mRNA level for the laminin A and B1 chains, type IV collagen and fibronectin, and increased the mRNA level for heparan sulfate proteoglycan and laminin B2. Carbo-prostacyclin did not affect cellular proliferation or thymidine incorporation. These results indicate that eicosanoids directly modulate matrix gene expression independently of hemodynamic influence, and independently of effects mediated by platelets, or mitogenesis. Furthermore, these findings suggest that the alterations in renal eicosanoid metabolism may directly participate in the pathogenesis of glomerulosclerosis and thus provide a rationale for therapy directed toward the specific inhibition of thromboxane in the treatment of progressive glomerular sclerosis.

Amplification of the arachidonic acid cascade: implications for pharmacologic intervention

The signal transduction pathway that results in prostaglandin production is thought to occur in a stepwise manner that involves agonist-stimulated action of a phospholipase that releases the second messenger arachidonic acid from membrane phospholipids. Prostaglandin endoperoxide synthase (PGH synthase) then converts arachidonic acid to the prostaglandin precursors. Further delineation of this cascade has recently occurred with the identification of two distinct prostaglandin endoperoxide synthases, PGH synthase-1 and PGH synthase-2. There is evidence that PGH synthase-1 may have broad cellular expression and may be constitutively expressed in most cells. In contrast, PGH synthase-2 expression may be more limited and has been shown to be stimulated by a variety of cytokines and growth factors. Dexamethasone inhibits the expression of an early response gene, TIS10, which is homologous to PGH synthase-2. The exact mechanism of PGH synthase-2 gene regulation in mesangial cells is unknown; however, it may be a potential site for pharmacologic intervention. Regulation of PGH synthase-2 could in turn modulate prostaglandin production and temper the production of extracellular matrix and thus scar formation that occurs in a wide variety of inflammatory renal diseases.

Effects of cicletanine on the urinary excretion of prostanoids and kallikrein, and on renal function in man

The effects of cicletanine, a new antihypertensive agent, on the prostaglandin-kallikrein system and the renin-angiotensin system were studied. A single oral dose of 200 mg cicletanine or placebo was administered to 9 healthy male volunteers, with samples of blood and urine obtained before and 2 hours after drug administration. Cicletanine increased the urine flow, urinary excretion of sodium, and fractional excretion of sodium by 47%, 115%, and 104%, respectively. While the excretion of 6-keto-prostaglandin-F1 alpha was enhanced significantly, urinary excretion of thromboxane-B2, prostaglandin-E2, and kallikrein were unchanged. Cicletanine also did not alter plasma renin activity, plasma aldosterone concentration, or creatinine clearance. These observations suggest that cicletanine may suppress sodium reabsorption at the nephron, and it may stimulate prostacyclin generation with no effect on that of thromboxane-A2. Thus cicletanine may be beneficial in the management of cardiovascular disorders in which the equilibrium between prostacyclin and thromboxane is disturbed.