Accurate placement of microvascular guide sutures

A simple technique to accurately place initial microvascular guide sutures is described. Enhanced suture placement enables anastomosis construction in situations in which the clamp must be placed very close to the vessel end or if the vessel lumen is distorted or poorly visualized. Because this technique eliminates the need for retraction on the guide suture tails, it is particularly useful for solo microvascular surgeons.

Gene therapy in the vasculature and the kidney

Gene therapy has many potential applications for the treatment of vascular disease. Though a number of tough problems remain to be solved, the potential specificity with which an almost limitless number of mechanisms could be targeted, and the success that has been achieved in animal models in vivo make it likely that we will see further rapid expansion of this technology, and therapeutic use of gene therapy in humans in the future.

Neutralizing TGF-beta1 antibody infusion in neonatal rat delays in vivo glomerular capillary formation 1

BACKGROUND

The interruption of transforming growth factor-beta (TGF-beta) signaling with dominant negative type II TGF-beta receptors in bovine glomerular endothelial cells abrogates capillary morphogenesis in vitro, and genetic defects in the TGF-beta1 signaling cascade in mice and humans result in abnormalities of blood vessel morphology. This study sought to determine whether TGF-beta1 participates in renal glomerular capillary development in vivo.

METHODS

To inhibit TGF-beta1 action, neutralizing anti-TGF-beta1 IgG was infused intra-arterially into the suprarenal aorta of three-day-old rats, and the glomerular endothelial cell appearance was evaluated two days later by immunohistochemical detection of the endothelium-specific von Willebrand factor, in situ analysis of vascular endothelial growth factor receptor binding, and morphometric study of developing glomerular structures by transmission electron microscopy.

RESULTS

The infusion of neutralizing the TGF-beta1 antibody markedly reduced the invasion of comma- and S-shaped bodies by endothelial cells, and inhibited organization of endothelial cells into capillaries in these structures. In addition, capillary lumen formation and endothelial cell fenestration in developing cortical, but not in deep, already mature glomeruli were inhibited by neutralizing TGF-beta1 antibody. Seven days after TGF-beta1 antibody infusion, glomeruli appeared normal, and no reduction in glomerular number was observed.

CONCLUSIONS

These findings suggest that TGF-beta1 plays a critical role in the formation of glomerular capillaries during renal development in the rat, and that flattening and fenestration of glomerular capillaries require the action of TGF-beta1.

Expression of SET is modulated as a function of cell proliferation

We explored a biological role of SET as it relates to cell proliferation and differentiation. Immunohistochemical staining demonstrated that the expression of SET was ubiquitous and diffuse over the whole embryo on gestational day 15. At a later stage of development, SET was expressed at relatively lower levels and localized to specific tissues and cells. On embryonic day 19, specific SET immunoreactivity was found in the epithelium of skin, respiratory tract, intestine, and retina as well as in muscle and cartilage. In these cells SET was stained mostly in the nucleus, which was supported indirectly by nuclear transport of enhanced green fluorescence protein-SET fusion proteins in ECV304 endothelial cells. Set mRNA expression was further confirmed in various cultured cells, including NIH 3T3 cells, L6 myoblast cells, human umbilical vein endothelial cells, and ECV304 cells. Using F9 teratocarcinoma cell lines, which were stimulated to differentiate into the two different cell lineages of parietal and visceral endoderm, we have further examined the role of SET. The expression of set mRNA and SET protein was diminished about three-fold in both differentiated endoderm cells compared to the undifferentiated F9 cells. However, when F9 cells were subjected to serum starvation, reduction of set mRNA abundance also took place at a similar level to that observed in response to differentiation. Consistent with this, quiescent L6 myoblast showed a marked downregulation of set mRNA compared to proliferating cells. These results suggest that SET is involved mainly in the regulation of cell proliferation rather than differentiation during embryonic development.

Chronic in vitro shear stress stimulates endothelial cell retention on prosthetic vascular grafts and reduces subsequent in vivo neointimal thickness

OBJECTIVE

The absence of endothelial cells at the luminal surface of a prosthetic vascular graft potentiates thrombosis and neointimal hyperplasia, which are common causes of graft failure in humans. This study tested the hypothesis that pretreatment with chronic in vitro shear stress enhances subsequent endothelial cell retention on vascular grafts implanted in vivo.

METHODS

Cultured endothelial cells derived from Fischer 344 rat aorta were seeded onto the luminal surface of 1.5-mm internal diameter polyurethane vascular grafts. The seeded grafts were treated for 3 days with 1 dyne/cm2 shear stress and then for an additional 3 days with 1 or 25 dyne/cm2 shear stress in vitro. The grafts then were implanted as aortic interposition grafts into syngeneic rats in vivo. Grafts that were similarly seeded with endothelial cells but not treated with shear stress and grafts that were not seeded with endothelial cells served as controls. The surgical hemostasis time was monitored. Endothelial cell identity, density, and graft patency rate were evaluated 24 hours after implantation. Endothelial cell identity in vivo was confirmed with cells transduced in vitro with beta-galactosidase complementary DNA in a replication-deficient adenoviral vector. Histologic, scanning electron microscopic, and immunohistochemical analyses were performed 1 week and 3 months after implantation to establish cell identity and to measure neointimal thickness.

RESULTS

The pretreatment with 25 dyne/cm2 but not with 0 or 1 dyne/cm2 shear stress resulted in the retention of fully confluent endothelial cell monolayers on the grafts 24 hours after implantation in vivo. Retention of seeded endothelial cells was confirmed by the observation that beta-galactosidase transduced cells were retained as a monolayer 24 hours after implantation in vivo. In the grafts with adherent endothelial cells that were pretreated with shear stress, immediate graft thrombosis was inhibited and surgical hemostasis time was significantly prolonged. Confluent intimal endothelial cell monolayers also were present 1 week and 3 months after implantation. However, 1 week after implantation, macrophage infiltration was observed beneath the luminal cell monolayer. Three months after the implantation in vivo, subendothelial neointimal cells that contained alpha-smooth muscle actin were present. The thickness of this neointima averaged 41 +/- 12 micrometer and 60 +/- 23 micrometer in endothelial cell-seeded grafts that were pretreated with 25 dyne/cm2 shear stress and 1 dyne/cm2 shear stress, respectively, and 158 +/- 46 micrometer in grafts that were not seeded with endothelial cells.

CONCLUSION

The effect of chronic shear stress on the enhancement of endothelial cell retention in vitro can be exploited to fully endothelialize synthetic vascular grafts, which reduces immediate in vivo graft thrombosis and subsequent neointimal thickness.

Expression of SET, an inhibitor of protein phosphatase 2A, in renal development and Wilms' tumor

The human gene set was originally identified as a component of the set-can fusion gene produced by a somatic translocation event in a case of acute undifferentiated leukemia. In the developing kidney, set was highly expressed in the zone of nephron morphogenesis. Recently, SET was shown to be a potent and specific inhibitor of protein phosphatase 2A, a family of major serine/threonine phosphatases involved in regulating cell proliferation and differentiation. The current study sought to define further the role of SET in the regulation of renal cell proliferation and tumorigenesis. The mRNA encoding SET was expressed at much higher levels in transformed human and rodent cell lines than in cultured renal epithelial and primary endothelial cells. Consistent with a role for SET in cell proliferation, set mRNA expression was markedly reduced in cells rendered quiescent by serum starvation, contact inhibition, or differentiation. Previous findings during renal development were extended by demonstrating that SET protein expression is also much greater in developing rat and human kidney than in fully differentiated, mature kidney. Finally, high levels of set mRNA and SET protein expression were found in Wilms' tumor, but not in renal cell carcinoma, adult polycystic kidney disease or in transitional cell carcinoma.

Shear stress and the endothelium

Shear stress and the endothelium. Vascular endothelial cells (ECs) in vivo are influenced by two distinct hemodynamic forces: cyclical strain due to vessel wall distention by transmural pressure, and shear stress, the frictional force generated by blood flow. Shear stress acts at the apical cell surface to deform cells in the direction of blood flow; wall distention tends to deform cells in all directions. The shear stress response differs, at least partly, from the cyclical strain response, suggesting that cytoskeletal strain alone cannot explain it. Acute shear stress in vitro elicits rapid cytoskeletal remodeling and activates signaling cascades in ECs, with the consequent acute release of nitric oxide and prostacyclin; activation of transcription factors nuclear factor (NF)kappaB, c-fos, c-jun and SP-1; and transcriptional activation of genes, including ICAM-1, MCP-1, tissue factor, platelet-derived growth factor-B (PDGF-B), transforming growth factor (TGF)-beta1, cyclooxygenase-II, and endothelial nitric oxide synthase (eNOS). This response thus shares similarities with EC responses to inflammatory cytokines. In contrast, ECs adapt to chronic shear stress by structural remodeling and flattening to minimize shear stress. Such cells become very adherent to their substratum and show evidence of differentiation. Increased adhesion following chronic shear stress has been exploited to generate vascular grafts with confluent EC monolayers, retained after implantation in vivo, thus overcoming a major obstacle to endothelialization of vascular prostheses.

TGF-beta type II receptor in rat renal vascular development: localization to juxtaglomerular cells

To further define the role of transforming growth factor-beta (TGF-beta) receptors in renal vascular development, detailed immunohistochemical studies of TGF-beta receptor expression were performed from gestational day 15 through adulthood. On gestational day 15, TGF-beta type II receptor immunoreactivity was restricted to perirenal stromal and vascular cells. On gestational day 17 TGF-beta type II receptor immunoreactive stromal cells were observed within the kidney, with the same distribution as stromal alpha-smooth muscle actin and renin immunoreactive cells, and intense stromal TGF-beta type II receptor immunoreactivity continued through postnatal day 5. As vascular development progressed, TGF-beta type II receptor, alpha-smooth muscle actin and renin immunoreactivity became progressively restricted to small renal arteries and arterioles. Expression of TGF-beta type II receptors and renin was very intense in afferent glomerular arterioles during postnatal days 5 to 15, and then became progressively restricted only to juxtaglomerular cells in the mature kidney. TGF-beta type I receptor (ALK-5, ALK-1 and ALK-2) immunoreactivity was not detected in stromal or vascular elements during development or in the mature kidney. Intense TGF-beta type II receptor expression in renal stromal vascular smooth muscle cell precursors and developing blood vessels suggests a role for the TGF-beta type II receptors in the formation of the renal vascular smooth muscle compartment. The continued intense expression in juxtaglomerular cells argues for a role in renin synthesis and/or release. The absence of ALK-5, ALK-1, and ALK-2 in developing vascular smooth muscle and mature juxtaglomerular cells indicates that the canonical view of TGF-beta signaling may not hold in these locations.

Successful delayed bilateral renal revascularization during active phase of Takayasu's arteritis

Successful bilateral renal revascularization was performed 24 days after the development of angiotensin converting enzyme-inhibitor-induced bilateral renal artery thrombosis and anuric acute renal failure in a patient with Takayasu's arteritis. Excellent results were obtained after an unusually long ischemic time for a patient with active-phase disease. The outcome suggests that aggressive surgical revascularization can benefit patients with renal failure caused by renal arterial occlusion during the active phase of Takayasu's arteritis.

Differential expression of transforming growth factor-beta receptors in rat kidney development

Transforming growth factor-beta 1 (TGF-beta 1) is strongly expressed during embryogenesis and in sites undergoing intense development and morphogenesis. Two receptor serine/threonine kinases (types I and II) have been identified as signal-transducing TGF-beta receptors. This study was undertaken to further explore the role of the distinct TGF-beta receptors during kidney development. The species-specific sequence information for the two T beta R-I, namely, activin receptor-like kinase-5 (ALK-5) and Tsk7L, in the rat was sought. Two full-length T beta R-I cDNAs were cloned from a neonatal rat kidney and lung libraries, and sequencing revealed that they were the rat homologs of human ALK-5 and murine Tsk7L. Both types I and II TGF-beta receptors are expressed in the kidney as determined by Northern blot analysis. T beta R-II mRNA abundance was significantly greater in the neonatal rat kidney compared with the adult rat kidney. Similarly, ALK-5 mRNA was more highly expressed in the fetal and neonatal rat kidney than the adult rat kidney. In contrast, there was no significant difference in Tsk7L mRNA abundance among the fetal, neonatal, and adult rat kidney. Thus, based on these findings, both T beta R-II and ALK-5 are developmentally regulated in the kidney. Increased expression of T beta R-II and ALK-5 proteins in the developing kidney was confirmed by immunohistochemistry. Interestingly, the two TGF-beta receptors did not entirely colocalize, raising the intriguing possibility that other TGF-beta signaling receptors may be involved.

TGF-beta and the endothelium during immune injury

During immune injury, activation of endothelial cells by inflammatory cytokines stimulates leukocyte adhesion to the endothelium, turns the endothelium from an anticoagulant surface to one that is frankly procoagulant, and results in the release of vasoactive mediators and growth factors. Cytokine activation of endothelial cells also results in increased endothelial cell TGF-beta 1 synthesis and enhanced activation of latent TGF-beta, the latter involving a shift of plasmin production from the apical to subendothelial surface. In cytokine-stimulated endothelial cells, TGF-beta hinders leukocyte adhesion and transmigration via inhibition of IL-8 and E-selectin expression. TGF-beta also profoundly diminishes cytokine-stimulated inducible nitric oxide synthase production and instead augments endothelial nitric oxide synthase expression. Thus, some of the TGF-beta actions on endothelium during immune activation can viewed as immunosuppressive. TGF-beta also influences mechanisms of vascular remodeling during the healing phase of immune injury. It stimulates PDGF-B synthesis by endothelial cells, causes bFGF release from subendothelial matrix, and promotes VEGF synthesis by non-endothelial cells. Together these mediators control angiogenesis, a critical component of the vascular repair phenomenon. Further, endothelial cell derived PDGF-B and bFGF influence the proliferation and migration of neighboring cells. Thus, endothelial cells and TGF-beta actions on the endothelium play important roles both during the initial phase of immune injury and during the later remodeling phase.

Smooth muscle cell proliferation in response to co-culture with venous and arterial endothelial cells

PURPOSE

The critical role of endothelial cells (ECs) in arterial disease is well established, but little is known of their role in venous disease. Previous studies suggest inherent differences between arteries and veins: arterial stenoses demonstrate a large lipid component, whereas hemodialysis-related venous stenoses are characterized by marked smooth muscle cell (SMC) proliferation. This study compares effects of venous versus arterial ECs on SMC proliferation in co-culture.

MATERIALS AND METHODS

Human saphenous vein ECs (HSV-ECs) or human aortic ECs (HA-ECs) were cultured on the underside of 10-micron, porous polycarbonate membranes and allowed to grow to confluence for 48 hours. After EC confluence, human aortic SMCs (HA-SMCs) were cultured on the membranes opposite the EC (day 0). On days 0, 1, 2, 4, 6, and 8, membranes were harvested (n = 3 per day), stained with Hoechst dye, and HA-SMCs were counted by fluorescence microscopy. Controls were HA-SMCs cultured alone. Comparisons were made by two-way multivariate analysis of variance.

RESULTS

During the entire 8-day period, there was significant induction of HA-SMC proliferation by both HSV-ECs (P = .0003) and HA-ECs (P = .0012). Maximal inductions were 88% +/- 11% for HSV-ECs (P = .0015) and 24% +/- 6% for HA-ECs (P = .0015). HSV-ECs exhibited a three- to ninefold greater induction than HA-ECs (P = .0003).

CONCLUSION

HSV-ECs induce adjacent HA-SMC proliferation, possibly in a paracrine manner to a significantly greater extent than HA-ECs.

Inhibition of capillary morphogenesis and associated apoptosis by dominant negative mutant transforming growth factor-beta receptors

Transforming growth factor-beta 1 (TGF-beta 1) induces angiogenesis in vivo and capillary morphogenesis in vitro. Two receptor serine/threonine kinases (types I and II) have been identified as signal transducing TGF-beta receptors. We explored the possibility of inhibiting TGF-beta-mediated events in glomerular capillary endothelial cells using a TGF-beta type II receptor (T beta R-II) transdominant negative mutant. A mutant TGF-beta type II receptor (T beta R-IIM), lacking the cytoplasmic serine/threonine kinase domain, was produced by polymerase chain reaction using rat T beta R-II cDNA as template. Since T beta R-II and TGF-beta type I receptor (T beta R-I) heterodimerize for signal transduction, the mutant receptor competes for binding to wild-type T beta R-I, hence acting in a dominant negative fashion. Glomerular capillary endothelial cells were stably transfected with T beta R-IIM, and four independent clones were expanded. That the T beta R-IIM mRNA was expressed was shown by reverse transcriptase-polymerase chain reaction, RNase protection assay, and Northern analysis. Presence of cell surface T beta R-IIM protein was shown by affinity cross-linking with 125I-TGF-beta 1. In wild-type endothelial cells, TGF-beta 1 (2 ng/ml) significantly inhibited [3H]thymidine incorporation to 63 +/- 10% of control (n = 4). In transfected endothelial cells carrying T beta R-IIM, TGF-beta 1 stimulated [3H]thymidine incorporation to 131 +/- 9% of control (n = 4, p < 0.005). Also, in wild-type endothelial cells, endogenous and exogenous TGF-beta 1 induced apoptosis and associated capillary formation. Both apoptosis and capillary formation were uniformly and entirely absent in transfected endothelial cells carrying T beta R-IIM. This represents the first demonstration that capillary morphogenesis in vitro is associated with apoptosis, and that interference with T beta R-II signaling inhibits this process in glomerular capillary endothelial cells.

Shear stress-conditioned, endothelial cell-seeded vascular grafts: improved cell adherence in response to in vitro shear stress

BACKGROUND

Prosthetic vascular grafts with adherent endothelial cell monolayers may prove useful for small-caliber vessel bypass. However, endothelial cells adhere poorly to prosthetic graft material, and they are stripped when exposed to in vivo shear stress. This study sought to determine whether in vitro shear stress conditioning improves endothelial cell adhesion and decreases thrombogenicity of endothelial cell-seeded grafts.

METHODS

The lumens of 1.5 mm (inside diameter) spun polyurethane polymer vascular grafts were seeded with bovine aortic endothelial cells and cultured in vitro for 6 days with or without continuous laminar shear stress, first at 1 to 2 dynes/cm2 for 3 days, then at approximately 25 dynes/cm2 for 3 days. Grafts preconditioned by shear stress and the static control grafts were then exposed to arterial shear stress at 25 dynes/cm2 for 25 seconds. The number of dislodged cells was counted, and the grafts were examined by light and scanning electron microscopy. Whole blood clotting time in the grafts was also determined.

RESULTS

Exposure of grafts to acute shear stress dislodged 1.35 x 10(6) +/- 0.44 x 10(6) cells from static grafts compared with 1.05 x 10(4) +/- 0.16 x 10(4) cells from grafts preconditioned by shear stress. By light and electron microscopy an intact endothelial monolayer was observed to cover the lumen of shear stress-conditioned grafts, whereas few cells remained on the luminal surface of grafts not previously exposed to shear stress. The clotting time in shear stress-conditioned grafts was significantly prolonged in relation to grafts not exposed to shear stress.

CONCLUSIONS

These findings show that endothelial cell adhesion and retention on vascular grafts in vitro is markedly enhanced by preconditioning the seeded endothelial cell monolayer with long-term shear stress. Consequently, vascular grafts containing shear stress-conditioned endothelial monolayers are less thrombogenic in vitro than small-caliber vascular grafts without intact endothelial cell monolayers.

Adhesion and differentiation of endothelial cells by exposure to chronic shear stress: a vascular graft model

Long-term patency of artificial vascular grafts for hemodialysis access and for bypass or interposition in small caliber arteries is limited due to neointimal hyperplasia and associated graft thrombosis. Given the anticoagulant and vasodilatory properties of endothelial cells, these problems could be partially overcome if grafts were seeded with an adherent monolayer of differentiated endothelial cells, prior to implantation. Endothelial cells in vivo are highly adherent and can resist disruption by hemodynamic shear stress at levels that far exceed physiological conditions. Endothelial cells in vivo also are highly differentiated, with an organized cytoskeleton, Weibel-Palade bodies, and basal stress fibers with focal adhesion plaques. In cell culture, endothelial cells rapidly lose many of their differentiated features, and endothelial cells on artificial surfaces, like vascular graft material, are not sufficiently adherent or differentiated to resist physiologic shear stress. We find that endothelial cells exposed to chronic shear stress in vitro, applied in a stepwise fashion over several days, are induced to become tightly adherent to the substratum and exhibit more differentiated features. Thus, pre-conditioning of endothelial cells seeded on vascular grafts with stepwise shear stress in vitro could be used to improve endothelial cell retention and differentiation for subsequent in vivo use.

Spatially restricted expression of set mRNA in developing rat kidney

A somatic translocation event fusing the novel gene set to the putative oncogene can has been implicated in the development of acute nonlymphocytic leukemia in humans. In this study, full-length cDNAs highly homologous with human set were cloned from a rat neonatal kidney library. The expression pattern of set mRNA was then examined in developing rat kidney. Two groups of set cDNAs (alpha and beta) with different translation initiation sites and open reading frames of 867 and 831 bp, respectively, were found. The predicted protein products are 33,385 and 32,085 Da in size and contain approximately 30% acidic residues, over half of them clustered at the COOH terminal, thus forming a long acidic tail. No signal peptide or membrane-spanning domains were identified, suggesting an intracellular protein product. By ribonuclease protection assay, both alpha and beta variants of set were expressed in kidney. On Northern blots of total kidney RNA, 3.0- and 2.2-kb mRNAs hybridized with the labeled set cDNA probe. Expression of both transcripts was four- to eightfold greater in neonatal compared with adult rat kidney. When neonatal rat kidneys were examined for set mRNA expression by in situ hybridization with 35S-labeled riboprobe, expression was densely localized in the cortical region of morphogenesis over primitive nephron structures, including S-shaped bodies. Thus mRNA for Set, a putative intracellular protein involved in leukemogenesis, is expressed in kidney.(ABSTRACT TRUNCATED AT 250 WORDS)

Rat mesangial cell hypertrophy in response to transforming growth factor-beta 1

Central features of progressive glomerular sclerosis are initial glomerular hypertrophy and subsequent accumulation of extracellular matrix proteins. Since TGF-beta 1 may play a key role in this glomerular response to injury, the present study sought to explore further TGF-beta 1 actions and regulated expression of its receptor in rat mesangial cells. The rat TGF-beta type II receptor (TGF-beta RII) homolog was cloned by screening a rat kidney cDNA library with a human TGF-beta RII cDNA probe, and sequenced. Expression of this receptor subtype in rat mesangial cells was then demonstrated by RNase protection assay, and by Northern blot analysis of poly (A)+ RNA, TGF-beta RII expression was down-regulated in cells treated with exogenous TGF-beta 1. Affinity cross linking studies demonstrated presence of this receptor on cell surface. Rat mesangial cells also expressed TGF-beta 1 and autoinduction by TGF-beta 1 was observed in the same cells, suggesting that this polypeptide may act in an autocrine fashion on mesangial cells, and that it may stimulate a positive autoamplification loop. TGF-beta 1 inhibited mesangial cell proliferation and stimulated significant overall protein and collagen production. Furthermore, mesangial cell size increased in response to chronic TGF-beta 1 treatment. These findings demonstrate that rat mesangial cells express key components of the TGF-beta system and raise the intriguing possibility that in the glomerular mesangium, TGF-beta 1 may not only induce extracellular matrix synthesis, but may also participate in the process of glomerular hypertrophy in response to injury.

Expression of rat fibroblast growth factor receptor 1 as three splicing variants during kidney development

Fibroblast growth factors (FGF) are known to participate in the processes of embryogenesis and angiogenesis. This study was undertaken to examine the transcriptional and posttranscriptional regulation of the FGF receptor 1 (FGFR-1) subclass in the embryonic rat kidney. Two full-length FGF receptor cDNAs were cloned using low-stringency screening of a neonatal rat kidney library with a chicken FGFR-1 cDNA probe. Sequencing revealed these cloned cDNAs to be rat homologues of the FGFR-1 subtype, with the two clones representing splicing variants beta and gamma of the FGFR-1. Evidence for renal expression of a third splicing variant (alpha) was obtained by use of the polymerase chain reaction. Splicing variants alpha and beta of FGFR-1 are predicted to produce cell-surface FGF receptors with three and two immunoglobulin-like domains, respectively, whereas the gamma-isoform may represent an intracellular form of the receptor. Although all three splicing variants were expressed in the developing kidney at days 14, 17, and 20 of gestation, at neonatal days 1 and 7 and in mature rats the beta-isoform was present in vastly larger abundance than alpha- and gamma-isoforms at all stages studied. Northern blot analysis revealed enhanced expression of FGFR-1 in the neonatal compared with the mature kidney. It is concluded that FGFR-1 is expressed in the kidney predominantly as the beta-isoform splicing variant and that expression of this receptor is enhanced during kidney development.

Sustained activation of PGE2 synthesis in mesangial cells cocultured with glomerular endothelial cells

Glomerular endothelial cells synthesize and release endothelin-1 (ET-1), and mesangial cells, normally closely apposed to endothelial cells in vivo, respond to ET-1 with contraction, proliferation, and prostaglandin E2 (PGE2) release. This study sought to determine whether chronic coculture of mesangial cells with glomerular endothelial cells alters mesangial cell PGE2 synthesis. Mesangial cells cocultured with endothelial cells were found to release PGE2 at rates much greater than those observed in mesangial cells not cocultured with endothelial cells. This effect persisted for at least 24 h after the mesangial cells were removed from coculture with endothelial cells. The increase in basal mesangial cell PGE2 synthesis was dependent on endothelial cell-derived ET-1. Despite the increase in basal PGE2 synthesis after coculture with endothelial cells, acute ET-1-stimulated PGE2 release was markedly blunted in mesangial cells that had been cocultured with endothelial cells when compared with mesangial cells in solo-culture. This lack of responsiveness was specific for ET-1 and resulted from a profound downregulation of mesangial cell endothelin receptors. Thus coculture with endothelial cells produces two apparently opposing and ET-1-dependent effects in mesangial cells, namely a sustained increase in basal PGE2 synthesis by the cells and a loss of responsiveness to further stimulation with ET-1. It is postulated that the induction of sustained PGE2 synthesis may also occur in vivo if endothelin release from endothelial cells is stimulated and may explain, in part, the extraordinary sensitivity of some patients with glomerular disease to cyclooxygenase inhibitors.

Endothelium-derived vasoactive mediators and renal glomerular function

Glomerular endothelial cells are located in extremely close proximity to glomerular mesangial cells, without intervening basement membrane. This close apposition of the two cell types suggest that interactions between the cells should readily occur. Given that endothelial cells are known to produce mediators which regulate the tone of underlying vascular smooth muscle cells, the hypothesis that glomerular endothelial cells can produce endothelium-derived relaxation factor and the potent vasoconstrictor endothelin-1 was examined. Pure cultures of glomerular endothelial cells were established in vitro. The cells expressed a number of characteristics that identified them as endothelial cells, namely Factor VIII related antigen, angiotensin I converting enzyme, and uptake of acetylated LDL. The glomerular endothelial cells responded to the calcium-mobilizing agonists bradykinin, ATP, thrombin and platelet activating factor with a significant rise in cytosolic calcium concentrations. Under basal conditions, the glomerular endothelial cells produced a mediator pharmacologically indistinguishable from EDRF, which raised cGMP levels in co-incubated mesangial cells approximately 4 to 5-fold. The calcium-mobilizing agonists further stimulated EDRF release by glomerular endothelial cells. Glomerular endothelial cells in culture were also found to express mRNA for endothelin-1, and to secrete this peptide into their supernatant. Furthermore, the calcium-mobilizing agonists markedly stimulated endothelin-1 release by activating endothelin-1 gene transcription. Glomerular mesangial cells respond to EDRF with a rise in cytosolic cGMP concentration and relaxation, and to endothelin-1 with a rise in cytosolic calcium concentration and contraction. It is therefore proposed that local release of EDRF and endothelin-1 by glomerular endothelial cells may participate in the regulation of glomerular hemodynamics through alterations in mesangial cell contractile tone.

Regulated expression of endothelin 1 in glomerular capillary endothelial cells

Endothelin (ET)-1 is a powerful vasoconstrictor known to be produced and secreted by endothelial cells lining large vessels. Because ET-1 stimulates glomerular mesangial cell contraction, glomerular capillary endothelial cells (GEN), normally situated in close apposition to mesangial cells, were examined for potential ET expression and secretion. Cultured bovine GEN released ET in a time-dependent fashion. ET secretion was significantly stimulated by bradykinin, an agonist known to activate phospholipase C in these cells. Preproendothelin 1 (preproET-1) mRNA levels in GEN rose in a biphasic manner on stimulation with bradykinin. The early increments (at 30 min) were not dependent on new protein synthesis, whereas the late rise (6 h after addition of bradykinin) appeared to be protein synthesis dependent. Neither early or late bradykinin-stimulated preproET-1 mRNA expression in glomerular endothelial cells was due to inhibition of mRNA breakdown. Both phases of preproET-1 mRNA expression were observed with other glomerular endothelial cell calcium-mobilizing agonists, namely thrombin, and were mimicked by the calcium ionophore ionomycin. By contrast, the protein kinase C activator phorbol myristate acetate only enhanced preproET-1 mRNA expression at 30 min and suppressed expression thereafter. It is concluded that GEN have the potential to express and secrete ET-1 in a phospholipase C-regulated fashion. Furthermore, because glomerular mesangial cells respond to this peptide, the findings raise the possibility of paracrine regulation of mesangial cell tone by glomerular endothelial cell-derived ET-1.

Tumor necrosis factor alpha activates soluble guanylate cyclase in bovine glomerular mesangial cells via an L-arginine-dependent mechanism

Endothelium-derived nitric oxide (NO) causes vasodilatation by activating soluble guanylate cyclase, and glomerular mesangial cells respond to NO with elevations of intracellular guanosine 3',5'-cyclic monophosphate (cGMP). We explored whether mesangial cells can be stimulated to produce NO and whether NO modulates mesangial cell function in an autocrine or paracrine fashion. Tumor necrosis factor alpha (TNF-alpha) raised mesangial cell cGMP levels in a time- and concentration-dependent manner (threshold dose 1 ng/ml, IC50 13.8 ng/ml, maximal response 100 ng/ml). TNF-alpha-induced increases in mesangial cGMP content were evident at 8 h and maximal at 18-24 h. The TNF-alpha-induced stimulation of mesangial cell cGMP production was abrogated by actinomycin D or cycloheximide suggesting dependence on new RNA or protein synthesis. Hemoglobin and methylene blue, both known to inhibit NO action, dramatically reduced TNF-alpha-induced mesangial cell cGMP production. Superoxide dismutase, known to potentiate NO action, augmented the TNF-alpha-induced effect. Ng-monomethyl-L-arginine (L-NMMA) decreased cGMP levels in TNF-alpha-treated, but not vehicle-treated mesangial cells in a concentration-dependent manner (IC50 53 microM). L-arginine had no effect on cGMP levels in control or TNF-alpha-treated mesangial cells but reversed L-NMMA-induced inhibition. Interleukin 1 beta and lipopolysaccharide (LPS), but not interferon gamma, also increased mesangial cell cGMP content. Transforming growth factor beta 1 blunted the mesangial cell response to TNF-alpha. TNF-alpha-induced L-arginine-dependent increases in cGMP were also evident in bovine renal artery vascular smooth muscle cells, COS-1 cells, and 1502 human fibroblasts. These findings suggest that TNF-alpha induces expression in mesangial cell of an enzyme(s) involved in the formation of L-arginine-derived NO. Moreover, the data indicate that NO acts in an autocrine and paracrine fashion to activate mesangial cell soluble guanylate cyclase. Cytokine-induced formation of NO in mesangial and vascular smooth muscle cells may be implicated in the pathogenesis of septic shock.

Leukotrienes stimulate neutrophil adhesion to mesangial cells: modulation with lipoxins

We have examined polymorphonuclear neutrophil (PMN) adhesion to mesangial cells (MC) in vitro and have assessed the actions of lipoxygenase (LO) products in this process. On exposure to either leukotriene B4 (LTB4), or leukotriene D4 (LTD4), 111In-labeled PMNs adhere to monolayers of cultured MC. These actions were rapid in onset (less than 5 min) and dependent upon leukotriene concentration (10(-9) to 10(-6) M) and the presence of divalent cations. Adhesion was sustained (0-30 min), and neither LTB4 nor LTD4 was metabolized to inactive products during PMN-MC interaction, as determined by their recovery after reverse-phase high-performance liquid chromatography. LTB4 was a PMN-directed stimulus, whereas LTD4 appeared to act on MC. A monoclonal antibody (TS 1/18) against the CD18 component of the PMN CD18/CD11 adhesion complex inhibited the LTB4-induced response, indicating involvement of this PMN glycoprotein in the adhesion process. In contrast, this antibody did not affect LTD4-induced adhesion, suggesting that this response was mediated by other adhesion epitopes. When added alone, neither lipoxin A4 (LXA4) nor lipoxin B4 (LXB4) provoked PMN adhesion to MC. In contrast, LXA4 and LXB4 at equimolar concentrations attenuated the LTD4- but not LTB4-induced response. Together, these results provide further evidence that LO-derived eicosanoids may constitute important early signals that regulate PMN-MC interaction in glomerular inflammation.

pH regulation and response to AVP in A10 cells differ markedly in the presence vs. absence of CO2-HCO3-

The fluorescent pH-sensitive dye 2',7'-bis(carboxyethyl)-5,6-carboxyfluorescein (BCECF) was used to determine the effect of ambient CO2-HCO3- on the regulation of intracellular pH (pHi) and the pHi response to arginine vasopressin (AVP) in A10 vascular smooth muscle (VSM) cells. Steady-state pHi averaged 7.04 +/- 0.02 in the absence and 7.25 +/- 0.01 in the presence of CO2-HCO3-. In the absence of CO2-HCO3-, virtually all (greater than 96%) of the acid extrusion from acidification occurred by amiloride-sensitive Na(+)-H+ exchange. However, in the presence of CO2-HCO3-, acid extrusion after acidification occurred by both Na(+)-H+ exchange and 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS)-sensitive Na(+)-dependent Cl(-)-HCO3- exchange. In CO2-HCO3(-)-containing media, amiloride-sensitive Na(+)-H+ exchange mediated 85% of acid extrusion at a pHi of 6.48, but the DIDS-sensitive acid extrusion mechanism (NA(+)-dependent Cl(-)-HCO3- exchange) was the dominant acid extrusion mechanism at a pHi of 6.94. Base exited A10 cells by a DIDS-sensitive process consistent with Na(+)-independent Cl(-)-HCO3- exchange. Both amiloride- and DIDS-sensitive processes regulated steady-state pHi in CO2-HCO3-. AVP (10(-7) M) alkalinized steady-state pHi in the absence of CO2-HCO3- (delta pHi = 0.08 +/- 0.01 pH units) by stimulating Na(+)-H+ exchange; however, AVP did not alter pHi of untreated cells in CO2-HCO3- (delta pHi = -0.01 +/- 0.01 pH units) because of concomitant stimulation of Na(+)-independent Cl(-)-HCO3-exchange. We conclude that the steady-state pHi, the mechanisms of pHi regulation, and the pHi response to AVP in A10 cells are critically influenced by the presence of extracellular CO2-HCO3-. Thus the potential contribution of pHi changes to VSM cell responses to vasoactive agents should be evaluated in the presence of CO2-HCO3-.

Heterogeneity of cell surface endothelin receptors

Two distinct cell surface endothelin receptors were identified, namely a 73-kDa protein referred to as ET-R1 and a 60-kDa protein named ET-R2. ET-R1 was expressed as the sole endothelin receptor on rat A10 vascular smooth muscle cells and C6 glial cells. Binding of 125I-ET-1 to these cells was inhibited by 50-200 pM endothelin-1 and -2, whereas endothelin-3 did not compete for this receptor subtype. Binding of 125I-ET-1 to intact A10 and C6 cells was reversible, indicating that ET-R1 is located on the cell surface. Affinity labelling of a single 73-kDa band on sodium dodecyl sulfate-polyacrylamide gels by 125I-ET-1 in A10 and C6 cells was inhibited by endothelin-1 but not by endothelin-3. In A10 cells, endothelin-1 but not endothelin-3 elicited a concentration-dependent increase in intracellular inositol trisphosphate levels. ET-R1 was also expressed in cultured rat glomerular mesangial cells based on findings of a subset of receptors with an apparent molecular mass of 73 kDa that bound 125I-ET-1 displacable by endothelin-1 and endothelin-2 but not by endothelin-3. These cells also expressed the ET-R2 receptor subtype, based on findings of a 60-kDa binding site that could be labeled by both 125I-ET-1 and 125I-ET-3. Labeling of ET-R2 by the radioactive endothelins-1 and -3 was inhibited competitively by endothelins-1, -2, and -3. Furthermore, ET-R2 was shown to be a functional receptor, as endothelin-3 caused inositol trisphosphate levels to rise in mesangial cells. An endothelin binding site with high affinity for endothelin-3 was also identified on rat PC12 pheochromocytoma cells, although the apparent molecular mass of this receptor could not be verified by cross-linking studies. Since endothelin-1 or -3 failed to augment inositol trisphosphate levels in these cells, this binding site could represent a third endothelin receptor subtype. Thus, two distinct functional receptors for endothelins were identified on rat cells, namely the 73-kDa ET-R1 which has an exceedingly low affinity for endothelin-3 and the 60-kDa ET-R2 which binds endothelin-3 with high affinity. Whether an additional endothelin receptor subtype exists in PC12 cells remains to be shown with certainty.

Dopamine1-receptor blockade inhibits ANP-induced phosphaturia and calciuria in rats

Atrial natriuretic peptide (ANP) is known to enhance the excretion of Pi and Ca, solutes reabsorbed primarily by the proximal tubule. Previous studies have shown that proximal tubule Na transport is inhibited by dopamine (DA), and that the natriuretic action of ANP is blunted by DA-receptor blockade. However, alterations in Na reabsorption cannot localize ANP or DA action to a specific nephron site. Therefore, the possibility that DA mediates the apparent proximal tubule effects of ANP was investigated with the use of Pi and Ca as proximal tubule markers. ANP was infused into normal rats in the presence and absence of specific DA-receptor antagonists, and Na, Pi, and Ca excretion rates were determined. ANP enhanced Na, Pi, and Ca excretion at doses that failed to alter glomerular filtration rate and mean arterial pressure (MAP). DA1-receptor blockade significantly blunted the influence of ANP on urinary Na, Pi, and Ca excretion, whereas DA2-receptor blockade was without effect. MAP and inulin and p-aminohippurate (PAH) clearances remained stable during DA-receptor blockade. Because endogenous ANP levels are elevated in rats with remnant kidneys, and because blockade of endogenous ANP reduces Pi and Ca as well as Na excretion in this model, the effect of DA1-receptor blockade on solute excretion was also examined in rats with 5/6 nephrectomy. DA1-receptor blockade significantly reduced absolute and fractional Na, Pi, and Ca excretion in rats with 5/6 nephrectomy, in the absence of measurable changes in MAP, inulin, or PAH clearance.(ABSTRACT TRUNCATED AT 250 WORDS)

Glomerular endothelial cells respond to calcium-mobilizing agonists with release of EDRF

To determine whether glomerular endothelial cells (GEN) may play a role in the local control of glomerular function by releasing endothelium-derived relaxing factor (EDRF), the effect of several agonists on GEN cytosolic calcium concentration ([Ca2+]i) and GEN EDRF release was determined. Bradykinin, ATP, thrombin, and platelet-activating factor (PAF) all increased [Ca2+]i in GEN in a concentration-dependent manner, whereas serotonin, acetylcholine, phenylephrine, and endothelin-1 were without effect. Coincubation of glomerular mesangial cells (GMC) with GEN augmented mesangial cell guanosine 3',5'-cyclic monophosphate (cGMP) content five- to sixfold, Bradykinin elicited a further concentration-dependent increase in GMC cGMP content in the presence but not absence of GEN. The GEN-dependent bradykinin-stimulated GMC cGMP accumulation was abolished by hemoglobin and methylene blue, blunted by gossypol, and augmented by superoxide dismutase. Other agonists capable of augmenting GEN [Ca2+]i also stimulated GMC cGMP accumulation in the presence but not in the absence of GEN. Thus cultured GEN release a factor that stimulates cGMP accumulation in adjacent mesangial cells which has the pharmacological characteristics of EDRF.

Brain natriuretic peptide: interaction with renal ANP system

Brain natriuretic peptide (BNP) has recently been found in porcine brain and has been shown to cause diuresis and natriuresis when injected in rats, effects similar to those caused by atrial natriuretic peptide (ANP). BNP is also synthesized in the cardiac atria and circulates in plasma. The amino acid sequence of the peptide resembles that of ANP particularly closely within the ring structure of the peptide. We examined the potential role of BNP in modulating renal function by assessing its ability to mimic the effects of ANP on rat glomeruli and in rabbit inner medullary collecting duct cells (IMCD). BNP bound with high affinity to glomeruli (Kd approximately 900 pM) and IMCD cells (Kd approximately 500 pM). In IMCD cells, BNP stimulated particulate guanylate cyclase (approximately 3-fold at maximum ligand concentration) and inhibited conductive 22Na+ uptake by 50% at concentrations at which ANP is also effective. In rat glomeruli, BNP bound with high affinity to the low-molecular-weight receptors but with lesser affinity to the higher-molecular-weight guanylate cyclase-linked receptors (Kd approximately 50 nM). In addition, the guanosine 3',5'-cyclic monophosphate accumulation response was less impressive in glomeruli than the guanylate cyclase response in IMCD tissue. Thus we conclude that BNP is of only slightly reduced affinity and potency for the ANP receptors in the kidney and probably acts through these receptors to exert its physiological effects.

Influence of Na+ intake on dopamine-induced inhibition of renal cortical Na(+)-K(+)-ATPase

The enzyme L-amino acid decarboxylase (L-AADC), found in abundance in rat proximal tubule cell cytosol, converts L-dopa to dopamine. Dopamine, in turn, suppresses proximal tubule sodium transport by inhibiting Na(+)-K(+)-ATPase activity. We sought to determine whether changes in dietary sodium intake in rats lead to adaptation of dopamine formation and dopamine-induced Na(+)-K(+)-ATPase inhibition. In rats on a high-salt (HS) diet, the maximal velocity (Vmax) of renal cortical L-AADC was 78 +/- 19% higher than that in rats on a low-salt (LS) diet. The Michaelis constant (Km) of the enzyme remained unchanged. In renal cortical tubule cell suspensions the L-dopa-induced inhibition of ouabain-sensitive oxygen consumption (QO2) was significantly greater in rats on HS diet than in rats on LS diet. Furthermore, L-dopa completely inhibited the nystatin-induced rise in QO2 in the HS but not in the LS group. Carbidopa, an inhibitor of L-AADC, abolished the L-dopa-induced inhibition of nystatin-stimulated QO2 in cells from HS rats and was without significant effect in cells from LS rats. L-Dopa-stimulated K+ efflux was greater in cells from HS rats at 28 +/- 1 nmol.min-1.mg protein-1, compared with 7 +/- 6 nmol.min-1.ng protein-1 in cells from LS rats. By contrast, ouabain-stimulated K+ efflux did not differ between the groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Expression and regulation of ANP receptor subtypes in rat renal glomeruli and papillae

The expression and regulation of atrial natriuretic peptide (ANP) receptor subtypes were examined in rat renal glomeruli and papillae. In glomeruli, approximately two-thirds of ANP binding sites represented guanylate cyclase-uncoupled ANP clearance receptors (ANPc) with a molecular mass of 64 kDa under reducing conditions. The remainder of glomerular ANP binding sites represented guanylate cyclase-coupled ANP receptors (ANPGC) with a molecular mass of 130 kDa. In rat papillae, only the 130-kDa ANPGC was expressed. In rats adapted to a low-salt diet, saline loading or acute ANP infusion resulted in a decrease in ANPC density, a difference that was not detected when glomeruli were first acidwashed to remove endogenous ANP, indicating that apparent regulation of ANPC reflected prior occupancy by endogenous ANP. Densities of glomerular ANPC and ANPGC were similar in spontaneously hypertensive rats (SHR) compared with those of the Wistar-Kyoto (WKY) controls. However, elimination of prior receptor occupancy revealed a significantly greater expression of glomerular ANPC in SHR compared with WKY rats, without significant differences in the density of the glomerular or papillary ANPGC subtype. The failure of the ANPGC subtype to be regulated may account for our previously reported findings that dietary salt intake does not affect glomerular ANP-stimulated guanosine-3',5'-cyclic monophosphate accumulation despite apparent regulation of ANP receptor density. Whether the increased expression of the ANPC subtype in SHR represents a primary defect or results from induction of ANP clearance receptor expression remains to be determined.

Identification and characterization of endothelin binding sites in rat renal papillary and glomerular membranes

The present study was designed to identify and characterize specific endothelin binding sites in membranes of rat renal papillae and glomeruli which appear to be target tissues for this new peptide hormone. Saturation binding studies indicate that the sites have a high and uniform affinity. The dissociation constants averaged 662 +/- 151 and 1309 +/- 123 pM and the receptor densities 7666 +/- 920 and 5831 +/- 348 fmol/mg protein for papillary and glomerular membranes, respectively. Endothelin 1, endothelin 3 and sarafotoxin all inhibited [125I]-endothelin binding with IC50's in the 100-300 pM range, whereas unrelated peptides, namely angiotensin II, atrial natriuretic peptide, and platelet-derived growth factor failed to compete for [125I]-endothelin binding. Deletion of the carboxyterminal tryptophan in endothelin 1 reduced its affinity for glomerular binding sites by 2 orders of magnitude. Specific endothelin binding to these membranes was maximal at pH 4 and was markedly inhibited as the pH was raised above 8. When [125I]-endothelin is covalently linked to glomerular membrane binding sites, SDS-PAGE of these solubilized membranes followed by autoradiography reveals a predominant specifically labeled band of 45 kDa. Whether this band represents a subunit of the endothelin receptor(s), the receptor proper, or an intracellular endothelin binding protein remains to be determined.

Endothelin action on vascular smooth muscle involves inositol trisphosphate and calcium mobilization

Cultured endothelial cells release a potent vasoconstrictor peptide, endothelin. Cumulative addition of synthetic endothelin to isolated rabbit aortic rings elicited a concentration-dependent increase in contractile tension which was endothelium-independent. In cultured rabbit vascular smooth muscle cells loaded with the fluorescent dye fura 2, endothelin induced a concentration-dependent increase in [Ca2+]i over the range of 0.01 to 100 nM. Moreover, in the absence of extracellular Ca2+, endothelin could still induce an increase in [Ca2+]i. In addition, endothelin stimulated 45Ca2+ efflux from preloaded vascular smooth muscle cells in the presence and absence of extracellular Ca2+, as well as stimulating 45Ca2+ influx in a concentration-dependent manner. Measurement of inositol phosphates in [3H]-myoinositol-labelled vascular vascular trisphosphate. Unlabelled endothelin inhibited (125I)-endothelin binding to cultured rabbit vascular smooth muscle cells in a concentration-dependent manner. Binding was not inhibited by other vasoactive hormones or calcium channel ligands, suggesting cell surface receptors specific for endothelin. We conclude that one of the initial membrane events in the action of endothelin is to induce phospholipase C-stimulated PIP2 hydrolysis and that this signalling mechanism is initiated by endothelin/receptor interaction at the plasma membrane.

Regulation of bovine glomerular endothelial cell growth in vitro

To enable the study of glomerular endothelial cell functions and interactions with other glomerular cells, bovine glomerular capillary endothelial cells were established in culture. Selective media were used to facilitate endothelial cell proliferation and to suppress glomerular mesangial cell growth. Glomerular endothelial cells were separated from other cell types by fluorescence-activated cell sorting or, alternatively, by cloning. Glomerular endothelial cells expressed angiotensin I-converting enzyme and factor VIII activity and acetylated LDL uptake, properties generally held to be specific for endothelial cells. Proliferation of subconfluent glomerular endothelial cells was stimulated by basic fibroblast growth factor and, in the presence of heparin sodium, by acidic fibroblast growth factor. Platelet-derived growth factor was without effect on glomerular endothelial cell proliferation. Coculture with mesangial cells markedly inhibited proliferation of subconfluent glomerular endothelial cells. By contrast, medium conditioned by confluent glomerular endothelial cells markedly enhanced proliferation of subconfluent glomerular endothelial cells. These findings suggest that glomerular endothelial cell growth is under autocrine and paracrine control.

Characterization and regulation by protein kinase C of renal glomerular atrial natriuretic peptide receptor-coupled guanylate cyclase

The nature and regulation of atrial natriuretic peptide (ANP)-sensitive guanylate cyclase in rat renal glomerular membranes was examined. By affinity crosslinking techniques, three bands with apparent molecular masses of 180, 130 and 64 kDa were specifically labeled with [125I]ANP. A specific antibody to the 180 kDa membrane guanylate cyclase of rat adrenocortical carcinoma recognized a 180 kDa band on Western blot analysis of solubilized, GTP-affinity purified glomerular membrane proteins. The same antibody completely inhibited ANP-stimulated guanylate cyclase activity in glomerular membrane fractions. Partially purified protein kinase C inhibited ANP-stimulated guanylate cyclase activity in glomerular membrane fractions. It is concluded that a 180 kDa ANP-sensitive guanylate cyclase is present in glomerular membranes, and that this enzyme is inhibited directly by protein kinase C.

Endogenous ANP augments fractional excretion of Pi, Ca, and Na in rats with reduced renal mass

Atrial natriuretic peptide (ANP) infusion increases fractional excretion of many solutes including sodium, chloride, bicarbonate, phosphate, calcium, and magnesium. Because fractional excretion of these solutes increases with advancing renal disease, and because plasma ANP levels are known to be elevated in chronic renal failure, we sought to determine whether ANP mediates increased solute excretion rates per nephron in rats following extensive renal ablation, a model of chronic renal failure. Because sodium restriction decreases plasma ANP levels in the setting of reduced renal mass, we also determined the effect of sodium restriction on sodium, phosphate, calcium, and magnesium excretion rates in rats with 5/6 nephrectomy (NX). We also assessed whether high endogenous ANP levels influence fractional sodium, phosphate, calcium, and magnesium excretion in rats with 5/6 NX, by inhibiting ANP action via infusion of a high-affinity ANP antiserum. Whole-kidney glomerular filtration rate in 5/6 NX rats averaged approximately one-third that of shams, and plasma ANP levels were significantly elevated in these rats above those of shams, but to a lesser extent in rats on low- vs. high-salt intakes. Fractional sodium, phosphate, and calcium, but not magnesium excretion rates were significantly greater in 5/6 NX rats on the higher sodium intake compared with those in 5/6 NX rats on the lower sodium intake. Moreover, in 5/6 NX rats on the higher sodium intake, ANP antiserum significantly reduced fractional sodium, phosphate, and calcium excretion, but was without effect on magnesium excretion. These data implicate endogenous ANP in promoting the adaptive increase in sodium, phosphate, calcium, but not magnesium excretion per nephron in chronic renal disease.

Locally formed dopamine inhibits Na+-K+-ATPase activity in rat renal cortical tubule cells

Dopamine, generated locally from L-dopa, inhibits Na+-K+-ATPase in permeabilized rat proximal tubules under maximum transport rate conditions for sodium. To determine whether locally formed dopamine inhibits Na+-K+-ATPase activity in intact cortical tubule cells we studied the effect of L-dopa on ouabain-sensitive oxygen consumption rate (QO2) and 86Rb uptake in renal cortical tubule cell suspensions. L-Dopa (10(-4) M) did not affect ouabain-insensitive QO2 or mitochondrial respiration. However, L-dopa inhibited ouabain-sensitive QO2 in a concentration-dependent manner, with half-maximal inhibition (K0.5) of 5 x 10(-7) M and a maximal inhibition of 14.1 +/- 1.5% at 10(-4) M (P less than 0.05). L-Dopa also blunted the nystatin-stimulated QO2 in a concentration-dependent manner, with a K0.5 of 5 x 10(-8) M and a maximal inhibition of 21.8 +/- 1.2% at 10(-5) M (P less than 0.05), indicating that L-dopa directly inhibits Na+-K+-ATPase activity and not sodium entry. Ouabain-sensitive 86Rb uptake was also inhibited by L-dopa (16.0 +/- 2.4%, P less than 0.05). Carbidopa (10(-4) M), an inhibitor of the conversion of L-dopa to dopamine, eliminated the effect of L-dopa on ouabain-sensitive QO2 and 86Rb uptake, indicating that dopamine rather than L-dopa was the active agent. The finding that the L-dopa concentration-response curve was shifted to the left by one order of magnitude in the presence of nystatin suggests that the inhibitory effect is enhanced when the intracellular sodium concentration is increased.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of ANP receptors in rabbit inner medullary collecting duct cells

The final urinary Na+ concentration is determined in the inner medullary collecting duct (IMCD) and is under hormonal control. In suspensions of IMCD cells we have previously shown that atrial natriuretic peptide (ANP) inhibits Na+ transport-dependent O2 consumption and causes an increase in cellular guanosine 3',5'-cyclic monophosphate (cGMP) content. In this study we sought to identify and characterize the receptor for ANP in these cells. Equilibrium binding studies revealed a single class of cell surface ANP receptors of high affinity (Kd = 66.2 pM) with a total number of 3,000 sites/cell. Specificity of these receptors was shown by the rank order of binding affinities for ANP analogues: ANP-(1-28) = ANP-(4-28) greater than ANP-(5-28) much greater than ANP-(5-25). We have further defined this receptor in a solubilized cell preparation and found it to be of molecular mass 130 kDa by affinity cross linking and sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis. This is the first characterization of an epithelial cell receptor for ANP; as in other systems this receptor appears to be linked to transport processes via the production of cGMP.

Interrelationships among atrial peptides, renin, and blood volume in pregnant rats

To determine how changes in intravascular volume are sensed by atrial and renal volume receptors during pregnancy and the puerperium, circulating atrial natriuretic peptide (ANP) levels and plasma renin activity (PRA) were measured in conscious chronically catheterized rats on days 9-10, 15-16, 19-20, and 22 of pregnancy, on the first postpartum day, and in nonpregnant controls. Blood volume measured in a separate group of anesthetized rats increased progressively during pregnancy, and circulating ANP levels tended to decline, although not significantly below the nonpregnant value of 132 +/- 9 pg/ml (mean +/- SE). PRA remained similar to the nonpregnant value of 5.5 +/- 0.6 ng angiotensin I.ml-1.h-1 until day 22 of pregnancy, when it rose to 14.1 +/- 1.8 ng angiotensin I.ml-1.h-1 (P less than 0.001 vs. nonpregnant). In pregnant rats, PRA was suppressed after uninephrectomy and chronic administration of deoxycorticosterone and saline, demonstrating the ability of this hormonal system to respond appropriately to further increments in volume induced during pregnancy. On the first postpartum day plasma ANP rose to 268 +/- 26 pg/ml, and PRA fell to 3.6 +/- 0.4 ng angiotensin I.ml-1.h-1 (P less than 0.005 and P less than 0.05 vs. nonpregnant values, respectively). Thus it appears that the increased blood volume in normal pregnancy is not sensed by renal or atrial volume sensors, presumably because it is accommodated by an enlarged maternal vascular compartment. In the puerperium, however, due to the decreased size of the maternal vascular compartment, atrial and renal volume sensors recognize the intravascular volume as expanded.(ABSTRACT TRUNCATED AT 250 WORDS)

Receptors for and effects of insulin and IGF-I in rat glomerular mesangial cells

Receptors for and biological effects of insulin and insulin-like growth factor I (IGF-I) were studied in cultured rat renal mesangial cells. Specific binding of 125I-IGF was over 200-fold greater (5.8%/0.2 mg cell protein) than the specific binding of 125I-insulin (0.2%/2 mg cell protein). Fifty percent inhibition of 125I-insulin binding was obtained with 8 x 10(-9) M unlabeled insulin. For 125I-IGF-I, 50% inhibition required 1.8 x 10(-9) M unlabeled IGF-I. 125I-IGF-I was also displaced by IGF-II and insulin but at 10-and 100-fold lower potencies, respectively, than IGF-I. Cross-linking of 125I-insulin and 125I-IGF-I to their receptors, using disuccinimidyl suberate (DSS), and identification of the receptor with sodium dodecyl sulfate-polyacrylamide gel electrophoresis and autoradiography showed a band with a molecular mass of 135 kDa, probably corresponding to the alpha-subunit of the insulin receptor and a major band with a molecular mass of 145 kDa for the alpha-subunit of the IGF-I receptor. Both insulin and IGF-I stimulated the incorporation of [3H]thymidine into DNA. A half-maximal effect was obtained at 1.6 x 10(-8) M for insulin and 1.2 x 10(-9) M for IGF-I. No additive effect on DNA synthesis was observed. Insulin at 8 x 10(-10) M increased the accumulation of [14C]glucose in mesangial cells, whereas IGF-I was 10-fold less potent.

A highly sensitive radioreceptor assay for atrial natriuretic peptide in rat plasma

To enable serial measurements of plasma atrial natriuretic peptide (ANP) concentrations in the rat, a microradioreceptor assay (RRA) for this hormone was developed. Glomerular microsomes bearing ANP receptors were used to bind ANP. The smallest quantity of ANP detectable by this method was 0.2 fmol/sample. By contrast, a radioimmunoassay for ANP was sensitive to 2.4 fmol/sample. The intra- and interassay coefficients of variation for the RRA were 4.1 and 11.6%, respectively. Recovery of 10, 20, 50, and 100 pM synthetic ANP added to unextracted rat plasma was essentially 100%. Biologically inactive, synthetic amino- and carboxy-terminal ANP fragments added to rat plasma were not detected. Plasma ANP was stable when measured four consecutive times at 90-min intervals in 10 fasting rats. In a separate group of rats, fasting plasma ANP levels averaged 34 +/- 3 and rose to 57 +/- 5 pM in the postprandial state (P less than 0.001), whereas levels in fasting time controls remained constant. It is concluded that the RRA for ANP described here detects ANP in microliter quantities of unextracted rat plasma. Thus serial measurements of ANP concentrations can be undertaken in rats without inducing major changes in the volume status.

Elevated plasma atrial natriuretic peptide levels in diabetic rats. Potential mediator of hyperfiltration

Infusion of atrial natriuretic peptide (ANP) increases the glomerular filtration rate (GFR), and ANP is released from cardiac myocytes in response to extracellular fluid volume expansion. Since diabetes mellitus is associated with glomerular hyperfiltration and volume expansion, we investigated the relationship between ANP and GFR in diabetic rats given insulin to achieve stable moderate hyperglycemia or normoglycemia. At 2 wk after induction of diabetes, moderately hyperglycemic diabetic rats exhibited elevations of plasma ANP levels averaging 281 +/- 28 pg/ml vs. 158 +/- 15 pg/ml in normoglycemic diabetic rats. In hyperglycemic rats, the GFR was also elevated on average to 2.24 +/- 0.28 ml/min as compared with 1.71 +/- 0.13 ml/min in normoglycemic diabetic rats. To test further the relationship between ANP and GFR in diabetes, moderately hyperglycemic diabetic rats were infused either with a specific ANP antiserum or with nonimmune serum. The infusion of specific ANP antiserum uniformly reduced the GFR on average from 2.38 +/- 0.1 ml/min to 1.60 +/- 0.1 ml/min, whereas the infusion of nonimmune serum was without effect. It is concluded that elevated endogenous ANP levels contribute to the hyperfiltration observed in early diabetes in the rat.

Atrial natriuretic peptide and the kidney

Studies addressing the mechanisms of atrial natriuretic peptide (ANP) action within the kidney are reviewed. The magnitude of the natriuretic response to ANP initially suggested inhibition of renal sodium transport. It now appears, however, that the renal response to ANP is largely dependent on ANP-induced alterations in renal hemodynamics. At the glomerulus, ANP-induced afferent arteriolar dilatation and efferent arteriolar constriction produce a rise in the glomerular capillary hydraulic pressure and thus an increase in the filtration fraction and glomerular filtration rate. Furthermore, angiotensin II-induced increments in renal perfusion pressure markedly augment ANP-induced NaCl excretion, whereas increments in peritubular oncotic pressure or reductions in renal perfusion pressure nearly abolish this natriuretic effect, thereby suggesting that changes in the peritubular physical factors, which govern tubule fluid reabsorption, are required to elicit the natriuretic action of ANP. In addition, increments in papillary vasa recta hydraulic pressures during ANP infusion argue for an important influence of ANP on fluid exchange in the renal papilla. There also is recent evidence to suggest that ANP directly inhibits papillary collecting duct NaCl reabsorption. This action of ANP is thought to contribute to the enhanced renal excretion of sodium-rich urine in response to ANP. Finally, in two models of chronic extracellular volume expansion, namely, mineralocorticoid excess and a reduction in nephron number with a high sodium intake, endogenous plasma ANP levels increased significantly above control levels.(ABSTRACT TRUNCATED AT 250 WORDS)

Atrial natriuretic peptide transcription, secretion, and glomerular receptor activity during mineralocorticoid escape in the rat

The mechanisms that mediate renal "escape" from the sodium-retaining effects of mineralocorticoids are incompletely understood. This study was undertaken to determine whether atrial natriuretic peptide (ANP) may play a role in the escape phenomenon. Immunoreactive ANP in rat plasma increased 2.5-fold above baseline values at 12 and 24 h after a single depot injection of desoxycorticosterone acetate in oil and returned to baseline thereafter. In addition, specific pre-pro-ANP messenger RNA content in rat atria was significantly elevated as early as 12 h after mineralocorticoid administration and remained elevated at 24, 48, and 72 h, indicating a prompt and sustained increase in ANP biosynthesis. Renal glomerular ANP receptor density was down-regulated appropriately with rising plasma ANP levels, and receptor affinity was unchanged. Thus, mineralocorticoid administration in the rat is a powerful stimulus for ANP release and for atrial myocyte ANP synthesis, which suggests a potential role for this hormone in overriding mineralocorticoid-induced renal sodium retention.

George E. Brown memorial lecture. Role of atrial peptides in body fluid homeostasis

Extracts of mammalian atria, but not ventricles, induce marked diuresis, natriuresis, and reduction in blood pressure when infused systemically in rats and dogs. These extracts also inhibit aldosterone biosynthesis and renal renin release. Natriuretic peptides, 21 amino acids and longer, have been isolated from atria of rodents and man, and share a nearly homologous amino acid sequence at the carboxyterminus. Natriuretic activity resides in a 17-amino acid ring formed by a disulfide bridge, and the C-terminal Phe-Arg appears necessary for full biological potency. The deoxyribonucleic acid-encoding atrial natriuretic peptides have been cloned and the gene structure elucidated. Reduction of the diuretic and natriuretic responses to an acute volume load by right atrial appendectomy first suggested a role for atrial peptides in the physiological response to plasma volume expansion. Subsequently, release of peptides with natriuretic and spasmolytic properties from isolated heart preparations in response to right atrial distension was demonstrated by bioassay and radioimmunoassay. The presence of these peptides in normal rat and human plasma in concentrations of 20-100 pM, and the findings of increased levels in response to acute and chronic plasma volume expansion, rapid atrial tachyarrhythmias, systemic hypertension, congestive heart failure, and renal insufficiency imply that they play an important role in body fluid homeostasis. The mechanisms by which atrial peptides increase renal salt and water excretion are as yet unclear. Renal vascular effects have been consistently demonstrated, and limited evidence for direct actions on tubule ion transport has also been reported recently. In vitro, these peptides cause precontracted vascular and nonvascular smooth muscle to relax, mediated by a direct action on smooth muscle cells. Specific receptors for these peptides have been characterized in crude membranes prepared from whole kidney homogenates and adrenal glomerulosa cells, in intact glomeruli and cultured glomerular mesangial cells, and in intact bovine aortic smooth muscle and endothelial cells. Natriuretic peptides stimulate cyclic guanosine monophosphate accumulation in target tissues, and augment particulate guanylate cyclase activity in membrane fractions, suggesting that cyclic guanosine monophosphate is the second messenger mediating their cellular action.