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T M Coffman

Publications and source records attributed to T M Coffman.

At least 55 records · Page 3Linked to original sources
PubMed1999

Effects of candesartan on angiotensin II-induced renal vasoconstriction in rats and mice.

This study determined the inhibitory effect of the angiotensin II (AngII) type I (AT1) receptor blocker candesartan on renal vascular reactivity in vivo. Reactivity to AngII before and during candesartan administration was assessed by measuring (by electromagnetic or ultrasonic flowmetry) renal blood flow responses to AngII in rats and mice. AngII produced greater renal vasoconstriction in 7-wk-old, spontaneously hypertensive rats than in Wistar-Kyoto rats. After indomethacin treatment, AngII (2 ng) produced 40% reductions in renal blood flow in both rat strains, without affecting systemic arterial pressure. Coadministration of candesartan blocked AngII effects in a dose-dependent manner, with similar levels of inhibition in spontaneously hypertensive rats and Wistar-Kyoto rats; maximal inhibition was 80%. In rats that had been pretreated (for 30 min) with intravenous candesartan, AngII-induced renal vasoconstriction was inhibited dose dependently up to 98%. To evaluate receptor subtype mediation, responses were compared in mice with or without the AT1A receptor (deleted by gene targeting). Intrarenal AngII (1 ng) caused a 32% reduction of renal blood flow in wild-type mice and an 8% reduction of renal blood flow in AT1A receptor-knockout mice. Ten nanograms of AngII were required to elicit 20% renal vasoconstriction in these mutant mice. Concurrent injection of candesartan caused dose-dependent inhibition of AngII up to 80%. The candesartan IC50 values for percentage changes in renal blood flow did not differ in the two groups of mice. These studies establish that candesartan is an effective, highly selective, AT1 receptor blocker, inhibiting renal vasoconstriction in rodents in a concentration- and time-dependent manner. Candesartan effectively blocks AT1A and AT1B receptors in renal resistance vessels of rodents, with similar efficacies in rats and mice.

Angiotensin II↗
PubMed1998

Reduced growth, abnormal kidney structure, and type 2 (AT2) angiotensin receptor-mediated blood pressure regulation in mice lacking both AT1A and AT1B receptors for angiotensin II.

The classically recognized functions of the renin-angiotensin system are mediated by type 1 (AT1) angiotensin receptors. Whereas man possesses a single AT1 receptor, there are two AT1 receptor isoforms in rodents (AT1A and AT1B) that are products of separate genes (Agtr1a and Agtr1b). We have generated mice lacking AT1B (Agtr1b -/-) and both AT1A and AT1B receptors (Agtr1a -/-Agtr1b -/-). Agtr1b -/- mice are healthy, without an abnormal phenotype. In contrast, Agtr1a -/-Agtr1b -/- mice have diminished growth, vascular thickening within the kidney, and atrophy of the inner renal medulla. This phenotype is virtually identical to that seen in angiotensinogen-deficient (Agt-/-) and angiotensin-converting enzyme-deficient (Ace -/-) mice that are unable to synthesize angiotensin II. Agtr1a -/-Agtr1b -/- mice have no systemic pressor response to infusions of angiotensin II, but they respond normally to another vasoconstrictor, epinephrine. Blood pressure is reduced substantially in the Agtr1a -/- Agtr1b -/- mice and following administration of an angiotensin converting enzyme inhibitor, their blood pressure increases paradoxically. We suggest that this is a result of interruption of AT2-receptor signaling. In summary, our studies suggest that both AT1 receptors promote somatic growth and maintenance of normal kidney structure. The absence of either of the AT1 receptor isoforms alone can be compensated in varying degrees by the other isoform. These studies reaffirm and extend the importance of AT1 receptors to mediate physiological functions of the renin-angiotensin system.

Adrenal Glands↗
PubMed1998

Coagulation defects and altered hemodynamic responses in mice lacking receptors for thromboxane A2.

Thromboxane A2 (TXA2) is a labile metabolite of arachidonic acid that has potent biological effects. Its actions are mediated by G protein-coupled thromboxane-prostanoid (TP) receptors. TP receptors have been implicated in the pathogenesis of cardiovascular diseases. To investigate the physiological functions of TP receptors, we generated TP receptor-deficient mice by gene targeting. Tp-/- animals reproduce and survive in expected numbers, and their major organ systems are normal. Thromboxane agonist binding cannot be detected in tissues from Tp-/- mice. Bleeding times are prolonged in Tp-/- mice and their platelets do not aggregate after exposure to TXA2 agonists. Aggregation responses after collagen stimulation are also delayed, although ADP-stimulated aggregation is normal. Infusion of the TP receptor agonist U-46619 causes transient increases in blood pressure followed by cardiovascular collapse in wild-type mice, but U-46619 caused no hemodynamic effect in Tp-/- mice. Tp-/- mice are also resistant to arachidonic acid-induced shock, although arachidonic acid signifi-cantly reduced blood pressure in Tp-/- mice. In summary, Tp-/- mice have a mild bleeding disorder and altered vascular responses to TXA2 and arachidonic acid. Our studies suggest that most of the recognized functions of TXA2 are mediated by the single known Tp gene locus.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗
PubMed1998

Downregulation of T cell receptor expression by CD8(+) lymphocytes in kidney allografts.

Allospecific CD8(+) T lymphocytes are an important component of the cellular response in allograft rejection. These cells recognize and engage MHC class I antigens, leading to allospecific cytolytic responses and graft rejection. In mouse kidney allografts that survive to 3 wk after transplantation, we noted that the majority of CD8(+) cells do not express surface alpha/beta T cell receptor alpha/beta(TCR), gamma/deltaTCR, or CD3. However, these CD8(+)TCR- cells did express surface markers characteristic of T cells, including Thy1.2, CD2, and CD5. In addition, the CD8(+)TCR- cells expressed mRNA for TCR Vbeta gene families, and nearly half stained positive for cytoplasmic Vbeta8 protein, suggesting that they are T cells that have downregulated alpha/betaTCR protein expression from their cell surfaces. When these surface TCR- cells were isolated from kidney allografts by flow cytometry and cultured in the presence of either allogeneic or syngeneic stimulators, nearly 100% of cells reacquired normal levels of alpha/betaTCR expression with disproportionate usage of Vbeta8 chains. After recovery of their surface TCR expression, the CD8(+)TCR- population demonstrated strong alloreactivity in culture. These results suggest that the substantial number of CD8(+)TCR- cells found in long-term surviving mouse kidney allografts are alpha/beta-T cells that have downregulated their cell surface expression of TCR. While in other systems this phenotype may identify cells that have engaged antigen, our results indicate that loss of TCR expression by CD8(+) kidney graft-infiltrating cells may not depend on antigen engagement and that elements in the microenvironment of the kidney graft play a key role in this process. Factors that modulate expression of TCR by graft-infiltrating lymphocytes may have an important role in regulating rejection responses.

Animals↗
PubMed1998

A genetic approach for studying the role of thromboxane A2 in the kidney.

Thromboxane A2 (TxA2) has been implicated in a number of processes in normal kidney physiology and as a mechanism for injury in renal disease. TxA2 is a biologically active derivative of arachidonic acid and has potent vasoconstrictive and platelet-activation functions. Its actions are mediated by binding to specific G-protein-associated receptors designated TP receptors. There are at least two isoforms of the human TP receptor, and pharmacological evidence suggests TP receptor heterogeneity in other species. TP receptors are located in the renal cortex, and there may also be TxA2 binding sites in the medulla. TP receptors are involved in some normal functions of the kidney, and there is considerable evidence that TP receptors may mediate renal damage in disease states. To assess directly the role of the TxA2 in normal kidney function and in murine models of human disease, we have used gene targeting to eliminate expression of the TP receptor in mice.

Animals↗
PubMed1998

Pressure-overload hypertrophy is unabated in mice devoid of AT1A receptors.

Mechanisms controlling cardiac growth are under intense investigation. Among these, the renin-angiotensin system has received great interest. In the current study, we tested the hypothesis that the renin-angiotensin system was not an obligate factor in cardiac hypertrophy. We examined the left ventricular hypertrophic response to a pressure overload in mice devoid of the AT1A receptor, the putative major effector of the growth response of the renin-angiotensin system. Aortic banding produced similar transband gradients in wild-type and AT1A knockout mice. The left ventricular mass-to-body weight ratio increased from 3.44 +/- 0.08 to 5.62 +/- 0.25 in wild-type ascending aortic-banded mice. The response in the knockout mice was not different (from 2.97 +/- 0.13 to 5.24 +/- 0.37). We conclude that the magnitude of cardiac hypertrophy is not affected by the absence of the AT1A receptor and its signaling pathway and that this component of the renin-angiotensin system is not necessary in cardiac hypertrophy.

Angiotensin II↗
PubMed1998

Renal growth and development in mice lacking AT1A receptors for angiotensin II.

To examine the role of the type 1A (AT1A) angiotensin receptor in renal growth and development, we analyzed F2 progeny from a series of crosses between F1 mice that were heterozygous for a targeted disruption of the AT1A receptor gene [Agtr1A-(+/-)]. Among 21-day-old weanling F2 mice, we found that 194 (32%) were homozygous for the wild-type allele Agtr1A-(+/+), 299 (49%) were Agtr1A-(+/-), and 119 (19%) were Agtr1A-(-/-). This differed significantly from the proportions predicted by Mendelian genetics (P = 0.01), suggesting that the complete absence of AT1A receptors is associated with a mild survival disadvantage. Agtr1A-(-/-) mice grew normally, and we found no significant differences in body weight or heart and kidney weights in Agtr1A-(+/+) and Agtr1A-(-/-) mice examined at 21, 60, and 100 days. Protein and DNA content of kidneys and hearts were also similar in weanling or adult Agtr1A-(+/+) and Agtr1A-(-/-) mice. By light microscopy with immunohistochemistry, kidneys from Agtr1A-(-/-) were essentially normal, with two exceptions: 1) there was marked hypertrophy of the juxtaglomerular apparatus (JGA) and proximal expansion of renin-producing cells along the afferent arterioles, and 2) some glomeruli showed evidence of mesangial expansion. We did not find the severe renal vascular lesions or papillary atrophy that have been observed in angiotensinogen- or angiotensin converting enzyme-deficient animals. We conclude that the AT1A receptor is not essential for the normal organogenesis of the kidney; however, its absence is associated with mild mesangial expansion and JGA hypertrophy.

Angiotensin II↗
PubMed1998

Gene targeting in physiological investigations: studies of the renin-angiotensin system.

Gene targeting using homologous recombination in embryonic stem cells provides an avenue for the direct application of precise molecular genetic interventions to the study of complex systems in whole animals. As such, it represents a powerful approach for physiological investigation. Although its applications in physiology were initially limited because of technical difficulties in performing whole animal experiments in mice, these difficulties have been rapidly overcome, and gene targeting has been used productively in physiological experimentation. Studies have been performed using mice in which genes in the renin-angiotensin system (RAS) have been altered by gene targeting, and these studies illustrate both the feasibility and the utility of this technique for addressing physiological issues. These studies have demonstrated novel roles for the RAS in the development and maintenance of kidney structure and have added to the understanding of how RAS gene products regulate blood pressure and renal function. Finally, these experiments may contribute to understanding how naturally occurring mutations in RAS genes cause hypertension.

Angiotensin I↗
PubMed1998

Thromboxane A2 modulates the fibrinolytic system in glomerular mesangial cells.

We examined the effects of thromboxane A2 (TxA2) on the activities of the plasminogen-plasmin system in glomerular mesangial cells. When mesangial cells are exposed to the TxA2 agonist U-46619, a substantial increase in production of plasminogen activator inhibitor-1 (PAI-1) protein is observed that is significantly greater than that induced by 10% serum alone. This increase in PAI-1 protein production is accompanied by an increase in steady-state levels of PAI-1 mRNA. This stimulation is specifically mediated by TxA2 (thromboxane prostanoid, TP) receptors, since U-46619 also stimulates PAI-1 expression in cells that are transfected with TP receptors, and this stimulation of PAI-1 production is completely blocked by the TxA2 receptor antagonist, SQ-29,548. Despite the increase in PAI-1 production, there was net stimulation of plasmin activity in the medium of mesangial cells that had been exposed to U-46619. Furthermore, U-46619 also caused an increase in tissue plasminogen activator (tPA) mRNA levels. Thus TxA2 stimulates the production of PAI-1 and plasminogen activators by mesangial cells through a receptor-dependent mechanism. In inflammatory renal diseases, the balance of these effects may modulate glomerular thrombosis and renal fibrosis.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗
PubMed1998

Urinary concentrating function in mice lacking EP3 receptors for prostaglandin E2.

The actions of prostaglandin (PG) E2 are mediated by four distinct classes of PGE2 E-prostanoid (EP) receptors (EP1 through EP4). However, the in vivo functions of the individual EP receptor subtypes have not been delineated. To study the functions of one of these subtypes, the EP3 receptor, we generated EP3-deficient (-/-) mice by gene targeting. EP3 -/- animals survived in expected numbers, reproduced, and had no obvious abnormalities in their major organ systems. Because the EP3 receptor is expressed at high levels in the renal medulla and cortical collecting duct, and because previous studies have suggested that the EP3 receptor might antagonize the effects of vasopressin in the distal nephron, we examined urinary concentrating functions in EP3 -/- mice. Basal urine osmolality (UOsm) was similar in groups of EP3 -/- and wild-type (EP3 +/+) mice. However, after inhibition of endogenous PGE2 production by indomethacin, UOsm increased significantly in EP3 +/+ but not in EP3 -/- mice. Despite this insensitivity to acute inhibition of prostanoid production, EP3 -/- mice concentrated and diluted their urine normally in response to a series of physiological stimuli. This suggests that PGE2 acts through the EP3 receptor to modulate urinary concentrating mechanisms in the kidney, but these effects are not essential for normal regulation of urinary osmolality.

Animals↗
PubMed1998

Immune cells in a mouse airway model of obliterative bronchiolitis.

Obliterative bronchiolitis (OB), a form of chronic lung rejection, affects 50% of all lung-transplant recipients and is a major cause of morbidity and mortality. We used the mouse tracheal allograft model of OB to quantitate inflammatory cells during disease progression to evaluate the pathogenesis of this disorder. Tracheas of BALB/c mice were implanted into C57BL/6, severe combined immunodeficiency (SCID), and BALB/c mice. Cyclosporin was administered at 25 mg/kg/d. Grafts were harvested at 2, 6, 10, and 15 wk, and analyzed immunohistochemically. Tracheal allografts developed epithelial injury and cellular infiltrates at 2 wk, epithelial denudation and complete luminal obliteration at 6 wk, and dense collagenous scarring by 15 wk. SCID allografts and isografts demonstrated intact epithelium throughout, although a mononuclear infiltrate was initially present at 2 wk in the SCID allografts. Immunohistochemical staining, using antibodies to mouse CD4(+) (T-helper lymphocyte), CD8(+) (T-cytotoxic/suppressor lymphocyte), and B lymphocytes, macrophages, and myofibroblasts, revealed large numbers of macrophages and CD4(+) and CD8(+) lymphocytes in allografts at 2 wk, compared with isografts. The allograft CD4(+)/CD8(+) ratio was 0.75 at 2 wk. Allografts demonstrated macrophage, myofibroblast, and CD4(+) predominance at 6 and 10 wk (CD4(+)/CD8(+) = 2/1), but by 15 wk had minimal cellularity and were densely scarred. SCID allografts demonstrated a macrophage-predominant infiltrate at 2 wk, with minimal cellularity at later time points. These results indicate that: (1) OB is predominantly an immunologic airway injury; and (2) CD4(+) and CD8(+) lymphocytes and macrophages play an important role in the evolution of airway inflammation and fibrosis. Additionally, this model suggests that chronic airway fibrosis follows a period of intense airway-directed, cell-mediated rejection.

Animals↗
PubMed1997

The prostaglandin receptor EP4 triggers remodelling of the cardiovascular system at birth.

Survival of newborn placental mammals depends on closure of the ductus arteriosus (DA), an arterial connection in the fetus which directs blood away from the pulmonary circulation and towards the placenta where oxygenation occurs. Here we show that morphological changes resulting in closure of the DA in mice are virtually identical to those observed in larger mammals, including humans, and that maintenance of the DA in the open, or patent, state in fetal mice is dependent on prostaglandin synthesis. This requirement is absent in mice lacking the prostaglandin E2 EP4 receptor (EP4(-/-) mice). In EP4(-/-) mice of the 129 strain, remodelling of the DA fails to occur after birth, resulting in a left-to-right shunt of blood and subsequently in death. This suggests that the neonatal drop in prostaglandin E2 that triggers ductal closure is sensed through the EP4 receptor. In contrast, 5% of EP4(-/-) mice of mixed genetic background survive, and selective breeding of these mice leads to a 21% survival rate, suggesting that alleles at other loci can provide an alternative mechanism for ductal closure.

Animals↗
PubMed1997

Modulation of eicosanoid metabolism in endothelial cells in a xenograft model. Role of cyclooxygenase-2.

Lipid inflammatory mediators are thought to play a critical role in the pathogenesis of vascular injury. Among the events which might cause the synthesis of eicosanoids in blood vessels is activation of the complement. To evaluate how complement might influence eicosanoid metabolism, we investigated endothelial cells exposed to xenoreactive antibodies and complement, as might occur in rejecting xenografts where severe vascular injury is a typical feature. While resting porcine aortic endothelial cells released only prostaglandin (PG) I2, endothelial cells stimulated with xenoreactive antibodies and complement released PGE2 and thromboxane A2 (TXA2), in addition to increased amounts of PGI2. This alteration in eicosanoid metabolism was associated with induction of cyclooxygenase (Cox)-2 and thromboxane synthase, but not Cox-1. Unlike results seen in other systems, the upregulation of Cox-2 and the subsequent release of eicosanoids by endothelial cells was not directly induced by complement but rather required production of IL-1alpha, which acted on endothelial cells as an autocrine factor. Since eicosanoids have a potent effect on inflammation, vascular tone and platelet aggregation, we postulated that the abnormalities in eicosanoid release induced by xenoreactive antibodies and complement might provide one explanation for the vascular injury, focal ischemia, and thrombosis observed in acute vascular rejection and other vasculitides mediated by complement.

Animals↗
PubMed1997

Nephropathy in human immunodeficiency virus-1 transgenic mice is due to renal transgene expression.

HIV-associated nephropathy (HIVAN) is a progressive glomerular and tubular disease that is increasingly common in AIDS patients and one of the leading causes of end stage renal disease in African Americans. A major unresolved issue in the pathogenesis of HIVAN is whether the kidney disease is due to renal cell infection or a "bystander" phenomenon mediated by systemically dysregulated cytokines. To address this issue, we have used two different experimental approaches and an HIV-1 transgenic mouse line that develops a progressive renal disease histologically similar to HIVAN in humans. In the murine model, kidney tissue expresses the transgene and in heterozygous adults, renal disease develops shortly thereafter. We demonstrate by terminal deoxynucleotide transferase-mediated dUTP-biotin nick-end labeling assay that similar to the disease in humans, apoptosis of renal tubular epithelial cells is a component of the molecular pathogenesis. To determine whether apoptosis is due to transgene expression or environmental factors, we treated fetal kidney explants (normal and transgenic) with UV light to induce transgene expression. Apoptosis occurred in transgenic but not normal littermates after stimulation of transgene expression. To confirm a direct effect of HIV expression on the production of HIVAN, we transplanted kidneys between normal and transgenic mice. HIVAN developed in transgenic kidneys transplanted into nontransgenic littermates. Normal kidneys remained disease free when transplanted into transgenic littermates. Thus, the renal disease in the murine model is intrinsic to the kidney. Using two different experimental approaches, we demonstrate a direct effect of transgene expression on the development of HIVAN in the mouse. These studies suggest that in humans, a direct effect of HIV-1 expression is likely the essential cause of HIVAN, rather than an indirect effect of cytokine dysregulation.

AIDS-Associated Nephropathy↗
PubMed1997

Angiotensin-II-receptors: new targets for antihypertensive therapy.

The renin-angiotensin system regulates blood pressure and sodium homeostasis through a series of coordinated substrate-enzyme interactions. These interactions result in the production of angiotensin II (AII), which exerts a number of diverse biologic effects mediated through AII cell-surface receptors. Dysregulation of this system is implicated in the pathogenesis of various forms of hypertension. Traditional therapy for hypertension has included angiotensin-converting enzyme inhibitors, which block the production of AII. However, a new class of drugs, AT1-receptor blockers, now offers a number of benefits by specifically blocking the effects of AII at its physiologically relevant receptor.

Angiotensin II↗
PubMed1997

Systemic autoimmune nephritogenic components induce CSF-1 and TNF-alpha in MRL kidneys.

MRL-Faslpr mice are an appealing strain to understand the importance of cytokines in the pathogenesis of autoimmune renal destruction, since injury is rapid and predictable. Colony stimulating factor 1 (CSF-1) and tumor necrosis factor alpha (TNF-alpha) are detected in the kidney and circulation prior to renal injury and continue to increase with progressive renal damage in MRL-Faslpr, Fas deficient mice, but not the congenic Fas intact MRL-(++) strain. Delivery of CSF-1, but not TNF-alpha, into the kidney via gene transfer incites local renal injury. By comparison, dual gene transfer of CSF-1 and TNF-alpha incites autoimmune renal injury that is far more severe than CSF-1 alone. The purpose of this study was to establish whether CSF-1 and TNF-alpha incites autoimmune renal injury that is far more severe than CSF-1 alone. The purpose of this study was to establish whether CSF-1 and TNF-alpha expression in the kidney of MRL-Faslpr mice induced by a circulating stimulant resulted from a primary defect in the kidney. Therefore, we transplanted (Tx) a MRL-(++) kidney without CSF-1, TNF-alpha and renal injury into an MRL-Faslpr recipient after removing nephritic kidney expressing CSF-1 and TNF-alpha. The Tx kidneys were examined after 2, 4, 5, 6, and 12 weeks. CSF-1 and TNF-alpha were rapidly induced in the MRL-(++) Tx kidney. CSF-1 and TNF-alpha were evident by two weeks and continually increased for 12 weeks post-transplantation. Within several weeks, the rapid expansion of M phi and T cells and induction of glomerulonephritis and interstitial nephritis in the MRL-(++) Tx kidney was similar to the age-matched native MRL-Faslpr kidney. In conclusion, we have constructed an experimental transplantation system that can explore whether cytokine expression in the kidney induced by a circulating stimulant is a result of a primary defect in the kidney. Using this approach, we established that the MRL-Faslpr kidney is not defective, but rather a circulating stimulant in the MRL-Faslpr mouse can induce CSF-1, TNF-alpha and renal injury in a normal MRL-(++) kidney. Thus, we exclude an intrinsic defect in the MRL-Faslpr kidney as the pathogenic mechanism responsible for tissue damage. We suggest purging the circulation of molecules that induce CSF-1 and TNF-alpha as a therapeutic strategy for autoimmune renal injury.

Animals↗
PubMed1997

Angiotensin II responses in AT1A receptor-deficient mice: a role for AT1B receptors in blood pressure regulation.

Most of the classic functions of the renin-angiotensin system are mediated by type 1 (AT1) angiotensin receptors, of which two subtypes, AT1A and AT1B, have been identified. However, distinct functions for these two AT1 receptors have been difficult to separate. We examined the pressor effects of angiotensin II in Agtr1A -/- mice, which lack AT1A receptors. In enalapril-pretreated Agtr1A -/- mice, angiotensin II caused significant and dose-proportional increases in mean arterial pressure. This pressor response was not blocked by pretreatment with sympatholytic agents but was completely inhibited by the AT1-receptor antagonists, losartan and candesartan, suggesting that it is directly mediated by AT1B receptors. Chronic treatment of Agtr1A -/- mice with losartan reduced systolic blood pressure from 80 +/- 5 to 72 +/- 4 mmHg (P < 0.04), suggesting a role for AT1B receptors in chronic blood pressure regulation. These studies provide the first demonstration of in vivo pressor effects mediated by AT1B receptors and demonstrate that, when AT1A receptors are absent, the AT1B receptor contributes to the regulation of resting blood pressure.

Angiotensin II↗