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Roland Schmitt

Publications and source records attributed to Roland Schmitt.

At least 19 recordsLinked to original sources
PubMed2006

Posttransplantation malignancy in a patient presenting with weight loss and changed bowel habits: a case report.

BACKGROUND: Advancements in immunosuppressive therapy have significantly improved patient and graft survival following renal transplantation. This is paralleled by an increasing occurrence of posttransplantation malignancy. CASE PRESENTATION: We report on a patient who presented with a history reminding of colon cancer seven years after receiving a kidney transplant. Initial diagnostic imaging seemed to confirm this diagnosis showing a constricting colonic lesion. To our surprise, colonoscopy findings were unremarkable. Review of the imaging studies revealed that the tumor-like picture was caused by the renal graft impressing the intestine. The following search for malignancy in other locations resulted in the diagnosis of glioblastoma multiforme of which the patient died several weeks later. CONCLUSION: Follow-up of renal transplant patients must include screening tests directed at tumor detection. Imaging studies and other tests in this patient group should be interpreted by physicians who are familiar with transplant related peculiarities.

Aged↗
PubMed2005

Hypothyroidism induces expression of the peptide transporter PEPT2.

The kidney is a target organ for thyroid hormone action and a variety of renal transport processes are altered in response to impaired thyroid functions. To investigate the effect of thyroid hormone on the expression of the renal proximal tubular high-affinity-type H(+)-peptide cotransporter (PEPT2) in rats, hypothyroidism was induced in animals by administration of methimazole (0.05%) via drinking water. After 7 weeks of treatment, hypothyroidism was confirmed by determining serum free T(3) and free T(4) concentrations. Northern blotting was used to examine the expression of PEPT2 mRNA in kidney tissues from hypothyroid rats compared to control rats. Hypothyroidism resulted in an increased level of total renal PEPT2 mRNA (121.1+/-3.3% vs. control 100+/-2.8%; p=0.008). The mRNA results were confirmed by immuno-blotting, which demonstrated significantly increased protein levels (162% vs. control 100%; p<0.01). Immunohistochemistry also revealed increased PEPT2 protein levels in the proximal tubules of treated compared to non-treated rats. In summary, PEPT2 is the first proximal tubule transporter protein that shows increased expression in states of hypothyreosis. As PEPT2 reabsorbs filtered di- and tripeptides and peptide-like drugs, the present findings may have important implications in nutritional amino acid homeostasis and for drug dynamics in states of altered thyroid function.

Animals↗
PubMed2004

Identification of a novel A-kinase anchoring protein 18 isoform and evidence for its role in the vasopressin-induced aquaporin-2 shuttle in renal principal cells.

Arginine vasopressin (AVP) increases the water permeability of renal collecting duct principal cells by inducing the fusion of vesicles containing the water channel aquaporin-2 (AQP2) with the plasma membrane (AQP2 shuttle). This event is initiated by activation of vasopressin V2 receptors, followed by an elevation of cAMP and the activation of protein kinase A (PKA). The tethering of PKA to subcellular compartments by protein kinase A anchoring proteins (AKAPs) is a prerequisite for the AQP2 shuttle. During the search for AKAP(s) involved in the shuttle, a new splice variant of AKAP18, AKAP18delta, was identified. AKAP18delta functions as an AKAP in vitro and in vivo. In the kidney, it is mainly expressed in principal cells of the inner medullary collecting duct, closely resembling the distribution of AQP2. It is present in both the soluble and particulate fractions derived from renal inner medullary tissue. Within the particulate fraction, AKAP18delta was identified on the same intracellular vesicles as AQP2 and PKA. AVP not only recruited AQP2, but also AKAP18delta to the plasma membrane. The elevation of cAMP caused the dissociation of AKAP18delta and PKA. The data suggest that AKAP18delta is involved in the AQP2 shuttle.

A Kinase Anchor Proteins↗
PubMed2004

Selectively reduced expression of thick ascending limb Tamm-Horsfall protein in hypothyroid kidneys.

Hypothyroidism causes major changes in the kidney by affecting its growth, structure, function, and biosynthesis of its specific gene products. As a consequence, the nephron shows a selective hypotrophy in the medullary portion of the thick ascending limb (TAL). Contrastingly, we have shown earlier that the abundance of the major ion transporter of the TAL, the furosemide-sensitive Na-K-2Cl cotransporter (NKCC2) was increased when related to kidney function in the hypothyroid organism. Synthesis of Tamm-Horsfall protein (THP), the most abundant urinary protein produced in the TAL, has been suggested to interfere with TAL function. We therefore studied the localization and synthesis rate of THP in the hypothyroid kidney. We used rats chronically treated with methimazole. Kidneys were processed for western blotting and histochemical evaluation. Morphologically the hypothyroid TAL displayed a selectively reduced epithelial cell height of its medullary portion. This was paralleled by decreased THP immunostaining and mRNA abundance. Western blotting indicated a 40% reduction in renal THP content ( P<0.005), and daily urinary THP excretion was 68% lower than in controls ( P<0.05). T3 substitution restored these parameters. To further confirm that changes were specific for THP and not merely the consequence of reduced kidney growth, the abundance of barttin, another distal tubular protein related to chloride transport, was tested as well. Barttin was increased by 43% in the hypothyroid rats. Together with our previous results showing increased NKCC2 expression in hypothyroidism, these results demonstrate a selective decrease in medullary THP synthesis. We suggest a potential involvement of THP in the renal functional changes associated with hypothyroidism.

Animals↗
PubMed2004

Protective effects of B2 preservation solution in comparison to a standard solution (histidine-tryptophan-ketoglutarate/Bretschneider) in a model of isolated autologous hemoperfused porcine kidney.

Reperfusion injuries after organ transplantation affect graft function and influence long-term graft survival. As hypothermic storage, which minimizes the extent of unspecific tissue injury after ischemia and reperfusion, is significantly influenced by the composition of preservation solutions, strategies to optimize the different components may lead to longer graft survival. In the present study the effects of the preservation solution B2 on early renal function and histopathological changes were compared to histidine-tryptophan-ketoglutarate solution (HTK, Bretschneider) in a model of isolated blood-perfused porcine kidneys. B2-preserved kidneys displayed a lower renal resistance and significantly better creatinine clearance as compared to HTK. Mean differences were also found for filtration fraction and sodium fraction reabsorption. The functional data were also related to histopathological changes. Together, these data indicate that the recently developed preservation solution B2 offers new principles of preservation and is a useful preservation solution for experimental isolated perfused kidney models. B2 may also be an interesting model for optimizing preservation within other organ perfusion models.

Animals↗
PubMed2003

Renal expression of sodium transporters and aquaporin-2 in hypothyroid rats.

Hypothyroidism is associated with significant abnormalities in the renal handling of salt and water. To address the involvement of tubular transport proteins in these abnormalities, rats were rendered pharmacologically hypothyroid and the abundance of major tubular transport proteins was assessed by immunoblot and immunohistochemistry. Hypothyroidism resulted in a marked reduction in kidney size and creatinine clearance along with decreased or unchanged total kidney abundance of the transport proteins. Whereas the proximal tubular type 3 Na/H exchanger (NHE3) and type 2 Na-phosphate cotransporter (NaPi2) stood out by their disproportionately reduced abundance, the bumetanide-sensitive type 2 Na-K-2Cl cotransporter (NKCC2) and aquaporin-2 (AQP2) were unaltered in their total kidney abundance despite a markedly lower kidney mass. The latter proteins in fact showed enhanced immunostaining. Decreased NHE3 and NaPi2 expression was most likely due to a combination of triiodo-l-thyronine (T(3)) deficiency along with a reduced glomerular filtration rate. The increased abundance of NKCC2 and AQP2 may have been caused by an increased action of vasopressin since urinary excretion of this hormone was elevated. On the other hand, the thiazide-sensitive Na-Cl cotransporter; the alpha-, beta-, and gamma-subunits of the amiloride-sensitive epithelial Na channel; and the alpha(1)-subunit of Na-K-ATPase showed a moderate decrease in total kidney abundance that was largely proportional to the smaller kidney mass. Although the observed expression of transporters was associated with a balanced renal sodium handling, altered transporter abundance may become functionally relevant if the hypothyroid kidney is challenged by an additional destabilization of the milieu interieur that has previously been shown to result in an inadequate natriuresis and clinical symptoms.

Animals↗
PubMed2003

Hemoperfused isolated porcine slaughterhouse kidneys as a valid model for pharmacological studies.

Mammalian models of isolated perfused kidneys provide an important tool to study pharmacological, toxicological, and physiological properties of drugs, hormones, and vasoactive substances. As organs from small laboratory animals are difficult to compare to human conditions, porcine and bovine kidneys permit better approaches to simulate human conditions. We developed an alternative model for pharmacological studies using isolated hemoperfused porcine kidneys from slaughterhouse animals to reduce laboratory animal experiments. Controlled pharmacological studies were established using furosemide (2 mg/100 g organweight) as a model drug. Kidneys were hemoperfused after a preservation period of 4.6 +/- 1.7 h. In comparison to the control period, furosemide application led to significant changes in renal parameters with urine flow: 4.2/1.7 mL/min*100 g (furosemide/control), urine-sodium: 108/77.5 mmol/L, sodium excretion: 0.47/0.14 mmol/min*100 g; all differences significant, p < 0.01. The parameters stabilized to normal values as found in the control period within a period of 80 min. A second group of laboratory-harvested kidneys was examined for differences and revealed limitations of the slaughterhouse organs in parameters such as oxygen consumption. In summary, the present study demonstrates the valid use of hemoperfused slaughterhouse kidneys as a pharmacological model of renal function within the limits of the use of slaughterhouse organs, and indicates that future studies using this alternative approach could reduce animal experiments.

Animals↗
PubMed2002

Contact-system activation in children with vasculitis.

BACKGROUND: The contact system triggers the kallikrein-kinin cascade, liberating bradykinin from high-molecular-weight kininogen. Effectors of the contact system have proinflammatory and vasoactive properties. Vasculitis is a condition characterised by inflammation around vessel walls, leading to secondary tissue damage for which the underlying molecular mechanisms are poorly understood. Our aim was to investigate contact-system activation in children with vasculitis. METHODS: We compared 17 children, aged 4-19 years, with vasculitis, engaging the skin, joints, intestines, or kidneys, with 21 controls, aged 2-18 years. We analysed proteolysis of high-molecular-weight kininogen by immunoblotting. Plasma bradykinin concentrations were quantified by ELISA. Kidney and skin biopsies were stained in situ for kinins. Concentrations of heparin binding protein (HBP) were quantified by ELISA. FINDINGS: We noted extensive proteolysis of high-molecular-weight kininogen in the plasma of 13 of 17 patients, but in only one of 21 controls (p<0.0001). Bradykinin concentrations were higher in the patients' plasma (median 320 ng/L, range <1-19680) than in plasma from controls (11 ng/L, <1-304; p=0.0004). Patients had local release of kinins at sites of inflammation in kidney and skin biopsies. HBP values were raised in patients (17.4 microg/L, 5.4-237.6) compared with controls (6 microg/L, 2.5-43.4; p=0.008). INTERPRETATION: Activation of the contact system could play a part in the pathogenesis of vasculitis, and explain the inflammation, pain, vasodilatation, and oedema seen in patients.

Adolescent↗
PubMed2002

[Hypo-osmolar hyponatremia as the chief symptom in hypothyroidism].

CASE HISTORY AND DIAGNOSIS: A 75-year-old male patient presented with a history of anorexia, muscle weakness, and increasing memory loss. He had mild pedal edema and decreased deep tendon reflexes. As the laboratory tests showed hypoosmolar hyponatremia and urinary sodium within the normal range, a syndrome of inappropriate ADH secretion (SIADH) was presumed. While neither the medical history nor any of the diagnostic procedures revealed any underlying pathology explaining the SIADH, laboratory tests showed significant hypothyroidism. Hypothyroid states are associated with significant changes in renal function, one of which is hypoosmolar hyponatremia. TREATMENT AND COURSE: Treatment included fluid restriction and hormone substitution and resulted in a quick correction of the hyponatremia and a clear improvement of the patient's cognitive function. CONCLUSION: It is concluded that the diagnosis of SIADH should only be made after thorough investigation of the adrenal and thyroid hormone status.

Aged↗