Biomedical subjects

A H Nielsen

Publications and source records attributed to A H Nielsen.

At least 19 recordsLinked to original sources

PubMed2006

Pulse-wave morphology and pulse-wave velocity in healthy human volunteers: examination conditions.

OBJECTIVE: Applanation tonometry for pulse-wave analysis (PWA) and determination of pulse-wave velocity (PWV) is a non-invasive method for assessment of the central aortic pressure waveform and indices of arterial stiffness. The objective of this study was to examine the influence of eating and smoking on PWA and PWV measurements in order to establish standard examination conditions. Furthermore, intra- and interobserver reproducibility and the effects of varying the site of measurements were observed. MATERIAL AND METHODS: Duplicate measurements of the radial pressure waveform and of the brachial and aortic PWV on the right and left side of the body were recorded in 23 healthy subjects by two trained observers. Measurements were performed in the fasting state and 3 h after a high-calorie meal, and before and 1 h after smoking a cigarette. RESULTS: Intake of a high-calorie meal as well as smoking caused significant changes in both PWA and PWV parameters and an inter-arm difference was observed. Intra- and interobserver reproducibility was good. CONCLUSIONS: Pulse-wave measurements by applanation tonometry should be undertaken in the same arm during fasting and smoking abstinence.

Adult↗

PubMed2006

Recent findings on sinks for sulfide in gravity sewer networks.

Sulfide buildup in sewer networks is associated with several problems, including health impacts, corrosion of sewer structures and odor nuisance. In recent years, significant advances in the knowledge of the major processes governing sulfide buildup in sewer networks have been made. This paper summarizes this newly obtained knowledge and emphasizes important implications of the findings. Model simulations of the in-sewer processes important for the sulfur cycle showed that sulfide oxidation in the wetted biofilm is typically the most important sink for dissolved sulfide in gravity sewers. However, sulfide emission and thereby potential hydrogen sulfide buildup in the sewer atmosphere is of particular importance in sewers constructed with large diameter pipes, in sewers constructed with steep slopes and in sewers conveying low pH wastewater. Precipitation of metal sulfides is only important when the sulfide concentration in the wastewater is low; i.e. less than 1 g Sm(-3).

Computer Simulation↗

PubMed2005

The uremic environment and muscle dysfunction in man and rat.

BACKGROUND: Patients reaching end-stage renal disease experience debilitating fatigue, with progression of this disease, rendering patients dysfunctional in their everyday lives. METHODS: In vivo measurements of muscle function, assessed using surface electromyography (EMG), were made on 25 patients prior to and after a session of hemodialysis (HD) treatment, along side in vitro measurements of muscle function in isolated rat muscles incubated in normal or uremic conditions approximating to those found in uremic rats (rat uremic: RU) or uremic humans (human uremic: HU). RESULTS: HD significantly affected plasma values, e.g. reducing urea (69%), creatinine (62%), potassium (23%) and phosphate (48%) concentrations in patients (all p < 0.01). Treatment also improved the EMG frequency of 2nd dorsal interosseous (fast-twitch) (p < 0.01), although no change was noted for vastus lateralis (slow-twitch). In isolated rat muscles, a uremic environment had no significant effect on slow-twitch soleus during field stimulation, however, in fast-twitch extensor digitorum longus, a significant 23% (RU) and 22% (HU) faster rate of decline in force was measured, compared to controls (p < 0.001 and p < 0.01, respectively). CONCLUSION: It is concluded that (1) muscle weakness and its electrophysiological correlates may be rapidly induced by uremic solutes and rapidly reversed when the solutes are removed by dialysis, and (2) fast-twitch muscles are more readily affected by uremic conditions than slow-twitch muscles.

Adult↗

PubMed2005

Effects of in-sewer processes: a stochastic model approach.

Transformations of organic matter, nitrogen and sulfur in sewers can be simulated taking into account the relevant transformation and transport processes. One objective of such simulation is the assessment and management of hydrogen sulfide formation and corrosion. Sulfide is formed in the biofilms and sediments of the water phase, but corrosion occurs on the moist surfaces of the sewer gas phase. Consequently, both phases and the transport of volatile substances between these phases must be included. Furthermore, wastewater composition and transformations in sewers are complex and subject to high, natural variability. This paper presents the latest developments of the WATS model concept, allowing integrated aerobic, anoxic and anaerobic simulation of the water phase and of gas phase processes. The resulting model is complex and with high parameter variability. An example applying stochastic modeling shows how this complexity and variability can be taken into account.

Aerobiosis↗

PubMed2005

Simulation of sulfide buildup in wastewater and atmosphere of sewer networks.

A model concept for prediction of sulfide buildup in sewer networks is presented. The model concept is an extension to--and a further development of--the WATS model (Wastewater Aerobic-anaerobic Transformations in Sewers), which has been developed by Hvitved-Jacobsen and co-workers at Aalborg University. In addition to the sulfur cycle, the WATS model simulates changes in dissolved oxygen and carbon fractions of different biodegradability. The sulfur cycle was introduced via six processes: 1. sulfide production taking place in the biofilm covering the permanently wetted sewer walls; 2. biological sulfide oxidation in the permanently wetted biofilm; 3. chemical and biological sulfide oxidation in the water phase; 4. sulfide precipitation with metals present in the wastewater; 5. emission of hydrogen sulfide to the sewer atmosphere and 6. adsorption and oxidation of hydrogen sulfide on the moist sewer walls where concrete corrosion may take place.

Biofilms↗

PubMed2004

Computations of intermittent transport in scrape-off layer plasmas.

Two-dimensional fluid simulations of interchange turbulence for geometry and parameters relevant for the scrape-off layer of magnetized plasmas are presented. The computations, which have distinct plasma production and loss regions, reveal bursty ejection of particles and heat from the bulk plasma in the form of blobs. These structures propagate far into the scrape-off layer where they are dissipated due to transport along open magnetic field lines. From single-point recordings it is shown that the blobs have asymmetric conditional wave forms and lead to positively skewed and flattened probability distribution functions. The radial propagation velocity may reach one-tenth of the sound speed. These results are in excellent agreement with recent experimental measurements.

Journal Article↗

PubMed2002

Angiotensin converting enzyme in bovine ovarian follicular fluid and its relationship with oestradiol and progesterone.

CONTENT: The purpose of the present study was to identify angiotensin converting enzyme (ACE) in bovine ovarian follicular fluid and to relate the ACE activity to the phase of the oestrous cycle, pregnancy, and the follicular fluid concentrations of oestradiol and progesterone. The ACE activity was similar to that found in bovine serum and was completely inhibited by the specific ACE inhibitor captopril. The 50% inhibitory concentration (IC50) was 1.4 x 10(-8) mol/l (range 0.8 x 10(-8) to 5.0 x 10(-8) mol/l; n=6), which is similar to that found in bovine and human serum. The ACE activity did not differ in the pre-ovulatory and luteal phase, pregnancy or cystic follicles. It correlated with the follicular fluid concentration of progesterone in cycling cows (rho=0.476; p < 0.005; n=36), but did not correlate with the diameter of the follicles, the follicular fluid concentration of oestradiol or the ratio between the oestradiol and progesterone concentrations. The demonstration of ACE in bovine ovarian follicular fluid provides further evidence for the presence of a local renin-angiotensin system in the bovine ovary.

Angiotensin-Converting Enzyme Inhibitors↗

PubMed2001

Uricosuric effect of losartan in patients with renal transplants.

BACKGROUND: The aim of the study was to evaluate the uricosuric effect of the angiotensin II receptor antagonist, losartan, in hypertensive patients with renal transplants who are treated with cyclosporin A (CsA). METHODS: Twenty-six patients with stable renal function and hypertension, 16 men and 10 women, median age 47 years (range, 25-63 years), were studied in an open randomized crossover trial, comparing a 2-week control period with a 2-week period of once-daily administration of 50 mg of losartan. The main outcome measurements were fractional excretion of uric acid (FE(uric acid)) based on 24-hr urine collections and plasma uric acid. RESULTS: The median FE(uric acid) was 5.7% (range, 2.4-10.4%) in the control period with a median change of +0.84% (range, -1.15% to +2.77%) in the losartan period (P<0.0002). Plasma uric acid was 0.47 mM (0.29-0.69 mM) in the control period with a change of -0.03 mM (-0.10 to 0.06 mM) in the losartan period (P<0.002). Diastolic blood pressure was 87 mmHg (70-97 mmHg) in the control period with a change of -3 mmHg (-13 to +6 mmHg) in the losartan period (P<0.005). There was no difference in systolic blood pressure between the two study periods. Plasma creatinine was 165 microM (102-356 microM) in the control period with a change of +9 microM (-36 to +60 microM) in the losartan period (P<0.01). Plasma potassium was 4.2 mM (3.0-4.7 mM) in the control period with a change of + 0.2 mM (-0.2 to +0.9 mM) in the losartan period (P<0.0005). CONCLUSIONS: Once-daily administration of 50 mg of losartan in hypertensive CsA-treated patients with renal transplants caused a 17% increase in FE(uric acid) and an 8% fall in plasma uric acid.

Adult↗

PubMed2001

Angiotensin-converting enzyme activity in the bovine uteroplacental unit changes in relation to the cycle and pregnancy.

The expression of the angiotensin-forming enzymes, renin and angiotensin-converting enzyme (ACE), were examined in the bovine uteroplacental unit. The ACE activity was determined in cell membrane fractions, and ACE and renin were localized by autoradiography and immunohistochemistry, respectively. In the myometrium, the ACE activity was significantly higher in dioestrous than in oestrous. ACE activity correlated negatively with the day of gestation in the endometrium and myometrium but positively in the placentome and allantoamniotic membrane. Autoradiography showed, that ACE was localized in vascular endothelial cells in all compartments. ACE was also expressed in the endometrial stroma and uterine glands, most pronounced in the outer part of the basal zone. In the intercotyledonary membrane and the placentome, the mesenchymal cells located near the trophoblast cells expressed ACE. Solitary macrophage- or monocyte-like cells showing intense renin immunoreactivity were found in the uterus, while the uterine and the glandular epithelial cells displayed inconsistent reactivity. No renin was observed in the placentomes or in the fetal membranes. The findings demonstrate a regulated expression of angiotensin-forming enzymes throughout the bovine uteroplacental unit. Whether this local renin-angiotensin system contributes to the highly regulated morphological and functional changes throughout the oestrous cycle and gestation remains to be established.

Angiotensin-Converting Enzyme Inhibitors↗

PubMed2001

Localization of the renin-angiotensin system in the bovine ovary: cyclic variation of the angiotensin II receptor expression.

Angiotensin (Ang) II may modulate reproductive function in the bovine ovary. Therefore, expression and localization of a local ovarian renin-angiotensin system (RAS) were investigated by elucidating the influence of the estrus cycle, pregnancy, and the presence of follicular cysts. Receptor analysis and autoradiography were used to characterize and localize Ang II receptors. Cyclic variations in the density of ovarian Ang II receptors were found with a higher value in estrus than in diestrus. The density in ovaries with follicular cysts was in the same order of magnitude as in estrus. The Ang II receptor type 2 (AT(2)) dominated in all three groups. Autoradiography showed that the majority of antral follicles and follicular cysts had intense AT(2) receptor binding in the theca externa. Binding was less intense in the theca interna, whereas there was no binding in the granulosa layer. In the corpora lutea, the AT(2) receptor was dominant in the capsule and in connective tissue infoldings, whereas no binding was observed in the luteal tissue. The type 1 Ang II receptor (AT(1)) was dominant in the stroma and showed no cyclic changes. Angiotensin-converting enzyme (ACE) activity was detected in all aspirated follicular fluids and homogenates of ovarian tissue. Autoradiography showed that most of the ACE was localized on endothelial cells. Renin immunoreactivity was found in granulosa and thecal cells of antral follicles and in luteal cells. Furthermore, solitary cells in the stroma, presumably macrophages, displayed intense staining. Our finding of cyclic changes support the concept of an active and regulated RAS in the bovine ovary.

Animals↗

PubMed2000

High plasma concentrations of prorenin in a transgenic animal model of nephropathy with overexpression of transforming growth factor-beta1 in the kidneys.

1. Plasma concentrations of prorenin were determined in a transgenic animal model of nephropathy induced by overexpression of transforming growth factor (TGF)-beta1 in the juxtaglomerular apparatus. 2. In both female and male mice, plasma concentrations of prorenin were higher in transgenic than in non-transgenic animals. In sexually mature mice, plasma prorenin concentrations were higher in males than in females in both transgenic and non-transgenic animals in accordance with a sexual dimorphism of the plasma concentration of prorenin. 3. The results indicate that TGF-beta1-like androgens increase prorenin secretion in the kidneys and may explain the increased plasma prorenin concentrations in patients with diabetic nephropathy.

Aging↗

PubMed1999

Species differences in expression of angiotensin II receptors and angiotensin-converting enzyme in human, canine and rat mitral valve leaflets.

In normal valvular collagen turnover in the rat, angiotensin (Ang) II and angiotensin-converting enzyme (ACE) seem to be involved. In common human and canine valvular diseases, changes in valvular collagen play a pathogenetic role and the valvular renin-angiotensin system is therefore of particular interest in these species. Healthy mitral valve leaflets and adjacent left ventricular myocardium were taken from five rats and five dogs immediately after euthanasia, and from five humans at autopsy. The valvular and myocardial Ang II receptors and ACE were detected and measured by quantitative autoradiography. In rat valves, high levels of Ang II receptors and ACE were found. In human and canine valves, insignificant levels were found. Significant myocardial levels of Ang II receptors and ACE were found only in the rat. The study demonstrated major species differences regarding the level of valvular and myocardial Ang II receptors and ACE in man, dog and rat. The lack of valvular Ang II receptors and ACE in man and dog, suggest that the renin-angiotensin system plays a minor, if any, role in the physiological valvular collagen formation in these two species. The findings in humans, however, need to be confirmed using fresh material.

Aged↗

PubMed1999

Dominance of type 1 angiotensin II receptor in the nonpregnant and pregnant bovine uterus.

The present study was undertaken to characterize, determine and localize angiotensin II receptors in the nonpregnant and pregnant bovine uterus. In addition, the concentration of active renin, which is responsible for the generation of angiotensin, was determined. Autoradiography and angiotensin II receptor binding studies showed that all compartments of the bovine uterus contained high concentrations of angiotensin II receptors. In general, the type 1 angiotensin II receptor (AT1) predominated over the AT2 receptor. In the endometrium, the highest density was found in the caruncles and the AT1 receptor was always predominant. The density of angiotensin II receptors in the endometrium increased at the beginning of pregnancy, but decreased and reached values similar to those in nonpregnant animals near term. In the myometrium, the density of angiotensin II receptors was highest at or near the endometrial-myometrial junction. In this area, the predominant type of angiotensin II receptor in the uterus of cyclic cows varied, whereas the AT1 receptor always predominated during pregnancy. Non-AT1 and non-AT2 binding sites were found in the same locations as the angiotensin II receptors, but at lower densities. With the exception of the pregnant endometrium, all compartments contained higher active renin concentrations than found in plasma, indicating local synthesis of renin. This study demonstrates a difference in the expression of types of angiotensin II receptor in the bovine uterus compared with other species. The high densities of angiotensin II receptors localized in several important areas imply that the renin-angiotensin system participates in regulation of growth and tissue function in the bovine uterus.

Animals↗

PubMed1999

Under control of the Ren-1c promoter, locally produced transforming growth factor-beta1 induces accumulation of glomerular extracellular matrix in transgenic mice.

Our purpose was to elucidate the hypothesis that paracrine-produced transforming growth factor (TGF)-beta1 regulates the accumulation of extracellular matrix (ECM) in renal glomeruli, a hallmark of diabetic nephropathy. To produce TGF-beta1 from the juxtaglomerular apparatus in mouse kidneys, we cloned a mouse Ren-1c promoter fragment (-4.100 to +6 base pairs) upstream of porcine TGF-beta1 (pTGF-beta1) cDNA, mutated to ensure secretion of biologically active TGF-beta beta1. The resulting transgenic mice had significantly more TGF-beta1 in their kidneys than was in those of nontransgenic controls, as confirmed by immunohistochemistry, and the production of TGF-beta1 was enhanced in vivo by captopril-induced stimulation of the Ren-1c promoter. Overproduction of pTGF-beta1 close to the glomerulus resulted in a local accumulation of ECM, composed partly of collagen type IV and laminin, and thickening of the basement membrane, characteristic features of diabetic nephropathy. Interstitial accumulation of ECM and signs of tubular atrophy were present only in older mice (>5 months of age). Results from in situ hybridization and immunohistochemistry suggest that pTGF-beta1 stimulated the production of endogenous TGF-beta1 along collecting ducts and connecting tubules. The increased amount of biologically active TGF-beta1, transgenic as well as endogenous, was corroborated by heightened proteoglycan synthesis from incubated kidney slices. This transgenic model demonstrates that sustained local expression of TGF-beta1 leads to glomerulopathy. We conclude that autocrine- or paracrine-produced TGF-beta1 may play a role in the development of glomerular diseases, such as diabetic nephropathy.

Animals↗

PubMed1998

Perioperative Doppler ultrasonography: renal detection of renal graft perfusion.

Irreversible damage of renal transplants may be prevented if insufficient graft perfusion can be detected perioperatively. Colour and spectral Doppler ultrasonography were performed in 30 consecutive renal transplants. The perfusion of the graft and the Resistive Index (RI) were evaluated perioperatively (perioperatively and less than 15 min postoperatively) and 24 h after the operation in all patients. In four cases (13.3%) RI > 0.9 was detected and immediate surgical correction of the cause led to a normalization (RI < 0.8) in all four cases. A RI < 0.9 required no intervention in 26 cases (86.7%). All renal grafts in this series were functioning 1 month postoperatively. In a comparative group, 30 consecutive transplants carried out at our institution without perioperative Doppler ultrasonography evaluation, a loss of four renal grafts perioperatively was recorded retrospectively. We conclude that perioperative ultrasonography Doppler evaluation may provide an easy applicable and reliable method for early detection of insufficient renal graft perfusion, allowing surgical correction before irreversible damage of the graft occurs. RI > 0.9 is pathological. A continuation of the study is required to clarify the long-term value of perioperative Doppler ultrasonography graft monitoring.

Adult↗

PubMed1998

Autoradiographic localization and characterization of angiotensin II receptors in the bovine placenta and fetal membranes.

Autoradiography and angiotensin (Ang) II receptor binding studies showed that all parts of the bovine placenta and fetal membranes contained high densities of Ang II receptors throughout gestation. The receptors were predominantly subtype 2 (AT2) receptors in the fetal and subtype 1 (AT1) receptors in the maternal compartment. In the allantoamnionic membrane, Ang II receptors were evenly distributed in the mesenchymal tissue, with the highest expression around the few arteries. In the intercotyledonary and cotyledonary allantochorionic membrane, AT2 receptors as well as the less-expressed AT1 receptors were located on mesenchymal cells, especially adjacent to the allantoic endoderm, trophoblast cell layer, and arteries. In the mesenchymal tissue of the placentome, Ang II receptors were mostly expressed at the main branches of the fetal villi of the cotyledons. In the maternal part of the placentome, mainly AT1 receptors but also low densities of AT2 receptors and non-AT1/non-AT2 Ang II binding sites were found close to the stalk and at the main branches of the maternal crypts. Autoradiography revealed no changes in the pattern of distribution of the Ang II receptors throughout gestation. It is suggested that Ang II has an effect on regulatory as well as growth processes in these tissues.

Animals↗

PubMed1997

Relationship between follicular fluid steroids and tissue renin concentrations and secretion rates in bovine ovaries.

The relationship between follicular fluid concentrations of oestradiol (E2) and progesterone (P4), and follicular wall tissue renin concentrations and in-vitro secretion rates was investigated. The follicular fluid concentrations of prorenin correlated negatively with oestradiol and the E2/P4 ratio, and positively with progesterone in accordance with earlier findings. The high concentrations of active renin and prorenin in the follicular wall tissue, and the secretion rates of both active renin and prorenin all correlated positively with oestradiol and the E2/P4 ratio, but negatively with progesterone. These findings suggest that atretic follicles have higher follicular fluid renin concentrations but lower tissue renin concentrations and in-vitro secretion rates than healthy non-atretic follicles. The high follicular fluid prorenin concentrations in atretic follicles are most likely caused by a high prorenin secretion rate earlier in the oestrus cycle. The existence of relationships between the follicular fluid steroids and the follicular wall concentrations and secretion rates of active renin and prorenin indicates an interaction between the reninangiotensin system and steroidogenesis, but it may also reflect regulation by common factors, such as gonadotropins.

Animals↗

PubMed1997

Angiotensin II receptors and renin in the porcine uterus: myometrial AT2 and endometrial AT1 receptors are down-regulated during gestation.

1. The aim of the present study was to characterize the angiotensin II (AngII) receptor subtypes in the porcine uterus and the variation of receptor densities and renin concentrations during gestation. 2. In myometrium from non-pregnant sows, the AngII receptors were almost exclusively AT2 receptors. During gestation, the AngII receptor density was decreased and the AT1 receptor became predominant in the last part of gestation as a result of a down-regulation of the AT2 receptor. 3. In the endometrium, the AT1 receptor was predominant both in non-pregnant sows and throughout gestation. The AngII receptor density was decreased during gestation as a consequence of down-regulation of the AT1 receptor. 4. The renin concentrations in the myometrium and endometrium of pregnant sows did not differ from those in non-pregnant animals. 5. The finding of enzymatically active renin and high densities of AngII receptors in the porcine uterus is in accordance with a functional renin-angiotensin system (RAS), which may be important for an increased vascular permeability and stimulated angiogenesis in early pregnancy and for contraction of the myometrial smooth muscle cells during parturition. The predominance of AT1 receptors in the endometrium of non-pregnant sows differs from an earlier finding in non-pregnant women, where AT2 receptors were predominant in the endometrium. This is in accordance with earlier studies, indicating species differences in the expression and possibly also the physiological roles of the RAS in reproductive tissues.

Angiotensin II↗