Search PubMed⌕ Search

Biomedical subjects

A Kristensen

Publications and source records attributed to A Kristensen.

At least 19 recordsLinked to original sources
PubMed2005

Lab-on-a-chip with integrated optical transducers.

Taking the next step from individual functional components to higher integrated devices, we present a feasibility study of a lab-on-a-chip system with five different components monolithically integrated on one substrate. These five components represent three main domains of microchip technology: optics, fluidics and electronics. In particular, this device includes an on-chip optically pumped liquid dye laser, waveguides and fluidic channels with passive diffusive mixers, all defined in one layer of SU-8 polymer, as well as embedded photodiodes in the silicon substrate. The dye laser emits light at 576 nm, which is directly coupled into five waveguides that bring the light to five different locations along a fluidic channel for absorbance measurements. The transmitted portion of the light is collected at the other side of this cuvette, again by waveguides, and finally detected by the photodiodes. Electrical read-out is accomplished by integrated metal connectors. To our knowledge, this is the first time that integration of all these components has been demonstrated.

Equipment Design↗
PubMed2005

Comparison of three multiple injection regimens for Type 1 diabetes: morning plus dinner or bedtime administration of insulin detemir vs. morning plus bedtime NPH insulin.

AIMS: This trial investigated the efficacy and safety of two different administration-time regimens with insulin detemir (IDet) to that of a conventional basal insulin regimen with NPH insulin (NPH). METHODS: This multinational, 16-week, open, parallel group trial included 400 people with Type 1 diabetes mellitus (DM) randomized to IDet either morning and before dinner (IDetmorn+din) or morning and bedtime (IDetmorn+bed), or to NPH morning and bedtime (NPHmorn+bed), all in combination with mealtime insulin aspart (IAsp). RESULTS: HbA1c was comparable between the three groups after 16 weeks (P = 0.64), with reductions of 0.39-0.49% points. Lower fasting plasma glucose (FPG) was observed with IDetmorn+din and IDetmorn+bed compared with NPHmorn+bed (9.8 and 9.1 vs. 11.1 mmol/l, P = 0.006), whereas the IDet groups did not differ (P = 0.15). Within-person variation in self-measured FPG was significantly lower for both IDet regimens (sd IDetmorn+din 2.5, IDetmorn+bed 2.6 mmol/l) than for NPHmorn+bed (sd 3.1 mmol/l, P < 0.001), but was comparable between the IDet groups (P = 0.48). Ten-point plasma glucose profiles were lower between dinner and breakfast in the IDetmorn+din group (P = 0.043), compared with the two other groups. Risk of overall and nocturnal hypoglycaemia was similar for the three groups. Lower mean bodyweight was observed with IDet compared with NPH after 16 weeks (difference: (IDetmorn+din)-1.3 kg, P < 0.001, (IDetmorn+bed)-0.6 kg, P = 0.050). CONCLUSIONS: Both IDet regimens were well tolerated and provided lower and less variable glucose levels with no, or less, weight gain than NPH at comparable HbA1c. IDet can be administered either at dinner or bedtime, with similar glycaemic control according to the need of the individual person.

Adolescent↗
PubMed2001

Observation of dynamical ordering in a confined Wigner crystal.

We present measurements of the conduction of nondegenerate free electrons along a low-dimensional channel at low temperatures, using surface-state electrons on liquid helium in novel microelectronic devices. Above 1 K, the electrons form an ideal classical Drude conductor. Below 1 K, Coulomb interactions produce electronic spatial order, leading to strong non-Ohmic effects and negative differential conductivity. Evidence is presented for self-organized current filaments in the channel, created by a nonequilibrium phase transition. Periodic conductance oscillations suggest an anisotropic spatial order with lines of electrons along the channel edges.

Journal Article↗
PubMed2001

Anti-thrombotic and haemorrhagic effects of active site-inhibited factor VIIa in rats.

Active site-inhibited factor VIIa (FFR-rFVIIa) competes with factor VIIa (FVIIa) for binding to tissue factor (TF) and exerts an anti-thrombotic effect. We report an evaluation of the anti-thrombotic properties of FFR-rFVIIa in a model of thrombosis involving two thrombogenic surfaces. Uncoated glass capillaries or glass capillaries coated with TF were incorporated into an arterioarterial shunt in the rat and the occlusion time (OT) of the shunt was determined. An anti-thrombotic activity of FFR-rFVIIa was shown only on the TF-coated surface: the OT of the shunt was significantly prolonged, from 167 +/- 34 s in control animals to 312 +/- 42 s after i.v. bolus administration of 4 mg/kg FFR-rFVIIa. This OT was similar to those observed with the uncoated shunts in untreated animals (353 +/- 84 s). In vitro preincubation of the TF-coated shunt with FFR-rFVIIa significantly prolonged the OT to 245 +/- 45 s in the absence of detectable amounts of FFR-rFVIIa in the plasma. rFFR-rFVIIa weakly prolonged the tail template bleeding time by a factor of 1.5. This effect was more pronounced in animals pretreated with heparin. The anti-thrombotic and prohaemorrhagic effects of FFR-rFVIIa were totally reversed by administration of an equidose of rFVIIa. These results provide new information on the pharmacological properties of FFR-rFVIIa that will be useful for its clinical development.

Animals↗
PubMed2001

Risk factors for male breast cancer--a case-control study from Scandinavia.

We report a population-based case-control study on risk factors for male breast cancer. Data on a broad range of previously suggested risk factors were collected in a set of Scandinavian breast cancer cases and matched controls. Incident cases (n = 282) with histologically verified carcinomas of the breast were identified from notification to the cancer registries of Denmark, Norway and Sweden over a 4-year period 1987-1991 and of these cases, 156 men could be approached and responded. Controls were identified through national central population registers and were matched individually for country, sex and year of birth. Controls with a diagnosis of breast cancer were excluded; 468 of 780 controls responded. Data on risk factors were collected by self-administered questionnaires mailed to the cases between land 2 years after diagnosis and to controls during the same period. The findings were compatible with an increased risk associated with family history of breast cancer (odds ratio (OR) = 3.3, 95% confidence interval (CI) 2.0-5.6), obesity 10 years before diagnosis (OR = 2.1, 95% CI 1.0-4.5) for BMI > 30, diabetes (OR = 2.6, 95% CI 1.3-5.3) and the use of digoxin and methyldopa (OR = 2.0 and 2.1, respectively). The association with family history of breast cancer has been repeated in several studies, while the relation to anthropometric measures has been equivocal. We could not substantiate some associations seen in other studies; namely those with high education, fertility, marital status, testicular injury, liver disease and religion. The detailed questions about gynaecomastia indicated that many cases reported signs of breast cancer as a gynaecomastia. This type of misunderstanding may explain the strong association with gynaecomastia seen in other studies. Several patients died before contact. Thus, risk factors related to a more aggressive male breast cancer or related to high risk of dying (e.g. liver cirrhosis, heavy smoking) may have been missed.

Anthropometry↗
PubMed2001

Comparison of the soluble basal insulin analog insulin detemir with NPH insulin: a randomized open crossover trial in type 1 diabetic subjects on basal-bolus therapy.

OBJECTIVE: Insulin detemir (NN304) is a soluble basal insulin analog developed to cover basal insulin requirements. This trial aimed to compare the blood glucose-lowering effect of insulin detemir with that of NPH insulin (NPH) and to evaluate the two treatments with regard to intrasubject variation of fasting blood glucose, incidence of hypoglycemia, dose requirements, and safety. RESEARCH DESIGN AND METHODS: This multicenter open randomized crossover trial in 59 type 1 diabetic subjects comprised a 2-week run-in period on a basal-bolus regimen with NPH insulin once daily, followed by two 6-week periods of optimized basal-bolus therapy with either once-daily insulin detemir or NPH insulin. RESULTS: The area under the curve, in the time interval 23:00-8:00, derived from 24-h serum glucose profiles, was not statistically significantly different for the two treatment periods (insulin detemir:NPH ratio 89.2:83.5, P = 0.59). The intrasubject variation in fasting blood glucose during the last 4 days of treatment was lower for insulin detemir compared with NPH (P < 0.001). Mean dose requirements of insulin detemir were 2.35 times higher (95% CI 2.22-2.48) compared with NPH. During the last week of treatment, fewer subjects experienced hypoglycemic episodes on insulin detemir (60%) compared with NPH treatment (77%) (P = 0.049). CONCLUSIONS: Insulin detemir was as effective as NPH in maintaining glycemic control when administered at a higher molar dose. The results indicate that insulin detemir may provide more predictable fasting blood glucose with lower intrasubject variation and reduced risk of hypoglycemia compared with NPH.

Adolescent↗
PubMed1993

Chromogranin A and pancreastatin-like immunoreactivity in serum of gastrinoma patients.

Gastrin and pancreastatin-like immunoreactivity were determined by radioimmunoassay methods and chromogranin A was determined by enzyme-linked immunoassay in sera from 18 patients with gastrinomas (Zollinger-Ellison syndrome) and in 20 age and sex matched controls. Gastrin serum levels in the gastrinoma patients were in the range 26-80,000 pmol/l, and in the controls 5-31 pmol/l. Chromogranin A serum levels in the gastrinoma group were in the range 6-2,700 ng/ml (mean +/- SEM: 400 +/- 147 ng/ml). The mean value of chromogranin A was significantly higher than in the control group (8 +/- 2 ng/ml, p = 0.008). The serum levels of pancreastatin-like immunoreactivity in the gastrinoma patients were in the range 23-1,994 pg/ml (597 +/- 123 pg/ml). The mean value of pancreastatin-like immunoreactivity in the gastrinoma group was significantly higher than in the control group (104 +/- 25 pg/ml, p = 0.0002). The levels of chromogranin A and pancreastatin-like immunoreactivity were significantly higher in patients with verified metastatic disease (p = 0.04, p = 0.01 respectively). There was a significantly positive correlation between levels of gastrin and pancreastatin-like immunoreactivity (r = 0.7, p = 0.002), while no correlation was found between gastrin and chromogranin A levels or between levels of chromogranin A and pancreastatin-like immunoreactivity. The study demonstrates an elevation of both chromogranin A and pancreastatin-like immunoreactivity in serum of gastrinoma patients. The lack of correlation between gastrin and chromogranin A, however, gives an indication that the gastrinoma cells are not the main source of serum chromogranin A elevation.

Adult↗
PubMed1992

Effects on the rat oxyntic mucosa of the histamine2-antagonist loxtidine and the H+, K(+)-ATPase inhibitor omeprazole.

The present study examined whether histamine could affect the growth of the enterochromaffin-like (ECL) cell and the parietal cell. The effects of the unsurmountable histamine H2-receptor antagonist loxtidine (80 mg/kg) and the H+, K(+)-ATPase inhibitor omeprazole (100 mumol/kg) were compared in female Sprague-Dawley rats. Both drugs were given by gavage once daily for 3 months. Omeprazole induced a more pronounced and sustained hypergastrinaemia than loxtidine. In spite of marked hypergastrinaemia during most of the day, even in the loxtidine-treated rats, the weights of the stomach and oxyntic mucosa were elevated only in the omeprazole-treated rats. The ECL cell density was slightly higher in the loxtidine- than in the omeprazole-treated rats. Both treatments elevated the gastrin-stimulated histamine release from the vascularly perfused stomach. The parietal cell density was unaffected by omeprazole treatment, whereas it tended to be reduced in the loxtidine-treated rats. Simultaneous administration of loxtidine and omeprazole reduced the sustained hypergastrinaemia induced by omeprazole given alone. The present study may indicate that histamine inhibits the growth of the ECL cell, but further studies are needed to elucidate if histamine has any trophic effect on the parietal cells.

Animals↗
PubMed1987

Some acute effects of monochromatic ultraviolet B irradiation on mouse epidermis measured by the tetrazolium-reduction test and determination of DT-diaphorase activity, with reference to carcinogenesis.

Some acute epidermal effects of monochromatic ultraviolet B (UVB) irradiation on hairless mouse skin were measured by the tetrazolium test (TZT), and by determining the DT-diaphorase activity in epidermal cells. Dose response and time course studies were carried out after UVB irradiation at 280, 290, 297 and 302 nm. Appropriate UV doses at all the wavelengths increased the cellular deposition of formazan (TZT). At higher doses the epidermal cells became too injured to react. Wavelengths at 280 and 290 nm seemed more injurious than those at 297 and 302 nm. There was, however, no increase in DT-diaphorase activity after UVB irradiation. This indicates that the increased formazan deposition (TZT) after UVB is more likely to be caused mainly by membrane effects. Detoxification mechanisms which activate DT-diaphorase, as often seen after cellular contact with chemical carcinogens, are not involved.

Animals↗
PubMed1987

Carcinogenic doses of methylnitrosourea induce dose response related delay in transit through S and G2 phases in mouse epidermis: a cell kinetic study.

The cell kinetic, tumorigenic and carcinogenic effects of the short acting, alkylating carcinogen N-methyl-N-nitrosourea (MNU) on hairless mouse epidermis were investigated. The epidermal mitotic rate, the mitotic index, and the number of basal and suprabasal cells were scored in histological sections. Incorporation of [3H]thymidine and flow cytometric analysis of cellular DNA and protein content were performed on isolated basal cells at intervals for up to 10 days after a single application of either 1 or 10 mg MNU. The ensuing tumor rates and yields were observed for up to 48 weeks after 1 mg MNU and 30 weeks after 10 mg MNU. Generally, MNU induced an initial delay in epidermal cell cycle progression with an accumulation of cells in the S and G2 phases. Some days after treatment the delayed cells were released and entered mitosis. One milligram MNU caused a moderate delay of cells in S and G2, lasting for 2-3 days, and this was followed by a release leading to an increased number of suprabasal cells on day 7. The highest dose of MNU caused a more pronounced delay in transit through S and G2 and seemed to be followed by rapid regenerative proliferation. The subsequent tumor crop after 10 mg was significantly higher than that seen after the lowest dose. The present cell kinetic results are consistent with previous data from the study of other carcinogens, all showing a carcinogen-induced initial reduction in DNA synthesis after appropriate doses. A delay in transit through G2 phase was found as well, indicating that a general delay in cell cycle progression may follow the application of most (or all) carcinogens.

Adenoma↗
PubMedDate not supplied

Neonatal alloimmune thrombocytopenia in a quarter horse foal.

Neonatal alloimmune thrombocytopenia is recognized as a spontaneous disease of human infants, piglets, and possibly mules, but it has not been previously reported in horses. A 1-day-old Quarter Horse foal presented to Michigan State University Large Animal Clinic with severe thrombocytopenia of unknown origin. Immunoglobulins that bound to the foal's platelets were identified in the mare's plasma, serum, and milk by indirect assays. The immunoglobulins were further shown to recognize platelets from the foal's full brother, born 1 year earlier. These findings, coupled with the clinical course of the foal during its period of hospitalization, strongly suggest that neonatal alloimmune thrombocytopenia can spontaneously occur in neonatal horses. This diagnosis should be considered for foals with severe thrombocytopenia when other causes can be excluded, and platelet antibody assays should be used to support this diagnosis.

Animals↗