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Biomedical subjects

R Landgraf

Publications and source records attributed to R Landgraf.

At least 271 records · Page 15Linked to original sources
PubMed1989

Blood glucose measurement by infrared spectroscopy.

For the development of an implantable artificial endocrine pancreas, a sensor for blood glucose measurement is needed providing a long-term stability. This goal can be achieved by the application of infrared spectroscopy which, unlike electrochemical sensors, responds directly to the glucose molecule. An investigation under physiological conditions revealed five glucose absorption bands in the near and middle infrared range. These are 1040, 1085, 1109, 1160 and 1365 cm-1. Only the 1040 cm-1 frequency coincides with none of the other infrared-active blood substances like proteins, lipids and urea. Nevertheless, the other absorption bands too, especially the 1109 cm-1 frequency, can be used for blood glucose measurement, if the superimposed absorptions are compensated. Methods for the compensation have been found. Technically feasible embodiments of an infrared glucose sensor are described.

Blood Glucose↗
PubMed1988

Measurement of septal release of vasopressin and oxytocin by the push-pull technique following electrical stimulation of the paraventricular nucleus of rats.

The release of vasopressin (AVP) and oxytocin (OXT) within the septum was studied with the push-pull perfusion technique in 6 conscious, freely behaving male rats. Push-pull perfusion was performed via a chronically implanted cannula and samples collected for 3 consecutive 30-min periods. Stimulating electrodes were implanted in both the left and right paraventricular nuclei 4 days before the experiment. Bilateral electrical stimulation (10-s trains every 4 min) of the paraventricular nuclei during the second 30-min period resulted in a significant increase in the release of both AVP and OXT (128% and 159% of control values respectively); release returned to the pre-stimulation value during the final 30-min collection.

Animals↗
PubMed1988

Central and peripheral release of vasopressin and oxytocin in the conscious rat after osmotic stimulation.

Vasopressin (AVP) and oxytocin (OXT) were measured by radioimmunoassay in push-pull perfusates and tissue samples of various brain areas, plasma and cerebrospinal fluid (CSF) of male rats in response to osmotic stimulation. Hypertonic saline caused a significant rise in plasma AVP and OXT and different changes in peptide contents, in the septum and hippocampus at 30 and 60 min after intraperitoneal injection. Push-pull perfusion (20 microliters artificial CSF/min, 30-min periods) of the septum and dorsal hippocampus of conscious, unrestrained animals revealed a significant, stimulus-evoked release of both AVP and OXT. This release was: (1) not always reflected by corresponding changes in the regional peptide content; (2) simultaneous with the peripheral release from the posterior pituitary; and (3) probably the result of synaptic/parasynaptic events as suggested by use of agents in the artificial CSF which either inhibit or facilitate the release from intact fibre terminals.

Animals↗
PubMed1988

Pancreatic transplantation using the duct occlusion technique.

Since 1979, the Munich Group has gathered experience with 100 consecutive pancreas transplants using the duct occlusion technique. At the present time, 40 of the pancreas grafts (44%) and 56 of the renal grafts (65%) of 90 patients who received both a pancreas and a kidney are still functioning. The mortality rate of 18% in the early period was relatively high. In the period from 1984 until 1988--using the simple transplantation technique--only one patient died. During this period, our overall results improved with the use of a modified surgical technique and different immunosuppressive and anticoagulative measures along with better patient selection. Normalization of the glucose metabolism seems to improve the rate of late diabetic complications. The duct occlusion technique in isolated pancreas transplants might have been a disadvantage in accounting for the poor results. With regard to metabolic studies, there is now ample evidence to suggest that successful pancreatic transplantation leads to complete normalization of glucose metabolism including normoglycemia in more than 70% of all patients. In addition, clinical data are accumulating that suggest successful pancreatic transplantation has a beneficial effect on the late secondary syndrome of Type I diabetes mellitus.

Cyclosporins↗
PubMed1987

Increased thromboplastic potential in diabetes: a multifactorial phenomenon.

Coagulation parameters, platelet aggregation, and thromboxane production as well as metabolic parameters were measured in 31 diabetic patients, 12 without and 19 with clinically manifest late complications, and in 14 healthy control subjects. Spontaneous in vitro aggregation as well as ADP, collagen, and arachidonic acid induced aggregation were higher in both groups of diabetic patients, without an increase in thromboxane B2 production. In diabetic patients with late complications an increase in fibrinogen, fibrinogen cyanogen bromide peptide, factor VIII related antigen, C1-esterase inhibitor, and antithrombin III was observed in comparison to healthy subjects. Fibrinogen, C1-esterase inhibitor, and factor VIII related antigen were already elevated in diabetic patients without clinically manifest late vascular complications. No strict correlations were found between serum glucose, glycosylated hemoglobin, and glycosylated albumin, on the one hand, and coagulation promoting or inhibiting factors, aggregation or thromboxane B2 production, on the other, in either control or diabetic subjects. Also no correlations existed between the coagulation parameters and the aggregation results. In vitro incubation of pooled normal plasma with different glucose concentrations had no influence on the methods by which the coagulation parameters were measured. These data indicate that rather early in the diabetic state many changes take place in different phases of the thrombostatic process, all resulting in an increased hemostatic diathesis.

Adult↗
PubMed1987

Immunoturbidimetric assay for the determination of microalbuminuria using the Hitachi analyser.

A sensitive and specific immunoturbidimetric method is described for the determination of low concentrations of urinary albumin using a Hitachi 704 or 705 analyser. The sensitivity was 1 mg/l and the precision attained was good (CV 15%, 7% and 6% for low, medium and higher albumin concentrations). The assay was used to determine urinary albumin excretion rates in healthy controls (less than 15 micrograms/min) and in type I diabetics. Since microalbuminuria (30-200 micrograms/min) seems to be a good predictor for the development of diabetic nephropathy and other late diabetic complications, this assay is suitable for the necessary screening and follow-up of diabetic nephropathy. In contrast to RIA methods, no radioactive tracers are needed.

Adolescent↗