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Biomedical subjects

J Kolb

Publications and source records attributed to J Kolb.

At least 19 recordsLinked to original sources
PubMed2006

Relativistic density functional calculations using two-spinor minimax finite-element method and linear combination of atomic orbitals for ZnO, CdO, HgO, UubO and Cu2, Ag2, Au2, Rg2.

In previous work the authors have presented a highly accurate two-spinor fully relativistic solution of the two-center Coulomb problem utilizing the finite-element method (FEM) and furthermore developed a relativistic minimax two-spinor linear combination of atomic orbitals (LCAO). In the present paper the authors present Dirac-Fock-Slater (DFS-) density functional calculations for two-atomic molecules up to super heavy systems using the fully nonlinear minimax FEM and the minimax LCAO in its linearized approximation (linear approximation to relativistic minimax). The FEM gives highly accurate benchmark results for the DFS functional. Especially considering molecules with up to super heavy atoms such as UubO and Rg2, the authors found that LCAO fails to give the correct systematic trends. The accurate FEM results shed a new light on the quality of the DFS-density functional.

Journal Article↗
PubMed2000

Absorption and metabolism of genistin in the isolated rat small intestine.

Uptake and intestinal metabolism of physiologically active genistin were studied in an ex vivo intestinal perfusion model; luminally applied concentrations were 5.9, 12.0, and 23.8 micromol/l. The intestinal absorption of genistin was 14.9% (+/-2.3, n=9), irrespective of the amounts applied. The majority of the absorbed genistin appeared as genistein glucuronide (11.6%), also recovered as the main metabolite on the luminal side (19.5%). Minor amounts of genistin (1.3%) and genistein (1.9%) were found on the vascular side, whereas 15.4% of applied genistin was luminally cleaved to yield genistein. Sulfate derivatives of genistein or genistin were not observed.

Animals↗
PubMed2000

Observations on the relationship between the extracellular changes of taurine and glutamate during cortical spreading depression, during ischemia, and within the area surrounding a thrombotic infarct.

Taurine and glutamate were monitored by microdialysis technique during various cerebral insults: a. Application of K+ triggered a cortical spreading depression (CSD). Taurine and glutamate increased concomitantly but recovery of glutamate was faster than that of taurine. b. Application of NMDA induced also CSD but only taurine increased. c. Induction of an infarct triggered repetitive CSDs. Taurine increased rapidly whereas glutamate rose slowly starting with some delay. d. After induction of ischemia, taurine and glutamate increased after onset of depolarisation. The increase of glutamate occurred late after a small, transient increase in parallel with the depolarisation. These data suggest a close functional relationship between the changes of both amino acids. Therefore, they should be monitored together especially in clinical settings: during excitation, only taurine will increase; during overexcitation, taurine will also increase but to a higher maximum followed by a moderate rise of glutamate; after energy failure, taurine will accumulate to its highest level followed by a continuous rise of glutamate.

Animals↗
PubMed2000

Isoflavones from tofu are absorbed and metabolized in the isolated rat small intestine.

Studies suggest a variety of biological effects of soybean isoflavones, but there is little information regarding small intestinal absorption and metabolism. The aim of this study was to investigate intestinal handling of luminally administered soybean-based tofu in an isolated preparation of the luminally and vascularly perfused rat small intestine (male Sprague-Dawley, approximately 45 d old). A synthetic emulsion free from blood components was used as vascular medium, with a perfluorocarbon as oxygen carrier. Luminal media consisted of tofu, predigested with pepsin and pancreatin and emulsified with bile acids, containing 39. 5 micromol/L genistein compounds and 19.1 micromol/L daidzein compounds. Viability of the organ preparation was maintained during the entire perfusion, confirmed by lack of significant differences between tofu and control perfusion experiments for arterial pressure, glucose consumption, oxygen uptake, lactate-pyruvate ratio and acid-base homeostasis. Daidzein (8.9%) and genistein (8.0%) compounds from tofu exhibited almost the same (P: > 0.05) absorption rate during small intestinal passage. The majority of the absorbed genistin appeared vascularly as genistein (4.4%), in addition to minor amounts of unchanged genistin (2.1%) and genistein glucuronide (1.5%). In the luminal effluent, a considerable increase of genistein (338%) as well as daidzein (190%) as cleavage products of the glucosides and malonyl-glucosides was observed. The distribution of daidzein compounds in the small intestine was not different from that of genistein compounds (P: > 0.05), except for the blood vessels, which had extremely low total amounts. Sulfate derivatives of genistein and daidzein compounds were not detectable. An effect of tofu ingredients was observed on absorption rate of genistin, on glucuronidation and on distribution of genistein glucuronide in the intestine.

Animals↗
PubMed2000

Absorption and metabolism of genistein in isolated rat small intestine.

Studies suggest a variety of biological effects for the isoflavonoid genistein, but there is little information regarding small intestinal absorption and metabolism. The aim of this study was to investigate the absorption and metabolism of luminally administered genistein in an isolated preparation of luminally and vascularly perfused rat small intestine. A synthetic perfusate free from blood components was used as vascular medium, with a perfluorocarbon as oxygen carrier. Luminal media consisted of a bicarbonate buffered sodium chloride solution spiked with genistein (12 micromol/L). Viability was maintained during the entire perfusion as indicated by no significant differences between genistein and control perfusions for perfusion pressure, lactate-pyruvate ratio, oxygen uptake and acid-base homeostasis. Luminal disappearance rate of genistein did not change throughout the entire perfusion time. After a significant increase until about 30 min, vascular appearance rate of total genistein reached an equilibrium. The intestinal absorption of luminally administered genistein was 40.6%, corresponding to an average uptake of 2.9 nmol. min(-1). g dry intestine(-1). The majority (31.3%) of the absorbed genistein appeared as genistein glucuronide, also recovered as the main metabolite on the luminal side (13.3%). Only small amounts of genistein (2.6%) and genistein glucuronide (2.9%) were found in the intestinal tissue. The results demonstrate a favorable uptake of genistein, a pertinent addition to the ongoing discussion about health benefits of isoflavones.

Animals↗
PubMed2000

Assessment of resveratrol bioavailability in the perfused small intestine of the rat.

Resveratrol, which is present in grapes, wine and peanuts, is believed to possess chemoprotective properties such as anticarcinogenic effects and to provide protection against cardiovascular diseases. Little is known, however, about its intestinal absorption. We investigated the absorption and metabolism of resveratrol by using an isolated preparation of luminally and vascularly perfused rat small intestine. A synthetic perfusate free from blood components was used as vascular medium with a perfluorocarbon as oxygen carrier. Luminal media consisted of a bicarbonate buffered sodium chloride solution spiked with resveratrol in physiological, nutritionally relevant concentrations (28, 34 and 57 micromol/l, respectively). Viability was maintained during the entire perfusion and no significant differences between resveratrol and control perfusions for oxygen consumption, arterial pressure, lactate-pyruvate ratio and acid-base homeostasis were observed. Vascular uptake of luminally administered resveratrol was 20.5%. The majority of the absorbed resveratrol was conjugated to yield resveratrol glucuronide (16.8%), which was also the main luminal metabolite (11.2%). Lesser amounts of resveratrol sulfate, 3.0% and 0.3%, were found on the luminal and vascular side, respectively, while only minute amounts of resveratrol and resveratrol conjugates (1.9%) were found in the intestinal tissue. The structures of the resveratrol conjugates were verified by liquid chromatography coupled with mass spectometry (LC-MS). The results demonstrate an ample uptake and metabolic conversion of resveratrol. The proposed perfusion model serves as a tool to evaluate intestinal absorption and metabolic handling of phytochemicals, a pertinent input to the ongoing discussion about their health benefits.

Animals↗
PubMed1998

Effects of subchronic administration of metrifonate on cholinergic neurotransmission in rats.

The effects of subchronic oral administration of metrifonate, a long-acting cholinesterase (ChE) inhibitor, on cholinergic neurotransmission were assessed in young adult male Wistar rats. Animals were treated twice daily with metrifonate. In a pilot study testing a 100 mg/kg dose of metrifonate for up to 14 days, ChE activity was found to steadily decrease to reach maximum inhibition levels of about 55%, 80% and 35% in brain, erythrocytes and plasma. Steady-state inhibition levels were attained by the 10th day of treatment. When metrifonate-treatment was discontinued, ChE activity in plasma returned to control levels within another day, while erythrocyte and brain ChE activity took more than 2 weeks to recover. In subsequent dose-response studies, metrifonate treatment was given for 3 and 4.5 weeks at doses of 0, 12.5, 25, 50, and 100 mg/kg, to different groups of animals, respectively. Correlation analysis indicted that brain ChE inhibition was more accurately reflected by erythrocyte than by plasma ChE inhibition, although all effects were highly correlated. The changes in ChE activity were not paralleled by changes in other parameters of the cholinergic neurotransmission, such as acetylcholine synthesis rate or acetylcholine receptor binding. It is therefore concluded that repeated administration of metrifonate to rats induces a long-lasting inhibition of ChE activity in a dose-related and predictable manner, which is neither subject to desensitization nor paralleled by counterregulatory downregulation of muscarinic or nicotinic receptor binding sites in brain.

Animals↗
PubMed1997

Lubeluzole blocks increases in extracellular glutamate and taurine in the peri-infarct zone in rats.

A microdialysis probe was positioned inside the peri-infarct zone of a photochemically induced neocortical infarct in rats. Extracellular glutamate rose within 20 min after the start of infarct induction and continued to increase during the 5 h observation period to 5.5-fold the pre-infarct baseline value of 0.8 +/- 0.4 micromol/l. Glutamine increased only 1.4-fold. Changes in peri-infarct glutamate were preceded by steep rises in taurine (a 3.9-fold increase from the baseline value of 2.8 +/- 0.7 micromol/l), which coincided with spreading depressions during infarct induction. Post-treatment with lubeluzole ((S)-4-(2-benzothiazolylmethylamino)-alpha-[(3,4-difluoro-phenoxy) methyl]-1-piperidineethanol, 1.25 mg/kg i.v.), a new cerebroprotective drug, blocked the peri-infarct increases of glutamate and taurine, whereas the R-enantiomer was ineffective. Since lubeluzole has previously been shown to stereospecifically decrease glutamate-activated nitric oxide (NO) toxicity in vitro, the present in vivo stereospecific effect of lubeluzole may be related to modulation of the cascade of NO toxicity, thus preventing NO toxicity-mediated increases in extracellular glutamate. Blockade of the peri-infarct taurine response suggests that lubeluzole also may have reduced cellular osmotic stress in the peri-infarct zone.

Animals↗
PubMed1996

The measurement of extracellular inorganic phosphate gives a more reliable indication for severe impairment of cerebral cell function and cell death than the measurement of extracellular lactate.

The measurement of cerebral extracellular lactate levels has been suggested to be used to monitor cerebral function in intensive care However, although an increase of extracellular lactate levels is a sensitive parameter for increased cellular activity in general, it will be shown that its prognostic value is limited in regard to the severity of the impairment of cellular function. As an alternative the measurement of the extracellular levels of inorganic phosphate (IP) or adenosine is proposed here: Whereas extracellular lactate levels increased rapidly to about the same extents during ischemia (IS) and spreading depression (SD), IP rose during IS only. Adenosine, on the other hand, increased during both events to a different degree. If, therefore, lactate was the only parameter to be monitored after a cerebral insult, the results would not allow to discriminate between a transient, spontaneously recovering event as a SD and a long lasting or an irreversible loss of cell function as in persisting ischemia/hypoxia. The measurement of IP, therefore, seems to be more suitable than that of lactate or adenosine since IP will appear within the extracellular space only after a sustained failure of membrane function. Thus, the measurement of IP changes turned out to be the more useful parameter for intensive care supervision.

Adenosine↗
PubMed1995

[MRI studies on the distensibility of cruciate ligaments of healthy knee joint].

AIM: Examination of the distensibility of the cruciate ligaments to evaluate the tense plasty of the cruciate ligaments. MATERIAL AND METHOD: A functional MR study was performed using a Magnetom Open (0.2 Tesla, Fa. Siemens). We measured the length and width of the anterior and posterior cruciate ligament in volunteers (n = 12), age 20-40. We examined in 4 knee positions between maximal extension and maximal flexion. RESULTS: Using the Wilcoxon test, the statistics do not show any significant difference between the length and width of the cruciate ligaments in the monoxial movement. CONCLUSION: Our results may support the operative tense plasty of the cruciate ligaments although the entire complex mechanical system has not been examined.

Adult↗
PubMed1993

Isolation of Chlamydia spp. from ostriches (Struthio camelus) (short report).

Post mortem examination of ostrich chicks (Struthio camelus) originating from a flock with a high mortality rate is described. The main pathological lesions found, indicated colibacillosis which was further corroborated by the isolation of pure culture E. coli. Furthermore Chlamydia spp. was isolated for the first time from ostriches. A detailed isolation procedure is presented. The association of colibacillosis with Chlamydia and the latency of Chlamydia is discussed.

Animals↗
PubMed1992

Extracellular changes of inorganic phosphate are different during spreading depression and global cerebral ischemia of rats.

Tissue levels of inorganic phosphate (iP-) and lactate (lac) increase during cerebral ischemia and cortical spreading depression (SD). Since cell membranes become leaky during these insults, iP- and lac were expected to leak into the extracellular space (ECS). In order to find out whether this occurs or does not, a microdialysis (MD) fiber was implanted into the cortex of anesthetized rats and extracellular lactate (lac(e)) and extracellular iP- (iPe-) were determined during various insults. Extracellular lactate increased to about the same extent during ischemia and SD. In contrast, iPe- increased during ischemia but not during SD. Instead, iPe- started to rise after SD and reached its maximum about 45 min later. The distinct pattern of iPe- in comparison to lac(e) during the above mentioned insults points to a qualitative difference of the underlying mechanisms: whereas lac appears within the ECS at any stressful situation, elevation of iP- within the ECS indicates depletion of energy stores in parallel to the lack of control of ion homeostasis.

Animals↗
PubMed1992

Lactate and pH change in close correlation in the extracellular space of the rat brain during cortical spreading depression.

pH sensitive microcelectrodes were used in combination with microdialysis (MD) technique to measure extracellular pH (pHe) and extracellular lactate (lace) within the cortex of rat brains during cortical spreading depression (SD). SD was induced by local K(+)-application and identified by DC recordings. It was accompanied by an extracellular acidification of 0.34 +/- 0.06 pH units and by a 2.8 +/- 0.80 fold increase of lace; the recovery of pHe took place within three phases, that of lace within 2 phases. The recovery of both parameters was complete about 45 min after the onset of SD. We conclude that the changes of lace and pHe are closely related. This indicates both lactate and protons to be transported in parallel.

Animals↗
PubMed1991

The internal reference technique in microdialysis: a practical approach to monitoring dialysis efficiency and to calculating tissue concentration from dialysate samples.

In microdialysis experiments, 'recovery' estimations are required to calculate extracellular concentrations of the compounds determined. Generally, relative recovery (RR) is determined in vitro as: RR = cd/cs, with (cd) being the concentration of a compound in a dialysate fraction and (cs) its known concentration within a sample solution. To determine recoveryin vivo, relative loss (RL) was defined RL = (cp-cd)/cp with (cp-cd) being the loss of a compound from the perfusate and (cp) its perfusate concentration. RL was determined in vitro and in vivo by adding an 'internal reference compound' to the perfusate. Here, 14C-labelled lactate was used as the compound of interest. Comparing RL and RR in vitro, we found both to be similar. In vivo, however, RL was 34% of RL(in) vitro (CSF) and 46% of RL(in) vitro in agar-containing CSF. During ischaemia, RL of lactate even decreased to only 35% of the pre-ischaemic control level. We conclude that RL and RR represent inverse measurements of 'recovery.' Whereas RR can only be determined in vitro, RL can be determined in vivo. We found recoveryin vivo to be different from recoveryin vitro. Moreover, recoveryin vivo decreased during ischaemia. By means of the measured recoveryin vivo extracellular lactate concentrations prior and during ischaemia were calculated. The results, therefore, validate the 'internal reference technique' as a practical method for estimating recoveryin vivo and for controlling dialysis efficacy in vivo even continuously.

Animals↗
PubMed1989

Influence of flunarizine on postischemic flow and energy metabolism in the isolated rat brain.

Isolated perfused rat brains were subjected to complete ischemia. Reperfusion was started 10 min after the negative DC-shift. In control brains, recovery of flow was retarded and, after 10 min of reperfusion, a delayed hypoperfusion developed. In flunarizine-treated brains, recovery of flow was considerably steeper, complete and without reduction during the further course of reperfusion. Additionally, restoration of energy metabolism and mitochondrial function was significantly improved. The effect on the energetic state of the brains was at least partly independent of the improvement of flow. This could be concluded from experiments in which reperfusion was commenced simultaneously with DC-negativation. In these experiments, flow recovery was prompt and complete in control as well as in treated brains. Nevertheless, treated brains exhibited after reperfusion significantly better ratios of ATP to ADP and normalized levels of lactate and succinate.

Animals↗
PubMed1983

Bioluminescent and fluorometric techniques for determinations of 19 metabolites of ADP/ATP-dependent transformations in energy metabolism in 200 (or 400) mg muscle.

A procedure is described for the determination of the following 19 metabolites in 200 mg gastrocnemius muscle from guinea pig: glucose 1-phosphate and 6-phosphate, fructose 6-phosphate, fructose 1,6-bisphosphate, glyceraldehyde 3-phosphate, dihydroxyacetone phosphate, 3-phospho- and 2-phosphoglyceric acid, phosphoenolpyruvate, pyruvate, glycerol, glycerol 3-phosphate, AMP, ADP, ATP, inorganic phosphate, creatine, creatine phosphate. Bioluminometric and fluorometric techniques for mono- and dinucleotide determinations were used. In the case of fluorometric measurement for NADH, 400 mg tissue were necessary. The coefficient of variation for assays on the same sample was 0.04 for bioluminometric techniques and 0.10 for fluorometric techniques.

Adenosine Diphosphate↗