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Biomedical subjects

L O Kristensen

Publications and source records attributed to L O Kristensen.

16 recordsLinked to original sources
PubMed1990

Impaired receptor binding and decrease in isoelectric point of lactoferrin after interaction with human monocytes.

The iron-binding glycoprotein lactoferrin binds to specific receptors on human monocytes as an initial step implicated in monocytic iron deposition. In this study, the properties of lactoferrin were studied after its interaction with human monocytes. Rebinding of lactoferrin to its monocytic receptor was grossly impaired and a small decrease in isoelectric point from 8.9 to 8.8 was observed. In contrast, antigenic and iron-binding properties of lactoferrin were preserved, the molecular weight by SDS-polyacrylamide gel electrophoresis was unchanged and no low-molecular fragments were detected by gel-filtration. These findings indicate that lactoferrin molecules cannot operate in a cyclic manner to deposit iron. Furthermore, these results might contribute towards explaining the complex disappearance kinetics observed for lactoferrin in plasma.

Chromatography, Gel↗
PubMed1989

Decrease in ureagenesis by partial hepatectomy does not influence acid-base balance.

It has been suggested that urea synthesis participates directly in body pH homeostasis by removal of bicarbonate. To elucidate this hypothesis sodium bicarbonate or sodium chloride was infused (11.5 mumol/min) for 90 min into control rats and into rats that had undergone an 85% hepatectomy immediately before starting the infusion. Urea synthesis rate was 2.6 +/- 0.3 mumol/min (mean +/- SE) in controls, and was significantly (P less than 0.01) reduced to 1.0 +/- 0.2 mumol/min in partially hepatectomized rats. At the start of bicarbonate infusion, pH was 7.38 and 7.34 in control and partially hepatectomized rats, respectively, and at the end of infusion, pH was 7.56 and 7.51. Standard bicarbonate at start of bicarbonate infusion was 21.9 and 21.3 mM in controls and partially hepatectomized, respectively, and it increased to 32.7 and 29.9 mM at end of infusion. In saline-infused rats a slight decrease of approximately 0.05 pH units was observed during the experiment, but again no difference emerged between control and partially hepatectomized rats. It is concluded that a major role of the liver in the regulation of acid-base balance is unlikely.

Acid-Base Equilibrium↗
PubMed1988

Lactoferrin-mediated transfer of iron to intracellular ferritin in human monocytes.

Interactions of 125I-59Fe-lactoferrin with human monocytes were studied. After 4 hours of incubation, the uptake of 59Fe exceeded that of 125I. In dissociation studies the cellular 59Fe-activity was only partly dissociable during 16 h, whereas the 125I-activity could be released nearly completely. Disruption of the cells and studies on the cytosolic phase were performed employing gel-filtration and affinity chromatography. An appreciable amount of lactoferrin was found in the cytosolic phase. About 50% of the cytosolic 59Fe-activity was bound to ferritin. The results suggest that lactoferrin is internalized into monocytes and that iron is transferred to ferritin. These cellular events may contribute to an understanding of the accumulation of iron in the monocyte/macrophage system observed during inflammatory conditions.

Cells, Cultured↗
PubMed1986

Effects of perturbation of the Na+ electrochemical gradient on influx and efflux of alanine in isolated rat hepatocytes.

Transmembrane alanine transport was studied in hepatocytes isolated from 48-h fasted rats. Aminooxyacetate was used to render alanine nonmetabolizable. Gramicidin D eliminated the transmembrane Na+ electrochemical gradient. At 135 mM Na+ and 0.1 mM alanine gramicidin D decreased the steady-state intracellular-to-extracellular alanine distribution ratio from 20.2 to 0.9. The underlying kinetic changes appeared to be a decrease in alanine influx to one-third of the control value and an increase in the rate constant of alanine efflux by a factor of 9. Analogous changes were observed when the Na+ gradient was decreased by ouabain. The inhibitory effect of gramicidin D on alanine influx was confined to the Na+-dependent, saturable component which showed a prominent increase in the apparent Km for alanine and a small decrease in the apparent Vmax. The effect of gramicidin D on alanine efflux was related to the increased cytosolic Na+ concentration: the rate constant of alanine efflux was increased by cytosolic Na+ with half-maximal stimulation at 30 mM; voltage-sensitive alanine efflux could not be demonstrated.

Alanine↗
PubMed1986

Associations between transports of alanine and cations across cell membrane in rat hepatocytes.

Alanine transport across the liver cell membrane is a regulated key process in the amino acid metabolism of the body. The majority of alanine influx in hepatocytes is Na+ dependent and is stimulated by intracellular negativity. The molar ratio between cotransported Na+ and alanine is 1:1. Alanine efflux is stimulated by intracellular Na+, whereas the role of the membrane potential is unclear. The transmembrane Na+ electrochemical gradient seems to be the exclusive driving force for cellular alanine accumulation. At a physiological Na+ gradient, intracellular alanine can exceed the extracellular concentration about 20-fold, but metabolism will exert a conspicuous sink effect. Na+-coupled uptake of alanine appears to be a challenge that triggers a sequence of regulatory events: increased cellular Na+ leads to an increase in active Na+-K+-pumping and thus in K+ influx; influx of alanine and cations tends to increase the cellular content of osmotically active substances implying a tendency to water uptake; cell swelling, even when modest, induces an increase in the permeability of a conductive pathway for K+ leading to net efflux of K+ (with accompanying anions) and cellular hyperpolarization. Net efflux of K+ prevents excessive cell volume increase during amino acid accumulation, whereas hyperpolarization tends to support the driving force for alanine influx (and anion efflux). The pathway for K+ efflux needs further characterization, but it may involve single-file diffusion with Ca2+ as an activator. This model suggests that cell volume regulatory processes mainly serve to compensate for changes in intracellular content of ions and metabolites during activation of specialized cellular processes.

Alanine↗
PubMed1979

Development of ketonemia in fasting patients with hyperthyroidism.

Concentrations of ketone bodies, free fatty acids, glycerol, lactate, glucose, insulin, glucagon and cortisol were determined 6-hourly during 36 hours of fasting in 4 hyperthyroid patients and in 4 euthyroid controls. The concentrations of ketone bodies were elevated in hyperthyroid patients from the beginning and increased during fasting more rapidly and to higher values as compared to the controls. After 6 hours of fasting the blood ketone concentrations were 1.1--1.8 mM in hyperthyroid patients and 0.3--0.6 mM in the controls. After 36 hours the concentrations had increased to about 3.5 mM and 1.4 mM in hyperthyroid and control subjects, respectively. The concentrations of free fatty acids were identical in the groups compared postprandially, but increased significantly more in the hyperthyroid patients than in the controls during fasting. The glycerol concentration was higher in the hyperthyroid group throughout the observation period. The concentrations of insulin were slightly higher in the hyperthyroid group than in the control, whereas the concentrations of the "ketogenic" hormones, glucagon and cortisol were identical in the compared groups. It is concluded that hyperthyroidism leads to an increased tendency to ketosis, that is partly explained by increased concentrations of free fatty acids and that might also involve a direct action of long term thyroid hormone excess on enzyme activities (e.g. carnitine acyltransferase in liver).

Adult↗
PubMed1979

Determination of unidirectional fluxes of phosphate across plasma membrane in isolated perfused rat liver.

In livers labeled with 32P by intraperitoneal injection 18 h before perfusion the unidirectional efflux of inorganic phosphate (Pi) was a linear function of the concentration of Pi in the intracellular exchangeable pool of Pi (range, 0--1 mumol/g liver). Calculations of the efflux were based on determination of the specific radioactivity of Pi in the intracellular exchangeable pool of Pi by a new method. Zero efflux was found at biopsy concentrations of Pi of about 1.8 mumol/g liver. The influx of Pi was calculated from the efflux and the net uptake of Pi; it was found to be related to the extracellular concentration of Pi in a fashion that was approximately linear. An increase in the concentration of Pi in the input medium gave rise to an increased influx and, with a time delay, also to a gradually increasing efflux. The increased efflux could be explained as a consequence of an increased intracellular concentration of exchangeable Pi.

Animals↗
PubMed1975

Renal function and the rate of disappearance of methotrexate from serum.

The disappearance of methotrexate (MTX) from serum was studied using H3-MTX. The overall elimination half-life (MTX T1/2) was well defined from one to about six hours after i.v. administration; in 25 patients it ranged from 102 min to 750 min and was inversely related to endogenous creatinine clearance, which ranged from 6 to 140 ml/min. The corresponding apparent volume of distribution, V, obtained by extrapolation tended to decrease at lower levels of renal function. The total clearance of MTX calculated in this period varied linearly with creatinine clearance. In patients with normal serum creatinine concentration, the half-life increased with advancing age, which reflects the concurrent age-dependent decrease in creatinine production and renal function. This illustrates the need for knowledge of renal function, not based solely on serum creatinine concentration, in patients treated with methotrexate or other drugs eliminated by the kidneys. In 9 patients the results were not affected by treatment with diuretics (furosemide, hydroflumethiazide). In four patients serum MTX concentration was measured for up to 24-72 hours. An increasing half-life of MTX with time was found, suggesting that the elimination kinetics of the drug would be most adequately described by a multi-compartment model.

Adult↗