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N J Birch

Publications and source records attributed to N J Birch.

At least 37 records · Page 2Linked to original sources
PubMed1992

Ileal mucosal absorption of bile acid in man: validation of a miniature flux chamber technique.

A method that allows the quantitative assessment of ileal mucosal cell uptake and transport of bile acids in mucosal biopsy specimens has been validated. Viability of the tissue was confirmed by maintenance of normal cell morphology, wet weight, extracellular space, porosity to polyethylene glycol-900, lactate dehydrogenase release, and transmucosal potential difference. Using 14C-taurocholic acid, absorption was shown to be directional, capable of working against a concentration gradient, reduced by metabolic inhibitors, and sodium dependent. The system showed saturation kinetics with an estimated Km of 10 mumol/l. At a standard substrate concentration of 10 mumol/l ileal mucosal bile acid absorption was compared in patients with colorectal cancer (n = 6), ulcerative colitis (n = 10), and slow transit constipation (n = 8). There was no significant difference in tissue uptake or transport between the three groups.

Bile Acids and Salts↗
PubMed1992

Magnesium, adenosine triphosphate, and catecholamine complexes: application of new means of identifying solute-solute interactions of biological significance using NMR chemical shift data.

The interaction of magnesium ions with biomolecular species is fundamental to the regulation of many biological processes. A mathematical technique to investigate such interactions is described. The concept of a pseudo-formation curve is discussed and the relevance and applicability of such constructions to the study of solute-solute interactions is outlined. Analysis of curves based on the published variation of chemical shift data of various nuclei of adrenaline and dichloroisoprenaline in aqueous solution, in the presence of increasing concentration of the complex Mg-ATP, is described. Unambiguous indentification of specific interactions and the stability of the species produced is shown to be feasible. Some variation of the values of formation constants deriving from different nuclei reflects the significance of molecular environmental factors on the parameters used.

Adenosine Triphosphate↗
PubMed1992

Isotopic differences in the lithium transport rate in human erythrocytes during simultaneous incubations with the stable isotopes 6Li and 7Li.

The membrane transport of the two stable lithium isotopes, 6Li and 7Li, by erythrocytes has been studied using a dual channel atomic absorption spectroscopic technique. 6Li appears to be taken up preferentially to 7Li, in the ratio of 10 to 40%, depending on the concentration of total lithium and on the lithium isotopic ratio in the external medium.

Biological Transport↗
PubMed1991

Brief communication: magnesium absorption in human ileum.

A novel technique utilizing samples of human distal ileum removed at surgery was used to study magnesium (Mg) absorption. Specimens of isolated absorptive mucosa were obtained by careful dissection of the tissue to remove the muscle layers, and were mounted in flux chambers. Mean tissue Mg concentration in human isolated intestinal mucosa was found to be within the postulated normal range for human tissue. Mucosal to serosal Mg transport was unaffected by ouabain or 2,4-dinitrophenol and sodium fluoride. Overall, the data indicate Mg absorption in distal ileum to be passive in nature, although a minor active transcellular component cannot be excluded.

2,4-Dinitrophenol↗
PubMed1990

Pharmacokinetics of lithium in patients treated with controlled release lithium formulations.

There has long been discussion as to the relative merits of the lithium formulations available in the UK. Two of these have been shown to exhibit similar pharmacokinetics in normal volunteers and both are now marketed as controlled release formulations. In this study the serum lithium profiles of these formulations were compared in patients at two centres during the first 4 h after the dose, and at 24 h. We were unable to show any significant difference between the formulations in respect of maximum serum lithium concentrations or the concentration at each time point.

Adult↗
PubMed1988

Magnesium interactions with lithium and sodium salts of adenosine triphosphate: an investigation by phosphorus-31 nuclear magnetic resonance spectroscopy.

Phosphorus NMR spectra were recorded for complexes of Na2ATP and Li4ATP with varying concentrations of magnesium, calcium and lithium. Each ion caused a shift in the phosphorus resonances, usually downfield, and a decrease in the 31P-31P coupling constant. The sodium ATP formed a 1:1 complex with each ion and a 1:2, ATP:Mg complex with magnesium whilst lithium ATP gave evidence to suggest the formation of bis(nucleotide) complexes.

Adenosine Triphosphate↗
PubMed1981

Lithium inhibition of phosphofructokinase.

The mode of action of lithium in prophylaxis of recurrent affective disorder is unknown although it has been suggested that lithium might compete with magnesium in magnesium dependent processes. We have previously shown pyruvate kinase to be inhibited by lithium and the present study demonstrates a small inhibition by lithium of phosphofructokinase that is also a major regulatory step in glycolysis. Inhibition of PFK was competitive with respect to ATP and magnesium and noncompetitive with respect to potassium and fructose-6-phosphate. Inhibition was enhanced at reduced concentrations of magnesium.

Adenosine Triphosphate↗
PubMed1980

Pharmacodynamic aspects of long-term prophylactic lithium.

In 90 male and female patients suffering from recurrent affective disorders who had been stabilised for long periods on lithium carbonate an investigation was carried out to determine factors influencing the dosage and excretion of lithium. The findings support the view that lithium excretion is largely controlled by osmotic factors and that it is a function of the overall renal efficiency. The dosage requirement is a function of both body surface area and weight which are closely correctly with measures of renal efficiency though there are also age and sex differences which are independent of body size.

Affective Disorders, Psychotic↗