Biomedical subjects

H M Middleton

Publications and source records attributed to H M Middleton.

23 records · Page 2Linked to original sources

PubMed1978

Jejunal phosphorylation and dephosphorylation of absorbed pyridoxine.HCl in vitro.

The phosphorylation and dephosphorylation of absorbed vitamin was studied in rat jejunal everted sacs during in vitro uptake of [3H]pyridoxine.HCl. Kinetic studies during 4-min incubations demonstrated that phosphorylation was saturable (Km, 13.3 micron; Vmax, 0.906 nmol/4 min/g wet tissue) and was significantly inhibited by both structural and metabolic inhibitors. Longer incubations (30-min) demonstrated similar saturation and inhibition of net phosphorylation. Dephosphorylation of the phosphate esters formed by the phosphorylation step also occurred, as demonstrated by pulse-chase experiments. Disappearance of these phosphates was initially rapid, approximated first order kinetics, and apparently was mediated by a phosphatase. Whereas phosphorylation did not appear to affect initial uptake rates for [3H]pyridoxine.HCl by the jejunum, net phosphorylation after more prolonged incubations qualitatively paralleled accumulation of total absorbed vitamin in tissue over the same time. The primary effect of phosphorylation during jejunal uptake of pyridoxine by rat jejunum was to increase the accumulation of absorbed pyridoxine in tissue during prolonged incubations. Dephosphorylation had the net effect of limiting the magnitude of that accumulation.

Animals↗

PubMed1977

Significance of changes in blood pressure and pulse rate after percutaneous liver biopsy.

Blood-pressure and pulse-rate changes were evaluated prospectively in 50 patients undergoing uncomplicated liver biopsies and retrospectively in 4 patients who, since 1973, had recognized postbiopsy hemorrhage requiring transfusion. In uncomplicated biopsies a wide range of variations in vital signs was encountered between "baseline" and "before" controls and between controls and postbiopsy measurements. To place the changes in perspective, percentile scales were developed for percent maximum deviation from control for systolic blood pressure, diastolic blood pressure, and pulse rate. Analysis of changes in patients with significant hemorrhage revealed; (1) marked changes in vital signs in the early (2-hr) postbiopsy period; (2) the association of early hypertensive changes with pain followed by later evidence of hemorrhage in two of the four patients; (3) the lesser helpfulness of pulse change (1 of 4 bleeders) as compared to blood pressure change (4 of 4 patients).

Biopsy, Needle↗

PubMed1977

Uptake of pyridoxine hydrochloride by the rat jejunal mucosa in vitro.

The kinetics of mucosal membrane transport of pyridoxine hydrochloride were evaluated in vitro in the rat jejunum. Utilizing everted sacs and a double-label isotope technique, short-term incubation within the period of initial linear tissue uptake indicated: 1) no evidence of saturation of uptake over a wide pyridoxine-HCl concentration range (0.01 muM-10 mM); 2) failure of 4-deoxypyridoxine (10 muM), anoxia, iodoacetamide (5 mM), Na+ replacement and ouabain (1 mM) to inhibit uptake of 2 muM pyridoxine-HCl significantly; and 3) a low Q10 value of 1.31. Using single-label techniques, sacs were also incubated for 1 hour in 2 muM pyridoxine HCl with determination of the apparent tissue water-mucosal fluid concentration ratio and chromatographic separation of the various forms of vitamin B6 in tissue. Results demonstrated a failure of pyridoxine in tissue water to achieve a concentration in excess of that in the incubation medium. Data, therefore, were most consistent with passive diffusion as the mechanism for in vitro jejunal mucosal uptake of pyridoxine-HCl in the rat.

Animals↗

PubMed1976

Liver-lung scan in the diagnosis of right subphrenic abscess.

To assess the value of liver-lung scanning in the diagnosis of right subphrenic abscess, 148 scans were reviewed against corresponding charts. Of 91 scans with adequate clinical data, overall scanning error was 19.3% with 14 false positive and 3 false negative scans. Among 49 scans (of the initial group of 91 studies) with presence or absence of actual pathology proved by surgery and/or autopsy, there were 3 true positive, 12 false positive, 29 true negative, and 3 false negative scans. Analysis of data indicated (1) lower accuracy of scan interpretations than generally reported, (2) low specificity for positive scans and high specificity for negative scans, (3) correlations of false interpretations with atypical degrees of liver-lung separation and with scanning defects in liver and lung, and (4) failure of rereading significantly to improve accuracy of interpretation.

Angiography↗

PubMed1975

Thiamine transport across the rat intestine. I. Normal characteristics.

The characteristics of normal thiamine transport across the intestine were studied in rats using intact intestinal loops and everted jejunal segments. In vivo studies with [35-S]-thiamine hydrochloride revealed, in all segments of small intestine, saturation kinetics for low thiamine concentrations (0.06 to 1.5 muM), but a linear relationship between high concentrations (2 to 560 muM) and absorption. Moreover, in vitro studies of net transmural flux using everted jejunal sacs demonstrated movement of [14-C]-thiamine hydrochloride against a concentration gradient only when low, but not when high, thiamine concentration was used, so that the serosal to mucosal ratio became significantly greater than the initial value of one. Pyrithiamine, 2 muM, dinitrophenol, 200 muM, norethylmaleimide, 100 muM, and ouabain, 10 muM, reduced the net transmural flux of 0.2 muM thiamine. In contrast, these inhibitors had no effect on 20 muM thiamine. When unidirectional flux across the jejunum was measured, saturation kinetics was again demonstrated for low thiamine concentrations. This phenomenon, however, was abolished by the addition of pyrithiamine, which exerted competitive inhibition on thiamine absorption. Anoxia and sodium lack reduced intestinal uptake of 0.5 muM thiamine to 58% and 74% of normal, respectively, but did not affect uptake of 50 muM thiamine. Lowering the marked with low thiamine concentrations (O10, 1.648) than with high concentration (Q10, 1.127). Stirring of the water layer reduced Km to 59% of unstirred value, while Vmax and permeability coefficient remained unchanged. Finally, movement of low concentration thiamine against an electrical gradient was observed under conditions of electrical short circuiting and zero potential difference. In contrast, no such effect was seen with high concentrations. These studies suggest that there exists in the rat a dual system of intestinal thiamine transport. At low concentrations, thiamine is absorbed by an active process; at high concentrations, transport across the intestine is largely a passive movement.

Animals↗