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Biomedical subjects

M Chan

Publications and source records attributed to M Chan.

At least 145 records · Page 8Linked to original sources
PubMed1985

Inhibitory effects of harvested proximal tubular fluid on Jv and delta cNa during acute saline volume expansion in the rat.

The present micropuncture experiments were carried out in male Wistar rats during isotonic saline volume expansion (VE) to explore the relative importance of peritubular physical forces and tubular factors on proximal tubular Na transport. Isotonic volume flux, measured by the shrinking drop technique was reduced from 3.53 +/- 0.09 X 10(-4) . mm3 . mm-2 . s-1 with the artificial fluid to 1.79 +/- 0.1 with harvested autologous proximal tubular fluid (HTF) (49%), but only to 2.77 +/- 0.1 (78% of control) with artificial tubular solution (AS), both during volume expansion. delta cNa was reduced from a control of 18.0 +/- 2.2 mmol . kg-1 -14.5 +/- 2.0 with AS (81%) and 10.0 +/- 2.4 with HTF (56%) during VE. Thus both isotonic volume flux as well as delta cNa were reduced to the same degree by saline VE. These results and those obtained previously with mannitol-saline VE, indicate the presence of a factor in harvested proximal tubular fluid of volume expanded rats which inhibits sodium and water transport independent of peritubular osmolarity.

Animals↗
PubMed1985

Acute volume expansion: rat proximal tubular Na transport inhibition by autologous tubular fluid without changes in Na permeability.

Sodium permeability (P22Na) and steady state transepithelial concentration differences of Na (delta cNa) were measured in stationary droplets in proximal tubules of rats in both the non-expanded (NE) and subsequent mannitol-saline volume-expanded (VE) state. The test solutions for tubular injection were either an artificial tubular solution (AS) in group I rats or harvested proximal tubular fluid (HTF) in a second group of rats (group II). delta cNa (mmol.kg-1H2O) was significantly reduced (p less than 0.001) with HTF in the VE state (12.1 +/- 0.8 SEM) when compared to HTF in the NE state (17.8 +/- 1.8) and AS in both NE (17.4 +/- 1.0) and VE (18.2 +/- 1.0). P22Na calculated from the half-time of disappearance of 22Na from the droplets, when using paired experiments were 8.1 +/- 1.7 X 10(-5) mm2.sec-1 and 7.3 +/- 1.8 with HTF in NE and subsequent VE and 8.6 +/- 1.1 and 7.7 +/- 0.8 with AS in NE and VE. These permeability results did not differ from each other significantly. In these experiments with zero net Na and water fluxes, the 32% reduction of delta cNa cannot be accounted for by an increased backleak of Na, since P22Na would have had to increase by 32%. These results therefore provide strong evidence for a factor present in proximal tubular fluid consequent upon VE which inhibits Na transport without altering transepithelial PNa, but do not exclude an effect of such a factor on the cellular Na entry step or the Na pump itself.

Animals↗
PubMed1984

Phosphate uptake by superficial and deep nephron brush border membranes. Effect of the dietary phosphate and parathyroid hormone.

Dietary phosphate restriction and acute parathyroidectomy in rat are known to be associated with a selective increase in phosphate uptake by renal cortical brush border membranes (BBM). Conversely, phosphate loading and parathyroid hormone (PTH) administration result in a decrease of this uptake. In the present study, we investigated whether the response of the membrane to these various stimuli implies similar or different modifications of the kinetic properties of this membrane, whether these modifications affect one or both of the two systems of phosphate transport previously described, whether both superficial and deep nephron populations are involved, and whether the two stimuli: dietary phosphate, and parathyroid activity, are additive or not. Kinetic studies of phosphate (PO4) uptake by BBM vesicles were performed in seven groups of rats: control (N), acutely thyroparathyroidectomized (TPTX), PTH loaded (PTH), phosphate loaded (P+), phosphate depleted (P-), phosphate depleted with acute thyroparathyroidectomy (P-TPTX), and phosphate depleted-PTH loaded (P-PTH). In each of these experimental conditions, superficial and deep nephrons were investigated. Results indicated that 1. BBM from deep nephrons present a greater capacity for PO4 transport than those from superficial nephrons; 2. Whereas a dual system of PO4 uptake is observed in superficial BBM, deep BBM present only one single system; 3. Phosphate in the diet influences PO4 uptake by BBM to a greater extent in the deep than in the superficial nephrons; 4. PTH status on the contrary, equally influences both populations; 5. TPTX does not significantly enhance PO4 uptake in phosphate depleted rats; however, PTH loading curtails this uptake; 6.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1984

Effect of temperature and pH on phosphate transport through brush border membrane vesicles in rats.

The kinetics of sodium gradient dependent phosphate uptake by the renal brush border membrane vesicles of the rat have ben studied under various conditions of temperature and pH. From 7 to 30 degrees C the Lineweaver-Burk plots are linear, and the apparent Km progressively increases from 54 to 91 microM. Above 30 degrees C, the apparent Km continues to increase to reach 135 microM at 40 degrees C, but a break is observed in the Lineweaver-Burk plots at the substrate concentration of 300 microM. The existence of this break, confirmed by the Eadie-Hofstee plot supports the hypothesis of a dual mechanism of phosphate transport, one for low concentrations of substrate with a Km of 100 microM and the other for high concentrations with a Km of approximately 240 microM. When the two components of the Eadie-Hofstee plot are analyzed according to a nonlinear regression program, these two values of Km become 70 microM and 1.18 mM, respectively. The Vmax continuously increases with temperature. However, the Arrhenius plot (In Vmax vs. 1/TK) shows an abrupt discontinuity at 23 degrees C. pH experiments were performed at 35 degrees C. In the absence of a proton gradient, increasing the pH from 6.5 to 7.5 and 8.5 decreases the apparent Km from 341 to 167 and 94 microM, respectively. When only the divalent form of phosphate is considered as the substrate, the apparent Km does not vary anymore with the pH and remains around the mean value of 105 microM. The uniformity of the apparent Km for the total phosphate uptake, when only the divalent phosphate is considered as being the substrate, suggests that this divalent form is the only one which is transported. Whatever the substrate considered, total phosphate or divalent phosphate, the highest Vmax is obtained at pH 7.5 which probably approximates the optimum pH inside the vesicles for the phosphate uptake.

Animals↗
PubMed1984

Sampling gastro-enterologists' opinions and attitudes at two world congresses.

This paper reports the results of a survey of gastro-enterologists' opinions and attitudes at the Stockholm, Sweden, Seventh World Congress (June 1982), elicited via a standard questionnaire in three languages. Respondents' replies were compared with those from the previous (Sixth) World Congress (Madrid 1978) on a variety of topics. As regards peptic ulcer, little change has occurred in the last four years concerning surgery, though highly selective vagotomy has become more common for duodenal ulcer. As regards drugs in routine use, this survey confirms the considerable rise in the proportion of centres prescribing H2 receptor blockers (from 48% in 1978 to 81% in 1982). As regards inflammatory bowel disease, there has been little change overall in surgical procedures though 'small' procedures have grown in popularity (such as diverting ileostomy), largely at the expense of colectomy. Most physicians would now recommend some form of cancer surveillance both for ulcerative colitis and Crohn's disease, the most popular modality being clinical examination plus sigmoidoscopy at 6-12 month intervals, with colonoscopy or barium enema every two years. As regards GI cancer detection, endoscopy is now the modality of choice both for gastric cancer and colo-rectal cancer. Finally, the majority of respondents confirm that they frequently encounter ethical problems both in connection with routine practice and research. By and large ethical committees were felt to be ineffective, and guidance on ethical matters (absent in many centres!) rarely takes a structured form. This last finding possibly lends weight to the O.M.G.E.'s intention to provide such guidance via its newly founded Ethical Committee.

Attitude↗
PubMed1983

Pichinde virus-specific cell-associated suppression of primary footpad swelling in an inbred strain of Syrian hamsters.

Pichinde virus causes a lethal disease after i.p. inoculation of adult MHA hamsters; other strains of Syrian hamsters are resistant to this lethal infection. During studies of cell-mediated immune responses to Pichinde virus, it was noted that MHA hamsters survived infection when the virus was given in the footpad. However, unlike the resistant LSH and LVG strains of hamsters, the MHA hamsters did not manifest a footpad swelling response. Failure of the MHA hamster to respond to a footpad inoculation of Pichinde virus was shown to be virus-specific and appeared to be mediated by a cell-associated suppressor mechanism.

Animals↗
PubMed1982

Chemical pulmonary burn injury and chemical intoxication.

Two large groups of patients with chemical pulmonary burns who sustained their injuries in the same environment were presented. Data from the blaze smoke analysis of two imitative experiments which were performed under the same conditions as were present when these patients sustained their burns showed a high concentration of carbon monoxide of 35700-571400 ppm and multivariable components of chemicals. The environmental conditions, the clinical course, laboratory findings and blaze analysis clearly demonstrated the close relationship between chemical pulmonary burn injury and chemical intoxication which increased the difficulty in treatment. Ideally, the initial treatment at the site of the fire is the application of 100 per cent oxygen in high flow by mask, and temporary artificial hyperventilation after hospitalization will give a satisfactory result if the fire victim suffers severe carbon monoxide poisoning. In order to treat chemical intoxication in the patient with chemical pulmonary burns successfully, we have adopted a regimen of 'over-loading fluid resuscitation', together with diuretics and positive end expiratory pressure (PEEP) under the monitoring of central venous pressure.

Burns, Chemical↗
PubMed1982

The effects of pH on the affinity of pirenzepine for muscarinic receptors in the guinea-pig ileum and rat fundus strip.

1 Dose-ratios obtained with pirenzepine on the guinea-pig ileum at 30 degrees C are indistinguishable from those obtained at 37 degrees C. 2. In 0.1 M NaCl at 37 degrees C the pKa of pirenzepine for the loss of its last ionizable proton is 8.2. The ionization of pirenzepine is therefore markedly affected by changes in pH in the physiological range. 3 In experiments with pirenzepine on guinea-pig ileum and rat fundus made over a range of pH, the dose-ratio increases with the proportion of the protonated form present. As expected, the slope of the graph of dose-ratio against proportion protonated depends on the concentration of antagonist. The changes in pH produce only small effects on dose-ratios obtained with pirenzepine monomethiodide. These effects of pH can account for some of the differences between estimates of the affinity of pirenzepine. 4 The logarithm of the affinity constant of the protonated form of pirenzepine for the receptors in guinea-pig ileum is estimated to be 6.93, compared with 6.94 for the receptors in rat fundus. However, for the non-protonated form the values appear to be below 5 for the ileum compared with about 6.4 for the rat fundus.

Animals↗
PubMed1980

Acute myelogenous leukemia with megakaryocytic myelosis.

A case of acute myelogenous leukemia terminating in megakaryocytic myelosis is reported. There was a severe, apparently neoplastic proliferation of megakaryocytes so different from that seen in acute granulocytic leukemia or myelofibrosis that a diagnosis of acute megakaryocytic myelosis was warranted. The clinical and pathologic findings of the case are presented in detail. The literature of this extremely rare hematologic disease is reviewed, and differentiation from chronic and malignant myelosclerosis is discussed.

Aged↗