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Biomedical subjects

O Frederiksen

Publications and source records attributed to O Frederiksen.

27 records · Page 2Linked to original sources
PubMed1977

Effects of cytochalasin B and dimethylsulphoxide on isosmotic fluid transport by rabbit gall-bladder in vitro.

1. Net fluid transport rate, transepithelial ohmic resistance and potential difference (p.d.), and unidirectional fluxes of Na+ were measured in rabbit gall-bladder preparations in vitro exposed on both sides to Ringer solutions of identical electrolyte composition. 2. Bilateral application of 1% dimethylsulphoxide (DMSO), the solvent for cytochalasin B, rapidly and reversibly depressed net fluid transport rate by 15% and increased the lumen positive p.d. by 1-5-2-0 mV. Resistance did not change significantly. These effects of DMSO were shown to be non-specific osmotic effects. 3. Cytochalasin B (10(-5)M) applied bilaterally caused: (a) a progressive inhibition of net fluid transfer rate to 40-50% of its control value within 60 min; the effect was partly reversible within 60 min and independent of the substrates glucose, glutamate and pyruvate; (b) a progressive depression of the mucosal-to-serosal Na+ flux within the first 30 min with no further change in the flux during the following 30 min of exposure to cytochalasin B; the effect was partly reversible within 70 min; (c) a rapid but moderate increase in the passive serosal-to-mucosal Na+ flux, which continued to increase gradually during the entire 60 min period of exposure to cytochalasin B; the effect was completely reversible within 70 min; (d) a prompt drop in ohmic resistance (30%) and p.d. (40%) with no further changes in these parameters during the following 60 min of exposure to cytochalasin B. The effect on resistance was partly reversible within 90 min; the effect on p.d. was completely reversible within 30 min. 4. The results are interpreted to indicate an early inhibitory action of cytochalasin B on the active transcellular pump mechanism and to suggest a cytochalasin B-mediated progressive increase in cell membrane permeability to sodium resulting ultimately in a highly leaky epithelium. The results are compatible with the concept that a mechanochemical process is involved in isosmotic transcellular transport of fluid across low-resistance epithelia.

Animals↗
PubMed1975

The effect on total renal and tubular function and plasma renin of a moderate isotonic saline load in rats anesthetized with amytal and inactin.

The renal effects of i.v. saline loading equal to 1% body weight (b.wt.) were studied in 2 groups of rats: group I was anesthetized with Amytal (15 mg/100 g b.wt. plus supplementary doses), group II with Inactin (12.5-15.0 mg/100 g b.wt.). In group I the saline load caused an increase in urine flow (+92%), solute excretion (+67%), inulin clearance (CIN) (+24%), PAH clearance (+31%) and absolute proximal reabsorption rate (+27%). Proximal fractional reabsorption and filtration fraction (FF) remained unchanged, while plasma oncotic pressure (COP) decreased by 10%. Plasma renin fell and there was an inverse relationship between renin concentration and proximal reabsorption rate. In group II urine flow and solute excretion increased after saline (+85% and 110%, respectively); CIN and absolute proximal reabsorption rate was lower than in group I and failed to increase after saline. Proximal fractional reabsorption was also lower and decreased after saline. COP as well as renin decreased as in group I, but no relationship between renin concentration and proximal reabsorption rate could be demonstrated. The data indicate that Inactin depresses both resting proximal tubular reabsorptive capacity and the tubular response to a physiological volume expansion. The results are compatible with the hypothesis that the renin-angiotensin system is significantly involved in regulation of proximal tubular function, while they are incompatible with the idea that peritubular COP plays any major role in this adjustment.

Aminohippuric Acids↗
PubMed1975

Sensitive osmometer function of juxtaglomerular cells in vitro.

The rate of renin release from viable juxtaglomerular cells was studied during prolonged superfusion of isolated rat renal glomeruli with Ringer solutions of differing osmolarities. 2. Reduction in osmolarity from 305 to 285 m-osmole/l. by lowering sucrose concentration caused renin release rate to double. A rise in osmolarity of 30 m-osmole/l. by raising sucrose concentration halved release rate. 3. The response to osmolarity was graded. During the first 30 min following a 20 m-osmole/l. decrease in osmolarity, 1-57 +/- 0-22% (S.E. of mean) of cellular renin content was released; three times this amount was released with a decrease of 50 m-osmole/l. The effect persisted at lower release rates for 60-90 min. 4. The juxtaglomerular cells were four to five times more sensitive to changes in osmolarity through sucrose than sodium chloride concentration. Changes in potassium chloride concentration (7-57 mM) had little effect. 5. Sodium chloride had no direct ionic effect on renin release outside its osmotic properties. 6. The findings support a previous proposal that the rate of renin release in vitro relates directly to the volume of the juxtaglomerular cell. The hypothesis is developed that a similar mechanism may underlie renin secretion in vivo.

Animals↗
PubMed1969

Transcellular transport of isosmotic volumes by the rabbit gall-bladder in vitro.

1. Fluid transport rate and oxygen consumption (Q(O2)) were studied in rabbit gall-bladder preparations in vitro exposed on both sides to identical Ringer solutions with NaCl concentrations (and osmolarities) varying from 70 to 140 m-equiv Na(+)/l.).2. The time sequence of acute effects on transport rate resulting from sudden changes in the NaCl concentration of the bathing solutions indicated that, (a) as a primary effect, fluid volume transfer rate remained unaffected whereas Na transport rate changed abruptly in direct proportion to the Na concentration of the bathing media; (b) a secondary, delayed and partly reversible depression of fluid transfer rate following elevation of the NaCl concentration was observed only when the rate of transport was relatively high initially.3. A fixed, and highly significant, linear relationship between changes in transport-linked oxygen consumption (DeltaQ(O2)) and measured net fluid volume transport (DeltaT(vol)) was found independent of the NaCl concentration of the bathing media, dQ(O2)/dT(vol) being 0.22 +/- 11% and 0.25 +/- 8% in bladders incubated in solutions containing 140 and 70 m-equiv Na(+)/l. respectively.4. Oxygen consumption per equiv of Na(+) (calculated) transported varied in inverse proportion to the Na concentration of the bathing media, dQ(O2)/dT(Na) being 0.0016 +/- 11% and 0.0036 +/- 8% in ;140 R' and ;70 R' solutions, respectively.5. Removal of K from the bathing solutions was followed by a gradual and partly reversible depression of fluid transport rate to a minimum level (about 100 x 10(-4) mul H(2)O. min(-1).mg(-1)) independent of the initial transport rate.6. It is concluded that the range of absorption rates of isosmotic fluid from the gall-bladder lumen represents a range of energy requiring capacities for transfer of fluid volume units; the data suggest that the intracellular (cytoplasmic) ion composition, depending on the presence of external K, as well as hormonal action may influence the capacity of the transcellular fluid transport mechanism.7. A model (a ;mechanical volume pump') for transcellular transfer of fluid volume units, allowing for flexible specificity with regard to the actively transported solutes, and requiring the presence of Na(+) and Cl(-), is proposed.

Animals↗