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Biomedical subjects

J Bourguet

Publications and source records attributed to J Bourguet.

At least 73 records · Page 4Linked to original sources
PubMed1979

Simultaneous minute by minute determination of unidirectional and net water fluxes in frog urinary bladder. A reexamination of the two barriers in series hypothesis.

Unidirectional and net water fluxes were simultaneously estimated in frog urinary bladder. The minute by minute tritiated water (3HOH) transepithelial flux and the net volume of fluid traversing the tissue were employed. It was observed that: (1) the time course of the increase in the 3HOH flux induced by antidiuretic hormone had a very similar pattern to that reported for the increase in the net movement. (2) Unstirred layers strongly affected the magnitude of the antidiuretic hormone-induced increase in 3HOH fluxes while the time course of the response was almost non-affected. In non-stimulated bladders 3HOH fluxes were poorly modified by medium stirring. New steady-state conditions for 3HOH fluxes were established 1 min after stirring rate modifications. (3) The simultaneously determined net water flux was not affected by a modification in the unstirred layers, indicating that the variations in the measured net water fluxes are a good estimation of the changes in the mucosal border permeability. (4) The presence of an osmotic gradient during hormonal challenge (implying net water fluxes, cell swelling and dilation of the intracellular spaces) did not modify the time course of 3HOH movements. These results suggest that the time course of the increase in water permeability is an intrinsic characteristic of the experimental system that could result from the addition of permeability units that increase in number during the development of the hormonal action.

Animals↗
PubMed1979

Influence of mucosal and serosal pH on antidiuretic action in frog urinary bladder.

Mucosal acidification to pH 6.5 reduced by 88% the oxytocin- (2.2 x 10(-8) M) elicited increase of water permeability in frog urinary bladder. Mucosal alkalinization (pH 10.5) increased by as much as 200% the response to the same concentration of oxytocin. These effects were not observed when supramaximal concentrations of oxytocin were imployed. Similar changes were found when the serosal pH was modified. The hydrosmotic responses elicited by serosal hypertonicity or cyclic AMP plus theophylline were also affected by mucosal or serosal changes of the hydrogen in concentration, suggesting an effect at a post-cyclic AMP level. Important interactions were found between luminal pH and serosal hypertonicity when experimental conditions were employed similar to those observed in the collecting duct of mammalian nephron. Freeze-fracture studies showed that the number of intramembranous aggregates of particles induced by ADH in the luminal membrane was reduced by mucosal acidification and augmented by an increase in medium pH.

Animals↗
PubMed1977

Adenosine stimulation of fluid transport across rabbit corneal endothelium.

The rate of fluid transport across rabbit corneal endothelium has been measured with an automatic volumetric method. The present resolution of the procedure is 1-3 nanoliters, and intervals of measurement can be made as small as seconds. In the presence of glucose, oxidized glutathione (GSSG), and adenosine, the maximal rates were 6.2+/-1.0 microliter/hr cm2, and 8.2+/-0.8 microliter/hr cm2 if a large portion of the stroma was dissected away. In the presence of glucose and GSSG only, the rates were lower, namely 3.7+/-0.5 microliter/hr cm2. The rates consistently increased or decreased when adenosine was added or deleted, respectively, during given experiments. The stimulation of fluid transport by adenosine was in the order of 40-50%. The results raise the possibility that this transport mechanism might be subject to metabolic control.

Adenosine↗
PubMed1976

Alterations in membrane-associated particle distribution during antidiuretic challenge in frog urinary bladder epithelium.

Frog urinary bladder epithelium has been examined by freeze-fracture electron microscopy of preparations previously fixed by glutaraldehyde either at rest or during antidiuretic challenge. All the agonists tested were observed to induce membrane particle clustering in the A face of the apical plasma membrane of granular cells. This was the case for the natural hormone (hypophysical extracts) and its presumed cellular mediator, adenosine 3',5'-monophosphate. Particle clustering was observed both in the presence and in the absence of water net flow and is thus independent of these movements. Clusters were also observed during hydrosmotic challenge by hypertonic serosal media, a condition which depresses transepithelial sodium transport. No complementary patterns of these A face clusters could be found on the B face. The significance of these membrane-associated particle clusters is discussed in terms of membrane structure and function.

Animals↗
PubMed1973

The effect of hypertonic media on water permeability of frog urinary bladder. Inhibition by catecholamines and prostaglandin E 1 .

The frog urinary bladder undergoes, in some conditions, a marked increase of its water permeability when incubated in hypertonic media. This increase was observed with various nonpermeant solutes. It seems to result from the shrinkage of an osmo-sensitive compartment of the tissue, probably the epithelial cells. Many similarities were found between this effect and the physiological increase in water permeability (hydrosmotic response) elicited by antidiuretic hormone (ADH): both were dependent on the physiological state of the animals, and although the response was slower after hyperosmolar than after hormonal challenge, the patterns of response were similar, and in both cases markedly dependent on bathing solution temperature. Norepinephrine and prostaglandin E(1), which in this tissue reduce the hydrosmotic action of ADH, presumably by inhibiting the adenyl cylase also reduced the effect of hyperosmolarity. Conversely this effect was potentiated by incubation in the presence of oxytocin, exogenous cyclic AMP, and theophylline, conditions in which the intracellular concentration of cyclic AMP is increased. These data demonstrate that the response to hyperosmolarity is elicited, at least partly, by mechanisms also involved in the physiological hydrosmotic response to ADH.

Animals↗