Tritium assay by liquid scintillation spectrometry. Comparison of tritium and deuterium oxides as tracers for body water

Studies on the movement of water through the isolated toad bladder and its modification by vasopressin

Measurements of diffusion permeability and of net transfer of water have been made across the isolated urinary bladder of the toad, Bufo marinus, and the effects thereon of mammalian neurohypophyseal hormone have been examined. In the absence of a transmembrane osmotic gradient, vasopressin increases the unidirectional flux of water from a mean of 340 to a mean of 570 µl per cm² per hour but the net water movement remains essentially zero. In the presence of an osmotic gradient but without hormone net transfer of water remains very small. On addition of hormone large net fluxes of water occur; the magnitude of which is linearly proportional to the osmotic gradient. The action of the hormone on movement of water is not dependent on the presence of sodium or on active transport of sodium. Comparison of the net transport of water and of unidirectional diffusion permeability of the membrane to water indicates that non-diffusional transport must predominate as the means by which net movement occurs in the presence of an osmotic gradient. An action of the hormone on the mucosal surface of the bladder wall is demonstrated. The effects of the hormone on water movement are most simply explained as an action to increase the permeability and porosity of the mucosal surface of the membrane.

The electrical characteristics of active sodium transport in the toad bladder

The mechanism responsible for active sodium transport in the urinary bladder of the toad appears to be located at the serosal boundary of the epithelial cell layer of the bladder. Studies of the potential step observed at the serosal boundary in the open-circuited state were undertaken in an attempt to define the factors responsible for its production. Glass micropipettes were used to measure the serosal potential step in bladders exposed on the serosal side to solutions of high potassium or of high potassium and low chloride concentration. Observed potentials exceed the maximum values which would have been expected if the serosal potential step were a potassium or chloride diffusion potential. Measurements of net cation flux exclude the possibility of a diffusion potential at this border due to the passive movement of any anionic species. The observed independence of transbladder potential and short-circuit current from the pH of the serosal medium over a wide range of pH makes it unlikely that the observed serosal potential step is a hydrogen ion diffusion potential. We conclude that the active sodium transport mechanism in toad bladder is "electrogenic."

Dynamics of deuterium turnover in the human body using 2(1)D(gamma, n) reaction

A rapid non-destructive and sensitive technique is used by which total body water and its rate of turnover (excretion) in human subjects can be easily measured. Subsequently, a simple calculation is made in estimating the total body fat and lean body mass. The measurements are, therefore, expected to shed useful light on the measurement technique as well as on the movement of body water in humans, and this will glean an understanding of physiological laws governing such movements. The method employs the activation of deuterium in water by bremsstrahlung radiations which are produced by stopping 3 MeV electrons in a gold target. The detection of photoneutrons, so obtained in the reaction 2(1)D(gamma, n), is accomplished by the capture of fission fragments in Solid State Nuclear Track Detector (SSNTD) issuing from the 235U(n, f) reaction. These fission events are then automatically counted by a spark counter. Thermal neutrons, required for the 235U fissioning, are obtained by employing a graphite moderator assembly at the core of which water and urine samples are being irradiated. The development of a few basic measurement parameters and their utilization in such measurements are also reported in the paper.

Intracellular and extracellular compartments of mammalian central nervous tissue

1. Isolated rabbit retina was used as a prototype of grey matter to study the partition of water and electrolytes between the intracellular and extracellular phase. Previously published morphologic, chemical, and functional evidence has shown that it can be maintained in vitro in a nearly physiological state.2. Following equilibration with mannitol or inulin, retinas were eluted in isotonic tris acetate at 0 degrees C, and measurements were made of the rates at which K(+), Na(+), Cl(-) and inulin or mannitol diffused from the tissue.3. K(+) was eluted slowly according to a single exponential decay. The Na(+) and Cl(-) elution curves demonstrated two phases which could be dissected into a rapid, multicomponent regression superimposed upon a slow exponential decrease.4. The volume of distribution of the readily elutable Na(+) equalled that of the readily elutable Cl(-) and corresponded closely to the volume of distribution of mannitol and inulin. On the basis of these and previously published data, the interstitial fluid was estimated to constitute 31% (w/w) of rabbit retina and 22% of rabbit brain.5. The composition of the extracellular fluid of retina resembled closely that of the medium in which the tissue had been previously incubated.6. Inulin, mannitol, and NaCl diffused through the less accessible portions of the extracellular space at rates which differed from one another as predicted from the diffusion coefficients of these solutes. Their diffusion through the more accessible portions of the extracellular space was apparently affected by bulk flow of the fluid.7. The intracellular concentrations of K(+), Na(+), and Cl(-) were estimated to be 148, 31, and 17 mM respectively.8. Na(+) and K(+) moved across the cell membranes at almost precisely the same rate under the conditions of the elution.