Water content and distribution of tritiated water in tissues of Australian desert rodents

Biological half-life and oxidative stress effects in mice with low-level, oral exposure to tritium

Tritium ((3)H) may enter the environment from human activities, particularly at production, processing, or waste storage sites such as the Department of Energy's Savannah River Site, a former nuclear production facility in South Carolina. Understanding the dynamics and potential adverse effects of tritium in exposed organisms is critical to evaluating risks of tritium releases at such sites. Previous studies estimated the biological half-life of tritium in mice to be approximately 1.13 d; however, these laboratory studies were not conducted under environmentally realistic conditions. In this study, designed to be more representative of environmental exposure, mice were allowed to drink water containing tritium (activity about 300 Bq/ml) for a period of 2 wk. The induction of oxidative stress from tritium exposure was evaluated by comparing the activities of antioxidant enzymes (catalase, glutathione peroxidase, and superoxide dismutase) in exposed and control mice. From this experiment, the biological half-life of tritium was determined to be 2.26 +/- 0.04 d, almost double previous estimates. While positive controls (x-ray irradiated mice) showed responses in antioxidant enzyme activity, there was no indication of oxidative stress induction in mice exposed to tritium at this concentration.

The use of an "internal standard" for control of the recovery in microdialysis

Microdialysis of intravenously injected theophylline in blood and in lung tissue was performed in two rats during anaesthesia. The recovery (dialysate extraction fraction) in blood was greater than the recovery in lung tissue and there was a change in recovery with time both in blood and in lung. The concentrations of theophylline in the dialysates were corrected for the recovery using caffeine as an "internal standard" in the perfusate as well as tritiated water injected into the rats. There was excellent agreement between the two different methods. Furthermore, the corrected concentration of unbound theophylline in the blood was in accordance with the simultaneously measured total concentration of theophylline in plasma when binding to plasma proteins was taken into account. The conclusion is that an "internal standard" for correction of the recovery is a useful method to approach the true concentrations of compounds in the extracellular water. The "internal standard" must be as equal as possible to the substance of interest.

The effects of water deprivation and salt load on water conservation efficiency in two Indian desert gerbils

The effects of water deprivation and intraperitoneal salt loading on urine volume and on various urinary constituents have been examined in two gerbil species of the Rajasthan desert, the Indian desert gerbil (Meriones hurrianae Jerdon) and the Indian gerbil (Tatera indica indica Hardwicke). During summer, hydrated T. indica excreted 0.782 ml urine.100 g-1.d-1 which was about 60.5% higher than the volume of urine excreted by hydrated M. hurrianae (0.487 ml.100 g-1.d-1). During winter, both species excreted around 1.5 ml urine.100 g-1.d-1. The experimental treatments caused reductions in urine volume in M. hurrianae from 40 to 76% during summer and from 35 to 71% in winter. Similar treatments in T. indica caused reductions in urine volume of 50-82% in summer and 5-60% in winter. The mean increase in urine osmolarity following various salt loading treatments in T. indica ranged from 3800 to 5761 mosmol.l-1 and from 4034 to 6255 mosmol.l-1 during summer and winter, respectively. The mean values of urine osmolarity for hydrated T. indica were 2831 and 3189 mosmol.l-1 during summer and winter, respectively. In M. hurrianae salt loading treatments caused increases of urine osmolarity between 3381 and 5646 mosmol.l-1 and between 4032 and 5434 mosmol.l-1, during summer and winter, respectively, over the values recorded for hydrated animals (summer = 3292; winter = 3294 mosmol.l-1). A maximum urine osmolarity of around 7000 mosmol.l-1 was found in both species when subjected to 2% salt-loading treatment. The treatments used in this study increased urinary urea level in both T. indica (3039-4056 mM) and in M. hurrianae (1900-2180 mM) compared to the level in their respective hydrated controls (T. indica = 1628 mM; M. hurrianae = 1372 mM). The results indicate that T. indica may be better adapted to produce more concentrated urine than M. hurrianae.

Flow dependent changes in the effective surface area of microdialysis probes

The relative efficiencies of microdialysis probes were determined both in vitro and in vivo using tritiated water. Tritiated water (THO) freely distributes throughout the fluid spaces of an experimental animal and, at equilibrium, the brain extracellular concentration of THO is the same as the plasma concentration. Microdialysis probes were inserted into the right caudoputamen of anesthetized rats. The rats were injected with THO and after one hour microdialysis samples were collected at flow rates between 0.2 and 10.0 ul/min. The in vitro relative efficiency for THO was computed as the ratio of the THO concentration in the dialysate to that of the solution the probe was immersed in. The in vivo relative efficiency was computed as the ratio of the concentration of THO in the brain dialysate to that measured in the plasma of the rat. Both the in vitro and in vivo relative efficiencies for THO decrease with increasing flow rates, but they differ from each other except at very low flow rates (less than 0.25 ul/min). The in vitro relative efficiency at a given probe flow is the maximum efficiency that can be attained in vivo at that flow. The surface of effective exchange (Se) is the fraction of that maximum which is attained in vivo. This study also demonstrates how the effective surface area can be computed at any probe flow rate and how it can be used as a correction factor.

Water balance of small lactating rodents--III. Estimates of milk production and water recycling in lactating Mus musculus under various water regimes

1. The exchanges of water between lactating female and young Mus musculus were modelled on the computer. 2. The model was used to estimate rates of milk production and water recycling in various litter sizes under various water regimes by following the time course of injected tritiated water. 3. The high correlation between estimated rates of milk production and actual growth rates of young was taken to indicate that the method gave if not the actual rates of milk production a very constant proportion of it. 4. Approximately 50% of the water secreted in milk is returned to the mother by recycling.