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Quantitative Aspects of the Water Balance in Lymnaea Stagnalis (L.)

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image of Netherlands Journal of Zoology
For more content, see Archives Néerlandaises de Zoologie (Vol 1-17) and Animal Biology (Vol 53 and onwards).

In the present investigation some aspects of the water balance in Lymnaea stagnalis (L.) were evaluated. Determinations were made of the blood and water volumes. Under various experimental conditions, influx and efflux rates of water, and urine production rates were measured. Further, the heart-kidney function was experimentally examined and osmotic pressure measurements were made on blood (under various conditions), pericardial fluid and urine. The study was commenced by a careful examination of the anaesthetic effects on the water balance of the snail. It was indicated that not only the heart-kidney system-normally responsible for a copious urine production-was affected, but disturbances of the water balance on a cellular level were also involved. Further, the observations made it possible to establish when recovery from anaesthesia to normal conditions is achieved by the animal. Knowledge of the recovery time was necessary, because in most experiments the snails were subjected to surgical techniques, carried out under anaesthesia prior to experimentation. It was found that during anaesthetization a maximum increase in the snail's weight (shell included) occurs of 8% and 14% for adult and juvenile snails, respectively. The total weight together with the heart rate (beats per minute) and the function of the kidney (tested with inulin excreted) returns to normal between 2 and 3 hours after anaesthetization. The blood osmotic pressure, 127 mOsm in normal snails, increases significantly during anaesthesia to 138 mOsm, followed by a rapid decrease in tap water with the osmotic value slightly but significantly below that of normal animals. The blood potassium of anaesthetized snails is not significantly higher than that of untreated animals. The surgical techniques applied were mainly aimed at the administration of foreign substances or sampling of the body fluids for analysis. Blood samples (10 μl) from the haemocoel were, with the aid of a catheter, periodically collected, after the administration of labelled inulin and tritiated water (10-20 μl) through the catheter. The catheter was inserted into the haemocoel via the penis complex. Catheterization and injection (in some cases through the praeputium) occurred under anaesthesia. The blood collected from the vena pulmonalis was subjected to osmotic pressure measurements. It was found that the mean value for 32 adults, reared in the laboratory in 6-8 mOsm tap water, was 127 (± 4) mOsm/kg (c. 0.4% NaCl). The same values were obtained for animals living in the wild. By applying a dilution method using labelled inulin, the blood and water volumes in the snail were determined. The data thus obtained allow the quantitative evaluation of the urine production rate and the total water flux rate. The blood volume (extra-cellular fluid) as a percentage of the body weight (shell excluded) is 45.4% in adults and 40.2% in juvenile snails. The total body water is 91.6% and 90.5% for adults and juveniles, respectively. The cellular water as a percentage of the body weight (48.0%) and of the body tissue weight (82.6%) was also determined. The experiments proved that inulin is a reliable indicator substance in the snail for volume measurements. An indirect measuring method, with labelled inulin acting as the indicator substance, was employed to obtain the urine production and clearance rates. The rate of production of urine is between 0.93 and 1.84 μl min-1 g-1 body weight in tap water, which amounts to an average output of 9% of the body weight per hour. A significant decrease of the urine production rate was found in saline solutions hyperosmotic to the blood, with a corresponding increase in the blood osmotic pressure. Increasing concentrations of the external medium (20-65 mOsm NaCl) resulted in a rise of the blood osmotic pressure. In deionized water the blood osmotic value decreased considerably. The urine to blood ratio of inulin (U/B) and the hypo-osmotic state of the urine indicate that water and solutes are resorbed from the kidney lumen. A mechanism of fluid transport through the kidney epithelium is discussed. The inulin concentration and the osmotic value of the pericardial fluid reveal that ultrafiltration in the heart (probably the atrium wall) is the first step in urine production. The measurements made of the clearance rate of inulin and the size of the reno-pericardial duct indicate that the amounts filtered off (c. 3 μl/min in adults) can be readily conveyed through the reno-pericardial duct. The efflux measurements, made with tritiated water, were performed on normal, on anaesthetized and on rinsed snails. The influx rates were determined on normal and on anaesthetized snails. A high permeability to tritiated water was found. The total water flux amounts to 378% of the body weight/hr. Half of the tritiated water disappears from the haemocoel within c. 11 minutes after injection. The efflux rate Ke is 3.76/hr. Reduced influx and efflux rates were obtained for anaesthetized snails if compared to the untreated animals. It was found that the calculated net water flux does not verify the relatively high amount of urine produced. This matter is discussed.

Affiliations: 1: (Zoological Department, Free University, Amsterdam, The Netherlands


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