SUMMARY1. Daily changes in water and electrolyte balance during pregnancy were investigated in rats housed in metabolism cages.2. Fluid intake was significantly elevated above control values from day 13 of pregnancy, with urine output failing to be raised to the same extent. This would result in an extensive fluid retention if extrarenal fluid losses were not substantially altered.3. Electrolyte intake increased from as early as the third day after mating with an accompanying increase in renal ionic excretion. A net retention of Na, Cl and K did not occur until the final week of pregnancy when the urinary output of these ions was reduced.4. In a parallel study, changes in plasma volume and composition throughout pregnancy were investigated. 5. A significant increase in plasma volume occurred from day 6 of pregnancy at a time well before fluid intake or urine output were altered. This indicates either an altered extrarenal output or. a shift of fluid between body fluid compartments.6. Maternal plasma sodium and total osmolality were reduced during the last week of pregnancy despite the salt retention, suggesting an increased fetal usage.7. Such findings are related to the known renal and endocrine changes of rat pregnancy.

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SUMMARY1. In rats receiving 200 gl. min-sodium chloride, glomerular filtration rate, single nephron glomerular filtration rate, and fractional reabsorption were measured at various points along the nephron, and ionic concentrations measured in early distal tubular fluid in virgin and 6, 12 and 19 day pregnant rats.2. Glomerular filtration increased progressively until the twelfth day ofpregnancy. At 19 days of pregnancy the glomerular filtration rate, while still above virgin levels, was reduced below 12 day pregnant levels.3. Single nephron glomerular filtration rates measured in proximal and distal tubules were different at both 12 and 19 days of pregnancy, indicating an alteration of tubuloglomerular feed-back. 4. A change in the ratio ofglomerular filtration rate: distal single nephron filtration rate indicated a redistribution of glomerular filtrate to juxtamedullary nephrons by the sixth day of pregnancy.5. Fluid reabsorption is similar up to the early distal tubule but it is not possible to say whether reabsorption is the same in proximal tubules. More fluid is reabsorbed by late distal tubules and collecting ducts in 12 and 19 day pregnant animals than in the virgin and 6 day pregnant animals.6. Changes in ion reabsorption by the loop of Henle occurred during pregnancy; sodium reabsorption was increased by the sixth day of pregnancy and potassium reabsorption by the twelfth day.

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Abstract. Metabolic and renal clearance techniques were used to examine kidney function in conscious and anesthetised streptozotocin diabetic rats. All diabetics showed an enhanced calcium and magnesium excretion compared to controls. However, the renal handling of these ions in relation to other electrolytes varied with different experiments. In non-infused conscious rats, the excretion of all ions was higher in diabetics, but the increased output of Ca2+ and Mg2+ was far greater than that of other electrolytes. In infused anesthetised diabetics only the outputs of Ca2+ and Mg2+ were significantly raised. This resulted from a significant reduction in the tubular reabsorption of both ions (% Ca2+ reabsorption: Controls 97.0±0.5; Diabetics 86.1±2.1; p<0.001). Insulin treatment reversed these changes. Major differences therefore exist in the renal handling of Ca2+ and Mg2+ in control and diabetic kidneys. Such differences do not simply parallel changes in the handling of other ions, and thus represent specific Ca2+ and Mg2+ lesions. Anesthetised infused diabetic rats also showed a reduced glomerular filtration rate and urine output compared to controls. Such differences may relate to an altered fluid balance in the two groups, different responses to surgery and anesthesia, or the degree of hyperglycemia in diabetic animals.