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SUMMARY1. Adult rats were unilaterally nephrectomized and the weight of the remaining kidney up to 42 days after the operation compared with that of rats of comparable weight which underwent a sham operation.2. After unilateral nephrectomy the rate of renal hypertrophy varied with the protein content of the diet: it was faster when animals were fed on a high protein diet (22 % casein) and lowest in animals fed on a low protein diet (7 % casein).3. In rats fed on a standard diet (18 % casein), after unilateral nephrectomy there was a sharp increase in glomerular filtration rate (G.F.R.), as measured by inulin clearance estimations; this was accompanied by an enhanced oxygen uptake and by an increase of RNA/DNA ratios in the renal cortex. Changes in rate of oxygen uptake and of RNA/ DNA ratios in the medulla were negligible.4. A marked increase in mitotic activity of cells of the cortex occurred only 48 hr after the operation. It lasted for about 2 days. No significant changes in mitotic activity of cells in the medulla were observed. 5. After its initial marked rise glomerular filtration rate in the renoprival kidney settled down to about 30-40 % above its pre-operative level, and remained at that level for the whole period of observation (6 weeks), while the increase of oxygen uptake returned to its control level in some 10-14 days. RNA/DNA ratios in the cortex remained high, but did not increase further. 6. The increase of RNA/DNA ratios in the renal cortex was correlated with a steady increase in the dry weight of the renoprival kidney.7. Water and solutes excretion were restored to normal in about 3-5 days after the operation.8. Though the increase in glomerular filtration rate may be the prime mover in the mechanism of compensatory renal hypertrophy, it does not explain why there is an increase in the size of tubules.

SUMMARY1. The ligation of one ureter is accompanied by compensatory hypertrophy of the contralateral kidney.2. The rate of growth of the contralateral kidney after ligation of the opposite ureter is similar to that observed after unilateral nephrectomy.3. Ligation of one ureter produced ipsilateral hydronephrosis. 4. The development of hydronephrosis was accompanied by a marked increase of DNA, suggesting hyperplasia, and of the rate ofanaerobic glycolysis, while the rate of oxygen uptake decreased, especially in the cortex.5. During compensatory hypertrophy of the contralateral kidney, after ligation of the opposite ureter, there were increases of RNA/DNA ratios and of oxygen uptake, especially marked in the cortex, and in every respect similar to those observed after unilateral nephrectomy.6. Ligation of one ureter resulted in an increase of glomerular filtration rate of the contralateral kidney similar to that observed after unilateral nephrectomy.7. The mechanisms of contralateral renal hypertrophy after ligation of one ureter and after unilateral nephrectomy are discussed. It is suggested that in both cases the prime mover to compensatory hypertrophy is the increase of glomerular filtration rate.

It has been suggested that the survival of animals deprived of water is in direct proportion to their ability to concentrate their urine, and that the high concentration of their urine is achieved at the expense of an increased secretion of the antidiuretic hormone. The problem investigated here was to see whether the decrease of the urinary volume observed in laboratory rats deprived of water was the sole factor in the mechanism of water preservation and if so, whether the reduction of urinary secretion was the result of a corresponding increase in secretion of the antidiuretic hormone. METHODSWhite adult male rats of body weight ranging from 250 to 325 g were fed on a standard diet, 100 g of which contained: protein 14 g, fat 4 g, and soluble carbohydrate 49 g; calorific yield 400 call 100 g. From its composition, it could be calculated that its metabolic water was 52 ml./100 g food: its amount of moisture (i.e. 'preformed water') was 13-0 ml./100 g. The water content of food and of faeces was estimated by drying in an oven at 1040 C for 48 hr. The rats were kept in metabolism cages, at a temperature of 210 C; the degree of humidity was not recorded. Urine separators were fixed to the cages and the faeces were collected separately in a vessel with narrow neck so as to diminish water evaporation. Whenever possible fresh faeces were collected for the estimation of their water content. For the estimation of its antidiuretic activity urine was collected in a solution of 3 % (v/v) acetic acid (final concentration, 0-2-0-3 %). Pituitary glands were removed, dried and extracted as specified in the British Pharmacopoeia (1953); the amount of acetic acid used in their extraction did not exceed 0-2 ml./gland of a 0-25 % acetic solution (Bentley & Dicker, 1955). Urine samples were analysed for their Na and K content, using an EEL flame photometer; occasional Cl estimations were performed.The antidiuretic activity of urine or of dissected neurohypophyseal glands was estimated by intravenous injection in rats under ethanol anaesthesia, with the water load kept constant (Dicker, 1953). The vasopressor activity of the neurohypophysis was estimated on rats anaesthetized with urethane and injected with dibenamine (Dekansky, 1952) and the oxytocic activity on a rat's isolated uterus (Holton, 1948). Each assay of the antidiuretic, vasopressor or oxytocic activity consisted of four doses, two of the standard and two of the unknown, the ratio, high to low dose, being the same for standard and unknown solutions. Results were expressed in terms of the antidiuretic or vasopressor activity of a solution of vasopressin, or in terms of oxytocic activity of a solution of oxytocin.

SUMMARY1. Pituitary glands of adult rats of both sexes, of lactating female and of new-born rats, incubated in a Locke solution, release both oxytocin and vasopressin. The amount of hormones released, during a measured period of incubation, is related to the actual hormone content of the gland.2. Increasing the concentration of KCI in the incubation medium, with CaO12 present and in concentration of at least 2-2 mm, produces an enhanced release of both hormones from pituitary glands of adults, but does not affect the release of hormones from glands of new-born animals.3. Addition of ouabain to the incubation medium produces a marked increase of the release of the hormones from glands of both adult and newborn rats. This is accompanied by an extrusion of K ion and an influx of Na ion. The effect of ouabain on the hormone release and the shift of ions can be reversed by subsequent addition of adenosine triphosphate.4. The increased release of hormones produced by ouabain, in glands from new-born rats, is unaffected by the presence or absence of CaCl2. In adults, however, the effect of ouabain, though present, is reduced in the absence of CaCl2.5. It is suggested that in glands from adult animals, the hormones must be freed from their attachment on the protein-carrier, neurophysin and that this can be achieved by the entry of calcium ion into the cell.