The mechanism of water diuresis in normal rats and rabbits as analysed by inulin and diodone clearances

Biology of the rabbit

In recognition of Dr. Nathan Brewer's many years of dedicated service to AALAS and the community of research animal care specialists, the premier issue of JAALAS includes the following compilation of Dr. Brewer's essays on rabbit anatomy and physiology. These essays were originally published in the ASLAP newsletter (formerly called Synapse), and are reprinted here with the permission and endorsement of that organization. I would like to thank Nina Hahn, Jane Lacher, and Nancy Austin for assistance in compiling these essays. Publishing this information in JAALAS allows Dr. Brewer's work to become part of the searchable literature for laboratory animal science and medicine and also assures that the literature references and information he compiled will not be lost to posterity. However, readers should note that this material has undergone only minor editing for style, has not been edited for content, and, most importantly, has not undergone peer review. With the agreement of the associate editors and the AALAS leadership, I elected to forego peer review of this work, in contradiction to standard JAALAS policy, based on the status of this material as pre-published information from an affiliate organization that holds the copyright and on the esteem in which we hold for Dr. Brewer as a founding father of our organization.

The acute toxic effects of hexachloro-1 : 3-butadiene on the rat kidney

A single intraperitoneal injection of hexochloro-1 : 3-butadiene (HCBD) at 100 mg/kg or above produced renal tubular necrosis in the rat by 24 h. Histological examination of the kidneys indicated damage to the straight portion of the proximal tubules. Urinary analysis showed diuresis, increased proteinuria and an increase in the excretion of N-acetyl-beta-D-glucosaminidase, and alkaline phosphatase at doses above 100 mg/kg. At doses below 100 mg/kg only a mild increase in protein excretion was observed. Twenty-four hours after 200 mg/kg HCBD, i.p., there was a marked decrease in the glomerular filtration rate (inulin clearance) and in the clearance of the organic anion (p-aminohippuric acid, PAH) and the organic cation (tetraethylammonium bromide, TEA) by the kidney. HCBD did not affect the accumulation of PAH or TEA by renal cortical slices when added in vitro at a concentration up to 0.1 mM. However, a decrease in PAH, but not TEA accumulation, was seen in renal cortical slices from rats treated with HCBD 24 h previously. Mercuric chloride (HgCl2), a known nephrotoxin, was used as a positive control for these studies. HCBD appears to specifically damage the straight portion of the proximal renal tubule and thereby selectively damage the organic anion transport system.

The biliary excretion of 3H-inulin and 3H-terbutaline in the unanesthetized rat

An animal model which permits sampling of arterial blood and bile from unanesthetized rats with uninterrupted enterohepatic circulation is described. Pharmacokinetic data concerning inulin (0.2 mumol kg-1) and terbutaline (1.8 mumol kg-1) after intraarterial injection are presented. The following values for inulin were obtained Vdbeta equals 0.25 ml g-1, plasma clearance equals 2.3 ml min-1 kg-1 and bile clearance equals 0.03-0.04 ml min-1 kg-1, which mainly are in agreement with data from the literature. For terbutaline the corresponding values were 0.58 ml g-1, 5.2 ml min-1 kg-1 and 0.12-0.98 ml min-1 kg-1, respectively.

Compensatory hypertrophy of the contralateral kidney after unilateral ureteral ligation

1. 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 of anaerobic 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.

Mechanism of compensatory renal hypertrophy

1. 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.

Determination of the renal clearance of inulin in rats: lowered values at low urine flow rates

The renal clearance of inulin (ClIN) was measured in anaesthetized male rats using a continuous intravenous infusion method.ClIN was independent of urine flow rate provided this was greater than 0.03 ml/minute.At flow rates lower than this, CIIN was reduced and appeared to correlate with the rate of flow.In experiments where a constant kidney function is required. e.g., pharmacokinetic studies, it is advisable to maintain urine, flow rates in the rat above 0.03 ml/minute.

The clearance of creatinine, inulin, para-aminohippurate and phenosulphothalein in the cat

Endogenous creatinine, inulin, para-amino-hippurate and phenolsulphothalein clearances for healthy cats are presented. The values for inulin and para-aminohippurate clearances (ml/kg/min) are similar to those for the dog. Creatinine clearance was less than inulin clearance values. Pnenolsulphothalein clearance may be a better index of glomerular rather than tubular function in the cat.

Effects of water diuresis and osmotic (mannitol) diuresis on urinary solute excretion by the conscious rat

1. The time course and extent of changes in urinary flow and in the outputs of urea, Na(+), K(+), and NH(4) (+) over a period of 7(1/2) hr in conscious rats during water and osmotic (mannitol) diuresis were determined, and compared with spontaneous changes in non-diuretic animals.2. In non-diuretic rats, a morning rise and subsequent decline in urinary osmolal, sodium, potassium and ammonium outputs occurred, possibly attributable to circadian rhythms.3. Water diuresis was accompanied by (i) a rapid increase in urea excretion during the phase of increasing urine flow, followed by a fall in later periods to values similar to those in non-diuresis, (ii) a slower increase in sodium output, continuing after the establishment of the constant water load, (iii) unchanged potassium excretion, but slightly increased ammonium outputs.4. Mannitol diuresis was accompanied by (i) a rapid increase in urea outputs which subsequently fell but remained significantly higher, (ii) a steep rise in sodium and potassium outputs to values which remained far higher than those in non-diuretic and water diuretic animals.5. The changes in mannitol diuresis are considered to result mainly from decreased tubular reabsorption, due to the lowered intraluminal sodium, potassium and urea concentrations and increased intratubular fluid flow. Some of the acute increase in urea excretion may be due to washout of medullary urea into the tubular fluid.6. In water diuresis, some of the changes in solute excretion may similarly result from altered tubular reabsorption, perhaps influenced by suppression of anti-diuretic hormone (A.D.H.). In addition, the slower changes in sodium output may be related to several consequences of change in body fluid volume.

Renal Blood Flow, Glomerular Filtration Rate, Renal PAH Extraction Ratio, and the Role of the Renal Vasomotor Nerves in the Unanesthetized Rabbit

The unanesthetized rabbit has been found to be a satisfactory animal for studying the renal circulation. Techniques for measuring renal clearances and cardiac output, for carrying out renal vein catheterization, and for measuring renal clearances separately for each kidney are described. Normal values are presented from data obtained from 86 rabbits. Renal blood flow and glomerular filtration rate were found to be stable, judged by the reproducibility of these measurements over a period of three hours. Renal PAH extraction ratios averaged 95.5% in 16 unanesthetized animals. In 12 animals renal blood flow was 6% higher in one chronically denervated kidney than in the contralateral innervated kidney, indicating a low degree of sympathetic vasoconstriction in the normal resting circulation of the rabbit. All the results were obtained in the rabbit in the course of moderate water and mannitol diuresis.

RENAL EFFECTS OF VERATRIDINE

Veratridine hydrochloride injected subcutaneously into unanaesthetized rats inhibited water diuresis. A linear relationship between log dose and antidiuretic effect could be established over the dose range 50 to 200 mug./100 g. of body weight. When veratridine hydrochloride was injected intravenously in doses from 10 to 30 mug./100 g., this relationship was also linear. In terms of its antidiuretic action, the alkaloid was approximately five times as effective when given intravenously. Rats anaesthetized with urethane responded to an intravenous injection with a more pronounced inhibition than unanaesthetized animals. Protoveratrine injected intravenously into unanaesthetized rats showed no clear relationship between dose and magnitude of antidiuretic effect. Veratridine hydrochloride injected intravenously had a pronounced hypotensive effect in both anaesthetized and unanaesthetized rats. Treatment with atropine did not affect this hypotensive action significantly. Atropine given subcutaneously 30 min. before an intravenous injection of veratridine hydrochloride abolished or diminished the inhibitory effect of veratridine on water diuresis. Veratridine hydrochloride injected intravenously into unanaesthetized rats caused a marked depression of the clearance of inulin and p-aminohippurate. In unanaesthetized rats with an osmotic diuresis, veratridine hydrochloride produced its usual antidiuretic effect. The urine of rats injected with veratridine hydrochloride produced an antidiuretic effect when injected intravenously into other animals. The antidiuretic potency of such urines was not affected by treatment with thioglycollate. Animals injected with veratridine excreted small amounts of a veratridine-like substance in the urine. These results do not suggest that veratridine in antidiuretic and hypotensive doses stimulated the neurohypophysis in the rat.

The effect of diuretics on the water excretion of protein deficient rats

Adult rats kept for eleven weeks on a diet deficient in protein lost weight and some developed scrotal oedema. The retention of bromsulphthalein was increased, but the thymol turbidity test was unaffected; the apparent plasma volume was increased.Water diuresis in the protein deficient animals was impaired. There was no apparent delay in the mean rate of water absorption from the whole gastro-intestinal tract although a delayed absorption of water from the intestine was found in some animals. The concentrations of total plasma proteins and plasma albumin were low as compared with normal animals, but the plasma sodium levels were within normal limits. The inulin clearance (glomerular filtration rate) of the animals on the protein-deficient diet was significantly lower than that of the controls.In normal rats, aminophylline and acetazolamide were diuretic. Caffeine and sodium benzoate did not increase the urine output and mersalyl was antidiuretic. In the protein deficient rats, cortisone acetate increased the water diuresis. Caffeine and sodium benzoate, aminophylline and acetazolamide did not significantly increase this response, mersalyl had an antidiuretic effect. Cortisone acetate increased the food and water intake of the protein deficient rats; it also increased the glomerular filtration rate.

Renal effects of protein-deficient vegetable diets; a functional and histological study

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