R.L. Anderson

The effects of high dietary levels of sodium saccharin on mineral and water balance and related parameters in rats.

The effects of sodium saccharin (NaS) treatment on mineral and water balance and a number of related parameters were studied over a 10-day period in 7-month-old Charles River CD rats. Eight groups of 10 male and 10 female rats were studied. In four of the groups the rats were the F1 offspring of rats that had been exposed to NaS at 1, 3, 5 or 7.5% in the diet and the offspring were treated with the same dietary levels of NaS as their parents. Prior treatment in two other groups was modified in order to evaluate the role of in utero exposure to NaS on the study parameters: rats in one group were only exposed in utero via dams fed diets containing 5% NaS while treatment in the other group did not include in utero exposure, but was started at birth via dams fed diets containing NaS and continued at a dietary concentration of 5% NaS. Second-generation rats in another group were fed diets containing 5% sodium hippurate (NaH), a compound with a number of physical and chemical properties similar to those of NaS; this group was included in order to evaluate the specificity of NaS and/or the effect of sodium on the study parameters. A group of untreated rats served as controls. Treatment-related effects were observed in most study parameters. In addition, a number of differences between male and female rats in baseline values and/or in response to NaS administration were observed. With increasing dietary levels of NaS body weights decreased, but there were increases in water consumption, faecal water content, and caecal weights. NaS treatment resulted in increased urine volume and decreased urine osmolality, changes in urine mineral concentrations (increased sodium, decreased potassium and zinc) and increases in fresh and dry bladder weights, bladder-tissue hydration, and mineral concentrations (sodium, potassium, magnesium and zinc) in bladder tissue. The parameters in which clear sex-related differences in baseline values were observed were body weight, food and water consumption, urine volume, urine osmolality, fresh bladder mass, bladder-tissue hydration and the concentrations of sodium, potassium, magnesium and zinc in the bladder tissue. With the exception of urine osmolality, the values were higher in females. Differences between males and females in response to treatment were observed for NaS consumption (increased in females), caecal weight (increased in females), NaS concentration in the urine (increased in males), and the concentration of sodium, potassium, magnesium and zinc in the bladder tissue (increased in males).(ABSTRACT TRUNCATED AT 400 WORDS)

Some changes in gastro-intestinal metabolism and in the urine and bladders of rats in response to sodium saccharin ingestion

In rats fed sodium saccharin in the diet changes in urine composition, increased bladder-tissue mass and, in males only, an accumulation of minerals in the bladder tissue have been observed. In this report evidence is presented that indicates that these changes are a consequence of the effects of sodium saccharin in the gastro-intestinal tract and are not due to systemic sodium saccharin. Sodium saccharin has been shown to inhibit gastro-intestinal enzymes that digest carbohydrates and proteins and to increase caecal absorption of mineral ions. The significance of these findings to saccharin-associated bladder tumorigenesis is discussed.

Short-Term Effects of Dietary Nitrilotriacetic Acid in the Male Charles River Rat Kidney

Trisodium nitrilotriacetate monohydrate was fed to male weanling Charles River rats for 28 days. Clinical evidence of urinary tract toxicity included hydronephrosis and nephromegaly. Microscopically, severe renal injury was recognized specifically as convoluted tubular cytoplasmic vacuolation and pelvic epithelial erosion. Hyperplasia occurred as a sequela to these specific cytotoxic alterations.

The effect of various saccharin forms on gastro-intestinal tract, urine and bladder of male rats

Sodium saccharin, potassium saccharin, calcium saccharin and the free acid when fed to young male rats at a level of about 200 mumol/g diet all produced an equivalent increase in the caecal enlargement indicating that this phenomenon was due to the saccharin ion and not the accompanying cation. The sodium and potassium salts caused greater polydipsia and polyuria than the calcium or free acid forms. Simple hyperplasia of the bladder was noted in the rats ingesting the sodium and potassium salts but not in those ingesting the calcium or free acid forms. The difference in urine and bladder response to the salt forms is not attributable to the difference in the total urinary saccharin or the urinary concentration of saccharin. These results suggest that excess water absorption from the lower bowel and the concomitant bladder responses are dependent upon monovalent cation absorption but independent of saccharin absorption.

An hypothesis of the mechanism of urinary bladder tumorigenesis in rats ingesting sodium saccharin

An hypothesis is presented of a mechanism for the sodium saccharin (NaS)-associated tumorigenesis of the urinary bladder that occurs in male rats. The ingestion of high doses of NaS is associated with increased urine volume and bladder mass. In rats with an inherently high urine output, the diuresis associated with NaS ingestion combined with the increasing diuresis that occurs with age in male rats results in a chronic demand for a bladder-volume increase that is met by excessive cell division of the bladder epithelium. This enhanced mitosis in the bladder epithelium can result in a significant incidence of bladder tumours. Male rats exposed to NaS during early life show an exacerbation of tumour incidence, and it is proposed that this is because the exacerbation of the effects of NaS on the gastro-intestinal and urinary tracts results in increased urine output and bladder hyperplasia in these rats.

Effect of inherent urine output on the response of male rats to 7.5% dietary sodium saccharin

Young male rats were preselected as high urine (57 g/kg body weight) or low urine (35 g/kg) voiders and were fed a diet containing 7.5% sodium saccharin (NaS) for 10 wk. Urine output was found to be a stable characteristic and high urine output was associated with increased water and feed consumption and increased weight gain. Rats responded in a very similar fashion to 7.5% dietary NaS regardless of their inherent urine output. NaS ingestion was associated with increases in water consumption, caecal mass and urine volume. Among rats that had ingested 7.5% dietary NaS for 10 wk there was a high incidence (12/20) of bladder epithelial hyperplasia. The results are discussed with regard to the concept that increased urine output is an important factor in NaS-induced bladder tumours.

Effect of saccharin ingestion on stool composition in relation to caecal enlargement and increased stool hydration

In an attempt to determine why sodium saccharin feeding causes caecal enlargement (Anderson & Kirkland, Fd Cosmet. Toxicol. 1980, 18, 353) and increased stool hydration (Anderson, Fd Cosmet. Toxicol. 1979, 17, 195), stools from rats fed diets containing 0, 1, 3, 5 or 7.5% sodium saccharin were analysed. Saccharin ingestion resulted in a small increase in stool ash but no change in lipid or non-saccharin nitrogen concentrations (mg/g dry stool). Saccharin treatment also resulted in a dose-dependent increase in the stool content of carbohydrate soluble in 1 N-NaOH. The results have led to the hypothesis that saccharin feeding results in a dose-dependent increase in the stools in the content of hygroscopic polysaccharides which may be derived from the diet or synthesized by an intestinal microorganism(s). The polysaccharide in conjunction with the high stool saccharin content causes caecal enlargement and increased stool hydration. A possible relationship between this effect of saccharin and urinary-tract toxicity is suggested.

Reversibility of nephrotoxicity induced in rats by nitrilotriacetate in subchronic feeding studies.

The reversibility of nitrilotriacetate (NTA)-associated nephrotoxicity was investigated by comparing renal tissues from rats fed nephrotoxic levels of NTA for 7 wk with those from rats allowed 5 wk of recovery after the 7-wk exposure. In addition the toxicity of 2% Na3NTA X H2O in the diet (73 mumol/g diet) was compared with that of 1.5% H3NTA (79 mumol/g diet). The two forms of NTA induced comparable renal tubular cell toxicity which was characterized by proximal convoluted cell vacuolation and hyperplasia. These effects were noted in all of the exposed animals although the extent of damage varied. This specific renal tubular cell toxicity was completely reversed during the 5-wk recovery period. Renal pelvic transitional cell toxicity was induced primarily by Na3NTA X H2O. Renal pelvic toxicity was characterized by hydronephrosis, and erosion, ulceration and hyperplasia of the transitional epithelium. All forms of renal toxicity except that accompanying hydronephrosis were reversed when Na3NTA X H2O feeding was discontinued.

Ethylenediaminetetra(methylenephosphonic acid): genotoxicity, biodistribution, and subchronic and chronic toxicity in rats.

Ethylenediaminetetra(methylenephosphonic acid), EDITEMPA, was tested for oral toxicity in rats in a 13-wk feeding study (at doses of 0, 5, 50 and 500 mg/kg/day) and in a chronic feeding study (at doses of 0, 4, 20 and 100 mg/kg/day). EDITEMPA was also tested for genotoxicity in the Ames, mouse lymphoma, unscheduled DNA synthesis, and in vivo cytogenetics assays. Additionally, absorption, distribution and excretion (ADE) studies were conducted following administration of [14C]EDITEMPA to rats by gavage and via the feed and drinking-water. The principal finding in the 13-wk study was mild anaemia in male and female rats given 500 mg/kg/day, which was resolved during a 9-wk recovery period. In the chronic study, there was no substantial evidence of any treatment-related toxicity or carcinogenicity. Differences in survival of control and treated females (noted late in the study) were interpreted to represent unusually good survival in controls; however, a compound-related increase in mortality could not be completely ruled out. Tests for genotoxicity were all negative. ADE studies revealed that [14C]EDITEMPA was poorly absorbed from the gastro-intestinal tract and that most of the absorbed dose was rapidly excreted by the kidneys or sequestered in bone. The gavage route of administration led to four- to six-fold increases in bone EDITEMPA levels as compared with administration in the feed and drinking-water, respectively. These results suggest that no significant toxicity or carcinogenicity concerns arise from EDITEMPA when it is administered in the feed at the concentrations tested. Reversible anaemia was seen only at very high doses and was interpreted as being secondary to EDITEMPAs ability to interfere with iron absorption and utilization. Localization of EDITEMPA in bone indicated a high degree of affinity for mineralizing tissues, consistent with its chelating properties. There was, however, no effect on bone resorption or mineralization. A comparison of human drinking-water levels of 3500 ppm EDITEMPA (based on a no-effect level of 100 mg/kg/day in rats) with the estimated worst-case exposure in humans of 0.01 ppm suggested a safety margin greater than 1 x 10(5).

Effect of saccharin on the ATP-induced increase in Na+ permeability in isolated chicken intestinal epithelial cells.

When isolated intestinal cells from 3-wk-old chickens are treated with exogenous ATP they undergo a dramatic increase in permeability towards Na+. The increase occurs instantaneously and maximum cell loading with Na+ occurs within 2 min. The response is dose dependent (0.1-1.0 mM-ATP) and results in as much as a 10-fold increase in unidirectional influx of 22Na+ into the cells. The resting cellular Na+ gradient and membrane potential are partially dissipated and consequently Na+-dependent transport of sugars and amino acids is inhibited. Sodium saccharin (20 mM), added at the same time as ATP, completely blocks the effect of ATP on Na+ permeability and preserves the functional capacity of the cells for Na+-dependent sugar or amino acid transport. Partial protection is afforded by 10 mM-saccharin. Saccharin added 2 min after ATP will reverse the enhanced Na+ permeability that has already been induced. In cells that have not been treated with ATP, saccharin induces enhanced sugar and amino acid gradients (P less than 0.05 in paired comparisons from the same cell preparation), indicating that it may also inhibit Na+ permeability of the unperturbed membrane and allow cells to establish higher Na+ gradients and/or membrane potentials. The effect of saccharin in blocking ATP-induced Na+ permeability occurs within 10 sec and at a much lower dose than that required for blockade of facilitated diffusional sugar transfer in these cells.