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Carcinogenicity of saccharin.

Saccharin is carcinogenic for the urinary bladder in rats and mice, and most likely is carcinogenic in human beings. The neoplasms of the urinary bladder are malignant and invade and metastasize. Male rats are more susceptible to urinary bladder carcinogenesis than female rats. Rats exposed as fetuses develop neoplasms more readily than rats exposed as weanlings. The lesions in the urinary bladder go through the stages of hyperplasia, hyperplastic nodules, and later carcinomas. The male of the human species ingesting saccharin, as for rats, is more susceptible to carcinogenesis of the urinary bladder than the female. Neoplasms of the urinary bladder in rats were not caused by stones, parasites, sodium, or impurities. There is a cocarcinogenic effect between saccharin and methylnitrosurea for the urinary bladder. Even through carcinomas of the urinary bladder are present in rats given the higher doses of saccharin, one was observed in a female rat given 0.5%. Chronic renal disease develops in rats ingesting saccharin. The disease is more advanced at the lower doses than at the higher doses, suggesting that saccharin at the lower doses does not reach the urinary bladder. Early neoplasms are seen in the renal pelvis of rats given the higher doses of saccharin. The risk ratios for urinary bladder carcinomas in human beings increase with both frequency andduration of saccharin usage. Benign and malignant neoplasms at all sites are significantly increased in mice and rats ingesting the higher doses of saccharin. These neoplasms are present in the reproductive and hematopoietic systems, and to a lesser extent in the lungs, vascular system and squamous epithelium. Neoplasms in some organs develop with the lower doses of saccharin. Lymphosarcomas of the lung are significantly increased in rats given 0.01% saccharin. Chronic renal disease in rats given saccharin interferes with the health and life span and consequently with development of neoplasms. Saccharin initiates neoplasms of the skin when its application is followed by croton oil. Epidemiological studies have not been done for neoplasms other than the urinary bladder in human beings.

Animals

Response of the rat to saccharin with particular reference to the urinary bladder.

Male and female Wistar rats were administered sodium saccharin for life (2 yr) either in the drinking water or diet. The maximum palatable dose of saccharin in the drinking water was found to be 2 g/kg/day and, even then, there was some voluntary restriction of fluid intake in the males. By contrast, double this dose--namely 4 g/kg/day, was palatable in the diet. A control group of rats of both sexes received saccharin-free diet and drinking water. Mild urothelial hyperplasias developed from 85 weeks in rats of both sexes receiving saccharin either in the drinking water or diet; the incidence was statistically significant in both the bladders and kidneys of rats receiving the higher dose of saccharin in the diet, but in the kidneys only of rats receiving the lower dose of saccharin in the drinking water. Telangiectasia of the vasa recta was significant in saccharin-treated rats of both sexes at both doses. A very low incidence of bladder tumours, exclusively in males receiving the higher saccharin dose in the diet was seen from 95 weeks. No consistent relationship between bladder epithelial hyperplasias and crystalluria could be demonstrated, although all 3 bladder tumours were associated with some form of mineralisation. Results suggest a particular susceptibility of males to saccharin treatment. The possibility that saccharin may promote, or enhance, the development of latent tumour cells already present in the experimental population, rather than initiate carcinogenesis per se is considered.

Animals

Renal tubular transport of saccharin.

These experiments were designed to examine the mechanisms involved in the renal excretion of the non-nutritive sweetener, saccharin. Renal transport of saccharin in female rats was quantitatively evaluated using renal cortical slices in vitro and renal clearances in vivo. Renal cortical slices actively accumulated saccharin. Accumulation was oxygen dependent, saturable and reduced in the presence of metabolic inhibitors (2,4-dinitrophenol and sodium azide) and other organic anions 1p-aminohippurate (PAH) and probenecid]. Furthermore, addition of acetate or lactate to the medium stimulated saccharin uptake whereas reducing potassium concentration in the medium significantly decreased saccharin accumulation. Addition of saccharin to medium containing PAH and N-methylnicotinamide produced a dose-related depression of PAH accumulation. Although N-methylnicotinamide accumulation also was reduced, the depression was not dose-related. The saccharin/inulin clearance ratio of 3.76 indicates that saccharin, like PAH, undergoes tubular secretion. These findings suggest that the primary route of renal elimination of saccharin is active tubular secretion. It is also suggested that saccharin and PAH may share a common transport system.

Animals

Functional decortication by cortical spreading depression does not prevent forced extinction of conditioned saccharin aversion in rats.

Conditioned taste aversion established in rats by association of saccharin drinking with subsequent lithium chloride intoxication decreased saccharin intake to 22% of normal consumption. Force-feeding saccharin to intact and functionally decorticate trained rats returned saccharin consumption on the next day to 62% (n equals 18) and 77% (n equals 19), respectively. Over-trained conditioned saccharin aversion was affected by forced extinction in a similar way (saccharin intake increased from 28% to 50% and 63%, respectively). Intact brain rats refused to swallow saccharin during forced feeding. while functionally decorticate animals showed no signs of aversion; but extinction was almost equal in both cases. Application of lithium chloride after forced feeding of saccharin in functionally decorticate rats neither prevented extinction of conditioned taste aversion nor reestablished the aversion habit extinguished earlier with intact brain. It is concluded that acquisition of the conditioned taste aversion requires cortical input to a short-term memory file, whereas decorticate extinction can be induced by subcortical gustatory processing analogous to the mechanism controlling feeding behavior during the preweaning period.

Animals

Mucociliary function of the eustachian tube: assessment by saccharin test in patients with dry perforations of the tympanic membrane.

The mucociliary function of the Eustachian tube was assess in 44 patients with dry perforations of the lympanic membrane by means of the saccharin test. A saccharin crystal was placed on the mucous membrane of the middle ear as close to the orifice of the Eustachian tube as possible, and the time taken for the patient to taste the saccharin was measured. The function of the Eustachian tube was also assessed by means of the aspiration test and by the Valsalva maneuver. No relationship was found between the results of the saccharin test, aspiration test, and the Valsalva maneuver. However, a correlation seems to exist between the hearing improvement obtained as determined by the postoperative air-bone gap, the positive or negative results of the saccharin test, and (in cases with positive saccharin test) the saccharin perception time.

Adolescent

Divergent responses to saccharin vs. sucrose availability after stress in rats.

Rats were exposed to 100 5-s inescapable, unpredictable shocks then had access to water and saccharin or sucrose solution for 5-6 days. Shock reduced daily drinking during saccharin tests (Experiments 1, 2B, 4) and increased daily drinking during sucrose tests (Experiment 2B). In addition, shock reduced body weight when saccharin, but not when sucrose, was available (Experiments 1, 2B). The specificity of the reductions to saccharin tests (Experiments 2B, 4), equal intake of flavors shortly after stress (Experiments 2B to 4), and failure of saccharin-naive and saccharin-familiar groups to differ (Experiment 3) argue against a neophobia interpretation. Normal or above-normal drinking during sucrose (Experiment 2B) or water-only (Experiment 4) tests indicate an absence of general hedonic, motoric, or hydrational deficits. Qualitative differences in the tastes of saccharin and sucrose may underlie their disparate effects on drinking after shock. Whatever the mechanisms, the present results show that even a severe stressor can decrease or increase ingestion, depending on the flavors available.

Animals

The relationship between saccharin and alcohol intake in rats.

Male rats were given daily sessions during which a palatable saccharin solution was available. Based on intakes averaged over 3 days, groups with low, intermediate, or high intake of saccharin were formed. These rats were then given daily sessions in which alcohol (2-8%) or water were available. Initially, sessions were conducted with rats on a food restriction schedule; in later sessions, food was available ad lib. When rats were food restricted, there were no differences among the groups in terms of alcohol or water intake. When the food restriction schedule was discontinued, alcohol intake in the intermediate and high saccharin intake groups was generally higher than that of the low saccharin group. On the final series of alcohol sessions, the high saccharin group consumed significantly more 2% and 6% alcohol than the low saccharin group. These results are consistent with reports which have found that rats selected for high or low alcohol intake have corresponding high and low intakes of saccharin.

Alcohol Drinking

Acquired preference for morphine but no d-amphetamine as a result of saccharine adulteration.

Consumption of morphine sulfate and d-amphetamine was studied in two groups of rats. In a choice situation, preference for both drugs remained low after 46 days of drinking. In two additional groups morphine and d-amphetamine solutions were prepared with 1% saccharine. Morphine drinking was significantly increased by saccharine adulteration, whereas drinking of amphetamine solutions decreased. Addition of saccharine to morphine solutions increased drinking in more than a simple additive way. Saccharine facilitates the acquisition of drug-directed behavior. The slope of the acquisition trials for the morphine-saccharine group was significantly different from horizontal (O-slope) and significantly different from the slope found for the morphine without saccharine group.

Animals

Abnormal taste preference for saccharin in hypothyroid rats.

Taste preferences for saccharin in concentrations ranging from 0.16 mM to 50 mM were determined in rats made hypothyroid with radioactive iodine and in their littermate controls. Hypothyroid rats demonstrated taste preferences for saccharin which were similar to those of controls only at very low (0.016 mM) or very high (49.0 mM) saccharin concentrations. At these concentrations of tastant, the preferences for tastant and water were similar to one another. At a concentration of 5.1 mM, preferences were also very similar in both groups but were very high. At intermediate saccharin concentrations of 1.1 and 3.0 mM, hypothyroid animals showed significantly lower percent preferences for the sweet tastant than did controls, mean +/- SEM (62.48 +/- 5.97 vs. 82.92 +/- 4.60, p = 0.0002) for the 1.1 mM concentration and (74.98 +/- 5.12 vs. 89.40 +/- 2.54, p = 0.0029) for the 3.0 mM concentration. These changes in taste preference for saccharin in hypothyroid rats were similar in direction and magnitude to those previously published by this laboratory using sucrose as the tastant. Thus, hypothyroid rats demonstrate abnormalities in taste preference for both the nonnutritive sweetener, sodium saccharin, as well as for the nutritive sweetener, sucrose.

Animals

Blockade of hippocampal long-term potentiation by saccharin.

Population spikes, population excitatory postsynaptic potentials and intracellular excitatory postsynaptic potentials were recorded in the CA1 area of guinea-pig hippocampal slices in response to low frequency stimulation of the stratum radiatum. Tetanic stimulation of the same afferents during an application of saccharin (10 mM, 10 min) failed to induced a long-term potentiation of the population spike, population excitatory postsynaptic potential and intracellularly recorded excitatory postsynaptic potential. A post-tetanic application of saccharin did not prevent long-term potentiation of the population spike from developing. Saccharin did not change the input resistance, the membrane potential or the ability to induce action potentials in the CA1 neurons. The slope of the intracellular excitatory postsynaptic potentials recorded in normal medium, in normal medium containing 2-amino-5-phosphonovalerate, or in Mg(2+)-free medium containing 6-cyano-7-nitroquinoxaline-2,3-dione was not significantly altered by saccharin. The depolarizations of CAI neurons produced by superfusion of N-methyl-D-aspartate or during a brief tetanic stimulation of the stratum radiation were also not altered by the drug. It therefore appears that saccharin blocks the induction of long-term potentiation by a mechanism that does not involve a blockade of N-methyl-D-aspartate receptors. Application of fluid samples collected from rabbit neocortical surface during a tetanic stimulation of the neocortex caused neurite growth in PC-12 cells, suggesting that growth-related substances were present in the collected samples. If these samples were superfused onto hippocampal slices, long-term potentiation developed. If however, the samples were co-applied with saccharin, neither neurite growth in PC-12 cells nor long-term potentiation in hippocampal slices was observed, raising the possibility that growth-related substances are involved in long-term potentiation.

6-Cyano-7-nitroquinoxaline-2,3-dione

Genetic effects of impure and pure saccharin in yeast.

Yeast cells were grown in media containing impure or purified saccharin preparations. Dose-dependent increases in frequencies of cells possessing aberrant cell morphologies were revealed by light microscopy. At each test dose, cells grown in impure saccharin exhibited up to sevenfold higher frequencies of mitotic crossing-over or gene conversion in three of four assays for genetic recombination than cells grown in purified saccharin from the same lot. With one exception, the sweetener produced by the Maumee process caused larger increases in recombination and gene reversion than the sweetener produced by the Remsen-Fahlberg process. The several test markers did not respond equally to any test saccharin. Cells grown in liquid media containing no saccharin or two of three test concentrations of saccharin produced cell titers that were approximately equivalent.

Cell Division

Inhibition by saccharin of glucose-6-phosphatase: effects of alloxan in vivo and deoxycholate in vitro.

Inhibition by saccharin of rat liver glucose-6-phosphatase (EC 3.1.3.9) generally decreased as the pH increased in the range pH 4-8. This pattern was exhibited by homogenates from control and alloxan-treated animals assayed each in the absence and presence of 0.2% (w/v) deoxycholate. Saccharin inhibited in competitive fashion with respect to glucose-6-phosphate (glucose-6-P). There was a small increase in Km (glucose-6-P) but not K1 (saccharin) values in alloxan-treated rats when assays were conducted in the absence of deoxycholate. In the presence of this detergent there was no significant difference in these kinetic parameters between the alloxan-treated and control groups. Deoxycholate decreased Km (glucose-6-P) and increased K1 (saccharin) values. Calculations using these kinetic parameters indicate that, under usual hepatic glucose-6-P concentrations and relatively high levels of saccharin in liver, the inhibition by saccharin of glucose-6-phosphatase is unlikely to be of major significance in vivo.

Alloxan

Buprenorphine's effects on self-administration of smoked cocaine base and orally delivered phencyclidine, ethanol and saccharin in rhesus monkeys.

The effects of buprenorphine on behavior reinforced by smoked cocaine base and orally delivered phencyclidine (PCP), ethanol and saccharin were compared. There were six groups of four to five rhesus monkeys. Group 1 contained four monkeys that had been trained to smoke cocaine base under progressive ratio (PR) or fixed ratio (FR) schedules. Up to eight smoke deliveries (2 mg/kg) were available during daily 3-hr sessions. Each delivery was separated by a 15-min timeout. The remaining groups received concurrent access to different combinations of orally delivered liquids as follows: group 2, PCP (0.25 mg/ml) and water; group 3, saccharin (0.03% w/v) and water; group 4, PCP and saccharin; group 5, ethanol (8% w/v) and water; and group 6, ethanol and PCP. Saline or buprenorphine (0.003, 0.012, 0.05, 0.2 and 0.8 mg/kg) injections were given i.m. 30 min before each session for 5 consecutive days. Buprenorphine produced a dose-dependent reduction in behavior maintained by PCP, ethanol or saccharin in all of the six groups. In group 1, the suppressant effects of buprenorphine on cocaine base smoking were greater in the two monkeys that responded under FR 5 schedules than in the two that responded under PR schedules. When PCP and saccharin were concurrently available (group 4), buprenorphine had a greater suppressant effect on PCP than when water was concurrently present (group 2). Buprenorphine produced nearly a complete suppression in saccharin-maintained responding at doses of 0.012 mg/kg and higher in groups 3 and 4. Buprenorphine reduced ethanol deliveries to about 50% at doses of 0.012 mg/kg and higher in group 5. When PCP and ethanol were concurrently available (group 6), buprenorphine had an effect on PCP and ethanol that was similar to that found when the drugs were available concurrently with water. These results suggest that buprenorphine suppresses behavior maintained by several drug and nondrug substances, and it further suppresses PCP-maintained behavior that is already reduced by a nondrug alternative reinforcer.

Administration, Oral

Promoting effect of saccharin and DL-tryptophan in urinary bladder carcinogenesis.

The existence of at least two stages in bladder carcinogenesis was evaluated in male Fischer rats using N-[14-(5-nitro-2-furyl)-2-thiazolyl]formamide (FANFT) fed for six weeks at a level of 0.2% of the diet as the initiator. Sodium saccharin and DL-tryptophan were fed at levels of 5 and 2% of the diet, respectively, as possible promoting chemicals, and they were fed either immediately after FANFT administration or after six weeks of FANFT plus six weeks of control diet. All surviving rats were killed at the end of two years. Both chemicals significantly increased the incidence of bladder tumors following FANFT feeding compared to six weeks of FANFT feeding followed by control diet, and the results were similar whether saccharin or tryptophan feeding was started immediately after FANFT feeding was concluded or after a six-week delay. Saccharin was considerably more potent as a promoting agent than was tryptophan, inducing higher incidences of bladder tumors and having a shorter latent period. Long-term administration of FANFT induced a 100% incidence of bladder cancer. Sequential epithelial changes were observed by scanning and transmission electron microscopy as well as by light microscopy. Pleomorphic microvilli were present on the superficial cells of all tumors examined and on the surface cells of hyperplastic bladder epithelium after six weeks of FANFT plus six weeks of saccharin, but not after six weeks of FANFT and six weeks of control diet. Rats fed only saccharin tryptophan, or control diet did not have bladder tumors or pleomorphic microvilli on bladder epithelium. These data suggest that saccharin and tryptophan might act as tumor-promoting agents during bladder carcinogenesis.

Animals

Altered saccharin preference during chronic dietary administration of lead in adult rats.

Procedural variables are crucial in using taste aversion as a measure of lead toxicity. Rats were given saccharin and water to drink while ingesting a diet containing lead acetate (PbAc). Rats showed high preference for saccharin (over water) before lead was introduced. Saccharian preference fell during PbAc ingestion and rose when PbAc was removed from the diet suggesting that saccharin preference may correlate with the physiologic action of the toxicant. When saccharin was introduced simultaneously with PbAc aversion was almost total, but recovered with continuous PbAc exposure. When saccharin was introduced after the start of PbAc exposure saccharin aversion diminished with the duration of presaccharin PbAc exposure.

Analysis of Variance

Saccharin sodium as a potential sweetener for antidotal charcoal.

This study explored if saccharin sodium, as a sweetener in activated charcoal formulations, would be sufficiently available to provide sweetness while not severely reducing charcoal's adsorption capacity. In vitro tests showed that charcoal takes up 40wt% of saccharin at a 1 g/liter concentration of saccharin in the residual fluid; 29.3wt% at 0.1 g/liter. A saccharin level of 0.1 g/g of charcoal in a carboxymethylcellulose formulation gave enough residual flavor to be appealing. Sodium salicylate, 1 g/liter and 10 g/liter, was used to test whether the 0.1 g/g level of saccharin would interfere with charcoal's ability to adsorb a typical drug. By use of colorimetric assay, it was shown that a 2 g charcoal per gram of salicylate (initial salicylate concentration of 1 g/liter), the extent of drug adsorption was reduced from 70% to 64%, at a 10 g/liter initial concentration, the reduction was 87% to 82%. Under the conditions tested, the antidotal mixture should be pleasantly sweet at a saccharin level of 1 g/10g charcoal, and little effect would be produced on the adsorption of sodium salicylate and other drugs that are well adsorbed by charcoal.

Adsorption

Single-locus control of saccharin intake in BXD/Ty recombinant inbred (RI) mice: some methodological implications for RI strain analysis.

The sac locus, with a major effect on saccharin preference, was discovered by Fuller (1974) in C57BL/6J (B6), DBA/2J (D2), and derived crosses, and is now supported in the BXD/Ty recombinant inbred (RI) series by a marked bimodal distribution in saccharin preference among 20 strains. The B6 allele led to increased saccharin preference compared to the D2 allele. Since the search for bimodal distributions reflecting major gene loci is an essential part of RI strain analysis, a new statistical method is proposed to test for bimodality, and comparisons are made to previously proposed methods. Another new RI method, quantitative trait loci (QTL) analysis, allows provisional detection and mapping of minor as well as major gene loci. Using this method as a screen, significant associations with saccharin preference were suggested with marker loci on portions of six chromosomes. One of these, the D12nyu1 locus on chromosome 12, was independently supported in a panel of standard (non-RI) inbred strains also tested for saccharin preference. It is unclear whether this reflects the sac locus.

Animals

Ibotenic acid lesion of the hypothalamic paraventricular nucleus produces weight gain but modifies neither preference nor aversion for saccharin.

We showed recently that bilateral ibotenic acid lesions of the lateral hypothalamus (LH) produced three main behavioral disturbances in the rat, i.e., an increase in the gustatory preference and aversion thresholds for saccharin, permanent body weight and water intake deficits, and an alteration of morphine-induced modulation of taste. The two first results could suggest that the modification of the gustatory thresholds and the ingestive deficits are closely interrelated. Given this situation, we hypothesized that, conversely, a brain lesion known to induce obesity and hyperdipsia would therefore decrease the gustatory preference and aversion thresholds for saccharin. In order to test this hypothesis we analyzed the effects of the bilateral lesion of the hypothalamic paraventricular nucleus (PVH) by injection of ibotenic acid (2 micrograms in each side) on saccharin preference. The main results are as follows: 1) The neurotoxin selectively destroyed parvicellular neurons while the magnocellular cells were spared. 2) In comparison to the normal daily gain in body weight of the sham-lesioned animals, the lesioned rats showed an enhanced weight gain that became significant from the third day after the surgery up until the day of sacrifice, 37 days later. 3) In contrast to electrolytic lesions of the PVH, the ibotenic acid lesions of this nucleus did not induce hyperdipsia. 4) Preference and aversion thresholds for saccharin were not significantly modified by the lesion. 5) Whereas low doses of morphine suppressed the preference for saccharin in sham-lesioned rats when the concentration of the sweetener solution was at the threshold value, this suppressive effect was not observed in PVH-lesioned rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals