2-year Rat Research Articles

Overview of the Preparation, Use and Biological Studies on Polyglycerol Polyricinoleate (PGPR)

The esterification of condensed castor oil fatty acids with polyglycerol gives a powerful water-in-oil emulsifier which is used by the food industry in tin-greasing emulsions and as an emulsifier with lecithin in chocolate couverture and block chocolate. A safety evaluation programme was under-taken in the late 1950s and early 1960s to determine whether this food emulsifier polyglycerol polyricin-oleate (PGPR), (Quest International trade name ADMUL WOL) presented any health implications for consumers. This programme included acute toxicity tests, subacute rat and chicken toxicity studies, a rat chronic toxicity/multigeneration reproduction study, rodent metabolism, carcinogenicity testing in rat and mouse and a human clinical evaluation. PGPR was found to be 98% digested by rats and utilized as a source of energy superior to starch and nearly equivalent to groundnut oil. There was no interference with normal fat metabolism in rats or in the utilization of fat-soluble vitamins. Despite the intimate relationship with fat metabolism, no evidence was found of any adverse effects on such vital processes as growth, reproduction and maintenance of tissue homeostasis. PGPR was not carcinogenic in either 2-year rat or 80-week mouse feeding studies. The human studies showed no adverse effects on tolerance, liver and kidney function, and fat balance at levels up to 10 g/day PGPR. The acceptable daily intake for PGPR which was set by JECFA in 1974 and the EC/SCF in 1979 is 7.5 mg/kg body weight/day. The UK FAC in 1992 estimated that the maximum per capita mean daily intake of PGPR is 2.64 mg/kg body weight/day. It can be concluded that the use of ADMUL WOL brand of PGPR in tin-greasing emulsions or in chocolate couverture does not constitute a human health hazard.

Effect of early body weight and moderate dietary restriction on the survival of the sprague-dawley rat

The effects of ad libitum (AL) feeding, moderate dietary restriction (DR), and initial (6-week) and one-year body weights on the two-year survival of the Sprague-Dawley (SD) rat were evaluated. DR-fed rats were given approximately 75 percent of the adult AL food intake. At two years, body weights of DR-fed males and females were approximately 69 and 58 percent of the AL-fed male and female body weights, respectively. The 2-year survival rate was 80 and 74 percent in DR-fed males and females, respectively, and 28 and 38 percent in AL-fed males and females, respectively. This increase in longevity indicates that DR-fed males and females in carcinogenicity studies would have 14.8 and 9.1 additional weeks of exposure in a 2-year period to test compounds, respectively, compared to AL-fed animals. There was no correlation between initial body weight and 2-year survival in DR or AL-fed rats. There was no association between 1-year body weight and 2-year survival among DR-fed rats. However, AL-fed rats with the greatest 1-year body weight had a lower 2-year average survival compared with the lightest AL-fed rats; this trend was statistically significant only in males. Body weights between the first and second years were statistically significantly correlated for both genders and feeding regimens but no correlation was observed between pretest and 2-year body weights. These findings demonstrate that initial body weight is not the determining factor of 2-year survival, but that the total adult food (caloric) intake is important. In conclusion, moderate dietary restriction prevented excessive body weight gain and greatly increased the 2-year survival of the SD rat. Initial body weights did not correlate to 2-year body weight gain and were not a predictive biomarker of 2-year SD rat survival.

On reference dose (RfD) and its underlying toxicity data base.

The toxicity data of pesticides were summarized and compared amongst different animal species and types of bioassays. These comparisons showed the expected inter-species and inter-bioassay variability. After quantitative and statistical analysis of these data, it was concluded that, on the average, a 2-year dog bioassay detected toxic responses at similar doses as a 2-year rat study, and that both of these bioassays detected toxic responses at lower doses than either a rat 2-generation bioassay, a rat developmental toxicity study, or a 2-year mouse bioassay. Although these chronic dog and rat bioassays were found to detect toxic responses at lower doses than the other studies listed, this analysis does not reflect the seriousness of the effects that were compared. Within the confines of this analysis, then, it appears that a 2-year dog and rat study, reproductive and developmental bioassays are a sufficient data base on which to estimate high confidence Reference Doses (RfDs), and furthermore, that an additional uncertainty factor is needed to estimate RfDs to account for this inter-species and inter-bioassay variability when fewer than this number of bioassays are available.

Preclinical safety evaluation of dilevalol (SCH 19927), an antihypertensive agent, in the rat

Dilevalol (SCH 19927) is an antihypertensive agent with direct vasodilating properties due to β 2-adrenergic receptor agonist activity and nonselective β-receptor blocking activity. In acute (single dose) oral and parenteral studies a low order of toxicity was observed. Clinical signs observed at the higher doses included salivation, prostration, tremors, and convulsions. In multidose oral studies dilevalol produced an increase in mean absolute and/or relative heart weights observed as early as 1 month in the high-dose (300 mg/kg) rats and at all dose levels (35, 90, 220 mg/kg) in rats treated for 1 year. There were no microscopic changes that could be associated with the change in heart weight. Intraalveolar macrophages were observed in the lung tissue of rats treated for 3 months or 1 year with an increase in relative lung weights noted in the high-dose (220 mg/kg) group treated for 1 year. In a 2-year rat study, no evidence of oncogenicity was observed. On the basis of these studies, dilevalol has a low order of toxicity and lacks oncogenic potential in the rat.

Neuroendocrine cell hyperplasia and neuroendocrine carcinoma of the rodent fundic stomach

Certain substances when given orally to rats have effects on the neuroendocrine cells of the fundic stomach. Such compounds also have effects on acid or its secretion, which is to a greater or lesser extent suppressed, with a consequent rise in serum gastrin, followed by an increase in the number of histamine-secreting ECl cells. These changes are seen with the histamine H 2 receptor antagonists loxtidine, SKF 93497, ICI 162,846 and ranitidine; with the hypolipidaemic agents clofibrate, ciprofibrate and benzofibrate; with sodium bicarbonate and pentagastrin; and with omeprazole, a potent inhibitor of the parietal cell proton pump mechanism. Changes in the pH of the rat stomach stimulate the neuroendocrine G cells of the pylorus to secrete gastrin, which acts on the ECL cells of the fundus causing the production of histamine, which is turn stimulates the parietal cell. This sequence leads to an excess of circulating gastrin, whihc is detectable within 5 days. Subsequently increases in the number of ECL cells occur, the hyperplasia being related to hypergastrinaemia and the degree of acid suppression. The hyperplastic response is rapid, being so obvious with loxitidine at 39 days that there is good reason to suppose ir could be well be detected earlier. Using omeprazole, hyperplasia was found at 28 days after oral doses of 140 mg/kg/day. In order to get an equivalent degree of acid suppression with ranitidine it was necessary to deliver 420 mg/kg/day by subcutaneous infusion using an osmotic minipump, when hyperplasia occured. Interestingly, only omeprazole produced a hyperplasia response of G cells. Such results reflect the covalent binding of omeprazole to the proton pump as opposed to the competitive binding of ranitidine to the histamine H 2 receptor site. In addition to ECL cell hyperplasia there is ample evidence from lifetime studies in rats and mice that neoplasia may result. Neuroendocrine carcinomas (carcinoids) of the rat fundic stomach have been observed with loxtidine, omeprazole, SKF 93479 and ICI 162,846. They are seen late the 2-year rat studies and are most unlikely to have arisen purely as an extension of the hyperplastic response. It is possible that the prolonged disturbance of gastric homoeostasis resulting from achlorhydria result in the production of a carcinogen or carcinogens, in which event it is not too suprising, in vier of the neuroendocrine hyperplasia, that the tumours seen are neuroendocrine carcinomas. There is no evidence that substances producing ECL cell hyperplasia are genotoxic.

Correlation of Data from the Strain A Mouse Bioassay with Long-Term Bioassays

Fifty-nine chemicals that had completed National Cancer Institute rat and mouse 2-year carcinogenicity tests were tested in the strain A mouse pulmonary tumor assay. Without knowledge of chemical identity, 53 chemicals were tested in strain A mice in one laboratory and 30 were tested in a second independent laboratory. Strain A tests on 24 of these chemicals were conducted in both laboratories. The strain A results were generally not predictive of the 2-year rat and mouse carcinogenicity test results. Furthermore, there was poor agreement of strain A results between the two laboratories. Although a variety of explanations may be invoked to explain the lack of concordance between the strain A tests and the 2-year rat and mouse tests, no one factor is sufficient to rationalize the poor concordance between strain A and 2-year carcinogenicity bioassay results.

Dyspnoea and thoracic spinal deformation in rats after oral prizidilol (SK&F 92657-A2).

Prizidilol (SK&F 92657-A2), an anti-hypertensive agent, has undergone a range of prescribed toxicity studies required for the investigation of possible adverse drug effects. During the second year of the 2-year rat oral study, a variety of symptoms were exhibited by males receiving 1600 mg of the compound day-1kg-1 by gavage. These animals became lethargic, slouched and developed dyspnoea which became progressively more severe during the course of the study. Necropsy of the affected rats revealed severely haemorrhagic lungs, cardiac hypertrophy and lordosis of the spine into the thoracic cavity. At the 2-year terminal kill, a proportion of the male rats receiving 100 and 400 mg of prizidilol day-1kg-1 were identified with similar but less severe spinal deformation. No female was found with spinal changes but all the rats receiving prizidilol showed haemorrhagic lungs and enlarged hearts. The lordosis of the affected males was always confined to the thoracic spine and this, along with the cardiac hypertrophy, presumably led to marked reduction in the volume of the thoracic cavity, inducing the dyspnoea. Thoracic vertebral body damage, possibly a precursor to the spinal deformities, was found in male rats from both drug-treated and control groups. The nature of the spinal lesion is at present under investigation.

A toxicologic evaluation of 5-ethoxy-3-trichloromethyl-1,2,4-thiadiazole (ETMT)

The following studies were conducted on 3-ethoxy-3-trichloromethyl-1,2,4-thiadiazole (ETMT, Terrazole), a soil fungicide: acute oral toxicity in rats, rabbits, and dogs; acute and subchronic percutaneous toxicity in rabbits; subchronic feeding to rats and dogs; 2-year feeding to rats and dogs; and a three-generation reproduction study in rats. CD rats, albino rabbits, and mongrel and beagle dogs were employed. The acute oral toxicity values (LD 50 ± SD) were: rats, 1077 ± 78 mg/kg; rabbits, 779 ± 532 mg/kg; dogs > 5000 mg/kg (premedicated with morphine). The test material was added to the diet of rats at levels of 0, 78, 156, 312, 625, and 1250 ppm (subchronic study) and 0, 10, 80, and 640 ppm (chronic study and reproductive study); and to the diet of dogs at levels of 0, 100, 400, and 1600 ppm (subchronic study); and 0, 10, 100, and 1000 ppm (chronic study). Three-month feeding in rats resulted only in growth inhibition at 1250 ppm and elevated liver to body weight ratios at 625 and 1250 ppm. Dogs fed 3 months showed a decrease in spleen-to-body weight ratios at all feeding levels and a higher liver-to-body weight ratio at 1600 ppm. No consistent adverse dose-related effects were apparent in the 2-year rat feeding study. The following findings were noted only in dogs that received the 1000-ppm diet: a lesser body weight gain, increases in SAP, SGOT, serum cholinesterase, BSP retention, liver weights; cholestatic hepatosis with secondary bile nephrosis. No adverse effects were apparent at 10 or 100 ppm. In the three-generation reproduction study, no adverse effects were apparent on fertility, gestation, viability, lactation, number of stillborn, and mean number of pups born and weaned per litter. Adverse effects occurred only on the 640-ppm diet and these consisted of lower weaning weights of offspring and depressed body weight gains of parent rats.

Toxicologic studies of petrolatum in mice and rats

The present studies were undertaken as a basis for determining the status of food grade petrolatum as a food additive under the terms of the Food Additives Amendment of 1958. The investigations of the petrolatum included 2-year rat feeding studies and single subcutaneous injections in mice followed by observation over an 18-month period. Previous work and the considerations leading to regulatory interest in the potential carcinogenicity of paraffin hydrocarbons have been reviewed in the extensive report on the toxicity of petroleum waxes by Shubik et al. (1962). Three specific color grades of petrolatum which met either USP XVI or NF XI (White or Yellow Petrolatum) were selected to represent the range of degrees of decolorization of petrolatum commonly used as direct food additives, or which may be incorporated in foods as an indirect additive, incidental to its use in processing.