Strains Of Female Rats Research Articles

Noninvasive Monitoring of Blood Pressure and Heart Rate during Estrous Cycle Phases in Normotensive Wistar-Kyoto and Spontaneously Hypertensive Female Rats.

Since 2015, the National Institutes of Health has called for its funded preclinical research to include both male and female subjects. However, much of the basic animal research that has studied heart rate and blood pressure in the past has used male rats. Male rats have been preferred for these studies to avoid the possible complicating effects of the female estrous cycle. The aim of the current study was to determine whether blood pressure and heart rates vary as a function of the estrous cycle phase of young normotensive Wistar-Kyoto (WKY) and Spontaneously Hypertensive (SHR) female rats. Blood pressure and heart rate were measured at the same time of day throughout the estrous cycle by using a noninvasive tail cuff sphygmomanometric technique. As expected, 16-wk-old female SHR rats had higher blood pressure and heart rates than did age-matched female WKY rats. However, no significant differences in mean, systolic, or diastolic arterial blood pressure or heart rate were detected across the different stages of the estrous cycle in either strain of female rats. Consistent with previous reports, heart rates were higher and showed less variation in the hypertensive SHR female rats as compared with the normotensive WKY female rats. These results indicate that studies measuring blood pressure and heart rate can include young female SHR and WKY rats with no effect of estrous cycle stage.

Effects of a Mixture of Five Pesticides in Low Doses on the Reproductive System of Three Strains of Female Rats.

Effects of a Mixture of Five Pesticides in Low Doses on the Reproductive System of Three Strains of Female Rats.

Behavioral and physiological effects of chronic mild stress in female rats

Anhedonia, a core symptom of clinical depression, refers to the loss of interest in normally rewarding stimuli; the chronic mild stress paradigm, an animal model of depression, was designed with this as an underlying feature. The procedure consists of the administration of a variety of ecologically relevant stressors over long durations. Its effects have been thoroughly investigated in male but not female rats. This study examines the appropriateness of stressors designed to evaluate the development and progression of depression in two strains of female rats, the effectiveness of two measures of anhedonia, and the relationship between stress reactivity and the estrous cycle. Changes in hedonic status were indexed for three weeks following a three week baseline period using two standard behavioral measures of anhedonia: sucrose intake and preference and thresholds for brain stimulation reward. Decreases in 24 h sucrose intake were observed in both strains during the first week of stress manipulations, and continued to decline thereafter for the remainder of the stress phase; in contrast, sucrose preference was unaffected by the stressors, indicating an overall reduction in fluid intake. No changes in the thresholds for brain stimulation reward were observed. The cyclical pattern of estrous was altered in both strains with a significant reduction in the number of regular cycles as a consequence of both the stressors and brain stimulation reward. Furthermore, cyclicity was not reinstated in many animals even six weeks after stress manipulations and behavioral tests had ceased. While the physiological measures suggest that the mild stressors are disruptive to female rats, the results of the behavioral tests are not consistent with the notion that the stressors induce an anhedonic state.

Problems in physiological experimental animal models investigated with factorial design

In the present study we investigated four variables using factorial design to decide if any of these could explain the variations in the control measurements of interstitial fluid pressure ( P if) in rat trachea that were experienced. This approach requires only a fraction of the animals normally needed when studying each factor separately. P if in tracheal tissue was measured with the servocontrolled counterpressure system using sharpened micropipettes. The measurements were performed over a period of 60 min and are presented as mean for every 15 min period. The factors investigated in the study were: three strains of female rats (Strain) two brands of diets (Food); two breeder companies (Source); and finally two batches of the same set of animals to repeat the experiment twice (Week), using a total of 48 animals. There was a highly significant effect within Strain the first week ( p=0.007), but this response was not observed the second week. The interaction between Strain×Week was significant ( p=0.007) while the main effects Strain or Week alone were not significant. The response pattern for Strain and Food was inconsistent for the two experimental weeks studied. These experiments made it possible for us to simultaneously test several factors and exclude these factors as the reason for the observed changes in our experiments since the experiments did not allow the conclusion that one or several of these factors could explain the variation in P if.

Strain and colony differences in the neurotoxic sequelae of MK-801 visualized with the amino-cupric-silver method

The strain and sex of a species under investigation may influence the animal's physiological response to a variety of stimuli. Strain and sex differences are important considerations when evaluating animal models. In the rodent MK-801 model of schizophrenia, degenerative changes occur widely in the main olfactory system and in a number of cortical brain regions. In the present report, we compare the effects of MK-801 neurotoxicity in two strains of female rats and also two lines within each strain. The magnitude and regional extent of the neurodegeneration detected with the amino-cupric-silver method varied markedly both between the Sprague-Dawley and Wistar rat strains and also between two lines derived from each strain. For example, terminal degeneration occurred in layer VI of somatosensory cortex and the central extended amygdala in Sprague-Dawley but not Wistar rats. Moreover, MK-801 treatment led to somatodendritic degeneration in the dentate gyrus of the dorsal hippocampus and basolateral amygdala in Wistar rats from Charles River Laboratories but not those from Ferreyra Institute. There are thus both strain and intrastrain differences in the magnitude of the neurodegenerative response to MK-801 treatment. The differing neurotoxicity of MK-801 between rat strains and between lines within a strain may reflect genetic variation and/or differences in hepatic biotransformation and thus the bioavailability of the drug between strains and lines within a strain.

Effect of estrogen on the expression of a cell-surface antigen associated with rat anterior pituitary somatotrophs

The long-term in vivo effect of diethylstilbestrol (DES) on the expression of a cell-surface antigen associated with the anterior pituitary somatotroph was studied in two strains of female rats using double immunofluorescence techniques. Mab WHC-1, a recently generated and characterized monoclonal antibody, was used to detect the antigen associated with somatotrophs, whereas rabbit anti-rat prolactin (rPRL) and anti-human growth hormone (hGH) antisera were used to identify mammotrophs and somatotrophs, respectively. In F344 rats, Mab WHC-1-positive cells increased from 13.8 ± 0.5% of total pituitary cells in normal anterior pituitaries to 34.2 ± 4.0% in DES-induced pituitary tumors. The number of mammotrophs also increased significantly from 58.0 ± 3.2% in controls to 75.9 ± 2.2% in tumors. On the other hand, somatotrophs decreased significantly in number following ovariectomy (OVX) and DES implantation (19.7 ± 0.5% vs. 6.1 ± 1.2%). Based on double immunofluorescence, the percentage of Mab WHC-1-positive cells, which were somatotrophs, decreased from 85.5 ± 2.7% in normal controls to 6.7 ± 1.5% in DES-induced tumors. On the other hand, the percentage of Mab WHC-1-positive cells which were mammotrophs increased significantly from 14.0 ± 1.4% to 86.1 ± 1.8% following OVX and DES implantation. A similar change was found in the number of somatotrophs and mammotrophs following the same treatment in Sprague-Dawley (SD) rats which did not develop pituitary tumors. In contrast to F344 rats, the number of Mab WHC-1-positive cells in SD rats decreased significantly from 32.4 ± 2.8% in sham-operated controls to 19.3 ± 2.9% in OVX + DES-implanted rats. Significant strain differences were found in the relative population of Mab WHC-1-positive cells, somatotrophs and mammotrophs. The results indicate a shift in the expression of Mab WHC-1-defined cell-surface antigens from the majority of somatotrophs to an increasing number of mammotrophs following long-term treatment of estrogen.

Immune Control System Modelling and Identification

Abstract A bilinear mathematical model of the imune system and its circulation is presented Then a joint algorithm for parameter and state estimation is derived. The estimation procedure is applied to the discrete bilinear stochastic model. Data for estimation is taken from a pure strain of female rats by means of compartmental tracer techniques for tagged lymphocytes.

Dietary induction of hepatic glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase, and malic enzyme in lean and obese female Zucker rats.

Responses of the hepatic lipogenic enzymes, glucose-6-phosphate dehydrogenase (G6PDH), 6-phosphogluconate dehydrogenase (6PGDH), and malic enzyme (ME) to starvation refeeding and diet shifting were determined in lean and obese female Zucker rats. Rats were either fed nonpurified diet, starved 48 hr, and then refed nonpurified diet or one of the refined carbohydrate diets containing either glucose, fructose, cornstarch, or sucrose for 72 hr, or shifted from nonpurified diet directly to one of the refined carbohydrate diets for 72 hr. Initial activities were greater in obese than lean rats for all three enzymes studied. Similar to other strains of female rats, lean Zucker rats failed to demonstrate a starve-refeed response when refed nonpurified diet. Obese female littermates showed a statistically significant increase in enzymes when refed a nonpurified diet. Both lean and obese female Zucker rats demonstrated increases in enzyme activities above controls when starved and refed any of the refined carbohydrate diets. The greatest responses were observed when female rats were starved and refed sucrose; activities increased 2.6- to 3.5-fold in lean and 3.0- to 4.3-fold in obese Zuckers. In lean females 50-70% of the starve-refeed response observed with G6PDH and ME can be accounted for by simply shifting from a nonpurified diet to the respective refined carbohydrate diet, whereas in obese females only 33-55% of the increase could be attributed to diet shifting. Plasma testosterone/estrogen ratios were consistently 1.5 times higher in obese than in lean female rats. This phenotypic difference may potentiate the heightened starve-refeed overshoot response observed in obese rats.

Qualitative and quantitative cancer risk assessment of 2, 3, 7, 8-tetrachloro-dibenzo-p-dioxin (2, 3, 7, 8-TCDD)

The carcinogenicity of 2,3,7,8-TCDD at multiple organ sites in animals has been well established by several cancer bioassays. Results of two of the most notable of these, the Kociba et al. (1978) rat feeding study and the National Toxicology Program (1980) gavage study in rats and mice showed hepatocellular carcinomas in two strains of female rats and male and female mice. Other tumor sites included carcinomas of the lung, tongue, hard palate and nasal turbinates, thyroid, and subcutaneous tissue. The evidence for carcinogenicity of 2,3,7,8-TCDD in animals is regarded as “sufficient” using the classification system of the International Agency for Research on Cancer (IARC). Two Swedish epidemiologic case-control studies (Hardell and Sandstrom, 1979; Eriksson et al. 1979, 1981) reported a significant five- to sevenfold excess risk of soft-tissue sarcomas (STS) from occupational exposure to chlorinated phenoxyacetic acid herbicides and/or chlorophenols. Additionally, several small cohort studies collectively exhibited an unusual cluster of STS, significantly increased over combined expected incidence. Problems with these studies do not appear to be sufficient to discount this excess risk. The human evidence alone for the carcinogenicity of 2,3,7,8-TCDD is “inadequate” using the IARC classification. However, for 2,3,7,8-TCDD in combination with chlorinated phenoxyacetic acid herbicides and/or chlorophenols, the human evidence is considered to be “limited.” The overall evidence for carcinogenicity considering both animal and human studies would place 2,3,7,8-TCDD alone in the IARC category 2B, meaning that the substance is probably carcinogenic in humans. The overall weight of evidence for 2,3,7,8-TCDD in combination with chlorinated phenoxyacetic acid herbicides and/or chlorophenols is regarded as IARC category 2A, also meaning that they are probably carcinogenic for humans. Using current EPA methodology for quantitatively estimating cancer risks, several animal data sets have been analyzed. Comparing the results, the upper-limit incremental unit risk estimate is 1.6 × 10 −2 for a lifetime exposure of 1 ng/kg/day. This estimate is derived from a lifetime feeding study (Kociba et al., 1978) in which 2,3,7,8-TCDD induced tumors of the liver, lungs, hard palate, and nasal turbinates in female rats. Incremental unit cancer risks are also extrapolated for lifetime 2,3,7,8-TCDD exposures in water and air. Based on continuous lifetime exposure to 1 ng/L 2,3,7,8-TCDD in drinking water, the upper-limit estimate of extra cancer risk per individual is 4.5 × 10 −3. For lifetime exposure to 1 pg 2,3,7,8-TCDD/m 3 in the ambient air, the upper-limit individual risk is 3.3 × 10 −5.