CFN Rats Research Articles

A longitudinal study of the relationship between aging and the duration of hexobarbital hypnosis in male CFN rats

The duration of hexobarbital hypnosis was determined for individual male CFN rats at three month intervals over their total adult lifespan. The mean duration of hexobarbital hypnosis for the cohort increased linearly with advancing age. However, the sleeptimes for individual rats fell into one of four categories (gradual increase, terminal step increase, no change, or not possible to assign) when assigned as a function of duration of response to the barbiturate over the lifespan of the animals. These results suggest that the generally well-accepted increase in duration of drug response in aging animals is neither a ubiquitous nor concomitant feature of aging. Furthermore, the varying results obtained for individual animals in this longitudinal study point out the possible error which may be attendant when utilizing pooled tissue extracts to examine hepatic monooxygenase activity in vitro in senescent rodents.

Asynchronous maturation of Plasmodium berghei exo-erythrocytic forms in rats

Sporozoites of Plasmodium berghei berghei (NK-65 strain) were inoculated intravenously into four-week-old CFN rats. Liver biopsies were taken at intervals and the density of exo-erythrocytic forms per mm 3 of liver were estimated. Results demonstrated asynchronous maturation and the gradual disappearance of exo-erythrocytic forms during the period 48 to 72 hours after infection.

Changes in hepatic microsomal membrane fluidity with age

There are changes in the mixed function oxidase enzymatic activities of rat hepatic microsomal membranes with age. However, the protein components of the mixed function oxidase system do not appear to change with age. The purpose of this study was to detect possible changes in the fluidity of the lipid component of the microsomal membrane with age. Hepatic microsomes were isolated by differential centrifugation from uninduced, male CFN rats aged 3, 12 and 26 mo. The microsomal membrane fluidity was measured using electron paramagnetic resonance after incorporation of a 5-nitroxide stearic acid spin label into the membrane. The order parameter S decreased with age from 0.586 ± 0.003 (3 mo) to 0.581 ± 0.002 (12 mo) to 0.569 ± 0.003 (26 mo) at 30°C. This indicated an increase in membrane fluidity with age. In membranes labeled with the 16-nitroxide stearic acid, a similar increase in membrane fluidity with age was observed. The order parameter of microsomal membranes from 3 and 26 mo rats was measured over the temperature range 18° to 31°C in steps of 0.9°C. A plot of the log of S versus the reciprocal temperature revealed a phase transition at 24°C in membranes from 26 mo rats, but no phase transition was observed in 3 mo old rats in this temperature range. The change in fluidity of the hepatic microsomal membrane with age may account for some of the observed changes in membrane-bound mixed function oxidase activities with age.

Amygdalin (Laetrile) Toxicity in Rodents

To the Editor.— Janardan D. Khandekar, MD, and Harlan Edelman in their article, Studies of Amygdalin (Laetrile) Toxicity in Rodents (242:169, 1979), reported lethality in rats from intraperitoneal injections of 250, 500, and 750 mg/kg for five days. At the two highest doses, a large number of deaths occurred promptly after only one or two injections. The authors do not appear to have sought an explanation for the discrepancy between their results and those of at least two other laboratories. 1,2 Wodinsky and Swiniarski 1 gave Sprague Dawley rats 500 and 1,000 mg/kg of amygdalin on days 1, 3, and 6; the first deaths did not occur until days 9 and 10, when untreated controls also died as a result of the Walker 256 tumors they bore. In studies by my colleagues and me 2 in Walker 256 tumor-bearing Wistar CFN rats, it was possible to give 1,000 mg/kg of

Inhibition of 2-Fluorenamine-Induced Mutagenesis in <italic>Salmonella typhimurium</italic> by Vitamin A<xref ref-type="fn" rid="FN2">2</xref>

Vitamin A alcohol (retinol) completely inhibited the mutagenicity of the carcinogen 2-fluorenamine (2-FA) in Salmonella typhimurium TA98 when the mutagen was activated by liver microsomes from CFN rats. The mutagenicity of 2-FA activated by 9,000Xg rat liver supernatant S9 was inhibited by retinol to a lesser degree. The decline in the number of his+ revertants was not an artifact due to bacterial killing, inasmuch as retinol was not toxic to the bacteria at levels that totally inhibited mutagenesis by 2-FA. Mutagenesis induced by adriamycin, an antibiotic that does not require metabolic activation for mutagenic potential, was unaffected by vitamin A. These results indicate that retinoids inhibit the metabolic activation of some chemical carcinogens to forms that can interact with DNA. Our findings are consistent with the hypothesis that retinoids may exert anticancer activity by inhibiting carcinogen activation, thereby inhibiting tumor induction. In addition to the more widely accepted role of retinoids in modulating the proliferation of epithelially derived neoplasms.

The Influence of a Chronic Environmental Stress on Radiation Carcinogenesis

The influence of a chronic environmental stress on the incidence of radiation-induced tumors, lens opacities, and survival times was determined. Female CFN rats were exposed to whole-body irradiation with either 300 rad of fission neutrons, 600 rad of 250 kV x rays, or sham irradiation. Within each irradiated group, rats were assigned to one of four environments: exposure to 25/sup 0/C until irradiated and immediately returned to (1) a 25/sup 0/C or (2) a 2/sup 0/C environment for duration of life; acclimation to a 2/sup 0/C environment for 40 days, irradiated, then returned to (3) a 2/sup 0/C or (4) a 25/sup 0/C environment. Postirradiation exposure to the 2/sup 0/C compared to the 25/sup 0/C environment reduced tumor incidence in the x- and neutron-irradiated groups, but reduced incidence of lens opacities only in the neutron-irradiated group. A 2/sup 0/C environment before and after irradiation produced similar results. Return of the 2/sup 0/C acclimated rats to a 25/sup 0/C environment increased incidence of tumors and lens opacities in the x-ray group, but reduced incidence of both in the neutron-irradiated rats. Chronic exposure to 2/sup 0/C reduced the tumor incidence of nonirradiated rats but did not change the incidence of lens opacities.more » Median life expectancy was reduced by exposure to the 2/sup 0/C environment. The data are consistent with the hypothesis that a chronic environmental stress initiated immediately after a carcinogen, in this study x or neutron radiation, may inhibit the malignant transformation. In view of other published data the stress-induced increase in metabolic rate may be an important factor in the inhibition.« less

Inhibition of cerebral protein synthesis by epileptic seizures without motor manifestations.

Repetitive seizures were induced electrically in 109 male CFN rats that were paralyzed and ventilated with oxygen. Compared with the results in paralyzed, oxygen-ventilated controls receiving sham shocks, incorporation of radioactive leucine into cerebral proteins was decreased up to twofold in the cerebral hemispheres, cerebellum, and brain stem of the experimental animals. The extent of inhibition increased with the duration of seizures. The size of the leucine and protein pools was unaffected by seizures, but the specific activity of the cerebral leucine pool was 61 to 64 percent greater in experimental animals. The findings provide a potential explanation of some of the complications that often follow sustained cerebral paroxysmal activity even in the absence of convulsions.

Inhibition by castration of aflatoxin-induced hepatoma in carbon tetrachloride-treated rats

The effect of castration on aflatoxin-induced hepatoma in CCl 4-treated CFN rats was investigated. After 40 days of recovery, rats castrated soon after weaning were given a total of 2.15 mg of aflatoxin B 1-equivalents in 10 doses during a 166-day treatment period. All rats were given 0.1 ml CCl 4 mixed with 0.1 ml of liquid paraffin at the same time treated animals were given aflatoxin. CCl 4 was given to potentiate the effect of aflatoxin. Deaths (20–80%) occurred in all groups before the experiment was terminated on day 396. The highest incidence of deaths (80%) occurred in intact rats of both sexes treated with aflatoxin, and hepatomas were found in all 4 survivors among these animals. No hepatomas were found in any of the 16 aflatoxin-treated surviving castrated rats (39% deaths), in 15 surviving intact control rats (35% deaths), and in 15 surviving castrated control rats (38% deaths).

Effect of parathyroid extract on bone phospholipid.

Cruess and Clark (1) studied the effect of hypervitaminosis D on the phospholipids of diaphyseal and metaphyseal long bone. All major phospholipid fractions were increased, and incorporation of 32P into these fractions was enhanced. This study is concerned with the effect of parathyroid hormone administration on the concentration of total lipid, phospholipid, and 32P incorporation into phospholipid in bone. Materials and Methods. Male CFN rats (130-150 g, Carworth, Inc.) were maintained on a regular diet of Lab-Blox and water ad libitum. Parathyroidectomy was performed by the cautery procedure of Munson (2) 2-4 days prior to hormone treatment. Control animals compared with parathyroid extract-treated animals were injected with a corresponding volume of solvent: 1.2% glycerol, 0.7% bovine serum albumin, and 0.2% phenol in physiological saline. Carrier-free H332PO4, glycerol-1,3-14C(10.6 mCi/mmole), ethanolamine-172-14C(3.7 mCi/mmole) and l-serine-14C(U) (7.5 mCi/mmole) were purchased from New England Nuclear Corp. and Nuclear Chicago. Bones were prepared and incubated according to Cruess and Clark (3). Femora and tibias were removed and the marrow cavity was flushed out by washing with a stream of cold saline through a fine needle. Tissues were incubated in 4 ml of Krebs-Henseleit bicarbonate buffer containing 10 mM glucose. H332PO4, glycerol, and serine were present in appropriate incubation mixtures at a concentration of 1.0 μCi/μmole/ml. Ethanolamine was added at 0.5 μC/μ-mole/ml. In experiments testing metabolic inhibitors, only a single tibia and femur were incubated in each flask; in all other experiments paired femora and tibias were used. All incubations were done at 37° for 4 hr. The gas phase was 95% oxygen-5% CO2, except when the anaerobic effect of 95% N2-5% CO2 was evaluated. Bones for lipid extraction were pulverized in a mortar with Dry Ice and extracted with chloroform-methanol.

Experimental microvascular suture anastomosis.

To evaluate the limits imposed by blood vessel size on success or failure of vascular anastomosis by suture techniques, tiny vessels in young CFN rats were anastomosed by microsuture technique, using the Zeiss operating microscope at 16 and 25 magnifications. In series I aortae averaging 1.3 mm external diameter prior to manipulation were divided transversely and rejoined by suture anastomosis. In series II inferior venae cavae averaging 2.7 mm external diameter prior to manipulation were similarly treated. In series III both of these procedures were performed in each animal. There were ten animals in each group. Of 40 consecutive anastomoses only three were not patent when the animals were sacrificed three weeks after surgery. Two of the failures were arterial, and one was venous. This high success rate was achieved only when certain refinements in technique had been perfected. The feasibility of suture anastomosis of extremely small veins as well as arteries has been demonstrated.

THE INFLUENCE OF THE ROUTE OF ADMINISTRATION OF 1-ALPHA-METHYLALLYLTHIOCARBAMOYL-2-METHYLTHIOCARBAMOYLHYDRAZINE ON REPRODUCTION IN RATS AND MICE

Summary. One hundred and eighty-six mature nonparous CFN rats and ninety-six mature nonparous Taconic mice were used to determine the effect of compound I.C.I. 33,828 on reproduction when administered by three different routes at dose rates of 8, 16 and 32 mg/kg. Females of both species were treated with the compound for 4 days before adding known fertile males to the female cages. Treatment continued for 11 days. Daily observations were made for spermatozoa in the vaginal smears of rats and for vaginal plugs in mice during this time. On the morning of the 12th day, treatment was stopped and the males were removed from the cages. The results showed that Compound I.C.I. 33,828 at 16 and 32 mg/kg was an effective antifertility agent in rats, regardless of the route of administration. In mice, it was not an effective antifertility agent when injected subcutaneously; however, it was an effective antifertility agent in mice when added to the diet at 32 mg/kg, but only partially effective at the 8 and 16 mg/kg levels.

Some effects of freezing the rat kidney in situ

The remaining kidneys of 300- to 500-gm uninephrectomized CFN rats were fast frozen in plastic capsules to −110 °C, with the use of liquid nitrogen, and then rapidly thawed. Postoperative urinary excretion became normal after the first 24 hours. Initial increases in blood urea nitrogen, creatinine, uric acid, and transaminase returned to control levels by one month. Systolic blood pressure was essentially unchanged by the procedure. Initial partial necrosis and subsequent scarring was almost completely replaced by normal renal parenchyma by the third postoperative month. All animals awaiting sacrifice at one year are well, eight months postfreezing.

COMPARATIVE CHANGES IN RADIOSENSITIVITY BETWEEN BONE MARROW AND A RAT TUMOR IRRADIATED UNDER ANOXIA.

The protective effect of low oxygen concentrations in the radiosensitivity of cells has been well established by numerous experiments both in vitro and in vivo (1, 4, 5, 12). Because some tumors probably contain areas of relative hypoxia or anoxia (10), there is a possibility of variation in radiosensitivity within the tumor volume, depending on the state of oxygenation of its individual cells. One way to eliminate this variation would be to remove all oxygen, thereby equalizing the radiosensitivity of all tumor cells as far as the oxygen effect is concerned. At the same time, the surrounding normal tissues would be rendered anoxic. The question to be determined is whether or not induced anoxia would protect tumor and normal tissues to the same degree; if so, nothing has been gained. If anoxia, however, protects the normal tissue to a greater degree, than the tumor, the net effect would be a relative increase in tumor radiosensitivity. The present experiment was carried out to test this hypothesis. The data demonstrate that anoxia has a greater radioprotective effect on a normal tissue (bone marrow) than on a tumor. Materials and Methods The experimental plan was to give radiation to the lower extremities of rats bearing tumor in both legs, while the vascular supply to the left lower extremity was temporarily occluded to render it anoxic. The radiosensitivities of the femoral bone marrow and tumor in the right leg (normally oxygenated) and left leg (anoxic) were measured by determining the duration of depression of DNA synthesis in these tissues. Animals and Tumor: Male CFN rats raised in our laboratory and weighing between 150 and 300 gm. were employed. The tumor was the Walker carcinosarcoma-256. When the tumors attained a diameter of 2 to 4 cm., the animals were anesthetized with intraperitoneal sodium pentothal (50 mg./kg.), and a laparotomy was performed. The left common iliac artery was dissected free from the vein, and an arterial clamp was applied. The laparotomy incision was partially sutured, and, after waiting fifteen to twenty minutes for the left leg to become anoxic, the animals were irradiated. The clamp was always released one hour after its application; the abdominal incision was then completely closed and the animals were returned to their cages. Irradiation: The anesthetized rats were given radiation in a specially made plastic cage and positioned under a cesium-137 teletherapy machine. A collimator formed a 6 × 6-cm. square field which covered the lower extremities, but part of the pelvis was also included in the radiation field. The source-to-top-of-cage distance was 9.5 cm. Halfway during irradiation the animals were turned over to equalize the tissue dose as much as possible. Measurements made in a water-filled phantom cage indicated that the tissue dose at the mid-plane of the irradiated part of the animal was 15 per cent lower than the surface dose, and in this report all doses are expressed as midplane.

Effect of microwave radiation on the hemopoietic system of the rat

Exposure of Osborne-Mendel, CFN, and Fischer strain rats to minimal doses of microwave radiation (24,000 megacycles) induced a significant leucocytosis, lymphocytosis, and neutrophilia after 7 hours of continuous exposure to 20 mw/cm 2 with recovery in 1 week; 10 minutes of continuous exposure to 20 mw/cm 2; and 3 hours of continuous exposure to 10 mw/cm 2 with recovery in 2 days. Effects on erythrocytes, hemoglobin, and hematocrit differed in the three strains used. In Osborne-Mendel and CFN rats, all values increased; in Fischer rats, they decreased.

Effect of X-Irradiation on Self-Stimulation of the Brain

RECENTLY it has been shown that the brain is sensitive to low doses of ionizing radiation1,2. Prolonged exposure to X-irradiation decreases lever-pressing by rats3. Conditional aversion to saccharin results from exposure of rats to γ-radiation4,5. Because radiation affects psychological tests based upon food or fluid intake, we studied the effects of X-irradiation on rats trained to press a lever for electrical stimulation of the brain6. A single electrode was permanently implanted in the posterior hypothalamus of 8 CFN rats. After a training period of 6 months, the rats received 600 r. acute whole-body X-irradiation. Radiation characteristics were : 250 kVp.; 15 m.amp.; focus-object distance 70 cm.; filters, 0.21 mm. copper inherent, 0.5 mm. copper parabolic and 1.0 mm. aluminium; half-value layer 1.92 mm. copper; 22.9 r./min. measured in air.

Changes in phosphorus metabolism of the gastrocnemius muscle in aging white rats.

SummaryChanges in the adenine nucleotide dephosphorylating system in the gastrocnemius muscle of aging male rats have been studied. The Mg-activated ATP-ase activity showed a pronounced fall from young to very old (senile) age in both the Sprague-Dawley and the CFN strains. However, in the former strain, old animals, typically exhibiting markedly greater losses in muscle mass and concomitant muscular dystrophy, also showed a greater decline in this enzyme on a unit muscle mass and even more so on an absolute body mass basis, than did the old CFN rats. In both strains, however, actomyosin (pH 9.0) ATP-ase as well as ATP content showed no significant changes from young to very old age. The role of the Mg-activated ATP-ase enzyme in energizing of skeletal muscle contraction and its possible significance in the physiology of senescence are discussed.

Serum protein abnormalities in 'runted' albino rats.

IN the course of previous investigations, we have observed that when either normal or neoplastic tissues of mouse origin are injected into new-born albino CFN rats (Carworth–Wistar origin) occasional animals will develop a wasting disease characterized by roughened scaly skin, sparse hair growth, failure to gain weight normally, and sometimes actual loss of weight1,2. This condition usually appears during the first 7–14 days of life and many of the animals so afflicted succumb within a few days. Others survive this crisis and live for at least 35 days. Apart from the sparse hair and stunted growth, these survivors are apparently normal.