Dextran anaphylactoid reaction in Sprague-Dawley CFY rats.

From a closed colony of randomly-bred Sprague-Dawley CFY rats about 23% failed to respond to intravenous dextran with the characteristic generalized anaphylactoid reaction, but still exhibited an inflammatory response when dextran was given into the foot pad. Brother-sister mating of rats showing the most expressed generalized reaction (reactor rats) yielded good responder offsprings, while the non-reactors had descendants completely unresponsive to systemic dextran. Brother-sister mating of selected non-reactor rats led to a gradual decrease in dextran paw oedema in the subsequent generations, and after the third mating, a complete local non-reactivity developed. In these rats the intradermal injection of dextran failed to increase vascular permeability, while the inflammatory response evoked by histamine, 5-HT, bradykinin, and compound 48/80 remained unchanged as compared to that of the reactor animals. These result show that the anaphylactoid reaction in Sprague-Dawley CFY rats is under genetic control.     

Quantitative characteristics of the systemic anaphylaxis model in Sprague-Dawley rats

Anaphylactic response intensity was quantitatively estimated by means of measuring mean arterial pressure (MAP) and heart rate (HR). Damage to intestinal mucosa was studied by means of morphometry. These indices grew in a dose-dependent way along with the amount of administered egg ovalbumin (OVA). The MAP and HR measurements seem to be useful in a quantitative elucidation of allergic sensitivity in laboratory animals.     

Retinal dystrophy in Sprague-Dawley rats.

A spontaneous retinal dystrophy was found in 4 percent of Sprague-Dawley-derived rats examined. The lesion occurred both unilaterally and bilaterally in equal frequency, but the incidence in the females was 2 times greater than in males. Retinal change consisted of focal or diffuse absence of the outer layers of the retina, but frank degenerative changes or progression of the lesion was not observed. The cause of the dystrophy was not determined, but its increased occurrence with increasing age of the rats suggests an age-related lesion.     

Increased radiosensitivity of cerebral capillaries in neonatal Gunn rats as compared to Sprague-Dawley rats.

The extent of petechial haemorrhages of the cerebral cortex examined between 14 hours and 4 days after X-irradiation to the head was compared in Sprague-Dawley and homozygous Gunn rats with congenital hyperbilirubinaemia. Animals 1 to 2 days old received single doses of either 250, 500 or 750 rad. By means of a special scoring scale the degree of the damage to the microvasculature was semi-quantitatively estimated. In both strains a significant difference in effect was obtained between 250 and 500 rad, but not between 500 and 750 rad. The shape of the dose-effect curve in Gunn rats was similar to that of Sprague-Dawley rats, but displaced upwards. In Gunn rats the effect of 250 rad was greater than that of 750 rad in Sprague-Dawley rats. Possible radiosensitizing mechanisms are discussed with reference to the literature and our results.     

Spontaneous neoplastic lesions in aged Sprague-Dawley rats.

Neoplastic lesions were observed in untreated aged Sprague Dawley (SD) rats throughout their lifespan starting at 5 weeks. Their mean survival times were 89 to 105 weeks of age. The total tumor incidences were 70 to 76.7% and 87 to 95.8% in males and females, respectively. The common neoplasmas were pituitary adenoma and adrenal pheochromocytoma in both sexes, testicular Leydig cell tumor in males and mammary gland tumors, thyroidal C-cell adenoma and uterine stromal polyp in females.     

Postnatal changes in the rheological properties of the aorta in Sprague-Dawley rats.

Postnatal changes in the rheological properties of the aortic wall were investigated in relation to morphological development of the wall in Sprague-Dawley (SD) rats at 3, 8 and 20 weeks old. The mechanical tensile characteristics of the longitudinal wall strip excised from the proximal thoracic aorta were assessed with stress-strain and stress-relaxation tests. Wall tension in the low and medium strain ranges was significantly lower in 3-week-old rats than in 8-week-old rats and in 8-week-old rats than in 20-week-old rats. Wall stress was significantly lower in 3-week-old rats than in 8- and 20-week-old rats mainly in the medium strain range, but was significantly greater in 3-week-old rats than in 8- and 20-week-old rats in the high strain range. The value of incremental elastic modulus at 3 weeks old was significantly smaller than that at 8 and 20 weeks old at a strain of 0.25 and significantly larger than that at 8 and 20 weeks old at a strain of 0.50. The value of relaxation strength at 5 min after the stretching was significantly greater at 3 weeks old than that at 8 and 20 weeks old. The wall was viscoelastic in the low and medium strain ranges at 3 weeks though large wall stress was generated in the high strain range. Histological investigation revealed that the smooth muscle layer, fine elastin fiber connecting thick elastin fibers and wall thickness were thin at 3 weeks old in comparison with those at 8 and 20 weeks old, though there was no significant difference in number of nuclei of the smooth muscle cells among the three age groups. Changes in the tensile characteristics of the wall reflected well those of the microstructure of the wall with growth. The rheological properties and microstructure of the aortic wall were close to maturation at 8 weeks in SD rats.     

Thermogenic responses to selective and nonselective beta-adrenerg agonists in hypothyroidism of Sprague-Dawley rats.

Resting oxygen consumption (VO2) and mitochondrial GDP binding were measured in hypothyroid and euthyroid rats after administration of selective and nonselective beta-adrenoceptor agonists (BRL 35135A and Isoprenaline--BRL, ISO). Resting VO2, VO2 increment and mitochondrial GDP binding after beta-agonists were lower in hypothyroid rats than in the euthyroid group. The reduced response was more marked for ISO than for BRL. These results suggest that BRL is acting on a beta-adrenoceptor which differs from beta-1 and beta-2 adrenoceptors, responsible for the effect of ISO. Activation of thermogenesis via this beta-3 adrenoceptor seems to be less dependent on permissive levels of thyroid hormones than on activation via beta-1 and/or beta-2 adrenoceptors.     

Urinary proteins in Sprague-Dawley rats with chronic progressive nephrosis.

By means of polyacrylamide concentration and electrophoresis on cellulose acetate strips, protein fractions have been determined in the urine of male Sprague-Dawley rats from 6 1/2-28 mo of age. An increasing percentage of albumin was expressed in the albumin/globulin ratios of 0.72, in a group of rats excreting a mean concentration of 1.91 mg/ml of protein in the urine, and 2.24 in a group of rats excreting, on the average, 17.62 mg/ml. A relative decrease in globulin, particularly of the alpha2 fraction, was shown. From a statistical model based on the regression parameters for 24-hr protein excretion and urine protein concentration, it was estimated that the doubling time for protein excretion was 3.2-3.69 mo. This interval is roughly one-half that reported for the Wistar rat.     

Some characteristics of TRH-induced grooming behavior in rats

Intracerebroventricular administration of TRH induces excessive grooming behavior that is characterized by an important contribution of the elements scratching and paw licking. As compared with other grooming inducing peptides, the pattern of TRH-induced grooming resembles that induced by beta-endorphin rather than those elicited by ACTH or bombesin. TRH-induced excessive grooming is suppressed by pretreatment with haloperidol, naloxone or neurotensin. Haloperidol suppresses TRH-induced grooming in a general way, whereas the suppressive effect of the other drugs is mainly due to a selective reduction of TRH-induced excessive scratching. Combined treatments of rats with TRH and a submaximal dose of ACTH, bombesin or beta-endorphin do not result in higher grooming scores than with single peptide treatment. Excessive grooming elicited by water immersion is not affected by TRH. It is concluded that TRH is undoubtedly an excessive grooming inducing peptide. In situations where excessive grooming is elicited by other peptides or by water immersion, TRH does not further activate the operating systems involved in the existing excessive grooming.     

Tumor necrosis factor-alpha induces vascular hyporesponsiveness in Sprague-Dawley rats.

The cytokine tumor necrosis factor-alpha (TNF alpha) is one of the major mediators of septic shock. Because vasodilation is a hallmark of sepsis and decreased vascular responsiveness has been implicated in the pathogenesis of septic shock, we studied the effect of TNF alpha on the mean blood pressure in conscious rats and vascular responsiveness to vasoconstrictors ex vivo using the standard organ bath method. Intravenous infusion of TNF alpha (0.006 or 0.06 mg/kg/hr for 10 hours) decreased mean blood pressure in a dose-dependent fashion. Contractile responses to norepinephrine were depressed dose-dependently in the aortic rings both with and without its endothelium. Aortic contractions by potassium depolarization were also depressed. These results suggest that TNF alpha induces non-specific vascular hyporesponsiveness, which is independent of the presence of the endothelium. The TNF alpha-induced vascular hyporesponsiveness might contribute to the hypotensive action of TNF alpha.