First Group Of Rats Research Articles

Long Term Duration of the Rapid Rejection Response in Rats Infected with Trichinella spiralis

Rapid rejection or the ability of a host to rapidly clear a second inoculum of L1 larvae of Trichinella spiralis has been described from several rat strains (McCoy, 1940, Am. J. Hyg. 32: 105-106; Castro et al., 1976, J. Nutr. 106: 14841491; Bell and McGregor, 1979, Inf. and Immun. 29: 186-193; Russell and Castro, 1979, J. Infect. Dis. 139: 304-312; Love et al., 1976; Immunology 30: 7-15), and at least one mouse strain (Wakelin'and Lloyd, 1976, Parasitology 72:173182). The ability of mice to reject L, larvae wanes within a few weeks following a sensitizing infection (Wakelin and Lloyd, 1976, loc. cit.). In rats, intestinal stimulation by a chemically abbreviated infection primes for a form of rapid rejection. The capacity to express rejection upon subsequent challenge, in this case, lasts only 5 to 6 wk (Bell and McGregor, 1979, loc. cit.). Castro and Harari (1982, Mol. Biochem. Parasit. 6: 191204), reported a strong rapid rejection response in rats immunized by infection 6 mo prior to the administration of a challenge inoculum. These findings in the rat host are compatible with the premise that the presence of encysted larvae may provide antigenic stimulation important in the long term maintenance of the rapid rejection response. The present experiment was carried out to gauge the persistence of the rapid rejection response in rats immunized by a primary infection. Two groups of outbred, male Sprague-Dawley rats (Hilltop Lab Animals, Chatsworth, CA) were studied. At 1 mo of age the first group of rats was immunized by an oral inoculation of 7 x 103 T. spiralis larvae. Larvae were obtained from male CF-1 mice according to published procedures (Castro and Fairbairn, 1969, J. Parasit. 66: 472-477) and administered by gastric intubation in 0.2 ml of saline. A second group of nonimmunized rats was used, also. We tested for the expression of the rapid rejection response of rats immunized 8 to 18 mo previously, using the nonimmunized rats as controls. Immunized rats were 9 to 19 mo of age (mean 13.4 ? 1.1 month, n = 10), and weighed between 536 and 813 gm (mean 677 ?+ 33.1, n = 10) at the time of the secondary infection. Nonimmunized counterparts ranged from 10 to 19 mo of age (mean 16.75 ?+ 1.5 months, n = 8) at the time of infection, which constituted a primary infection. Each immunized and nonimmunized rat was infected with 7 x 103 larvae as described above. Twenty-four hr after receiving the secondary and primary infections, respectively, rats were killed by a blow to the head. The small intestine was removed from each rat and divided into anterior and posterior halves. These were perfused intraluminally with 60 ml of saline (38 C) to remove debris. Worms embedded in the mucosa were collected and counted according to established procedures (Castro and Fairbairn, 1969, loc. cit.). Statistical methods used to evaluate data were Student's t-test (Snedecor and Cochran, 1967, Statistical methods, 6th ed., University Press, Ames, Iowa). The levels of significance determined were presented in the text. The number of larvae recovered from the small intestinal mucosa are presented in Figure 1. The 95% confidence interval (CI) for the number of worms recovered from non-immunized rats is presented. The number of worms recovered from 3 of 10 immune rats fell within the 95% CI (Fig. 1). The number of worms recovered from the remaining 7 rats was below the CI. These results indicated that 2 populations existed within the previously infected (immunized) rats; 1 group of 7 rats exhibiting rapid rejection (responders) and a second group comprised of 3 rats, not exhibiting the response (nonresponders). There was a 90% reduction in the number of worms in the anterior small intestine of responder rats as compared to nonresponders and no difference in the number of worms recovered from the posterior small bowel. The well known affinity of worms for the proximal small intestine following infection (Dick and Silver, 1980, J. Parasit. 66: 472-477) is evident, also, in this report. The strong rapid rejection

Desensitization of the pituitary gland induced in vivo by luteinizing hormone-releasing hormone (LRH) or by the LRH-analogue buserelin does not affect the autonomous secretion of luteinizing hormone and follicle stimulating hormone as observed in vitro.

Three-weeks ovariectomized rats were sc implanted with Alzet osmotic minipumps which released either LRH or the LRH-analogue buserelin at the rate of 250 ng/h. Control rats were implanted with a silastic 'shampump'. After explantation, 6 days later, the pituitary glands of part of these rats were exposed to the maximally active LRH concentration of 1 micrograms/ml for a period of 6 h, using a perifusion system. In a second group of rats explantation and perifusion was done not directly, but 5 days after cessation of the LRH pre-treatment. After 6 days in vivo pre-treatment with LRH or with buserelin the pituitary LH and FSH stores were partially depleted, the depletion after buserelin being stronger than after LRH. The pituitary glands of the first group of rats showed rates of both maximally LRH-stimulated and unstimulated (autonomous) LH- and FSH-secretion which were strongly impaired, the impairment after buserelin being stronger than after LRH. In the group with a 5 days interval between in vivo LRH/buserelin pre-treatment and explantation the pituitary LH and FSH stores were restored to the range of pre-treatment levels. Of these pituitaries the autonomous secretion of LH and FSH as well as the maximally LRH-stimulated secretion of FSH was restored to the normal level; the maximally LRH-stimulated secretion of LH, however, remained depressed, indicating that 5 days after cessation of exposure to LRH or to buserelin, and in spite of restored pituitary LH/FSH contents, the sensitivity of the LH releasing system to LRH was still subnormal.(ABSTRACT TRUNCATED AT 250 WORDS)

Organomegaly and histopathology in an animal model of mucopolysaccharidosis induced by suramin.

The trypanocidal drug suramin causes glycosaminoglycan and sphingolipid accumulation in the rat, thus simulating a mucopolysaccharidosis (Constantopoulos et al. 1980). In this paper we report on the extent and nature of the morphological changes that occur in the liver, kidneys, spleen, heart, lung and brain as a result of short or long term suramin administration. The first group of rats received a single intravenous injection of suramin (500 mg/kg) and was sacrificed 3-9 days after the injection. The second group received low doses of suramin (50-90 mg/kg) at 2-3 weekly intervals over 3 months. Samples of the above mentioned organs were processed for light and electronmicroscopy and the remainder of the tissue weighed and assayed for total protein, DNA and RNA content. In both groups of rats, suramin caused an abnormal enlargement of the spleen, kidney, lung and liver, splenomegaly being the most pronounced. The total protein, and DNA content did not alter in the treated rats, however, the RNA content of the spleen increased 100%, 9 days after injection and there was a small but consistent increase in RNA content of the liver, kidney and lung. Significant pathological changes were observed in these organs and also in the brain and heart. The changes were similar in many respects to the pathology seen in the lysosomal storage disorder, mucopolysaccharidosis and further support the proposition that the suramin treated rat might be a useful experimental animal model of the disease. Several mechanisms by which suramin might produce organomegaly in the rat are discussed.

The Inhibition of Ischemic Lesions of the Rat Gastric Mucosa by a Novel Serotonin- Antagonist: a Light and Electron Microscopic Study

Two methods that provoke severe lesions in the rat gastric wall were used to study the pathologic action of serotonin. In a first group of rats 1 mg/kg of compound 48/80 was injected IV. The lethal shock that follows within about 30 minutes was prevented by subcutaneous administration of a H1- antagonist. This treatment did not suppress the gastric gland activity, in particular the gastric secretion, and resulted in time-related lesions situated in the gastric corpus and to a lesser extent in the antrum. In a second group of rats similar lesions were induced by slow infusion of 30 μg/kg/min serotonin into the femoral vein. The earliest observed light microscopic events concerned mucosal vessel appearance. Most of the vessels were heavily dilated and engorged with blood cells. The most important ultrastructural changes were seen in the various epithelial cells. These were characterized by an early disappearance of intramitochondrial granular deposits. In a later stage progressive necrosis of the epithelial cells was observed. Lesions evolving from focal edematous erosions into deep necrotic and hemorrhagic wounds were found throughout the whole gastric wall. These final severe lesions were attributed to a local vascular congestion which led to cellular ischemia and a consequent energy deficiency of the mucosal cells. When rats were orally pretreated with the novel serotonin-antagonist R 41 468 at a dose of 0.63 mg/kg, the light and electron microscopic picture was almost completely comparable to that of unchallenged animals. This indi cates that R 41 468 is a potent antagonist of peripheral venoconstriction induced by infused exogenous serotonin as well as by released endogenous serotonin.

Effect of L-dopa treatment on cerebral amino acid levels in rats after portocaval anastomosis.

L-Dopa therapy has been suggested as effective in the reversal of hepatic coma both in humans and in animals. Beneficial effects have been reported also in chronic hepatic encephalopathy. There are many possible mechanisms through which L-dopa could ameliorate this pathological state. The present study was carried out to clarify whether the L-dopa effect could be mediated through an improvement of the brain neutral amino acid patterns, since it competes for the same transport carrier at the blood-brain barrier. A first group of rats was orally administered L-dopa (10 mg/100 g body weight daily) for 1 month following portocaval anastomosis. A second group was intraperitoneally injected (1.5 mg/100 g body weight daily) for 1 week, a month after portocaval shunt. Amino acid levels were determined in plasma and in four cerebral regions. No beneficial effects were observed clinically (in general condition, body weight, or hypertonic posture) in rats receiving L-dopa compared to controls. The large increase of tyrosine, phenylalanine, tryptophan, histidine, and glutamine that occurs in the cerebral tissue after portocaval shunt was also not affected by L-dopa administration. In conclusion, in this experimental condition we had no clinical improvement in shunted animals receiving L-dopa. Moreover, this compound did not seem to influence the pathological increase of aromatic amino acids in the brain, which is considered to play an important role in hepatic encephalopathy.

Vascular effects of arginine vasopressin during fluid deprivation in the rat.

The vascular effects of arginine vasopressin (AVP) were examined in conscious Sprague-Dawley rats. In six control rats, synthetic AVP at a dose of 40 ng/kg, injected as an intravenous bolus, resulted in a rise in mean arterial blood pressure (BP) from 127 to 149 mm Hg (P < 0.005). No tachyphylaxis was observed after a second AVP bolus administered 30 min later, as BP increased from 125 to 150 mm Hg, P < 0.005. In a second group of six rats, 1-deamino penicillamine, 2-(O-methyl) tyrosine AVP ([dPTyr (Me)]AVP), was administered intravenously at a dose of 10 mug/kg, just before the second AVP bolus. In this group of studies BP rose from 124 to 150 mm Hg (P < 0.01) after the first AVP bolus, but not after the second AVP bolus, which was administered after [dPTyr (Me)]AVP (129 vs. 129 mm Hg, NS). To assess the effect of this AVP pressor antagonist on BP in rats with suppressed endogenous vasopressin, six water-diuresing rats (mean urinary osmolality, 99 mosmol/kg H(2)O) were administered the analogue at the same dose as the first group of rats. The analogue exerted no demonstrable effect on mean BP (128 before vs. 129 mm Hg after [dPTyr (Me)]AVP, NS). In these rats, mean radioimmunoassayable levels of AVP were at or below the detectable limits of our assay (0.5 pg/ml). In contrast, six rats in which endogenous AVP was stimulated by fluid deprivation for 24 h (mean urinary osmolality, 2,489 mosmol/kg H(2)O and mean AVP level of 21.6 pg/ml) had a marked fall in BP when administered the AVP analogue. In these animals [dPTyr (Me)]AVP caused a fall in BP from 124 to 110 mm Hg (P < 0.005). This fall in blood pressure was due to a fall in peripheral vascular resistance (0.35 vs. 0.30 mm Hg/ml per min per kg, P < 0.02) after [dPTyr (Me)]AVP, as cardiac index remained unchanged. To eliminate the possibility that this AVP analogue was antagonistic to endogenous pressor substances other than AVP, additional studies were performed. In homozygous Brattleboro (diabetes insipidus) rats receiving exogenous AVP, the vasopressin analogue lowered BP (133 to 112 mm Hg, P < 0.001), but failed to lower BP (112 vs. 112 mm Hg) in rats not receiving AVP. BP in a group of bilaterally nephrectomized Sprague-Dawley rats, after 24 h of fluid deprivation, fell from 130 to 118 mm Hg (P < 0.02) after the AVP analogue, precluding an effect of the analogue on lowering BP by inhibiting the renin-angiotensin system. Finally, the AVP analogue failed to alter the pressor response to exogenous infusions of either norepinephrine or angiotensin II. These results demonstrate that (a) the AVP analogue [dPTyr (Me)]AVP abolishes the pressor effect of large exogenous doses of AVP; (b) the analogue has no effect on BP in rats with suppressed or absent endogenous AVP; (c) the depressor effect of the analogue does not involve antagonism of the vasoconstrictors, norepinephrine or angiotensin; and (d) most importantly, BP fell significantly after AVP antagonist administration in intact, conscious, fluid-deprived rats with elevated endogenous AVP levels. This effect of the AVP antagonist to block endogenous AVP and lower BP was primarily due to a fall in peripheral vascular resistance.

Indomethacin does not attenuate the hypotensive effect of captopril, a converting enzyme inhibitor in Goldblatt hypertensive rats.

OMATA, K., OTSUKA, Y., CHIBA, S., ITOH, T., GOTOH, T., IMAI, Y., SAKURAI, Y., SATOH, M., HARUYAMA, T., HIWATARI, M., SATOH, K., KAITOH, A., ABE, K. and YOSHINAGA, K. Indomethacin Does Not Attenuate the Hypotensive Effect of Captopril, a Converting Enzyme Inhibitor in Goldblatt Hypertensive Rats. Tohoku J. exp. Med., 1981, 134 (1), 9-19-Whether or not prostaglandins (PGs) have anything to do with the hypotensive effect of a converting enzyme inhibitor, Captopril (SQ 14, 225), was studied in two kidney one clip Goldblatt hypertensive rats. Four to 10 weeks after clipping the left renal artery of male Splague-Dawley rats, 50mg/kg of captopril (Group 1, n=7) or 12.5mg/kg of indomethacin (Group 2, n=7) were infused for 4hr under the conscious state. For the subsequent 4hr, both 50mg/kg of captopril and 12.5mg/kg of indomethacin were infused in both groups of rats. Mean blood pressure (MBP) was recorded continuously. Plasma renin activity (PRA) and urinary excretion rate of PGE (UPGE) were measured by radioimmunoassay. Urinary sodium (UNa) and potassium (UK) excretions were measured by a flame photometer. After captopril infusion the pressor response to the injection of 100ng of angiotensin I decreased from 29.1± 4.2 to 4.8±1.6mmHg, and that of angiotensin II increased from 35.9±3.6 to 75.0±5.1mmHg (p<0.01), while the response to norepinephrine did not change. Indomethacin did not affect these pressor responses. In the preinfusion period MBP, PRA or UPGE was not different significantly in the two groups of rats. The infusion of captopril decreased MBP from 202±11 to 119±7.5mmHg (p<0.01) in the first group of rats. After the additional infusion of indomethacin MBP further decreased to 100±12mmHg, depsite the significant decrease of UPGE from 915±34 to 109±28pg/hr (p<0.01), and PRA increased from 22.1±4.2 to 34.1±7.1ng/ml/hr. UNa did not change after captopril infusion but decreased significantly after indomethacin infusion from 49.0±5.0 to 22.8±3.5μEq/hr. In the second group captopril also decreased MBP from 187±7 to 119±15mmHg (p <0.01), and increased PRA from 24.1±6.1 to 43.3±6.9ng/ml/hr (p<0.01) despite the significant decrease of UPGE from 1219±294 to 413±101pg/hr by the pretreatment with indomethacin. UNa did not change in any period. The decrease of MBP was significantly correlated with the level of PRA prior to the infusion of captopril in both groups (r=-0.69, p<0.01). UK did not change significantly in any period in the two groups of rats. Our data that indomethacin did not attenuate the hypotensive effect of captopril indicate that PGs do not participate in the hypotensive effect of captopril and that the hypotensive effect of captopril is mainly due to the inhibition of renin-angiotensin system in two kidney one clip Goldblatt hypertensive rats.

Effect of fasting and parathyroid hormone injection on plasma 45Ca concentrations in rats.

Young male rats were administered 45Ca 5 days to 2 weeks prior to use. All rats were either parathyroidectomized (PTX) or thyroparathyroidectomized (TPTX) and given several days to recover from surgery. The first group of rats were maintained on a 12 h dark-fed and 12 h light-fasted daily cycle. The remainder of the rats were used for parathyroid hormone (PTH) studies (0.1-0.6U/g body weight) following which blood samples were obtained from the tail for 1 to 6 h. Two groups of these rats were bilaterally nephrectomized 18 h before PTH injection. Two contrasting results were obtained: in PTX (or TPTX) rats maintained on the closely regulated food and light regime, plasma 45Ca concentrations rose markedly each day at the start of the fasting period and then fell slowly. Total plasma calcium values fell throughout the fasting period. A similar rise and fall was also observed in 45Ca values of rats experimentally fasted after being maintained with food continuously available. In contrast, in all PTX or TPTX rats, PTH injections was followed by an equal rise in both plasma calcium and 45Ca values so that for the first few hours plasma 45Ca specific acitvity was unchanged. These data are consistent with the concept of a bone fluid compartment (BFC) separated by a cellular interface from the primary extracellular fluid space (ecf). It is postulated that through this cellular interface calcium is actively "pumped" from the BFC to the ECF. The rise in plasma 45Ca values at the start of fasting is explained on the basis of decreased entry of stable calcium from the gastrointestinal tract and a continued movement of calcium and 45Ca from the BFC to the ECF. The concomitant increase in plasma calcium and 45Ca during the first few hours after PTH injection is explained by a rapid action of PTH to increase the rate of calcium movement from BFC to ECF by its action at the cellular interface, without altering 45Ca specific activity until such time as dissolution of bone crystals is required as a supply of calcium.

Influence of Excess Dietary Molybdenum on Rat and Calf Liver and Heart Enzymes

Experiments were designed to study the effect of excess dietary molybdenum on various enzymes of the liver and cytochrome oxidase of the heart of a monogastric and a ruminant animal in an attempt to gain information as to the mechanism of molybdenosis in animals. Rats fed diets containing added molybdenum at 500 and 800 ppm showed molybdenum toxicity symptoms, including diarrhea and decreased rate of growth. These diets did not affect tyrosine oxidase activity or concentration of copper in the liver, but caused an increase in the concentration of molybdenum in this organ and a reduction in liver respiration and liver xanthine oxidase. A second group of rats was fed highmolybdenum diets which raised the concentration of molybdenum in the liver but did not cause diarrhea. These rats also showed a reduction in liver xanthine oxidase activity. Thus, it appears that possible decreased utilization of protein, resulting from diarrhea as exhibited by the first group of rats, was not solely responsible for the reduced xanthine oxidase activity noted. Also, increased liver molybdenum concentration per se can influence the level of the enzyme. A slight lowering in blood uric acid concentration was observed in these rats. The cytochrome oxidase activity in the heart was not affected. The concentration of molybdenum found in the liver upon feeding 500 ppm molybdenum in the diet was not exceeded when 800 ppm was fed. It appears that there may be a liver “threshold” for molybdenum of 500 ppm or less; above this dietary level, liver storage is not increased. Calves maintained on diets containing 200 and 400 ppm molybdenum were observed to have increased concentrations of molybdenum in the livers, but no decrease in liver respiration or xanthine oxidase or in heart cytochrome oxidase.

EFFECTS OF DESOXYCORTICOSTERONE ACETATE IN THE ALBINO RAT1

IT is ESTABLISHED that some patients with Addison’s disease given large doses of desoxycorticosterone acetate develop cardiac dilatation and signs of circulatory failure (I). Similar doses in normal dogs cause marked polydipsia and polyuria and result inperiodic muscular weakness associated with very low serum potassium levels (2). The present study is concerned with the effects of prolonged administration of this drug in albinorats. In a preliminary experiment the treated rats failed to show effects similar to those seen in the human patient or in the dogs but changes in the weight of the testes and pituitary glands directed attention to the endocrine organs in subsequent groups. Group I. Due to the striking effect of the drug on serum potassium levels of human patients and dogs, the first group of rats was maintained on a low K diet (3) throughout theperiod of observation.

Effect of Dinitrophenol, Sodium Citrate, Sodium Bicarbonate, and Citric Acid upon Distribution of Cholesterol

The report of Marie that sodium citrate administered by mouth or intravenously reduced the blood cholesterol of rabbits 60% led us to try its effect upon blood cholesterol of other species. It is of interest in this connection to note that dogs with a hyperpyrexia induced by the administration of 10 mg./kg. dinitrophenol showed an increase in blood cholesterol, the initial value of 161 mg. % being elevated to 285 mg. % 2 hours after injection of the drug. These observations led us to continue the study with albino rats. Five groups of 5 rats each were placed upon a diet similar to that suggested by Chanutin and Ludewig, in which extracted casein was substituted for extracted dried beef. To this cholesterol deficient diet, cholesterol was then added to the extent of 2%. The first group of rats received no supplement and served as control animals. In the second group, each animal received a daily subcutaneous injection of 1 mg. dinitrophenol per 100 gm. body weight. To the third, 0.2 gm. sodium citrate per 100 gm. body weight was given in aqueous solution by stomach tube. The fourth and fifth groups received NaHCO3 and citric acid solutions, respectively, by stomach tube, in order to determine, if possible, the ion responsible for any change in the distribution of cholesterol. These 2 substances were given in amounts furnishing separately the same quantities of sodium and citrate ions as received by the animals in Group 3 on the sodium citrate supplement. Each animal of the fourth group, therefore, received 0.14 gm. NaHCO3, and of the fifth group 0.11 gm. citric acid daily, per 100 gm. body weight. At the end of 3 days the rats were killed, the blood from each group pooled and analyzed for total and free cholesterol, total fatty acids, and lipoid P.

Effect of prostatectomy on integration of muscular movements of the white rat

An attempt to study the effect of prostatectomy on muscular coördination and efficiency was made by means of the so-called“rope problem.” White albino rats are trained to walk across a room over a tightly stretched rope starting from a platform at one end and ending at another platform on which food is placed at the other end of the room. This problem or method of study is an excellent one for the development of muscles and training of their coördination. The animals at first cannot cross the rope at all and slip off it repeatedly, hanging by the front legs. After fifty trials, however, they learn to coördinate their movements and eventually can run over the entire length of the rope rapidly and without swaying or slipping off. After such a prolonged trial one notices a marked improvement in the tonus and strength of the entire musculature of the animals. In the present investigation the effect of prostatectomy was studied on the coördination of muscular movements. Two sets of experiments were performed. In the one group of rats, the animals were trained on the rope until they mastered the problem perfectly. They were then prostatectomized and allowed to recover. After recovery the animals were quickly retrained and it was found that there was no evident change in the integration of muscular movements produced by the extirpation of the prostate glands. In the second set of experiments, another group of rats were prostatectomized after seven trials on the rope before they had completely mastered the problem. The animals were allowed to rest and after recovery from the operation training on the rope was again begun. It was soon noticed that this group of rats learned to run across the rope very poorly and indeed after even a much longer period of training than the first group of rats (80 trials) in this second group of animals rhythmic progression was very poorly established.