Induction of intestinal cytochrome P450 (CYP3A) by rifampicin in beagle dogs

Both male and female beagle dogs (four dogs/sex) were orally treated with rifampicin (Rif) at the dose of 10 mg/kg/day for 7 days and an additional eight dogs (four dogs/sex) were used as a control. The inducible effect of Rif on intestinal cytochrome P450, especially CYP3A enzyme, was investigated by measuring microsomal testosterone 6beta-hydroxylation (6beta-OHT) activity, immunoblot and ELISA analysis. In male dogs, microsomal 6beta-OHT activity in the duodenum, upper, middle and lower part of the jejunum and the ileum of the control was 229, 204, 194, 129 and 57 pmol/min/mg protein, while the activity of the Rif-treated dogs significantly increased to 456, 486, 430, 192 and 138 pmol/min/mg protein, respectively. The activity of intestinal 6beta-OHT in the control and Rif-treated female dogs showed almost similar levels to those observed in the corresponding male dogs. The activity of intestinal 6beta-OHT in both control and Rif-treated dogs was specifically inhibited by anti-CYP3A12 antiserum. The apparent K(m) value for 6beta-OHT activity in all sections of the small intestine was comparable with that in the liver, and no significant changes were observed in between control and Rif-treated dogs. In both control and Rif-treated dogs, immunoblotting of intestinal microsomes with anti-CYP3A12 antiserum produced a band indistinguishable from that of purified CYP3A12 or of immunoreactive CYP3A12 in liver microsomes. A significant increase in intestinal CYP3A content by Rif treatment was quantitatively verified by the ELISA analysis and the magnitude of its increase correlated well with that of 6beta-OHT activity elevation. Furthermore, the results of immunohistochemistry using the anti-CYP3A12 antiserum indicated that CYP3A protein was specifically distributed in epithelial cells throughout the small intestine and appeared to be predominant at the apical side of villus cells. These results demonstrate that Rif induces not only hepatic CYP3A12 but also intestinal CYP3A in dogs.     

Reinnervation of pulmonary stretch receptors

The Breuer-Hering reflex (BHR) reappears 12-14 wk after surgical lung denervation in beagle dogs (J. Appl. Physiol. 54: 1451-1456, 1983). To demonstrate that this is due to reinnervation of pulmonary stretch receptors, we recorded nerve activity from regenerated branches of the left vagus nerve in five beagle dogs. Ten days postdenervation the BHR was absent, whereas by 19 mo it was clearly present. Multifiber pulmonary afferent activity was observed in all five dogs with single-fiber activity observed in three. Sectioning the right vagus nerve did not alter the BHR, but sectioning all the regenerated branches of the left vagus abolished the reflex. In two additional dogs studied 17 mo postsurgery, recordings were made from few fiber nerve bundles of the left cervical vagus. Nerve activity was increased during gentle stroking of the surface of the left upper and lower lobes, indicating receptive fields in both lobes. These data demonstrate that reinnervation of pulmonary stretch receptors does occur and provides evidence that reinnervation of these receptors is responsible for return of the BHR after pulmonary denervation.     

Analysis of renal immune-deposits in canine leishmaniasis. Preliminary results

Previous studies carried out on 34 dogs spontaneously infected by Leishmania infantum showed the presence of kidney lesions characterized by immunologically mediated glomerular and tubular damage. Glomerular immune-deposits were studied in 13 of these dogs. Immunoglobulins were isolated from kidney tissues by acid elution; IgG fractions from eluates, obtained by ammonium sulfate precipitation, were subjected to clonotypic analysis by autoradiography after isoelectrofocusing (IEF) using 125I radiolabelled goat IgG fraction-anti Fab2 of dog IgG. Idiotypic characterization of IgG eluted from kidney tissues was performed by IEF and autoradiography using both 125I radiolabelled membrane antigens of L. infantum extracted by Triton x 100 and 125I radiolabelled dog IgG for rheumatoid or anti-idiotypic activity. The IgG deposited in the kidney tissues of examined dogs were polyclonal and a specific activity against Leishmania membrane antigens was revealed. Meanwhile an anti-IgG activity of deposited immunoglobulins was not observed.     

Effect of aspirin on the pressor activity of endothelin

To examine the inhibition of prostaglandins to the pressor activity of endothelin, hemodynamic changes of dogs pretreated with aspirin in response to endothelin were compared with those of control. In control dogs, endothelin rose blood pressure due to vasoconstriction, with a transient vasodilation in some dogs in the initial phase. In dogs treated with aspirin, the initial vasodilation and the subsequent vasoconstriction were also noted, but the zenith of the total peripheral resistance was observed earlier, compared with control dogs. Thus, prostaglandins do not appear to have a role in the initial vasodilatory action of endothelin, but may modify the long lasting vasoconstriction in the late phase.     

Increased Feeding Speed Is Associated with Higher Subsequent Sympathetic Activity in Dogs

Although the domestication process has altered the feeding behavior of dogs, some breeds still demonstrate a remarkable ability to gorge, and will eat exceptionally large quantities of food whenever it is available. Lesions in the ventromedial hypothalamus increase appetite and lead to obesity, suggesting that the autonomic nervous system plays an important role in feeding. Focusing on the autonomic activities closely involved in food intake, we investigated sympathetic activities before and after feeding in dogs. The subjects were 56 healthy dogs of 21 different breeds (29 males and 27 females). Based on feeding habits, the 56 dogs were divided into three groups: Fast (n = 19), Slow (n = 24) and Leftover (n = 13). The feeding speed and the amount of food per mouthful of the Fast dogs were significantly greater than those of the Slow and the Leftover dogs. The plasma norepinephrine level in dogs of the Fast group was significantly increased after feeding, while those in the Slow and Leftover groups were significantly decreased after feeding, compared with the pre-feeding concentrations. The low frequency/high frequency ratio of heart rate variability is a good indicator of sympathetic activity and was also significantly higher in the Fast group than in the other groups. Delayed feeding using automatic feeding equipment decreased the plasma norepinephrine concentration and low frequency/high frequency ratio observed after feeding in dogs of the Fast group. In conclusion, dogs eating rapidly with less chewing, which indicates increased sympathetic activity during feeding, may benefit from delayed feeding. The slow eating may activate the parasympathetic nervous system after feeding, which could enhance the activity of the digestive system.     

Serum hemolytic activity in dogs infected with Babesia gibsoni

The hemolytic activity in serum of Babesia gibsoni-infected dogs was examined. When the activity was assayed in a reaction system consisting of similar concentrations of the serum and canine red blood cells to those in blood, significant hemolysis was observed. The activity of the serum of B. gibsoni-infected dogs, either naturally or experimentally, was always higher than that of uninfected animals. Moreover, in the experimental infection with B. gibsoni, the change in serum hemolytic activity was parallel to those of anemia and parasitemia, whereas it was inversely parallel to that of the hematocrit value. The present study revealed the presence of a hemolytic factor(s) in the serum of B. gibsoni-infected dogs, suggesting that the progressive anemia was due to hemolysis by the factor(s).     

Stages in the development of neuroses in the dog and effects of preparations with antidepressive and tranquilizing properties

In modelling of neuroses, successive stages of development of this pathology were observed in dogs. The first stage is characterized by circular disturbances of conditioned activity, vegetative shifts of compensatory character and intensification of individual characteristics of behaviour. At the second stage, parallel with sharp disturbances of conditioned reflexes and with vegetative dystonia, a distortion of emotional reactions was observed in dogs. It is essential that resumption of neurotization episodes in experiments on dogs with the second stage of disease promoted a development of depressive-like states. Diazepam corrected the behavioural and vegetative shifts at the first stage of neurosis. Non-typical antidepressants eliminated the manifestation of symptoms complex of the disease, especially at prolonged treatment.     

Environmental factors affecting seasonal variation in immunity of clinically normal dogs

A whole blood lymphocyte stimulation test, an in vitro corollary of in vivo cell mediated immunity, was done with blood collected monthly from eleven dogs for a period of three years (August, 1977 through August, 1980). Seasonal variations in immunity were observed to occur. These fluctuations were analyzed for possible association with 22 environmental, solar, and meteorological parameters. Of the six independent variables significantly entering the predictive regression equations, sunspot activity (monthly mean daily number of sunspots) was most prominent, showing a significant negative correlation in 10 of the 11 dogs. This suggests that solar activity might be associated with some activity on earth, e.g., geomagnetism which in turn might affect immune response.     

Variation of hepatic methotrexate 7-hydroxylase activity in animals and humans

This study deals with individual and species variations in the converting activity of methotrexate (MTX) to 7-hydroxymethotrexate in animals and humans. When MTX 7-hydroxylase was assayed in six human liver cytosols, a 48-fold range of intersubject variation of the activity was observed. The variations were correlated to the concentrations of aldehyde oxidase activity in human subjects assayed with benzaldehyde as a substrate. Species differences of liver MTX 7-hydroxylase activity were also observed. The activity was highest in rabbits, followed by rats, hamsters, and monkeys but was undetectable in dogs. Strain differences of MTX 7-hydroxylase activity based on aldehyde oxidase activity were also observed in rats and mice. The results suggest that aldehyde oxidase functions as MTX 7-hydroxylase in livers of animals and humans, and the observed differences of MTX 7-hydroxylase activity are due to variations in the amount of aldehyde oxidase present.     

Increased monoamine oxidase and semicarbazide-sensitive amine oxidase activities in white adipose tissue of obese dogs fed a high-fat diet

Adipocytes express two types of amine oxidases: the cell surface semicarbazide-sensitive amine oxidase (SSAO) and the mitochondrial monoamine oxidase (MAO). In human abdominal subcutaneous adipose tissue, it has been reported that SSAO substrates stimulate glucose transport and inhibit lipolysis while MAO activity is decreased in obese patients when compared to age-matched controls. However, no information has been reported on visceral WAT. To further investigate the obesity-induced regulations of MAO and SSAO in white adipose tissue (WAT) from different anatomical locations, enzyme activities and mRNA abundance have been determined on tissue biopsies from control and high-fat fed dogs, an obesity model already described to be associated with arterial hypertension and hyperinsulinemia. MAO activity was increased in the enlarged omental WAT of diet-induced obese dogs, but not in their mesenteric WAT, another intra-abdominal fat depot. Subcutaneous WAT did not exhibit any change in MAO activity, as did the richest MAO-containing tissue: liver. Similarly, SSAO was increased in omental WAT of diet-induced obese dogs, but was not modified in other WAT and in aorta. The increase in SSAO activity observed in omental WAT likely results from an increased expression of the AOC3 gene since mRNA abundance and maximal benzylamine oxidation velocity were increased. Finally, plasma SSAO was decreased in obese dogs. Although the observed regulations differ from those found in subcutaneous WAT of obese patients, this canine model shows a tissue- and site-specific regulation of peripheral MAO and SSAO in obesity.     

Salutary effects of moderate hypothermia on the circulatory and myocardial consequences of acute coronary occlusion in dogs

The efficacy of moderate hypothermia with rewarming in attenuating the myocardial and circulatory consequences of acute coronary ligation was studied in open-chest, anesthetized dogs. Thirty minutes after ligation of the proximal left anterior descending coronary artery, 14 dogs were surface-cooled to 27 degrees C, maintained at this temperature for 2 hr, rewarmed to normothermic levels, and monitored for an additional hour. Fifteen dogs were maintained for a corresponding time period after coronary ligation at normothermic levels. Dogs maintained normothermic demonstrated significant depression (from preligation values) of dP/dt, cardiac output (CO), stroke volume (SV), and left ventricular stroke work and power (LVSW, LVSP) at elevated levels of left ventricular end-diastolic pressure (LVEDP). Dogs subjected to the hypothermic procedure demonstrated decreased inotropic status during hypothermia, but with rewarming, exhibited significantly greater values of left ventricular pressure, dP/dt, CO, SV, LVSW, and LVSP at lower values of LVEDP than observed in dogs maintained normothermic. Increased dysrhythmic activity was not observed during hypothermia. Hearts from dogs subjected to the hypothermic protocol demonstrated qualitatively greater dehydrogenase activity both at the periphery and in the center of the nonperfused region. The results suggest that moderate hypothermia during evolving myocardial infarction may preserve left ventricular cardio- and hemodynamics and thus may be useful in delaying morphological and functional deterioration until definitive treatment can be instituted.     

Effect of glucagon on glomerulopressin production in diabetic dogs

Glucagon (21.5 +/- 0.23 ng/min/kg) was infused through the portal vein of normal or pancreatectomized dogs. It was observed that a dose of glucagon that produces no significant change in the glycemia of normal dogs has a very small activity in the production of glomerulopressin and does not alter glomerular filtration rate (GRF). In pancreatectomized dogs this same dose of glucagon also does not alter glycemia but it induces a large increase in the production of glomerulopressin and GFR. Our results suggest that in pancreatectomized dogs glomerulopressin production is more sensitive to glucagon infusion than in normal dogs.     

Change in cerebral bioelectric activity during whole body hypothermia and regional cooling of the head]

Two series of experiments were conducted on dogs. In the first series of experiments dogs were subjected to deep hypothermia with an external chilling of the organism; in the second series-to the isolated deep hypothermia of the head with the maintenance of normothermia in the organism. Bioelectrical activity of the brain and circulation minute volume were recorded in the animals of both series. As revealed, depression of the bioelectrical activity was more pronounced and a prevalence of slow waves was observed in general hypothermia; at the same time a more even reduction of the electrical activity in all the EEG frequencies under study was seen in the series with local hypothermia. A reduction of the circulation minute volume was also more pronounced in the first series of experiments; in the authors' opinoin this was associated with the difference in the character of the EEG evolution with the same depth of hypothermia of the brain.     

Effects of Short-Distance Recreational Mushing on Oxytocin,Gastrin, and Creatinine Kinase in Sled Dogs

A considerable increase in creatinine kinase (CK) activity and gastrin hormone due to exercise has been observed in sled dogs during endurance mushing races; however, there have been no studies on sled dogs during recreational mushing. Although oxytocin hormone is involved in social behaviors and empathy, it has not been studied in sled dogs. This study aimed to assess changes in plasma CK activity, and gastrin and oxytocin concentrations in adult sled dogs used in touristic mushing in North Patagonia, Argentina. Blood samples were collected before, during, and after the winter season of 2017. Creatinine kinase activity measurement was done using an enzymatic assay. Hormone analyses were performed using commercial Enzyme-Linked InmunoSorbent Assay kits. Results showed an expected two-fold increase in CK activity during the winter, with recovering basal values after winter (< 400 UI/L), low and stable levels of gastrin (9.4 ± 8.8 pg/mL), and a slight increase in oxytocin (23%) after mushing activities. No evidence indicated gastrin alterations or muscular damage from touristic mushing, but an oxytocin increase would indicate a stimulation of the brain reward system.     

Protracted release of the LHRH agonist avorelin (MF 6001) from two depot formulations in dogs and men

Summary Avorelin is a new superagonist of natural luteinizing-hormone-releasing-hormone. Avorelin has been formulated in high molecular weight polylactic glycolic acid to afford protracted and continuous release of the peptide from subcutaneous implants. Two different formulations (10 and 15 mg) were tested first in dogs and then in men during a clinical phase II trial. Chemical castration was maintained for at least 6 months in dogs with both formulations. A similar duration of activity (approximately 6 months) was observed in men.     

Systemic efficacy of nodulisporic acid against fleas on dogs

Nodulisporic acid A (NSA) is a novel natural product from a new structural class that was shown previously to have insecticidal activity against blowfly larvae. To determine if there was useful systemic efficacy against fleas (Ctenocephalides felis). NSA was evaluated in an artificial membrane flea feeding device and in dogs. In the artificial membrane flea feeding device, adult C. felis were allowed to feed on bovine blood containing various concentrations of NSA through a Parafilm membrane. NSA killed the fleas with a 50% lethal concentration of 0.68 microg/ml and was approximately 10-fold more potent than the systemic insecticide ivermectin. In the initial probe dog test, a single beagle was challenged with 100 C. felis before oral dosing with 15 mg/kg of NSA. Flea counts conducted at 72 hr postdosing showed an 88% reduction relative to control. Re-challenge of the same dog at 5 days postdosing showed 50% reduction of fleas at day 7, demonstrating some residual flea activity. In a confirmatory study, 8 dogs were challenged with 100 fleas just before oral dosing with 15 mg/kg of NSA (4 dogs) or vehicle (4 dogs). There was 99% reduction of fleas at 48 hr postdosing in the NSA-treated dogs relative to control. Additional challenges with 100 fleas were performed on these 8 dogs at 48-hr intervals to determine the duration of efficacy, and there was 97, 51, and 0% reduction of fleas relative to control on days 4, 6, and 8, respectively. No adverse effects were observed in the dogs in these studies. These data show that NSA has potent oral activity in the dog for the control of fleas, while lacking overt mammalian toxicity.     

Influence of blood sera from dogs subjected to ischemia and recirculation on incorporation of14C-amino acids in vitro

Incomplete ischemia of the spinal cord was produced in dogs by 40 min occlusion of the abdominal aorta that was followed by 5–40 min of recirculation. Amino acid incorporation into ribosomes in vitro in the presence of venous blood sera was estimated. The most significant reduction in incorporation was produced by sera of the dogs following a short recirculation period (5–10 min). No significant changes were observed at the end of the ischemic period nor at longer periods of recirculation. The decrease in incorporation might be the consequence of inactivation or absence of a substance stimulating polypeptide synthesis in vitro, normally present in blood sera of intact dogs, that temporarily loses its activity during recirculation.     

Subacute endotoxemia in dogs with experimental cirrhosis and ascites: effects on kidney function

To study the effect of low-grade continuous endotoxemia in normal and cirrhotic dogs, osmotic minipumps were filled with Escherichia coli endotoxin, implanted subcutaneously and arranged so that the endotoxin could be infused intravenously over a 7-day period in doses ranging from 2.5 to 100 micrograms/h. Observations were made at 3 and 7 days postinfusion. In normal dogs (N = 9), there was no effect on cardiac output or arterial pressure when doses as high as 50 micrograms/h were delivered into the circulation. Neither was there an effect on inulin or p-aminohippurate (PAH) clearances. At doses of 100 micrograms/h, dogs suffered a marked decrement in cardiac output, blood pressure, and renal perfusion and became lethargic at 3-7 days. In cirrhotic dogs, doses of 25 micrograms/h which had no effect in the control dogs, caused a significant decline in the glomerular filtration rate (59-21.5 mL/min) and CPAH (147-66 mL/min) at a time when cardiac output and blood pressure remained normal. At doses of 50 micrograms/h, cardiac output and blood pressure declined markedly and the dogs deteriorated quickly following 3-5 days of endotoxin. When endotoxin (25 micrograms/h) was given to dogs with acute biliary obstruction (serum bilirubin = 9.8 +/- 0.1 mg/dL) or to dogs with chronic thoracic caval constriction (which produced portal hypertension and ascites), no effect was observed on either central hemodynamics or renal perfusion. The selective renal vasoconstrictor effect observed in cirrhotic dogs could not be abolished by intravenous phentolamine or propranolol, inhibitors of alpha- and beta-adrenergic activity, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)     

Kinetic aspects of enzyme activity changes in blood plasma during canine hemorrhagic shock

The kinetics of the increase in activities of eight enzymes in plasma was investigated in hemorrhagic shock in dogs (8.0 kPa, 120 min). The time-course of enzyme activity changes in shock differed between animals and depended on their sensitivity to shock. In the shock-sensitive group of dogs an exponential activity increase was already observed in the hypotension period. However, the dogs of the less shock-sensitive group showed a delay of enzyme release with significantly less pronounced elevation of all enzyme activities except creatine kinase. The initial exponential rise of enzyme activities, which approximately followed first-order kinetics, was quantitatively characterized by the release rates. There was a close correlation between the molecular weights of enzymes and their release rates during shock in both groups of dogs. The relevance of the results to mechanisms of enzyme transport from the cell into the blood is discussed.