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Percutaneous laser discectomy has developed as a new modality in the treatment of herniated intervertebral discs. An experimental study of percutaneous nucleolysis using a carbon dioxide laser beam was performed in 10 dogs, each dog having 2 intervertebral disc spaces treated, for a total of 20 discs. The intradiscal pressure decreased in all instances with the drop ranging from 10% to 55% at the L2-L3 disc and 40% to 69% at the L4-L5 disc. The macroscopic and microscopic studies showed vaporization of the nucleus pulposus, and in 8 spaces, thermal damage to the end plate was observed. This study suggests that carbon dioxide laser nucleolysis is easy and effective, but 300 J of laser energy can damage the end plates in some intervertebral discs in dogs.

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This work was carried out to test the hypothesis that the high level of salivary secretion containing much Na+ and the volume of fluid sequestered in the foregut of ruminants play an important part in water and Na+ homeostasis. Saliva flow and composition and water and Na+ balance in the rumen have been measured in hydrated and dehydrated cows with esophageal fistulas. Reduction of voluntary feed intake in beef cattle during water deprivation was related to the stage of dehydration. Salivary secretion rate was linearly related to voluntary feed intake (r = 0.96) and inversely and linearly related to plasma osmolality (r = 0.88). The reduction in the volume of water stored in the rumen contributed to the major portion (55%) of the total water loss. Utilization of gut water attenuated the rise in blood plasma osmolality, and this may be connected with an animal's ability to continue eating despite dehydration.

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The occurrence of late complications in implanted cardiac prosthetic valves has emphasized the need for the development of an animal model in which these complications are reproducible. Sheep constitute an excellent model for chronical and pathological studies of prosthetic devices. In our experience, survival of sheep following implantation of prosthetic valves is closely related to postoperative serum colloid osmotic pressure (C.O.P.). The normal range as measured in 28 healthy sheep was 16.67 +/- 0.55 mm Hg. A protocol was developed to maintain the colloid hydrostatic pressure gradient (C.H.P.G.) as close as possible to the normal physiological range, and to delay the extubation until the C.O.P. was within this range, and the C.H.P.G. greater than 7 mm Hg. Using the above protocol, a new tri-leaflet polyurethane valve was inserted into eight, five to seven month old sheep in place of the mitral and tricuspidal valves. One hour after terminating the extacorporeal circuit, the C.O.P. was measured at 13.10 +/- 0.96; but within five to six hours, it rose to 17.1 +/- 1.1. During the same period, the C.H.P.G. increased from 3.02 +/- 0.96 to 7.6 +/- 0.50 mm Hg. The postoperative period was uneventful, and all animals survived. We have thus concluded that the routine measurement and monitoring of C.O.P. constitutes a guide of great clinical importance.

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An experimental double-blind study to evaluate the effectiveness of a constant current stimulator was performed on 30 young pigs that underwent a spinal fusion at the level of L5-L6. The group of animals with an active bone-growth stimulator showed a statistically significant increase of osteoblastic activity with bone formation.

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The antibacterial activity of canine pancreatic fluid was investigated in an attempt to understand the resistance of this organ, when intact, to ascending bacterial infections. The pancreatic fluid demonstrated bactericidal activity against Escherichia coli, Shigella species, Salmonella species, and Klebsiella pneumoniae; bacteriostatic activity against coagulase-positive and coagulase-negative staphylococci and Pseudomonas aeruginosa; and fungistatic activity against Candida albicans. There was no demonstrable antibacterial activity against Bacteroides fragilis and Streptococcus faecalis. The antibacterial activity was dialyzable and pH dependent, but independent of heat, the activity of several digestive pancreatic enzymes, and the bacterial inoculum. Electron micrographs of Escherichia coli exposed to pancreatic fluid did not demonstrate changes in the bacterial cell wall. Tracer studies of susceptible bacteria demonstrated decreased leucine uptake when briefly exposed to pancreatic fluid. The antibacterial activity was found by column chromatography to be a small molecular peptide. It is likely that pancreatic antibacterial factors protect the pancreas from ascending bacterial infections and operate along with other factors in the homeostasis of the upper small bowel flora.

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The hypothesis that addition of proline may save dietary protein for milk production was tested by administration of proline to two goats through a duodenal cannula. Because proline is synthesized by the mammary gland in vitro from arginine, the effect of proline supplementation on arginine uptake by the gland was tested in vivo. Arginine uptake, calculated from arterio-venous difference, dropped significantly in both animals, especially in the morning 1 h after milking, when a low-protein diet was fed. Milk production and total nitrogen in milk were not affected significantly by proline supplementation. A trend was toward decrease of milk orotic acid and an increase of milk fat due to proline supplementation.

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The healing process was studied of five surgical wounds in sheep caused by the implantation of pacemaker electrodes in the vaginal or vulvar submucosa, while the electrodes were being used for impedometric measurements of the tissue surrounding them. Separate measurements of conductance (G) and capacitance (C) were carried out at frequencies ranging from 10 Hz to 100 kHz. The highest specific conductance at 100 kHz (mumho/cm) was observed on the 3rd postoperative day - 3095 +/- 172 SEM (n = 5), at which time the wound area was considerably swollen. Thereafter, the conductance gradually decreased and stabilized in 17-20 days at 2194 +/- 54 when the healing process was terminated. The decreasing impedance angle and tissue phase angle indicated that during the healing process cell volume decreased and cell density increased.

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Tissue electrical conductance (G) and capacitance (C) were measured in vulvar and vaginal tissues of ewes by a spectroimpedographic method at frequencies from 10 Hz to 100 kHz. The calculated specific conductance (mumho/cm) at 100 kHz was 3082 +/- 20 (s.e.m.) in oestrus and 2153 +/- 16 in dioestrus (n = 8) (P < 0.001). The impedance angle and the tissue phase angle increased during oestrus, indicating that cell volume increased and cell density decreased in comparison with dioestrus. The ratio of conductivities at higher and lower frequencies showed that extracellular water content was maximal during oestrus and coincided with standing heat.

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Pancreatic excretion of ampicillin was evaluated in normal dogs and in dogs with induced pancreatis. A 100-mg/kg ampicillin dose administered intravenously induced mean peak serum levels of 100 micrograms/ml, and a 200-mg/kg intravenous dose induced a mean peak serum level of 273 microgram/ml. Ampicillin serum levels did not differ between the group of normal dogs and those with pancreatitis. In normal dogs, the peak pancreatic fluid ampicillin concentration after the 100-mg/kg dose was 0.4 microgram/ml, and that after the 200-mg/kg dose was 2.7 micrograms/ml. In dogs with pancreatitis, the mean peak ampicillin concentration in the pancreatic fluid after the 100 mg/kg dose was 19 micrograms/ml, and that after the 200-mg/kg dose was 38.5 micrograms/ml. Pancreatic fluid ampicillin concentrations were therapeutic in dogs with pancreatitis and subtherapeutic in normal dogs.

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In an experimental study of 60 rabbits (120 preparations) in which a bilateral fibular osteotomy was performed, a group of 40 rabbits had ligation of the vena cava, and a group of 20 rabbits were used as controls. The results were evaluated by microscopic study by H&E, PAS abd Alcian Blue staining and showed that venous stasis accelerates the process of fracture healing by increasing fibroblastic and osteoblastic proliferation and bone production. The effects of changes in pH, and concentrations of oxygen and carbon dioxide are suggested as the factors that modify the mechanism of osteogenesis, and greater quantities of mucopolysaccharide substances were observed at the fracture site in the group with venous stasis.

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Clindamycin phosphate in dosage of 15 mg/kg was administered intravenously to dogs. Serum and pancreatic juice clindamycin concentrations were assayed. Pancreatic juice clindamycin concentrations varied between 1.32--5.5 micrograms/ml. Clindamycin was still detectable in the pancreatic juice 4 1/2 h after its administration. Clindamycin, in combination with other antimicrobials, may be potentially effective in the prophylaxis and therapy of some of the infectious complications associated with pancreatitis.

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The acute effects of direct injections with various cytotoxic compounds into the prostates of adult dogs were studied microscopically. The effects remained localised to the site of injection, with no diffusion of the agents into other areas of the prostate. No systemic effects were observed despite the high concentrations used. The main histological changes consisted of local aseptic necrosis at the injection site surrounded by atrophy of the acinar epithelium.

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