Melvin B. Dennis

A Reproducible Animal Model of Acute Bleeding Ulcer—The “Ulcer Maker”

An instrument has been developed which creates an experimental model of an acute bleeding gastric ulcer. The diameter and depth of these gastric ulcers are reproducible. The instrument can be used endoscopically or at laparotomy. Using this ulcer model nonsurgical modalities for the treatment of upper gastrointestinal bleeding can be compared in a controlled manner. This standard experimental model may also facilitate comparison of results among different research groups.

Evaluation of electrofulguration in control of bleeding of experimental gastric ulcers.

The safety and efficacy of electrofulguration for control of bleeding from standard canine experimental gastric ulcers was studied. At settings of 2, 5, and 8 on a Valleylab SSE-3 generator, 0.5-sec applications provided effective hemostasis. However, a setting of 2 required an excessive number of applications. Settings of 5 and 8 showed deep injury to the muscularis externa when examined histologically. In an attempt to reduce the depth of injury, a more easily ionizable gas mixture of 50% argon gas and 50% CO2 was compared to CO2 alone. At a generator setting of 5 with 0.5-sec applications the argon-CO2 mixture produced slightly less deep injury than CO2 alone, but the difference was not significant. Although electrofulguration was effective in stopping bleeding in these experiments, the tissue injury was unpredictable and deep.

Failure of cyanoacrylate tissue glue (Flucrylate, MBR4197) to stop bleeding from experimental canine gastric ulcers

A plastic tissue adhesive, trifluoroisopropyl 2-cyanoacrylate (FlucrylateTM, MBR4197), was tested for hemostatic efficacy in acute laparotomy experiments using a canine model of acute bleeding gastric ulcer. An improved delivery system suitable for endoscopic use was developed. Hemostatic efficacy of the adhesive was tested in both briskly bleeding ulcers and in oozing ulcers after partial treatment with a heater probe. In pilot studies at laparotomy, primary and adjunctive cyanoacrylate therapy of 81 bleeding ulcers were evaluated in seven unheparinized foxhounds. Hemostasis was produced in 11% of ulcers treated with cyanoacrylate alone and in 31% of ulcers treated with cyanoacrylate as an adjunctive after partial heater-probe treatment; no sham-treated control ulcers stopped bleeding under the conditions of the experiment. To evaluate FlucrylateTM using our standard heparinized ulcer model, a randomized study was performed in six heparinized foxhounds at laparotomy. Ulcers were randomized to treatment with cyanoacrylate alone, adjunctive cyanoacrylate, heater probe alone or untreated control. Sham-treated control ulcers or ulcers treated with cyanoacrylate alone did not stop bleeding; 42% of ulcers treated with cyanoacrylate as an adjunctive stopped bleeding; all ulcers treated with a heater probe stopped bleeding. In this experimental model of acute bleeding gastric ulcer, trifluoroisopropyl 2-cyanoacrylate (FlucrylateTM, MBR4197) did not stop severe bleeding and was unpredictable as an adjunctive treatment.

The multisection tissue slicer: A simpler technique for assessing the maximal depth of experimental injury

A new device, the multisection tissue sampler, has been developed to accurately identify the area of maximal tissue damage after experimental coagulation of bleeding ulcers. Fixed ulcers are sliced into 1-mm strips and then examined with a dissecting microscope. The technique was validated by comparing visible changes in one ulcer slice with changes observed microscopically in the mirror image slice. This device is a less time-consuming method of histologic analysis that may be of value in other areas of endoscopic research.

Implanted Right Atrial Catheters for Continuous Infusion of Solutions into Dogs

Silastic catheters were fabricated and aseptically implanted through the skin into the jugular vein of 64 dogs with the intravascular tip located in the right atrium. Solutions were infused through the catheter at 2 to 2.5 mL/h by a portable pump worn by the dog. Following 9.2 Gy total body irradiation (TBI) and allogeneic bone marrow transplantation (BMT), succinyl acetone, an experimental chemotherapeutic agent, was infused into 34 dogs. Hematopoietic growth factors were infused into an additional 30 dogs, two of which had 9.2 Gy TBI and an autologous BMT, and four of which had 4.0 Gy TBI and no BMT. All dogs received continuous oral and parenteral antibiotics while the catheters were in place. All catheters functioned well until electively removed (n = 28) or until the dogs died or were euthanized (n = 36) at 12 to 68 days after implantation. Mean length of catheter function was 30.3 +/- 1.5 (SEM) days. No catheters were dislodged and there was no evidence of catheter-related blood loss or sepsis. Semiquantitative cultures of 5 catheters were negative, but Staphylococcus epidermidis was isolated from 3 of 7 catheters cultured in broth. Six dogs had thrombosis adjacent to the intravascular catheter tip. The catheters were well tolerated and facilitated successful long-term infusion of solutions into dogs.

Videoendoscopy: An Effective and Efficient Way to Perform Multiple Visceral Biopsies in Small Animals

Because major surgery is usually required to obtain biopsies of abdominal organs, regulations tend to limit the number of procedures on individual animals to one. This study was conducted to develop a more humane, minor, comparatively cost-effective, minimally invasive surgical procedure, which reduces surgical trauma and the number of animals used. Biopsy techniques were developed in two nonsurvival rabbit surgeries. Safety and efficacy of multiple procedures were assessed in survival studies on four rabbits. Anesthesia was induced with ketamine/xylazine and maintained with isoflurane. Initial carbon dioxide insufflation (6 mmHg) was achieved through a Veress needle. A triangulated 5-mm port technique allowed introduction of pediatric 3.5- to 5.0-mm laparoscopic instruments. Biopsies of liver, spleen, kidney, and full-thickness bowel were obtained and evaluated for suitability (size) for polymerase chain reaction, in-situ hybridization, and histopathology studies. Animals in survival studies were assessed for infection, pain, bleeding, adhesion development, bowel function, and intestinal stenosis. All had normal appetite and stools within 48 h postoperatively. Biopsies obtained from either a Tru-Cut Biopsy Needle, 3.5- to 5.0-mm biopsy cups, or with the aid ofa pre-tied loop were adequate for all studies. There was no postoperative bowel obstruction, wound infection, or bleeding. Mean hematocrit decrease at 24 h postoperative was 3.4% +/- 6.7%. Adhesions formed at 9/52 (17%) evaluable sites. Multiple visceral organ biopsy under videoendoscopic guidance constitutes a minor procedure and is a promising means for longitudinal studies in animals. Utility for ill animals remains to be determined.

An Animal Model for Fungal Peritonitis: Evaluation of Therapeutic Options

An animal model for fungal peritonitis was developed and is described. This model was used to compare various therapeutic options for Candida albicans peritonitis. Twenty-four rabbits were treated on three different protocols. Results from these protocols confirm the clinical observation that removal of the catheter is necessary for successful treatment of fungal peritonitis. Further, the combination of catheter replacement and imidazole anti-fungal therapy appears to be curative in this animal model, and suggests that by using this protocol, discontinuation of peritoneal dialysis may not be necessary.

The treatment of rejection. A trial of acetylsalicylic acid, dipyridamole, and heparin.

Serial studies of platelet and fibrinogen survival were performed in 26 nonimmunosuppressed dogs after allogenic renal transplant operations. Treatment with acetylsalicylic acid, dipyridamole, and heparin failed to improve the selective platelet destruction which occurred in untreated animals, and it did not improve postoperative longevity. There was a high incidence of postoperative wound and intrarenai hemorrhage after heparin treatment. These results are consistent with the hypothesis that platelet destruction is a consequence rather than the cause of acute graft rejection, and it is concluded that antithrombotic therapy is not of practical benefit in preventing acute rejection.