Ira M. Gourley

Use of magnetic resonance spectroscopy in the evaluation of skin flap circulation.

The assessment of events that occur in elevated skin flaps has been largely by indirect methods. A method was sought that gives direct, reproducible, and accurate data about physiological and biochemical changes that occur during flap elevation and during periods of altered blood flow.Because of its ability to monitor changes in the levels of high energy phosphorus metabolites (ATP or adenosine triphosphate, PCr, or phosphocreatin, Pi, or inorganic phosphate), 31p magnetic resonance spectroscopy (MRS) holds promise of providing direct assessment of the metabolic status and biochemical changes that occur during skin flap elevation.MRS monitoring was performed on raised abdominal skin flaps of 12 rats. Abdominal flaps in 4 animals served as controls with and without total vascular occlusion while arterial blood flow was manipulated in 4 flaps and venous flow in 4 flaps. The results have validated the ability of MRS to determine cellular levels of ATP, PCr, and Pi in skin flaps, and to measure intracellular pH through the chemical shift of the Pi resonance.

Effects of combination cyclosporine/mizoribine immunosuppression on canine renal allograft recipients

Heterotopic renal allografts following bilateral nephrectomies were placed in 21 healthy mongrel dogs. One group of 11 dogs received cyclosporine (5 mg/kg/ 24 hr, orally), and 1 group of 10 dogs received cyclosporine and mizoribine (5 mg/kg and 3 mg/kg/24 hr, orally). Body weights, blood cell counts, serum chemistry profiles, serum electrolyte levels, urinalysis with cytology and culture, lymphocyte stimulation assays, immunoglobulin levels, whole blood levels of cyclosporine, and serum levels of mizoribine were followed. At the end of each survival period, necropsy and histopathologic examinations were performed. The mean survival time for the cyclosporine group was 12.8 ± 7 days. The mean survival time for the cyclo-sporine/mizoribine group was 33.6 ± 16.4 days, significantly longer (P=.0006) than the cyclosporine group. Death in the cyclosporine/mizoribine group was attributed to the combined effects of renal allograft rejection and development of a mizoribine-dependent enteritis. Serum levels of mizoribine were greater in the last half of the survival period due to compromised renal excretion of the drug. There were no complications due to infection, myelosuppression, or hepatotoxicity. Combination cyclosporine/mizoribine immunosuppression enhanced canine renal allograft survival in this study. Monitoring serum concentrations of mizoribine is imperative to determine toxic (enteritis) levels. Availability of an intravenous form of mizoribine would facilitate immunoregulation during periods of variable intestinal absorption or renal excretion.

Composite Vascularized Free-Rib and Pleural Transfer for Laryngotracheal Reconstruction

A free rib pleura composite vascularized transfer for repair of a defect in the canine upper airway is discussed and the results are reported. The procedure was carried out on eight dogs. One dog died from the anesthetic. Three surgical failures resulted from technical difficulties: failure of the vascular anastomosis, torsion of the vascular pedicle, and hemorrhage. Four dogs successfully maintained their airways, although one demonstrated bone absorption. Bone scanning, angiography, tetracycline labeling, and light microscopy confirmed active osseous metabolism of the rib, providing further evidence of the adequacy of periosteal circulation in maintaining normal rib metabolism. Scanning electron microscopy and conventional light microscopy demonstrated the development of a healthy respiratory epithelium. Thus a free flap of rib and attached pleura will provide adequate skeletal support and a moist, functioning, epithelial lining in a single-stage operation for reconstruction of a laryngotracheal defect in the normal dog.

Mizoribine serum levels associated with enterotoxicity in the dog.

To prevent or minimize mizoribine enterotoxicity in organ transplant recipients and to differentiate mizoribine enterotoxicity from other causes of enteritis, serum levels of mizoribine that produced subclinical and clinical signs of enterotoxicity were determined in the dog. When mizoribine was administered orally at 12-hr intervals, half the dogs studied showed clinical evidence of gastrointestinal disturbances (vomiting, diarrhea, and anorexia) without histopathologic signs of enterotoxicity. Using a 24-hr oral-dose schedule, clinical signs of gastrointestinal disturbances and histopathologic evidence (mucosal degeneration, crypt degeneration, and necrosis) of enterotoxicity were encountered when the mean 12-hr mizoribine serum level was 0.97 +/- 0.4 microgram/ml or greater. Histopathologic signs of enterotoxicity with repeated positive fecal occult blood assays and without clinical signs of gastrointestinal disturbances occurred when the mean 12-hr serum level was 0.53 +/- 0.17 microgram/ml or greater. Oral administration of cyclosporine did not exacerbate mizoribine enterotoxicity in the dog when administered with mizoribine at a dose that produced histopathologic signs of enterotoxicity.

Recovery of free muscle grafts in rat: improvement is associated with an increase in cyclic adenosine monophosphate concentration or use of the condition/test paradigm

The muscle fibers in freely grafted skeletal muscles degenerate and are replaced by new fibers which develop within the graft. Myogenesis in regenerating muscle recapitulates, to a large extent, developmental myogenesis and may depend on similar modulating influences. In addition to the generation of new fibers, functional recovery of free muscle grafts also requires reinnervation and revascularization of the new fibers. Recovery of function should be improved by enhancing either myogenesis or reinnervation and revascularization. We have used two procedures, shown previously to stimulate peripheral nerve regeneration, to improve the morphologic and functional recovery of free, orthotopic grafts of rat extensor digitorum longus muscle. Each of the procedures was effective, but had potentially different sites of action. The first procedure, the condition/test paradigm, presumably increases the rate and extent of graft reinnervation. The second procedure, continuous infusion of the adenylate cyclase activator forskolin during the first 21 days after grafting, may influence both myogenesis and nerve regeneration. Each procedure increased regenerating muscle fiber size and functional capacity, and forskolin also significantly increased capillary density and fatigue resistance.

Pathologic studies of acute rejection of mismatched feline musculocutaneous flaps: Effect of cyclosporine and prednisolone

The gracilis musculocutaneous flap was developed as an allograft model to study acute rejection and immunosuppression in the cat. Twelve adult cats received a MLC incompatible flap. Six of the cats received cyclosporine oral solution and prednisolone (0.5 mg/kg/24hr) for 100 days and six cats were not treated. Trough whole-blood levels of cyclosporine in the treatment group were maintained at approximately 750 ng/ml for 70 days, then 500 ng/ml for the remaining 30 days. Three flaps failed due to technical problems; 5 flaps were studied in the treatment group and 4 in the untreated group. All 5 flaps in the treatment group survived the 100 day treatment period and were rejected 30±26 days following cessation of treatment. Prior to discontinuation of treatment, with the exception of one cat, inflammatory changes associated with rejection were not observed in biopsy specimen. The flaps in the untreated group survived 13±1.5 days. Histopathologic examination of the flaps revealed little difference in the appearance of acute rejection and rejection after cessation of therapy. The most prominent lesion was a vasculitis with extensive perivascular lymphohistocytic inflammation. The lymphoid infiltrates consisted predominantly of T cells of both major classes (CD4 and CD8). Full-thickness epidermal necrosis and subsequent bacterial invasion followed vascular compromise.