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Biomedical subjects

C W Hewitt

Publications and source records attributed to C W Hewitt.

At least 91 records · Page 5Linked to original sources
PubMed1985

Composite tissue (limb) allografts in rats. I. Dose-dependent increase in survival with cyclosporine.

The dose-response effect of cyclosporine on rat limb transplant prolongation was investigated across the LBN-to-LEW histocompatibility barrier. This composite tissue allograft model has been shown to represent a strong transplantation barrier. Median limb allograft survival times increased in a dose-dependent manner with low cyclosporine doses, and then reached a plateau at higher levels. The cyclosporine dose that produced half-maximal survival based on a 20-day treatment was only 3.7 mg/kg/day. Histopathology revealed that the rejection process was distinctly different in limb allografts treated with cyclosporine compared with non-cyclosporine-treated controls. Rejection appeared to be delayed or partly arrested in certain areas of cyclosporine-treated limb allografts. These studies represent an initial step in laying the experimental foundation for clinical transplantation of composite tissue allografts using cyclosporine-induced immune suppression.

Animals↗
PubMed1985

Composite tissue (limb) allografts in rats. II. Indefinite survival using low-dose cyclosporine.

Cyclosporine has reawakened interest in transplantation of peripheral composite tissue allografts (CTA) of skin, muscle, bone, vessel, and nerves. The purpose of this study was to examine whether cyclosporine could produce indefinite survival of CTA. Two groups of LEW recipients of LBN limb transplants were given different long-term treatments of cyclosporine. Tolerance was achieved in many of the animals. Several possibilities for the mechanism of this tolerance are discussed.

Animals↗
PubMed1985

Immunosurgery.

After being leaders in the field of transplantation, plastic surgeons became inactive in this field. Interest is reviving with the advent of the new immunosuppressant drug cyclosporine, as well as new knowledge of the immune mechanism. New generations of immunosuppressive drugs may allow allografting in patients with massive burns, limb transplants, and possibly even allografts of facial structures.

Antibodies↗
PubMed1982

Efforts to enhance survival of limb allografts by prior administration of whole blood in rats using a new survival end-point.

Injecting whole blood into the recipient before surgery can significantly prolong renal transplant survival in rats. Therefore, experiments were performed in rats to study the effects of prior administration of whole blood on the survival of limb allografts. Tests to quantitate survival of the allografts included monitoring the internal temperature of the leg, assaying serum creatine kinase levels, and testing for alloantibodies. Lewis recipients of (BN x LEW)F1 limb transplants that received 1 ml of BN or (BN x LEW)F1 whole blood before surgery had mean survival times that were longer compared with controls as measured by a 10 F change in temperature. In a test-retest experiment, decline of temperature proved to be a reliable quantitative determination of limb allograft survival since a difference of only 5.6% was observed in the mean number of days of graft survival between two separate groups of control Lewis recipients. Moreover, combined data demonstrated that control Lewis recipients of (BN x LEW)F1 limb allografts averaged 24.0 days of graft survival based on a 10 F decline in temperature with a 95% confidence interval of +/- 6.3 days. It is concluded that prior administration of whole blood can produce significant prolongation of survival in organ transplantation, but it is not as effective in enhancing survival of limb allografts. It is also concluded that internal temperature measurement of limb allografts is an easy, effective, and quantitative method of monitoring rejection.

Animals↗
PubMed1982

Murine immunosuppression with mycoviral dsRNA.

The effect of three different size molecular weight species of mycoviral dsRNA on the immune response to sRBC was tested in C57Bl/6 mice. The various dsRNA species were extracted from electrophoresis polyacrylamide-agarose slab gels. Their molecular weights ranged from 1.0 x 10(6) daltons to 3.5 x 10(6) daltons. All three sizes of mycoviral dsRNA significantly (p less than 0.0001) suppressed the hemolytic antibody titer of mice 8 days after immunizations with 15 micrograms dsRNA/mouse and 10(8) sRBC when compared to control mice which received only sRBC. No immune suppression was observed in any of the mice challenged with a second sRBC immunization 60 days after the first inoculations. Hemagglutination titers at this time were typical of a secondary antibody response to sRBC. In conclusion these three molecular weight mycoviral dsRNA species appeared to be potent immunosuppressors when approximately 15 micrograms/mouse were used.

Adjuvants, Immunologic↗
PubMed1981

Enhancement of rat renal allografts with various immunogens.

Lewis rat recipients of Brown Norway (BN) and Dark Agouti (DA) kidneys were tested for enhanced survival after they were injected with various immunogens. Lewis recipients of BN kidneys injected with either BN whole blood, bone marrow cells, red blood cells, or DA whole blood had enhanced survival. Lewis recipients of BN kidneys injected with either BN plasma or BN thymocytes did not have enhanced survival. Lewis recipients of DN kidneys injected with DA blood had enhanced survival. Lymphocytotoxins were found infrequently in recipients with rejected renal allografts. Active enhancement of the rat renal graft may be produced by immunization with cells that express serum determined or cell determined antigens.

Animals↗
PubMed1980

A simple method for the isolation of platelet-free lymphocyte suspensions from rat whole blood.

A simple technique for obtaining platelet-free lymphocyte suspensions from rat whole blood for use in complement-dependent microcytotoxicity assays is presented. Rat lymphocytes were purified by filtering buffy coat preparations containing thrombin over nylon fiber columns prior to Ficoll-Hypaque centrifugation. The addition of thrombin to buffy coat preparations significantly (P < 0.001) enhanced platelet retention on the nylon fiber columns. This procedure yielded lymphocyte suspensions which had a 98% mean reduction in platelet contamination compared to lymphocyte preparations which were purified using only Ficoll-Hypaque centrifugation. The thrombin-nylon fiber filtration method produced lymphocyte suspensions containing an average of 98% lymphocytes, and the total yield of lymphocytes isolated from 2 ml of blood averaged 2.85 X 10(6) cells. The sensitivity of complement-dependent microcytotoxicity assays was increased by the use of the thrombin-nylon fiber-filtered platelet-free lymphocyte preparations compared to the use of platelet-contaminated lymphocyte suspensions.

Animals↗
PubMedDate not supplied

Intracellular calcium buffering declines in aging adrenergic nerves.

Stimulation-evoked norepinephrine release from rat tail artery adrenergic nerves increased with advancing age in the Fischer-344 rat when function of norepinephrine uptake mechanisms and prejunctional alpha-2 adrenoceptors were blocked. When calcium channels were bypassed with the ionophore, ionomycin (4 microM), norepinephrine release from aged nerves (20 months) was still elevated as compared to 6-month-old nerves. Norepinephrine release stimulated by high K+ was also higher in 20-month nerves. The intracellular calcium chelator, 1,2 bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetomethylester (BAPTA/AM), was used to determine whether age-related increases in norepinephrine release could be reversed with the addition of an artificial intracellular calcium buffer. Exposure to BAPTA/AM decreased stimulation-evoked norepinephrine release in both old and young tail arteries; however, the effect was significantly greater in older arteries. When mitochondrial calcium uptake was compromised using the uncoupler of mitochondrial oxidative phosphorylation, dinitrophenol, BAPTA caused a further decrease in stimulation-evoked norepinephrine release in 20-month tail arteries with much less effect in 6-month-old nerves. These results suggest that intracellular calcium buffering is less efficient in older nerves.

Aging↗
PubMedDate not supplied

A sheep model for thoracic aortic surgery in the presence of systemic coagulopathy.

Surgical repair of aneurysms, traumatic injuries, or congenital anomalies of the thoracic aorta are associated with high morbidity and mortality mainly as a result of excessive and uncontrollable hemorrhage from diffuse coagulopathy. We developed a model in sheep that simulates this coagulopathic state for experimentation with thoracic aorta surgery. This experimental animal model involves administering a 600-mg aspirin suppository once a day for the 2 days preceding surgery and a final dose on-call to surgery. Prior to cross-clamping the aorta, an intravenous (i.v.) bolus of heparin (400 IU/kg) was administered. Thirty minutes later, the i.v. heparin bolus was repeated. Pre- and intraoperative activated clotting time was 101 +/- 10 s and >1500 s (p < .0001); prothrombin time, 21 +/- 1 s and >100 s (p < .0001); and activated partial thromboplastin time, 20 +/- 1 s and >50 s (p < .0001), respectively. We utilized a partial cross-clamp-and-sew technique to anastomose a woven, gelatin-impregnated, 16-mm tube graft end-to-side to the descending thoracic aorta. Mean total blood loss was 1367 +/- 282 mL, which included mean blood loss from time of release of aortic cross-clamp to close (422 +/- 135 mL) and mean total blood output from chest tube drain (945 +/- 203 mL). The mean time to achieve hemostasis at suture lines after aortic cross-clamp release was 15.5 +/- 6.6 min. In conclusion, a sheep model with induced coagulation defects was successfully developed and reproducible for experimentation involving thoracic aortic surgery.

Anastomosis, Surgical↗
PubMedDate not supplied

Transmyocardial laser revascularization: current status.

Transmyocardial laser revascularization (TMLR) has been widely evaluated for treatment of the ischemic myocardium either in conjunction with coronary artery bypass grafting or as sole therapy. Clinically, it has shown significant improvement for angina symptoms, but the mechanism by which this modality works is unknown at this time. The original premise on which transmyocardial revascularization was established depended on its ability to essentially generate channels that would directly carry blood from the ventricle into the ischemic myocardium. This theory, however, has not been substantiated, so other mechanisms have been postulated. This article gives a historical perspective on the advent of transmyocardial revascularization and the many animal and human studies that have paved the way for its clinical use. Current controversies are examined, along with the new advances in laser technology and where the future of TMLR is headed.

Animals↗
PubMedDate not supplied

Multiple oblique illumination and high-definition microscopy for breast fine-needle aspirates.

The ability of multiple oblique illumination (MOI) and high-definition microscopy (Edge R-400 3-D microscope) to improve resolution of cellular detail in the evaluation of cytopathological specimens of Pap smears and thyroid fine-needle aspirates (FNAs) has been demonstrated. However, previous experiments showed that the advantages of MOI and high-definition stereo microscopy were less certain for the breast FNAs. We hypothesized that these findings were due to the lack of sample thickness for the breast FNA specimens. To test this hypothesis, we analyzed breast FNA specimens that were significantly thicker (10.5 microm). The number of lights (1, 2, 3, 4) and the angle of light (+1.5, 0, -3) were varied independently, creating 12 groups. Three images at each combination of settings were digitally captured and analyzed to obtain a histogram. The coefficient of resolution (Cr) was calculated to mathematically evaluate the grayscale histograms for intensities (0-255), where Cr = [¿IM - IN¿ x (N)] (IM, median pixel intensity; IN, measured pixel intensity; and N, number of pixels at given intensity). Mean Cr values demonstrated that the angle of light obliquity was not a factor in altering the resolution and contrast (p = .9). However, there was a significant increase in resolution, as measured by mean Cr values, as the number of lights was successively reduced from four lights to one light. Thus, the thicker specimen did show that increases in resolution were a significant function of the number of lights utilized.

Biopsy, Needle↗
PubMedDate not supplied

A novel technique in a sheep model for evaluating prosthetic heart valve performance.

There have been many various animal studies to evaluate the structural integrity and antithrombogenicity of prosthetic heart valves. We were interested in developing a novel sheep model to study the thrombogenicity of mechanical heart valves placed into the systemic circulation but without the need for cardiac bypass. Also, we wanted to minimize the risk ofparaplegia from complete thoracic aortic clamping. Six sheep underwent left lateral thoracotomy for placement of a mechanical heart valve in parallel with the descending thoracic aorta. A valved conduit with a dacron tube graft sutured to the back end was fashioned. Employing partial aortic occlusion with a side-biting clamp, the proximal and distal ends were anastomosed in an end-to-side fashion. Once flow was confirmed through the graft, the native aorta was occulded with umbilical tape. The sheep received no postoperative anticoagulation. The median operative time and estimated blood loss (EBL) was 170 min and 250 cc, respectively. Patency of the valved conduits was confirmed during the initial procedure, and there was no incidence of paraplegia postoperatively. Two animals expired shortly after extubation and at necropsy the valved conduits were patent with preserved valve function. The four survivors were sacrificed a median of 37 days postoperatively. Prior to euthanasia, the valved conduits were evaluated in situ with ultrasound. In all cases, the valves had clot formation at the hinges, which prevented active movement of the leaflets. This novel in vivo technique provides an alternative in testing the thrombogenicity of prosthetic heart valves without cardiac bypass or the risk of paraplegia in an animal that is extremely sensitive to complete aortic cross-clamp.

Anastomosis, Surgical↗