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Biomedical subjects

R Mainwaring

Publications and source records attributed to R Mainwaring.

8 recordsLinked to original sources
PubMed1998

Separation of omphalopagus twins: unique reconstruction using syngeneic cryopreserved tissue.

Omphalopagus twin girls were admitted for evaluation of possible separation and repair at age 7 days. Prenatal sonographic diagnosis occurred late in the third trimester and was followed by cesarean section delivery shortly thereafter. Results of extensive evaluation over the next 7 days including x-rays, computed tomography and ultrasound scan of the head and torso, and cardiac catheterization showed: the gastrointestinal tracts were separate and normal, the livers were joined but had separate biliary and vascular systems, and the hearts were separate with vastly different anatomy and function. One twin (twin A) had a normal heart with a small insignificant VSD. Twin B had a single ventricle, an incompetent A-V valve, stenotic pulmonic valve, ASD, PDA, and congenital heart block. Hemodynamic support of twin B was almost entirely from twin A. The vascular communications between the two consisted of a major connection between the internal mammary arteries and large arterial and venous connections traversing the joined livers. Because of continued deterioration of twin B, separation was undertaken at age 15 days. The separation included dividing the liver and the multiple large vascular connections. Two teams then reconstructed each twin separately. Twin B began showing signs of cardiac decompensation shortly after separation in spite of placement of a pacemaker, pulmonary artery banding, and ligation of the PDA. Cardiac function rapidly deteriorated and she died. Tissue from her chest wall was cryopreserved and placed in the tissue bank. Twin A underwent closure of her abdomen, and received a temporary bovine pericardial patch over the chest defect. She subsequently underwent placement of a graft of twin B's rib cage to bridge the bony chest defect and skin flap closure. She is presently taking a normal diet and thriving at home at age 18 months. The use of cryopreserved tissue from a syngeneic source provides a unique method of reconstruction in this situation.

Abdomen↗
PubMed1995

Metabolic parameter, bleeding, and weight changes in U.S. women using progestin only contraceptives.

Our objective was to determine the effect of progestin-only contraceptives on metabolic parameters, bleeding patterns, and weight changes during the first year of use. Seventy-one women (> 95% Caucasian), who were advised regarding contraception alternatives, self-selected levonorgestrel implants (n = 44), depo-medroxyprogesterone acetate (n = 22), or oral norethindrone (n = 5). One year later, 11 levonorgestrel implant and five depomedroxyprogesterone acetate patients were randomly selected to compare (pre- and post-progestin use) levels of cholesterol, triglycerides, low density lipoprotein (LDL), high density lipoprotein (HDL), very low density lipoprotein (VLDL), apolipoproteins A-1 and B-100, bilirubin, and sex hormone binding globulin. Monthly bleeding and spotting records were kept in each group. Body weights were also monitored in each group. No statistically significant differences in metabolic parameters were found between pre- and post-progestin use in the levonorgestrel implant and depo-medroxyprogesterone acetate groups. Continued bleeding patterns were more prominent in the levonorgestrel implant and oral norethindrone groups than in patients receiving depo-medroxyprogesterone acetate. No significant weight gain was detected in any group. No changes in metabolic parameters or weight were noted over the one year of use of levonorgestrel implants or depo-medroxyprogesterone acetate. Depo-medroxyprogesterone acetate had the highest incidence of amenorrhea.

Administration, Oral↗
PubMed1989

Differentiating pancreatic pseudocyst and pancreatic necrosis using computerized tomography.

Ten per cent of patients with acute pancreatitis will develop pancreatic complications. Differentiating pancreatic pseudocyst formation from pancreatic necrosis may be difficult based on clinical grounds. The purpose of this study was to evaluate the role of computerized tomography in differentiating these processes. A retrospective analysis was performed of 40 patients who developed pancreatic complications following an episode of acute pancreatitis and who subsequently underwent operation for drainage of their pancreatic fluid collections. All 40 patients had abdominal CT scans performed before surgery and the patients were then categorized on the basis of CT findings as having (1) a pseudocyst with a well-defined cyst wall, (2) peripancreatic fluid marked by the absence of a cyst wall, and (3) a combination of a pseudocyst as well as free peripancreatic fluid. Patients with pseudocysts had an average hospital stay of 14 +/- 2 days, a hospital morbidity rate of 16%, and a hospital mortality rate of 0%. In contrast, patients with peripancreatic fluid collections had an average hospital stay of 43 +/- 4 days (p less than 0.01) and hospital morbidity and mortality rates of 74% (p less than 0.01) and 22% (p less than 0.05), respectively. Patients with both pseudocysts and peripancreatic fluid collections behaved in a similar fashion to patients with peripancreatic fluid alone as characterized by a prolonged hospital stay and a high incidence (80%) of postoperative complications. At one year follow-up, 89% of the patients with pseudocysts were asymptomatic, whereas only 13% (p less than 0.01) of patients with peripancreatic fluid were symptom free. These data demonstrate that pseudocyst and peripancreatic fluid collections have markedly different biologic characteristics both in their short-term and long-term behavior. The results suggest that CT scanning can differentiate these processes and may help in directing the appropriate surgical therapy.

Acute Disease↗
PubMed1989

Purine-enriched asanguineous cardioplegia retards adenosine triphosphate degradation during ischemia and improves postischemic ventricular function.

Myocardial dysfunction after induced ischemic arrest is an important problem in cardiac surgery. Adenosine-5'-triphosphate content in myocardial tissue remains depressed for days after ischemia, perhaps because of reperfusion washout of diffusable purine substrates. Left ventricular function is also depressed after ischemia, but its relationship to absolute tissue adenosine triphosphate content is unclear. We tested the hypothesis that arresting hearts with a cardioplegic solution containing adenosine, hypoxanthine, and ribose would result in improved tissue adenosine triphosphate content and left ventricular function after 1 hour of normothermic global ischemia in dogs supported by cardiopulmonary bypass. Animals with ischemic arrest initiated with a crystalloid cardioplegic solution containing adenosine 100 mumol/L, hypoxanthine 100 mumol/L, and ribose 2 mmol/L demonstrated significant improvement (p less than 0.05) during postischemic reperfusion. A significant correlation (p less than 0.05) existed between myocardial adenosine triphosphate content and the recovery of left ventricular function. These experiments demonstrate that an asanguineous cardioplegic solution containing adenosine, hypoxanthine, and ribose maintains myocardial adenosine triphosphate content during ischemia and reperfusion and enhances functional recovery during the postischemic period.

Adenosine↗
PubMed1988

Adenosine stimulates glucose uptake in the isolated rat heart.

Adenosine (Ado) is a potent coronary vasodilator. Recent studies suggest that Ado may also have an important effect on myocardial carbohydrate metabolism. To determine whether Ado has a direct effect on myocardial glucose uptake, a recirculating, constant-flow, isolated rat-heart preparation was used. The hearts were perfused with Krebs-Henseleit buffer solution with an initial glucose concentration of 11 mmol/L. A control group was compared with hearts treated with Ado infusions (50 and 100 micrograms/min) or insulin (100, 200, and 300 microU/ml). In a separate series of experiments, nitroprusside was used to evaluate the effect of a nonspecific coronary vasodilator. The rate of glucose uptake was calculated as the amount of glucose removed from the perfusate normalized for heart weight and time. Developed pressure (DP) was assessed with an intraventricular balloon, and the coronary perfusion pressure (CPP) was monitored. At the end of 1 hour, the hearts were freeze-clamped and adenine nucleotide content was measured with HPLC. Ado treatment increased glucose uptake by 80% and 140%, respectively, at the two infusion rates (p less than 0.001). Myocardial adenosine triphosphate content was 18% and 26% higher in the Ado-treated hearts than in the controls (p less than 0.001). Ado also decreased the mean DP by 30% and 36% (p less than 0.001) and decreased CPP by 10% and 22%, respectively (p less than 0.001). Insulin increased glucose uptake in a similar dose response fashion but had no effect on myocardial nucleotide content, DP, or CPP. Nitroprusside decreased CPP but had no effect on glucose uptake, adenine nucleotide content, or DP. These results suggest that Ado may have a direct effect on glucose uptake independent of its properties as a coronary vasodilator.

Adenosine↗
PubMed1985

Separation of complexes containing protein A and IgG or Fc gamma fragments by high-performance liquid chromatography.

Protein A of Staphylococcus aureus is a bivalent Fc receptor that can form complexes with immunoglobulin G (IgG) or Fc gamma fragments that activate humoral (e.g., complement) and cellular (e.g., lymphocyte) components of the immune system both in vitro and in vivo. To obtain complexes formed between protein A of Staphylococcus aureus (SpA) and rabbit IgG or Fc gamma fragments for purposes of characterizing their compositions and studying their biological activities, we have used high-performance liquid chromatography to separate complexes in 20 min. Complexes were prepared with trace amounts of 125I-SpA and 131I-IgG or 131I-Fc gamma to simplify the analyses. With excess molar amounts of IgG or Fc gamma the complexes have the molecular formulas [(IgG)2SpA]2 or [(Fc gamma)2SpA]2. With excess SpA, complexes corresponding to (IgG)(SpA) or (Fc gamma)(SpA) are formed, perhaps with other complexes that have different ratios of components. Since SpA is a rod-shaped molecule it elutes at a molecular weight corresponding to 240,000 rather than the true value of 42,000. This behavior is reflected in the elution of certain complexes at shorter retention times than expected on the basis of actual molecular weights, and facilitates separation of complexes from free IgG or Fc gamma. The true molecular weights and molecular formulas of complexes isolated by HPLC were verified by ultracentrifugation. This HPLC method was used to study the interconversion and stability of complexes.

Animals↗
PubMed1985

Complexes prepared from protein A and human serum, IgG, or Fc gamma fragments: characterization by immunochemical analysis of ultracentrifugation fractions and studies on their interconversion.

Protein A of Staphylococcus aureus is an Fc receptor for IgG that has been used as a therapeutic reagent to treat cancer in humans and experimental animals. We used ultracentrifugation combined with analysis of isolated fractions by radioimmunoprecipitation and competitive radioimmunoassay with chicken antibodies that bind free protein A or protein A in complexes but do bind free immunoglobulin reagents to localize and characterize the types of complexes formed with different molar ratios of 125I-protein A and human 131I-IgG alone or in serum, and 131I-Fc gamma fragments. This approach offers a distinct advantage over direct counting of radioactivity in the fractions because resolution of complexes and free reagents is much improved. With excess 131I-IgG or 131I-Fc, all the 125I-protein A is present only in complexes that contained 4 molecules of immunoglobulin reagent and 2 molecules of protein A (4:2 complexes), whereas with excess 125I-protein A the stoichiometry of the complexes was 1:1. We have also shown the preformed 4:2 and 1:1 complexes will interconvert in the presence of added excess protein A or IgG, respectively, and that fresh IgG will exchange with IgG or Fc gamma in preformed complexes. Because protein A has been found to elute from an immobilized reagent used in serotherapy of human cancer and is present in a large excess of IgG, the 4:2 complexes may play an active role in the tumoricidal or toxic reactions observed.

Antigen-Antibody Complex↗