Biomedical subjects

E A Pomfret

Publications and source records attributed to E A Pomfret.

27 records · Page 2Linked to original sources

PubMed1989

Measurement of choline and choline metabolite concentrations using high-pressure liquid chromatography and gas chromatography-mass spectrometry.

We have developed a reproducible and sensitive procedure for the isolation and measurement of choline, phosphocholine, glycerophosphocholine, phosphatidylcholine, lysophosphatidylcholine and acetylcholine in a single 100-mg sample of biological tissue. Tissues were spiked with 14C-methyl- and 2H-methyl- or 15N-choline labeled internal standards for each compound. They were extracted with chloroform/methanol/water and the aqueous and organic phases were dried. The organic phase was resuspended in chloroform/methanol (1/1, v/v) and an aliquot was applied to a silica-gel thin-layer chromatography plate. The plate was developed in chloroform/methanol/water (65/30/4, v/v). Segments which cochromatographed with external standards of phosphatidylcholine and lysophosphatidylcholine were stained, scraped, and hydrolyzed in 6 M methanolic-HCl at 80 degrees C for 60 min, liberating free choline. The aqueous phase was resuspended in methanol/water and injected onto a silica HPLC column. Choline and its metabolites were eluted using a binary nonlinear gradient of acetonitrile/ethanol/acetic acid/1 M ammonium acetate/water/0.1 M sodium phosphate (800/68/2/3/127/10, v/v changing to 400/68/44/88/400/10, v/v). Peaks were detected with an on-line radiometric detector, collected, and dried under vacuum. Each choline ester was digested in 6 M HCl at 80 degrees C to form choline. Choline was then converted to the propionyl ester and demethylated with sodium benzenethiolate. This volatile derivative was then isolated using gas chromatography and measured with a mass selective detector. Deuterated internal standards were used to correct for variations in recovery. Choline, glycerophosphocholine, phosphocholine, phosphatidylcholine, lysophosphatidylcholine, and acetylcholine were measured in rat liver, heart, muscle, kidney, plasma, red blood cells, and brain and in human plasma.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗

PubMed1988

Rat and human mammary tissue can synthesize choline moiety via the methylation of phosphatidylethanolamine.

The normal mammal requires large amounts of choline for maintenance and growth of tissue mass. Since milk, the only food for neonates, has many-fold higher free choline concentration than does maternal plasma, it is possible that mammary gland can synthesize choline molecules. The only known mammalian pathway for the synthesis de novo of choline molecules is catalysed by phosphatidylethanolamine N-methyltransferase (PeMT), which synthesizes phosphatidylcholine (PtdCho) via sequential methylation of phosphatidylethanolamine (PtdEtn) using S-adenosylmethionine (AdoMet) as a methyl donor. We identified PeMT activity in rat mammary tissue, and differences in affinities for substrate, as well as in activities as a function of pH, suggest that at least two distinct enzyme activities are involved [i.e. one catalysing the methylation of PtdEtn to form phosphatidyl-N-methylethanolamine (PtdMeEtn) and the other catalysing the methylation of PtdMeEtn and phosphatidyl-NN-dimethylethanolamine (PtdMe2Etn) to form PtdMe2Etn and PtdCho, respectively]. The relationships between AdoMet concentrations and PtdCho formation from endogenous PtdEtn in rat mammary homogenate were complex: a sigmoidal component (with a Hill coefficient of 2.2), requiring 55 microM-AdoMet for half saturation (Vmax. = 9 pmol/h per mg of protein), and a high affinity component (Kapparent = 8.7 microM and Vmax. = 3.8 pmol/h per mg of protein) were identified. When exogenous PtdMe2Etn was added as substrate, PtdCho formation exhibited Michaelis-Menten kinetics for AdoMet, and its affinity for AdoMet was high (Kapparent = 9 microM, Vmax. = 85 pmol/h per mg of protein). In the presence of endogenous substrates, the rates of PeMT-catalysed PtdCho formation within homogenates of rat mammary tissue were similar in tissue from lactating and non-lactating animals. When exogenous PtdMe2Etn was added to homogenates of rat mammary tissue, tissue from lactating rats made twice as much PtdCho as did tissue from non-lactating rats. Isolated mammary epithelial cells also exhibited PeMT activity; the rate of formation of PtdCho was much greater in intact versus broken cells. We also identified PeMT activity in homogenates of mammary tissue from non-lactating humans. The rate of PtdCho formation was of similar magnitude to that seen in rat tissue. This evidence supports the hypothesis that some of the choline found in milk could have been synthesized de novo in the mammary gland.

Animals↗

PubMed1988

Uptake of choline by rat mammary-gland epithelial cells.

The neonatal mammal requires especially large amounts of choline to sustain growth. Much of this choline is derived from the newborn's only source of food, milk. The concentration of choline in rat milk [182 +/- 24 microM (S.E.M.)] was much higher than that in maternal serum (11.6 +/- 0.9 microM), suggesting that a mechanism capable of concentrating choline into milk must exist. We characterized choline uptake by mammary epithelial cells (the site of milk production) of the lactating rat. We observed two uptake processes, one saturable and obeying Michaelis-Menten kinetics, and the other non-saturable and linear. At physiological blood choline concentrations, the saturable component of choline uptake predominated. The saturable component had Kapp. = 35 +/- 16 microM, and Vmax. = 1.24 +/- 0.19 nmol/h per mg of protein. Saturable uptake of choline was inhibited by hemicholinium-3. Ca2+ was required for uptake, but Mg2+ was not. Replacement Na+ with K+, Li+ or sucrose inhibited transport. Ouabain did not inhibit choline uptake. Choline concentration in epithelial cells was 67.7 +/- 1.9 nmol/g wet wt. at the start of incubation at 37 degrees C and rose to 80.9 +/- 6.5 nmol/g wet wt. over 30 min. Much of the choline accumulated by the mammary gland (in the presence of endogenous concentrations of choline) remained in the form of choline (50 +/- 1.2%), phosphatidylcholine (12 +/- 2.3%), lysophosphatidylcholine (0.1 +/- 0.03%), betaine (7 +/- 0.3% and phosphocholine (6 +/- 0.5%). In addition, we isolated 25 +/- 1.2% of choline-derived radiolabel in an unidentified compound.

2,4-Dinitrophenol↗

PubMed1988

Fewer metabolites of dietary choline reach the blood of rats after treatment with lithium.

Choline is an important precursor for the biosynthesis of acetylcholine, phosphatidylcholine and sphingomyelin. It is also a major source of labile methyl groups. Lithium is an important component of the treatment of bipolar affective illness, and it inhibits choline transport across membranes. We studied the effect of lithium treatment upon the appearance in blood, liver and intestine of metabolites formed from dietary choline. Rats were treated for 9 days with 2 mEq/kg lithium carbonate or water. Animals were fasted overnight, and on the 10th day were fed with a solution containing radiolabeled choline chloride. The lithium-treated groups also received 2.0 mEq/kg lithium as part of this solution. After an oral dose of 1 ml of a 1 mM choline solution, the lithium-treated animals had significantly lower levels of choline-derived radiolabel in blood than did controls at 30, 60, 120, and 180 minutes (47% (+/- 5%; SEM), 51% (+/- 7%), 59% (+/- 4%) and 74% (+/- 9%), respectively). We observed similar decreases of the accumulation in blood, at 180 minutes after the dose, of choline-derived radiolabel when choline was administered at lower or higher concentrations. After an oral treatment containing 0.1, 1 or 10 mM choline, lithium treated animals accumulated 69% (+/- 6%; SEM), 66% (+/- 11%) and 72% (+/- 7%) as much radiolabel in serum as did controls. Most of the radiolabel found in blood at 180 minutes was in metabolites of choline which are formed within liver (betaine and phosphatidylcholine). The diminished accumulation of radiolabel in serum after lithium treatment was not due to increased accumulation of label by erythrocytes, liver or gut wall. We suggest that lithium influences the release by liver of betaine and phosphatidylcholine.

Animals↗

PubMed1987

Dose-response relations in urinary excretion of trimethylselenonium in the rat.

75Se-labeled selenite was administered to fasting rats by orogastric intubation (1.5-3000 micrograms/kg body wt). Urine was collected and characterized for total radioactivity as well as for radiolabeled trimethylselenonium (TMSe). At lower doses of selenite (up to 500 micrograms/kg body wt), 30% of the administered dose was excreted. At higher doses of selenite, fractional urine excretion decreased as a function of the dose. The observed decrease in fractional urine excretion was not caused by changes in the absorption of the administered radiolabel. There was a direct relationship between the amount of the administered dose of selenite (up to 1500 micrograms/kg body wt) and the proportion of urinary [75Se] excreted as TMSe. Pretreatment with seleno compounds (10 or 100 micrograms Se/kg body wt as selenite, or selenomethionine) for 35 d before a challenge dose of [75Se]selenite did not influence the excretion of total [75Se] or of [75Se]TMSe in urine. Ingestion of a choline-deficient diet, which should deplete the availability of methyl groups, did not have any effect on excretion of total [75Se] or of [75Se]TMSe in urine after a challenge dose of [75Se]selenite (500 micrograms/kg body wt). The data presented here permit the following conclusions: 1) Production of TMSe is dose dependent, 2) production of TMSe from a single acute dose does not depend on the history of selenium intake and 3) rats fed a methyl-deficient diet are able to eliminate Se via formation of TMSe.

Animals↗

PubMed1985

Early peritoneal mesothelioma: a treatable malignancy.

37 patients with malignant peritoneal mesothelioma were studied to assess the efficacy of combined therapy. 14 patients presented after 1982. Of 6 patients treated intensively, all remain alive with no evidence of disease by computed tomographic scan at 9-36 months. Of 8 patients treated palliatively, 5 are dead. (5 had stable disease, 1 has progressed despite all treatment, and 2 were not treated.) Survival of the intensively treated group is significantly better than that of other stage I patients in this series. Patients under 40 had a significantly better survival rate than older patients.

Adolescent↗

PubMed1983

Peritoneal mesothelioma: natural history and response to chemotherapy.

Twenty-three patients with malignant peritoneal mesothelioma seen at the Dana Farber Cancer Institute and the University of Maryland Cancer Center from 1968 to 1982 were studied to assess the natural history of the disease and the efficacy of current treatment. Asbestos exposure was reported by 57%. Of 18 patients receiving a doxorubicin-containing regimen, 14 had measurable or evaluable disease. One complete response, four partial responses and one regression (in a patient with evaluable but not measurable disease) were observed, ranging in duration from 6 to 36 months. A single patient remains disease free for more than 36 months after subsequent radiotherapy. Significant clotting abnormalities (including disseminated intravascular coagulation, massive thrombosis, fatal pulmonary emboli, Coombs-positive hemolytic anemia, and phlebitis) occurred in 22% of the patients. Trends toward decreased survival were observed for smokers, patients presenting with ascites, and those with stage II-IV disease.

Adult↗

PubMedDate not supplied

Liver regeneration after living adult right lobe transplantation.

BACKGROUND: The purpose of this study was to describe liver regeneration in patients undergoing living-adult liver transplantation. METHODS: This prospective study included 10 donors and eight recipients who had a total of 65 computed tomographic (CT) scans. All patients had preoperative CT ( n = 18), and follow-up CT scans ( n = 47) were obtained for up to 14 months after transplantation. Liver and spleen volumes were measured by hand tracing each organ on the axial portal venous phase images. RESULTS: Both donors and recipients showed immediate increases in liver volume. However, liver regeneration was significantly faster and reached a higher peak in recipients than in donors. Splenic volume in donors demonstrated an initial increase followed by a decline, reaching the preoperative volume after 1 year. Splenic volume in recipients demonstrated immediate decline postoperatively. CONCLUSION: Restoration of liver volume occurred rapidly after transplantation, but followed different patterns in donors and recipients. Deviation from these patterns warrants further investigation.

Adult↗

PubMedDate not supplied

Early postoperative glucose control predicts nosocomial infection rate in diabetic patients.

OBJECTIVES: To determined the relationship between perioperative glucose control and postoperative nosocomial infection rate is 100 consecutive diabetic patients undergoing elective surgery. DESIGN AND PATIENTS: One hundred initially uninfected diabetic patients undergoing elective surgery were prospectively monitored for perioperative glucose control and postoperative nosocomial infection rate. Glucose control was determined by the attending surgeon or diabetologist. SETTING: A large tertiary care hospital that serves as the in-patient facility for a local diabetes center. MAIN OUTCOME MEASURES: All patients were screened for infection preoperatively. Only initially uninfected patients were enrolled, and all patients received perioperative antibiotic coverage. Perioperative glucose control and postoperative nosocomial infection rate were monitored prospectively. APACHE II scores were determined on all patients. Patients were stratified into two groups: those with relatively "good" perioperative glucose control (all values < or = 220 mg/dL) and those with "poor" control (at least one value > 220 mg/dL). Contingency tables were generated, comparing nosocomial infection rates vs perioperative glucose control. Correlation coefficients between APACHE II score and maximum and mean glucose values were also determined. RESULTS: A serum glucose > 220 mg/dL on postoperative day one (POD 1) was a sensitive (87.5%) but relatively nonspecific (33.3%) predictor of the later development of postoperative nosocomial infection. In patients with hyperglycemia (> 220 mg/dL) on POD 1, the infection rate was 2.7 times that observed (31.3% vs 11.5%) in diabetic patients with all serum glucose values < 220 mg/dL. When minor infection of the urinary tract was excluded, the relative risk for "serious" postoperative infection increased to 5.7 when any POD 1 blood glucose level was > 220 mg/dL. On the basis of correlation coefficients between serum glucose values and APACHE II score, only 18% of the variance in the highest serum glucose could be explained by disease severity alone. CONCLUSIONS: We conclude that diabetic patients undergoing major cardiovascular or abdominal surgery have an increased risk of infection that is further exacerbated by early postoperative hyperglycemia. The high rate of nosocomial infection observed in diabetic patients with poor glucose control suggests that hyperglycemia itself may be an independent risk factor for the development of infection. Efforts to improve perioperative glucose homeostasis in diabetic patients may reduce the incidence of nosocomial infection and thereby improve outcome.

APACHE↗