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Biomedical subjects

M H Tan

Publications and source records attributed to M H Tan.

At least 127 records · Page 7Linked to original sources
PubMed1979

Correlations between the leukocyte adherence inhibition microassay and in vivo tests of transplantation resistance.

The leukocyte adherence inhibition (LAI) microassay detects tumor-associated antigen(s). Extracts of colon carcinoma (MCA-38 and B16 melanoma tumors, both syngeneic to the C57BL/6J mice) are recognized only by peritoneal cells from mice bearing the corresponding tumor. To ascertain whether this in vitro antigenic recognition correlates with the ability of the host to recognize and reject a tumor in vivo, serial LAI microassays were performed synchronously with experiments designed to test the ability of mice bearing tumors to reject live secondary tumor challenges. Concomitant tumor immunity was present in the MCA-38 tumor-bearing mice on 3 occasions from 5 to 15 days from primary inoculation. In the B16 system, concomitant immunity was present on one occasion 10 days after primary inoculation. These results in turn were paralleled with the specific in vitro recognition of tumor antigens as detected by the LAI microassays. Loss of immunity in the "eclipse" phase of tumor development, as detected by concomitant tumor immunity, was paralleled by nonreactivity of the indicator cells in the LAI microassay.

Adenocarcinoma↗
PubMed1978

The lipoprotein lipase system: new understandings.

Hypertriglyceridemia, a risk factor for premature atherosclerosis, may result from decreased use of plasma triglycerides by tissues. The removal of triglycerides is mediated by the enzyme lipoprotein lipase (LPL). Heparin releases LPL from tissues and post-heparin plasma lipolytic activity (PHLA) has been extensively used to elucidate the mechanism of hypertriglyceridemia in various diseases. There is evidence to show that postheparin plasma contains enzymes other than LPL. Hence data on total PHLA are difficult to interpret. Availability of assays for the LPL component of PHLA has clarified equivocal findings in certain hypertriglyceridemic states. However, the LPL component is also heterogeneous. The LPL "isoenzymes" from various extrahepatic tissues behave differently under various metabolic conditions. Therefore, to understand properly the LPL system it is necessary to study the specific tissue LPL. Furthermore, the serum activator for LPL is now characterized. Its importance is evidenced by the recent discovery of a hypertriglyceridemic patient deficient in this apoprotein.

Adipose Tissue↗
PubMed1978

A model of glucose-insulin homeostasis in man that incorporates the heterogeneous fast pool theory of pancreatic insulin release.

Current physiologic knowledge about glucose-insulin homeostasis in liver, brain, pancreas, kidney, peripheral tissues, and central vascular organs has been synthesized to form a whole-system mathematical model of glucose metabolism in normal, ideal man. In addition to data of other workers, results from more than 100 intravenous glucose tolerance tests, including variable dosage, variable duration of infusion, and double pulse studies, were used to determine model structure and parameters. Model and clinical testing have focused particularly on the fast phase of insulin response to vascular glucose. The model incorporates blood circulation and equilibration of substances between vascular and interstitial spaces, and it assumes constant fractional clearance of insulin by liver and kidney. Studies using a double pulse of glucose suggest that the time derivative of glucose level is not the sole or predominant influence on fast phase insulin release, but that preinfusion glucose level and/or previous glucose exposure of the pancreas are also important. Variable dosage glucose studies suggest that the amount of insulin released during the fast phase rather than the insulin release rate is regulated by the glucose level. A two-pool, heterogeneous threshold mechanism for beta cell response to glucose is presented that is compatible with the clinical results.

Computers↗
PubMed1977

Murine colon adenocarcinoma: syngeneic orthotopic transplantation and subsequent hepatic metastases.

Syngeneic murine colon adenocarcinoma (MCA-38) cells were transplanted in the submucosa of distal colon, proximal colon, cecum, ileum, jejunum, and duodenum of male C57BL/6 mice, with local lymphoid follicles used as points of entry. The tumor grew best at the cecum and led to liver and mesenteric lymph node metastases in 8 and 9 weeks, respectively, after transplantation. Histologically, a local inflammatory reaction involving polymorphonuclear leukocytes was observed within 48-72 hours following transplantation; after this time, the microscopic tumor foci began to grow progressively. Mononuclear lymphoid cells of the gut-associated lymphoid tissue did not infiltrate the progressively growing tumor; however, polymorphonuclear leukocytes were constantly observed at the tumor periphery in the lamina propria. The studies indicated that orthotopic transplantation as a model system can provide a means of examining the role of the local immune response as a focus of host resistance and as a factor in metastatic tumor spread. The findings also suggested the usefulness of this model in immunotherapeutic and chemotherapeutic studies of secondary hepatic disease.

Adenocarcinoma↗
PubMed1977

Serum insulin response to slow-rise glucose infusion in "genetic prediabetics" (offspring of two diabetic parents).

The insulin response to a programed slow-rise glucose infusion designed to mimic the postprandial rise in glucose was studied in five offspring of two diabetic parents (ODP) and seven normal subjects. The ODP had higher mean blood glucose levels towards the end of the infusion and during the postinfusion period. The rates of glucose disappearance calculate during the postinfusion period were comparable in the two groups. Despite the apparent similarity of serum insulin levels of ODP and normal subjects, the amount of insulin secreted per unit of glycemic stimulus was lower in the ODP group. When the glucose infusion test was preceded by an acute load of glucose, similar findings in the insulin secretory dynamics were found in the ODP group. These data suggest that an impairment in insulin secretion exists in ODP when they are challenged by the slow rise of blood glucose achieved by this type of an intravenous glucose infusion.

Adult↗
PubMed1977

The effects of long-term therapy with oral hypoglycemic agents on the oral glucose tolerance test dynamics in male chemical diabetics.

The effect of fixed doses of oral hypoglycemic agents and placebo (diet alone) on the blood glucose, serum insulin, triglyceride, and cholesterol responses during oral glucose tolerance tests done annually for up to four years' follow-up was studied, in a double-blind manner, in five groups of mild male chemical diabetics. The drugs used were chlorpropamide (100 mg. O.D.), tolbutamide (500 mg. b.i.d.), phenformin (50 mg. O.D.), acetohexamide (250 mg. O.D.), and placebo. Each subject was given an individualized diet aimed at attaining and maintaining ideal weight. Comparison by chi-square analysis between the placebo group and each of the drug groups showed (a) no significant differences with regard to the number of subjects with normal glucose tolerance in each of the tests and (b) no change in the insulin secretion dynamics. Comparison between the initial test and each of the subsequent tests within each group showed (a) a greater number of subjects with normal glucose tolerance in the first follow-up test in the chlorpropamide group only, (b) no change in the insulin secretion dynamics except in the chlorpropamide group, where there was an increased insulin/glucose ratio in the first follow-up test, and (c) no change in the fasting serum triglyceride and cholesterol levels.

Acetohexamide↗
PubMed1977

The significance of lipoprotein lipase in rat skeletal muscles.

Lipoprotein lipase was assayed in extracts of acetone-ether powders of rat skeletal muscles. Enzyme activity in soleus had typical characteristics of lipoprotein lipase in other tissues: inhibition by molar NaCl and protamine sulfate and activation by the human apolipoprotein, R-glutamic acid. Activity in muscles with predominantly red fibers (soleus, diaphragm, lateral head of gastrocnemius and anterior band of semitendinosus) was higher than in those with predominantly white fibers (body of gastrocnemius and posterior band of semitendinosus). No effect of a 24 hour fast upon enzyme activity was observed in ten skeletal muscles, but activity decreased substantially in four adipose tissue depots and increased slightly in heart muscle with fasting. Four minutes after intravenous injection of labeled lymph chylomicrons, skeletal muscles with predominantly red fibers incorporated several times more chylomicron triglyceride fatty acids than thos with predominantly white fibers. Estimated lipoprotein lipase activity in total skeletal muscle was about two-thirds that in total adipose tissue of rats fed ad libitum. After a 24 hour fast, total activity in skeletal muscle was about twice that in adipose tissue. These data suggest that a substantial fraction of lipoprotein lipase is in skeletal muscle of rats and that this tissue, especially its red fibers, is an important site of removal of triglycerides from the blood.

Adipose Tissue↗
PubMed1976

Amino acid levels across normal forearm muscle and splanchnic bed after a protein meal.

To characterize further the role of blood cells in amino acid transport, four normal volunteers were asked to ingest 200 g of broiled ground sirloin within a 10-min period. Blood samples from a radial artery, a deep vein draining forearm muscle bed, and a tributary of the hepatic vein were obtained prior to and for 4 hr after the meal and analyzed for various hormones and substrates. At rest, analysis of arterio-deep venous differences across the forearm revealed the blood cell and plasma amino acid compartmentmental contents to be relatively constant except for alanine and glutamine. Whole blood arterio-hepatic venous (A-HV) amino acid differences were not significantly different from zero; however, blood cell A-HV difference analysis revealed a significant release of threonine from the splanchnic bed while plasma A-HV difference analysis revealed modest but significant releases of glutamate and ornithine and uptakes of phenylalanine and histidine. After the ingestion of the meat meal, plasma and blood cell levels of almost all of the measured amino acids increased significantly. Notable exceptions included glycine and alanine, levels of which did not change significantly and glutamine. The arterial blood cell content of the latter amino acid paradoxically decreased while arterial plasma levels increased significantly. Most importantly, large quantities of branched chain amino acids were released from the splanchnic bed and removed by forearm muscle. These data suggest that the blood cells of normal man do actively participate in amino acid transport, and that the magnitude and direction of change induced by the ingestion of a proteins meal varies with the individual amino acid.

Abdomen↗
PubMed1976

Murine colon adenocarcinomas: methods for selective culture in vitro.

Two murine colon adenocarcinoma cell lines were established from primary cultures. The MCA-38 cell line was begun by treatment of the primary culture with trypsin to remove the fibroblastoid elements. The MCA-36 epithelial cells were sensitive to trypsin; therefore, the growth medium of MCA-36 primary cultures was augmented with collagenase to release the tumor-cell elements from the fibroblast network. These tumor elements were dissociated with trypsin and placed in tissue culture. Each cell line was cultured for at least 10 passages in vitro and gave rise to tumors when reimplanted in vivo.

Adenocarcinoma↗
PubMed1975

Serum insulin and growth hormone response patterns in monozygotic twin siblings of patients with juvenile-onset diabetes.

To detect abnormalities in the secretion of insulin and growth hormone in monozygotic twin siblings of patients with juvenile-onset diabetes, their responses during oral, cortisone-primed oral, and intravenous, glucose tolerance tests and intravenous tolbutamide tests were compared to those of matched controls. The twins had higher mean serum insulin levels during all tests, but differences reached statistical significance (P less than 0.02) only in the cortisone-primed test. Growth hormone levels were higher in the twins (P less than 0.04) in the intravenous tolbutamide tolerance test. The frequency of abnormal oral glucose tolerance tests among controls, diabetic monozygotic twins and the offspring of two diabetic parents was also compared. Twins and controls had nearly the same frequency of normal tests; however, the diabetic offspring had a significantly higher (P less than 0.001) prevalence of abnormal tests. These data suggest that magnitudes of environmental and genetic factors operating in monozygotic "pre-diabetic" children of diabetic parents.

Adolescent↗
PubMedDate not supplied

Follow-up intervention: its effect on compliance behavior to a diabetes regimen.

This study tested the hypothesis that follow-up intervention (by telephone calls and home visit) affects compliance in patients with non-insulin-dependent diabetes mellitus (NIDDM). Sixty NIDDM patients were randomly assigned to two groups--a control group, which received the standard protocol (3-day educational program and a review session 1 month after the program); and an intervention group, which received the standard protocol as well as a series of four telephone calls and one home visit by a registered nurse over a 3-month period. Compliance to prescribed regimens was determined by analyzing three sets of data: changes in pre- to poststudy glycosylated hemoglobin (HbA1c) values; changes in pre- to poststudy weight; and frequency with which self-monitoring of blood glucose (SMBG) was practiced. Results showed that SMBG practice was significantly better for the intervention group. No significant differences were seen in poststudy HbA1c values and weight changes between the two groups. Follow-up intervention by telephone calls and home visit can enhance patient compliance to certain aspects of the prescribed diabetes management plan.

Adult↗