Vilma Lauris

Localized Intraperitoneal Action of Insulin on Rat Diaphragm and Epididymal Adipose Tissue in Vivo

1. The intraperitoneal injection of 100 μU. of insulin together with a tracer amount of glucose-U-C-14, also injected imraperitoneally, resulted over a period of two hours in a three- to fivefold increase in the incorporation of labeled glucose carbon into the glycogen of diaphragm-or epididymal adipose tissue. When the dose of insulin injected was 10,000 μU., the incorporation of glucose carbon into diaphragm was increased twenty-five- to fiftyfold, and that into epididymal fat glycogen ten- to twentyfold. These doses of insulin injected intraperitoneally were without effect upon tissues not in direct contact with the peritoneal cavity, such as heart muscle, trapezius muscle, and subscapular brown fat, while incorporation of labeled glucose into liver was either unaffected or decreased. These results were qualitatively and quantitatively similar, whether the trace amount of labeled glucose was injected intraperitoneally or intravenously. 2. When the same amounts of insulin were injected intravenously instead of intraperitoneally, together with a Jrace amount of labeled glucose, the pattern of tissue responsiveness was totally different, a small effect upon glucose carbon incorporation into glycogen being observed in only two tissues, the rhythmically contracting diaphragm and heart muscle tissues. 3. When the animals were fasted prior to the intraperitoneal injections of glucose without or with insulin, the responsiveness to insulin of diaphragm muscle was either unchanged or increased, while the response of epididymal adipose tissue to insulin decreased, this decrease being quite marked after a seventy-two-hour period of fasting. 4. These results obtained in vivo tend to support the hypothesis of the importance of insulin “binding” to tissues as a factor controlling the responsiveness of individual tissues to insulin. The results also indicate that in vivo rat diaphragm muscle is at least as sensitive to insulin as rat epididymal adipose tissue, if not more so.

Hepatic Glucose Phosphotransferases Variations Among Species

Glucokinase activity (ATP :D-glucose-6-phosphotransferase, E.C. 2.7.1.2) was assayed in various species, including man (Homo sapiens). Low or absent activities were found in the toadfish (Opsanus tau) cat (Felis domesticus), guinea pig (Cavia porcellus), calf (Bos taurus), and man, and higher activities in the bullfrog (Rana catesbeiana), dog (Canis familiaris), rabbit (Oryctolagus cuniculus), mouse (Mus musculus), rat (Rattus norwegicus), and sand rat (Psammomys obesus). Fasted mice and dogs failed to show a decrease in activity. Sand rats with spontaneous diabetes or rendered diabetic by diet also failed to show a reduction in activity. The role of the enzyme in the regulation of blood glucose concentration remains speculative.

Monolayer culture of a human pancreatic beta-cell adenoma

Abstract Monolayer cultures were prepared from a human beta-cell adenoma by dissociating the cells with a trypsin-collagenase solution. Cultures were grown in medium 199 containing 10% fetal bovine serum and 300 mg 100 ml glucose. They were maintained for a total of 2 mo and subcultured three times during this period. Insulin release from the primary cultures during the initial 24 days declined from approximately 150 to 40 mU per culture per 2 days, and then stabilized at this level prior to subculture on day 34. Subcultures became rapidly overgrown with fibroblastoid cells; after two subcultures, insulin release averaged approximately 1.5 mU per culture per 2 days. Reducing the glucose concentration in the medium from 300-100 mg 100 ml produced only a 7% reduction in insulin release, which conceivably helps to explain the high fasting insulin-to-glucose ratios observed in patients with these tumors. These data confirm that cell cultures derived from such tumors offer a unique model for studying human beta cells.

Studies on experimental diabetes in the Wellesley hybrid mouse. II. Serum insulin levels and response of peripheral tissues.

SummaryA hybrid of C3Hf and I strains of mice (the “Wellesley” mouse) results in an animal with a predisposition to diabetes mellitus. In this study it was found that animals that developed the diabetic syndrome had elevated levels of immunoreactive insulin in their serum, and peripheral tissues thatin vitro were less responsive to insulin. Dietary restriction prevented the diabetes from occurring as well as maintaining insulin sensitivity in peripheral tissue.RésuméLhybride F1 produit par le croisement des souches de souris C3Hf et I (souris de Wellesley) est prédisposé au diabète. Dans cette étude nous avons observé que les animaux devenus diabétiques avaient des taux élevés dinsuline immunoréactive sérique et que leurs tissus périphériques étaient moins sensibles à laction de linsulinein vitro. Un régime hypocalorique a pu prévenir lapparition du diabète et maintenir une sensibilité normale à linsuline.ZusammenfassungDie Kreuzung von C3Hf und I Mäusestämmen ergibt ein F1 Hybrid (die “Wellesley” Maus) mit Veranlagung für Diabetes mellitus. Bei der Untersuchung dieser Tiere wurde festgestellt, daß solche, bei denen das diabetische Syndrom sich entwickelt hatte, erhöhte Spiegel von immunreaktivem Insulin im Serum aufwiesen, und daß ihre peripheren Gewebein vitro weniger empfindlich auf Insulin reagierten. Diät-beschränkung verhinderte das Auftreten von Diabetes und bewahrte die Insulinempfindlichkeit der peripheren Gewebe.

Studies of insulin release and rat pancreatic islet metabolism with diastereomers of D-glucose

Studies of insulin release with diastereomers and other analogues of D-glucose demonstrated that only sugars which undergo oxidation to CO2 stimulated insulin release by the pancreatic islet. None of the non-metabolizable diastereomers of glucose stimulated insulin release in the presence of a sub-stimulatory concentration of glucose for fuel. Although 5.5 mM glucose formed 77% as much CO2 as 16.7 mM mannose and twice that of 16.7 mM fructose, 5.5 mM glucose did not stimulate insulin release whereas 16.7 mM mannose and fructose did stimulate insulin release. These results indicate that the important stimulus for glucose-induced insulin release involves metabolism of glucose, but that the stimulus does not involve solely a fuel function of glucose.

Assay of serum insulin and insulin-like activity on adipose tissue and muscle in vivo☆

Sera from 4 normal subjects were analyzed for insulin and insulin-like activity by immunoassay, adipose tissue bioassay and a combined in vivo bioassay using C14 glucose incorporation into muscle and adipose tissue glycogen and adipose tissue fatty acids. Marked individual differences were noted between the values for serum insulin or ILA obtained by each assay, although each individual exhibited rather constant values.