Below selected tests of the Diabetes Screen are listed
Permanent jugular vein catheter implants for intravenous substrate infusion
Under surgical anesthesia a silicone catheter is inserted into the left external jugular vein, fixed in position and the sealed catheter end adjusted under the skin. Six to seven days after surgery and when mice have fully recovered, catheters can be used for intravenous substrate infusions.
This test determines the amount of glucose necessary to compensate for raised plasma insulin concentrations without causing hypoglycemia allowing to discriminate whole body and organ-specific insulin sensitivity. By means of a continuous insulin infusion, the plasma insulin concentration is acutely raised in conscious animals and maintained at a high but physiological level for two hours. The resulting decline in plasma glucose concentration is counteracted by a glucose infusion administered at a variable rate. Via repeated plasma glucose concentration measurements and adjustments of the glucose infusion rate euglycemia is maintained. The steady-state glucose infusion rate (GINF) equals whole body glucose utilization and is considered an index of an organism’s insulin sensitivity to exogenous insulin. To assess whole body glucose turnover, a continuous [3-3H]glucose infusion is administered during a two hour basal period and continued throughout the subsequent euglycemic-hyperinsulinemic clamp. All infusions are applied via a permanent jugular catheter. Insulin-stimulated glucose uptake in individual tissues is estimated after intravenous injection of a 2-deoxy-D-[1-14C]glucose bolus under steady-state conditions. Plasma [3-3H]glucose, 3H2O (measurement of whole-body glycolysis rate) and 2-[14C]DG concentrations under basal conditions and during the euglycemic-hyperinsulinemic clamp are measured in deproteinized plasma samples. At the end of the experiment animals are deeply anesthetized and various organs immediately dissected and freeze-clamped in liquid nitrogen. The rate of whole body glucose turnover is calculated as the ratio of the [3-3H]glucose infusion rate and plasma [3-3H]glucose specific activity during “steady-state”. Hepatic [3-3H]glucose production (HGP) is determined by subtracting the “steady-state” glucose infusion rate (GINF) from the rate of whole body glucose turnover. 2-[14C]DG uptake in tissues is calculated from plasma 2-[14C]DG AUC and tissue 2-[14C]DG-6-phosphate content. In general glucose clamps are carried out in male mice as in females insulin-mediated glucose turnover is affected by fluctuations of estradiol and progesterone during the estrous cycle.
This test measures pancreatic β-cell sensitivity in response to physiological elevations in plasma glucose concentrations. By means of a primed, intravenous glucose infusion plasma glucose concentrations are acutely raised above baseline. Via repeated plasma glucose concentration measurements and adjustment of the glucose infusion rate accordingly hyperglycemia is maintained. Insulin, secreted from pancreatic β-cells is quantified in plasma samples and represents β-cell sensitivity to hyperglycemia. Steady state glucose infusion rates can be used to assess peripheral whole body glucose homeostasis.
Compound and drug challenge tests
Tests can be applied to investigate the action of compounds and drugs in treating diabetes and its complications in experimental diabetes mouse models (db/db, New Zealand Obese).
Diet challenge tests
“Tailor-made” experimental diet challenges can help to better understand mechanisms implicated in diabetes pathophysiology. The spectrum ranges from diets high in particular fatty acids capable of inducing non-alcoholic fatty liver disease (NAFLD) accompanied by hepatic insulin resistance to diets inducing, accelerating, or preventing obesity or pancreatic β-cell atrophy.
Morphological islet characterisation
Selected examples for immunohistochemical assays in pancreatic islets are displayed below.
Anti-insulin (red) and anti-glucagon (brown)