This study examined the effects of exercise on glucose metabolism in adipocytes from female rats. Female rats were exercised by swimming six hours per day, five days per week for eight weeks. There was no variation in body weight gain (P > 0.05) between the exercise and control animals through the experimental period. The swimmers' fat cells were smaller (P < 0.05) than those of the sedentary controls of the same age. The rates of glucose oxidation of both C-1 and C-6 glucose were significantly higher (P < 0.05) in the exercise rats' adipocytes at all insulin concentrations. The sedentary control rats' adipocytes showed no significant response at any insulin concentration. Thus, exercise is a significant stimulus to cause increased oxidation rates in the adipocytes from exercising rats. These data also indicate that glucose transport, not defective glucose oxidation, is the limiting mechanism that accounts for the decreased responsiveness of adipocytes from sedentary control animals.

The purpose of this investigation was to determine the relationship between calcium and glucose uptake following muscle contraction with the use of the calcium channel blocker dantrolene. In previous studies an exercise model has been used to investigate the role of calcium during post-exercise glucose uptake. This study utilized electrical stimulation. It has been shown that exercise-induced glucose uptake is calciummediated, but to date no one has shown that glucose transport induced by electrical stimulation is calcium-mediated. Twenty four male Sprague Dawley rats weighing 140 g were sacrificed and their epitrochlearis muscles were removed. Four treatment groups were established: control, muscle incubated in glucose (4mM); insulin, muscles incubated in glucose (4mM) and insulin (1000uU/ml); electrical stimulation, at 50 Hz for two five minute intervals separated by one minute rest periods; insulin (1000uU/ml) and electrical stimulation at 50 Hz for two five minute intervals separated by one minute intervals. Each group consisted of contain 8-10 muscle preparations. Glucose uptake was measured through the use of a double label of radioactive mannitol and 3-O-methylglucose and analyzed using liquid scintillation. This project followed a randomized group design. Treatments were measured with a one way ANOVA. / School of Physical Education

Hypoglycemia is a severe side effect of insulin overdose in the diabetic population and can result in various neurological sequalae including seizures, coma, and brain death. There is still a limited understanding of the generation and propagation of hypoglycemic seizures, which may exacerbate hypoglycemia-induced neuronal damage. Moreover, glucose reperfusion after a period of transient hypoglycemia has been shown to cause neuronal hyperexcitability which can have further damaging effects. Gap junctional communication can be involved in the spread of hypoglycemic injury in two ways: 1) by providing a cytoplasmic continuity in which seizures can easily propagate and 2) by engaging the astrocytic network in metabolic compensation as well as enhancing astrocytic buffering of K+. This study aims to investigate the role that gap junctions play during brain energy deprivation. Results from these experiments show that gap junction blockade can have a neuroprotective role during hypoglycemia and glucose reperfusion.

No description available.

An acute increase in hypothalamic glucose and its downstream metabolite lactate lower glucose production (GP) and plasma glucose (PG) levels in normal rodents. However, the effectiveness of this nutrient-sensing mechanism in metabolic disease is unknown. We assessed the effects of intracerebroventricular (i.c.v.) or intra-hypothalamic glucose and lactate on in vivo glucose kinetics in conscious rats. Study I revealed that i.c.v. lactate lowered PG via a suppression of GP in rodents with uncontrolled diabetes and diet-induced insulin resistance. Study II demonstrated that i.c.v. glucose was ineffective at suppressing GP in uncontrolled diabetic rodents or rodents with a prior 24 h whole-body or hypothalamic hyperglycemic insult. When PG levels per se were normalized in diabetic rodents hypothalamic glucose sensing to lower GP was rescued. As such, sustained hyperglycemia per se impairs hypothalamic glucose effectiveness in diabetes. Further studies are necessary to determine defective mechanisms upstream of lactate metabolism hindering CNS glucose sensing.

An acute increase in hypothalamic glucose and its downstream metabolite lactate lower glucose production (GP) and plasma glucose (PG) levels in normal rodents. However, the effectiveness of this nutrient-sensing mechanism in metabolic disease is unknown. We assessed the effects of intracerebroventricular (i.c.v.) or intra-hypothalamic glucose and lactate on in vivo glucose kinetics in conscious rats. Study I revealed that i.c.v. lactate lowered PG via a suppression of GP in rodents with uncontrolled diabetes and diet-induced insulin resistance. Study II demonstrated that i.c.v. glucose was ineffective at suppressing GP in uncontrolled diabetic rodents or rodents with a prior 24 h whole-body or hypothalamic hyperglycemic insult. When PG levels per se were normalized in diabetic rodents hypothalamic glucose sensing to lower GP was rescued. As such, sustained hyperglycemia per se impairs hypothalamic glucose effectiveness in diabetes. Further studies are necessary to determine defective mechanisms upstream of lactate metabolism hindering CNS glucose sensing.

Graduation date: 1992

Typescript. / Thesis (Ph. D.)--University of Hawaii, 1967. / Bibliography: leaves 96-104. / xi, 104 l illus., tables

The harvesting of immature mammalian oocytes (eggs) and their maturation in a laboratory environment, known as in-vitro maturation (IVM), provides an alternative to the harvesting of mature oocytes for in-vitro fertilisation (IVF) programs. The nutrient environment of an oocyte matured in vitro is known to have a significant effect on its potential to successfully mature, and it is desirable for the in-vitro nutrient environment to mimic the natural environment in vivo. This thesis describes an interaction between mathematical modelling and experimental investigation designed to build upon understanding of the nutrient environment of the oocyte in vivo, which is difficult to determine via experiment alone. A general mathematical model of nutrient transport to the oocyte, through its surrounding cumulus cells is developed. This model is applicable in-vivo and in-vitro across several species and to a number of important nutrients. Nutrient transport in this system - the cumulus-oocyte complex (COC) - is of particular importance, as it is this system that is normally removed for IVM treatments, and its solution under in-vivo conditions allows the nutrient concentration reaching the oocyte to be determined, given a known concentration immediately surrounding the COC. To successfully apply this model, parameters representing the rate of nutrient transport into cells within the COC must be accurately determined. These parameters are determined by a combination of experimental procedures and mathematical modelling in the case of an important nutrient to oocyte development, glucose. This work gives insight into the concentration dependence of glucose uptake into cell types that are important in regulating oocyte development, and to the behaviour of the oocyte itself with regard to glucose uptake. Finally models to describe the transport of two key nutrients, oxygen and glucose, from the vascular system in the ovary, through the ovarian follicle to the oocyte are developed. These make use of experimental results found in the study of glucose transport in the COC, and show that the geometry of the follicle has a significant impact on the nutrient environment of the COC, and hence by inference the nutrient environment of the oocyte. Work discussed in this thesis has been published [31, 156] and submitted for publication [30]. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1374636 / Thesis (Ph.D.) -- University of Adelaide, School of Mathematical Science, 2009

The insulin-dependent uptake of glucose by adipose and muscle tissues is accomplished through the regulated vesicle trafficking of the GLUT4 glucose transporter to the plasma membrane. The distal trafficking events comprising the tethering, docking and fusion of GLUT4 vesicles with the plasma membrane are poorly defined, but represent vital steps in this pathway. This dissertation encompasses a series of complementary studies that have provided new insights into how these events are regulated in the adipocyte. The Sec1p homologue Munc18c, is believed to play a central role in the docking of GLUT4 vesicles by controlling SNARE complex assembly. Munc18c was shown to bind the t-SNARE Syntaxin4 and form a stable complex in vivo. Protein binding studies demonstrated that Munc18c interacts with Syntaxin4 via an evolutionarily conserved N-terminal binding mode and the formation of the Munc18c/Syntaxin4 hetero-dimer was shown to promote SNARE complex assembly. In contrast to previous reports, I propose that Munc18c is positive regulator of SNARE assembly and vesicle docking. The exocyst complex is thought to promote the tethering of exocytic GLUT4 vesicles with the plasma membrane. Yeast two-hybrid screens revealed interactions between the exocyst subunits Sec6 and Exo70 and the SNARE-associated proteins Munc18c and Snapin, respectively. Snapin was subsequently shown to have a novel role in GLUT4 trafficking. These interactions suggest Munc18c and Snapin provide a course for cross-talk between the exocyst complex and the SNAREs to stimulate GLUT4 vesicle tethering and docking. In addition to its interactions with Munc18c and Snapin, the exocyst was also found to interact with the GTP-bound form of RalA, a small GTPase regulated by insulin. RalA was almost exclusively localised to the plasma membrane of the adipocyte and a novel role for the RalA/exocyst interaction in GLUT4 trafficking was demonstrated. Specifically, overexpression of a GTP-deficient RalA mutant significantly inhibited insulin-stimulated GLUT4 appearance on the plasma membrane. In addition to its role in GLUT4 trafficking, a novel role for RalA was demonstrated in insulin release from pancreatic -cells, indicating that RalA may represent a universal component of regulated exocytosis. It is becoming increasingly apparent that vesicle trafficking events from yeast to mammals rely on similar protein complexes which communicate through multiple protein interactions, ensuring vesicle transport is highly coupled. Similarly, the Munc18c studies demonstrate that while mammalian cells have evolved to fulfil specialised functions throughout the body, some proteins appear to have retained the biochemical properties of their ancestors, emphasing the importance of this family of proteins throughout eukaryotic vesicle transport. In contrast, proteins such as RalA have evolved only in higher eukaryotes and appear to play a universal role in vesicle transport despite vast differences in the specialised functioning of mammalian cells.