Comparative study on the preventing effects of oral vanadyl sulfate and dietary restriction on the age-related glucose intolerance in rats

Dietary Restriction against Parkinson's Disease: What We Know So Far

Dietary restriction (DR) is defined as a moderate reduction in food intake while avoiding malnutrition. The beneficial effects of DR are being increasingly acknowledged in aging and in a series of age-related neurodegenerative disorders, for example, Parkinson's disease (PD). To date, the pathogenesis of PD remains elusive and there is no cure for it in spite of intensive research over decades. In this review, we summarize the current knowledge on the efficacy of DR on PD, focusing on the underlying mechanisms involving general metabolism, neuroendocrinolgy, neuroinflammation, gut microbiome, and so on. We anticipate that this review will provide future perspectives for PD prevention and treatment.

Effects of long-term cranberry supplementation on endocrine pancreas in aging rats

The effects of long-term cranberry consumption on age-related changes in endocrine pancreas are not fully understood. Here we treated male Fischer 344 rats with either 2% whole cranberry powder supplemented or normal rodent chow from 6 to 22 month old. Both groups displayed an age-related decline in basal plasma insulin concentrations, but this age-related decline was delayed by cranberry. Cranberry supplementation led to increased β-cell glucose responsiveness during the oral glucose tolerance test. Portal insulin concentration was 7.6-fold higher in rats fed cranberry, coupled with improved β-cell function. However, insulin resistance values were similar in both groups. Total β-cell mass and expression of pancreatic and duodenal homeobox 1 and insulin within islets were significantly enhanced in rats fed cranberry relative to controls. Furthermore, cranberry increased insulin release of an insulin-producing β-cell line, revealing its insulinotropic effect. These findings suggest that cranberry is of particular benefit to β-cell function in normal aging rats.

The intravenous glucose tolerance test in cannulated Wistar rats: a robust method for the in vivo assessment of glucose-stimulated insulin secretion

INTRODUCTION

Glucose-stimulated insulin secretion (GSIS) is critical in mammalian fuel homeostasis and is diminished early in the evolution of beta-cell dysfunction, ultimately contributing to the development of Type 2 diabetes. We sought to standardise and validate the intravenous glucose tolerance test (IVGTT), a commonly used technique to assess GSIS, in anaesthetised and conscious cannulated male Han Wistar rats.

METHODS

Male Han Wistar rats were cannulated via the right jugular vein and left carotid artery. Anaesthetised and chronically cannulated conscious models underwent IVGTT using increasing doses of glucose (0.2, 0.5 and 1.0 g glucose/kg LBM) or following pre-treatment with Exendin-4 (EX-4) before receiving a 0.5 g glucose/kg LBM bolus dose. Blood glucose, plasma insulin and plasma C-peptide were measured at time-points throughout the experiments.

RESULTS

Dose-dependent increases in blood glucose, insulin and C-peptide (where measured) were observed following administration of increasing doses of an intravenous glucose bolus in both the anaesthetised and conscious cannulated rats. The 0.5 g glucose/kg LBM bolus resulted in an intermediate response and was used in the second part of the study. EX-4 pre-treatment in combination with glucose resulted in GSIS potentiation, as assessed by plasma insulin measurement alone (anaesthetised model) or insulin and C-peptide measurements (conscious model).

DISCUSSION

The IVGTT was standardised in anaesthetised and conscious cannulated male Han Wistar rats by performing a glucose dose response study and validated by examining GSIS potentiation using EX-4. Based on these results, the 0.5 g glucose/kg LBM bolus dose is recommended as the dose to use to assess GSIS in any standardised screening phase of new compounds with the potential to enhance glucose-sensitive pancreatic function. The experimental conditions described in these studies could be transferred to disease models for more detailed assessment of novel compound efficacy.