Leptin is secreted from adipose tissue, and is thought to act as a 'lipostat', signalling the body fat levels to the hypothalamus resulting in adjustments to food intake and energy expenditure to maintain body weight homeostasis. In addition, plasma leptin concentrations have been shown to be related to insulin sensitivity independent of body fat content, suggesting that the hyperleptinemia found in obesity could contribute to the insulin resistance. We investigated the effects of leptin on insulin binding by isolated adipocytes. Adipocytes isolated from Sprague-Dawley rats exhibited a dose-dependent reduction in the uptake of 125I-labelled insulin when incubated with various concentrations of exogenous leptin. For example, addition of 50 nM leptin reduced total insulin binding in isolated adipocytes by 19% (P < 0.05). Analysis of displacement curve binding data suggested that leptin reduced maximal insulin binding in a dose-dependent manner, but had no significant effect on the affinity of insulin for its binding site. We conclude that leptin directly inhibited insulin binding by adipocytes, and the role of leptin in the development of insulin resistance in obese individuals requires further investigation.
Recent studies suggest the glycemic response of different mixed meals cannot be predicted from the glycemic index (GI) of individual carbohydrate foods. Postprandial glucose levels following five different mixed meals in six noninsulin-dependent diabetic volunteers were therefore assessed. Each meal comprised 50% carbohydrate, 30% fat, and 20% protein, varying only in type of carbohydrate. The carbohydrate exchanged in each meal (potato, white bread, rice, spaghetti, or lentils and barley) contributed 37% of total meal calories. The correlation between predicted glucose response and postprandial glucose area was highly significant; estimated meal GI was virtually proportional to the actual mean glycemic response. These results demonstrate that the relative glycemic effects of mixed meals can be predicted from the GI of their carbohydrate components, again stressing the importance of type of carbohydrate in regulating postprandial blood-glucose levels.
It is common for constipation to occur following severe spinal cord injury (SCI). Although a bowel management program including a high fibre diet is an integral part of rehabilitation, 1 the effect of a high fibre diet on large bowel function in SCI has not been examined. The aims of this study were to assess the nutrient intake of SCI patients, to determine baseline transit time, stool weight and evacuation time and to assess the effect of addition of bran on large bowel function. Eleven subjects, aged 32 ± lO.5 years participated in the study. The level of injury ranged from C 4 to Tl 2 ; only one patient had an incomplete injury. Baseline mean energy intake was 7823± 1443 kJ/d, protein intake 93±21 g/d, carbohydrate intake 209 ± 39 g/d and mean dietary fibre intake 25 ± 8 g/d. Mean baseline stool weight was 128 ± 55 g/d and bowel evacuation time was 13 ± 7.4 min/d. Three subjects who consumed < 18 g dietary fibre/d had low stool weights of 60-70 g/d and two had very delayed transit times that were too slow to enable quantitation. Mean mouth to anus transit time was 51.3±31.2 h, mean colonic transit time 28.2±3.5 h, right colonic transit time 5.9±4.5 h, left colonic transit time 14.5 ± 5.2 h and rectosigmoid colonic transit time 7.9 ± 5.6 h. Following the addition of bran, dietary fibre intake significantly increased from 25 g/d to 31 g/d (P
OBJECTIVE: To investigate the effects of leptin administration to Psammomys obesus, a polygenic animal model of obesity and type 2 diabetes mellitus. DESIGN: Longitudinal intervention study utilising three separate leptin treatment protocols lasting 7 ± 14 d. MEASUREMENTS: Body weight and food intake were measured daily, body fat and muscle content were estimated by carcass analysis on completion of the study. Blood glucose, plasma insulin, leptin, triglycerides and cholesterol were measured at baseline and twice each week during the study. RESULTS: Relatively high doses of leptin were required to signi®cantly reduce food intake and body fat content in lean Psammomys obesus, but had no discernible effect on their obese littermates. CONCLUSION: As a species, Psammomys obesus appear to be relatively insensitive to the effects of leptin administration, compared with other rodents. Obese Psammomys obesus are leptin resistant relative to their lean littermates.
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