ABOLISHING INCREASES IN INSULIN SENSITIVITY IN POSTMENOPAUSAL WOMEN

缺乏运动和过量和不适当的热量摄入会刺激内脏肥胖的发展，而内脏肥胖与2型（非胰岛素依赖型）糖尿病、高血压和冠心病（CHD）的风险增加有关。运动和饮食限制都被成功地用作减脂的手段。此外，运动，无论是否减少脂肪，都可以降低患糖尿病、高血压和冠心病的风险，但其效果并不一致。特别是，关于运动强度对胰岛素敏感性、体脂减少或高血压和冠心病风险的影响，目前还没有达成共识。我们的前提是，如果要有效地利用运动来预防或减少不同的健康风险，或作为激素作用机制分析的工具，就需要更好地了解运动强度的剂量依赖性效应。我们两年前开始的初步研究测试了高强度步行运动训练可以增加基础搏动生长激素（GH）分泌的假设。初步结果支持这一假设，但此外还显示，训练强度的增加减弱了通常伴随运动训练的胰岛素敏感性的增加（用胰岛素敏感性的间接测量来评估）。本研究的目标是：(1)在更大的18名受试者组中重复观察到的胰岛素敏感性在高训练强度下的衰减，使用更具体的胰岛素敏感性测试，Bergman频繁采样的静脉葡萄糖耐量试验（FSIVGTT）；(2)确定运动强度对胰岛素敏感性的影响是身体脂肪量和分布变化的结果还是独立的结果；(3)在更大的18名受试者中重复观察到的高强度运动训练15至30周期间搏动GH分泌的增加；(4)收集运动强度对血脂（高密度脂蛋白胆固醇、低密度脂蛋白胆固醇和甘油三酯）的影响的一些初步信息，这些血脂也构成发生冠心病的风险。

Inactivity and excessive and inappropriate caloric intake stimulate development of visceral obesity that is associated with increased risks of type 2 (non-insulin-dependent) diabetes, hypertension, and coronary heart disease (CHD). Both exercise and dietary restriction have been successfully used as a means of body fat loss. In addition, exercise, with or without fat loss, can reduce risks of diabetes, hypertension, and CHD but its effects have not been consistent. In particular, there is little consensus regarding the effects of exercise intensity on either insulin sensitivity, body fat loss, or risks of hypertension and CHD. Our premise is that if exercise is to be used effectively to prevent or reduce different health risks or to be used as a tool in mechanistic analyses of hormone action, a better understanding of dose-dependent effects of exercise intensity is needed. Our pilot study, initiated two years ago, tested the hypothesis that exercise training at high walking intensities could increase basal pulsatile growth hormone (GH) secretion. The preliminary results supported this hypothesis, but in addition revealed that increases in training intensity attenuate increases in insulin sensitivity (assessed with an indirect measure of insulin sensitivity) that usually accompany exercise training. The goals of the present study are to (1) replicate in a larger group of 18 subjects the observed attenuation of insulin sensitivity at high training intensities with the more specific test of insulin sensitivity, Bergman's frequently sampled intravenous glucose tolerance test (FSIVGTT); (2) determine whether the effect of exercise intensity on insulin sensitivity is a consequence of, or independent of, changes in body fat mass and distribution; (3) replicate in a larger group of 18 subjects the observed increases in pulsatile GH secretion between 15 and 30 weeks of exercise training at high training intensities, and (4) collect some preliminary information on the effects of exercise intensity on plasma lipids (HDL-cholesterol , LDL-cholesterol, and triglycerides) which also constitute a risk of developing CHD.