Lewis M I, LoRusso T J, Fournier M
Division of Pulmonary/Critical Care Medicine, Cedars-Sinai Medical Center, University of California Los Angeles School of Medicine, 90048, USA.
J Appl Physiol (1985). 1997 Apr;82(4):1064-70. doi: 10.1152/jappl.1997.82.4.1064.
Young growing animals appear to have significantly reduced "nutritional to short periods of unstressed starvation compared with adults, with resultant growth arrest and/or atrophy of diaphragm (Dia) muscle fibers. The aim of this study was to assess in an adolescent rat model of acute nutritional deprivation (ND; 72 h) the impact of insulin-like growth factor I (IGF-I), with or without added growth hormone (GH), on the cross-sectional areas (CSA) of individual Dia muscle fibers. Five groups were studied: 1) control (Ctr); 2) ND; 3) ND given IGF-I (ND/IGF-I); 4) ND given GH (ND/GH); and 5) ND given a combination of IGF-I and GH (ND/IGF-I/GH). IGF-I was given by a subcutaneously implanted osmotic minipump (200 microg/day), whereas GH was administered twice daily by a subcutaneous injection (250 microg every 12 h). Isometric contractile and fatigue properties of the Dia were determined in vitro. Forces were normalized for muscle CSA (i.e., specific force). Dia fiber type proportions were determined histochemically, and fiber CSA was quantified by using a computer-based image-processing system. Total serum IGF-I concentrations were significantly reduced in ND and ND/GH animals, compared with Ctr, and elevated in the groups receiving IGF-I. The provision of growth factors did not alter the contractile or fatigue properties of ND animals. Dia fiber type proportions were similar among the groups. In ND animals, there was a significant reduction in the CSA of types I, IIa, IIx, and IIc Dia fibers compared with Ctr. The administration of IGF-I alone or in combination with GH to ND animals significantly diminished the reduction in Dia fiber size. GH alone had no effect on Dia fiber size in ND animals. We conclude that with acute ND the peripheral resistance to the action of GH appears to be bypassed by the administration of IGF-I alone or in combination with GH.
与成年动物相比，幼年生长中的动物在短期无应激饥饿期间的营养状况似乎显著降低，导致膈肌（Dia）肌纤维生长停滞和/或萎缩。本研究的目的是在急性营养剥夺（ND；72小时）的青春期大鼠模型中，评估胰岛素样生长因子I（IGF-I）单独或联合生长激素（GH）对单个Dia肌纤维横截面积（CSA）的影响。研究了五组：1）对照组（Ctr）；2）ND组；3）给予IGF-I的ND组（ND/IGF-I）；4）给予GH的ND组（ND/GH）；5）给予IGF-I和GH组合的ND组（ND/IGF-I/GH）。IGF-I通过皮下植入渗透微型泵给药（200微克/天），而GH通过皮下注射每日两次给药（每12小时250微克）。在体外测定Dia的等长收缩和疲劳特性。将力归一化为肌肉CSA（即比力）。通过组织化学方法确定Dia纤维类型比例，并使用基于计算机的图像处理系统对纤维CSA进行量化。与Ctr组相比，ND组和ND/GH组动物的血清总IGF-I浓度显著降低，而接受IGF-I的组中浓度升高。生长因子的提供并未改变ND组动物的收缩或疲劳特性。各组之间的Dia纤维类型比例相似。与Ctr组相比，ND组动物的I型、IIa型、IIx型和IIc型Dia纤维CSA显著降低。单独给予IGF-I或与GH联合给予ND组动物可显著减少Dia纤维大小的降低。单独给予GH对ND组动物的Dia纤维大小没有影响。我们得出结论，在急性ND情况下，单独给予IGF-I或与GH联合使用似乎可以绕过GH作用的外周阻力。
