Riggs T R, Wise H D, Motz K L
Am J Physiol. 1978 Sep;235(3):E304-10. doi: 10.1152/ajpendo.1978.235.3.E304.
Diaphragms from rats under 24-h-old did not show the well-known increased transport of alpha-aminoisobutyrate found in older tissues in respone to insulin in vitro. A small effect was apparent by 3 days, and stimulation increased as donor rats aged (up to 4--5 wk). One-day diaphragms also had greater uptake than older tissues, due to both decreased Km and elevated Vmax. The change in insulin sensitivity did not result from alteration in the transport system used by alpha-aminoisobutyrate because uptake showed characteristics of the A system at both 1 day and older. Results suggest instead that the 1-day tissues had been made insulin-resistant by high insulin levels in donor animals. Plasma insulin levels of 1-day-old rats were 5 times those of 5-day animals. Elevating the plasma insulin levels of 5-day or 25- to 35-day rats led to a decreased effectiveness of insulin in vitro in stimulating alpha-aminoisobutyrate transport into their diaphragms. In the older animals, the stimulation was inversely proportional to the plasma insulin level 2 h after insulin injection.
24小时龄以下大鼠的膈肌，在体外对胰岛素刺激的反应中，未表现出老龄组织中常见的α-氨基异丁酸转运增加的现象。3日龄时可见轻微效应，随着供体大鼠年龄增长（至4 - 5周），刺激作用增强。1日龄的膈肌对α-氨基异丁酸的摄取也比老龄组织多，这是由于Km降低和Vmax升高所致。胰岛素敏感性的变化并非源于α-氨基异丁酸所使用的转运系统的改变，因为1日龄及老龄时摄取均表现出A系统的特征。相反，结果表明1日龄组织因供体动物体内高胰岛素水平而产生了胰岛素抵抗。1日龄大鼠的血浆胰岛素水平是5日龄动物的5倍。提高5日龄或25至35日龄大鼠的血浆胰岛素水平，会导致胰岛素在体外刺激α-氨基异丁酸转运至膈肌的有效性降低。在老龄动物中，胰岛素注射后2小时，刺激作用与血浆胰岛素水平呈反比。
