Henriksen E J, Munoz K A, Aannestad A T, Tischler M E
Department of Exercise and Sport Sciences, University of Arizona, Tucson 85721.
J Appl Physiol (1985). 1994 Jun;76(6):2814-9. doi: 10.1152/jappl.1994.76.6.2814.
The adaptive responses of myocardial protein metabolism to chronic increases in work load were evaluated in juvenile female Sprague-Dawley rats. Rats were studied under four conditions: normal weight bearing (N), voluntary wheel running (WR) for < or = 4 wk, head-down-tilt suspension for 7 days (HS), or wheel running (2 or 3 wk) followed by 7 days of suspension (WR-HS). WR activity plateaued after 2 wk at 16 km/day and was maintained through week 4. WR did not affect normal whole body growth. Protein metabolism was studied by measuring heart protein content and in vivo fractional rate of protein synthesis with the [3H]phenylalanine "flooding dose" method. Two weeks of WR increased (P < 0.05) absolute heart protein content (22%) and protein synthesis (21%) relative to age-matched N group values. These differences in protein content and synthesis were maintained for > or = 4 wk. Rats failed to gain significant body weight during suspension. Heart protein content increased (P < 0.05) by 12% to 26% as did protein synthesis (14% to 22%) in HS compared with N group. In WR-HS group, cardiac protein content and protein synthesis were maintained at significantly elevated levels. These findings indicate that 1) high-volume WR by young rats provides a convenient noninvasive method for producing rapid and substantial cardiac hypertrophy, which results, at least in part, from enhanced cardiac protein synthesis; and 2) head-down suspension of sedentary juvenile rats leads to increased cardiac protein synthesis, which helps to increase cardiac protein content despite a lack of whole body growth.
在幼年雌性斯普拉格 - 道利大鼠中评估了心肌蛋白代谢对慢性工作负荷增加的适应性反应。在四种条件下对大鼠进行研究：正常负重（N）、自愿轮转跑步（WR）≤4周、头低位倾斜悬吊7天（HS）或轮转跑步（2或3周）后再悬吊7天（WR - HS）。WR活动在2周后达到稳定状态，为16公里/天，并维持到第4周。WR不影响正常的全身生长。通过测量心脏蛋白含量和用[3H]苯丙氨酸“饱和剂量”法测定体内蛋白质合成分数率来研究蛋白质代谢。与年龄匹配的N组相比，2周的WR使绝对心脏蛋白含量增加（P < 0.05）（22%），蛋白质合成增加（21%）。蛋白质含量和合成的这些差异维持≥4周。在悬吊期间大鼠体重未显著增加。与N组相比，HS组心脏蛋白含量增加（P < 0.05）12%至26%，蛋白质合成增加（14%至22%）。在WR - HS组中，心脏蛋白含量和蛋白质合成维持在显著升高的水平。这些发现表明：1）幼鼠进行大量WR提供了一种方便的非侵入性方法来产生快速且显著的心脏肥大，这至少部分是由于心脏蛋白合成增强所致；2）久坐的幼年大鼠头低位悬吊导致心脏蛋白合成增加，尽管缺乏全身生长，但这有助于增加心脏蛋白含量。
