Maltin C A, Delday M I, Hay S M, Innes G M, Williams P E
Rowett Research Institute, Bucksburn, Aberdeen.
Br J Nutr. 1990 May;63(3):535-45. doi: 10.1079/bjn19900140.
Twenty-three British Friesian bull calves at approximately 7 d of age were allocated to one of four treatments: controls untreated (five calves), a group (Clen) given 1 mg clenbuterol/kg diet (five calves), a group (GH) given a daily subcutaneous injection of 3.5 mg bovine pituitary growth hormone (GH) (five calves) and a group (Clen + GH) given a combination of clenbuterol as in the Clen group with GH as in the GH group (seven calves). All calves were given milk-substitute at levels adjusted weekly according to metabolic live weight. The animals were slaughtered over the weight range 150-170 kg. Samples of semimembranosus and triceps muscles were excised at slaughter. Treatment with GH produced approximately a threefold increase in mean daily serum GH concentration. Calves given Clen + GH were heaviest at slaughter and the combined treatment produced a significantly higher (P less than 0.01) feed conversion ratio. Administration of clenbuterol either alone or in combination with GH increased the cross-sectional area of both fast twitch glycolytic (FG), and fast twitch oxidative glycolytic (FOG) fibres in both muscles. In contrast GH produced little change in fibre size in semimembranosus muscle, although FOG fibres in triceps were slightly larger than in controls. Neither Clen nor GH resulted in any change in fibre percentage frequency in either muscle. Treatments involving clenbuterol produced a significant decrease in muscle glycogen concentration. Muscles from all three treatment groups tended to show small increases in protein and RNA concentration compared with the controls. Muscles from animals treated with GH alone exhibited an increase in DNA concentration not seen in muscles from the two other treatment groups. Overall, the differential response to the two agents suggested that clenbuterol does not mediate its effects via the GH axis, and that an additive response in terms of protein anabolism may be achieved from the use of a combination of clenbuterol plus GH.
23头约7日龄的英国弗里生公牛犊被分配到四种处理组之一：未处理的对照组（5头犊牛）、给予1毫克克伦特罗/千克日粮的组（Clen组，5头犊牛）、每日皮下注射3.5毫克牛垂体生长激素（GH）的组（GH组，5头犊牛）以及给予与Clen组相同剂量克伦特罗和与GH组相同剂量GH组合的组（Clen + GH组，7头犊牛）。所有犊牛均按代谢活重每周调整水平给予代乳品。这些动物在150 - 170千克体重范围内屠宰。屠宰时切除半膜肌和肱三头肌样本。用GH处理使平均每日血清GH浓度增加了约三倍。给予Clen + GH组的犊牛在屠宰时最重，联合处理产生了显著更高（P小于0.01）的饲料转化率。单独或与GH联合使用克伦特罗均增加了两块肌肉中快肌糖酵解型（FG）和快肌氧化糖酵解型（FOG）纤维的横截面积。相比之下，GH对半膜肌纤维大小影响不大，尽管肱三头肌中的FOG纤维比对照组略大。Clen和GH均未导致任何一块肌肉中纤维百分比频率的变化。涉及克伦特罗的处理使肌肉糖原浓度显著降低。与对照组相比，所有三个处理组的肌肉蛋白质和RNA浓度均有小幅增加。单独用GH处理的动物的肌肉DNA浓度增加，这在其他两个处理组的肌肉中未观察到。总体而言，对这两种药物的不同反应表明，克伦特罗并非通过GH轴介导其作用，并且使用克伦特罗加GH的组合在蛋白质合成代谢方面可能实现相加反应。
