Alteration of collagen synthesis and cross-link profile by beta-adrenergic agonists

人类医学广泛使用-肾上腺素能激动剂（ß-AA）如盐酸克仑特罗作为支气管扩张剂来控制哮喘和慢性肺阻塞性疾病的症状。长期（大于或等于一天）使用与肌肉细胞中胶原蛋白积累增加有关，并可导致心脏和骨骼肌组织疾病。这不仅是人类医学的问题，也是动物农业的问题，因为在加拿大，ß-AA ractopamine hydrochloride （RAC）和zilpaterol hydrochloride （ZIL）被批准用作生长促进剂和再分配剂，以提高牛的瘦肉产量和饲料效率。RAC和ZIL有可能影响肌内胶原蛋白，这表明它们也可能影响肉类的食用质量，因为胶原蛋白的数量及其成熟的、热稳定的交联的密度与韧性的增加有关。申请人最近的研究表明，在牛日粮中添加RAC并没有增加牛肌肉中的总胶原蛋白，但却降低了热稳定性胶原交联吡啶（PYR）的密度(摩尔（0.23和0.17摩尔PYR/摩尔胶原，对照组与RAC相比，P < 0.001）和每克生肌（2.86和2.60 nmol PYR/g生肌，对照组与RAC相比，P < 0.05）。申请人及其团队的进一步研究表明，植入雌激素-孕激素生长促进剂（HGP）的肉牛也没有改变臀中肌（GM，上里脊）中的总胶原浓度，但确实增加了摩尔（0.38至0.43 mol EC/mol胶原，对照与处理，P < 0.05）和每克生肌（4.34至4.78 nmol/g生肌）上另一种成熟胶原交联埃利希色素原（EC）的浓度。对照组与治疗组比较，P < 0.05)。此外，随着HGP的使用，PYR浓度从0.18 mol PYR/mol胶原增加到0.21 mol PYR/mol胶原（P < 0.1）。这些结果表明，胶原蛋白对熟牛肉韧性的贡献可能随着ß-AA的使用而降低，而随着类固醇生长促进剂的使用而增加。在牛肉工业中广泛使用市售的生长促进物质，尽管它们对体重增加、饲料效率和胴体成分的影响是众所周知的，但它们对肌内胶原蛋白的影响却不为人所知。这些结果首次表明，ß-AA和HGP可以影响肌内成熟胶原交联的密度，改变胶原对熟牛肉韧性的贡献。HGP和ß-AA在骨骼肌胶原中产生不同的结构修饰，表明这些生长促进剂对胶原合成和周转的响应机制明显不同；因此，提出的研究的短期目标是阐明ß-AA和HGP影响胶原交联的生化途径。这些目标是一个长期研究计划的下一个合乎逻辑的步骤，该计划致力于研究控制胶原蛋白合成和交联的机制及其对肉类品质的影响。这项研究是全面了解胶原蛋白合成控制机制的基础，不仅在动物生产中有广泛的应用，而且在人体损伤或疾病治疗过程中预防组织纤维化，并将有助于培养六名高素质人才。

The use of beta-adrenergic agonists (ß-AA) such as clenbuterol as bronchial dilators in human medicine to control the symptoms of asthma and chronic pulmonary obstructive disease is widespread. Long-term (greater than or equal to one day) use is associated with increased accumulation of collagen in muscle cells, and can lead to both cardiac and skeletal muscle tissue diseases. This is a concern not only to human medicine but to animal agriculture as well because the ß-AA ractopamine hydrochloride (RAC) and zilpaterol hydrochloride (ZIL) are approved for use in Canada as growth promotants and re-partitioning agents to increase lean meat yield and feed efficiency in cattle. That RAC and ZIL have the potential to affect intramuscular collagen suggests that they may also affect meat eating quality because the quantity of collagen and the density of its mature, heat-stable crosslinks have been linked to increased toughness. Recent research by the applicant indicated that supplementation of cattle diets with RAC did not increase the total collagen in the muscles of cattle, but did decrease the density of the heat-stable collagen crosslink pyridinoline (PYR) on a molar (0.23 and 0.17 mole PYR/mole collagen, control versus RAC, P < 0.001) and per gram raw muscle (2.86 versus 2.60 nmol PYR/g raw muscle, control versus RAC, P < 0.05) basis. Further research by the applicant and her team showed that the implantation of beef cattle with estrogen-progesterone hormone growth promotants (HGP) also did not change total collagen concentration in the gluteus medius muscle (GM, top sirloin), but it did increase the concentration of another mature collagen crosslink Ehrlich's Chromogen (EC) on a molar (0.38 to 0.43 mol EC/mol collagen, control versus treated, P < 0.05) and per gram raw muscle basis (4.34 to 4.78 nmol/g raw muscle, control versus treated, P < 0.05). Additionally, there was a trend for the concentration of PYR to increase with HGP use from 0.18 (control) to 0.21 mol PYR/mol collagen (P < 0.1). These results suggested that the contribution of collagen to cooked beef toughness may decrease with ß-AA administration but increase with the use of steroidal growth promotants. The use of commercially available growth promoting substances in the beef industry is widespread and although their effects on body weight gain, feed efficiency and carcass composition are well known, their impact on intramuscular collagen is not. These results are the first to indicate that administration of ß-AA and HGP can affect the density of intramuscular mature collagen crosslinks and change the contribution of collagen to cooked beef toughness. That HGP and ß-AA produced different structural modifications in skeletal muscle collagen indicated that the mechanisms of collagen synthesis and turnover in response to these growth promotants were markedly different; consequently, the short term objectives of the proposed research are to elucidate the biochemical pathways by which ß-AA and HGP affect collagen crosslinking. These objectives are the next logical steps in a long term research program devoted to investigating the mechanisms controlling the synthesis and crosslinking of collagen and its impact on meat quality. This research is fundamental to fully understand the control mechanisms of collagen synthesis systemically and will have broad applications not only for animal production but for the prevention of tissue fibrosis during the treatment of human injury or disease and will contribute to the training of six highly qualified personnel.