Further studies are needed to examine the effects of regular Isoacteoside exercise training on these inducers in endothelial cells. Although the older increase the risk of cardiovascular disease, the present 
study recruited healthy middle-aged and older subjects. Therefore, it should focus on the effect of exercise training on apelin production in the elderly patient. In conclusion, we investigated the effects of regular aerobic exercise on plasma apelin concentrations in middle-aged and older adults before and after 8-week aerobic exercise training. After the exercise training intervention, plasma apelin levels increased along with plasma NOx levels, whereas arterial stiffness decreased. Additionally, the plasma apelin level was negatively correlated with carotid b-stiffness, and also was positively correlated with the plasma NOx level. Thus, the increase in plasma apelin levels may partly contribute to the improvement in arterial stiffness and NO bioavailability resulting from aerobic exercise training in middleaged and older adults. Collagens are the main structural component of animal tissues and represent about a third of all proteins in the human body. At least twenty eight types of vertebrate collagen are defined, of which type I collagen is most abundant and perhaps best described. Type I collagen molecules 20(S)-Notoginsenoside-R2 consist of three polypeptide a-chains, approximately 1000 residues in length, each with repeating GlyXaa-Yaa primary amino acid sequences folded into the defining triple helical conformation of collagen. Type I collagen is a heterotrimer of two a1 and one a2 chains. Two recent crystallographic studies indicate an a1:a1:a2 registry, with the a2 in the C-terminal trailing position. Type I collagen gene products exhibit clear tissue-specific properties despite having an identical primary sequence in all tissues. Pos ranslational and processing variations in collagen chain biosynthesis are a significant source of these structural and functional differences. Indeed, cross-linking chemistry and pos ranslational variations are distinct between type I collagens from skin, tendon and bone. Furthermore collagen glycosylation and cross-linking properties can vary within the same tissue during growth and development. Collagen a-chains undergo many pos ranslational modifications and processing steps before triple helix formation occurs, including prolyl 4-hydroxylation, lysyl hydroxylation and subsequent glycosylation and prolyl 3-hydroxylation. Upon or shortly after secretion from the cell, the N- and C-propeptides are proteolytically removed and telopeptide domain lysine and hydroxylysine residues are converted to aldehydes by lysyl oxidase in preparation for cross-linking and fibril formation. Interest in the biological significance of collagen pos ranslational modifications has increased in the last decade with new insights from the pathobiology of bri le bone disease. Several recessively inherited forms of osteogenesis imperfecta have recently been shown to result from disruptions to collagen pos ranslational modifications, processing and trafficking. Notably, significant differences in phenotype are observed with seemingly subtle collagen pos ranslational variations. For example, the loss or reduction of triple helical 3-hydroxyproline, triple helical hydroxylysine or telopeptide Hyl can result in osteogenesis imperfecta.