Growth hormone influences the content and composition of collagen in the aorta from old rats.

Collagen and elastin are major components of the aortic extracellular matrix and crucial in determining the stiffness of the aorta. We recently showed that growth hormone (GH) changes the mechanical properties, content and composition of aortic collagen from young rats. In the present study, the effect of GH on aorta from old rats was investigated. Old female rats (18(1/2)-20(1/2) months) were injected with either GH (5 mg/kg per day; n=15) or vehicle (n=14) for 80 days. Mechanical and biochemical properties of the thoracic aorta were investigated. Long-term GH injections increased the body weight of female rats by 47% accompanied by a threefold increase in serum IGF-I. The diameter of the aorta was increased by 5%, resulting in a 10% increase in the cross-section of the aortic lumen. Growth hormone increased the content of collagen per sample by 6% and increased the amount of type I collagen relative to type III collagen. No changes in the mechanical properties or elastin content per sample were found. In conclusion, GH induced a substantial growth of old rats. However, although the diameter and the collagen content were increased, the mechanical properties of the aorta were preserved in the GH-injected rats.