Insulin is best known as the hormone needed to process sugar, but it has another function, muscle growth, increasing blood flow through muscle tissue, encouraging nutrients to disperse from blood vessels and itself serving as a biochemical signal to boost muscle protein synthesis and cell proliferation. Recently, Dr. Elena Volpi of the University of Texas Medical Branch at Galveston, senior author of a paper on the study published in the September issue of Diabetologia, and colleagues have recognized a new kind of insulin resistance, one to age-related changes in the vascular system, a phenomenon quite different from the insulin resistance seen in diabetes. "These were older subjects with perfect glucose tolerance," Dr. Volpi said. This loss of responsiveness to insulin plays a major role in the loss of physical strength that occurs as people grow older. The researchers also found that by increasing insulin levels above the normal range in elderly test subjects, they can restore the impaired muscle-building process responsible for age-related physical weakness. The UTMB researchers are now testing whether using drugs to dilate muscle blood vessels during insulin exposure can improve muscle growth in older people. "Preliminary data suggest that this treatment may be effective, but these data are not yet published," Dr. Volpi said. "On the other hand, in a paper we published two years ago in Diabetes, we showed that a single bout of aerobic exercise—a staple of diabetes treatment—may also improve muscle growth in response to insulin in older, nondiabetic people." Volpi’s group is now conducting a larger, NIH-funded clinical trial to determine if aerobic exercise and nutritional supplementation for six months can also boost muscle size and function in sedentary but otherwise healthy seniors. UTMB’s Sealy Center on Aging and Claude D. Pepper Older Americans Independence Center are recruiting seniors from the Galveston-Houston area for the study. For more information, call 800-298-7015.
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