The National Institute of Aging has awarded $5 million to a USC-led research team to investigate what happens to muscle in seniors when certain declining hormones are returned to youthful levels.

Fred Sattler, professor of medicine at the Keck School of Medicine of USC, is principal investigator for the four-year study, which will examine how testosterone and growth hormones, commonly dubbed GH or HGH, influence muscle and metabolism in those over age 65.

Levels of these hormones decline as a person ages, just as muscle mass wanes with the passing of years. Researchers believe that restoring hormone levels might improve seniors’ muscle tissue - and quality of life.

“We’d like to see if restoring these hormones to optimal levels can boost muscle proteins and help maintain muscle strength, power and function,” Sattler said.

E. Todd Schroeder, postdoctoral fellow at the Keck School and adjunct assistant professor in the Department of Biokinesiology and Physical Therapy, is a co-investigator and project manager for the study, which involves clinical centers at USC, Harbor-UCLA Medical Center and Tufts University.

Investigators at Washington University in St. Louis will perform several important analytical assays. Stanley P. Azen, Keck School professor of preventive medicine, will oversee the study’s data coordinating center.

Muscle loss with age poses a looming problem. By the year 2030, the number of Americans older than 65 will climb to 70 million. People 85 years or older will make up the fastest-growing segment of the population.

Skeletal muscle mass - all the muscles that enable people to move, lift and push - reportedly declines about 15 percent between the third and eighth decades of life, and as much as 30 percent afterward.

Muscle seems to be lost in certain areas, such as the thighs, that especially can hurt seniors’ ability to walk rapidly, rise from a chair and do other activities necessary to daily living.

Just as seniors lose muscle, their testosterone levels also fall. At least a quarter of men over age 60 reportedly have such low levels of testosterone that they are “hypogonadal,” and most have blood levels that are substantially lower than when they were in their 30s.

Similarly, about 35 percent of men over 60 are GH-deficient. These hormones continue to fall over the rest of a lifetime.

Researchers will sign up three dozen men ages 65 through 90 at each of the three centers for a total of 108 participants in their study.

The men will be assigned randomly into two groups: one in which participants have their testosterone levels restored to those of a young man, and another in which they maintain the typical level of an older man.

Besides testosterone, each participant will receive one of two doses of GH or a placebo.

Testosterone for the study comes in the form of AndroGel, an alcohol-based gel made by Solvay Pharmaceuticals Inc. Participants will administer GH, provided by Genentech Inc., through nightly injection under the skin, just as is done with insulin.

The study will last 16 weeks, with follow-up tests 12 weeks later.

After undergoing a series of initial health assessments, blood tests and body scans, the participants must return to USC’s Health Sciences campus about once a month for evaluations.

All scans, tests and screenings are free of charge.

Researchers will examine everything from how hormones support the development of microscopic muscle fibers to whether both hormones help seniors’ muscles grow more powerful.

The USC investigators also plan to recruit another 36 participants in late 2003 to perform a related study on resistance training.

“This will be unique,” Sattler said. “Nobody has looked at the interactions between exercise and androgen therapy and their effect on strength and function in older people.”

Although the current study is open only to men, researchers are laying groundwork for future similar studies of women.

For information about the study, or for details on enrollment eligibility, call (323) 442-2498.