Steroids boost muscles for the long haul

Experiments in mice suggest effects don’t end when doping does

PUMPED UP  Mouse muscles treated with steroids (right) grow bigger than ones in undrugged animals (left). Steroids increase the number of nuclei in a muscle cell, which may help the muscle pump back up long after the steroids are gone. 

J.C. Bruusgaard/ University of Oslo

Steroids may continue to boost muscle-building capacity long after a person stops taking the drugs, a new study of mice suggests. The finding could mean that athletes who cheat by taking anabolic steroids should be suspended from competition for a decade or longer.

The research also suggests that building muscles in youth may have benefits that last into old age.

In the new study, researchers led by Kristian Gundersen, a physiologist at the University of Oslo, tested the effect of steroids on female mice. The team had previously shown that exercise builds new nuclei in muscle cells (SN: 9/11/10, p. 15). Nuclei are the cellular compartments where DNA is stored, and muscle cells typically have multiple nuclei. Increasing the number of nuclei gives muscles the capacity to build more proteins.

Doses of the steroid testosterone caused the mice to add nuclei to their muscles, the researchers report October 28 in the Journal of Physiology. After two weeks of steroid treatment, the muscle cells had up to 66 percent more nuclei per muscle fiber. Mice that didn’t get steroids, but had surgery that cut one muscle to make another work harder, had 51 percent more nuclei in the overworked muscle. Mice that got both steroids and surgery built 92 percent more nuclei in their uncut muscle.

The mice’s muscle cells also bulked up, but eventually shrank back to pre-steroid size after the drugs were stopped. The new nuclei didn’t go away, though, Gundersen’s team found. Steroid-treated muscles kept their ill-gotten nuclei for at least three months, which corresponds to about a decade in humans’ life span. The effect may last even longer, but the researchers did not extend the experiment to find out.

When muscles were worked three months after the steroid treatment stopped, the muscle mass of animals that previously took testosterone bounced back right away, bulking up 31 percent in the first six days. Mice that never took steroids only added about 6 percent to their muscle mass during that time.

“In my career it has been rare to see such clear results,” Gundersen says. “It is more dramatic than I thought it would be.”

Other researchers are also impressed with the results.

“There’s no question it’s very interesting data and it’s very strong,” says Bengt Saltin, a physiologist at the University of Copenhagen. “This should be a hotter topic in muscle research and physiology,” he says. Elderly people often have trouble with muscle wasting, and the new study suggests that working out in young adulthood could help old muscles regain vigor with exercise later.

Lawrence Schwartz, a cell biologist at the University of Massachusetts Amherst, agrees. “The implication is once you have these nuclei, you never lose them.”

Both researchers also say that before antidoping agencies can decide how long cheating athletes should be barred from competition, similar research to see how long steroids exert their influence would need to be done on humans.

“I suspect the basics of muscle physiology are going to be very similar,” Schwartz says of mice and humans. But given the side effects of steroids and the difficulty of studying large samples of muscle in living people without causing harm, “I don’t see any easy, or even an ethical way of doing this in humans.”

Tina Hesman Saey is the senior staff writer and reports on molecular biology. She has a Ph.D. in molecular genetics from Washington University in St. Louis and a master’s degree in science journalism from Boston University.

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