U. Iowa study finds biological link between pain a...( A recent University of Iowa study re...)

A recent University of Iowa study reveals a biological link between pain and fatigue and may help explain why more women than men are diagnosed with chronic pain and fatigue conditions like fibromyalgia and chronic fatigue syndrome.

Working with mice, the researchers, led by Kathleen Sluka, Ph.D., professor in the Graduate Program in Physical Therapy and Rehabilitation Science in the UI Roy J. and Lucille A. Carver College of Medicine, found that a protein involved in muscle pain works in conjunction with the male hormone testosterone to protect against muscle fatigue.

Chronic pain and fatigue often occur together -- as many as three in four people with chronic, widespread musculoskeletal pain report having fatigue; and as many as 94 percent of people with chronic fatigue syndromes report muscle pain. Women make up the majority of patients with these conditions.

To probe the link between pain and fatigue, and the influence of sex, the UI team compared exercise-induced muscle fatigue in male and female mice with and without ASIC3 -- an acid-activated ion channel protein that the team has shown to be involved in musculoskeletal pain.

A task involving three one-hour runs produced different levels of fatigue in the different groups of mice as measured by the temporary loss of muscle strength caused by the exercise.

Male mice with ASIC3 were less fatigued by the task than female mice. However, male mice without the ASIC3 protein showed levels of fatigue that were similar to the female mice and were greater than for the normal males.

In addition, when female mice with ASIC3 were given testosterone, their muscles became as resistant to fatigue as the normal male mice. In contrast, the muscle strength of female mice without the protein was not boosted by testosterone.

"The differences in fatigue between males and females depends on both the presence of testosterone and the activation of ASIC3 channels,
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