Biological Link Between Pain And Fatigue Discovered

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Biological Link Between Pain And Fatigue Discovered

http://www.sciencedaily.com/releases/2008/04/080407153037.htm

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,

which suggests that they are interacting somehow to protect against

fatigue, " Sluka said. " These differences may help explain some of the

underlying differences we see in chronic pain conditions that include

fatigue with respect to the predominance of women over men. "

The study, which was published in the Feb. 28 issue of the American

Journal of Physiology -- Regulatory, Integrative and Comparative

Physiology, indicates that muscle pain and fatigue are not

independent conditions and may share a common pathway that is

disrupted in chronic muscle pain conditions. The team plans to

continue their studies and investigate whether pain enhances fatigue

more in females than males.

" Our long-term goal is to come up with better treatments for chronic

musculoskeletal pain, " Sluka said. " But the fatigue that is typically

associated with chronic, widespread pain is also a big clinical

problem -- it leaves people unable to work or engage in social

activities. If we could find a way to reduce fatigue, we could really

improve quality of life for these patients. "

In addition to Sluka, the UI research team included Lynn Burnes, a

research assistant and lead author of the study; Kolker; Jing

son; and Roxanne Walder. The study was funded in part by grants

from the National Institute of Arthritis and Musculoskeletal and Skin

Diseases.