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Voluntary Activity, Cardiovascular and Muscular Responses to Anemia in Rats

Neuromuscular Research Laboratory and Brain Research Institute, University of California, Los Angeles

This study was designed to identify the effects of anemia on voluntary activity and performance on a treadmill, and on selected physiological parameters that are related to work performance. Twenty adult rats were divided equally into a control (C) group that had about 7 ml of blood removed retroorbitally and immediately replaced i.p., six times over a period of 15 weeks; and an anemic (A) group that was bled similarly but reinjected with serum plus physiological saline to replace the blood volume removed. Voluntary activity was significantly less in the A than C group when the hemoglobin (Hb) dropped to less than about 11 g/100 ml. Seventeen weeks after the initial bleeding, a controlled treadmill test was given. Heart rates were significantly higher in A (410 beats/minute) than C group (370 beats/minute) after a 3 minute period of exercise. After an exhaustice run, blood lactate was higher in A than C rats. Mean running time for C rats was 23.3 ± 2.5 and 11.0 ± 1.5 minutes for the A group. Twitch tension (7 Hz) of the gastrocnemius (in situ) was 50% and 30% of resting tension after 5 minutes of stimulation in C and A groups, respectively. No difference in the rate of fall of tension was observed when the muscle was tetanized (150 Hz). These data are demonstrating that exercise places a significantly greater cardiovascular and metabolic stress on anemic than control rats. The significance of this stress is suggested by the low maximal work capacity on the treadmill as well as in the relative fatiguability of in situ stimulated muscles. Because voluntary activity changed within a few days of when Hb was elevated or lowered beyond a critical point of approximately 11.0 g Hb/100 ml, these data suggest that Hb is more critical than iron stores in causing the depressed voluntary activity.

KEY WORDS: • anemia • voluntary activity • muscle fatigue

Manuscript received 15 October 1976.