Changes in work tolerance associated with metabolic and physiological adjustment to moderate and severe iron deficiency anemia.

The time course of metabolic and physiological adjustment to moderate iron deficiency anemia (MIDA, 8 g Hb/dl) and to severe iron deficiency anemia (SIDA, 4 g Hb/dl) was studied in adult, male Sprague-Dawley rats at 3, 7, 14, 30, 60, 90, 150, and 360 days, respectively. Our previous studies using the same rats used in the present study indicated that bone marrow iron was absent and plasma iron was significantly lower (p less than 0.001) in MIDA and SIDA relative to control. The following results with MIDA and SIDA rats are all expressed relative to control values. Red cell 2,3-diphosphoglycerate ranged from 45 to 146% greater in MIDA over the 360-day period and was 130% greater in SIDA at 30 days. Exhaustive run time consistently averaged 64 +/- 3% (SEM) less in MIDA over the time course and was further lowered to 18% in SIDA at 30 days. Heart rates of MIDA were elevated (p less than 0.05) at 180 days but lower (p less than 0.001) at 360 days in response to exercise. Resting heart rates of MIDA were the same at 180 and 360 days. Heart rates of SIDA were elevated (p less than 0.05) at rest and during exercise at 30 days. Organ weight/body weight changes indicated cardiomegaly in MIDA from 90 to 150 days which reverted to normal at 360 days; splenomegaly in MIDA from 90 to 360 days; and kidney atrophy in MIDA at 60 and 90 days which reverted to normal thereafter; in SIDA cardiomegaly and splenomegaly were present at 30 days. These results indicate that the onset and magnitude of physiological and metabolic adjustments occur in proportion to the severity of the anemia, and despite compensatory adjustments in parameters related to work performance, a new stable, lowered level of work tolerance is reached.