Changes in Myoglobin Content of the High Altitude Acclimatized Rat

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Abstract
A method is described for the assay of myoglobin in all myoglobin containing tissues of the rat, in particular the heart and diaphragm. Total body myoglobin increased 70% above sea level values, both in animals taken from sea level to 12,500 feet and in animals born and reared at 12,500 feet. In comparison with the muscle hemoglobin concentration increase of 50%, the blood hemoglobin concentration increased only 25% above sea level values. Whole body content of myoglobin was determined directly, and this amounted to 17.3 mg/100 gm of body weight, or to 42.3 mg/100 gm of wet muscle. Partition of the body myoglobin among seven muscle groups was ascertained. Heart, diaphragm and the two masseters contain only about 10% of the total myoglobin. Evaluation was made of the factors that have been suggested to explain the disparity in the originally reported myoglobin increases at high altitude of Hurtado et al. and more recent work. It is clear that failure to obtain the increase in the rat is attributable to the use of intermittent rather than continuous high altitude exposure. Evidence for full acclimatization in the animals here used was adduced. The suggestion is made that myoglobin maintains an optimal oxygen gradient between the cell plasma membrane and the mitochondria, and in so doing is involved in dynamic relation to cellular oxidation.