Changes in myoglobin content of the high altitude acclimatized rat.

A method is described for the assay of myoglobin in all mvoglobin containing tissues of the rat, in particular the heart and diaphragm. Total body myoglobin increased 707~ 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 500/& 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/Ioo gm of body weight, or to 42.3 mg/Ioo 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 el 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 T HERE exists a remarkably varied literature about myoglobin, which when considered with findings in the present study and the modern work on cellular organization suggests a dynamic role of the pigment in muscle function. The possibility that an increased amount of myoglobin is a means of muscle adaptation to high altitude bears importantly on the question of the role of the pigment, and it has stimulated much work involving hypoxic exposure of animals. Although more recent work exists, the review of Millikan is, nevertheless, still pertinent and informative (I). The present study was undertaken in order to clarify the apparently contradictory results of myoglobin changes following hypoxic exposure as studied by Hurtado et al. (2), on the one hand, and by Clark et al. (3), Bowen and Received for publication November 3, 1955. l This investigation was carried out under Contracts NTonr-29504 and Nonr-2223r between the Office of Naval Research and the Univ. of California. Eads (4), Bowen and Poe1 (5) and Poe1 (6), on the other hand. It now seems that the reported differences arose out of failure to obtain the truly acclimatized state in the latter group of studies. In the present study, critical evaluation was made of the factors upon which depends the determination of body myoglobin content. The facilities of the White Mountain Research Station at 12,500 feet altitude have afforded a unique opportunity to study fully acclimatized rats, and rats born and reared at the location. PROCEDURES AND METHODS Three major classes of rats were used in this study, designated SL, P and Fx, all having derived from LongEvans stock at the Berkeley laboratory. Animals maintained and assayed at Berkeley, designated SL, for Berkeley is essentially at sea level, served as the controls for the high altitude groups, P and F2. The P animals were rats taken from Berkeley at body weights between 150 and 190 gm and which were removed to the White Mountain Station at 12,500 feet, where all remained for 23 months before assaying. These animals were designated P, representing the 549 by 10.0.33.3 on July 9, 2017 http://ajple.physiology.org/ D ow nladed fom 550 BURTON E. VAUGHAN AND NELL0 PACE c z z . . l heot cleared ond T.700 ultracentrifuged o heat cleared and dialyzed