Equilibrium distribution of radioxenon in tissue: xenon-hemoglobin association curve

In vitro and in vivo studies were made of the equilibrium distribution of radioxenon in various organs and tissues of the dog and the xenon uptake compared with a water standard. Tissue-blood partition coefficients were calculated. The radioxenon-hemoglobin association curve was determined for dog and human hemoglobin and methemoglobin. The uptake of radioxenon by blood, due in particular to xenon-hemoglobin affinity, was appreciably greater than uptake either by water or by most other body tissues. Fat and brain were notable exceptions. Consequently, tissue-blood partition coefficients were about eight for fat, one for brain, and significantly less than one for other tissues studied. Acceptable accuracy for blood flow determinations with a radioxenon inert gas diffusion method would seem to depend on the use of a partition coefficient correction in turn corrected at least for the existing hemoglobin concentration. The uptake of xenon by hemoglobin had the characteristics of a solubility or a quasi-solubility phenomenon. The problem of the nature of the interaction is apparently not resolved.

Submitted on June 19, 1961

Role of bacteria in the oxidation of myoglobin

The addition to steaks of cell suspensions of a number of aerobic bacteria and of Saccharomyces cerevisiae greatly increased the rate of discoloration. Low inocula resulted in the more rapid appearance of the brown color of metmyoglobin, whereas high cell populations quickly produced the purple color of myoglobin. Sonically treated suspensions of Pseudomonas geniculata produced similar changes in surface color but less rapidly. No such effect was observed with Lactobacillus plantarum.The visible changes in color were found to be associated with the oxygen demand of the surface tissue including, of course, the demand of any contaminating microorganisms. Inhibitors of respiratory activity inhibited the rate of discoloration under normal atmospheric conditions. However, when the oxygen level in the atmosphere was reduced, the inhibitors had no significant effect. In an oxygen-free atmosphere, the steak surfaces were the purple color of myoglobin; at 10 mm oxygen pressure, the pigment was oxidized to metmyoglobin and the surface was brown in color. No bacterial activity was necessary for pigment oxidation under low oxygen pressures. Addition of dilute solutions of glucose oxidase resulted in rapid oxidation of the meat pigment to metmyoglobin both in extracts and on steak surfaces. More concentrated solutions resulted in further oxidation as evidenced by the appearance of a green color. Horseradish extract with a high peroxidase activity added with H(2)O(2) resulted in rapid oxidation of the pigment but neither were very effective alone, although H(2)O(2) did result in a browning reaction in aged steaks. It is concluded that the primary role of the bacteria in meat discoloration is in the reduction of the oxygen tension in the surface tissue. The implications of the data are discussed and a possible mechanism of myoglobin oxidation is proposed.

Transport of Oxygen through Hemoglobin Solutions

An expression is derived for the steady-state diffusion rate of oxygen through a solution or suspension of oxygen-carrying particles. Several special cases of interest are discussed and compared with the data of Hemmingsen and Scholander. Their observed dependence of the rate of specific oxygen transport on pressure and pH is consistent with the present expression.

Effect of short-term vitamin E deficiency on guinea pig skeletal muscle myoglobin

Myoglobin concentration was determined in gastrocnemius and masseter muscles of guinea pigs maintained up to 15 days on vitamin E-deficient and vitamin E-supplemented diets. A statistically significant increase in myoglobin was noted in muscles of animals on the deficient diet for 15 days. That the increase was real and not apparent was attested by studies of total nitrogen, noncollagen nitrogen, percentage of solids and muscle wet weight, all of which were the same in control and experimental muscles. Histological sections and creatine excretion studies confirmed the impression of mild, incipient nutritional dystrophy.