[Presence of endogenous inhibitors of the respiratory chain in organs and tissues of rat].

14 organs and tissues of the rat were tested for inhibitors of the respiratory chain. Electron transfer particles (ETP) from beef heart mitochondria served as test object. The respiratory measurements were carried out in the presence of serum albumin to avoid the reversible inhibition by fatty acids. Inhibition of the NADH oxidase system was observed with testicle, ovary, placenta, amnion, mammary gland, sceletal muscle, skin, liver, kidney, spleen, lungs and brain; the succinate oxidase system was inhibited by preparations from testicle, placenta, amnion, mammary gland, sceletal muscle and skin. Moreover, a self-inhibition of the succinate oxidase activity of the homogenates was observed with brain, liver and placenta. The respiration of the homogenates was inhibited by the respiratory inhibitor RF from rabbit reticulocytes in any case tested. With some objects besides inhibitions also stimulatory effects on the respiration of ETP appeared (vesicular gland, sceletal muscle, spleen, lungs). The inhibitory activities of the rat organs and tissues disappeared in most cases by heat treatment (10 min, 60 degrees C). A part of the inhibitors was sensitive against storage as well as freezing and thawing. They might be lipids (e.g. slow irreversible inhibition by fatty acids not relieved by serum albumin) or inhibitory proteins like RF and enzymes (proteinases and phospholipases). A protein nature is likely for the NADH oxidase inhibitors from liver, kidney, lungs, brain, sceletal muscle and placenta as well as for the succinate oxidase inhibitor from testicle. The results presented suggest the universal distribution and action of endogenous respiratory inhibitors. Presumably they occur in all mitochondria-containing cells. Their primary biological importance may be the triggering of the degradation of mitochondria. High inhibitory activities are present in cells with a high rate of renewal of the mitochondria and furthermore in maturation, differentiation and involution processes which are accompanied by a decline of the number of mitochondria.