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Summary. Superoxide dismutase activity was slow throughout the cell cycle of surface cultures of Physarum polycephalum. This activity increased markedly when the organism was induced to spherulate. Glutathione (GSH) and hydrogen peroxide (H202) concentrations changed very little during the cell cycle. During spherulation GSH decreased; H202 and the cyanide-resistant respiration of plasmodial homogenates increased.

A variety of stressful environmental conditions are known to stimulate the activity of the hypothalamic-pituitary-adrenal complex. An increase in the population density of animals in natural as well as in laboratory conditions leads to adrenal hypertrophy, increased secretion of corticosteroids, as well as other responses associated with elevated release of ACTH (1-5). Slices of adrenal glands isolated from animals under situations of social or population density stress show enhanced corticosteroid release (2, 3). ACTH administration in vivo causes an increase in the capacity for 11 @-hydroxylation by adrenal mitochondria in vitro (6, 7). Physiological studies dealing with crowding stress are hampered by the complexities involving quantification of the stressor and adaptive responses of the adrenal in terms of blood corticosterone determinations (8). Since adrenal mitochondrial 1 1 P-hydroxylase activity can serve as an index of ACTH stimulation, measurement of this reaction in vitro offers a means of evaluating a stress response. The objective of the present investigation was to study the effects of various crowding densities in rats on the in vitro capacity of adrenal mitochondria to carry out the 11 P-hydroxylation reaction.Materials and methods. Male Holtzman rats, initial body weight 150-170 g, were housed in wire mesh cages and fed on Purina laboratory chow and tap water ad Zibiturn. The rats were maintained at 22-23" on a 14-hr light/lO-hr dark cycle. The normal control rats were provided 110 cm2 of floor space per rat. For crowding, the animals were housed at 50 or 30 cm2 of floor space per rat. Animals were kept under these con-' Supported in part by a grant (NGL-44-007-006) from NASA. Nomenclature of chemicals for which trivial names or abbreviations are used: deoxycorticosterone , DOC, 2 l-hydroxy-4-pregnene-3,20-dione; corticosterone, B , 11 p, 2 l-dihydroxy-4-pregnene-3,20-dione; NADPH, reduced nicotinamide adenine dinucleotide phosphate.ditions for 3 weeks before adrenals were obtained.Since the hypothesis to be tested pertained to alterations in mitochondrial 11 phydroxylation in response to stressassociated elevation of endogenous ACTH, it was appropriate to validate the experimental procedure by employing hypophysectomized and ACTH-treated rats. Male rats were hypophysectomized through the intraaural approach using a Hoffman-Reiter stereotaxic instrument to position the animal. Adrenal glands were obtained from the hypophysectomized animals and from controls on Days 1, 5 , and 10 following surgery. Exogenous ACTH (2 or 10 IU/rat; ACTHAR, Armour) was injected sc into intact male rats. Control animals were injected with isotonic saline. Adrenal glands were obtained 24 hr following injection. Both the removal of the adrenal glands and the subsequent incubation of mitochondria were carried out at approximately the same time of day.Animals were decapitated, adrenal glands were removed and placed on filter paper moistened with 0.25 M sucrose in a cold chamber. In the hypophysectomized rats, the sella t...