Effects of “crowding” on endocrine function and retention of the digenean parasite Microphallus pygmaeus in male and female albino mice

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Abstract
The effects of housing density on endocrine organ weights and on retention of the parasite Microphallus pygmaeus by male and female mice arc described. A reduction in gonadal function with increasing housing density was found in each sex. Male mice showed clear evidence of greater adrenocortical activity at higher densities but this was not as clearly defined in females. Animals of both sexes showed a decline in relative weights of both thymus and spleen at the highest densities. The number of parasites recovered, a standard time interval after introduction by stomach tube, was increased significantly in both males and females housed at higher densities. The results suggest that a progressive increase in population density in both male and female mice stimulates pituitary-adrenocortical activity and that there is concomitant suppression of gonadal function. The change in susceptibility to the parasites may also be a direct or indirect consequence of the change in pituitary-adrenocortical activity, on immunological responses or intestinal physiology, such as an increase in the duration of exposure to adverse pH values.