Distribution of 5 alpha-reductase in the epididymis of the tammar wallaby (Macropus eugenii) and dependence of the epididymis on systemic testosterone and luminal fluids from the testis.

The activity of 5 alpha-reductase was much higher in the caput and corpus epididymidis than in the cauda epididymidis. Orchidectomy caused a reduction in 5 alpha-reductase activity in the caput and corpus epididymidis, and regression of the epithelium and reduction in mass of all regions of the epididymis. Subsequent testosterone therapy caused a substantial increase in amount of epithelium and overall mass of the cauda epididymidis but showed little or no increase in any of the responses measured in the caput and corpus epididymidis. We concluded that the caput and corpus epididymidis of the tammar respond to factors other than testosterone, probably some constituent in the luminal fluid, and therefore are homologous with the initial segments of the epididymis in eutherians.