Steroid hormone content of the gonads of the tammar wallaby during sexual differentiation

The gonads of the tammar wallaby, Macropus eugenii, are sexually indifferent at birth (Day 0) despite the fact that phenotypic sexual differentiation has already commenced as evidenced by the presence of a scrotum in males and mammary anlagen in females. The seminiferous cords of the testis first become clearly recognizable on Day 2 of pouch life, and ovarian differentiation is recognizable by Day 10. To monitor the endocrine development of the gonads during sexual differentiation of the urogenital tract, we measured the steroid hormone content in 92 pools of gonads from male and female tammar pouch young from the day of birth to 206 days of pouch life. Progesterone, estradiol, and dihydrotestosterone concentrations were low (less than 0.05 ng/mg protein) in both ovaries and testes at all stages examined, and testosterone concentrations were uniformly low in ovaries. Testosterone concentrations in testes were low on Days 0-4, averaging about 0.2 ng/mg protein; they rose by Days 5-10 to an average of 0.9 ng/mg protein, remained elevated until about Day 40, and thereafter fell to values similar to those in the ovaries. The phallus and urogenital sinus were able to convert testosterone to dihydrotestosterone from the earliest stages examined (Days 10 and 11). Thus in the tammar wallaby, as in eutherian mammals, testosterone is the androgen secreted by the developing testis, and dihydrotestosterone is formed in certain androgen target tissues.