Abstract
Levels of 4-androstenedione (A), 5α-dihydrotestosterone (DHT) and testosterone (T) in plasma collected from the heart or the jugular vein were measured in 61 male fetal dogs at between 38 and 60 days of gestation and 55 male neonatal dogs at between 0 and 50 days after birth. Testicular descent and histology were investigated after euthanasia of the fetuses and neonates. Although the testis still lay on the caudal ridge of the kidney in the 38- and 40-day-old fetuses, the gonad had slightly migrated from the kidney by 42 days of gestation. The testis approached the internal inguinal ring at Day 0 after birth and had passed through the inguinal canal at Day 5 after birth. The inguinal passage was the active phase of testicular descent. Both testes were drawn into the scrotum after 35 days of age. The number of gonocytes in the semini ferous cords had increased in the 58-day-old fetus, and Leydig cells in the stroma had become obvious because of morphological development and the formation of cell clumps. Plasma A levels in the male fetuses decreased temporarily after birth and plasma DHT increased provisionally at 54 and 58 days of gestation. Plasma T levels in the male neonates increased markedly after birth. These findings suggest that testicular descent in the dog fetus is accelerated by the DHT and T secretory function of the Leydig cells which increased after 54 days of gestation.
