Ultrastructural and biochemical characteristics of Leydig cells from newborn androgen-insensitive rats.

Leydig cells of testis of newborn pseudohermaphrodite (tfm) rats have an ultrastructure similar to that of the normal, containing well developed organelles and inclusions. The cytoplasm is filled with smooth endoplasmic reticulum forming a network of interconnected tubules. Lipid droplets are surrounded by cisternae of smooth endoplasmic reticulum and are in close association with pleomorphic mitochondria. Many of the latter are cup-shaped and have tubular cristae and intramitochondrial dense bodies. Essentially, these are characteristics of normal Leydig cells. Accordingly, the production of testosterone by testes from newborn tfm rats is the same as that by testes from normal newborns and adults. However, it is significantly higher than that by testes of tfm adults. Also, the plasma testosterone levels of newborn tfm rats are the same as in the normal newborn, but lower than in normal adults and much lower than in adult tfm animals. Thus, since in the tfm rat the morphology of Leydig cells, androgen production, and maintenance of plasma levels of testosterone are normal in the newborn, but become abnormal with advancing age, it appears that defective androgen action rather than insufficient androgen production is the cause of male pseudohermaphroditism.