Metabolism in vivo of steroids by the canine testes

The formation of testosterone in vivo has been investigated in anesthetized dogs by infusing radioactive steroids via the left spermatic artery and isolating radioactive testosterone in venous blood obtained from the left spermatic vein. The data from such experiments indicate that the formation of 17α-hydroxypregnenolone and the metabolism of this steroid to testosterone is a major route in the biosynthesis in vivo of testosterone from pregnenolone by the canine testis.

• 1.

  1. When an equal amount of [4⁻¹⁴C]progesterone and 17α-hydroxy[7α-³H]pregnenolone were infused at a constant rate by the spermatic artery, the concentration of ³H in isolated spermatic vein testosterone was from 3–8 times that of ¹⁴C.

• 2.

  2. When [7α-³H]prenenolone was infused by the left spermatic artery for 5 min, more [³H]17α-hydroxypregnenolone than [³H]progesterone was found in the left testis at the end of this infusion.

• 3.

  3. The problem of preferred metabolism to testosterone in vivo by testicular tissue is discussed.