Final answer:
Increased levels of inhibin would decrease Sertoli cell activity.
Step-by-step explanation:
Increased levels of inhibin would decrease Sertoli cell activity. Inhibin is released by the Sertoli cells when the sperm count is too high. It inhibits the release of Gonadotropin-releasing hormone (GnRH) and Follicle-stimulating hormone (FSH). This slows down spermatogenesis, reducing testosterone secretion.