If it's been a while since you took seventh-grade sex-ed, then you'll appreciate a quick refresher course. We all know about the penis, but it's nothing more than the means to an end. The real baby-making action takes place in the testes -- the organs that make male reproductive cells, or sperm. And this only because steroids from the hypothalamus and pituitary gland tell the testes to do their stuff.
The stuff begins in the seminiferous tubules, where precursor cells known as spermatogonia develop. These sperm wannabes then move to the epididymis, a structure located behind the testes. There, the cells line up and inch their way through coils and coils of ramen-noodle-like ductwork. As they make the long journey through the epididymis, they mature into the cute little tadpoles we know as sperm. From there, it's a quick jaunt, usually during sexual intimacy, along the vas deferens, to the urethra and then out the penis.
Who knew male reproduction could be so complicated? Luckily, the process provides four pivotal intervention points to foil the sperm-making machinery.
- First, you could manipulate hormones to stop sperm production. If you increase testosterone in a man's bloodstream (usually via intramuscular injections), the brain will stop secreting Gonadotropin-releasing hormone (GnRH), which suppresses levels of luteinizing hormone (LH) and follicle-stimulating hormone (FSH), thus halting sperm production.
- Next, you could target sperm-production sites in the seminiferous tubules. For example, spermatogonia arise from stem cells before undergoing meiosis, a special kind of cell division that results in cells with half the normal number of chromosomes (23 in humans). Drugs could derail either the stem cells or the precursor sperm cells as they undergo meiosis.
- Another option involves hijacking sperm in the epididymis, where the cells learn to swim like Michael Phelps and gather the enzymes necessary to penetrate an awaiting egg. You could introduce a drug that interferes with sperm motility, in essence stripping them of their backstroke. Or you could block enzymes in the sperm head, rendering it incapable of fertilizing an egg.
- Finally, you could let the sperm develop normally but block their exit. Filling the vas deferens with an opaque material or cutting the tube would prevent the sperm from merging with other fluids produced by the seminal vesicles, prostate and Cowper's glands. Men would still produce semen, but it wouldn't contain any egg-seeking missiles.
Over the years, researchers (and tired parents) have tried a variety of contraceptive devices, techniques and therapies that exploit one of these scenarios. Next, we'll look at a few mainstays of male contraception to understand their limitations and why scientists continue to look for a better sperm trap.