How Thyroid Hormone Controls Baby Testicles and Fertility
Thyroid Hormone Deiodination and Action in the Gonads.
Not medical advice. For informational purposes only. Always consult a healthcare professional. Terms
Your thyroid hormone is like a traffic light for baby testicles: too much stops growth, too little lets cells keep dividing. A special enzyme (DIO3) turns off the hormone locally so testicles grow right. If the hormone gets in too easily (MCT8), testicles get too big. In women, low thyroid signals in the ovary link to lower fertility signs.
Surprising Findings
Hypothyroidism (low thyroid) in baby rats led to larger testicles — the opposite of what most would expect.
People assume low hormone = slow growth, but here, low thyroid = prolonged cell division = bigger organs. It’s a ‘stop signal’ failure, not a ‘go signal’ deficiency.
Practical Takeaways
If you’re struggling with infertility and your thyroid blood tests are ‘normal,’ ask your doctor to check for tissue-level thyroid resistance or receptor expression (if available).
Not medical advice. For informational purposes only. Always consult a healthcare professional. Terms
Your thyroid hormone is like a traffic light for baby testicles: too much stops growth, too little lets cells keep dividing. A special enzyme (DIO3) turns off the hormone locally so testicles grow right. If the hormone gets in too easily (MCT8), testicles get too big. In women, low thyroid signals in the ovary link to lower fertility signs.
Surprising Findings
Hypothyroidism (low thyroid) in baby rats led to larger testicles — the opposite of what most would expect.
People assume low hormone = slow growth, but here, low thyroid = prolonged cell division = bigger organs. It’s a ‘stop signal’ failure, not a ‘go signal’ deficiency.
Practical Takeaways
If you’re struggling with infertility and your thyroid blood tests are ‘normal,’ ask your doctor to check for tissue-level thyroid resistance or receptor expression (if available).
Publication
Journal
Current opinion in endocrine and metabolic research
Year
2018
Authors
Arturo Hernandez
Related Content
Claims (3)
Thyroid hormone doesn’t directly make sex hormones like testosterone or estrogen, but it helps the body’s sex glands work properly so they can produce these hormones at the right levels.
When baby rats don't have a special protein called MCT8 that helps thyroid hormone get into cells, their testicles grow bigger and keep growing longer than normal—suggesting this protein usually helps stop testicles from getting too big too fast.
In mice and rats, a specific protein called THRA is the main way thyroid hormone works in the testes. If this protein is missing or broken, the damage caused by too much thyroid hormone goes away—meaning THRA is needed for the hormone to affect the cells that make sperm and testosterone.