Somebody please explain for me why we have infertility in cases of exogenous androgen intake?
If we give testosterone which is needed for sperm maturation then why they have low sperm count and infertility?
Exogenous androgen administration results in increased testosterone level in the circulation which will send a negative feedback to the pituitary and there will be low LH secretion.
When there's low LH, the Leydig cells are not stimulated to produce testosterone and so the "local" testosterone level will be low and this will cause a failure of sperm maturation.
Also the peripheral high testosterone can be aromatized and such patients may develop peripheral estrogen effects as well.
--Typical USMLE question about a patient taking testosterone will give the following lab info
Low LH, Normal FSH, High testosterone, Low sperm count
--You should differentiate that from gonadal failure in which you have
High LH, High FSH, Low testosterone, Low sperm count (example Klinefilter)
--Also differentiate from secondary hypogonadism in which you have
Low LH, Low FSH, Low testosterone, Low sperm count (example Kallman syndrome)