Testosterone the principle male sex hormone is needed for normal production of sperm cells. Testosterone is secreted in testicles. A small amount of this hormone is also secreted by adrenal glands.
The developing sperm cells are supported by Sertoli cells. Sertoli cells are situated within seminiferous tubules of testes. These cells provide nourishment to developing sperms and support them.
The process of spermatogenesis (the process of production of sperms) is extremely sensitive to fluctuations in surrounding environment. The process very quickly varies to fluctuation of hormone concentration and temperature. High concentration of testosterone is required in surrounding area where sperms develop. The supportive sertoli cells maintain the environment needed for development of sperms. These cells produce a binding protein which concentrates testosterone in the surrounding environment where spermatogenesis takes place.
Low levels of testosterone slow down the process of spermatogenesis or sperm production. Hence all measures have to be taken to maintain the normal level of testosterone to increase sperm count and sperm motility.