Under normal conditions in the male, GnRH (gonadotropin-releasing hormone) is released in a slow, pulsatile manner, regulating the pituitary hormones FSH and LH. LH and FSH have a regulatory effect on the testis and thus on the release of sex hormones such as testosterone.
Testosterone in turn has a regulatory effect on GnRH, thus closing the hormonal cycle. All hormones must work within a concentration range where they are functional, if their concentrations are both above and below this range fertility can be accepted.
In a man with elevated stress levels, elevated blood concentrations of cortisol (the stress hormone) have been seen. Elevated concentrations of stress hormone interact by altering the frequency of GnRH pulses and thereby dysregulating the other hormones of the hypothalamus-pituitary-testes axis.
As a result, testosterone concentrations in the testis may be reduced, compromising spermatogenesis (the creation of spermatozoa).