Other factors besides hyperestrogenemia have been invoked
to explain the relative suppression of LH seen in obesity
(28, 40). An increase in endorphins has a negative effect on
the GnRH production by the hypothalamus, and endogenous
opioids may be increased in obesity. Blank et al. (41) compared
the effects of GnRH and naloxone infusion versus
saline injection in five obese and five normal-weight men
aged between 20 and 38 years. At baseline, obese men had
significantly lower T levels than control subjects. After
GnRH infusion, LH levels significantly increased in both
obese and normal-weight men; however, FSH levels increased
only in normal-weight men, denoting a certain level
of pituitary suppression associated with obesity. After infusion
of naloxone, LH levels increased only in obese males
and not in normal-weight men.