Current concepts of β-endorphin physiology in female reproductive dysfunction

β-Endorphin has a role in the regulation of the normal menstrual cycle and possibly in the onset of puberty. We have reviewed the evidence pointing to an alteration in this neuropeptide that may contribute to the pathogenesis of various reproductive dysfunctions. Elevated or high levels of β-endorphin have been associated with exercise-associated amenorrhea, stress-associated amenorrhea, and polycystic ovarian syndrome (Table 2). Depressed or low levels of β-endorphin have been associated with PMS and menopause. Alterations in the levels of β-endorphin may change the pulsatile release of GnRH via noradrenergic and/or dopaminergic pathways. We have primarily focused on β-endorphin as representative of the endogenous opioid peptides, but other opioid peptides may also contribute to the pathogenesis of various types of reproductive dysfunction. Perhaps it will become possible to characterize and hone our understanding of the function of β-endorphin and the other substances composing the endogenous opioid peptides. A better understanding of their role in physiological as well as pathophysiological processes may allow for the development of rational approaches to the treatment of specific disorders pertaining to reproduction. Many questions remain unanswered. Among the most relevant are: what is the precise mechanism of action by which β-endorphin exerts its influence on pulsatile GnRH release? Is there a functional relationship between CNS and peripheral (serum) levels of β-endorphin? Are the detected changes in β-endorphin levels merely associated, or are they a cause of a particular disorder? Since it took almost 40 years between the time prostaglandins were first discovered and eventual realization of their clinical application, it may take some time before the β-endorphin story is complete.