3.4.1.1 Beta-endorphin
The qualitative effects of androgens on beta-endorphin concentrations
depend on the region examined. In many regions, particularly in plasma
and pituitary, androgenic activity consistently increases beta-endorphin
concentrations. For instance, castration decreases beta-endorphin in
plasma, whole pituitary, anterior pituitary, and the neurointermediate
lobe of the pituitary (Hong et al., 1982; Petraglia et al., 1982).
Confirming a role for androgens, these effects are partially reversed
following chronic treatment with testosterone (Petraglia et al., 1982).
Similarly, gonadectomized rats exhibit lower beta-endorphin
concentrations in plasma, anterior pituitary, neurointermediate lobe,
and hypothalamus relative to intact rats (Pluchino et al., 2009). The
latter effects are reversed by chronic treatment with testosterone in a
dose-dependent manner, but not by the testosterone metabolite, DHT.
Chronic administration of exogenous androgens to intact male rats also
increases beta-endorphin concentrations. For instance, chronic androgen
treatment with the AAS, boldenone undecylenate,
1-de-hydro-17a-methyltestosterone, nandrolone decanoate, and
testosterone 17b-cypionate increases beta-endorphin in the midline of
thalamus in intact male rats (Harlan et al., 2000). Finally, in intact
male rats, chronic treatment with nandrolone significantly increases
beta-endorphin concentrations in the ventral tegmental area (Johansson
et al., 1997), a region heavily implicated in opioid reinforcement and
addiction (Fields & Margolis, 2015).
Androgens decrease concentrations of beta-endorphin under some, albeit
limited, conditions. For instance, chronic treatment with the exogenous
androgens, boldenone undecylenate, nandrolone decanoate, and
testosterone cypionate, decreases beta-endorphin within the rostral
arcuate nucleus (Menard et al., 1994). Moreover, castration increases
beta-endorphin concentrations in the medial basal hypothalamus, and this
effect is reversed by chronic treatment with testosterone (Wardlaw,
1986). When taken collectively, these latter findings represent
exceptions to the general rule that androgens increase concentrations of
beta-endorphin in both plasma and tissue.