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.