LC-MS analysis of androgen metabolites in serum and urine from east African chimpanzees (Pan troglodytes schweinfurthii).

Testosterone regulates a wide variety of behavioral and physiological traits in male vertebrates. It influences reproductive and aggressive behaviors and is used as a marker of gonadal activity. While testosterone is the primary biologically active male gonadal steroid in the blood, it is metabolized into a variety of related steroids when excreted via urine and feces. To monitor endocrinological profiles studies on wild-living animals primarily rely on non-invasively collected samples such as urine or feces. Since a number of androgen metabolites that are found in high concentrations in these matrices do not stem exclusively from gonadal production, but are also produced by the adrenal cortex, the metabolism and excretion pattern of testosterone and its characteristic metabolites have to be investigated. Here, we compare the levels of 11 androgens and their metabolites in serum and urine (after hydrolytic/solvolytic cleavage of conjugates) from female, and intact and castrated male chimpanzees to investigate whether they were of testicular or adrenal origin. For serum, significant differences in concentrations were found only for native testosterone. For urine, testosterone concentrations showed the largest differences between intact and castrated males, and intact males and females, while no differences were seen between females and castrated males. Epitestosterone levels revealed the same pattern. These differences in urinary concentrations could also be seen for 5α-androstane-3α,17β-diol (androstanediol), and less clearly for 5α-dihydrotestosterone (5α-DHT), etiocholanolone, and androsterone. In urine of males, significant correlations were found between the levels of testosterone and 5α-androstane-3α,17β-diol, as well as between testosterone and epitestosterone. Therefore, the clearest urinary markers of gonadal activity in male chimpanzees seems to be testosterone itself.