Assessment of urine and fecal testosterone metabolite excretion in Chinchilla lanigera males

Endemic chinchilla (Chinchilla spp.) populations are nearly extinct in the wild (South America). In captive animals (Chinchilla lanigeraand C. brevicaudata), reproduction is characterized by poor fertility and limited by seasonal breeding patterns. Techniques applied for studying male reproductive physiology in these species are often invasive and stressful (i.e. repeated blood sampling for sexual steroids analysis). To evaluate endocrine testicular function, the present experiments were designed to (a) determine the main route of testosterone excretion ( 14 C-testosterone infusion in four males); (b) validate urine and fecal testosterone metabolite measurements (HPLC was used to separate metabolites and immunoreactivity was assessed in all metabolites using a commercial testosterone radioimmunoassay, and parallelism, accuracy and precision tests were conducted to validate the immunoassay); and (c) investigate the biological relevance of the techniques applied (quantification of testosterone metabolite excretion into urine and feces from five males injected with hCG and comparison between 10 males and 10 females). Radiolabelled metabolites of 14 C-testosterone were excreted, 84.7 ± 4.2 % in urine and 15.2 ± 3.9 % in feces. A total of 82.7 ± 4.2% of urinary and 45.7 ± 13.6% of fecal radioactivity was excreted over the first 24 h period post-infusion (metabolite concentration peaked at 8.2 ± 2.5 h and 22.0 ± 7.0 h, respectively). Several urinary and fecal androgen metabolites were separated by HPLC but only fecal metabolites were associated with native testosterone;