A safer method for studying hormone metabolism in an Asian elephant (Elephas maximus): accelerator mass spectrometry

Noninvasive hormone assays provide a way to determine an animal's health or reproductive status without the need for physical or chemical restraint, both of which create unnecessary stress for the animal, and can potentially alter the hormones being measured. Because hormone metabolism is highly species-specific, each assay must be validated for use in the species of interest. Validation of noninvasive steroid hormone assays has traditionally required the administration of relatively high doses of radiolabelled compounds (100 µCi or more of (14)C labeled hormone) to permit subsequent detection of the excreted metabolites in the urine and feces. Accelerator mass spectrometry (AMS) is sensitive to extremely low levels of rare isotopes such as (14)C, and provides a way to validate hormone assays using much lower levels of radioactivity than those traditionally employed. A captive Asian bull elephant was given 1 µCi of (14)C-testosterone intravenously, and an opportunistic urine sample was collected 2 hr after the injection. The sample was separated by HPLC and the (14)C in the fractions was detected by AMS to characterize the metabolites present in the urine. A previously established HPLC protocol was used, which permitted the identification of fractions into which testosterone sulfate, testosterone glucuronide, and the parent compound testosterone elute. Results from this study indicate that the majority of testosterone excreted in the urine of the Asian bull elephant is in the form of testosterone sulfate. A small amount of testosterone glucuronide is also excreted, but there is no parent compound present in the urine at all. These results underscore the need for enzymatic hydrolysis to prepare urine samples for hormone assay measurement. Furthermore, they highlight the importance of proper hormone assay validation in order to ensure accurate measurement of the desired hormone. Although this study demonstrated the utility of AMS for safer validation of noninvasive hormone assays in nondomestic species, this methodology could also be applied to studies of nutrient metabolism and drug pharmakokinetics, both areas in great need of further study in wildlife species.