Detecting Adreno-Cortical Activity in Gorillas: A Comparison of Faecal Glucocorticoid Measures Using RIA Versus EIA

The conservation community is concerned that the remnants of highly endangered Mountain gorilla are being exposed to enormous stressors in their habitat but no assay has been validated to monitor stress markers in their fecal medium. Non specific ICN Corticosterone RIA and Munro Cortisol EIA were validated for measurement of free-ranging Mountain gorilla Faecal Glucocorticoids Metabolites (FGM) to non-invasively detect effect of environmental stressors on the adrenocortical activity in gorillas. Parallelism and quantitative recovery of FGM showed that the RIA and EIA can reliably measure corticoid metabolites in this medium. High Performance Liquid Chromatography confirmed presence of FGM in faecal extracts. Peak immunoreactive metabolites constituting 35.43% of FGM measured by the RIA co-eluted with maximum corticosterone radioactivity, the EIA measured multiple immunoreactive peak metabolites which were less polar than the cortisol, corticosterone and DOC standard hormones. For Lowland gorilla, peak FGM eluted at fractions 27 and 53 under the 100% Isocratic gradient (San Diago protocol), and 20-80% Methanol gradient (National Zoo protocol) respectively; while peak FGM eluted at fraction 8 and 47 in Mountain gorilla under 100% Isocratic and 20-80% Methanol gradients respectively. After injection of Lowland gorilla with long acting Adrenal Cortico-trophic Hormone (ACTH) gel (150U Acthar Gel), urinary cortisol increased by 5-fold (p<0.05) within the first 6 h and then decreased to original values by 24 h. FGM were significantly elevated (p<0.05) between 72 and 96 h (RIA) and between 48 and 120 h (EIA) and there after decreased towards the pre-ACTH levels. Both assays detected a 2-fold increase in FGM 48 h post ACTH. Mean pre-ACTH and post- ACTH FGM amounts measured by RIA were 36 times (p<0.05) more than those measured by the EIA. For field application FGM were measure from three free-ranging Mountain gorilla individuals before and after chasing the gorilla family from fields. Between the 2 nd and 3 rd day of chase, FGM (RIA) increased by 44, 21 and 71% in the silverback, adult female and infant respectively. We conclude that measurement of FGM using ICN RIA and Munro Cortisol EIA offers a practical promise to non-invasively monitor adreno-cortical activity in gorillas.