Stress and Adrenal Function in The Platypus (Ornithorhynchus anatinus).

Abstract

The platypus is a difficult species to maintain in captivity and very few zoo animals attain a natural lifespan. Although the failure of some individuals to acclimatise to captivity appears to be related to stress there have been few studies on the stress response of this species. Preliminary data, that we presented previously, indicated that platypuses exhibited a marked and rapid adrenal response, with catecholamine concentrations being extremely high within 15 minutes of disturbance. Plasma glucocorticoid concentrations also rose rapidly after animals were entangled in nets. This was accompanied by a rise in free fatty acid (FFA) concentrations but no significant change in plasma glucose levels. The latter indicates that the platypus, like the echidna, is resistant to the glucose mobilising effects of glucocorticoids. This paper presents further data to support the earlier findings. In matched sets of blood samples, from individual animals, glucocorticoid concentrations rose from around 100 nmol/L at 15 minutes after entangled in the net, to 300 nmol/L by 65 minutes after disturbance. Dexamethasone treatment caused a marked decline in plasma glucocorticoids, in comparison to untreated control animals, indicating that negative feedback control of ACTH secretion occurs in the platypus. Further, subsequent treatment with ACTH caused a rise in plasma glucocorticoids in comparison to untreated control animals. These data indicate that while the adrenal response in the platypus is very large its control is similar to most other mammals.