Physiological stress in captive Greater rheas (Rhea americana): Highly sensitive plasma corticosterone response to an ACTH challenge

LÉCHE ALVINA; BUSSO, J.M..; HANSEN, C; NAVARRO J.L.; MARIN R.H.; MARTELLA M. B.

GENERAL AND COMPARATIVE ENDOCRINOLOGY

ACADEMIC PRESS INC ELSEVIER SCIENCE

Año: 2009 vol. 162 p. 188 - 191

0016-6480

Up to the present no studies have been conducted either on baseline concentrations of adrenal hormonesor on hormonal responses to stress in Greater rhea (Rhea americana) and most ratite species. The aims ofthis work were to assess the presence of corticosterone in plasma of Greater rhea, to validate a corticosterone125I-radioimmunoassay for determining corticosterone levels in plasma samples and to study theactivation of the adrenal gland after an adrenocorticotrophic hormone (ACTH) challenge. Six captiveGreater rhea juveniles of 10 months of age received an intravenous ACTH injection. Blood samples weretaken at 0 min (baseline pre-ACTH levels), and post-injection at 15, 30, 60 min and at 24 and 48 h. Thehigh pressure liquid chromatography (HPLC) analysis of pooled plasma showed that corticosterone isthe glucocorticoid found in the plasma of Greater rhea. Biochemical assays of standard validation (e.g.,parallelism, exogenous corticosterone recovery) showed that measurements of corticosterone presentin the plasma of the Greater rhea provided by commercial corticosterone 125I-radioimmunoassay wereaccurate and precise. ACTH challenge induced a more than 40-fold increase in plasma corticosteroneat 60 min post-ACTH (from 4.0 to 166.5 ng/ml, on average). The corticosterone response to ACTH inGreater rhea was higher than is usual in birds, an apparently typical characteristic of ratites.