Abstract
In order to quantify serum cortisol levels in the killer whale Orcinus orca and the bottlenose dolphin Tursiops truncatus, we have established a specific radioimmunoassay (RIA) system. Two kinds of antisera against cortisol (i. e., cortisol-3-(O-carboxymethyl)-oxime-BSA (FKA404) and cortisol-21-succinil-BSA (FKA402)) were used for RIA. High performance liquid chromatography/RIA analysis of serum extract has revealed that FKA404 reacts more specifically with cortisol in the sera without remarkable crossreaction with other corticoids.
The cortisol RIA system using FKA404 as an antiserum was validated. Intra and inter assay coefficient of variation were 1.9% and 3.2%, respectively. The minimum detectable quantity of cortisol was 0.052ng/ml. The competition curves for serum samples of the two cetacean species were parallel to the standard curve. These results indicate that this system is suitable for the measurement of cortisol in the killer whale and the bottlenose dolphin.
Serum cortisol levels (mean±SE) measured by the RIA with FKA404 was 3.8±1.8ng/ml in bottlenose dolphins. In killer whales, serum cortisol levels in the morning were significantly higher (2.5±0.8ng/ml) than those in the evening (1.5±0.5ng/ml). This result in killer whales coincided with studies in diurnal terrestrial mammals including humans.
