Concentrations, metabolic clearance rates, production rates and plasma binding of cortisol in Antarctic phocid seals

• Published in: Acta Endocrinologica
• Main Authors: Liggins, Graham C, France, John T, Schneider, Robert C, Knox, Bruce S, Zapol, Warren M
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: Bioscientifica 1993
• Subjects: Endocrinology; General Medicine; Endocrinology, Diabetes and Metabolism; Antarctic; The Antarctic; Weddell; Antarc*; Antarctic Fur Seal; Elephant Seals; Southern Elephant Seals; Weddell Seal
• Online Access: http://dx.doi.org/10.1530/acta.0.1290356; https://eje.bioscientifica.com/view/journals/eje/129/4/acta_129_4_015.xml

We have reported previously that plasma of the Weddell seal, a member of the phocid family, contains a very high concentration of cortisol. The present study was undertaken to determine whether high cortisol levels were common to seals in the Antarctic environment, or to other phocidae, and to determine the mechanism of the hypercortisolaemia. High levels of cortisol (0.82–2.38 μmol/l) were found in 4 phocidae (Weddell, crabeater, leopard and Southern elephant seals), whereas levels in a member of the otariid family (Antarctic fur seal) were similar to human values. Metabolic clearance rates (MCR) and production rates (PR) of cortisol were determined in the field in Weddell (N = 1), crabeater (N= 3) and leopard (N= 3) seals following bolus injections of [ 3 H] cortisol. The MCR and PR did not differ between the three phocids, but whereas the MCR of 410–590 1/day was twice that of human values, the PR of 460–1180 μmol·m −2 ·d −1 was up to 40-fold greater. The binding capacity of corticosteroid-binding globulin (CBG) was equal to or greater than the plasma concentrations of cortisol, resulting in relatively low concentrations of free cortisol. We conclude that hypercortisolaemia is maintained in phocid seals mainly by a high production rate—the highest (corrected for surface area) reported in any species. The relatively low cortisol levels in otariid seals studied in the same environment suggest that the high PR in phocidae is unrelated to the harsh climatic conditions, but may be part of their adaptation for diving to extreme depths. The phocid seals and New World primates have similarly high levels of cortisol and a high PR but CBG in the primates has low binding capacity and affinity and cortisol is mainly free.