Glucocorticoids in the blood plasma of the platypus Ornithorynchus anatinus.

Blood samples were obtained from two male and two female platypuses at various times after capture and anaesthesia for other experimental purposes. In samples obtained during ketamine-xylazine or pregnanediol anaesthesia 15-24 h after capture, the concentration of total glucocorticoids, measured as 'cortisol equivalent' in a radioligand assay, was 207-620 nmol/l. In samples taken 14-35 h after injection of dexamethasone (0.2 mg/kg) total glucocorticoid concentration was 79-88 nmol/l. Individual glucocorticoids were isolated on columns of Sephadex LH-20 and measured separately against appropriate standards. In all except two haemolysed samples obtained from a male that died 25 h after capture, the major glucocorticoid behaved as cortisol, contributing 77-94% of the total. The remainder was made up of varying proportions of substances behaving as corticosterone, 11-deoxycortisol and cortisone. In the haemolysed samples from the moribund animal the major reactive substance, contributing 52-54% of the total, behaved as cortisone. The total adrenal gland weight of this animal was 747 mg, compared with 200-286 mg in two others, suggesting preceding exposure to stress. Equilibrium dialysis and polyacrylamide gel electrophoresis (PAGE) revealed no evidence for a transcortin-like glucocorticoid- and progesterone-binding protein in platypus plasma. However, as in the echidna, there was a heat-labile, high-capacity binding system migrating with albumin on PAGE. Glucose was undetectable in the plasma of the moribund animal and only 1.7-2.8 mmol/l in the initial plasma samples from the others. In two animals, injection of glucose i.p. and dexamethasone i.m. was followed by an increase in the plasma concentration of glucose to the range 3.8-9.9 mmol/l and commencement of normal swimming and feeding activity for the next 36-48 h.