CORTICOSTEROID SECRETION IN THE MONOTREME TACHYGLOSSUS ACULEATUS

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Abstract
SUMMARY: Corticosteroid secretion and excretion by the Australian monotreme Tachyglossus aculeatus was investigated by assay of peripheral blood, adrenal venous blood, urine and faeces. Free corticosteroids could be demonstrated in only one out of five samples of peripheral whole blood, in which trace amounts of cortisol and corticosterone were detected at concentrations of the order of 0·1–0·2 μg./100 ml. Quantitatively, the major corticosteroid detected in adrenal venous blood of three males and one female was identified as corticosterone, at concentrations of 8–25 μg./100 ml. whole blood. Lesser amounts of cortisol were detected in samples of adrenal venous blood from two males and the female, the ratios 'F:B' being 0·25 and 0·40 in the males, and 0·13 in the female. The highest rate of corticosterone secretion was only 2·6 μg./100 mg. adrenal/hr. or 1·17 μg./kg. body weight/hr. No free or conjugated corticosteroids were detected in either urine or faeces. Zimmermann chromogens were found in both urine and faeces, and total daily excretion varied unpredictably from undetectable levels to a maximum of only 25 μg./kg. body weight/day.