Biosynthesis of Adrenocortical Steroids by Monotremes: Echidna (Tachyglossus Aculeatus) and Platypus (Ornithorhynchus Anatinus)

The secretion of aldosterone and its regulation by ACTH and angiotensin II were investigated in conscious, unrestrained echidnas with chronically implanted jugular catheters. Aldosterone was measured by radioimmunoassay after extraction and isolation by silica gel thin-layer chromatography. The mean concentration of aldosterone in blood plasma of five male and three female echidnas was only 5.4 +/- 1.3 (S.E.M.) pg/ml. During stress (surgery and anaesthesia) the mean concentration increased to 17.6 +/- 3.8 pg/ml. Infusion of beta 1-24 ACTH at a rate of 5 units/kg per h increased the plasma concentration of aldosterone to 53.8 +/- 9.8 pg/ml. Infusion of angiotensin II at rates of 100 and 500 ng/kg per h also increased aldosterone concentration, to 24.1 +/- 8.6 and 35.1 +/- 10.9 pg/ml respectively. Production and metabolic clearance rates were measured by the constant-rate infusion of [3H]aldosterone and found to be 5.0 +/- 2.2 ng/kg per h and 14.3 +/- 1.3 ml/kg per min respectively in the unstimulated state. Production rate was increased approximately sevenfold by the infusion of ACTH at 5 units/kg per h and fourfold and sixfold by infusion of angiotensin II at 100 and 500 ng/kg per h respectively. Metabolic clearance decreased following the infusion of ACTH or angiotensin II. Direct measurement of secretion rate by the collection of adrenal venous blood from three anaesthetized, laparotomized echidnas gave values of 9.4, 15.6 and 8.8 mg/kg per h. It is concluded that the adrenal secretion of aldosterone in the echidna is extremely low compared with that in other mammals but the response to stress, ACTH and angiotensin II indicates the presence of typical mammalian control mechanisms for its secretion.

Section: Discussionsupporting

confidence: 82%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Secretion of Aldosterone in the Monotreme Mammal, Tachyglossus Aculeatus

Sernia¹,

McDonald²

1981

“…Previous workers have shown that cortisol is the major adrenal corticosteroid secreted by marsupials: American opossum (Didelphis virginiana) ; Australian possum (Trichosurus vulpécula) (Weiss & McDonald, 1966 a;Chester Jones, Vinson, Jarre« & Sharman, 1964;Weiss, 1968;Khin Aye Than & McDonald, 1973); wombat (Vombatus hirsutus) (Weiss & McDonald, 1966¿>;Coghlan & Scoggins, 1967a); kangaroo (Macropus giganteus, Megaleia rufus) (Weiss & McDonald, 1967;Coghlan & Scoggins, 1967 a); quokka (Setonix brachyurus) (Ilett, 1969); koala (Phascolarctos cinereus) (Weiss & Richards, 1970) ; native cat (Dasyurus viverrinus) and Tasmanian Devil (Sarcophilus harisii) (Weiss & Richards, 1971) and by one species of monotreme, the platypus (Ornithorhynchus anatinus) (Weiss, 1973). Corticosterone has been shown to be the major corti¬ studying the physiological adaptation of wild mammals to changes in their sodium status.…”

Section: Introductionmentioning

confidence: 99%

Blood Corticosteroids in Australian Marsupial and Placental Mammals and One Monotreme

Oddie¹,

Blaine²,

Bradshaw³

et al. 1976

Peripheral blood corticosteroid levels were determined in nine species of Australian marsupial (Eastern grey kangaroo, black-tailed, Bennett's and pademelon wallabies, quokka, wombat, koala and Western native and tiger cats), one species of monotreme (echidna) and one placental Australian mammal (dingo). Animals were obtained or bled with minimal disturbance and came from areas considered to have adequate sodium content of the vegetation. Aldosterone, corticosterone, cortisol, 11-deoxycorticosterone and 11-deoxycortisol were measured and levels found to be similar to five introduced eutherian species (sheep, cow, dog, fox and man) with the exception of the koala and the wombat. Cortisol was the predominant corticosteroid, except in the koala, which produced corticosterone in relatively the greatest quantity, and the wombat which produced more 11-deoxycortisol. Steroid levels were generally low in the wombat. ACTH administered to the koala changed its pattern of corticosteroid secretion from predominantly corticosterone to cortisol. In the dingo, administration of ACTH caused rises in corticosteroid levels similar to those seen in most other eutherian mammals.

“…The combined weight of the adrenal glands in this monotreme, measured within 24 h of capture, is 257 ±41 mg/kg (Weiss, 1973). The major glucocorti¬ coid in the blood plasma, and in some incubates of adrenocortical tissue, has been identified as cortisone and the plasma total glucocorticoid concentration has been estimated as being 140-150 pg/1 (Weiss, 1973).…”

Section: Introductionmentioning

confidence: 92%

Glucocorticoids in the blood plasma of the platypus Ornithorynchus anatinus

McDonald

Than²,

Evans³

1988

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.