Adrenocortical functions in marsupials

McDonald, I. R.

doi:10.1007/978-1-349-02721-7_21

Cited by 17 publications

(19 citation statements)

References 57 publications

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“…The dose of dexamethasone chosen was inter¬ mediate to the highest (4 mg/kg) and lowest (27 pg/kg) dose known to cause suppression of stress-induced increases in the concentration of plasma glucocor¬ ticoid 10-24 h later in the rat (Sirritt & Cohen, Kramer et al 1981) and man (Jones, 1979). The dose of ACTH was based on previous experience with a closely related species Antechinus stuartii which, like other marsupial species so far investigated, is less sensitive than eutherian mammals to the glucocorticoid-stimulating action of ß-ACTH(l-24) (Bradley, 1977;McDonald, 1977). The timing of these injections relative to the time of blood sampling was determined and later validated by experiments on the laboratory-held animals, as described in Results.…”

Section: Methodsmentioning

confidence: 99%

Failure of glucocorticoid feedback in males of a population of small marsupials (Antechinus swainsonii) during the period of mating

McDonald¹,

Lee²,

Than³

et al. 1986

Journal of Endocrinology

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In an investigation of the factors leading to the increase in the concentration of plasma free glucocorticoid, which results in immunosuppression and death after mating of all males in natural populations of a small shrew-like marsupial, the dusky antechinus (Antechinus swainsonii), the integrity of the glucocorticoid feedback control of the concentration of plasma cortisol was examined by use of dexamethasone-suppression tests. Injection of 0.2 mg dexamethasone/kg i.m. caused a marked fall in the concentration of plasma cortisol 17 h later, approximately 2 months and 2 weeks before the annual mating period in mid-July. However, the same dose had no significant effect on the increased concentration of plasma cortisol characteristic of the mid- to late July mating period. Injection of 100 i.u. ACTH/kg i.m. caused a significant increase in the concentration of plasma cortisol 6-7 h later on all occasions, indicating that the responsiveness of the adrenal cortex to ACTH did not change. Pretreatment with dexamethasone had no effect on the ACTH-stimulated cortisol concentration, ruling out a possible direct effect of dexamethasone on adrenocortical secretion in this species. Dexamethasone also reduced the concentration of plasma testosterone when the level was low, before the mating period, but not when the level was high, at the beginning of the mating period. It is concluded that, in association with a rapid increase in the concentration of plasma testosterone, an increase in aggression and intense mating activity, glucocorticoid feedback control of ACTH secretion is impaired.(ABSTRACT TRUNCATED AT 250 WORDS)

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Section: Methodsmentioning

confidence: 99%

Failure of glucocorticoid feedback in males of a population of small marsupials (Antechinus swainsonii) during the period of mating

McDonald¹,

Lee²,

Than³

et al. 1986

Journal of Endocrinology

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“…In common with most other marsupials, the total corticosteroid concentration in the peripheral plasma of quokkas, as measured by radioligand assay without chromatography, is low when compared with most eutherian mammals (see McDonald, 1977). Chromatography on the Sephadex LH-20 columns indicated that the major contributor to the total cortico¬ steroid concentration was usually cortisol, although corticosterone could contribute more than 50%, and relatively minor amounts of 11-deoxycortisol were also present.…”

Section: Discussionmentioning

confidence: 99%

PLASMA CORTICOSTEROIDS AND THE EFFECT OF ADRENOCORTICOTROPHIN IN A MACROPODID MARSUPIAL (SETONIX BRACHYURUS, QUOY & GAIMARD)

McDonald¹,

Bradshaw²

1977

Journal of Endocrinology

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The total corticosteroid concentrations in the peripheral plasma of unanaesthetized, undisturbed quokkas were 0\m=.\75\ m=+-\ 0\m=.\10 (s.e.m.) and 0\m=.\93\ m=+-\ 0\m=.\14\g=m\g/100ml in male and female quokkas respectively. Repeated sampling for periods of 36\p=n-\49h disclosed irregular fluctuations over the range 0\ m=. \ 4\ p=n-\ 5\ m=. \ 0\ g=m\ g/ 100ml, but no evidence for a regular periodicity. The major corticosteroid was usually cortisol but corticosterone contributed 25\p=n-\50% of the total unstimulated corticosteroid concentration. Relatively minor concentrations of 11-deoxycortisol were detected.Constant-rate i.v. infusion of ACTH caused a significant increase in the concentration of total corticosteroids in the plasma; this increase was detectable at a dose of 0\m=.\05i.u. ACTH/kg/h, and rose to approximately 15 times the control value at a dose of 2\m=.\0 i.u./kg/h. This increase was due mainly to a change in the concentration of cortisol. Synthetic (\ g=b\ 1\ p=n-\ 24) and porcine ACTH were equipotent. The sensitivity of the quokka to ACTH was approximately one-tenth that of another marsupial (Trichosurus vulpecula) or 1/160 that of man.Moderate disturbance increased the concentration of corticosteroids in the plasma to the same level as that caused by infusion of 0\m=.\1i.u. ACTH/kg/h, the increase being mainly in the cortisol fraction. High-affinity binding of cortisol and corticosterone by plasma proteins was demonstrated. The maximum binding capacities for cortisol were 3\m=.\89\ m=+-\ 0\m=.\5and 3\m=.\02\ m=+-\ 0\m=.\6\g=m\g/100 ml in female and male quokkas respectively. The mean association constant was 3\ m=. \ 2\ m=x\1081/mol at 4 \ s=deg\ C and 5\ m=. \ 5\ m=x\1071/mol at 36 \ s=deg\ C. The maximum binding capacity for corticosterone was approximately one-third that of cortisol.

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“…Honey possums have extremely large adrenal glands relative to their body mass, averaging 1,603 § 223 mg kg ¡1 (Oates et al 2007), compared with adrenals from other marsupials and eutherian mammals that typically fall within the range of 100-200 mg kg ¡1 (Chester Jones 1957;McDonald 1977). Resting faecal cortisol levels are also extremely high, averaging 4-6 g g ¡1 (Oates et al 2007) some thousand times higher than levels of 2-10 ng g ¡1 , Fig.…”

Section: Metabolismmentioning

confidence: 99%

The physiology of the honey possum, Tarsipes rostratus, a small marsupial with a suite of highly specialised characters: a review

Bradshaw

2011

J Comp Physiol B

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Field and laboratory studies of the iconic nectarivorous and 'pollenivorous' honey possum, Tarsipes rostratus, are reviewed with the aim of identifying aspects of its physiology that are as yet poorly understood and needed to implement management strategies for its long-term conservation. Dietary specialisations include the loss of teeth, a modified gut with a high rate of passage, exceptionally low minimum nitrogen requirements, an apparently high basal metabolic rate and a permanently polyuric kidney. In contrast, its reproductive physiology is plesiomorphic, combining aspects such as a post-partum oestrus, embryonic diapause, photoperiodicity and extended maternal care that are usually separate characteristics of other marsupial groups. In common with a number of other marsupials, the honey possum has the potential for trichromatic colour vision and has been the subject of several studies attempting to correlate visual quality with ecological realities. Field physiological studies have established its high rates of nectar and pollen intake needed to maintain energy balance and highlight the need for a constant intake from floral sources. Early allometric studies suggesting that the honey possum's relatively low reproductive rate may be linked to a diet limited in protein have not been supported and nitrogen intakes in the field exceed by a factor of 10 the animal's basic requirements for balance. Measurements of rates of protein turnover in field-caught lactating females suggest that they divert nitrogen from the protein pool to milk production by reducing rates of degradation, rather than by increasing rates of synthesis of protein. Although not yet an endangered species, the honey possum's habitat has been drastically reduced since European occupation of Australia and future-targeted research on the animal's unique physiology and habitat linkage is needed that can be translated into effective management practices. Only then will its long-term survival be assured.

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Adrenocortical functions in marsupials

Cited by 17 publications

References 57 publications

Failure of glucocorticoid feedback in males of a population of small marsupials (Antechinus swainsonii) during the period of mating

Failure of glucocorticoid feedback in males of a population of small marsupials (Antechinus swainsonii) during the period of mating

PLASMA CORTICOSTEROIDS AND THE EFFECT OF ADRENOCORTICOTROPHIN IN A MACROPODID MARSUPIAL (SETONIX BRACHYURUS, QUOY & GAIMARD)

The physiology of the honey possum, Tarsipes rostratus, a small marsupial with a suite of highly specialised characters: a review

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