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SUMMARY
Aldosterone, cortisol and corticosterone were measured in the peripheral blood of wombats and kangaroos from two areas of south east Australia. Increased blood levels of aldosterone were found in animals of both species from an area low in dietary sodium. Cortisol concentrations ranged from 0·08 to 0·83 μg./100 ml. blood in the wombat and from 0·60 to 4·20 μg./100 ml. blood in the kangaroo. Corticosterone concentrations ranged from 0·02 to 0·42 μg./100 ml. blood in the wombat and from 0·07 to 0·38 μg./100 ml. blood in the kangaroo.
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ABSTRACT
Cortisol was infused, intravenously, for 4 h continuously into 5 chronically cannulated ovine fetuses at 111-120 days of gestation (term is 142-152 days). The dose used was 100 μg/h, and raised fetal blood cortisol concentrations from 8.2±4.0 to 56.5±19.0 nmol/l (values are mean ± SEM). The effects observed were 1) a 4-5 fold increase in sodium and chloride excretion, 2) a doubling of potassium excretion and free water clearance, 3) no significant changes in urine pH, urea and creatinine excretions, and 4) an increase in urine osmolality from 129±7.5 to 154.4±11.3 mosmol/kg water. There were no significant changes in any of the measured parameters in 5 fetuses infused with 0.9% NaCl for 4 h. It is suggested that the hyponatremia and inability to retain sodium observed in many premature or very low birth weight babies may be due to the fact that their kidneys are behaving as fetal rather than neonatal organs and responding to the high plasma cortisol concentrations found in such babies with a natriuresis.
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The blood clearance rate (BCR) of cortisol was measured in non-pregnant ewes and in pregnant ewes and their intact or bilaterally adrenalectomized fetuses. In pregnant sheep the placental transfer of cortisol in both directions was established. The BCR of cortisol in the non-pregnant sheep was 51·7±4·9 (s.e.m.)1/h (n = 36) or 1·151/h per kg body weight. This was lower than that in the pregnant ewe (97–143 days of gestation) of 76·9±4·21/h (n = 9) or 1·851/h per kg.
In the intact fetus the BCR was 8·2±0·261/h (n = 10) over the same period of gestation. The percentage of the maternal production rate of cortisol transferred to the fetus was 1·4±0·11% (n = 9) and the placental transfer from fetus to mother was 19·5±1·5% (n = 8). The BCR in pregnant ewes bearing bilaterally adrenalectomized fetuses was not significantly different from that of mothers of intact fetuses (58·4±7·71/h; n = 6). The BCR of adrenalectomized fetuses was 8·4±1·371/h (n = 8). The placental transfer of cortisol from mother to fetus was sufficient to account for all the cortisol measured in adrenalectomized fetuses and in intact fetuses of 100–121 days of gestation. However, it accounted for only 37% of the cortisol measured in fetuses of 122–135 days of gestation and 12% or less in fetuses older than 136 days of gestation.
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* Department of Physiology, University of Melbourne, Parkville, Victoria 3052, Australia, † Department of Surgery, Austin Hospital, Studley Road, Heidelberg, Victoria 3084, Australia, and ‡ Howard Florey Institute of Experimental Physiology and Medicine, University of Melbourne, Parkville, Victoria 3052, Australia
(Received 19 October 1977)
Aldosterone is present in the peripheral blood of ovine foetuses from at least 60 days until term at 147 ± 5 days (Wintour, Brown, Denton, Hardy, McDougall, Oddie & Whipp, 1975). To determine the biological significance of this steroid in the foetus, infusions of aldosterone were made into foetuses bearing chronic vascular and bladder cannulae and the urinary sodium: potassium Na+: K+) ratio was measured before, during and after infusion. Silastic cannulae (0·76 mm internal diameter, 1·65 mm outer diameter) were placed 6–8 cm into the left carotid arteries and right jugular veins of seven ovine foetuses between 86 and 120 days of gestation and a
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ABSTRACT
9α-Fluorocortisol has been postulated to have 'hypertensinogenic' as well as 'mineralocorticoid' and 'glucocorticoid' activity. The present study examined the blood pressure and metabolic effect in sheep of the structurally related steroids 9α-fluorodeoxycorticosterone (9α-FDOC) and 9α-fluorocorticosterone (9α-FB). Infusions of these fluorinated steroids at 0·63 and 0·67 mg/day respectively for 5 days produced falls in plasma potassium, but only 9α-FB increased urine volume. 9α-FDOC raised mean arterial pressure by 11 mmHg and 9α-FB raised it by 14 mmHg. Addition of a 9α-fluoro group appears to increase both 'mineralocorticoid' and 'hypertensinogenic' steroid potencies.
J. Endocr. (1985) 104, 291–294
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ABSTRACT
The ability of opioid peptides to affect plasma immunoreactive ACTH concentrations was examined in conscious sheep. Plasma concentrations of ACTH were significantly increased by an i.v. infusion of Met-enkephalin and its analogue (FK-33824). There was a dose-dependent increase in plasma concentrations of ACTH with a graded administration of FK-33824. The combined effect of Met-enkephalin and ovine corticotrophin-releasing factor (oCRF) or FK-33824 and oCRF on plasma concentrations of ACTH was greater than the effect of each peptide when given individually. This study demonstrates that Met-enkephalin and its analogue stimulate ACTH release in sheep.
J. Endocr. (1986) 111, 463–467
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Howard Florey Institute of Experimental Physiology and Medicine, University of Melbourne, Parkville, Victoria 3052, Australia
(Received 14 March 1978)
Administration of adrenocorticotrophin (ACTH; 80–100 i.u./day) to conscious trained sheep for 5 days produces a significant rise in blood pressure within 24 h which is maintained over a 5 day period of treatment. The increase in blood pressure is accompanied by an increase in cardiac rate, hypokalaemia, hypernatraemia and, initially, urinary retention of sodium; subsequently there is a natriuresis and an increase in both water intake and urine output (Scoggins, Coghlan, Denton, Fan, McDougall, Oddie & Shulkes, 1974). During the last third of gestation, the response to intravenous angiotensin II in the ewe is depressed to about 15% of the response observed in non-pregnant animals, but is not reduced further by sodium deficiency (Blair-West, Coghlan, Denton, Scoggins & Wintour, 1972); pregnant ewes can, however, be made hypertensive by constriction of the
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Plasma renin activity (PRA) and blood aldosterone and deoxycorticosterone levels were measured in Australian lungfish. Plasma renin activity was depressed after intravenous infusions of iso-osmotic (0·6%) NaCl but not after hypo-osmotic (0·3%) infusions. The presence of PRA in this fish is consistent with prior reports of renal renin activity in other sarcopterygian fishes. The results of the infusion experiments suggest that a fall in plasma osmolality or electrolyte concentrations may oppose the reduction in renin release in response to volume expansion.
Aldosterone and deoxycorticosterone were identified in the blood of Neoceratodus. The concentrations of both appeared higher in females than in males. Infusions of [5-valine]-angiotensin II amide for 2–4 h at rates known to increase blood pressure in this species did not alter blood aldosterone concentrations. This negative finding may suggest that the renin/angiotensin system is not involved in aldosterone regulation in Neoceratodus or that angiotensin receptors involved in regulation of steroidogenesis have a greater specificity for endogenous angiotensin than do vascular receptors.
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SUMMARY
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.
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Comparisons of aldosterone responses to [des-Asp1]-angiotensin II and angiotensin II, often at single dose levels, have shown a wide range of potency ratios. Therefore four-point dose–response comparisons were performed in sodium-replete sheep, using i.v. infusion rates of angiotension II and angiotensin II amide that reproduced the physiological range of blood concentration of angiotensin II for sheep. Angiotensin III was infused i.v. at the same rates. Effects on arterial blood pressure, cortisol secretion rate, adrenal blood flow and plasma levels of Na+ and K+ were also compared. The potency ratio, angiotensin III: angiotensin II amide, was 0·87 for actual aldosterone secretion rate and 0·90 for the calculated increase in aldosterone secretion. For angiotensin III: angiotensin II the ratios were 0·80 and 0·91 respectively. These ratios were not significantly different from 1·00 but the tendency for angiotensin II to be slightly more potent was probably due to a contribution from derived angiotensin III during infusion of angiotensin II. Angiotensin II or angiotensin II amide was ∼ four times as potent as angiotensin III in raising arterial blood pressure. Cortisol secretion rate was slightly but significantly increased by all peptides at the higher infusion rates. Infusions had no effect on adrenal blood flow or plasma levels of Na + but raised plasma levels of K + slightly. These results confirm the conclusion from adrenal arterial infusion experiments that angiotensin II and III are almost equipotent in stimulating aldosterone secretion in sheep.
