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Search for other papers by J. S. JENKINS in
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SUMMARY
The extra-hepatic metabolism of cortisol in man has been studied in vitro by incubation of [4-14C]cortisol with tissue slices.
Kidney tissue was the most active, followed by prostate; thyroid, skeletal muscle and synovial membrane were much less effective. Cortisone was quantitatively the predominant metabolite but C-20-reduced derivatives of cortisol and cortisone were also present. There was evidence for the oxidation of the side chain by kidney and prostate, but no ring A-reduced compounds were found.
Kidney slices did not reduce the 11-oxo group of cortisone but this reaction proceeded readily with liver slices.
Some evidence for extra-hepatic metabolism of cortisol in vivo by the tissues of the forearm was obtained by infusing [4-14C]cortisol into the brachial artery.
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SUMMARY
Chronic foetal—maternal cortisol interrelationships were studied in five time-dated pregnant ewes. Serial blood samples were obtained from ewe and foetus simultaneously for several weeks before and including parturition. Plasma cortisol was measured by both fluorometry and isotopic competitive protein binding. The data indicate that maternal cortisol levels are slightly higher than those in the foetus during the latter part of gestation until approximately 1 week before parturition. During the last week of gestation, especially 4–5 days before delivery, a marked increase in foetal cortisol levels was noted. Administration of amino-glutethimide to the foetus 1 week before delivery did not alter cortisol levels in either foetus or ewe. The results suggest that parturition in sheep is a culmination of events initiated by active foetal adrenocortical secretion.
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pituitary portal circulation of sheep ( Engler et al. 1999 ). Accordingly, the role of AVP as an activator of the hypothalamus–pituitary–adrenal gland (HPA) axis must be greater than that of CRH. ACTH is known to stimulate cortisol secretion from the
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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 Animal Science, University of California, Davis, California 95616, U.S.A.
(Received 8 October 1974)
Few studies have dealt with diurnal cortisol rhythm in sheep (McNatty, Cashmore & Young, 1972; McNatty & Young, 1973). The present results elucidate further the circadian rhythm of ovine plasma cortisol and describe the effect of sudden and continuous cage restraint.
Experimental methods and conditions were reported in detail by Holley & Evans (1974). Six mature rams were sampled at 4 h intervals for 32 days. On day 17 the animals were placed singly in small cages. Throughout the experiment the sheep received lucerne pellets at 16.00 h and the lighting schedule was maintained at 14 h light: 10 h darkness. Plasma cortisol was determined in duplicate without correction for other steroids as described by Bassett & Hinks (1969) and adjusted for extraction efficiency.
Fig. 1. Daily percentage variations (means ± s.e.m.) in plasma cortisol
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SUMMARY
Albumin was isolated from ovine plasma and its affinity for cortisol was determined by equilibrium dialysis at 37°. The value of Ka [σp a ] for a 1 % (w/v) albumin solution was 0·275 which is similar to the value for human plasma albumin.
The affinity constant of transcortin in ovine plasma was determined by equilibrium dialysis of diluted plasma at several concentrations of cortisol. The value found, Kt (37°) = 0·87 x 108 l./mole, is close to that found for human plasma transcortin by Mills (1962).
The concentration of transcortin in ovine plasma, expressed as cortisolbinding capacity, was 6–49 μg. (mean 24 μg.) cortisol/l. These concentrations are much lower than those found in human plasma. The observation of Lindner (1964) that cortisol binding capacity did not increase during pregnancy in sheep has been confirmed.
In sheep which were accustomed to handling, the mean concentration of cortisol in plasma was 17·8 μg./l. and of this amount 59% was bound to transcortin, 19 % to albumin and 22 % was not bound to protein.
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The concentrations of cortisol-binding proteins in pre-scapular lymph of sheep were determined. Albumin was measured by the method of Watson & Nankiville (1964), based on the solubility of albumin in 1% (w/v) trichloroacetic acid in propan2-ol: water (93:7, v/v) and measurement of the extinction at 220 nm. The ratio of albumin-bound to unbound cortisol was taken to be 0·275A, where A is albumin concentration (g/100 ml) (Paterson & Hills, 1967).
Transcortin concentration, expressed as cortisol-binding capacity, was measured by the method of Doe, Fernandez & Seal (1964): portions of lymph (2 ml) containing 0·5 μCi (0·5 μg) tritium-labelled cortisol were incubated for 1 h at 37 °C, and after cooling rapidly to 4 °C were filtered through Sephadex G 50 gel at the same temperature. Transcortin was also measured by the equilibrium dialysis method of Paterson & Hills (1967): diluted lymph (1:2, v/v) was dialysed against saline solutions of tritium-labelled cortisol
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To evaluate the role of the liver in cortisol catabolism the extraction ratio of both cortisol and cortisone by the organs of the splanchnic area was estimated in guinea-pigs anaesthetized with pentobarbitone. The [3H]cortisol and [3H]cortisone concentrations were measured in portal and sus hepatic venous plasma during a constant infusion of [3H]cortisol or [3H]cortisone. The extraction ratio of cortisol was estimated to be 10–14% in the splanchnic area and the viscera, while in the liver it had a small negative value suggesting that the liver had produced as much or more cortisol than it had taken up. All the cortisone (95%) formed from cortisol in the viscera was eliminated from the plasma compartment by the liver. Some 75–80% of the infused cortisone was converted to cortisol; rather less of the infused cortisol was converted to cortisone (32%). Using estimates of plasma flow derived from sham-operated animals, the uptake of cortisol by the various organs was calculated. The splanchnic area extracted 41% of the infused cortisol from the plasma: 25–27% as cortisol and 13–16% as cortisone. The liver appeared to take up cortisone preferentially. The conversion of cortisone into cortisol within the liver seems to be important in limiting the amount of cortisol removed from the plasma by the splanchnic area. The liver is also important in inactivating the steroids although other sites are probably also involved.
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SUMMARY
The binding of plasma cortisol to transcortin at 37° c was studied in normal men and in non-pregnant and pregnant women. The mean concentrations of transcortin were 8, 11·5 and 14 × 10−7 moles/l. and the percentages of the binding sites occupied by cortisol were 45, 24 and 40%, respectively. The mean values of the equilibrium constants were 2·9, 1·8 and 4·6 × 107 l./mole, suggesting that there might be a qualitative difference in transcortin from the three groups. The mean concentration of diffusible cortisol was 1·12 μg./100 ml. in men and 0·65 μg./100 ml. in non-pregnant and pregnant women.
The significance of these findings is discussed.
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SUMMARY
To assess the renin–aldosterone system in a large mammal, simultaneous morning activities of plasma renin and concentrations of aldosterone and cortisol were measured in 25 thoroughbred horses. Renin was relatively low in all horses (0·16±0·02 (s.e.m.) ng angiotensin I/ml per h), levels of aldosterone in plasma were 527±130 pmol/l and levels of cortisol in plasma were 141±11 nmol/l. Levels of aldosterone were significantly correlated with levels of renin in all horses (r = 0·62, P < 0·001) but not with those of cortisol, and renin was negatively correlated with age in male horses (r = −0·54. P < 0·05). Horse plasma renin had a pH optimum of 6·0.
These data suggest that the thoroughbred horse has a functioning renin–aldosterone system characterized by levels of plasma renin activity that are much lower relative to those of other mammalian species.
