Search Results
You are looking at 1 - 10 of 11 items for
- Author: J. Y. F. PATERSON x
- Refine by access: All content x
Search for other papers by J. Y. F. PATERSON in
Google Scholar
PubMed
Search for other papers by F. HILLS in
Google Scholar
PubMed
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.
Search for other papers by J. Y. F. PATERSON in
Google Scholar
PubMed
Search for other papers by F. HILLS in
Google Scholar
PubMed
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
Search for other papers by J. Y. F. PATERSON in
Google Scholar
PubMed
SUMMARY
The apparent rate of dissociation of transcortin-bound cortisol in human plasma was measured. After establishing equilibrium between plasma proteins and endogenous and added [3H]cortisol, this was perturbed by addition of a known amount of exogenous cortisol. Plasma protein-bound [3H]cortisol was then measured by gel filtration at timed intervals.
This system can be described by six differential equations, one each for unbound, albumin-bound and transcortin-bound cortisol and [3H]cortisol. The rate constants for the transcortin—cortisol reaction were estimated by numerical solution of these equations, using arbitrary rate constants for the albumin—steroid reaction.
At 2 °C the dissociation of transcortin-bound cortisol has a rate constant of 0·00041 s−1, at 10 °C 0·00179 s−1 and at 22 °C 0·0353 s−1. At 37 °C the reaction was very rapid and equilibrium appeared to be attained in less than 5 s. The rate constant could only be estimated by using the Arrhenius equation, In (k) = const + E/RT, and was found to be 0·633 s−1.
The rate constants for cortisol—plasma protein interaction were applied to a differential equation model for the splanchnic uptake of cortisol. Using experimental measurements of the visceral and hepatic uptake of cortisol in sheep the rate constant for the visceral removal of cortisol was found to be 0·0299 ± 0·0065 (s.e.m.) s−1 and the hepatic constant was 0·4674 ± 0·0540 (s.e.m.) s−1. In normal conscious sheep the total splanchnic uptake of cortisol appeared to be derived 42% from unbound, 31% from albumin-bound and 27% from transcortin-bound steroid.
Search for other papers by J. Y. F. PATERSON in
Google Scholar
PubMed
Search for other papers by F. A. HARRISON in
Google Scholar
PubMed
SUMMARY
The uptake of cortisol by the gastro-intestinal tract and by the liver was estimated in sheep by measurement of [3H]cortisol concentrations in portal and hepatic venous plasma during constant infusion of tritium-labelled cortisol, with simultaneous measurement of plasma flows.
The total splanchnic uptake of cortisol was 57 ± 4 (s.e.m.)% of the measured rate of cortisol secretion, 45% by the liver and the remainder by the gastro-intestinal tract. The splanchnic extraction of cortisol could be related to plasma flow, and was less efficient at higher flows. It could also be related to plasma cortisol concentration, and was more efficient at higher concentrations. The splanchnic uptake of cortisol was closely correlated with the flow of unbound cortisol into the region, and was 1·61 times that influx. There is therefore partial dissociation of plasma protein-bound cortisol during the splanchnic uptake.
About 25% of secreted cortisol is converted to cortisone at extrahepatic sites, and is removed from plasma by the liver.
Search for other papers by J. Y. F. PATERSON in
Google Scholar
PubMed
Search for other papers by F. A. HARRISON in
Google Scholar
PubMed
SUMMARY
Tritium-labelled cortisol was administered to sheep by intravenous infusion at constant rate for up to 4 hr. When the infusion was stopped, [3H] cortisol disappeared rapidly from plasma and its concentration could be described by a double exponential function. There was good agreement between the results from 50 experiments on 11 sheep. In pregnant ewes, there was no noticeable difference in the rate of disappearance of [3H]cortisol from plasma until about 2 weeks before lambing, when the rate became more rapid.
These data were interpreted in terms of a two-compartment model of cortisol distribution. The central compartment contains about 42 μg. cortisol and may be identical with the cortisol contained in whole blood volume. The outer compartment contains about 130 μg. cortisol; less than half of this compartment may be in intercellular fluids, partly bound to protein, and the remainder in intracellular fluids.
In pregnant ewes near term there is a decrease in plasma cortisol concentration which appears to result from expansion of plasma volume. The decrease in unbound cortisol concentration probably results in a decrease in the size of the outer compartment of cortisol. This may contribute to the observed increase in the rate of disappearance of [3H] cortisol from plasma, but this change may also coincide with the initiation of secretion of cortisol by the foetus, at about 1 or 2 μg./min.
Search for other papers by F. A. HARRISON in
Google Scholar
PubMed
Search for other papers by J. Y. F. PATERSON in
Google Scholar
PubMed
SUMMARY
Tritium-labelled cortisol was injected intravenously, as a single dose, in 12 experiments on seven sheep with autotransplanted left adrenal glands, in which cortisol secretion rate could be measured directly by sampling adrenal venous blood.
In all experiments, curves which represented sums of two exponential terms could be fitted to the estimates of specific activity of plasma cortisol. The interpretation of the data was based on the distribution of cortisol in two miscible pools, and the calculated rates of cortisol turnover were much greater than the cortisol secretion rates which were measured directly and simultaneously.
Simultaneous injection of Evans blue suggested that 1–2 min. was needed for complete mixing of the injected dose in plasma, during which time labelled cortisol leaves plasma with a half-time of about 1 min. It is concluded that such conditions do not provide a satisfactory basis for tracer kinetic analysis.
Search for other papers by J. Y. F. PATERSON in
Google Scholar
PubMed
Search for other papers by F. A. HARRISON in
Google Scholar
PubMed
SUMMARY
Tritium-labelled cortisol was infused intravenously for about 4 hr. into sheep with autotransplanted left adrenal glands. The specific activity of plasma cortisol became constant about 2 hr. after beginning the infusion, and in almost all experiments, the rate of cortisol secretion and the concentration of cortisol in plasma were constant during the remainder of the period of infusion.
The rate of cortisol turnover was calculated as the ratio of the rate of infusion of labelled cortisol and the constant specific activity which was attained during infusion. Within the limits of experimental error, the calculated rate of cortisol turnover in 55 experiments was equal to the simultaneously measured rate of cortisol secretion.
In sheep which were accustomed to handling, the rate of cortisol secretion was about 12 μg./min. and the concentration of cortisol in plasma was about 18 μg./l. The rate of cortisol secretion did not change during pregnancy in ewes, but there was a decrease in the concentration of cortisol in plasma in the last 2 weeks before lambing.
Search for other papers by J. Y. F. PATERSON in
Google Scholar
PubMed
Search for other papers by J. L. LINZELL in
Google Scholar
PubMed
SUMMARY
In pregnant and in lactating goats the rate of cortisol secretion was measured by continuous intravenous infusion of tritium-labelled cortisol. Uptake of cortisol by the mammary gland was measured by simultaneous sampling of blood from the carotid artery and superficial epigastric vein, and measurement of mammary blood flow. In pregnant goats the rate of cortisol secretion was 9 μg/min but in preparturient and in lactating goats the rate was about 32 μg/min. There was a small but significant difference in cortisol concentration between the carotid artery and mammary vein. In pregnant goats the mammary uptake of cortisol was about 0·2 μg/min; this was increased to about 1·3 μg/min in preparturient and in lactating animals. Negligible quantities of cortisol were secreted in the milk.
Cortisol was administered by continuous infusion for 4 h into two lactating goats. Although there was some stimulation of milk secretion it seems likely that it resulted from a systemic rather than local action of cortisol.
Search for other papers by J. Y. F. PATERSON in
Google Scholar
PubMed
Search for other papers by J. L. LINZELL in
Google Scholar
PubMed
SUMMARY
Glucose entry rate was measured by primed infusion of [2-3H]glucose, and cortisol secretion rate by infusion of [1,2-3H2]cortisol, in two cows from 142 days before calving to day 287 of lactation. Mammary blood flow and the mammary uptake of glucose and cortisol were also measured.
In late pregnancy, cortisol secretion rate was 8·6 ± 3·17 (s.d.) μg/min and plasma cortisol concentration was 1·8 ± 0·52 μg/l. During parturition in one animal the secretion rate was 92 μg/min and plasma cortisol concentration was 15 μg/l. During lactation the secretion rate (26·4 ± 7·14 μg/min) and plasma cortisol concentration (5·6 ± 0·73 μg/l) were significantly greater than in dry cows. The mammary uptake of cortisol was 3 to 4% of the secretion rate in both dry and lactating cows.
Glucose entry rate was 5·77 ± 2·250 (s.d.) mg/min/kg0·75 in dry cows and there was no significant mammary uptake of glucose. During lactation the glucose entry increased to 9·45 ± 1·881 mg/min/kg0·75. Mammary uptake of glucose was 3·56 ± 1·949 mg/min/kg0·75. The non-mammary utilization of glucose, glucose entry less mammary uptake, was the same for dry and lactating cows.
There was a good correlation between glucose entry and milk yield, and between mammary uptake of glucose and milk yield. Since the mammary arterio-venous glucose concentration difference was relatively constant, it is suggested that the change in mammary blood flow may determine the change in glucose uptake and milk yield.
Search for other papers by F. A. HARRISON in
Google Scholar
PubMed
Search for other papers by I. R. McDONALD in
Google Scholar
PubMed
Search for other papers by J. Y. F. PATERSON in
Google Scholar
PubMed
SUMMARY
The apparent rate of cortisol turnover was determined in conscious and anaesthetized sheep by injection of tritium-labelled cortisol. Simultaneously, the rate of cortisol secretion was determined by collection of adrenal venous blood. The apparent rate of cortisol turnover was found to be two to three times the rate of cortisol secretion.
