Brain HSP70 mRNA expression is linked with plasma cortisol levels in goldfish (Carassius auratus) exposed to a potential predator

We previously found that when goldfish were exposed to a potential predator, bluegills, the goldfish experienced an increase in HSP70 mRNA expression in the brains and increased plasma cortisol levels. In the present study, we examined the potential causative relationship between HSP70 mRNA expression and plasma cortisol levels. Cortisol agonists (corticotropin releasing factor and cortisol) and antagonists (metyrapone and betamethasone) were used to modulate plasma cortisol levels. HSP70 mRNA expression and plasma cortisol levels were analyzed by Northern blotting and ELISA, respectively. Goldfish treated with the cortisol agonists showed marked increases in plasma cortisol levels and also in brain HSP70 mRNA expression. When goldfish were exposed to bluegills, plasma cortisol levels increased and HSP70 mRNA expression was enhanced after 6 hr. However, pre-treatment with the cortisol antagonists 24 hr prior to the exposure inhibited the enhancement as well as the increase in plasma cortisol levels. These results suggest that plasma cortisol plays a key role in the enhancement of brain HSP70 mRNA expression in goldfish stressed by exposure to bluegills.     

Cortisol-suppressible dexamethasone-nonsuppressible cyclic Cushing's disease with evidence of clinical and biochemical remission with bromocriptine.

We report a rare case of a 57-year-old female patient with Cushing's disease who had clinically and biochemically proven cyclicity. There were periodic increases in plasma ACTH and cortisol and urinary free cortisol and 17-OHCS. Plasma CRH was undetectable and plasma ACTH responded to exogenous CRH when basal plasma cortisol was relatively low. Neither plasma ACTH nor cortisol responded to dexamethasone (oral and intravenous) but plasma ACTH was clearly suppressed by cortisol infusion. With 40 mg/day bromocriptine, the periodic hypercortisolemia disappeared and the patient was maintained on remission. The response of plasma cortisol to dexamethasone suppression test was also normalized.     

Plasma cortisol in men--relationship with atherosclerosis of retinal arteries

The production of cortisol increases in acute stress but the effects of chronic stress on plasma cortisol are still controversial. Stress on the other hand plays a role in coronary artery disease (CAD) and carotid atherosclerosis. Since there is no data about plasma cortisol and atherosclerosis of the retinal arteries, the purpose of this study was to explore the relationship between plasma cortisol in 101 adult males with the degree of their retinal vessels atherosclerosis. The results were compared with those in 47 matched apparently healthy men with no retinal vessels changes. The atherosclerotic changes of retinal vessels were determined by direct ophthalmoscopy and graded (1-4) according to Scheie. Morning plasma cortisol levels were determined by radioimmunoassay using commercial kits. The results were compared by using chi-square test. No association between morning plasma cortisol concentrations and retinal vessels atherosclerosis could be found. The results of this study do not support a role for physiological levels of plasma cortisol in the development of atherosclerosis, at least of the retinal arteries, in men.     

Does RU486 modify hormonal responses to handling stressor and cortisol treatment in fed and fasted rainbow trout?

This study examines the effect of the steroid analogue, RU486, on the physiological responses of fed and chronically fasted rainbow trout to an acute handling stressor. This potent ligand of the glucocorticoid receptor was administered as a slow-release implant either alone, or in combination with cortisol. There were temporal changes in plasma cortisol concentrations following administration of cortisol implants in both fed and fasted trout. By day 14, plasma cortisol levels in fed fish were similar in all treatment groups, but in fasted fish, the effect of cortisol administration on plasma cortisol concentrations was still evident; RU486 administered with cortisol, did not affect this response. Cortisol administration also elicited a small, but significant increase in plasma GH concentrations in fed rainbow trout and in plasma glucose concentrations in fasted animals. RU486-treatment prevented these responses. Conversely, whereas RU486 alone had no effect on hepatic 5'-monodeiodinase activity, when administered with cortisol it enhanced the marked suppressive effect of cortisol evident in both fed and fasted groups, suggesting that it may exert an interactive effect with cortisol on this process. Stressor-related changes in plasma cortisol, glucose, GH and thyroid hormone concentrations were evident in both fed and fasted groups; however, there was no evidence of a suppressive effect of RU486 treatment on any of the measured plasma parameters. Although RU486 did not prevent the stressor-related changes, the post-stressor cortisol profiles in RU-treated trout were extremely erratic compared with the oil-treated controls. This implies a disturbance of the normal interactions of the components of the hypothalamus-pituitary-interrenal tissue axis.     

Plasma cortisol and corticosterone concentrations in the golden hamster, (Mesocricetus auratus)

Because some recent studies of hamster adrenocortical function have depended on older studies that may have been inadequate or misinterpreted, the present study re-examined plasma corticosterone and cortisol concentrations in hamsters under several conditions to determine which plasma glucocorticoid predominated in this animal. Sensitive radioimmunoassays were used to measure separately the two glucocorticoids in the basal condition, after adrenocorticotropin (ACTH) treatment, after acute stress, and after chronic stress. In the basal condition, corticosterone concentrations were 3-4 times higher than those of cortisol. After stimulation, this difference disappeared, but rarely were any hamster's cortisol levels higher than their corticosterone levels. Both ACTH and acute stress elevated plasma corticosterone and cortisol concentrations, but only plasma cortisol concentrations were elevated following chronic stress. The dissociation between cortisol and corticosterone concentrations after chronic stress suggests that the two glucocorticoid hormones in the hamster may be regulated independently. The data also indicate that both corticosterone and cortisol should be measured when assessing adrenocortical function in the hamster.     

Effect of o,p'-DDD on cortisol metabolism in Cushing's syndrome of various etiology

Effects of o,p'-DDD on parameters of cortisol metabolism were studied in 3 patients with Cushing's syndrome (ectopic ACTH-syndrome, Cushing's disease, and adrenal cancer). Before o,p'-DDD treatment, plasma cortisol, urinary 17OHCS, and urinary free cortisol were elevated in all patients. These parameters correlated well with each other in ectopic ACTH-syndrome and Cushing's disease. However, in adrenal cancer, urinary 17OHCS did not correlate with either plasma cortisol or urinary free cortisol, while the latter two parameters did. During o,p'-DDD, urinary 17OHCS rapidly declined in a patient with ectopic ACTH syndrome and a patient with Cushing's disease before plasma cortisol or urinary free cortisol decreases. Consequently the positive correlations of urinary 17OHCS with the other parameters were lost. In a case of adrenal cancer, urinary 17OHCS again did not correlate with plasma cortisol or urinary free cortisol. In these conditions, plasma cortisol and urinary free cortisol still significantly correlated. The present results demonstrated the limit of urinary 17OHCS as the index of the cortisol secretion rate both in some cases of adrenal cancer and in patients taking o,p'-DDD. It is suggested that urinary free cortisol should be utilized as a more accurate index for the cortisol secretion rate in such circumstances.     

Consequences of acute stress and cortisol manipulation on the physiology, behavior, and reproductive outcome of female Pacific salmon on spawning grounds

Life-history theory predicts that stress responses should be muted to maximize reproductive fitness. Yet, the relationship between stress and reproduction for semelparous salmon is unusual because successfully spawning individuals have elevated plasma cortisol levels. To tease apart the effects of high baseline cortisol levels and stress-induced elevation of cortisol titers, we determined how varying degrees of cortisol elevation (i.e., acute and chronic) affected behavior, reproductive physiology, and reproductive success of adult female pink salmon (Oncorhynchus gorbuscha) relative to different states of ovulation (i.e., ripe and unripe). Exhaustive exercise and air exposure were applied as acute stressors to manipulate plasma cortisol in salmon either confined to a behavioral arena or free-swimming in a spawning channel. Cortisol (eliciting a cortisol elevation to levels similar to those in post-spawn female salmon) and metyrapone (a corticosteroid synthesis inhibitor) implants were also used to chemically manipulate plasma cortisol. Cortisol implants elevated plasma cortisol, and impaired reproductive success; cortisol-treated fish released fewer eggs and died sooner than fish in other treatment groups. In contrast, acute stressors elevated plasma cortisol and the metyrapone implant suppressed plasma cortisol, but neither treatment significantly altered reproductive success, behavior, or physiology. Our results suggest that acute stressors do not influence behavior or reproductive outcome when experienced upon arrival at spawning grounds. Thus, certain critical aspects of salmonid reproduction can become refractory to various stressful conditions on spawning grounds. However, there is a limit to the ability of these fish to tolerate elevated cortisol levels as revealed by experimental elevation of cortisol.     

The changes in plasma cortisol and urinary free cortisol by an overnight dexamethasone suppression test in patients with Cushing's disease

We studied the suppressibility of cortisol secretion in 15 patients with Cushing's disease by measuring morning plasma cortisol level as well as the 24-hour urinary free corisol (UFC) excretion following single doses of increasing amounts of dexamethasone (ranging from 0.5 to 32 mg) given at 11 p.m. The mean plasma cortisol level in patients with Cushing's disease was twice as high as in normal subjects, whereas the mean UFC in these patients was 6 times as high. Plasma cortisol in seven patients were suppressed by less than 4 mg of dexamethasone (in 2 cases, less than 0.5 mg; in 3 cases, less than 2 mg; and in 2 cases less than 4 mg). In these cases, basal plasma cortisol and UFC were less than 25 micrograms/dl and 350 micrograms/day, respectively. Among the other eight patients, plasma cortisol was partially suppressed in 5 cases and not suppressed in 3 cases by high doses of dexamethasone (16-32 mg). In these cases the basal plasma cortisol and UFC were more than 25 micrograms/dl and 350 micrograms/day, respectively. There was a significant correlation between the basal plasma cortisol and UFC (r = 0.687, p less than 0.01). These data suggest that the suppression by increasing amounts of dexamethasone in most cases with Cushing's disease was related to the severity of hypercortisolism.     

The effects of cortisol and testosterone on renal function in male Antechinus stuartii (Marsupialia)

Seasonal changes in the physiology of Antechinus stuartii result in complete male mortality after mating. The most important endocrine changes in males are large rises in plasma testosterone and cortisol concentrations. Glomerular filtration rate (GFR) in males declines coincident with high plasma testosterone and cortisol. In the present study GFRs were measured in males captured in May (when endogenous plasma testosterone and cortisol levels are low) and given depot injections of either saline, testosterone-only, cortisol-only or testosterone plus cortisol at doses designed to mimic plasma levels during the mating period. GFR decreased significantly with testosterone injection, independent of cortisol treatment. Urinary concentrations of sodium and chloride, and osmolality decreased significantly with cortisol treatment, although the addition of testosterone reversed the effect. Total urinary excretion of electrolytes was similar between groups. Plasma potassium levels significantly increased in testosterone plus cortisol treated males. Plasma sodium levels significantly increased and plasma chloride significantly decreased in all groups treated with cortisol. Water consumption significantly increased in all cortisol-treated males and food consumption significantly increased in all testosterone-treated males. The seasonal renal functional changes observed in A. stuartii were mimicked by testosterone administration. Accepted: 23 January 1998     

A nonlabeled method to evaluate cortisol production rate by modeling plasma CBG-free cortisol disposition

This study aimed to develop a nonlabeled method for the measurement of cortisol production rate to evaluate adrenal function. The cortisol production rate determination requires that of cortisol clearance, which is not a parameter but a variable resulting from the saturable binding of cortisol to corticosteroid-binding globulin (CBG). Our method is based on evaluation of the plasma clearance of the CBG-free cortisol fraction. This parameter was evaluated from a pharmacokinetic model of total plasma cortisol disposition that takes into account specific binding of the corticoid to CBG in the plasma. We have shown that the CBG-free cortisol kinetics and CBG-binding parameters thus evaluated are not statistically different from those obtained by the radioisotopic method and equilibrium dialysis, suggesting that the plasma CBG-free cortisol clearance is independent of the total plasma cortisol concentrations and represents the actual parameter of cortisol elimination. We validated this modeling approach by using it to calculate the in vivo entry rate of cortisol mimicked by the perfusion of cortisol at a known rate.     

Uptake and removal of cortisol by canine erythrocytes in various electrolyte solutions

The uptake of free cortisol by canine RBC was studied by incubating the cells in various Ringer-Locke solutions, saline, plasma, and plasma to which EDTA was added. The uptake of cortisol by RBC was similar in all electrolyte solutions; however, uptake was significantly less when RBC were incubated in plasma. The removal of both exogenous and endogenous cortisol from RBC was studied by washing the cells in various electrolyte solutions. Although the percentages of steroid removed per wash were not significantly different when cells were washed with Ringer-Locke solutions, saline washed RBC to which no cortisol was previously added gave significantly less steroid per wash. These data indicate that Na⁺, K⁺ and Ca⁺⁺ do not affect the permeability of these cells to cortisol and that the cortisol associated with canine RBC is loosely bound.     

Conditions for assessing cortisol in sheep: the total form in blood v. the free form in saliva

Cortisol is often used as a stress indicator in animal behaviour research. Cortisol is commonly measured in plasma and can also be measured in saliva. Saliva contains only the free form of cortisol, which is biologically active, and saliva sampling is not invasive and may therefore be less stressful. Our study aims to guide the choice between the measurements of cortisol in plasma v. saliva depending on experimental conditions. We analysed the effect of the level of cortisol in plasma on the concentration of cortisol in saliva compared to plasma and the effect of saliva sampling v. jugular venepuncture on the cortisol response. In Experiment 1, blood and saliva were collected simultaneously under conditions in which the expected cortisol release in blood varied: in an undisturbed situation or after the isolation of lambs from their pens or the administration of exogenous ACTH (six animals per treatment). In Experiment 2, we subjected lambs to saliva sampling, venepuncture or neither of these for 8 days to evaluate how stressful the sampling method was and whether the animals habituated to it by comparing the responses between the first and last days (four animals per treatment). All animals were equipped with jugular catheters to allow regular blood sampling without disturbance. Samples were collected 15 min before any treatment was applied, then at various time points up to 135 min in Experiment 1 and 45 min in Experiment 2. In Experiment 1, we observed a strong correlation between salivary and plasma cortisol concentrations (r = 0.81, P < 0.001). The ratio between salivary and plasma cortisol concentrations was 0.106 on average. This ratio was higher and more variable when the cortisol concentration in plasma was below 55 nmol/l. In Experiment 2, venepuncture induced a larger cortisol response than saliva sampling or no intervention on day 1 (P < 0.02); this difference was not observed on day 8, suggesting that sheep habituated to venepuncture. We recommend the measurement of cortisol in saliva to avoid stressing animals. However, when the expected concentration in plasma is below 55 nmol/l, the cortisol in saliva will reflect only the free fraction of the cortisol, which may be a limitation if the focus of the experiment is on total cortisol. In addition, if cortisol is measured in plasma and blood is collected by venepuncture, we recommend that sheep be habituated to venepuncture, at least to the handling required for a venepuncture.     

ADRENAL FUNCTION IN WILD AND REHABILITATED PACIFIC HARBOR SEALS (PHOCA VITULINA RICHARDII) AND IN SEALS WITH PHOCINE HERPESVIRUS-ASSOCIATED ADRENAL NECROSIS

Adrenal function in harbor seals (Phoca vitulina richardii) was evaluated using adrenocorticotrophic hormone (ACTH) stimulation tests and fecal cortisol levels. The effect of ACTH administration on plasma cortisol and aldosterone levels in five free-living and 14 rehabilitated harbor seal pups was determined using enzyme immunoassay and radioimmunoassay, respectively. In free-living seals, injection of ACTH caused a significant increase in mean plasma cortisol but not of mean aldosterone levels 60 min postinjection. In these seals, mean initial plasma aldosterone was significantly higher than initial levels in rehabilitated seals, while initial cortisol levels were similar. Of the rehabilitated seals, eight died with adrenal cortical necrosis associated with herpesvirus inclusions, while six lived to be released. In the seals that were released, both mean initial cortisol levels and response to ACTH decreased through rehabilitation. In the seals that died, mean initial cortisol and response to ACTH increased through rehabilitation. The differences between initial cortisol levels in seals that lived and those that died were significant at weeks two and four of rehabilitation but not at the week of admission. There was considerable individual variation in initial plasma aldosterone levels and responses to ACTH, although initial aldosterone levels were significantly higher in rehabilitated seals that died than in seals that lived. Seals with adrenal necrosis associated with herpesvirus infection did not have decreased adrenal hormone responses to ACTH. Differences between initial hormone levels and responses to ACTH in different groups of seals may be associated with differing stress levels. Fecal cortisol assays were not a useful method of assessing adrenal function in these seals, as measured levels did not correlate with plasma cortisol levels.     

Plasma ACTH, cortisol and aldosterone concentrations in chronically cannulated ovine fetuses and in lambs injected with ovine corticotropin releasing factor

Synthetic oCRF was intravenously injected into 3 groups of 5 chronically cannulated ovine fetuses in utero on days 120, 130 and 137 of gestation (10 micrograms/fetus). The respective twin fetuses were used as controls. Ovine CRF was also intravenously injected into 4 groups of 6 lambs on days 1, 3, 7 and 20 after birth (5 micrograms/kg bw). Fetal plasma ACTH and cortisol concentrations increased significantly following oCRF as early as 120 days of gestation without changing maternal plasma cortisol concentrations. The ACTH and cortisol response to CRF increased gradually on stages 130 and 137 of gestation, but on the other hand, plasma aldosterone did not change. In newborns, after oCRF, the pituitary response gave peak values at 10 min for plasma ACTH and adrenal response gave peak values at 15 min for plasma cortisol. Between 1 and 20 days, plasma ACTH and cortisol changes after oCRF decreased in older animals while aldosterone level remained unchanged. In animals receiving both treatments on days 1 and 20, plasma cortisol levels were increased for longer than in animals treated once.     

Regulation of maternal ACTH in ovine pregnancy: does progesterone play a role?

Pregnancy is characterized by increased plasma adrenocorticotropic hormone (ACTH) and cortisol. Studies suggest that progesterone acts as an antagonist at mineralocorticoid receptors. Therefore, we tested the hypothesis that chronic progesterone, produced by treatment of nonpregnant ewes or during pregnancy, will result in increased plasma ACTH relative to the plasma cortisol concentrations. We studied three groups of ewes: ovariectomized nonpregnant, nonpregnant treated with progesterone, and pregnant ewes. In two series of studies, ewes were adrenalectomized and replaced with 0.35 mg x kg(-1) x day(-1) or 0.5 mg x kg(-1) x day(-1) cortisol. In both studies, aldosterone was infused at 3 microg x kg(-1) x day(-1). In the first study, additional infusions of cortisol over 24 h were used to increase daily replacement doses to 0.5, 1, or 1.5 mg x kg(-1) x day(-1), and intact pregnant and nonpregnant ewes were studied with infusions of cortisol at 0, 0.5, and 1 mg x kg(-1) x day(-1). In adrenalectomized ewes chronically replaced to 0.35 mg x kg(-1) x day(-1) cortisol, plasma ACTH concentrations were decreased significantly in the nonpregnant progesterone-treated ewes compared with the ovariectomized nonpregnant ewes. With 0.5 mg x kg(-1) x day(-1) cortisol, plasma ACTH levels were greater in pregnant ewes than in nonpregnant ewes with or without progesterone. Overall plasma ACTH levels at 0.35 mg x kg(-1) x day(-1) were significantly related to the plasma protein concentration, suggesting that the ACTH levels in the hypocorticoid ewes are most closely related to plasma volume. Across all steroid doses, ACTH was positively related to plasma proteins and progesterone, and negatively related to cortisol. We conclude that increased progesterone does not alter the feedback relation of cortisol to ACTH, but may modulate ACTH indirectly through plasma volume.     

Effects of neurotrophic stress on maternal metabolism and binding of plasma cortisol in late pregnant guinea-pigs and their fetuses

The maternal metabolic clearance rate (MCR) and the binding of cortisol in the plasma of fetus and mother were estimated 8 days before term in conscious pregnant guinea-pigs, control or subjected to a neurotrophic stress (they were immobilized for 3 h in a dark room in front of an intermittent luminous flash). The maternal MCR of cortisol dropped during pregnancy related to an increase in corticosteroid binding globulin (CBG) and the stress mimicked these changes with a decrease in MCR and a rise in CBG. The increase in cortisol concentrations occurring in the fetal plasma after maternal stress could be related to the increase in free cortisol in the stressed mother. Nevertheless, although the fetal CBG did not rise after maternal stress, the increase in free cortisol in the fetal plasma remained moderate, due to the numerous free sites of CBG and albumin for cortisol.     

Comparison of two rapid cortisol radioimmunoassays for use in the fetal sheep.

Cortisol radioimmunoassays (RIA's) utilizing highly specific antisera combined with a simple ethanol protein precipitation procedure (ETOH-PPT) are widely utilized to measure cortisol in human plasma. This same type of RIA has been assumed specific for measurement of cortisol in the plasma of several different species of experimental animals. In order to test this assumption as applied to fetal ovine plasma, we compared an ETOH-PPT cortisol RIA with another rapid cortisol assay which utilizes a dichloromethane extraction (DM-E) step. The DM-E assay in turn was compared with a chromatographic assay previously shown to be highly specific for measurement of fetal plasma cortisol in this species. Fetal ovine plasma cortisol concentrations determined by the DM-E method were nearly identical to the concentrations obtained by the specific chromatographic RIA procedure. On the other hand, the ETOH-PPT RIA grossly overestimated cortisol concentrations when compared with the DM-E RIA. While the rapid DM-E RIA appears to be suitable for use in fetal ovine plasma, the widely used ETOH-PPT RIA yields spuriously high and unpredictable values and must be considered unreliable. These comparisons demonstrate the need for careful reassessment of steroid assays prior to their application in experimental animals even though they have been previously documented as specific in human plasma.     

The nonsuppressibility of plasma cortisol persists after pregnancy

To determine if normal balance is restored to the hypothalamic-pituitary-adrenal axis after pregnancy, we compared the dexamethasone suppressibility of plasma cortisol in women four days after delivery of their infant, with that of nonpregnant women. Plasma concentrations of cortisol before dexamethasone administration were similar in the post-partum women and in women taking oestrogen contraceptives, but both were higher than in normally cycling women. After dexamethasone, plasma cortisol in the post-partum women was significantly higher than in both oestrogen-taking and normally cycling nonpregnant women. The reduced dexamethasone-suppressibility of plasma cortisol, which is characteristic of pregnancy, extends into the post-partum period.     

Cortisol and glucose responses in juvenile brown trout subjected to a fluctuating flow regime in an artificial stream

In an artificial stream channel, wild 1 year old brown trout Salmo trutta were exposed to fluctuations in flow and water level to simulate hydro-peaking conditions downstream of a hydropower installation. Blood plasma cortisol concentrations reached a maximum of 59·4 ± 35·3 ng ml⁻¹ (mean ± 95% CL) 2h after the end of down-ramping. Return to the pre-exposure cortisol level was achieved within 6 h. When subjected to daily cyclical fluctuations over 7 days, plasma cortisol levels were significantly elevated (61·3 ± 26·8 ng ml⁻¹) on the first day compared to undisturbed fish (4·9 ± 3·7 ng ml⁻¹). On the fourth and seventh day, no elevation in plasma cortisol above control levels was observed. No changes in blood glucose that could be attributed to the stressor were found. There was no correlation between plasma cortisol and blood glucose levels. The short-lived cortisol response to daily fluctuations indicates a rapid habituation to this Stressor.     

Plasma cortisol concentrations before and after social stress in rainbow trout and brown trout

Two related experiments examined the relationship between plasma cortisol concentrations and the development of social hierarchies in fish. In the first, rainbow trout, Oncorhynchus mykiss, and brown trout, Salmo trutta, were observed for dominance interactions when confined within single-species pairs for 4, 48, or 168 h. Subordinate members of a pair exhibited significantly higher cortisol concentrations than dominant and single fish, but the pattern of cortisol elevation differed between the two species, being quicker to rise and increasing to a higher level in rainbow trout. Cortisol concentrations were correlated with behavioural measurements; the more subordinate the behaviour exhibited by a fish, the higher its cortisol concentration. Social stress was a chronic stressor, and no acclimation to social status occurred during the week. In the second experiment, measurements of plasma cortisol were made before pairing of rainbow trout and then after 48 h of confinement in pairs. Subordinate fish demonstrated significantly higher concentrations of plasma cortisol both before and after social stress. It therefore appears that in addition to cortisol being elevated during periods of social stress, an association may exist between initial cortisol levels and the likelihood of a fish becoming subordinate.