Changes in blood cortisol, glucose and lactate in carp retained in anglers'keepnets

Capture of carp Cyprinus carpio from holding tanks by dipnet, or from semi-natural conditions by rod and line, elicits a physiological stress response characterized by elevation of plasma cortisol levels. The transfer of carp to keepnets subsequent to capture does not increase or reduce the magnitude or duration of this response and in both cases plasma cortisol levels have returned to pre-stress levels within 24 h of the initial disturbance. The postcapture plasma cortisol elevation is accompanied by disturbances in plasma glucose and lactate levels but these are less consistent in severity and duration than the cortisol response. These data suggest that the retention of fish in keepnets following capture, does not represent a source of stress additional to that imposed by capture and has no effect on the rate of recovery of the fish from the initial capture stress.     

Differences in plasma cortisol and cortisone dynamics during stress in two strains of rainbow trout (Oncorhynchus mykiss)

Plasma levels of cortisone, a steroid hormone of potential physiological significance in fish, have rarely been measured. This study examines the interrelationship between circulating levels of cortisone and the major teleost corticosteroid, cortisol, in the blood of two strains of rainbow trout subject to confinement stress, a condition know to stimulate corticosteroidogenic activity. In unstressed fish from both strains, mean plasma cortisol levels were within the range 0.4–7.5 ng ml⁻¹. Mean plasma cortisone levels were within the range 7.1–15.9 ng ml⁻¹. Plasma cortisol levels were elevated within 5 min of the onset of strees and reached peak values within 45 min, although there was a marked difference betweed the maxima observed in the two strains (strain 1:70 ng ml⁻¹; strain 2:150 ng ml⁻¹). The rate of increase of plasma cortisone levels during strees was more rapid than that of cortisol, maximum values (strain 1:100ng ml⁻¹; strain 2:160 ng ml⁻¹) being reached within 10 to 20 min of the onset of stress. This rapid stress-induced elevation of plasme cortisone has not previously been reported in fish. We suggest that rapid conversion of cortisol to cortisone during the initial response to stress accounts for the appearance of large amounts of cortisone in the blood, indicating that circulating for the appearance of large amounts of cortisone in the blood, indicating that circulating levels of cortisol alone do not fully reflect the secretory activity of the interregnal during the initial of cortisol alone do not fully the secretory activity of the interregnal during the initial phase of the stress response. The results also indicate that the rate of clearance of cortisone from the circulation may be a major factor in determining stress-stimulated levels of plasma cortisol.     

Effects of copper on the acute cortisol response and associated physiology in rainbow trout

The aim of this study was to determine the effects of chronic waterborne copper (Cu) exposure on the acute stress-induced cortisol response and associated physiological consequences in rainbow trout (Oncorhynchus mykiss). Trout were exposed to 30 μg Cu/L in moderately hard water (120 mg/L as CaCO(3)) for 40 days, following which time the acute cortisol response was examined with a series of stressors. At 40 days, a 65% increase in Cu was observed in the gill, but no accumulation was observed in the liver, brain or head kidney. Stressors such as air exposure or confinement did not elicit an increase in circulating cortisol levels for Cu-exposed fish, in contrast to controls. However, this inhibitory effect on the acute cortisol response appeared to have few implications on the ability of Cu-exposed fish to maintain ion and carbohydrate homeostasis. For example, plasma Na(+), Ca(2+) and glucose levels as well as hepatic glycogen levels were the same post-stress in control and Cu-exposed fish. Trout were also challenged with exposure to 50% seawater for 48 h, where Cu-exposed trout maintained plasma Na(+), glucose and hepatic glycogen levels. However, Cu-exposed fish experienced decreased plasma K(+) levels throughout the Cu exposure and stress tests. In conclusion, chronic Cu exposure resulted in the abolition of an acute cortisol response post-stress. There was no Cu accumulation in the hypothalamus-pituitary-interrenal axis (HPI axis) suggesting this was not a direct toxic effect of Cu on the cortisol regulatory pathway. However, the lack of an acute cortisol response in Cu-exposed fish did not impair the ability of the fish to maintain ion and carbohydrate homeostasis. This effect on cortisol may be a strategy to reduce costs during the chronic stress of Cu exposure, and not endocrine disruption as a result of toxic injury.     

The effects of capture, handling, confinement and ectoparasite load on plasma levels of cortisol, glucose and lactate in the coral reef fish Hemigymnus melapterus

Tropical labrids Hemigymnus melapterus sampled underwater had low plasma levels of cortisol, glucose, and lactate. Plasma cortisol levels were elevated by capture stress within 5–6 min, while glucose and lactate levels were not. Plasmalevels of cortisol and glucose increased after 2–4 h of handling and transport to the laboratory. Levels of cortisol and glucose fell with laboratory acclimation back to values similar to those found in wild fish. Parasitism by gnathiid isopods across an order of magnitude of isopod numbers had no effect on plasma levels of cortisol or glucose. Thus, H. melapterus has a stress response similar to that shown by temperate species, and relatively high parasite loads are not apparently stressful to fish in the wild. This may be related to the counterproductive effects of physiological stress responses on the immune system or behaviour-modulated processes that counter parasitic invasion.     

Endocrine and metabolic responses to stress in a laboratory population of the tropical damselfish Acanthochromis polyacanthus

The effects of confinement and exercise on the stress response of the spiny damselfish Acanthochromis polyacanthus were investigated in a laboratory stock of fish. Cultured spiny damselfish had basal plasma cortisol values (<16 ng ml⁻¹) similar to those found in wild fish, and basal plasma glucose and lactate levels that were similar to those found in other teleosts. Plasma cortisol concentrations increased in response to stress with a latency period of 5–10 min. Removal of the stressor resulted in partial recovery of cortisol levels by 24 h. Plasma glucose levels increased in response to stress in all experiments with significant increases occurring within 15 min of the imposition of stress. Elevations in plasma glucose concentrations were not initially reflected in changes in liver or muscle glycogen content, with significant reductions in liver glycogen concentrations only occurring in response to extended periods of stress. In contrast to many temperate species, plasma lactate concentrations did not consistently increase in response to stress, suggesting that the stress response in spiny damselfish is not strongly characterized by anaerobiosis.     

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.     

Cortisol influences the antipredator behavior induced by chemical alarm cues in the Frillfin goby

We evaluated the effect of increased plasma cortisol levels on fish antipredator behavior induced by conspecific chemical alarm cues. The experimental model for the study was the Frillfin goby Bathygobius soporator. We first confirmed that the alarm substance induces typical defensive antipredator responses in Frillfin gobies and described their alarm substance cells (epidermal ‘club’ cells). Second, we confirmed that intraperitoneal cortisol implants increase plasma cortisol levels in this species. We then demonstrated that exogenous cortisol administration and subsequent exposure to an alarm substance decreased swimming activity to a greater extent than the activity prompted by either stimulus alone. In addition, cortisol did not abolish the sheltering response to the alarm chemical cue even though it decreased activity. As predators use prey movements to guide their first contact with the prey, a factor that decreases swimming activity clearly increases the probability of survival. Consequently, this observation indicates that cortisol helps improve the antipredator response in fish.     

Tissue-Specific Induction of Hsp90 mRNA and Plasma Cortisol Response in Chinook Salmon following Heat Shock, Seawater Challenge, and Handling Challenge

In studying the whole-body response of chinook salmon (Oncorhynchus tshawytscha) to various stressors, we found that 5-hour exposure to elevated temperature (mean 21.6°C; + 10.6°C over ambient) induced a marked increase in Hsp90 messenger RNA accumulation in heart, brain, gill, muscle, liver, kidney, and tail fin tissues. The most vital tissues (heart, brain, gill, and muscle) showed the greatest Hsp90-mRNA response, with heart tissue increasing approximately 35-fold. Heat shock induced no increase in plasma cortisol. In contrast, a standard handling challenge induced high plasma cortisol levels, but no elevation in Hsp90 mRNA in any tissue, clearly separating the physiological and cellular stress responses. We saw no increase either in tissue Hsp90 mRNA levels or in plasma cortisol concentrations after exposing the fish to seawater overnight. Received October 1, 1999; accepted January 21, 2000     

Short-term physiological changes in turbot and seabream juveniles exposed to exogenous ammonia

Seabream and turbot juveniles (40-520 g) were exposed to constant exogenous NH5-N concentrations (1.27-4.27 mmol/l; pH, 8.15). In 96 hr acclimated fish, plasma TA-N (total ammonia nitrogen) contents were positively correlated to ambient ammonia concentrations. The LD50 were 2.2-2.5 mmol/l TA-N in both species. There were no marked osmoregulatory disturbances and plasma urea-N, thyroid hormones levels and gill (Na-K)-ATPase activities were only affected at the highest concentrations. Liver GOT, GPT and GIDH activity dose-response were low and species dependent. In cannulated and non-cannulated turbot exposed to half 96 hr LC50 (lethal ambient concentration for 50% of the population), there was a rapid, pronounced and prolonged increase in plasma TA-N, followed by an immediate decline when exogenous ammonia supply was stopped. Maximum loading and unloading were observed within 1-3 hr. Plasma cortisol levels indicated a stressful situation in exposed fish (150 ng/ml) and a quick recovery capacity. In dose and time response experiments, the most relevant physiological indicator of ammonia stress was blood TA-N content. Other parameters tested led either to transient or low amplitude responses except when fish approached death.     

Cortisol in teleosts: dynamics,mechanisms of action,and metabolic regulation

Cortisol is the principal corticosteriod in teleost fishes and its plasma concentrations rise dramatically during stress. The relationship between this cortisol increase and its metabolic consequences are subject to extensive debate. Much of this debate arises from the different responses of the many species used, the diversity of approaches to manipulate cortisol levels, and the sampling techniques and duration. Given the extreme differences in experimental approach, it is not surprising that inconsistencies exist within the literature. This review attempts to delineate common themes on the physiological and metabolic roles of cortisol in teleost fishes and to suggest new approaches that might overcome some of the inconsistencies on the role of this multifaceted hormone. We detail the dynamics of cortisol, especially the exogenous and endogenous factors modulating production, clearance and tissue availability of the hormone. We focus on the mechanisms of action, the biochemical and physiological impact, and the interaction with other hormones so as to provide a conceptual framework for cortisol under resting and/or stressed states. Interpretation of interactions between cortisol and other glucoregulatory hormones is hampered by the absence of adequate hormone quantification, resulting in correlative rather than causal relationships.The use of mammalian paradigms to explain the teleost situation is generally inappropriate. The absence of a unique mineralocorticoid and likely minor importance of glucose in fishes means that cortisol serves both glucocorticoid and mineralocorticoid roles; the unusual structure of the fish glucocorticoid receptor may be a direct consequence of this duality. Cortisol affects the metabolism of carbohydrates, protein and lipid. Generally cortisol is hyperglycaemic, primarily as a result of increases in hepatic gluconeogenesis initiated as a result of peripheral proteolysis. The increased plasma fatty acid levels during hypercortisolaemia may assist to fuel the enhanced metabolic rates noted for a number of fish species. Cortisol is an essential component of the stress response in fish, but also plays a significant role in osmoregulation, growth and reproduction. Interactions between cortisol and toxicants may be the key to the physiology of this hormone, although cortisol's many important housekeeping functions must not be ignored. Combining molecular approaches with isolated cell systems and the whole fish will lead to an improved understanding of the many faces of this complex hormone in an evolutionary and environmental framework.     

Cold shocks: a stressor for common carp

The stress response of common carp Cyprinus carpio was studied by evaluating plasma cortisol, glucose and lactate after single or multiple rapid temperature drops (ΔT: 7, 9 or 11° C). All three amplitudes used induced a significant rise in plasma cortisol levels. Peaks occurred within 20 min after onset of the cold shock. No stress-related secondary metabolic changes were observed in any of the experiments described: plasma glucose levels remained unaffected and plasma lactate levels dropped. Carp of 60 days old showed a significant stress response, although plasma cortisol levels were lower than those observed in carp of 120 days. Furthermore, fish that had experienced multiple cold shocks showed an overall lower cortisol response than fish experiencing a single cold shock, indicating that habituation to this stressor occurred.     

CRF-related peptides contribute to stress response and regulation of appetite in hypoxic rainbow trout

Hypoxia stress suppresses appetite in a variety of fish species, but the mechanisms mediating this response are not known. Therefore, given their anorexigenic and hypophysiotropic properties, we investigated the contribution of forebrain corticotropin-releasing factor (CRF) and urotensin I (UI) to the regulation of food intake and the hypothalamic-pituitary-interrenal (HPI) stress axis in hypoxic rainbow trout. Exposure to 50 and 35% O(2) saturation for 24 h decreased food intake by 28 and 48%, respectively. The 35% O(2) treatment also increased forebrain CRF and UI mRNA levels, plasma cortisol, and lactate. Exposure for 72 h to the same conditions resulted in similar reductions in food intake, increases in plasma cortisol proportional to the hypoxia severity, and increases in forebrain CRF and UI mRNA levels in the 50% O(2) treatment. Relative to saline-infused fish, chronic intracranial infusion of the CRF receptor antagonist alpha-helical CRF((9-41)) reduced the appetite-suppressing effects of 24-h exposure to 35% O(2) and blocked the hypoxia-induced increase in plasma cortisol. Finally, forebrain microdissection revealed that 50 and 35% O(2) exposure for 24 h specifically increases preoptic area CRF and UI mRNA levels in proportion to the severity of the hypoxic challenge and either has no effect or elicits small decreases in other forebrain regions. These results show that CRF-related peptides play a physiological role in regulating the HPI axis and in mediating at least a portion of the reduction in food intake under hypoxic conditions in rainbow trout and demonstrate that the response of forebrain CRF and UI neurons to this stressor is region specific.     

Effects of adrenocorticotropin stimulation on cortisol dynamics of pregnant gilts and their fetuses: implications for prenatal stress studies

The effect of adrenocorticotropic hormone (ACTH) administration on plasma cortisol concentrations was determined in pregnant gilts and their fetuses. In a first experiment, 100 IU ACTH (Synacthen Depot) was administered intramuscularly to the gilts every second day from Days 49 to 75 of gestation. ACTH injections were carried out at 08:00 h and, thereafter, 10 blood samples were taken within the following 8h via jugular catheters. Blood samples were analysed for plasma cortisol concentrations, and results were compared with values from animals which were treated with physiological saline and untreated animals (blood sampling only). The values for plasma cortisol concentrations increased until 3h after ACTH applications to a mean maximum level of 276.5+/-17.2 nmol/l in the whole 4-week stimulation period. Plasma cortisol levels did not return to pre-treatment values within the 8 h post-injection. No differences in cortisol levels were found between the physiological saline and untreated control, and no habituation of the adrenocortical response to ACTH was found during the 4-week stimulation period. In a second experiment, 100 IU ACTH were administered to pregnant gilts at gestation Day 65. After 3 h, fetuses were recovered under general anaesthesia and blood samples were taken from the umbilical vein, artery, and, after decapitation, from periphery. Application of ACTH to the sows significantly increased their plasma cortisol concentrations (P<0.001), and also increased plasma cortisol concentrations in peripheral blood samples from the fetuses (P=0.09) and in the umbilical vein (P<0.001) and artery (P<0.01), respectively. Plasma ACTH concentrations did not differ in fetuses from ACTH-treated or control sows. The results show that in gilts the adrenocortical response to an exogenous application of Synacthen Depot is consistent over time during mid-gestation. Furthermore, cortisol but not ACTH levels were increased in fetuses from ACTH-treated sows, indicating that maternal cortisol can cross the placenta during mid-gestation. The stimulation of maternal cortisol release through exogenous ACTH with subsequent elevation of fetal cortisol levels is, therefore, a useful approach for studying effects of elevated maternal glucocorticoids in prenatal stress studies in pigs.     

Changes in free and total plasma cortisol levels in juvenile haddock (Melanogrammus aeglefinus) exposed to long-term handling stress

We measured changes in free and total plasma cortisol levels, plasma glucose, gill hsp70 levels, and growth in haddock (Melanogrammus aeglefinus) subjected to a long-term handling stress (15 s out of water, each day, for 4 weeks), and the effect of this long-term stress on the ability of haddock to respond to an acute stressor. The acute stressor was a single handling stress, and fish were sampled at 1, 6, and 12 h post-stress. During the long-term stress study, free and total plasma cortisol levels increased significantly (10-fold) in the stressed group after the second week. However, the percentage of free cortisol was already significantly elevated by the first week (control 17%, stressed 55%), and remained high during the second week (control 35% and stressed 65%). After 3 and 4 weeks of handling, both free and total cortisol declined in stressed fish to levels that were not significantly different from pre-stress values. Control fish grew significantly more than stressed fish (by 32% and 18%, respectively) over the 4 week study, and condition factor only increased in control fish. Although fish from the control group showed elevated total plasma cortisol levels (to 47 ng mL(-1)) 1 h after the acute stress, and the levels in stressed fish were comparable to those for the control fish, no significant increase in plasma cortisol was measured in the group subjected to the long-term stress. Free plasma cortisol levels did not increase significantly in either group following the acute stress. However, free plasma cortisol levels were significantly higher in long-term stress group, as compared with the control group, at 6 h post-stress. Plasma glucose and gill hsp70 levels were not altered by either the long-term stress or acute stressor. Our data indicate that cortisol (free and total), but not glucose or hsp70, appears to be adequate to assess short- and long-term stress in haddock.     

Exercise training and the stress response in rainbow trout, Salmo gairdneri Richardson

Plasma levels of catecholamines, cortisol, and glucose were monitored in rainbow trout during a 6-week forced swimming exercise programme. Compared to resting non-exercised controls, resting trained fish had lower levels of epinephrine, norephinephrine, cortisol, and glucose during the last 3 weeks of training. Initially, trained fish that were swimming had higher levels of epinephrine than resting trained fish. After 2 weeks of exercise, swimming did not significantly elevate epinephrine levels in trained fish. Glucose levels were consistently greater in swimming fish than in resting fish. At the end of the training period, exercised trout had lower (15–20%) oxygen consumption rates while resting or swimming than unexercised fish.
After a 5-month forced swimming exercise programme plasma levels of catecholamines and glucose were monitored in trained and untrained cannulated rainbow trout after 2 min of mild agitation. Trained fish showed an immediate (within 1 min) increase in the levels of epinephrine, but not norepinephrine and a delayed (within 15 min) increase in the levels of plasma glucose. Epinephrine levels returned to pre-stress levels within 15 min. Untrained fish had no significant increase in the plasma levels of norepinephrine, epinephrine, or glucose.     

Effect of high‐dose vitamin C supplementation on growth,tissue ascorbic acid concentrations and physiological response to transportation stress in juvenile silver pomfret,Pampus argenteus

This study investigated the effect of high‐dose vitamin C supplementation on growth, tissue ascorbic acid concentrations and physiological response to transportation stress in juvenile silver pomfret, Pampus argenteus (initial average weight 6.2 ± 0.2 g). Three practical diets were formulated to contain 100 (control), 450 and 800 mg ascorbic acid/kg diet, respectively, supplied as l‐ascorbyl‐2‐polyphosphate. Each diet was fed to triplicate groups of fish in circular tanks (3 m ø, 1.5 m depth) (60 fish/tank) for 9 weeks. Growth did not change significantly with dietary vitamin C levels, although an improvement tendency with an increase in vitamin C supplementation was observed. Ascorbic acid concentrations in the liver and muscle of fish fed diets containing graded levels of vitamin C were positively correlated with dietary levels of this vitamin. Tissue ascorbic acid concentrations significantly increased with increasing vitamin C supplementation. After 9 weeks, the fish were subjected to transportation stress for 4 h to determine the influence of high vitamin C supplementation on the physiological response to this stressor. Serum cortisol, glucose and lactate levels significantly increased in stressed fish. Serum cortisol and glucose concentrations after stress were significantly higher in fish fed the control diet (7.91 μg L^?1 and 0.80 mm , respectively) than in the other groups. However, there were no significant differences in serum cortisol and glucose levels after stress between the 450 and 800 mg kg^?1 diets. No significant change could be found in serum lactate levels after stress among the different treatments. In conclusion, the dietary administration of high doses of vitamin C could reduce stress in silver pomfret and increase the survival of fish under stress conditions.     

Cortisol and thyroid hormone responses to acid stress in the brown trout, Salmo trutta L.

Individual cannulated brown trout monitored during exposure to acidic water showed increased plasma cortisol after 3 h at pH 4.0 with low (0.05 mm) or high (2.8 mm) calcium (Ca) content, and after 2 days in acidic water with a high Ca content. Most fish did not survive for 2 days in acidic water with a low Ca content. Non-cannulated fish showed a similar increase in mean plasma cortisol after 2 days in high-Ca acidic water (pH 4.0–4.6), but not in acidic water of a low Ca content. After 7 days of exposure to acidic water, plasma cortisol appeared to recover when there was a high Ca content but increased 20-fold when Ca content was low. In cannulated fish severe acid stress resulted in a marked and rapid thyroid response. Plasma thyroxine (T₄) was elevated after 3 h exposure to acidic water of both low and high Ca content and remained elevated for 2 days of acid exposure with high Ca. In non-cannulated fish an increase in mean T₄ was apparent only after 7 days in low-Ca acidic water. Plasma triiodothyronine (T₃) levels were not significantly altered by any of the acid regimes. Plasma glucose of cannulated fish was elevated within 3 h of acid-exposure and remained elevated after 2 days in high-Ca acidic water.     

Interference of o,p'DDD with interrenal function and cortisol metabolism in Sarotherodon aureus (Steindachner)

The purpose of this study was to investigate possible effects of organochlorine residues on cortisol balance in a freshwater fish. The combined stress of netting, handling and blood sampling in Sarotherodon aureus normally results in a twofold increase of circulating cortisol, within 30–60 min. Fish treated with o,p'DDD (50 mg kg⁻¹) had higher resting level of cortisol than before treatment (155.8±12.7 v. 86.9± 11.2 ngmh⁻¹; n=16). No further increase in cortisol level occurred in these fish after exposure to stress; this inability to respond was maintained for more than 120 days. A recovery of the response to ACTH by superfused interrenal tissue from the treated fish was observed 255 days after treatment. Successive blood sampling of o,p'DDD-treated fish, injected intracardially with labelled cortisol, have shown that the half-life of the steroid in the circulation is prolonged by 370% compared with controls. The hepatic metabolism of cortisol was studied by incubating liver slices with the labelled hormone. Hepatic tissue from o,p'DDD-treated fish metabolized cortisol slower than livers from controls. The high resting level of cortisol in plasma of fish treated with o,p'DDD may be attributed to the retarded metabolism of the steroid by the liver. The lack of augmented cortisol levels in response to stress is attributed to the interference of the organochlorine with the response of the interrenal tissue to the stress-induced surge of endogenous ACTH.     

Poor water quality suppresses the cortisol response of salmonid fish to handling and confinement

Confinement of brown trout in small troughs of static water for 1 h at a density of six fish 251⁻¹ stimulated the hypothalamic-pituitary-interrenal axis and resulted in an elevation of plasma cortisol from basal levels (less than 2 ng m1⁻¹) to about 100 ng m1⁻¹, the degree of stimulation being dependent upon water temperature. Confinement at a density of 30 fish 251⁻¹ resulted in a 50% suppression of this response. It is demonstrated that this effect is mediated by changes in water chemistry and not by crowding per se . Experimental manipulation of the water chemistry showed that reduced pH (7.1 → 6.3), elevated free CO₂ (63 → 520 μmoll⁻¹) or elevated ammonia (8 → 1300 μg 1⁻¹ as total ammonia nitrogen) had no individual effects on the interrenal response to acute confinement. Elevated ammonia in combination with reduced pH significantly increased the plasma cortisol levels in response to acute confinement, whereas a combination of reduced oxygen (100 → 20% saturation), elevated free CO₂ and elevated ammonia markedly suppressed (∼ 50%) the cortisol response of both brown trout and rainbow trout to acute confinement in a manner similar to that observed with trout at high densities. A compensatory increase in plasma cortisol levels was observed during the subsequent recovery of fish which had been confined for 1 h in water of poor quality. These findings are discussed in relation to the exposure of fish to multiple stresses and to the role of corticosteroids in the stress response.     

Ovine corticotropin-releasing hormone stimulation test in patients with chronic renal failure: pharmacokinetic properties, and plasma adrenocorticotropic hormone and serum cortisol responses

The data on the status of the hypothalamic-pituitary-adrenal (HPA) axis in haemodialysis (HD) patients are conflicting. Moreover, a state reminiscent of Cushing's syndrome has been reported in this group of patients. Corticotropin-releasing hormone (CRH), that is produced by the hypothalamus and modulates the secretion of adrenocorticotropic hormone (ACTH), has been shown to be useful as a provocative test of the HPA axis. We investigated the effect of exogenous ovine CRH (oCRH) on plasma levels of ACTH and cortisol in 13 chronic HD patients. The plasma concentrations of immunoreactive CRH following oCRH administration were similar in patients and controls. In all patients, oCRH given intravenously as bolus injection caused a further increase in the already elevated levels of cortisol. The mean basal plasma levels of ACTH were within the normal range. There was, however, a blunted ACTH response to oCRH. We conclude that the HPA axis in chronic HD patients retains the ability to respond to exogenous oCRH. The patterns of the ACTH and cortisol response to this peptide resemble those observed in chronic stress (depression, anorexia nervosa). Besides, the kinetics of disappearance of oCRH indicate that the kidney may not be the major organ that metabolizes oCRH.