Effects of chronic stress on plasma corticosterone, ACTH and prolactin

Rats were placed in a stressful environment for 24 hr per day and levels of plasma hormones were measured after varying numbers of days in the environment. Rats were habituated to operant chambers placed in sound-attenuated enclosures. Food pellets were available by lever press on a FR1 schedule. After 3 days of habituation, rats in the “stressed” group were trained to pull a ceiling chain to avoid or escape shock. Following training, stress trials, consisting of a consecutive sequence of 5 sec each of a warning light, warning tone and 0.16, 0.32, 0.65, 1.3 and 2.6 mA of footshock, occurred approximately once per 5 min around-the-clock. For the first day, the sequence was terminated when the ceiling chain was pulled. On subsequent days, 90% of all shock presentations could be avoided or escaped by chain pull; the remaining 10% of trials were inescapable and the entire sequence was presented. Control rats lived in identical chambers without presentation of shock. Rats were sacrificed after 1, 2, 3, 4, 7 or 14 days in this environment and levels of plasma corticosterone, ACTH and prolactin were determined. Levels of plasma corticosterone were elevated during the first 7 days in the stressful environment, but returned to control values by day 14. Levels of plasma ACTH and prolactin were similar in stressed and control rats at all time points measured. These data suggest that stress-induced changes in glucocorticoids but not in ACTH or prolactin might mediate some of the physiological changes that occur as the result of chronic stress.     

Growth hormone and prolactin response to rehydration during exercise: effect of water and carbohydrate solutions

Summary The effect of progressive rehydration with either water or a carbohydrate solution on the plasma growth hormone (GH) and prolactin (PRL) response to exercise was examined together with plasma somatostatin. Five subjects underwent four 3-h experimental sessions at 36°C in which 25-min exercise periods alternated with 5-min rest periods. The sessions were conducted without fluid replacement (DH) or under rehydration with either water or isosmotic carbohydrate solutions AISO (acid) or NISO (neutral). The fluid was given every 10 min after the 1st h of exercise. Plasma GH increased significantly (p < 0.01) under DH after 2 and 3 h of exercise; this increase was prevented by rehydration with water, AISO and NISO. Plasma glucose was significantly higher following AISO and NISO rehydration compared with DH. This possibly influenced the GH response, but there was no difference between plasma glucose levels under DH and water rehydration at any time. The solutions tended to attenuate the increase in heart rate, rectal temperature and plasma cortisol, suggesting that the lack of GH response under rehydration conditions is a result of decreasing physiological stress levels. The GH response could not be explained by plasma somatostatin, which tended to decline in all sessions. Plasma PRL did not increase in any of the sessions, confirming that exercise without rehydration is a more potent stimulator of GH than of PRL. It is concluded that progressive rehydration with water is sufficient to prevent the exercise-induced increase in plasma GH.     

Relationships of stress responses with plasma oxytocin and prolactin in heifer calves

Oxytocin and prolactin are potential candidates for the regulation of behavioral and physiological stress responses in the brain. To investigate the neurobiological basis of individual differences in stress responses in cattle, we examined the association of behavioral and hypothalamo-pituitary-adrenal axis reactivity to acute stressors and basal and stimulated levels of oxytocin and prolactin. Twenty Holstein heifer calves aged 2 weeks were subjected to a 10 min open-field test (OFT) followed by presentation of a feeding bucket for 15 min in the OF. If the calf contacted the bucket, a blast of air was applied to its muzzle (surprise test). Jugular blood samples collected before and after both tests were analyzed for oxytocin, prolactin, and cortisol. Relationships of basal and percent change in oxytocin or prolactin with behavioral responses in each test and percent change in cortisol were analyzed using principal components analysis and Spearman rank correlations. Plasma cortisol and prolactin concentrations were significantly elevated by the tests (p < 0.005), but plasma oxytocin concentration did not significantly change (p > 0.1). Four principal components explained 56.1% of the total variation: curiosity, general activity, fearfulness, and dependence on humans. Curiosity was inversely correlated with basal oxytocin level (rS = − 0.683, p < 0.05). General activity was positively correlated with prolactin reactivity (rS = 0.448, p < 0.05) and inversely with oxytocin reactivity to the novel environment (rS = − 0.717, p < 0.05). Fearfulness tended to correlate positively with basal oxytocin level (rS = 0.583, p < 0.1). Dependence on humans correlated with none of the hormonal parameters. The relationships of basal oxytocin level with curiosity and fearfulness for novel environments are of particular interest for future study.     

Effects of ether stress on prolactin and corticosterone levels in prenatally-stressed male rats as adults

The effect of a potent prenatal stressor on adult levels of prolactin and corticosterone was investigated in male rats. It was found that prenatal stress had no effect on initial levels of either of these two hormones. Ether stress levels of prolactin were significantly lower in prenatally-stressed animals compared to prenatally-nonstressed subjects, whereas corticosterone levels in response to ether stress were only marginally affected in prenatally-stressed animals reared by prepartally-stressed mothers. It is suggested that alterations in endocrine function in the adult animal may result from prenatal stress effects on the development of neural mechanisms that regulate the hormonal response to ether stress.     

Contribution of hGH20K variant to blood hGH response in sauna and exercise

Summary Exercise-induced increases in blood somatotropin (hGH) have always been considered in terms of quantity of the circulating molecules. Knowing that the hypophysis can release several GH species, we investigated the differential release in blood of total hGH (hGH_T) and the main hGH variant (hGH_20K) molecules in six trained male swimmers exposed to three different conditions known to favor GH release in blood: 45 min – 70% maximum oxygen uptake bicycling and swimming, and 20 min of sauna bathing. Based on the binding specificity of hGH antibodies, hGH_20K was isolated then assayed using the Nichols immunoradiometric assay system. All three experimental conditions produced significant (P < 0.001) elevations in blood hGHT and hGH_20K. In all three cases, mean blood hGH_20K contribution to blood hGH_T was relatively constant (11.9, SE 0.7%). Rises in rectal temperature were not statistically related to the changes in blood hGH_T. This demonstration of a relatively constant elevation in hGH_20K during bicycling, swimming, and sauna bathing can hardly explain the large differences in blood hGH_T responses reported in literature under similar conditions.     

Changes in the susceptibility of red blood cells to oxidative and osmotic stress following submaximal exercise

Red blood cell (RBC) susceptibility to oxidative and osmotic stress in vitro was investigated in cells from trained and untrained men before and after submaximal exercise. Whilst no significant change in peroxidative haemolysis occurred immediately after 1 h of cycling at 60% of maximal aerobic capacity ( _max), a 20% increase was found 6 h later in both groups (P<0.05). The RBC osmotic fragility decreased by 15% immediately after exercise (P<0.001) and this was maintained for 6 h (Ps<0.001). There was an associated decrease in mean cell volume (P<0.05). Training decreased RBC susceptibility to peroxidative haemolysis (P<0.025) but it did not influence any other parameter. These exercise-induced changes were smaller in magnitude but qualitatively similar to those found in haemopathological states involving haem-iron incorporation into membrane lipids and the short-circuiting of antioxidant protection. To explore this similarity, a more strenuous and mechanically stressful exercise test was used. Running at 75% _max for 45 min reduced the induction time of O₂ uptake (peroxidation), consistent with reduced antioxidation capacity, and increased the maximal rate of O2 uptake in RBC challenged with cumene hydroperoxide (P<0.001). The proportion of high-density RBC increased by 10% immediately after running (P<0.001) but no change in membrane-incorporated haem-iron occurred. In contrast, treatment of RBC with oxidants (20–50 mol·l^–1 in vitro increased cell density and membrane incorporation of haem-iron substantially. These results showed that single episodes of submaximal exercise caused significant changes in RBC susceptibility to oxidative and osmotic stress. Such responses may account for the increase in RBC turnover found in athletes undertaking strenuous endurance training.     

Voluntary body water and salt deficits as a cause of differences between men in their tolerance to heat

Summary Forty-nine unacclimatised Bantu mine workers divided into two groups were subjected to a standard heat exercise stress. One group had sweat losses replaced by drinking water and the other had no water at all. Salt and water deficits were measured by an indirect method based on the volume of urine and salt excreted over the four-hour period of the test. These excretions were correlated with the fourth-hour temperature response and showed good correlations. The difference in heat tolerance was found to be due to a difference in salt and water deficit. Osmolal clearance and free water clearance were additional measurements which showed agreement in the findings of the relative salt and water deficits.Blood chemistry and sweat physiology and chemistry could not discriminate between the heat intolerant and heat tolerant subjects.Certain features of blood and urine chemistry of water replacements and water deprivation were shown.

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Abbreviations RT₂ Rectal temperature at the end of the second hour - RT₄ Rectal temperature at the end of the fourth hour - HR₂ Heart rate at the end of the second hour - HR₄ Heart rate at the end of the fourth hour - SK₂ Skin temperature at the end of the second hour - SK₄ Skin temperature at the end of the fourth hour - Nac Sodium concentration - Nae Sodium excretion - Clc Chloride concentration - Cle Chloride excretion - Kc Potassium concentration - Ke Potassium excretion - U vol Urine volume - C_osm Osmolal clearance - F.W.C. Free water clearance - r Correlation coefficient - OSM Osmolality - Mosm Milliosmols - A.M. Before the test - P.M. After the test - S. Significant at the 5% level - N.S. Not significant at the 5% level     

Attenuation of the cutaneous blood flow response during combined exercise and heat stress

Skin blood flow (SkBF) was measured in six male subjects using laser-Doppler velocimetry, with zero-gradient auditory canal temperature (T_ac) used as an index of body core temperature (T_c). Subjects performed incremental, upright cycling commencing at 40% peak power ( _peak: 10 min), increasing every 4 min by 5 % _peak thereafter. Trials were conducted in hot (ambient temperature (T_a) 36.7 ±0.2°C, relative humidity (rh) 46.1 ±3.2%; _peak ±S.D.), and neutral environments (T_a 19.6 ±0.3°C, rh 50.2 ±1.4%). SkBF increased with T_ac in all subjects. Attenuation of SkBF occurred at the same T_ac, relative SkBF and cardiac frequency (f _c) between environments, but at a lower exercise intensity (40.8 ±0.8% versus 55.8 ±3.0% _peak) in the hot environment (p<0.05). Data indicate that T_c thresholds for SkBF attenuation may exist. However, it is suggested that attenuation thresholds coincided with a reduced central blood volume, which may occur at a critical level of cutaneous blood pooling.     

Effect of exercise to rest ratio on plasma lactate concentration at work rates above and below maximum oxygen uptake

Summary The metabolic and physiological responses to different exercise to rest ratios (E: R) (2:1, 1: l, 1:2) of eight subjects exercising at work rates approximately 10% above and below maximum oxygen uptake ( ) were assessed. Each of the six protocols consisted of 15 1-min-long E : R intervals. Total work (kJ), oxygen uptake ( ), heart rate (f _c and plasma lactate concentrations were monitored. With increases in either E : R or work rate, andf _c increased (P <0.05). The average (15 min) andf _c ranged from 40 to 81 %, and from 62 to 91% of maximum, respectively. Plasma lactate concentrations nearly doubled at each E : R when work rate was increased from 90 to 110% of and ranged from a low of 1.8 mmol -I^–1 (1: 2–90) to a high of 10.7 mmol·1^–1 (2:1–110). The 2:1–110 protocol elicited plasma lactate concentrations which were approximately 15 times greater than that of rest. These data suggest that plasma lactate concentrations during intermittent exercise are very sensitive to both work rate and exercise duration.     

Response of plasma endorphins,prolactin and catecholamines in women to intense heat in a sauna

Summary Concentrations of immunoreactive-endorphin (ir-E), corticotropin, cortisol, prolactin and catecholamines in plasma were followed in 11 healthy women during and after exposure to intense heat in a Finnish sauna bath, and compared to those in a similar control situation without exposure to heat. Heat stress significantly increased prolactin and norepinephrine secretion; the percentage increases from the initial plasma concentrations varied from 113 to 1280% (mean 510%) and from 18 to 150% (mean 86%), respectively. The response of the plasma levels of epinephrine, ir-E, corticotropin and cortisol to heat exposure was variable. Compared to the control situation, no statistically significant effect of heat exposure on the plasma levels of these hormones was found.     

Morphometrical variations of prolactin cells in response to prolonged and systemic administration of Met-enkephalin in female rats

Summary A stimulatory effect on prolactin secretion had been describe after acute and systemic administration of met-enkephalin, but the effects of this opioid after chronic administration has not been reported, and the response of mammotroph cells is not clear. As a complement to previous studies, a morphometric analysis (light and electron microscopy) was carried out on prolactin cells from female rats treated chronically with met-enkephalin. Clear features of cellular hyperactivity appeared after chronic and systemic administration of the opioid, and these persisted for two weeks. The changes consisted in increases of cellular, cytoplasmic and nuclear areas, volume and surface densities of the Golgi complex and rough endoplasmic reticulum, as well as the numbers of exocytotic figures. These morphological alterations were paralleled by an increase in serum prolactin levels as detected by RIA. It is concluded that the increase in the synthesis and secretory activity of prolactin cells following chronic and systemic administration of met-enkephalin is very similar to those observed after acute and intraventricular administration.     

Hormone response of diabetic patients to exercise at cool and warm temperatures

Summary Both exercise and high ambient temperatures stimulate the secretion of counterregulatory hormones which can change glucose homeostasis. We studied whether in diabetic patients there are any differences in the hormonal response to exercise performed at cool or warm ambient temperatures. A study was performed on eight male insulin-dependent patients at rest and during exercise at + 10° C and + 30° C. Exercise consisted of three consecutive 15-min periods at 60% of maximal aerobic capacity. The concentrations of plasma lactate and counterregulatory hormones at rest were similar at warm and cool temperature, whereas prolactin concentration was higher (P < 0.01) at +30° C. Exercise resulted in an increase in noradrenaline, growth hormone and prolactin (P < 0.01), prevented the diurnal decrease in cortisol, but had no effect on glucagon. Hormone responses to exercise were similar at + 10° C and at +30°C, except for cortisol and noradrenaline which showed greater responses at warm than at cool temperatures. This may have been due to the higher relative work load at warm compared to cool temperatures as suggested by the higher heart rate and greater increase of lactate at +30° C. These data indicate that within a range of ambient temperatures commonly occurring in sports, the response of counterregulatory hormones is largely independent of ambient temperature in insulin-dependent diabetic patients.     

The effects of face cooling during hyperthermic exercise in man: evidence for an integrated thermal, neuroendocrine and behavioural response

The present study investigated whether face cooling reduced both the perceived exertion (RPE) and prolactin (PRL) release during hyperthermic exercise. Ten, non-heat-acclimated males (23 +/- 2 years; maximal oxygen consumption, 56 +/- 7 ml kg(-1) min(-1) [mean +/- s.d.]) exercised for 40 min on a cycle ergometer at 65% of their peak aerobic power, at an ambient temperature of 33 degrees C (27% relative humidity) with (FC) and without face cooling as a control (CON). With FC, forehead temperature was maintained approximately 6 degrees C lower than CON, while other skin sites were similar or slightly warmer in the FC condition. Rectal temperature increased by approximately 1.5 degrees C with the same time course in both conditions. A relative bradycardia was observed during FC, with heart rate approximately 5 beats min(-1) lower than CON (P < 0.05). Mean plasma lactate was lower during FC (FC, 5.0 +/- 0.3 mmol l(-1); CON, 5.9 +/- 0.3 mmol l(-1); P < 0.05) but no differences were observed for plasma glucose, which remained constant during exercise. Levels of PRL were maintained at 175 +/- 17 mIU l(-1) during exercise for FC, while values for CON increased to a peak of 373 +/- 22 mIU l(-1) so that towards the end of the exercise, for the same rectal temperature, PRL was significantly lower in the FC condition (P < 0.05). Global and breathing RPE were reduced but only towards the end of the 40 min of exercise during FC, whilst subjective thermal comfort was significantly lower during FC (P < 0.05). We confirm the substantial effect that FC has on the secretion of PRL during hyperthermic exercise but show that it makes a relatively small contribution to the perception of effort when compared to the effect of a cool total skin area as occurs with exercise in a thermoneutral environment.     

Migration of T-lymphocytes into bone marrow as an initial response to stress

From 6 to 9 h after the beginning of the response to stress caused by immobilization for 6 h, cells with antigenic (θ-antigen) and functional (helper cells) characteristics of T-lymphocytes appeared in the bone marrow of CBA mice. Migration of T-lymphocytes into the bone marrow is regarded as a mechanism for increasing the nonspecific reactivity of the body.     

Plasma catecholamines during endurance exercise of different intensities as related to the individual anaerobic threshold

The study investigated the concentrations of free plasma catecholamines (CAT), adrenaline and noradrenaline, in comparison to heart rate and lactic acid concentrations during endurance exercises (EE) of different intensities related to the individual anaerobic threshold (IAT). A group of 14 endurance trained male athletes took part in the tests on a treadmill. After an exhausting incremental graded test (increasing 0.5 m · s^–1 every 3 min) to determine t he IAT, the subjects performed EE of 45 min in randomized order with intensities of 85%, 95%, 100% and 105% (E85–E105) of the IAT. The heart rate and CAT increased continuously during all EE. The CAT reacted sensitively to EE above IAT (E105) and showed an overproportional increase in comparison to EE performed with an intensity at or below IAT. At the same time, at exercise intensities up to IAT (E85–E100) a lactate steady state was observed whereas mean lactate concentrations increased during E105. The changes of lactate concentration allowed a better differentiation between E85–E100 as CAT measurements. In E95, E100 and E105 there was a partial overlap of heart rate, which in contrast to lactate concentration only differed by about 5%, so that small variations in heart rate could have coincided with considerable differences of exercise intensity when working at intensities near or above IAT. It was concluded that the range of IAT seemed to represent a real physiological breakpoint which corresponded to the aerobic-anaerobic transition.     

Dynamics and topography of human temperature regulation in response to thermal and work load

Summary Climatic chamber experiments were carried out with male subjects who were submitted to various rapid temperature changes. All experiments were performed first with the subjects at rest and later at work on a bicycle ergometer. The aims of the study were 1) to obtain quantitative data enabling to determine effects of a) abrupt thermal load, b) abrupt work load, and c) combined load on the topography and the dynamics of temperatures and effectors, and 2) to answer the question whether the effects of combined load may be computed by a linear superposition of pure thermal plus pure work load.Skin temperatures generally respond more directly to abrupt changes of thermal than of work load. This is in contrast to the dynamic behaviour of central temperatures which moreover exhibit the interesting effect of a transient paradoxical respone both to the onset of work and of thermal load.Time constants of the dynamics of metabolic heat production are high in response to changes of thermal load as compared to the time constants at the onset and end of worl. Generally the time constants of skin temperatures are shorter at rest than at work. Temperature topography changes only to a small extent in exercising subjects.The central temperature increase to combined thermal and work load is not significantly different from the added amount of temperature increases due to pure thermal and to pure work load. This suggests a quasi-linear superposition of both thermal effects and confirms, in accordance with further evidence of this and former studies, the hypothesis that work load does not interfere non-linearly with the regulatory processes. However, an input from thermosensitive elements in the muscles should be assumed.Supported by the Deutsche Forschungsgemeinschaft, SFB 114     

Fitness as a determinant of oxygen uptake response to constant-load exercise

Summary Exercise performed above the lactate threshold (Θ _La) produces a slowly-developing phase of oxygen uptake ( ) kinetics which elevates above that predicted from the sub-Θ _La -work rate relationship. This phenomenon has only been demonstrated, to date, in subjects who were relatively homogeneous with respect to fitness. This investigation therefore examined whether this behaviour occurred at a given absolute or whether it was a characteristic of supra-Θ _La exercise in a group of subjects with over a threefold range ofΘ _La (990–3000 ml O₂·min⁻¹) and peak (1600–5260 ml O₂·min⁻¹). Twelve healthy subjects performed: 1) exhausting incremental cycle ergometer exercise for estimation ofΘ _La ( ) and peak , and 11) a series of constant-load tests above and below for determination of the profile and efficiency of work. During all tests expired ventilation, and carbon dioxide production were monitored breath-by-breath. The efficiency of work determined during incremental exercise (28.1±0.7%, ,n=12) did not differ from that determined during sub- constant-load exercise (27.4±0.5%,p>0.05). For constant-load exercise, rose above that predicted, from the sub- -work rate relationship, for all supra- work rates. This was evident above 990 ml O₂·min⁻¹ in the least fit subject but only above 3000 ml O₂·min⁻¹ in the fittest subject. As a consequence the efficiency of work was reduced from 27.4±0.5% for sub- exercise to 22.6±0.4% (p<0.05) at the lowest supra- work rate (i.e. +20 W, on average). The efficiency of work generally decreased further at the higher supra- work rates. We conclude that the response to constant-load exercise includes an additional slow phase of the kinetics for all exercise intensities above irrespective of the fitness of the subject. Consequently, measurements of the aerobic efficiency of work during constant-load exercise must rigorously constrain the exercise intensity to the sub- domain. Supported by grants from the John D. and Catherine T. Mac-Arthur Foundation, USPHS RR 00865-15, and NIH HL 07694-01