Acute Stress Situations Research Articles

Involvement of NK1 receptors in metabolic stress markers after the central administration of substance P

Substance P (SP) is involved in the pathophysiology of several psychiatric disorders and is considered a central stress neurotransmitter. Endogenous SP does not inhibit the initial extent of the HPA axis response to restraint stress, but reduces the duration of the stress suggesting that SP plays an important role in the transition between acute and chronic stress. Stress hormones can alter metabolic functions in white adipose tissue and liver. The HPA axis is the endocrine pathway that promotes lipolysis elevating free fatty acid levels (FFA) in blood, besides indirectly causing hyperglycemia. In the present study, changes in the blood levels of stress markers in the anxiogenic-like effects of SP, as evaluated on the elevated plus-maze (EPM), were studied in adult male rats. Serum corticosterone was used as the traditional stress marker, while the plasma FFA and glucose were used as alternative anxiety/stress markers. Our findings show: (a) elevated corticosterone levels, confirming the aversive situation induced by SP (behaviorally assessed in the EPM) and indicating SP as a “chemical” stressor; (b) elevated levels of FFA and glucose, indicators of stress-induced mobilization of energy substrates, confirming the stressor effect of SP; (c) FFA levels can be used as an accurate, sensitive and reliable index of acute stress situations, including in the anxiogenic-like effect of SP, with the FFA response being as good as corticosterone as a stress marker in this case; (d) NK1 receptors involvement in the underlying mechanisms of the behavioral and metabolic effects of SP. Finally, our study indicates that some of these physiological variables are positively related to the stressor intensity.

Highly proliferative endothelial colony forming cells isolated from pigs with acute myocardial infarction showing high affinity on bare metal stent

Background: Coronary stent implantation can cause significant injury of vessel endothelium with an inflammatory reaction which contributes to neointimal proliferation and thrombosis resulting in-stent restenosis. Endothelial progenitor cells (EPCs) can be differentiated into endothelial cells that protect the vascular wall from damage. Acute myocardial infarction (AMI) induced in a porcine model leads to an increase in circulating high proliferative potential-endothelial colony forming cells (HPP-ECFC). This study was designed to test whether isolated porcine HPP-ECFC could be grown on bare metal coronary stent. Methods and Results: AMI was created by a PTCA balloon catheter with the proximal left anterior descending (LAD) artery being occluded just distal to the first septal perforator for 45min. Peripheral blood samples were drawn at baseline and immediately post deflation of the balloon. Circulating mononuclear cells (MNC) were isolated and cultured. Colonies of HPP-ECFC (>2000 cells/colony) were identified by a single cell assay and sorted by flow cytometry. After labeling with PKH26, the HPP-ECFC were seeded into culture slides at a density of 5 x 104 cells/cm2 with bare coronary stents (AVE, NIR, and ACS; 3 stents/each group). At day 5, the cells seeded on the stents were labeled with a nuclear DAPI stain. HPP-ECFC can only be detected in the post-MI samples and were increased 15-fold. In co-culture, HPP-ECFC coverage on the stent surface began on day 3 and complete coverage of stents occurred after day 5. The cells displayed a similar growth pattern in all of the stents and cell quantification is ongoing. Conclusion: This preliminary data demonstrates that the number of circulating HPP-ECFC significantly increases in the acute stress situation in a porcine AMI model. These cells had a high affinity to adhere to bare metal stent surfaces. HPP-ECFC coated stents may accelerate reendothelization after interventional procedures. Dongni Fong, Lan Huang, Mervin C. Yoder, Keith L. March, Dongming Hou www.iupui.edu/~icvbm Figure 1A & B. ‘Cobblestone’ morphology and Cytometry shows expression of CD31 and rare CD45. Conclusions Our findings demonstrate that peripheral blood HPP-ECFCs were increased in number following the myocardial ischemia insult in our porcine model. These cells showed a great affinity to adhere to the BMS surface. We postulate that HPP-ECFC coated stents may accelerate the re-endothelization process, prevent neointimal proliferation, and stent thrombosis. • The HPP-ECFCs were labeled by PKH26 (Sigma-Aldrich) according to the manufacturer’s instructions. • The expanded and sterilized AVE, ACS and NIR stents (n = 3/each) were separately placed into each well of 24-well plate after rinsing with culture medium.

Change of digesta passage rate in dairy cows after different acute stress situations

Six dairy cows received 3 treatments after morning meal, in a double Latin square design. Treatments were ACTH challenge (SYN), hoof trimming (TRIM) and saline (CTR). Measurements included: plasma cortisol and metabolic profile during the 24 h after treatments; the rate of digesta passage, faecal dry matter and pH. Both acute stress situations vs CTR caused a rapid and similar rise in plasma cortisol (P<0.001), while plasma glucose increased only in response to TRIM. Plasma concentrations of urea and BHB were increased for several hours after both stress situations. Most importantly, the transit time of digesta was reduced with SYN and TRIM (P<0.05). Our data demonstrate a reduced forestomach motility during acute stress and confirm a possible negative linkage between stress and gut functions, perhaps independent of diet composition. The mechanism seems linked to increased ACTH or cortisol rather than corticotrophin-releasing factor.

Cortisol and Immune Measures in Boars Exposed to Three-day Administration of Exogenous Adrenocorticotropic Hormone

The aim of the study was to evaluate the effect of adrenal stimulation by adrenocorticotropic hormone (ACTH) on blood cortisol concentration and on circulating total and differential leukocyte counts during and in the 16 days after ACTH administration. Swedish Landrace boars aged approximately 6-7 months were used. ACTH-treated animals (n = 7) were given ACTH intravenously at 10 microg/kg body mass for 3 days. A control group of animals (n = 7) received 1 ml of sterile 0.9% saline intramuscularly. ACTH induced a highly significant increase (p>0.0001) in serum cortisol in treated boars. On the day after the last ACTH dose, the cortisol concentration was significantly higher, but the level of significance was lower than during ACTH administration (p>0.05). During ACTH treatment, a significant increase was recorded in total leukocyte count and neutrophil percentage (p>0.05 to p>0.0001), along with the increase in blood cortisol concentration, whereas percentage lymphocyte count showed a significant decrease. Lymphopenia disappeared upon cessation of treatment, but neutropenia developed in the week after treatment. On all three days of ACTH challenge, the neutrophil-to-lymphocyte ratio was significantly increased. An increase in eosinophil percentage was recorded on treatment days 1 and 2, whereas ACTH treatment had no effect on basophil percentage. In conclusion, three-day administration of ACTH to young boars during restraint caused effects similar to acute stress situations, as suggested by disappearance of the effects on immune function after the last drug dosage.

Changes in S100B cerebrospinal fluid levels of rats subjected to predator stress

Predator stress is a type of psychogenic stress induced by an innate recognition of threat. S100B, a calcium-binding protein secreted by astrocytes, has been associated with neurotrophic or neurotoxic action in several neuropsychiatric disorders. It has been recently demonstrated that serum S100B levels in rats are increased after stress by immobilization [S. Scaccianoce, P. Del Bianco, G. Pannitteri, F. Passarelli, Relationship between stress and circulating levels of S100B protein, Brain Res. 1004 (2004) 208–11]. This study aimed to measure cerebrospinal fluid (CSF) S100B in rats after an acute stress situation, which is induced by exposure to a predator. S100B was measured in CSF and in hippocampal and cortical slices by ELISA. Forty-three male Wistar rats, aged 70 days, were randomly assigned to handled (control) or stressed groups (exposed to a cat for 5 min). CSF and brain tissue were removed 1 or 24 h after the procedures. Rats exposed to the cat demonstrated a biphasic change in CSF S100B levels. An increase was observed at 1 h after cat exposure, and a decrease was observed 24 h later, although this was not accompanied by changes in S100B content in hippocampus or cerebral cortex. The effectiveness of the stressor used was confirmed by increased freezing response (during cat exposure) and increased anxiety in the plus maze test (1 h after cat exposure). These results indicate that CSF S100B is changed by stress, reinforcing the possibility that this protein is involved in the adaptive response to stress and/or in secondary neuropsychiatric disorders.

HPA axis and memory.

The hormones of the hypothalamus-pituitary-adrenal (HPA) axis influence memory in situations of acute and chronic stress. The present review tries to summarize the current state of knowledge by describing the enhancing as well as the impairing effects of stress or glucocorticoid (GC) treatment documented in animals and humans. GCs secreted during the acquisition of a stressful task facilitate consolidation. However, acute stress (or GC treatment) unrelated to the task impairs performance. The effects of acute stress are additionally modulated by gender, age and the emotional valence of the learning material. Chronic stress in rodents has mostly impairing effects on memory and hippocampal integrity. However, other regions of the brain, such as the prefrontal cortex, are also sensitive to stress. In humans, similar observations have been reported in several patient populations as well as in older subjects. The potential to reverse these effects using behavioural or pharmacological approaches needs to be explored.

Cell apoptosis and hemodialysis-induced inflammation

Hemodialysis patients exhibit a defective immune response leading to an increased susceptibility of infections and neoplasms. Far from being helpful, dialytic therapy per se also may be responsible for this acquired immunodeficiency. Dialysis membranes and bacterial products present in dialysis water may trigger and even perpetuate an abnormal mononuclear cell activation. Upon contact with cellulosic dialysis membranes, monocytes display an increased expression of surface markers of cell activation, such as adhesion molecules CD18, CD49, CD54 and the lipopolysaccharide (LPS) ligand (CD14). Moreover, proinflammatory cytokines as IL-1beta and TNF-alpha are released both in vivo and in vitro when monocytes are exposed to cellulosic membranes. Of special interest is the fact that end-stage renal disease patients undergoing hemodialysis exhibit an increased mononuclear cell apoptosis. This apoptosis is directly related to the degree of biocompatibility of the dialysis membrane. Apoptosis is activated when monocytes enter in contact with the cellulosic dialysis membrane through cell surface receptors linked to G-proteins. In early steps of apoptosis signaling, pertussis toxin-sensitive G proteins are coupled to protein kinase C (PKC)-dependent phosphorylative mechanisms. Furthermore, recent evidence support that the execution phase of apoptosis is mediated by a caspase-3 dependent pathway. Finally, very recent available data support that monocytes subjected to repeated activation suffer a process of accelerated senescence, as demonstrated by the senescent phenotype (CD14 and CD32) expressed and their shortened telomeric length. This senescent profile may generage a defective cellular response in acute stress situations, explaining (at least in part) the altered immune response observed in hemodialysis patients.

Nutrition artificielle et greffe de cellules souches hématopoı̈étiques

Nutritional support becomes essential after bone marrow transplantation. Nutritional assessment must be systematic before and after transplantation. This assessment could allow for the rapid replacement of an inefficient oral nutrition by artificial nutrition. Parenteral nutrition seems to be preferentially used, but enteral nutrition is well tolerated. Energetic and protein supply could be the same to that recommended in other acute stress situations. In the last decade, several publications have shown that parenteral glutamine supplementation could reduce infectious risk, length of stay and hospital cost, especially after allogenic transplantation. But glutamine isn't effective to reduce mortality. Results with other immunonutrients, like medium-chain triglycerides or branched-chain amino-acids, are insufficient to recommend their prescription. Practical recommendations and new data about enteral nutrition could enable to optimize nutritional management of bone marrow transplantation patients.

Personality in Extreme Situations: Thinking (or Not) under Acute Stress

To investigate the role of emotional experience and understanding in acute stress situations, the relations between three individual difference variables (clarity, attention, and intensity) and cognitive difficulties under acute stress were examined. Fifty-nine firefighter trainees completed personality measures several weeks before engaging in a series of four live-fire exercises. Individuals who were typically clear about their emotions (high clarity) reported fewer instances of cognitive difficulties, such as “blanking out” and being unable to think clearly during the exercises. Emotional intensity and attention to emotion were unrelated to reports of these symptoms.

Effects of oxidative stress on the expression of antioxidative defense enzymes in spontaneously hypertensive rat hearts

Little is known concerning the effect of oxidative stress on the expression of antioxidative enzymes in the decompensated cardiac hypertrophy of spontaneously hypertensive rats (SHR), considered as a model of dilative cardiomyopathy in man. Superoxide dismutase (SOD), catalase, and glutathione peroxidase (GPx) were characterized in isolated perfused hearts of 18 month old SHR and the age-matched normotensive control Wistar-Kyoto (WKY) rats, before and after 30 min infusion of 25 μM H 2O 2. After infusion of H 2O 2, aortic flow decreased in WKY from 26.2 ± 2.2 to 16.0 ± 0.8 ml/min ( p < .05) but not in SHR (18.2 ± 1.9 vs. 20.7 ± 2.2 ml/min). This protection was related to the higher myocardial activities of GPx, MnSOD and CuZnSOD in SHR, compared with those of the WKY group. Although total SOD activity in the SHR fell after H 2O 2 exposure (to 1.81 ± 0.13 from 3.56 ± 0.49 U/mg of protein), catalase activity increased (to 2.46 ± 0.34 from 1.56 ± 0.29 k min −1mg −1protein), compared with the pre-infusion period ( p < .05 in each case). In additional studies, hearts were subjected to 30 min of global ischemia followed by 30 min of reperfusion. The results obtained in ischemic/reperfused hearts show the same changes in enzyme activities measured as it was observed in H 2O 2 perfused hearts, indicating that oxidative stress is independent of the way it was induced. The higher catalase activity derived from elevated mRNA synthesis. The antioxidative system in dilative cardiomyopathic hearts of SHR is induced, probably due to episodes of oxidative stress, during the process of decompensation. This conditioning of the antioxidative potential may help overcome acute stress situations caused by reactive oxygen species in the failing myocardium.

THE IMPORTANCE OF ANDROGEN ON NORADRENERGIC RESPONSES OF VAS DEFERENS ISOLATED FROM ACUTELY STRESSED RATS

This study investigated the importance of androgen on responses to α and β (norepinephrine) and α1(phenylephrine and methoxamine) agonists in vasa deferentia isolated from adult, immature, cryptorchid, and castrated rats submitted to swimming-induced acute stress. The participation of adrenergic nervous terminals was also investigated. Acute stress was shown to induce a significant subsensitivity to norepinephrine only in vas deferens from adult rats with normal levels of androgens. In addition, sympathetic denervation of the vas deferens prevented the appearance of subsensitivity. Subsensitivity was not seen when the experiments were carried out using phenylephrine and methoxamine. This shows that subsensitivity to norepinephrine in this acute stress situation may depend on other factors such as neuronal uptake, but not on α1-adrenoceptor response. Thus, when animals are exposed to acute stressogenic situations, this subsensitivity requires physiological levels of androgens to establish, and may also be involved in body homeostasis.

Relations between oral stereotypies, open-field behavior, and pituitary–adrenal system in growing dairy cattle

REDBO, I. Relations between oral stereotypies, open-field behaviour, and pituitary–adrenal system in growing dairy cattle. PHYSIOL BEHAV 64(3) 273–278, 1998.—The aim of this study was to investigate possible differences between calves with or without stereotypies concerning their behavioural reaction to an acute stress situation such as an open field and their behavioural and pituitary-adrenal responses to long-term tethering. Behavioural observations, open field tests, sampling for baseline adrenocorticotropic hormone (ACTH), and adrenocortical response tests after synthetic ACTH administration were made on 48 4- to 7-months-old dairy calves housed in tether stalls. Behavioural observations and blood sampling for baseline ACTH and cortisol determination after synthetic ACTH were repeated a year later in the same animals. Individual stereotypy levels showed a high correlation between calf values and heifer values ( p < 0.001). Baseline ACTH in the calves was related to individual stereotypy levels ( p < 0.05) in that the calves with higher stereotypy levels had lower ACTH values. The release of cortisol after injection of synthetic ACTH was considerably higher in the animals as heifers than when they were calves ( p < 0.001). There was a relation between adrenocortical response to ACTH and stereotypy level in the heifers, showing that the higher the stereotypy level, the lower the cortisol response ( p < 0.05). In the open field tests, the calves with the highest stereotypy levels moved around least but explored most. In conclusion, this study shows that growing dairy cattle with relatively high levels of oral stereotypies differ from individuals devoid of, or with low stereotypy levels, in behavioural response patterns to a short-term stressor such as an open field in adreno–cortical responses to exogenous ACTH and in baseline ACTH after 2 weeks of tethering.

The roles of free radicals, peroxides and oxidized lipoproteins in second messenger system dysfunction.

In living tissue, cells are constantly exposed to a wide variety of sources of oxidative stress under both physiologic and pathologic situations [1]. In most circumstances, the cell’s built-in defense mechanisms ensure that these stresses do not overwhelm the normal functioning of the cellular machinery [1]. In situations of acute or chronic stress or disease, however, these defense mechanisms may be overwhelmed or incapacitated. When this occurs, the cell may be destroyed, or its ability to properly function impaired, which in turn may lead to secondary disease processes.KeywordsCalcium TransientPhosphoinositide TurnoverCholesterol Ester HydroMessenger Signaling PathwayFree Radical InteractionThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Vasopressin and oxytocin in stress.

Though oxytocin and vasopressin are similar in structure and are produced in the same brain regions, they show specific responses under stress conditions. In humans, increases in peripheral blood vasopressin appear to be a consistent finding during many acute stress situations, while in rats, vasopressin secretion is unresponsive to several stimuli known to induce ACTH and catecholamine release. Even decreases in vasopressin levels during stress were described. In accordance with others, we observed enhanced vasopressin release in response to stress stimuli with an osmotic component such as hypertonic saline injection but also during exposure of rats to a warm environment. Immobilization stress which fails to induce vasopressin release was reported to increase hypothalamic vasopressin mRNA and plasma vasopressin levels in chronically adreno-demedullated rats. Unlike vasopressin, oxytocin may be considered a typical stress hormone responding to osmotic as well as other stress stimuli. We found that acute exposure of rats to immobilization stress resulted in an increase in oxytocin mRNA level. In addition, we have shown that magnocellular neurons of the paraventricular nucleus, but not the supraoptic nucleus, are essential for oxytocin release during immobilization stress. The release of posterior pituitary hormones represents an important component of the stress response.

Alcohol, anxiolytics and social stress in rats.

The main objective was to compare the anxiolytic-like profiles of alcohol, diazepam and gepirone along the stress intensity gradient which characterizes consecutive phases of a social confrontation. The acute social stress situation consisted of initially placing the experimental rat as an intruder into the homecage of a resident while the resident was not present, termed the "anticipatory" phase, thereafter permitting brief physical agonistic interactions with the re-introduced resident until the intruder was forced into a submissive supine posture and emitted ultrasonic vocalizations (USV), and eventually exposing the intruder to the resident's threats for 1 h, while being shielded from potential injurious attacks. The hyperthermia, measured via telemetry, in the "anticipatory" phase prior to defeat and in reaction to threats, was decreased by alcohol, gepirone and diazepam; alcohol and gepirone were also effective in attenuating "anticipatory" tachycardia. Alcohol, like gepirone and diazepam, also decreased defensive responses and ultrasonic vocalizations in the "anticipatory" phase of the confrontation, but none of these drugs affected defensive reactions to threats which immediately followed defeat. Gepirone had no systematic sedative effects throughout the confrontation; infact, it dose-dependently reduced the stress-induced suppression of locomotor activity during the "anticipatory" phase. In contrast, at higher doses, alcohol as well as diazepam had marked sedative effects as evidenced by several behavioral parameters (i.e. lie, crouch, walk). The anxiolytic-like profile of hyperthermia, tachycardia, USV and defensive behavior in the "anticipatory" phase of the confrontation by alcohol, gepirone and diazepam contrasted with the lack thereof during the more intense reactive phase. This differential pattern of effects appears to be relevant to the clinical distinctions between anticipatory anxiety and other affective disturbances.

Behavioral and autonomic responses to intermittent social stress: differential protection by clonidine and metoprolol.

The present study investigated physiological and pharmacological characteristics of socially "stressed" animals. Specifically, we examined (1) to what degree autonomic and behavioral "stress" reactions during intermittent confrontations between an intruder male adult Long-Evans rat with an aggressive resident undergo habituation, and (2) to what extent the defeat-experienced animal can be protected against these "stress" reactions with clonidine or metoprolol, two adrenergic agents with clinical anxiolytic effects. We developed an acute social stress situation that consisted of initially placing an experimental rat as an intruder into the homecage of a resident while the resident was not present, thereafter permitting brief physical agonistic interactions with the reintroduced resident until the intruder was forced into a submissive supine posture and emitted ultrasonic vocalizations (USV), and eventually exposing the intruder to the resident's threats for one hour, while being shielded from potentially injurious attacks ("threat encounter"). Over the course of the initial 4-weekly threat encounters the acute tachycardia but not the hyperthermic stress responses decreased in magnitude. Following the first three threat encounters core temperature (Tc) was significantly elevated for at least 3 h. The Tc was already elevated when the repeatedly defeated intruder was confronted with the olfactory cues of the resident's cage. This conditioned "anticipatory" hyperthermia developed in the course of the first three confrontations and was paralleled by a decrease in exploratory and motor behavior and by an increase in defensive behaviors and in both types of USV emitted in the "low" (20-30 kHz) and the "high" (31-70 kHz) frequency range. Clonidine (0.01-0.1 mg/kg, IP), an alpha 2-adrenergic agonist and metoprolol, a beta-adrenergic blocker (1.0-10.0 mg/kg, IP), dose-dependently prevented the tachycardic response to stress. Only clonidine, but not metoprolol, also attenuated the rise in Tc during the 1-h agonistic interaction. Clonidine decreased those aspects of motor behavior (e.g. rearing, walking) that are of lesser "cost" for the individual but maintained high levels of defensive reactions and increased the duration of "low" USV. The high doses of clonidine (0.06, 0.1 mg/kg) attenuated the homeostatic regulation and sedated the intruder while exposed to threats during a social confrontation. The absence of attenuation of the high level of defensive behavior and the prolonged "low" USV suggest a stress intensification by the higher doses of clonidine. In conclusion, after the fourth encounter, the autonomic, behavioral and vocal response pattern prior to and during repeated weekly confrontations show no evidence for habituation for the following 6 weeks.(ABSTRACT TRUNCATED AT 400 WORDS)

Influence of the acute stress on agonist-stimulated phosphoinositide hydrolysis in the rat cerebral cortex

Morinobu Shigeru, Norihiko Kuwayama Tomiko Kawanami, Naoyuki Okuyama, Michihiro Takahashi, Shiro Totsuka and Masao Endoh: Influence of the Acute Stress on Agonist-Stimulated Phosphoinositide Hydrolysis in the Rat Cerebral Cortex. Prog. Neuro-Psychopharmacol. & Biol. Psychiat. 1992, 16(4):561–570. 1. 1. The present study was carried out in order to elucidate the influence of the acute stress on α 1-adrenergic, serotonin-2 (5-HT 2) and muscarinic cholinergic (M-Ach) receptors-mediated phosphoinositide (PI) hydrolysis in rat cerebral cortex slices. 2. 2. In rat cerebral cortex slices, noradrenaline (NA), serotonin (5-HT) and carbachol stimulated [ 3H]inositol-monophosphate (IP 1) accumulation in a concentration-dependent manner. 3. 3. The forced swimming test (FST) for 15 min induced a significant reduction of 5-HT-stimulated [ 3H] IP 1 accumulation, but this stress situation did not produce a significant alteration of NA- and carbachol-stimulated [ 3H] IP 1 accumulation. 4. 4. The FST for 15 min did not affect the density and affinity of α1-adrenergic, 5-HT 2 and M-Ach receptors. 5. 5. In a mild acute stress situation, the intracellular signal transduction mediated by 5-HT was promptly inhibited as compared to the signal transduction mediated by NA or carbachol. This inhibition may be induced by an acute uncoupling of 5-HT 2 receptor-mediated intracellular signal transduction.

Brief Uncontrollable Stress and Psychological Parameters Influence Human Plasma Concentrations of IgM and Complement Component C3

Thirty-eight men participated in a study of immunological, hormonal, and psychological parameters before and after acute stress situations. A brief but acute stress was repeated daily for 4 days. This exposure caused the plasma levels of IgM and C3 to increase from Basal Day to Experimental Day 4. Significant correlations between endocrine and immunological parameters, and also between psychological measures and immunological parameters, were found. Use of psychological defense was related both to endocrine and immunological changes. The authors concluded that psychological stress may influence immunological functions both indirectly, by hormonal changes, and directly, by nervous regulation during brief but acute stress periods.

Risks Associated With Dietary Sodium Reduction in the Spontaneous Hypertensive Rat Model of Hypertension

Sodium balance is maintained by a complex set up of hemodynamic, hormonal and neural mechanisms that affect intake, reabsorption and excretion. The focus of the following research was on the cardiovascular and neuroeffector effects of dietary Na reduction primarily in normotensive Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR) raised from 4 to 15 weeks on a control Na diet (CNa: 12 mmol per 100 g food) or various low Na diets (LNa: 0.5 to 3 mmol per 100 g food). With regards to hemodynamics and volume regulation, the lowest Na diet reduced blood pressure 15% and raised resting heart rate (20%) in SHRs but not WKYs. Blood volume, hematocrit, plasma electrolytes, extracellular volume, and cardiac output were not different between diets or strains. However, both LNa strains were abnormally sensitive to blood loss and showed attenuated pressor responses to both acute and chronic stress situations. Cardiac function was not altered by LNa treatment in either rat strain although structural compensations occurred. LNa treatment significantly attenuated the pressor reduction in mesenteric blood flow during stress which was primarily due to reduction in noradrenergic transmitter release and not due to altered receptor sensitivity, density, or Na/K ATPase activity. Compensatory sympathetic activity was increased as was sodium conservation through humoral mechanisms which maintained homeostasis. However, further neurohumoral compensation was markedly reduced. The data suggests that the hygienic sodium intake in humans should be experimentally defined before generalized measures are taken to reduced dietary sodium use throughout society.

S-Mg Does Not Change Inversely to S-FFA During Acute Stress Situations

The apparently divergent changes in serum magnesium (S-Mg) and serum free fatty acids (S-FFA) in stress situations associated with elevated levels of circulating adrenaline were studied experimentally in 12 healthy volunteers, who were each given three adrenaline infusions (0.05 micrograms/kg bw/min over one hundred twenty minutes). Before the adrenaline infusions the volunteers were treated for three days with either a non-selective beta-blocking agent (propranolol) or a beta-1-selective agent (atenolol) or with placebo. Six of the volunteers underwent a fourth adrenaline infusion after pretreatment with a beta-2-selective beta-blocking agent (ICI 118551). S-Mg and S-FFA were determined every fifteen minutes. After pretreatment with placebo, adrenaline infusion caused an increase in S-FFA from 0.22 +/- 0.20 mmol/L (mean +/- SD) to max 0.59 +/- 0.39 mmol/L after thirty minutes of adrenaline infusion (p less than 0.001). At one hundred twenty minutes S-FFA had decreased to 0.35 +/- 0.26 mmol/L. Thirty minutes after cessation of the adrenaline infusion, S-FFA had returned to the same level as before the infusion. S-Mg before the adrenaline infusion was 0.83 +/- 0.05 mmol/L, rose to 0.85 +/- 0.05 at fifteen minutes, and then decreased to 0.78 +/- 0.05 at one hundred thirty-five minutes (p less than 0.05). Pretreatment with atenolol did not change this pattern, although the changes in S-FFA and S-Mg were of a smaller magnitude but still statistically significant.