Acute stress in rats produces a rapid and sustained increase in prostacyclin production in aortic tissue: dependence on corticosterone

Severe Trauma and Hemorrhage Leads to Platelet Dysfunction and Changes in Cyclic Nucleotides in The Rat

INTRODUCTION

Rats subjected to polytrauma and hemorrhage develop a coagulopathy that is similar to acute coagulopathy of trauma in humans, and is associated with a rise in prothrombin time and a fall in clot strength. Because platelet aggregation accounts for a major proportion of clot strength, we set out to characterize the effects of polytrauma on platelet function.

METHODS

Sprague-Dawley rats were anesthetized with isoflurane. Polytrauma included laparotomy and damage to 10 cm of the small intestines, right and medial liver lobes, right leg skeletal muscle, femur fracture, and hemorrhage (40% of blood volume). No resuscitation was given. Blood samples were taken before and after trauma for the measurement of impedance electrode aggregometry, and intracellular levels of cyclic adenosine and guanosine monophosphate (cAMP, cGMP), inositol trisphosphate (IP3), and adenosine and guanosine triphosphates (ATP, GTP).

RESULTS

Polytrauma significantly increased the response of collagen (24%) and thrombin (12%) to stimulate platelet aggregation. However, aggregation to adenosine diphosphate (ADP) or arachidonic acid (AA) was significantly decreased at 2 (52% and 46%, respectively) and 4 h (45% and 39%). Polytrauma and hemorrhage also led to a significant early rise in cAMP (101 ± 11 to 202 ± 29 pg/mL per 1,000 platelets), mirrored by a decrease in cGMP (7.8 ± 0.9 to 0.6 ± 0.5). In addition, there was a late fall in ATP (8.1 ± 0.7 to 2.2 ± 0.6 ng/mL per 1,000 platelets) and GTP (1.5 ± 0.2 to 0.3 ± 0.1). IP3 rose initially, and then fell back to baseline.

CONCLUSIONS

Polytrauma and hemorrhage led to a deficit in the platelet aggregation response to ADP and AA after trauma, likely due to the early rise in cAMP, and a later fall in energy substrates, and may explain the decrease in clot strength and impaired hemostasis observed after severe trauma.

Acute restraint stress induces endothelial dysfunction: role of vasoconstrictor prostanoids and oxidative stress

We hypothesized that acute stress would induce endothelial dysfunction. Male Wistar rats were restrained for 2 h within wire mesh. Functional and biochemical analyses were conducted 24 h after the 2-h period of restraint. Stressed rats showed decreased exploration on the open arms of an elevated-plus maze (EPM) and increased plasma corticosterone concentration. Acute restraint stress did not alter systolic blood pressure, whereas it increased the in vitro contractile response to phenylephrine and serotonin in endothelium-intact rat aortas. NG-nitro-l-arginine methyl ester (l-NAME; nitric oxide synthase, NOS, inhibitor) did not alter the contraction induced by phenylephrine in aortic rings from stressed rats. Tiron, indomethacin and SQ29548 reversed the increase in the contractile response to phenylephrine induced by restraint stress. Increased systemic and vascular oxidative stress was evident in stressed rats. Restraint stress decreased plasma and vascular nitrate/nitrite (NOx) concentration and increased aortic expression of inducible (i) NOS, but not endothelial (e) NOS. Reduced expression of cyclooxygenase (COX)-1, but not COX-2, was observed in aortas from stressed rats. Restraint stress increased thromboxane (TX)B(2) (stable TXA(2) metabolite) concentration but did not affect prostaglandin (PG)F2α concentration in the aorta. Restraint reduced superoxide dismutase (SOD) activity, whereas concentrations of hydrogen peroxide (H(2)O(2)) and reduced glutathione (GSH) were not affected. The major new finding of our study is that restraint stress increases vascular contraction by an endothelium-dependent mechanism that involves increased oxidative stress and the generation of COX-derived vasoconstrictor prostanoids. Such stress-induced endothelial dysfunction could predispose to the development of cardiovascular diseases.

Acute neuro-endocrine profile and prediction of outcome after severe brain injury

OBJECT

The aim of the study was to evaluate the early changes in pituitary hormone levels after severe traumatic brain injury (sTBI) and compare hormone levels to basic neuro-intensive care data, a systematic scoring of the CT-findings and to evaluate whether hormone changes are related to outcome.

METHODS

Prospective study, including consecutive patients, 15-70 years, with sTBI, Glasgow Coma Scale (GCS) score ≤ 8, initial cerebral perfusion pressure > 10 mm Hg, and arrival to our level one trauma university hospital within 24 hours after head trauma (n = 48). Serum samples were collected in the morning (08-10 am) day 1 and day 4 after sTBI for analysis of cortisol, growth hormone (GH), prolactin, insulin-like growth factor 1 (IGF-1), thyroid-stimulating hormone (TSH), free triiodothyronine (fT3), free thyroxine (fT4), follicular stimulating hormone (FSH), luteinizing hormone (LH), testosterone and sex hormone-binding globulin (SHBG) (men). Serum for cortisol and GH was also obtained in the evening (17-19 pm) at day 1 and day 4. The first CT of the brain was classified according to Marshall. Independent staff evaluated outcome at 3 months using GOS-E.

RESULTS

Profound changes were found for most pituitary-dependent hormones in the acute phase after sTBI, i.e. low levels of thyroid hormones, strong suppression of the pituitary-gonadal axis and increased levels of prolactin. The main findings of this study were: 1) A large proportion (54% day 1 and 70% day 4) of the patients showed morning s-cortisol levels below the proposed cut-off levels for critical illness related corticosteroid insufficiency (CIRCI), i.e. <276 nmol/L (=10 ug/dL), 2) Low s-cortisol was not associated with higher mortality or worse outcome at 3 months, 3) There was a significant association between early (day 1) and strong suppression of the pituitary-gonadal axis and improved survival and favorable functional outcome 3 months after sTBI, 4) Significantly lower levels of fT3 and TSH at day 4 in patients with a poor outcome at 3 months. 5) A higher Marshall CT score was associated with higher day 1 LH/FSH- and lower day 4 TSH levels 6) In general no significant correlation between GCS, ICP or CPP and hormone levels were detected. Only ICPmax and LH day 1 in men was significantly correlated.

CONCLUSION

Profound dynamic changes in hormone levels are found in the acute phase of sTBI. This is consistent with previous findings in different groups of critically ill patients, most of which are likely to be attributed to physiological adaptation to acute illness. Low cortisol levels were a common finding, and not associated with unfavorable outcome. A retained ability to a dynamic hormonal response, i.e. fast and strong suppression of the pituitary-gonadal axis (day 1) and ability to restore activity in the pituitary-thyroid axis (day 4) was associated with less severe injury according to CT-findings and favorable outcome.

Construction Noise Induces Hypercoagulability and Elevated Plasma Corticosteroids in Rats

Although animals housed for research purposes are strictly monitored for lighting, temperature, and humidity, the acoustic environment receives less attention. In a retrospective study, we investigated the effect of construction-induced noise on coagulation using thromboelastography in a group of healthy control rats. Animals were unintentionally exposed to noise due to construction in the vicinity of the animal care facility where these rats were housed. We compared the results to those of age-, gender-matched nonexposed rats. There was a significant shortening of the reaction (R) time ( P = .009) and a trend toward an increase in coagulation index (CI; P = .09), indicating hypercoagulability. The short R time and increase in CI were correlated with an elevated plasma cortisol and corticosterone, indicating that the hypercoagulability seen in these rats is stress induced. Noise is a stress factor for which animals need to be monitored, particularly if those animals are selected as controls for hemostasis studies.

Arachidonic acid metabolism in glucocorticoid-induced hypertension

1. Products of metabolism of arachidonic acid, such as 20-hydroxyeicosatetraenoic acid (20-HETE), thromboxane A(2) (TXA(2)) and prostaglandin I(2) (PGI(2)), regulate vascular tone. Among them, 20-HETE is a potent constrictor in small arteries that also has natriuretic properties. The present study investigated changes in urinary concentrations of 20-HETE and metabolites of TXA(2) and PGI(2) in glucocorticoid-hypertension in rats, a sodium-independent model. 2. Male Sprague-Dawley rats were treated with saline, adrenocorticotrophic hormone (ACTH; 0.2 mg/kg) or dexamethasone (20 microg/kg) by daily s.c. injection for 12 days. Systolic blood pressure (SBP) was measured using the tail-cuff method. Metabolic cages were used for 24 h urine collection. Thymus weight and urinary concentrations of 20-HETE, TXA(2) and PGI(2) were determined. 3. In the present study, SBP was increased by both ACTH (from 102 +/- 2 to 134 +/- 7 mmHg; n = 10; P < 0.01) and dexamethasone (from 106 +/- 5 to 122 +/- 4 mmHg; n = 10; P < 0.01). Thymus weight, a marker for glucocorticoid activity, was significantly decreased by both ACTH and dexamethasone (56 +/- 9 and 76 +/- 5 mg/100 g bodyweight, respectively; n = 10; P' < 0.01) compared with the saline control (151 +/- 5 mg/100 g bodyweight; n = 20). Urinary 20-HETE excretion was increased by ACTH (501 +/- 115 pmol/g creatinine; n = 10; P' < 0.05) but not by dexamethasone (126 +/- 13 pmol/g creatinine; n = 10) compared with the saline control (219 +/- 54 pmol/g creatinine; n = 20). Neither ACTH nor dexamethasone affected urinary excretion of TXB(2) or PGI(2) compared with the saline control. 4. In conclusion, ACTH but not dexamethasone increased urinary 20-HETE excretion in male Sprague-Dawley rats. Urinary concentrations of the metabolites TXB(2) and PGI(2) were unchanged in both models of glucocorticoid-hypertension. The vasoconstrictor 20-HETE may play a role in the genesis of ACTH-induced hypertension.

Behavioral effects of local microinfusion of pituitary adenylate cyclase activating polypeptide (PACAP) into the paraventricular nucleus of the hypothalamus (PVN)

Pituitary adenylate cyclase activating polypeptide (PACAP) has been implicated in the regulation of several autonomic and neuroendocrine functions. In the hypothalamic paraventricular nucleus (PVN), for example, PACAP-immunoreactive fibers densely innervate corticotropin-releasing hormone (CRH)-containing neurons in the medial parvocellular region, suggesting that PACAP acts to mediate stress responses. Therefore, we examined the behavioral effects of an intra-PVN PACAP injection (25 pmol) in combination with a mild stressor. PACAP or artificial cerebrospinal fluid (aCSF) was microinjected into the PVN (0.25 l) and then animals were restrained or placed in their home cage for 5 min. Exploratory activity (total distance traveled) and scored behaviors (face washing, body grooming, wet dog shakes, and rearing) were observed in a familiar open field for 10 min. In animals receiving aCSF, there were no behavioral differences between restrained and unrestrained groups. For the entire 10-min observation period, animals receiving PACAP, whether restrained or not, displayed elevated face washing and body grooming with decreased locomotor activity and rearing. Among PACAP-injected animals, restrained animals displayed increased body grooming compared to unrestrained animals during the first 2 min in the open field suggesting a summation of the effects of peptide injection and stressor. The observed elevation in grooming is consistent with previous studies reporting similar increases following electrical-, NMDA-, CRH-, or stressor-induced activation of the PVN. Thus, at the level of the PVN, PACAP may act as an excitatory neuropeptide and augment behavioral responses to stressors.

Acute noise stress analgesia in relation to 5-HT2 and μ-opioid receptor changes in the frontal cortex of young mice

A number of studies have reported that exposure to stress provoked behavioural changes, including analgesia, in rodents. Differences have been observed in these responses to different types of stress and a link between hormones and neurotransmitters proposed. We studied the effect of acute noise stress on nociception and the possible changes in the serotonergic and opioidergic systems in young mice of both sexes. Naloxone pre-treatment was also investigated. Noise stress was produced by a sound source, nociception was measured by the hot-plate test and binding characteristics were evaluated by a radioligand binding technique using membrane preparation from the total frontal cortex. Acute noise stress provoked an antinociceptive effect, associated with an increase in plasma corticosterone levels, a decrease in the number of 5-HT2 receptors in stressed male and female mice and a decrease in the number of mu receptors in both sexes. The behavioural and biochemical effects were antagonized by 1 mg/kg of naloxone. Acute noise stress behaves like other types of stress on nociception. The opioidergic system seems to be involved in this behaviour but also the serotonergic system may play a role. Sex differences were detected in the number of 5-HT2 and mu receptors between male and female mice not subjected to stress, while the percentage decrease in 5-HT2 and mu receptors did not differ significantly between the two sexes.

Pituitary adenylate cyclase-activating polypeptide (PACAP) mimics neuroendocrine and behavioral manifestations of stress: Evidence for PKA-mediated expression of the corticotropin-releasing hormone (CRH) gene

The physiologic response to stress is highly dependent on the activation of corticotropin-releasing hormone (CRH) neurons by various neurotransmitters. A particularly rich innervation of hypophysiotropic CRH neurons has been detected by nerve fibers containing the neuropeptide PACAP, a potent activator of the cAMP-protein kinase A (PKA) system. Intracerebroventricular (icv) injections of PACAP also elevate steady-state CRH mRNA levels in the paraventricular nucleus (PVN), but it is not known whether PACAP effects can be associated with acute stress responses. Likewise, in cell culture studies, pharmacologic activation of the PKA system has stimulated CRH gene promoter activity through an identified cAMP response element (CRE); however, a direct link between PACAP and CRH promoter activity has not been established. In our present study, icv injection of 150 or 300 pmol PACAP resulted in robust phosphorylation of the transcription factor CREB in the majority of PVN CRH neurons at 15 to 30 min post-injection and induced nuclear Fos labeling at 90 min. Simultaneously, plasma corticosterone concentrations were elevated in PACAP-injected animals, and significant increases were observed in face washing, body grooming, rearing and wet-dog shakes behaviors. We investigated the effect of PACAP on human CRH promoter activity in alphaT3-1 cells, a PACAP-receptor expressing cell line. Cells were transiently transfected with a chloramphenicol acetyltransferase (CAT) reporter vector containing region - 663/+124 of the human CRH gene promoter then treated for with PACAP (100 nM) or with the adenylate cyclase activating agent, forskolin (2.5 muM). Both PACAP and forskolin significantly increased wild-type hCRH promoter activity relative to vehicle controls. The PACAP response was abolished in the CRE-mutant construct. Pretreatment of transfected cells with the PKA blocker, H-89, completely prevented both PACAP- and forskolin-induced increases in CRH promoter activity. Furthermore, CREB overexpression strongly enhanced PACAP-mediated stimulation of hCRH promoter activity, an effect which was also lost with mutation of the CRE. Thus, we demonstrate that icv PACAP administration to rats under non-stressed handling conditions leads to cellular, hormonal and behavioral responses recapitulating manifestations of the acute stress response. Both in vivo and in vitro data point to the importance of PACAP-mediated activation of the cAMP/PKA signaling pathway for stimulation of CRH gene transcription, likely via the CRE.

Effects of acute restraint stress on endogenous adrenomedullin levels

Adrenomedullin (ADM) is a 52 amino acid peptide, with a potent hypotensive/vasodilatory action. Levels of ADM are significantly elevated in patients with hypertension, and it has been postulated that such stressor-related increases may serve a regulatory or protective function. The current study assessed the effects of acute restraint stress on ADM levels in regions of the brain, plasma and peripheral tissue including heart, lung and the adrenal glands of rats. This stressor, known to stimulate sympathetic activity as well as the hypothalamic-pituitary adrenal (HPA) axis, produced a significant increase in ADM levels in the pituitary gland, plasma and adrenal glands, all of which are key components of the HPA axis. The results suggest a regulatory and/or protective role for ADM in countering HPA activation following a variety of physiological and psychological stressors.

Vascular and hemodynamic effects of behavioral stress in borderline hypertensive and Wistar-Kyoto rats

In borderline hypertensive rats (BHR), behavioral stress produces hypertension, which has been attributed to increases in sympathetic nervous system activity and peripheral changes in vascular structure. However, the mechanisms mediating development of stress-induced hypertension have not been well defined. Experiments were designed to determine hemodynamic effects and changes in small mesenteric artery (approximately 300 microns) vascular reactivity in response to 10 days of air-jet stress (2 h/day) in BHR and in Wistar-Kyoto (WKY) rats. The acute stress-induced increase in mean arterial pressure (AP) was impaired in WKY rats compared with BHR on day 1, and habituation developed to the increase in AP in BHR, but not WKY rats. Conversely, WKY rats adapted to the stress-induced tachycardia to a larger extent than BHR. The mechanisms mediating endothelium-dependent relaxation to acetylcholine (ACh) were altered in small mesenteric arteries isolated from WKY rats and BHR after 10 days of air-jet stress. Inhibition of nitric oxide synthase activity had a significantly larger inhibitory effect on ACh-induced relaxation in vessels from stressed compared with control BHR. Also, cyclooxygenase products contributed to ACh-induced relaxation of small mesenteric arteries from stressed WKY rats, but not control WKY rats. Endothelium-independent relaxation to nitroprusside was impaired in vessels from stressed WKY rats, but not stressed BHR. Finally, contraction to phenylephrine was impaired in vessels from stressed BHR, but not WKY rats. In conclusion, changes in vascular reactivity induced by air-jet stress appear to correlate with, and may contribute to, the differential hemodynamic adaptations to stress observed in WKY rats and BHR.