Biomedical subjects

E Shohami

Publications and source records attributed to E Shohami.

At least 109 records · Page 6Linked to original sources

PubMed1988

Dexamethasone and indomethacin do not affect brain edema following head injury in rats.

Head trauma was induced in rats by a weight-drop device, falling over the exposed skull over the left hemisphere. The neurological state of the rats was evaluated by a neurological severity score at 1 h and 18 h post head trauma. At 18 h post head trauma, rats were decapitated and tissue from the vicinity of the injury and from a corresponding area in the contralateral hemisphere was taken for specific gravity (SG) determination using linear gradient columns. Slices were taken from the same sites for incubation in Krebs-Ringer solution, and the concentrations of prostaglandin (PG)E2, 6-keto-PGF1 alpha, and thromboxane B2 accumulated in the medium during 1 h were measured by radioimmunoassay. In one experimental group, rats were pretreated with intraperitoneal dexamethasone sodium phosphate (4 mg/kg) 18 and 2 h before head trauma, and a third dose was given 8 h post head trauma. Another group was treated with intraperitoneal indomethacin (10 mg/kg) 1 h before and 7 h after head trauma. Other groups were treated immediately and 8 h after head trauma with 4, 8, 15, or 30 mg/kg of dexamethasone sodium phosphate. Another group of rats was treated with free dexamethasone (10 mg/kg) right after head trauma and 8 h later. Head trauma induced edema, as expressed by decreased SG, in the left hemisphere of all traumatized rats. Neither treatment protocol affected the neurological severity score of the injured rats or the SG of the contused hemisphere. PG synthesis, on the other hand, was significantly reduced following indomethacin or free dexamethasone, both in sham and traumatized rats, but not in dexamethasone sodium phosphate-treated rats. We conclude that pretreatment with indomethacin, dexamethasone sodium phosphate, or dexamethasone, used in the present protocols, does not affect posttraumatic cerebral edema. Thus, the role of PGs as mediators of edema formation remains unclear.

Animals↗

PubMed1988

Experimental closed head injury in rats: mechanical, pathophysiologic, and neurologic properties.

A model of closed head injury in rats was developed using a calibrated weight-drop device. The development of edema was studied in various brain regions (cerebral hemispheres, brain stem, cerebellum) using a linear specific gravity gradient column. Regional brain tissue density was measured within 1 min, at 15 and 60 min, 18 h, 4 and 10 days after injury to the left cerebral hemisphere, and was compared with values in sham-operated and control rats. Significant edema (i.e., reduced specific gravity) occurred only in the traumatized hemisphere and was maximal at 18 h. A neurologic severity score (NSS) was developed to evaluate the status of the rat after injury. Specific gravity was significantly correlated with NSS at 18 h after injury. The affected hemisphere displayed hemorrhagic lesions as early as one hour post head trauma (HT), which evolved into hemorrhagic necrosis at 18 h. A pathologic score, evaluated 18 h post HT based on size and severity of the lesion, was correlated with the NSS and evaluated for each rat at one hour and 18 h postimpact. This correlation was found to be highly significant. This model of brain injury may be useful in future studies on the effects of therapeutic agents.

Animals↗

PubMed1988

Comparison of soluble dexamethasone sodium phosphate with free dexamethasone and indomethacin in treatment of experimental neoplastic spinal cord compression.

In an experimental rat model of neoplastic spinal cord compression, the in vivo effect of steroidal and nonsteroidal anti-inflammatory agents on the water content, prostaglandin E2 (PGE2) production, and specific gravity of the compressed cord segments were assessed, as well as the effect on the course of the disease. Paraplegic animals presented a consistent increase in the water content, PGE2 synthesis, and specific gravity in the compressed cord segments. The effect of treatment given on onset of paraplegia with either dexamethasone sodium phosphate (Dex-p; 10 mg/kg twice daily), or free dexamethasone (F-dex; 8.25 mg/kg twice daily) or indomethacin (10 mg/kg twice daily), was evaluated after 30 hours of therapy. Both F-dex and indomethacin eliminated spinal cord edema but varied in the rate of inhibitory effect on PGE2 production (dexamethasone less than indomethacin). Dexamethasone sodium phosphate failed to reduce spinal cord edema and PGE2 synthesis, but specific gravity changes were corrected by each of the administered agents. Evaluation of the effect of treatment on the course of the disease required dose reduction by 50% for Dex-p and F-dex, and to 25% for indomethacin, to avoid lethal toxicity. Treatment was started on appearance of the first sign of neurologic dysfunction (Grade 1) and continued to paraplegia (Grade 5). In the saline-treated rats, the mean time interval between Grades 1 and 5 was 2.7 +/- 0.3 days. Free dexamethasone, Dex-p, and indomethacin significantly prolonged this interval by 57%, 54%, and 48% respectively (P less than 0.005). The three agents differed in their ability to control the increases in water content and in PGE2 production, but proved almost equally effective in the prompt control of the specific gravity changes.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1988

Indomethacin and dexamethasone treatment in experimental neoplastic spinal cord compression: Part 2. Effect on edema and prostaglandin synthesis.

Edema formation and prostanoid production (prostaglandin E2 (PGE2), thromboxane B2 (TXB2), and 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha) were studied in a model of neoplastic epidural cord compression (NSCC) in rats harboring a thoracolumbar tumor. Tumor-free and tumor-bearing animals were randomized for three treatments at 12-hour intervals with saline, dexamethasone (10 mg/kg i.p.), or indomethacin (10 mg/kg i.p.). Increase in water content was observed only in the compressed lumbar cord segments of paralyzed rats; the cervical and thoracic segments did not differ from controls. The rate of release of prostaglandins was evenly distributed along the spinal segments in tumor-free rats. In tumor-bearing rats, a consistent significant increase in PGE2 production was found in the compressed lumbar segment in the presence of neurological dysfunction: early (limp tail), P less than 0.05; paraplegia, P less than 0.001. A significantly elevated PGE2 synthesis preceded the increase in water content by 2 to 3 days. A 2-fold increase in TXB2 was detected in only one of three experiments, and synthesis of 6-keto-PGF1 alpha was elevated to 4 times the normal value (P less than 0.005) in two of three experiments. Dexamethasone failed to inhibit prostaglandin synthesis in the spinal cord of normal controls or paralyzed rats, whereas in nonneural tissues (liver, uterus) it reduced synthesis of the three metabolites by at least 50%, thus demonstrating a differential effect on central nervous system (CNS) vs. non-CNS tissues. Dexamethasone also failed to reduce the increased water content of the compressed segments.(ABSTRACT TRUNCATED AT 250 WORDS)

6-Ketoprostaglandin F1 alpha↗

PubMed1988

Experimental closed head injury in rats: prostaglandin production in a noninjured zone.

In a model of closed head injury in rats, a calibrated weight drop device was allowed to fall onto the skull's convexity over the left hemisphere 1 to 2 mm lateral from the midline. Prostaglandin (PG) levels were determined in the frontal cortex region remote from the site of injury where no macroscopic damage could be seen. Differential patterns of temporal changes were evident for PGE2, PGD2, thromboxane (TX) B2, and 6-keto-PGF1 alpha in the contused hemisphere, but no changes were found in the contralateral hemisphere. The major changes in PG levels were increased levels of PGD2 and 6-keto-PGF1 alpha that persisted from 18 hours until 10 days after injury. The ratio between TXB2 and 6-keto-PGF1 alpha, which reflects the vascular tone, increased during the early postinjury period (15 minutes and 1 hour) and decreased later, up to 10 days. Thus, a sustained imbalance in favor of the vasodilator is apparent; this may suggest an improved blood supply to the region. Both PGD2 and PGI2 have protective effects in the brain. We suggest that their endogenous increase may be part of a repair mechanism at the periphery of the injured zone.

6-Ketoprostaglandin F1 alpha↗

PubMed1987

Increased thromboxane A2 and 5-HETE production following spinal cord ischemia in the rabbit.

Ischemia was induced for 25 min in the spinal cord of rabbits followed by a long term period of recirculation. At various time points of recirculation (5, 30 min, 4, 18 hr and 1 wk) slices were taken from the ischemic region and incubated for 45 min in Krebs-Ringer solution. The levels of the eicosanoids, PGE2, PGD2, PGF2 alpha, TXB2, 6-keto-PGF1 alpha and 5-HETE accumulated in the incubation medium were measured by radioimmunoassay. TXB2, release was found to be increased at an early (5 min) and late (1 wk) period of reperfusion. A seven-fold increase in the release of 5-HETE was found 5 min after reperfusion that tended to stay elevated at 18 hr and 1 week of recirculation. PGI2 synthetase activity decreased by 40% at 30 min, with return to normal at later time points. The ratio of TXA2/PGI2 was significantly higher than control at 30 min and 1 wk. The synthesis of PGE2, PGD2 and PGF2 alpha was maintained at normal levels throughout the complete course of reperfusion. No changes in eicosanoid synthesis were noted in remote spinal cord regions. The significant increase of TXA2 synthesis at 5 min and 1 wk of reperfusion may point to a role of this arachidonate metabolite in the acute events and in the later stages of neurological dysfunction. The enhanced release of 5-HETE, a metabolite of 5-HETE, suggest an enhanced formation of leukotriene B4 and peptide leukotrienes and a potential role for these 5-lipoxygerase metabolites of arachidonate in ischemia injury to the brain and the spinal cord.

Animals↗

PubMed1987

Therapeutic effect of dexamethasone in T-2 toxicosis.

T-2 Toxin is a mycotoxin that induces toxemia characterized by numerous hematological and biochemical changes. We have previously shown that prostaglandin (PG) production in brain tissue is increased following T-2 toxin. The present study was designed in order to test the effect of dexamethasone on brain prostaglandins and survival of rats subjected to T-2 toxin. Furthermore, the effect of BW 755c, a dual inhibitor of the cyclooxygenase and lipoxygenase pathways of arachidonate metabolism, on the survival of rats exposed to T-2 toxin was also examined. The present study demonstrated that dexamethasone increases the survival of rats exposed to a highly lethal T-2 toxicosis. This effect was demonstrated at low as well as high doses and at different times after T-2 administration. Dexamethasone depressed PGE2 levels in the brain cortex 6 hr after T-2 toxin but abolished the reduction of PGE2 in brain cortex seen 24 hr after T-2. BW 755c had no consistent effect on the survival of rats in T-2 toxicosis. It is suggested that dexamethasone might be a useful therapeutic agent in T-2 toxicosis in animals and humans, but its mechanism of action remains obscure.

4,5-Dihydro-1-(3-(trifluoromethyl)phenyl)-1H-pyraz↗

PubMed1987

Head injury induces increased prostaglandin synthesis in rat brain.

Head injury was induced in the left hemisphere of rats. The rats were killed at various time intervals after trauma (immediately, 15 min, 1 and 18 h, and 4 and 10 days), and the rates of synthesis and release of prostaglandin PGE2, 6-keto-PGF1 alpha, and thromboxane TXB2 from cortical slices of both hemispheres were studied. The rate of synthesis of PGE2 after 18 h was six and four times higher than control in the contused and contralateral hemispheres, respectively. By 10 days post-trauma, both hemispheres had normal rate of PGE2 release. TXB2 and 6-keto-PGF1 alpha synthetases were affected already 15 min after the injury, and a similarly elevated rate of synthesis was found in both hemispheres. The maximal effect was detected after 1 or 18 h with return to normal after 4 or 10 days for TXB2 and 6-keto-PGF1 alpha, respectively. Tissue specific gravity was determined for both hemispheres using linear gradient columns. The results of these determinations indicate that development of edema occurs in the contused hemisphere as early as 15 min post trauma; it reaches its maximal level at 18 h and returns to normal at 10 days. Arterial pressure was monitored, and a transient increase was found at 10 min post trauma. We suggest that the production of edema after brain injury may be related to the increased rate of PGE2 and PGI2 synthesis, which occurs at similar time intervals after injury.

6-Ketoprostaglandin F1 alpha↗

PubMed1987

Adenosine triphosphate stimulates inositol phospholipid metabolism and prostacyclin formation in adrenal medullary endothelial cells by means of P2-purinergic receptors.

In the adrenal medulla, chromaffin cells secrete high concentrations of catecholamines, ATP, peptides and other factors that must pass through an endothelial cell barrier to enter the bloodstream. We have measured the effect of several of these chromaffin cell secretory products on cultured bovine adrenal medullary endothelial cells and have found that only ATP stimulates prostacyclin formation. The stimulation of prostacyclin formation by ATP coincides with the metabolism of inositol phospholipids and the accumulation of the putative second messenger inositol trisphosphate. The time course, concentration dependence, and P2-purinergic receptor specificity were similar for ATP-stimulated prostacyclin formation and ATP-stimulated inositol phospholipid metabolism. Thus, the increase in prostacyclin formation may be secondary to mobilization of intracellular Ca2+ by inositol trisphosphate, leading to activation of phospholipase A2, liberation of arachidonic acid, and the conversion of arachidonic acid to prostacyclin. We propose that the function of ATP, which is often colocalized with cell-specific hormones in secretory cells, may be to regulate blood flow in the adrenal medulla and other endocrine tissues by interacting with adjacent endothelial cells.

6-Ketoprostaglandin F1 alpha↗

PubMed1987

Thromboxane and 5-HETE increase after experimental spinal cord injury in rabbits.

Eicosanoids are known mediators of inflammation, vascular permeability, and are involved in microcirculatory blood flow regulation. To study their potential involvement in the pathophysiology of CNS trauma we used a rabbit spinal cord trauma model. Rabbits were subjected to lumbar spinal cord trauma produced by a modification of the Allen weight-drop method. TXB2, 6-keto-PGF1 alpha, PGE2, and 5-hydroxyeicosatetraenoic acid (5-HETE) release from spinal cord slices incubated ex vivo were measured by radioimmunoassay at 5, 30 min, 24 hrs, and 2 wks after trauma. Five and 30 min after trauma the TXB2/6-keto-PGF1 alpha ratio was elevated and the release of 5-HETE at 5 min after trauma increased in the injured spinal cord whereas release of 6-keto-PGF1 alpha and PGE2 remained at base-line levels. In the thoracic spinal cord, TXB2 and 6-keto-PGF1 alpha release were increased at 30 min after trauma. Release of 5-HETE from the injured spinal cord was also elevated 24 hrs after trauma. Two wks after trauma, TXB2 and 6-keto-PGF1 alpha release were also elevated in the injured spinal cord. Measurements of tissue water content by microgravimetry indicated progressive edema in the injury site while histopathological evaluation indicated progressive damage and tissue destruction. The results of this study suggest that eicosanoids may be involved in the pathophysiology of spinal cord trauma through two potential mechanisms: 1) site specific increase in the TXB2/6-keto-PGF1 alpha ratio immediately following trauma which is due primarily to an increase in TXA2 synthesis; 2) the increase synthesis of 5-HETE which signals the activation of the 5-lipoxygenase pathway of arachidonate metabolism and production of mediators that are involved in inflammatory mechanisms and may affect local blood flow regulation and blood-spinal cord barrier integrity.

6-Ketoprostaglandin F1 alpha↗

PubMed1987

Experimental neoplastic spinal cord compression: evoked potentials, edema, prostaglandins, and light and electron microscopy.

Spinal cord compression was induced in Fischer rats by percutaneous inoculation of 10(6) cells of malignant fibrous histiocytoma anterior to the T13 vertebral body. Paraplegia and incontinence occurred in all animals after 14-27 days (median, 23 +/- 3.0 days). Autonomic dysfunction and a measurable increase in tumor volume were documented with the use of computer tomography. The tumor penetrated the vertebral bone, invaded the epidural space, and gradually compressed the lumbar spinal segments. Electron-microscopic examination revealed dilated intermyelin spaces containing exuded homogenous material and extravasated leukocytes and erythrocytes. Myelin breakdown was accompanied by the presence of lipid-laden macrophages. Sequential recording of somatosensory evoked potentials (SEP) revealed a progressive increase in the latency of the cervical responses, which preceded the onset of clinical signs. In the presence of paraplegia, spinal cord conductivity was abolished. The levels of the prostaglandins TXB2, 6-keto-PGF1 alpha, and PGE2 were measured in the compressed and remote spinal cord segments during the presymptomatic and symptomatic periods. Only PGE2 was significantly elevated (P less than 0.001) in the paraplegic rats, all along the spinal cord segments. A significant increase in water content was measured in the compressed lumbar segments in the presymptomatic period, and when paralysis set in it was increased in the adjacent low thoracic area as well. Tissue specific gravity was significantly increased only in paraplegic rats in the compressed (P less than 0.01) and the adjacent low thoracic areas (P less than 0.05) but no significant change occurred during the presymptomatic period. Multiple mechanisms play a role in the pathogenesis of neurologic symptoms in neoplastic spinal cord compression.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1987

Effect of dexamethasone on prostaglandin synthesis in various areas of the rat brain.

Glucocorticoid hormones are known to inhibit the production of prostaglandins in many cell types and tissues. The effect of these hormones on the biosynthesis of brain tissue is not yet clear. In the present study we investigated the effect of dexamethasone on the release of prostaglandin E2 (PGE2), thromboxane B2 (TXB2), and 6-keto-PGF1 alpha from various brain areas of male rats. Slices from cortex, hippocampus, hypothalamus, and striatum taken from rats pretreated with dexamethasone 4 mg/kg body weight or vehicle, 18 h and 2 h prior to killing, were incubated in Krebs-Ringer-bicarbonate for 1 h. The accumulation of PGs in the medium was determined by radioimmunoassay. Pretreatment with dexamethasone significantly reduced the release of all PGs from the cortex by 40-50%. In the striatum and hippocampus only TXB2 was reduced by approximately 40%. In the hypothalamus the effect of dexamethasone was not significant. When slices of the same brain areas from intact rats were incubated for 1 h in the presence of 40 microM dexamethasone, only the release of PGE2 from the cortex was reduced (by 30%). These results suggest that glucocorticoids can inhibit PG synthesis in brain tissue, and that the cortex is the most sensitive area to the inhibitory effect of the hormone.

6-Ketoprostaglandin F1 alpha↗

PubMed1986

1,25-Dihydroxyvitamin D3 enhances prostaglandin E2 production by monocytes. A mechanism which partially accounts for the antiproliferative effect of 1,25(OH)2D3 on lymphocytes.

Partial removal of monocytes from human peripheral blood mononuclear cells, or the addition of indomethacin, reduced the antiproliferative effect of 1,25(OH)2D3 on mitogen-stimulated mononuclear cells. Addition of 1,25(OH)2D3 (1 nM) to mitogen-stimulated mononuclear cells caused a 2-4-fold increase in prostaglandin E2 production during the second day of culture. The inhibitory effect of 1,25(OH)2D3 on lymphocyte proliferation is greatly augmented up to 7-fold in the presence of prostaglandin E2. We conclude that monocytes are involved in the inhibitory effect of 1,25(OH)2D3 on the mitogenic stimulation of human lymphocytes and that their action is probably mediated by prostaglandins.

Calcitriol↗

PubMed1986

T-2 toxemia and brain prostaglandins.

T-2 toxin is a trichothecene mycotoxin which is a member of a family of closely related sesquiterpenoids. It was recently shown that T-2 toxemia is associated with elevated plasma levels of eicosanoids. To study further the effect of T-2 on the cyclooxygenase pathway of arachidonate we examined the release of PGE2, TXB2 and 6-keto-FGF1 alpha from brain tissue exposed to T-2 toxin in vivo or in vitro. Administration of T-2 toxin (0.75 or 2 mg/kg) to conscious rats caused a transient increase in the rate of the release of 6-keto-PGF1 alpha and TXB2 from brain slices taken from the cortex (C); no effect was found in the hypothalamus (HT) or the nucleus tractus solitarius (NTS) region of the medulla oblogata. PGE2 showed time and dose related increments (over 5 folds) in both the C and HT but not in the NTS. Incubation of cortical or hypothalamic slices in oxygenated Krebs buffer with a wide range of T-2 toxin concentrations (10(-9)-10(-3) M) demonstrated a complex response: stimulation of PGE2 and TXB2 release from C slices at 10(-7) M (greater than 40%, p less than 0.01 and 20%, p less than 0.05, respectively) and inhibition at high concentrations (greater than 10(-4) M) of all PGs studied. Hypothalamic slices showed decrease in all PGs released by very low (10(-9)-10(-8)) or very high (10(-4) M) concentrations of T-2. These studies are consistent with the possibility that the arachidonate cascade in the central nervous system might have a role in the pathophysiology of trichothecene mycotoxicosis.

6-Ketoprostaglandin F1 alpha↗

PubMed1986

Effects of hypoxia and anoxia on the ex vivo release of prostaglandins from mouse cortical slices.

Arachidonic acid is transiently accumulated in the brain as a result of a variety of pathological conditions. The synthesis and release of some of its metabolites, namely, prostaglandin E2 (PGE2), thromboxane B2 (TXB2), and 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha) from cortical slices of mice were studied following exposure to 6 min of hypoxia (7% O2), 45 s of anoxia, and 5 min-4 h of reoxygenation following anoxia. Hypoxia induced a slight increase in the rate of TXB2 release and a slight decrease in the rate of PGE2 release, whereas 6-keto-PGF1 alpha was unaffected. Anoxia (45 s) followed by reoxygenation induced a transient increase in the release of PGE2 and of 6-keto-PGF1 alpha with a return to the normal rate at 30 min and 2 h of recovery, respectively. However, the rate of TXB2 synthesis and release reached its peak (twofold increase) after 1 h and remained significantly higher than the control rate even after 4 h of normal air breathing. Our results demonstrate that hypoxia and anoxia, even of short duration, selectively trigger the activity of thromboxane synthetase and that this elevated rate of synthesis and release persists long after normal oxygen supply is restored. We suggest that enhanced thromboxane synthesis, with normal prostacyclin levels, might have a role in the pathophysiology of ischemic cell damage.

6-Ketoprostaglandin F1 alpha↗

PubMed1986

A new animal model for action myoclonus.

Morphine was injected into a catheter implanted chronically into the intrathecal space of rats. Three to eight minutes after drug administration, 80% of the rats developed arrhythmic stimulus-sensitive jerks that lasted up to 1 hr. The morphine-induced myoclonic activity was markedly reduced by naloxone. Methadone, pethidine, and etorphine failed to produce the syndrome. In spinally transected rats, morphine injected below the level of transection did not produce the syndrome. No significant changes in PaCO2 and PaO2 were produced by morphine before and throughout the period of myoclonic activity. Neither did induced hypoxia augment the effect of morphine. However, irreversible hypoxic-ischemic cell changes were noticed in some brain regions. The phenomenon described here resembles the human syndrome of action myoclonus and may serve as an animal model for studying the mechanism of that neurological disorder.

Animals↗

PubMed1985

Regional distribution of prostanoids in rat brain: effect of insulin and 2-deoxyglucose.

Prostaglandin synthesis in the brain has been suggested as a component in the control mechanism of the cerebral circulation. During insulin-induced hypoglycemia there is a significant increase in local cerebral blood flow in various brain regions, however, regional loss of autoregulation occurs under these conditions. In the present study the regional distribution of PGE2, TXB2 (the stable metabolite of thromboxane) and 6-keto-PGF1 alpha (the stable metabolite of prostacyclin) was determined in rat brain following decapitation. Three groups of rats were treated with either saline, insulin or 2-deoxyglucose and their brains were rapidly removed one hour later. Samples from the cortex hypothalamus, hippocampus, striatum, nucleus accumbens and cerebellum were assayed by RIA for the content of PGE2, TXB2 and 6-keto-PGF1 alpha. The levels of all three compounds in control rats were the lowest in the striatum and cerebellum, while in the cortex and hippocampus their levels were 4-6 times higher. Insulin had selective effect on the post decapitation levels of prostanoids. It increased PGE2 in the n. accumbens and TXB2 in the hippocampus, and reduced 6-keto-PGF1 alpha and TXB2 in the cortex. 2-DG reduced all PGs in the cortex and 6-keto-PGF1 alpha in the hypothalamus and hippocampus. The results demonstrate that discrete brain areas have a differential capacity to accumulate PGs following decapitation. This capacity is selectively affected by insulin and 2-DG.

6-Ketoprostaglandin F1 alpha↗

PubMed1985

Effect of acute hypoxia on ascorbate content of plasma, cerebral cortex, and adrenal gland.

Levels of ascorbic acid (AA) in the plasma, brain, and adrenal gland of rats were determined after 15 min of hypoxia (PaO2 less than 25 mm Hg) and following asphyxia. In rabbits, AA plasma levels were followed up to 75 min of reoxygenation following 15 min of hypoxia of the same severity. A significant increase (approximately 70%) in AA levels was found in plasma of rats and rabbits after hypoxia and asphyxia. This increase was found to be transient, with a return to normal levels within 1 h after resumption of normal oxygenation. Pretreatment with dexamethasone reduced the increase in AA level in both rabbits and rats. Adrenalectomy in rats, performed 24 h before the experiment, abolished the response to hypoxia. Ascorbate levels in the cerebral cortex, hypothalamus, and adrenal gland of awake rats subjected to hypoxia or asphyxia were found to be the same as in normoxic rats. Our results suggest that the observed changes in plasma AA levels are probably mediated through adrenocorticotropic hormone and that the adrenal gland is the major source of ascorbate efflux into the circulation during oxygen deprivation.

Adrenal Glands↗