Haruan has been proved to influence the different phases of wound healing process. The current research focuses on the effects of haruan on the different constituents of extracellular matrix of healing wounds in normal and diabetic rats. Anaesthetized normal and streptozotocin induced diabetic rats were provided with excision wounds at the back and then animals were divided into four groups as: group 1, wounds treated with cetrimide+haruan cream; group 2, wounds treated with haruan cream; group 3, wounds treated with cetrimide (commercial) cream; and group 4, wounds untreated and served as control. Animals were sacrificed after 3, 6, 9 and 12 days. These wounds were used to determine the hexosamine, protein, uronic acid and glycosaminoglycan contents and the wound contraction. The results suggested a marked increase (P<0.05) in the uronic acid, hexosamine and dermatan sulfate contents on day 3 of group 1 when compared with groups 2-4. Wound contraction of group 1 was also markedly enhanced of group 1 (P<0.01) when compared with groups 2- 4. On the basis of these results, we conclude that haruan enhances the synthesis of different glycosaminoglycans in healing wounds, which are the first component of extracellular matrix to be synthesized during the wound healing process. The enhanced levels of glycosaminoglycans may help in the formation of a resistant scar and enhanced wound contraction represents the positive influence of haruan on the fibroplastic phase of wound healing.
This study examined the effects of vitamin E on the prevention of aspirin-induced gastric lesions. The study was divided into two phases. Phase 1 determined the effects of various doses of palm vitamin E on the factors affecting mucosal integrity. Thirty-two male rats of the Sprague-Dawley strain (200-250 g) were randomly divided into four groups. Group I was fed a normal diet (control), Groups II, III and IV were fed a diet supplemented with palm vitamin E in a dose of 60 mg/kg food, 100 mg/kg food and 150 mg/kg food, respectively. The rats were killed after 4 weeks of feeding for the determination of gastric malondialdehyde (MDA), acid and mucus content. There was a significant decrease in gastric MDA and gastric acid in all the palm vitamin E supplemented groups compared to control. However, these doses of palm vitamin E had no significant effect on gastric mucus. The phase 2 study determined the effect of multiple doses of palm vitamin E and tocopherol on the prevention of aspirin-induced gastric lesions. Fifty rats of the same weight and strain were randomized into seven groups. Group I was fed a normal diet; groups II to IV were fed with a palm vitamin E enriched diet in doses of 60 mg, 100 mg and 150 mg/kg food, respectively; groups V to VII were fed with a tocopherol-enriched diet in doses of 20 mg, 30 mg and 50 mg/kg food, respectively. After 4 weeks of feeding with the respective diets the rats were challenged with a single intra-gastric dose of 400 mg/kg body weight aspirin suspended in propylene glycol. The rats were killed 6 h post-aspirin exposure for the determination of gastric lesion index and gastric parameters as mentioned in the phase I study. The gastric lesions index was significantly lower in all the vitamin E groups compared to control. The lowest ulcer index was observed in the groups that received 100 mg of palm vitamin E and 30 mg tocopherol in the diet. However, there was no significant difference in ulcer indices between palm vitamin E and tocopherol-treated groups. The lower ulcer index was only accompanied by lower gastric MDA content. We conclude that both palm vitamin E in doses of 60 mg, 100 mg and 150 mg/kg food as well as tocopherol in doses of 20 mg, 30 mg and 50 mg/kg food are equally effective in preventing aspirin-induced gastric lesions. The most probable mechanism is through their ability in limiting the lipid peroxidation that is involved in aspirin-induced gastric lesions.
Plant-based polyphenolic compounds have been reported to possess cardiovascular health benefits. Several dietary sources, including herbs and spices, fruits and vegetables, and tea and wine, contain an array of biologically active compounds that have been shown to be effective in retarding oxidation of low-density lipoproteins (LDL) and promoting vascular relaxation. In the present study four different plant sources, both edible and non-edible, were evaluated for potential activity. Organic extracts enriched in polyphenols were prepared from palm fronds (Elaesis guineensis); lemongrass (Cymbopogon citrates); papaya shoots (Carica papaya) and green chilli (Capsicum frutescenes) and tested for their ability to prevent in vitro oxidation of LDL, and for potential vascular relaxation actions. Rings of rat thoracic aorta and isolated perfused mesenteric vascular beds were mounted in organ baths, contracted using a half-maximal dose of noradrenaline and exposed to cumulative additions of test extracts. Palm frond extract resulted in considerable relaxation (>75%) in both preparations and was found to be endothelium-dependent as removal of endothelium or inhibition of endogenous nitric oxide (NO) led to a total loss in relaxant activity. Lemongrass extract caused a greater relaxation action in the mesenteric preparation compared to aortic rings, and appears to be mediated via NO-independent and non-prostanoid mechanisms. Of the extracts tested, palm fronds also demonstrated the highest antioxidant capacity, as determined by the ferric reducing activity/potential assay, and resulted in a significant delay (P < 0.05) in the oxidation of LDL. Collectively, these preliminary findings lend further support to the potential cardiovascular actions of plant polyphenols and also identify oil palm fronds as containing constituents that promote vascular relaxation via endothelium-dependent mechanisms.
Vitamin E is composed of various subfamilies that include tocopherols and tocotrienols. These compounds have antioxidant properties but differ in structure, dietary source and potency. In this study we evaluated the efficacy of alpha-tocopherol as an antioxidant and its role in wound closure in normal and streptozotocin-induced diabetic rats. The healing of 6 cm linear incisions created on the back of each male Sprague-Dawley rat (250-300 g) was monitored by measuring the length of the wounds daily. The rats were divided into two categories; normal and streptozotocin-induced diabetic rats. For each category, the animals were further divided into two groups; those untreated and those receiving 200 mg/kg bodyweight alpha-tocopherols daily by oral gavage. All rats were fed standard food and water ad libitum. Blood samples were taken at 0, 5 and 10 days after the wounds were created for the determination of malondialdehyde levels and red cell superoxide dismutase, catalase and glutathione peroxidase activities. The results showed that alpha-tocopherol reduced plasma malondialdehyde levels, increased glutathione peroxidase activity and accelerated the rate of wound closure in treated rats.
Reproductive dysfunction in the female diabetic rat is associated with impaired hypothalamic-hypophyseal system, anovulation, insufficiency of ovarian steroidogenesis and spontaneous failure of pregnancy. Formation of decidua, the highly modified endometrium of pregnancy and pseudopregnancy could only be achieved when the uterus was sensitized by a sequence of oestrogen and progesterone. In this study, we examined whether the impaired expression of endometrial decidualization in the pseudopregnant rat is linked with diabetes-associated hypersecretion of testosterone. Rats were made pseudopregnant by sterile mating. Diabetes was induced by streptozotocin on day 1 p.c. Deciduogenic stimulus was given on day 5 p.c. Treatment of cyproterone acetate (10 mg kg(-1)) was scheduled from day 5 through day 9 p.c. Animals were killed on day 10 p.c, and the degree of endometrial decidual growth, plasma levels of oestradiol, progesterone, ACTH and testosterone were determined. Results showed that compared to controls there was a concomitant drop in endometrial decidual growth concurrently with impaired levels of oestradiol and progesterone in diabetic pseudopregnant rats. ACTH and testosterone levels were, however, profoundly elevated. Cyproterone acetate treatment in the diabetic pseudopregnant rat resulted in a simultaneous elevation of oestradiol and progesterone, which eventually helped the endometrial differentiation to decidua in the diabetic pseudopregnant rat parallel to controls. Present experimental data suggest that diabetes-associated impaired endometrial decidualization in the pseudopregnant rat is possibly caused by testosterone-induced oestrogen deficiency.
The effects of bisphenol A and nonylphenol on pubertal development in the intact juvenile/peripubertal male Sprague-Dawley rats was observed in this study from PND23-52/53. Two groups of rats were administered orally with either 100 mg/kg body weight of nonylphenol or bisphenol A. Another group of rats were administered orally with a mixture of 100 mg/kg body weight of nonylphenol and bisphenol A. Control group was administered with the vehicle of Tween-80 with corn oil (1:9 v/v). Observations made in this study included growth, age at preputial separation, thyroid, liver, testis and kidney weight and histology, epididymal and seminal vesicle plus coagulation gland weight. Nonylphenol and bisphenol A have been observed to cause delay in puberty onset as well as testicular damage in the treatment groups when compared to the control; spermatogenesis was affected in most treated rats. Bisphenol A also caused the enlargement of the kidney and hydronephrosis. Administration of nonylphenol and bisphenol A as a mixture has caused less than additive effects.
The effects of long-term administration of tocotrienol on hepatocarcinogenesis in rats induced by diethylnitrosamine (DEN) and 2-acetylaminofluorene (AAF) were investigated by determining the activities of gamma-glutamyl transpeptidase (GGT), alkaline phosphatase (ALP), glutathione S-transferases (GSTs), and glutathione (GSH) levels in blood and liver. Twenty-eight male 7- to 8-wk-old Rattus norwegicus rats, weighing 120-160 g, were used in this study. The rats were divided into four treatment groups: a control group on a basal diet, a group fed a basal diet supplemented with tocotrienol (30 mg/kg food), a group treated with DEN/AAF, and a group treated with DEN/AAF and fed a diet supplemented with tocotrienol (30 mg/kg food). Blood was collected monthly, and GGT, ALP, and GSH levels were determined. The rats were killed after 9 mo, and the livers were examined morphologically. Grayish white nodules (2/liver) were found in all the DEN/AAF-treated rats (n = 10), but only one of the rats treated with DEN/AAF and supplemented with tocotrienol (n = 6) had liver nodules. A significant increase in the level of blood and liver GSH, ALP, and GGT activities was observed in the DEN/AAF-treated rats. Liver GSTs were similarly increased with DEN/AAF treatment. Tocotrienol supplementation attenuated the impact of the carcinogens in the rats.
The effect of palm oil, a widely used vegetable oil, rich in tocotrienols, on peroxidation potential of rat liver was examined. Long-term feeding of rats with palm oil as one of the dietary components significantly reduced the peroxidation potential of hepatic mitochondria and microsomes. As compared to hepatic mitochondria isolated from rats fed control or corn oil-rich diet, those from palm oil-fed group showed significantly less susceptibility to peroxidation induced by ascorbate and NADPH. However, in microsomes, only NADPH-induced lipid peroxidation was significantly reduced in rats fed palm oil rich-diet. Though the accumulation of thiobarbituric acid reactive substances during ascorbate-induced lipid peroxidation in mitochondria from rats fed corn oil-rich diet supplemented with tocotrienol-rich fraction (TRF) of palm oil was similar to that of control rats, the initial rate of peroxidation was much slower than those from control or corn oil fed diets. Our in vitro studies as well as analyses of co-factors related to peroxidation potential indicated that the observed decrease in palm oil-fed rats may be due to increased amount of antioxidants in terms of tocotrienol as well as decrease in the availability of substrates for peroxidation.
1. This study examines the effect of Hoe 140, a bradykinin (BK) 2 receptor antagonist, indomethacin and prednisolone on chronic adjuvant arthritis of the knee in rats. We also evaluated the influence of Hoe 140 on BK-forming enzymes in the synovial and paw tissues. 2. Adjuvant arthritis was induced in male Sprague-Dawley rats in the right knee by injecting 0.05 ml of a fine suspension of heat-killed Mycobacterium tubercle bacilli in liquid paraffin (5 mg/ml). 3. Hoe 140 (1.5 mg/kg i.p.), indomethacin (2.5 mg/kg orally) and prednisolone (3.0 mg/kg orally) administration for 9 days resulted in significant suppression of knee joint swelling. Plasma and tissue kallikrein levels were raised (P < 0.01) in the synovial and paw tissues of adjuvant arthritic rats. Hoe 140 treatment reduced (P < 0.05) tissue kallikrein but increased (P < 0.01) plasma kallikrein levels in synovial tissue. 4. Hoe 140 treatment did not alter (P > 0.05) the raised plasma and tissue kallikrein levels in the paw tissue. The findings indicate that Hoe 140 may be a useful anti-inflammatory agent and BK plays a major role in this adjuvant-induced arthritis model.
The effects of vitamin C and aloe vera gel extract supplementation on induced hepatocarcinogenesis in male Sprague-Dawley rats (120-150 g) by diethylnitrosamine (DEN) and 2-acetylaminofluorene (AAF) was investigated. The severity of the carcinogenesis process was determined by measuring gamma-glutamyl transpeptidase (GGT) and the placental form of glutathione S-transferase (GSTP) histochemically in situ and in plasma and liver fractions. In addition, plasma alkaline phosphatase (ALP) and liver microsomal uridine diphosphate glucuronyl transferase (UDPGT) activity were also determined. Administration of DEN/AAF caused an increase in the surface area and number of enzyme-positive foci (both GGT and GSTP) compared with control. Supplementation of vitamin C or aloe vera gel extract to the cancer-induced rats suppressed this increase significantly (P < 0.05; P < 0.001). Increases in liver UDPGT, GGT, and GSTP activities were also observed with cancer induction that were again suppressed with either vitamin C or aloe vera gel supplementation. Plasma GGT in the DEN/AAF rats were determined monthly for the duration of the experiment and found to be reduced as early as 1 mo with aloe vera gel supplementation and 2 mo with vitamin C supplementation. In conclusion, vitamin C and aloe vera gel extract supplementation were found to be able to reduce the severity of chemical hepatocarcinogenesis.
11 beta-Hydroxysteroid dehydrogenase (11 beta-OHSD) is a microsomal enzyme that catalyzes the dehydrogenation of cortisol (F) to cortisone (E) in man and corticosterone (B) to 11-dehydrocorticosterone (A) in rats. 11 beta-OHSD has been identified in a wide variety of tissues. The differential distribution of 11 beta-OHSD suggests that this enzyme has locally defined functions that vary from region to region. The aim of this study was to investigate the effects of the glucocorticoids B and dexamethasone (DM), the mineralocorticoid deoxycorticosterone (DOC), and the inhibitors of 11 beta-OHSD glycyrrhizic acid (Gl) and glycyrrhetinic acid (GE) on 11 beta-OHSD bioactivity at the hypothalamus (HT) and anterior pituitary (AP). Male Wistar rats were treated with GI or were adrenalectomized (ADX) and treated with either B, DM, or DOC for 7 days. All treatments were in vivo except GE, which was used in vitro. At the end of treatment, homogenates of HT and AP were assayed for 11 beta-OHSD bioactivity, expressed as the percentage conversion of B to A in the presence of NADP, 11 beta-OHSD bioactivity is significantly higher (P < 0.0001) in the AP compared with the HT. Adrenalectomy significantly increased the enzyme activity in the AP (P < 0.05), an effect reversed by B or DM. ADX rats treated with DOC showed decreased enzyme activity in the AP (P < 0.001) but increased the activity in the HT (P < 0.0001). Gl increased activity in both HT and AP, whereas GE decreased activity significantly. We conclude that the modulation of 11 beta-OHSD is both steroid specific and tissue specific.
1. Glucocorticosteroid may relieve bronchospasm by mediating changes in the muscarinic receptor concentration and/or its affinity. 2. Cholinergic muscarinic receptors were determined by using Scatchard's plots from radioligand binding assays of 0.13-3.2 nM [3H]quinuclidinyl benzylate binding to the membrane fraction of bronchial smooth muscle (BSM). 3. The concentration of muscarinic receptor in BSM of normal rat was 57 +/- 3 fmol mg protein and the dissociation constant was 0.07 +/- 0.02 nM. Dexamethasone and corticosterone reduced muscarinic receptor concentration to 50-60% of basal with no changes in receptor affinity. No changes were found in rat treated with deoxycorticosterone. 4. These findings suggest that glucocorticoids but not mineralocorticoid relieve bronchospasm at least partly by reducing the cholinergic hypersensitivity.
We have evaluated the effects of a B2 receptor antagonist (B5630) of kinins on BK and captopril-induced acute hypotensive responses in anaesthetized SHR. Intravenous treatment of BK (1.0 microgram) and captopril (0.3 mg/kg) caused significant (p < 0.05) fall in the SBP and DBP. Whereas BK caused greater fall in the SBP (p < 0.05), DBP (p < 0.01) and duration of hypotension (p < 0.05) when administered after captopril (Fig 1 and 2). All the hypotensive effects of BK and captopril were significantly antagonised (p < 0.05) in the presence of B5630 (2.0 mg/kg). Further, the duration of hypotensive responses of BK and captopril were blocked (p < 0.05) by B5630. The agonists and BK-antagonist did not cause significant (p > 0.05) alterations in HR during the entire investigation. These findings provide evidence to support the suggestion that B2 receptor might be involved in the regulation of the hypotensive actions of BK and captopril. Kinins should also have valuable functions in the antihypertensive property of captopril-like drugs.
Long-term glucocorticoid treatment is associated with severe side effects, such as obesity and osteoporosis. A palm oil-derived vitamin E mixture had been shown previously to be protective against osteoporosis in rats given 120 microg/kg dexamethasone daily for 12 weeks. In this study we determined the effects of two isomers of vitamin E (i.e., palm oil-derived gamma-tocotrienol and the commercially available alpha-tocopherol, 60 mg/kg of body weight/day) on body composition and bone calcium content in adrenalectomized rats replaced with two doses of dexamethasone, 120 microg/kg and 240 microg/kg daily. Treatment period was 8 weeks. gamma-Tocotrienol (60 mg/kg of body weight/day) was found to reduce body fat mass and increase the fourth lumbar vertebra bone calcium content in these rats, while alpha-tocopherol (60 mg/kg of body weight/day) was ineffective. Therefore, in conclusion, palm oil-derived gamma-tocotrienol has the potential to be utilized as a prophylactic agent in prevention of the side effects of long-term glucocorticoid use.
1. The effects of corticosteroid pretreatment on acetylcholine (ACH)-induced contraction of bronchial smooth muscle (BSM) were studied. 2. ACH dose-response curves for dexamethasone (DM)- and corticosterone (B)-treated but not deoxycorticosterone (DOC)-treated BSM were significantly shifted to the right; this provides evidence that glucocorticoid treatment reduced the sensitivity of BSM to ACH. 3. Morphine enhanced BSM contraction in response to ACH by 20%. DM suppressed this enhancement. 4. These findings correlated well with the reduction of muscarinic receptor numbers in BSM by glucocorticoids in our previous study. In addition, glucocorticoids reduced the sensitivity of BSM to opioids.
Fracture healing is a complex process, which is more complicated if the bone is osteoporotic. One of the vitamin E isomers, α-tocopherol, has been found to prevent osteoporosis and improve bone fracture healing but its role in the healing of osteoporotic fractures is still unclear. We carried out a study on the effects of α-tocopherol supplementation on osteoporotic fracture healing using an ovariectomized rat model, whereby we focused on the early phase of fracture healing, that is, the phase with excessive production of free radicals. Twenty-four female Sprague-Dawley rats were divided into three groups: sham-operated (SO), ovariectomized-control (OVC), and ovariectomized + α-tocopherol supplementation (ATF) groups. The right femora of all the rats were fractured at mid-diaphysis and K-wires were inserted for internal fixation. After 2 weeks of treatment, the rats were euthanized and the femora were dissected out for measurement of callous volume by CT-scan and radiological staging of callous formation and fracture healing. The oxidative parameters of the fractured femora were also measured. The results showed that the callous volume and callous staging were not different between the groups. However, the fracture healing stage of the OVC group was lower than the SO group, while α-tocopherol supplementation in the ATF group had improved the healing until it was comparable to the SO group. The activities of the anti-oxidatant enzymes, superoxide dismutase, and glutathione peroxidase in the ATF group were found to be significantly higher than in the OVC group. In conclusion, α-tocopherol improved fracture healing but had no effect on the callous volume and staging. The improvement in fracture healing may be due to the increased activities of the anti-oxidatant enzymes in the bone during the early phase of fracture healing of osteoporotic bone.
Excessive sodium (Na+) intake in modern society has been associated with several chronic disorders such as hypertension. Several studies suggest that early life events can program physiological systems and lead to functional changes in adulthood. Therefore, we investigated behavioral and neuroendocrine responses under basal conditions and after 48 h of water deprivation in adult (60-day-old Wistar rats) male, Wistar rats originating from dams were offered only water or 0.15 mol/L NaCl during pregnancy and lactation. Early life salt exposure induced kidney damage, as shown by a higher number of ED-1 positive cells (macrophages/monocytes), increased daily urinary volume and Na+ excretion, blunted basal water intake and plasma oxytocin levels, and increased plasma corticosterone secretion. When challenged with water deprivation, animals exposed to 0.15 mol/L NaCl during early life showed impaired water intake, reduced salt preference ratio, and vasopressin (AVP) secretion. In summary, our data demonstrate that the perinatal exposure to excessive Na+ intake can induce kidney injury in adult offspring and significantly affect the key mechanisms regulating water balance, fluid intake, and AVP release in response to water deprivation. Collectively, these novel results highlight the impact of perinatal programming on the homeostatic mechanisms regulating fluid and electrolyte balance during exposure to an environmental stress (i.e. dehydration) in later life.
Although melatonin lowers blood pressure in spontaneously hypertensive rats (SHR), its effect following antenatal and postpartum supplementation on the subsequent development of hypertension in SHR pups remains unknown. To investigate this, SHR dams were given melatonin in drinking water (10 mg/kg body weight/day) from day 1 of pregnancy until day 21 postpartum. After weaning, a group of male pups continued to receive melatonin till the age of 16 weeks (Mel-SHR), while no further melatonin was given to another group of male pups (Maternal-Mel-SHR). Controls received plain drinking water. Systolic blood pressure (SBP) was measured at 4, 6, 8, 12 and 16 weeks of age, after which the kidneys were collected for analysis of antioxidant enzyme profiles. SBP was significantly lower till the age of 8 weeks in Maternal-Mel-SHR and Mel-SHR than that in the controls, after which no significant difference was evident in SBP between the controls and Maternal-Mel-SHR. SBP in Mel-SHR was lower than that in controls and Maternal-Mel-SHR at 12 and 16 weeks of age. Renal glutathione peroxidase (GPx) and glutathione s-transferase (GST) activities, levels of total glutathione and relative GPx-1 protein were significantly higher in Mel-SHR. GPx protein was however significantly higher in Mel-SHR. No significant differences were evident between the three groups in the activities of superoxide dismutase, catalase and glutathione reductase. In conclusion, it appears that while antenatal and postpartum melatonin supplementation decreases the rate of rise in blood pressure in SHR offspring, it however does not alter the tendency of offspring of SHR to develop hypertension.
1. Free radicals generated by ferric nitrilotriacetate (FeNTA) can activate osteoclastic activity and this is associated with elevation of the bone resorbing cytokines interleukin (IL)-1 and IL-6. In the present study, we investigated the effects of 2 mg/kg FeNTA (2 mg iron/kg) on the levels of serum IL-1 and IL-6 with or without supplementation with a palm oil tocotrienol mixture or alpha-tocopherol acetate in Wistar rats. 2. The FeNTA was found to elevate levels of IL-1 and IL-6. Only the palm oil tocotrienol mixture at doses of 60 and 100 mg/kg was able to prevent FeNTA-induced increases in IL-1 (P < 0.01). Both the palm oil tocotrienol mixture and alpha-tocopherol acetate, at doses of 30, 60 and 100 mg/kg, were able to reduce FeNTA-induced increases in IL-6 (P < 0.05). Therefore, the palm oil tocotrienol mixture was better than pure alpha-tocopherol acetate in protecting bone against FeNTA (free radical)-induced elevation of bone-resorbing cytokines. 3. Supplementation with the palm oil tocotrienol mixture or alpha-tocopherol acetate at 100 mg/kg restored the reduction in serum osteocalcin levels due to ageing, as seen in the saline (control) group (P < 0.05). All doses of the palm oil tocotrienol mixture decreased urine deoxypyridinoline cross-link (DPD) significantly compared with the control group, whereas a trend for decreased urine DPD was only seen for doses of 60 mg/kg onwards of alpha-tocopherol acetate (P < 0.05). 4. Bone histomorphometric analyses have shown that FeNTA injections significantly lowered mean osteoblast number (P < 0.001) and the bone formation rate (P < 0.001), but raised osteoclast number (P < 0.05) and the ratio of eroded surface/bone surface (P < 0.001) compared with the saline (control) group. Supplementation with 100 mg/kg palm oil tocotrienol mixture was able to prevent all these FeNTA-induced changes, but a similar dose of alpha-tocopherol acetate was found to be effective only for mean osteoclast number. Injections of FeNTA were also shown to reduce trabecular bone volume (P < 0.001) and trabecular thickness (P < 0.05), whereas only supplementation with 100 mg/kg palm oil tocotrienol mixture was able to prevent these FeNTA-induced changes.
1. The present study examined the effect of naloxone (NAL), glycyrrhizic acid (GCA), deoxycorticosterone (DOC) and dexamethasone (DEX) on daily repeated 2 h chronic restrained stress (RS) on the locomotor activity (LA) of rats tested in the open field arena to elucidate the possible roles of opioids, glucocorticoids and mineralocorticoids in response to stress. 2. Intact and adrenalectomized (ADX) rats were either injected with 0.1 mL of NAL (0.32 microgram/100 g BW), 2.4 mg/kg DOC or 120 micrograms/kg DEX or had 1.0 mg/mL GCA dissolved in their drinking water or normal saline (for the ADX group) dissolved in their drinking water. 3. In intact groups, treatment with NAL completely blocked the stress response and treatment with GCA, DOC and DEX partially prevented the stress response. Adaptation occurred on either days 4, 5, 6 or 7 for intact rats treated with DEX, DOC, GCA or control rats, respectively. All ADX control rats died following the first 2 h RS. Adrenalectomized rats treated with DEX or DOC adapted later compared with intact rats, while rats given either GCA or NAL were unable to block or adapt to chronic RS. 4. These findings demonstrate that the stress response is primarily mediated by endogenous opioids, in that it is blocked by NAL. Both mineralocorticoids and glucocorticoids, which can act centrally to inhibit endorphins, partially blocked the stress response. The effect of GCA in intact rats was similar to that of both DEX and DOC in intact rats. Adrenalectomized rats treated with GCA (despite their lack of endogenous corticosterone) showed a stress response that was significantly different from the other ADX groups, implying that GCA had effects independent of endogenous corticosterone.