Effect of pentoxifylline on endothelaemia and hypothalamic-pituitary-adrenocortical axis activation in female rats under stress exposure

Endothelial dysfunction may belong to negative consequences of stress exposure accompanied by activation of several stress systems including the hypothalamic-pituitary-adrenocortical (HPA) axis. The present experiments were aimed at testing the hypotheses that i) immobilization (IMO) stress results in sustained increase in endothelaemia for 24 h and that ii) pentoxifylline, a drug with endothelium protective properties, attenuates the rise in endothelaemia and HPA axis activation in female rats as shown previously in males. Circulating endothelial cells increased immediately after the IMO for 2 h, returned back to control levels at 12 h and increased again at 24 h. Stress-induced rise in adrenocorticotropic hormone (ACTH) and corticosterone levels was particularly high immediately after the IMO. Pretreatment with pentoxifylline (20 mg/kg subcutaneously for 7 days) attenuated the rise in endothelaemia and adrenal corticosterone measured at 24 h following IMO. Plasma levels of ACTH and proopiomelanocortin gene expression in the anterior pituitary were not affected by pentoxifylline treatment. The present results indicate that IMO stress in female rats induces a biphasic rise in endothelaemia early at the time of stress exposure and than 24 h thereafter. Based on these data and our previous study we can conclude that intensive stress has a negative influence on endothelial cells in both sexes and no gender differences seem to be present in the protective action of pentoxifylline.     

Nitric oxide mediates the interleukin-1beta- and nicotine-induced hypothalamic-pituitary-adrenocortical response during social stress.

We investigated the role of nitric oxide (NO) in the interleukin 1beta (IL-1beta) and nicotine induced hypothalamic-pituitary-adrenal axis (HPA) responses, and a possible significance of CRH and vasopressin in these responses under basal and social stress conditions. Male Wistar rats were crowded in cages for 7 days prior to treatment. All compounds were injected i.p., nitric oxide synthase (NOS) inhibitors, alpha-helical CRH antagonist and vasopressin receptor antagonist 15 min before IL-1beta or nicotine. Identical treatment received control non-stressed rats. Plasma ACTH and serum corticosterone levels were measured 1 h after IL-1beta or nicotine injection. L-NAME (2 mg/kg), a general nitric oxide synthase (NOS) inhibitor, considerably reduced the ACTH and corticosterone response to IL-1beta (0.5 microg/rat) the same extent in control and crowded rats. CRH antagonist almost abolished the nicotine-induced hormone responses and vasopressin antagonist reduced ACTH secretion. Constitutive endothelial eNOS and neuronal nNOS inhibitors substantially enhanced the nicotine-elicited ACTH and corticosterone response and inducible iNOS inhibitor, aminoguanidine, did not affect these responses in non-stressed rats. Social stress significantly attenuated the nicotine-induced ACTH and corticosterone response. In crowded rats L-NAME significantly deepened the stress-induced decrease in the nicotine-evoked ACTH and corticosterone response. In stressed rats neuronal NOS antagonist did not alter the nicotine-evoked hormone responses and inducible NOS inhibitor partly reversed the stress-induced decrease in ACTH response to nicotine. These results indicate that NO plays crucial role in the IL-1beta-induced HPA axis stimulation under basal and social stress conditions. CRH and vasopressin of the hypothalamic paraventricular nucleus may be involved in the nicotine induced alterations of HPA axis activity. NO generated by eNOS, but not nNOS, is involved in the stress-induced alterations of HPA axis activity by nicotine.     

Vasopressin pressor receptor-mediated activation of HPA axis by acute ethanol stress in rats

The plasma arginine vasopressin (AVP), ACTH, and corticosterone levels and the hypothalamic corticotropin-releasing hormone (CRH) content were measured after oral administration of 1 ml of 75% ethanol to rats, a model known to induce acute gastric erosions and stress. Elevated plasma AVP, ACTH, and corticosterone levels were detected 1 h after ethanol administration. Treatment with the vasopressin pressor (V(1)) receptor antagonist [d(CH(2))(5)Tyr(Me)-AVP] before ethanol administration significantly reduced the ACTH and corticosterone level increases. A higher hypothalamic CRH content was measured at 30 or 60 min after ethanol administration. V(1) receptor antagonist injection, 5 min before ethanol administration, inhibited the rise in hypothalamic CRH content. The protein synthesis blocker cycloheximide prevented the hypothalamic CRH content elevation after stress. The AVP-, CRH-, and AVP + CRH-induced in vitro ACTH release in normal anterior pituitary tissue cultures was also prevented by pretreatment with the V(1) receptor antagonist. The results support the hypothesis that stress-induced AVP may not only act directly on the ACTH producing anterior pituitary cells but also indirectly at the hypothalamic level via the synthesis and release of CRH.     

Exposure to chronic stress downregulates corticosterone responses to acute stressors

We used captive European starlings (Sturnus vulgaris) to test whether corticosterone responses differed in birds held under normal laboratory conditions or conditions of chronic stress. Surprisingly, both basal corticosterone concentrations and corticosterone responses to acute stress were significantly reduced when birds were chronically stressed. To determine the mechanism underlying this reduced response, animals under both conditions were injected with lactated Ringer's solution (control), adrenocorticotropin (ACTH), arginine vasotocin (AVT), or dexamethasone (DEX). ACTH increased corticosterone concentrations above stress-induced levels in both cases, although maximum responses were lower in chronically stressed birds. AVT did not augment the corticosterone response under nonchronically stressed conditions, but it did under chronically stressed conditions. DEX reduced maximal corticosterone concentrations in both cases. Neither ovine nor rat corticotropin-releasing factor (CRF) altered normal stress responses. These data indicate that changes in responsiveness of the hypothalamic-pituitary-adrenal axis to ACTH and AVT serve to downregulate corticosterone responses during chronic stress. Furthermore, these data lead to the following hypothesis: ACTH output from the pituitary limits maximum corticosterone concentrations under normal conditions, but reduced AVT release from the hypothalamus regulates lower corticosterone concentrations under chronic stress conditions.     

Chronic administration of the non-peptide CRH type 1 receptor antagonist antalarmin does not blunt hypothalamic-pituitary-adrenal axis responses to acute immobilization stress.

Antalarmin is a pyrrolopyrimidine compound that antagonizes corticotropin-releasing hormone (CRH) type 1 receptors (CRHR1). In order to assess the effects of antalarmin treatment on hypothalamic-pituitary-adrenal (HPA) function we measured the plasma concentrations of adrenocorticotropic hormone (ACTH) and corticosterone in animals treated with either antalarmin or vehicle for 1 week or for 8 weeks. We found that antalarmin treatment for 1 week did not affect basal concentrations of ACTH or corticosterone. In contrast, treatment for 8 weeks significantly lowered basal ACTH and corticosterone concentrations and also significantly decreased the basal corticosterone to ACTH ratio, indicating decreased basal adrenocortical responsiveness to ACTH. However, immobilization stress resulted in ACTH and corticosterone concentrations that were the same in animals treated with vehicle or antalarmin for either 1 or 8 weeks. We conclude that even though 8-week antagonism of CRHR1 by the non-peptide antalarmin blunts basal concentrations of ACTH and corticosterone, and affects the adrenal responsiveness to ACTH, it does not blunt the HPA response to acute stress, and it does not appear to cause stress-induced adrenal insufficiency.     

Repeated handling, restraint, or chronic crowding impair the hypothalamic-pituitary-adrenocortical response to acute restraint stress.

The purpose of the present study was to assess whether, and to what extent prior handling, restraint or social crowding stress during 3-10 days affects the hypothalamic-pituitary-adrenocortical (HPA) response to an acute short-lasting restraint stress. Also the effect of a feedback inhibitory mechanism of corticosterone in the impairment of HPA axis by these stressors was investigated. Male Wistar rats were pretreated with handling 1 min/day for 3-10 days, restraint 2 times daily for 3-7 days and crowding stress for 7 days before exposure to acute restraint stress in metal tubes for 10 min. Some group of rats received exogenous s.c. corticosterone either once 25 mg/kg or 2 times daily 10 mg/kg for 3-10 days before restraint stress. After the last restraint the rats were decapitated and their trunk blood was collected for the measurement of plasma ACTH and serum corticosterone levels. Handling for 3-7 days, restraint for 3-7 days, and crowding for 7 days and a single pretreatment with corticosterone--all significantly and to a similar extent inhibited the restraint stress-induced increase in ACTH and corticosterone secretion. Chronic pretreatment with corticosterone blunted the restraint stress-induced increase in HPA axis activity. These results indicate that repeated short-lasting stress induced by handling, restraint, or crowding potently attenuates the acute restraint stress-induced stimulatory action of the HPA axis. They also indicate adaptive action of moderate stress on the HPA axis response to acute stress. The results also suggest that a short-lasting hypersecretion of corticosterone during psychological stress may induce a prolonged feedback inhibition of the HPA axis activity. The attenuation of HPA axis response by prior handling has also obvious methodological implications.     

Repeated stress alters the ability of nicotine to activate the hypothalamic-pituitary-adrenal axis

Acute nicotine administration has been shown to activate the hypothalamic-pituitary-adrenal (HPA) axis and stimulate secretion of adrenocorticotrophic hormone (ACTH), corticosterone/cortisol and beta-endorphin (beta-END) in both rodents and humans, raising the possibility that activation of the HPA axis by nicotine may mediate some of the effects of nicotine. Since stress can increase the risk of drug use and abuse, we hypothesized that repeated stress would increase the ability of nicotine to stimulate the secretion of HPA hormones. To test our hypothesis, mice were exposed to repeated stress (swimming in 15 degrees C water for 3 min/day for 5 days) and killed 15 min after injection of saline or nicotine (0.1 mg/kg, s.c.). Repeated exposure to stress increased the ability of nicotine to stimulate plasma ACTH (p<0.05) and beta-END (p<0.05), but not corticosterone secretion. In contrast, repeated exposure to stress increased the post-saline injection levels of corticosterone (p<0.05), but not ACTH and beta-END. The present results suggest that chronic stress leads to an enhanced sensitivity of some components of the HPA axis to a subsequent nicotine challenge.     

Long-term salt loading impairs pituitary responsiveness to ACTH secretagogues and stress in rats

Male Wistar rats were allowed to drink tap water ad lib (W), 2% saline (S) or 2% saline containing dexamethasone (S + D, 1 mg/l) for 7 days. On the 8th day rats were subjected to a 3-min ether stress. Plasma ACTH, corticosterone and prolactin concentrations were determined before and after ether exposure. Prestress concentrations of plasma ACTH were low and did not vary among the three groups. In response to ether stress W rats exhibited twice as high plasma ACTH concentrations as did S rats. Rats of the S + D group exhibited a small but statistically significant ACTH response. Plasma corticosterone concentration in S rats was increased while in S + D rats was significantly decreased under resting conditions compared to that in W rats. Ether stress caused large increases in plasma corticosterone concentrations in W and S rats while a small but statistically significant increase was observed in S + D rats. Prolactin responses to ether were smaller in groups S and S + D than in group W. To test whether the decreased ACTH response to ether exposure was a result of a decreased sensitivity of corticotrope cells to corticotropin releasing factor (CRF)-41 or arginine vasopressin (AVP), adenohypophysial fragments from W, S and S + D rats were incubated in the presence of different doses of CRF-41 or AVP. Pituitary fragments obtained from W rats secreted larger amounts of ACTH than did pituitaries from S rats in response to either CRF-41 or AVP.(ABSTRACT TRUNCATED AT 250 WORDS)     

Corticotropin-releasing hormone and pituitary-adrenocortical responses in chronically stressed rats

Brain corticotropin-releasing hormone (CRH) concentration and pituitary adreno-cortical responses were examined in chronically stressed rats: body restraint stress (6 h/day) for 4 or 5 weeks. Stressed rats showed a reduction in weight gain. CRH concentration in the median eminence and the rest of the hypothalamus were not different between control and chronically immobilized rats. The anterior pituitary adenocorticotropic hormone (ACTH) concentration was elevated in chronically stressed rats, whereas plasma ACTH and corticosterone levels did not differ from the control values. The median eminence CRH concentration was reduced to the same extent at 5 min after onset of ether exposure (1 min) in chronically immobilized rats and controls. However, plasma ACTH and corticosterone showed greater responses to ether stress in chronically immobilized rats than in control rats. Plasma ACTH and corticosterone responses to exogenous CRH were not different between control and chronically immobilized rats, while the response to arginine vasopressin (AVP) was significantly greater in chronically immobilized rats. These results suggest that chronic stress caused an increase in the ACTH-secreting mechanism and that pituitary hypersensitivity to vasopressin might at least be partly responsible for this.     

Stress mediated changes in hypothalamic corticotropin releasing factor-like immunoreactivity

Hypothalamic corticotropin releasing factor-like immunoreactivity (CRF-LI), plasma ACTH and corticosterone levels were measured by radioimmunoassay over a two hour period of restraint stress. The results of this study demonstrate a significant decrease in hypothalamic CRF-LI levels 15 and 30 minutes after the start of restraint stress which is followed by a significant increase at 60 minutes that is abolished by cycloheximide pretreatment. Plasma ACTH and corticosterone levels were significantly elevated after 15, 30, 60, 90, and 120 minutes of restraint stress. These results are consistent with a release of CRF from the hypothalamus during stress. The cycloheximide-sensitive increase in hypothalamic CRF-LI indicates that synthesis of CRF-41 occurs during prolonged stress. These results suggest that the response of an organism to exposure to a long-term, high intensity stress involves both the release and synthesis of CRF-41.     

Age and food deprivation affects expression of the glucocorticosteroid stress response in Magellanic penguin (Spheniscus magellanicus) chicks

We examined how the glucocortical stress response in free-living Magellanic penguin (Spheniscus magellanicus) chicks changes with age and whether adrenocortical function of chicks within a brood varies in relation to food provisioned by adults. Chicks showed little corticosterone response to capture stress shortly after hatching, an intermediate response around 45-d posthatch, and a robust stress response near fledging. However, in response to an adrenocorticotropic hormone (ACTH) challenge, hatchlings were capable of secreting corticosterone at adult-like levels. The larger sibling in broods of two showed a similar gradual stress-response development pattern. In contrast, by day 45, when differences in body condition were well established between siblings, the smaller, food-deprived chicks significantly increased baseline levels of corticosterone but showed normal stress-induced levels. Near fledging, baseline levels had returned to normal, but stress-induced levels were lower than expected. Similar to altricial species, normally developing semialtricial Magellanic penguin chicks do not express a robust corticosterone stress response until near fledging. Chronic stressors such as food deprivation cause corticosterone use to be up-regulated earlier than expected. However, in cases of extended chronic stress, down-regulation may ensue, thus avoiding the negative effects of chronically elevated levels of corticosterone.     

Dietary tyrosine suppresses the rise in plasma corticosterone following acute stress in rats

Acute, uncontrollable stress increases norepinephrine (NE) turnover in the rat's brain (depleting NE) and diminishes the animal's subsequent tendency to explore a novel environment. Pre-treatment with tyrosine can reverse these adverse effects of stress, presumably by preventing the depletion of NE in the hypothalamus. Numerous studies suggest that NE inhibits the release of adrenocorticotropic hormone (ACTH) by suppressing corticotropic releasing factor (CRF) secretion in the hypothalamus. In the present study, we found that pre-treatment with supplemental tyrosine not only prevented the behavioral depression and hypothalamic NE depletion observed after an acute stress, but also suppressed the rise in plasma corticosterone. These results support a role for brain NE in stress-induced corticosterone secretion and demonstrate that supplemental tyrosine can protect against several adverse consequences of such stress.     

Early stress and genetic influences on hypothalamic-pituitary-adrenal axis functioning in adulthood.

During early development, environmental challenges set the stage for permanent changes in the functioning of the pituitary-adrenal stress response. Since these data have been reported almost exclusively in single rat strains the role of phenotypic and genotypic factors in shaping the stress response is relatively unknown. This study examined whether the phenotypic/genetic profile of the rat influences the long-term response to challenge after early exposure to stress. Two strains of Sprague-Dawley rats were used in this study: one is a stress-induced animal model of "learned helpless" (LH) behavior and the other a resistant strain developed through selective breeding. Stress-induced adrenocorticotropic hormone (ACTH) and corticosterone release was monitored in adult congenital learned helpless (cLH) rats and congenital non-learned helpless (cNLH) rats. The rats were exposed to cold stress or maternal deprivation (on either postnatal day 7 or day 21). After the early acute stress exposure, animals remained undisturbed until challenged in adulthood (day 90) with footshock stress. In cLH animals (adults) early cold stress (particularly after acute stress on postnatal day 21) and maternal deprivation stress resulted in an enhancement of stress-induced ACTH release compared to nonstressed cLH and cNLH controls. In contrast, adrenal responsiveness was generally suppressed in cLH animals that were acutely stressed with cold stress or maternal deprivation stress early in life. The above results suggest that the genetic/phenotypic profile of the animal is a determinant in the changes observed in the adult stress response after early exposure to stressors.     

Effect of immobilization and concurrent exposure to a pulse-modulated microwave field on core body temperature, plasma ACTH and corticosteroid, and brain ornithine decarboxylase, Fos and Jun mRNA

Exposure of humans and rodents to radiofrequency (RF) cell phone fields has been reported to alter a number of stress- related parameters. To study this potential relationship in more detail, tube-restrained immobilized Fischer 344 rats were exposed in the near field in a dose-dependent manner to pulse-modulated (11 packets/s) digital cell phone microwave fields at 1.6 GHz in accordance with the Iridium protocol. Core body temperatures, plasma levels of the stress-induced hormones adrenocorticotrophic hormone (ACTH) and corticosterone, and brain levels of ornithine decarboxylase (Odc), Fos and Jun mRNAs were measured as potential markers of stress responses mediated by RF radiation. We tested the effects of the loose-tube immobilization with and without prior conditioning throughout a 2-h period (required for near-field head exposure to RF fields), on core body temperature, plasma ACTH and corticosteroids. Core body temperature increased transiently (+/-0.3 degrees C) during the initial 30 min of loose-tube restraint in conditioned animals. When conditioned/tube-trained animals were followed as a function of time after immobilization, both the ACTH and corticosterone levels were increased by nearly 10-fold. For example, within 2-3 min, ACTH increased to 83.2 +/- 31.0 pg/dl, compared to 28.1 +/- 7.7 pg/dl for cage controls, reaching a maximum at 15-30 min (254.6 +/- 46.8 pg/dl) before returning to near resting levels by 120 min (31.2 +/- 10.2 pg/dl). However, when non-tube-trained animals were submitted to loose-tube immobilization, these animals demonstrated significantly higher (3-10-fold greater) hormone levels at 120 min than their tube-trained counterparts (313.5 +/- 54.8 compared to 31.2 +/- 10.2 pg/dl; corticosterone, 12.2 +/- 6.2 microg/dl compared to 37.1 +/- 6.4 microg/dl). Hormone levels in exposed animals were also compared to those in swim-stressed animals. Swimming stress also resulted in marked elevation in both ACTH and corticosterone levels, which were 10-20 fold higher (541.8 compared to 27.2-59.1 pg/dl for ACTH) and 2-5 fold higher (45.7 compared to 8.4- 20.0 microg/dl for corticosteroids) than the cage control animals. Three time-averaged brain SAR levels of 0.16, 1.6 and 5 W/ kg were tested in a single 2-h RF-field exposure to the Iridium cell phone field. When RF-exposed and sham-exposed (immobilized) animals were compared, no differences were seen in core body temperature, corticosterone or ACTH that could be attributed to near-field RF radiation. Levels of Odc, Fos and Jun mRNA were also monitored in brains of animals exposed to the RF field for 2 h, and they showed no differences from sham-exposed (loose-tube immobilized) animals that were due to RF-field exposure. These data suggest that a significant stress response, indicated by a transient increase in core body temperature, ACTH and corticosterone, occurred in animals placed in even the mild loose-tube immobilization required for near-field RF exposure employed here and in our other studies. Failure to adequately characterize and control this immobilization response with appropriate cage control animals, as described previously, could significantly mask any potential effects mediated by the RF field on these and other stress-related parameters. We conclude that the pulse-modulated digital Iridium RF field at SARs up to 5 W/kg is incapable of altering these stress-related responses. This conclusion is further supported by our use of an RF-field exposure apparatus that minimized immobilization stress; the use of conditioned/tube-trained animals and the measurement of hormonal and molecular markers after 2 h RF-field exposure when the stress-mediated effects were complete further support our conclusion.     

Pituitary cyclic AMP and plasma hormone responses to epinephrine administration in vivo

The present study was conducted to characterize the in vivo effects of epinephrine administration on levels of pituitary cyclic AMP and plasma hormones. Rats were injected with saline or epinephrine bitartrate (1 mg/kg lP) and sacrificed by decapitation 1, 5, 15, 30 or 60 min post-injection. Levels of pituitary cyclic AMP and plasma ACTH, beta-endorphin, beta-LPH, corticosterone and prolactin were determined by radioimmunoassays. The injection procedure itself was somewhat stressful as demonstrated by increased levels of plasma prolactin and ACTH 5 min following either saline or epinephrine injection. This "stress" response was rapid and short-lasting for the pituitary hormones. The response of the adrenal hormone, corticosterone, to saline injection was slower in onset and longer in duration. Pituitary cyclic AMP levels did not increase following saline injection. Epinephrine-injected animals displayed markedly elevated plasma levels of ACTH, beta-endorphin and beta-LPH at 15, 30 and 60 min as compared to control or saline-injected rats. In addition, levels of pituitary cyclic AMP were increased over 10 fold at these times. Levels of plasma prolactin, a stress-responsive hormone, were not significantly increased in epinephrine-injected animals as compared to saline-injected rats indicating that these later responses seem to be specific to epinephrine rather than to stress.     

Naloxene enhances stress-induced increases in noradrenaline turnover in specific brain regions in rats

Male Wistar rats were injected subcutaneously with either saline or naloxone, 1 mg/kg or 5 mg/kg, 10 min before exposure to 1-hour immobilization-stress. Control animals were sacrificed 70 min after respective injections. Levels of noradrenaline (NA) and its major metabolite, 3-methoxy-4-hydroxyphenylethyleneglycol sulfate (MHPG-SO₄) in seven discrete brain regions and plasma corticosterone levels were fluorometrically determined. Immobilization stress caused significant elevations of plasma corticosterone which were not affected by pretreatment with naloxone. In the hypothalamus, amygdala and thalamus, immobilization-stress caused significant elevations of MHPG-SO₄ levels, and naloxone at 5 mg/kg significantly enhanced these stress-induced elevations virtually without affecting the basal level of the metabolite. In contrast, in the hippocampus, cerebral cortex and pons plus medulla oblongata, MHPG-SO₄ levels were elevated by stress, but were not affected by naloxone pretreatment. The effect of naloxone on stress-induced reductions of NA levels was unclear, since naloxone by itself (5 mg/kg) significantly decreased the amine levels in 5 of 7 brain regions examined. These results indirectly suggest that endogenous opioid peptides in the hypothalamus, amygdala and thalamus are partly involved in the stress process and attenuate increases in NA turnover induced by stress.     

The effect of centrally administered ghrelin on pituitary ACTH cells and circulating ACTH and corticosterone in rats

Ghrelin is a brain-gut peptide known for its growth hormone (GH)-releasing and appetite-inducing activities. This natural GH secretagogue (GHS) was originally purified from rat stomach, but it is expressed widely in different tissues where it may have endocrine and paracrine effects. The central effects of ghrelin on adrenocorticotropic hormone (ACTH) cells, ACTH release and subsequent corticosterone release from adrenal glands remains to be clarified. The aim of this study was to specifically determine the morphological features of ACTH-producing pituicytes and blood concentration of ACTH and corticosterone after central administration of ghrelin. Five doses of rat ghrelin or PBS (n=10 per group) were injected every 24 h (1 microg of ghrelin in 5 muL PBS), into the lateral cerebral ventricle of male rats. Results showed that ghrelin increased (p<0.05) absolute and relative pituitary weights compared to controls (58% and 41% respectively). Morphometric parameters, i.e. the volume of the ACTH cells, nuclear volume, and volume density were all increased (p<0.05), by 17%, 6% and 13%, respectively, 2 h after the last ghrelin treatment. Ghrelin increased circulating concentrations of ACTH and corticosterone (p<0.05) by 62% and 66%, respectively. The data provide clear documentation that intracerebroventricular ghrelin stimulates ACTH cell hypertrophy and proliferation, and promotes ACTH and corticosterone release. Determining the role of ghrelin in physiological stress responses and whether control of the peptide's activity would be useful for prevention and/or treatment of stress-induced diseases remain important research goals.     

Comparison of plasma ACTH and corticosterone levels after embryo bursectomy

Plasma levels of both adrenocorticotropic hormone (ACTH) and corticosterone (B) were determined in embryos (day 15 of incubation), chicks (day 3 after hatch) and young chickens (8 weeks). Experimental animals were bursectomized at 80 hr of incubation, i.e., before any anlage of the bursa of Fabricius could develop. Bursectomized (BFX) animals were compared to sham-operated controls (T), in basal, resting condition and 7 (ACTH) or 14 min (B) after ether stress was delivered for 30 sec. Basal B and ACTH levels seemed not to be significantly modified in BFX embryos, chicks and chickens. Hypophysial and adrenocortical response to stress appeared more precociously in BFX embryos (day 15 of incubation) than in intact ones (day 19). The non stress-responsive period that was observed for one week after hatch of T birds did not appear in 3-day-old BFX chicks whose both B and ACTH stress-induced levels were as high as in intact adults. In contrast, adrenocortical and pituitary corticotropic responses to stress were markedly impaired (by 50%) in adult BFX chickens as compared to intact controls.     

The involvement of nitric oxide and prostaglandins in the cholinergic stimulation of hypothalamie-pituitary-adrenal response during crowding stress.

The aim of the present study was to determine the effect of social crowding stress and significance of nitric oxide (NO) and prostaglandins (PG) generated by constitutive and inducible nitric oxide synthase (NOS) and cyclooxygenase (COX) in the stimulation of hypothalamic-pituitary-adrenal (HPA) axis by cholinergic muscarinic receptor agonist carbachol. Inhibitors of neuronal NOS (nNOS) L-NNA, general NOS L-NAME and inducible NOS (iNOS) aminoguanidine, as well as inhibitors of COX-1, piroxicam, and COX-2, compound NS-398 were administered 15 min prior to carbachol to control or crowded rats (24 rats in cage for 7, during 3 and 7 days). In stressed rats L-NAME, L-NNA and aminoguanidine significantly intensified the carbachol-induced ACTH and corticosterone secretion, like in control rats. Piroxicam, markedly decreased the carbachol-induced ACTH and corticosterone response under either basal or stress conditions. Compound NS-398 did not markedly alter the carbachol-induced HPA response in control and stressed rats. Crowding stress (3 days) significantly impaired the i.c.v. prostaglandin E(2)-induced ACTH response. Corticotropin releasing hormone (CRH) receptor antagonists, alpha-helical CRH [9-14], given i.c.v. did not alter the PGE(2)-evoked corticosterone response in either control or stressed rats, indicating that hypothalamic CRH is not involved in the PGE(2)-induced central stimulation of HPA axis. In control rats L-NAME considerably enhanced, while L-arginine, a physiological NOS substrate, abolished the PGE(2)-induced ACTH and corticosterone response. In stressed rats this NOS blocker significantly increased and L-Arg reduced the stimulatory effect of PGE(2) on ACTH and corticosterone secretion. The carbachol-induced corticosterone response was significantly increased by pretreatment with nNOS inhibitor L-NNA and was considerably reduced by indomethacin, a general COX inhibitor. Pretreatment with both antagonists left the carbachol-induced corticosterone level unchanged, suggesting an independent and reciprocal effect of NO and PG in the cholinergic stimulation of pituitary-adrenocortical response. These results indicate that in the stimulatory action of muscarinic agonist, carbachol, NO is an inhibitory transmitter under basal and crowding stress conditions. This psychosocial stress does not functionally affect the NOS/NO systems. Prostaglandins are involved in the cholinergic muscarinic-induced stimulation of HPA response to a significant extent in non-stressed rats. PGE(2) may be involved in the carbachol-elicited HPA response under basal and stress conditions. Prostaglandins released in response to muscarinic stimulation did not evoke the hypothalamic CRH mediation. NO significantly impairs and PG stimulates the carbachol-induced HPA response in rats under basal and social stress conditions.