Adrenocortical involvement during diverse stress in soft-shelled turtle Lissemys p. punctata Bonnoterre

Adrenocortical responses to diverse stressful situations (dehydration, formaldehyde treatment and salt loading) were studied in the adult female soft-shelled turtle, Lissenmys p. punctata. Dehydration, formaldehyde treatment (formalin, 1%: 0.1 ml/100 g body weight daily) or salt loading (NaCl, 1%: 0.1 ml/100 g body weight daily) treatments consecutively for 7 days caused hypertrophy of the adrenocortical cells with their nuclear diameter increased, and depletions of adrenal cholesterol and ascorbic acid concentrations followed by decreased acid phosphatase and alkaline phosphatase activities in turtles. Corticosterone levels were elevated in both the adrenal gland and serum of turtles after dehydration and formalin stress, but the hormone level remained unaltered after salt loading in turtles. The results suggest active involvement of adrenal cortex in stress for homeostasis in Lissemys turtles.     

Effect of prenatal stress on the pituitary-adrenal axis in blue foxes

Handling is a source of stress for farm bred blue foxes. The influence of handling during the late gestation period on the pituitary--adrenal axis was studied in 10-day old male and female blue foxes. Cortisol and progesterone were measured by radioimmunoassay in the plasma, adrenal homogenates, and in vitro incubates from animals of both sexes. Adrenals were incubated in vitro in the absence or presence of ACTH. In addition, the adrenal weight and plasma concentration of ACTH were assessed. In cubs of both sexes, the adrenal weight was decreased after prenatal stress. The plasma concentration of progesterone and the adrenal cortisol in vitro production were elevated in the prenatally stressed female cubs, as compared to the control, along with the adrenal progesterone in vitro production in prenatally stressed male cubs. The adrenal cortisol and progesterone content and plasma ACTH and cortisol concentrations were not affected by prenatal stress. In conclusion, the results of this study suggest that the prenatal stress induced by handling pregnant vixens can affect the pituitary--adrenal axis in neonatal offspring, this effect being more pronounced in female cubs.     

Dynamic measure of production rate of cortisol in the mature guinea-pig in response to the stress of anesthesia: Effect of estradiol

The effect of estradiol on adrenal secretion rate of cortisol in response to a stress induced by anesthesia, was examined by comparing the metabolic clearance rate and the production rate of cortisol between males and females and after estradiol administration in castrated animals. Metabolic clearance rates of cortisol (MCR) were significantly higher (+30%) in males than in females. Castration lowered the MCR of cortisol in males and had no significant effect in females. After estradiol administration, a fall in the MCR of cortisol concomitant with a rise in blood cortisol level was observed especially in males in which the effect of treatment was more marked than in females and highly significant. The production rate of cortisol was identical in males and females and was slightly increased in estradiol-treated males and females. The data indicate that estradiol had an inhibitory effect on metabolic clearance of cortisol, which caused an important rise of blood cortisol levels in response to stress and which prevented an increase in the adrenal response to the stress. Since the pituitary adrenal cortex can respond in a normal way to stress, the low value of MCR of cortisol could be the limiting factor in the adrenal secretion rate of cortisol in estrogen-treated guinea-pigs.     

cGMP-dependent protein kinase type II regulates basal level of aldosterone production by zona glomerulosa cells without increasing expression of the steroidogenic acute regulatory protein gene

The renin-angiotensin-aldosterone system plays a pivotal role in the regulation of salt and water homeostasis. Here, we demonstrate the expression and functional role of cGMP-dependent protein kinases (PKGs) in rat adrenal cortex. Expression of PKG II is restricted to adrenal zona glomerulosa (ZG) cells, whereas PKG I is localized to the adrenal capsule and blood vessels. Activation of the aldosterone system by a low sodium diet up-regulated the expression of PKG II, however, it did not change PKG I expression in adrenal cortex. Both, activation of PKG II in isolated ZG cell and adenoviral gene transfer of wild type PKG II into ZG cells enhanced aldosterone production. In contrast, inhibition of PKG II as well as infection with a PKG II catalytically inactive mutant had an inhibitory effect on aldosterone production. Steroidogenic acute regulatory (StAR) protein that regulates the rate-limiting step in steroidogenesis is a new substrate for PKG II and can be phosphorylated by PKG II in vitro at serine 55/56 and serine 99. Stimulation of aldosterone production by PKG II in contrast to stimulation by PKA did not activate StAR gene expression in ZG cells. The results presented indicate that PKG II activity in ZG cells is important for maintaining basal aldosterone production.     

On the mechanism of action of plant adaptogens with particular reference to cucurbitacin R diglucoside.

Cucurbitacin R diglucoside (DCR), one of the active principles of Bryonia alba L. root was found to have an effect on the production of corticosteroids and the biosynthesis of eicosanoids in the adrenal cortex, isolated adrenocortical cells, blood plasma, and leukocytes under stress and stress-free conditions in vitro and vivo. DCR prevents stress-induced alterations of eicosanoids in blood and moderately stimulates the adrenal cortex to adapt organism to stress, because a moderate increase in corticosteroid secretion protects the defense system of organisms from becoming hyperactive. DCR enhances sensitivity to stress due to the effects of eicosanoids and corticosteroids.     

Effect of Prenatal Stress on the Pituitary–Adrenal Axis in Blue Foxes

Handling is a source of stress for farm bred blue foxes. The influence of handling during the late gestation period on the pituitary–adrenal axis was studied in 10-day old male and female blue foxes. Cortisol and progesterone were measured by radioimmunoassay in the plasma, adrenal homogenates, and in vitro incubates from animals of both sexes. Adrenals were incubated in vitro in the absence or presence of ACTH. In addition, the adrenal weight and plasma concentration of ACTH were assessed. In cubs of both sexes, the adrenal weight was decreased after prenatal stress treatment. The plasma concentration of progesterone and the adrenal cortisol in vitro production were elevated in the prenatally stressed female cubs, as compared to the control, along with the adrenal progesterone in vitro production in prenatally stressed male cubs. The adrenal cortisol and progesterone content and plasma ACTH and cortisol concentrations were not affected by prenatal stress. In conclusion, the results of this study suggest that the prenatal stress induced by handling pregnant vixens can affect the pituitary–adrenal axis in neonatal offspring, this effect being more pronounced in female cubs.     

Induction of 5-aminolevulinate synthase by activators of steroid biosynthesis

Different cytochromes P450 are involved in steroid biosynthesis. These cytochromes have heme as the prosthetic group. We previously reported that ACTH, an activator of glucocorticoid biosynthesis in adrenal, requires heme biosynthesis for a maximal response. In the present study, we investigated the effect of ACTH, and the effect of two activators of the adrenal mineralocorticoid synthesis, endothelin-1 and low sodium diet on 5-aminolevulinate-synthase (ALA-s) mRNA. ALA-s is the rate-limiting enzyme in heme biosynthesis. It was found that infusion of rats with ACTH for 1 h caused an increase of adrenal ALA-s mRNA and activity accompanied by an increase in plasma corticosterone. CYP21, a cytochrome involved in the synthesis of both corticosterone and aldosterone, was not modified at the RNA level in adrenal glands by 1 h of ACTH infusion. Consistently, infusion of endothelin-1 for 1 h increased ALA-s mRNA and aldosterone content in adrenal gland without modifying CYP21 mRNA levels. To study if ALA-s is also regulated by the main physiological stimuli that increase adrenal mineralocorticoid secretion, we fed rats with low salt diet for 2 or 15 days. Low salt diet treatment increased adrenal gland ALA-s mRNA levels. On the other hand, the rapid stimulation of ALA-s mRNA by ACTH which acts through cyclic AMP was confirmed in H295R human adrenocortical cells, the only human adrenal cell line that has a steroid secretion pattern and regulation similar to primary cultures of adrenal cells. Our findings suggest that the acute activation of adrenal steroidogenic cytochromes by trophic hormones involves an increase in heme biosynthesis which will favor the production of active cytochromes.     

Effect of sodium intake on aldosterone and corticosterone production, the serum sodium concentration and body weight in infant rats during weaning period.

1. The effect of a low salt (LS, 0.3% NaC1) and control (HS, 1% NaC1) diet on in vitro aldosterone and corticosterone production, the serum corticosterone level, the serum sodium concentration and adrenal and body weight was studied in 30-day-old male rats, some of which were weaned prematurely at the age of 15 days (PW) and some left with the female up to the end of the experiment (NW). 2. Aldosterone production in the control (HS-NW) animals was 1.07+/-0.07 mug/100 mg adrenal/hour (mean +/-S.E.M.), in HS-PW animals 0.6+/-0.07 (P less than 0.01), while in LS-NW and LS-PW animals it rose to 1.59+/-0.1 and 1.81+/-0.14 respectively. The effect of the salt regimen was significant in both the NW group (P less than 0.01) and the PW group (P less than 0.01). Premature weaning did not inhibit aldosterone production in LS-PW animals. 3. Corticosterone production in animals fed on the control diet was 1.81+/-0.16 mug corticosterone/100 mg adrenal/hour in HS-NW rats and 0.91+/-0.09 in the HS-PW group (P less than 0.01). On the low salt diet it fell to 1.4+/-0.11 in LS-NW rats (HW-NW) vs LS-NW: P less than 0.01) and to 0.4+/-0.06 in LS-PW animals (HS-PW vs LS-PW: P less than 0.01). The difference between LS-NW and LS-PW was likewise statistically significant (P less than 0.01). Changes in production were not accompanied by parallel changes in the serum corticosterone level, where an analysis of variance showed no significant difference. 4. The low salt diet reduced the serum sodium concentration in both NW and PW animals (HS-NW 132.9+/-0.86 mEd HS-PW 132+/-0.86, LS-PW 128.5+/-1.16: P less than 0.01). The differences between NW and PW animals were not significant. 5. A low salt intake also reduced the body weight both of animals left with the female (HS-NW vs LS-NW: P less than 0.01) and of prematurely weaned animals (HS-PW vs LS-PW: P less than 0.01). Early weaning significantly affected body weight in LS animals only, the body weight of LS-PW animals being significantly lower than that of LS-NW animals (P less than 0.02). 6. The results show that infant rats are hypersensitive to a low salt intake at the end of the weaning period and that this phenomenon is not mediated by lower reactivity of the zona glomerulosa and of its regulation.     

Induction of phosphatidylinositol 3-kinase-mediated endocytosis by salt stress leads to intracellular production of reactive oxygen species and salt tolerance

Salt imposes immediate problems for plant cells, such as osmotic stress, impaired ion homeostasis and sodium toxicity, followed by a secondary oxidative stress caused by generation of reactive oxygen species (ROS). Here, we analyzed the production of ROS during salt stress. We show that salt stress triggered plasma membrane internalization, resulting in the production of ROS within endosomes. The intracellular ROS were produced by NADPH oxidase in response to the ionic but not the osmotic stress. Both endocytosis and ROS production were suppressed in phosphatidylinositol (PtdIns) 3-kinase (PI3K) mutants, PI3K being a key regulator of vesicle trafficking in animals and plants, and by wortmannin, which is a specific inhibitor of PI3K and PI4K. Endocytosis and the production of ROS were rescued by supplementation of seedlings with exogenous PtdIns 3-phosphate (PtdIns3P), less with PtdIns4P, but not with PtdIns(4,5)P(2). Surprisingly, despite reduced oxidative stress, the mutants and the wortmannin-treated plants exhibited a phenotype overly sensitive to salt, as also resulted from treatment with diphenyleneiodonium, a suicide inhibitor of NADPH oxidase, suggesting a positive role for ROS in salt tolerance. In summary, our results show that salt stress responses, such as increased plasma membrane endocytosis and the intracellular production of ROS, are coordinated by phospholipid-regulated signaling pathways, and suggest that ROS act in the signal transduction of the salt tolerance response.     

The Effect of Salt Stress on the Production of Canthaxanthin and Astaxanthin by Chlorella zofingiensis Grown Under Limited Light Intensity

The fresh water green microalga Chlorella zofingiensisis known to accumulate ketocarotenoids – primarily astaxanthin but also canthaxanthin – when grown under stress conditions of high light irradiance and low nitrogen. We found that salt stress can replace light stress with respect to inducing carotenoid production: cells of C. zofingiensis grown under low light irradiance and subjected to salt and low nitrogen stress accumulated higher amounts of total secondary carotenoids than those growing under high light and low nitrogen stress. Furthermore, C. zofingiensis growing under conditions of salt stress and low light accumulated higher amounts of canthaxanthin than astaxanthin. It is suggested that for canthaxanthin accumulation under salt stress, light is not a limiting factor, but for astaxanthin accumulation high light irradiance is mandatory. These results may be applied in the future for the commercial production of canthaxanthin by C. zofingiensis in systems in which light availability is poor.     

Steroidogenesis in adrenal glands of young and adult female mice with hyperexpression of the Aguoti gene

Dominant mutation Agouti yellow (AY) leads to ectopic overexpression of the Agouti gene and yellow coat color in mice. Furthermore, the mutation Ay increased adrenal response to emotional stress. The study assessed whether pleiotropic effect of the mutation Ay on adrenals function was dependent on sex and age. 3- and 15-week old female C57B1/6J mice of two agouti-genotypes: Ay/a (ectopic Agouti-gene overexpression) and a/a (absence of Agouti-protein), were investigated. Cyclic AMP level (adenylate cyclase activity) and corticosterone production in adrenal isolated cells stimulated by ACTH and dibutyrul cAMP (db-cAMP) were measured. ACTH increased cAMP accumulation to the same extent in Ay/a- and a/a-mouse adrenal cells of both ages. The dibutyrul cAMP-induced corticosterone production was higher in Ay/a than in a/a-mouse adrenal cells of both ages. The ACTH-induced corticosterone production in 3-week- old Ay/a-m/CQ was lower and in 15-week old Ay/a-mice was higher than in a/a-mice of the respective ages. The ACTH- and db-cAMP-induced steroidogenesis was not changed in Ay/a-mice and decreased in a/a-mice with age. Thus, in females as well as in males, the mutation Agouti yellow did not affect adenylate cyclase activity, increased db-cAMP-induced corticosterone production and disturbed development of adrenal cortex.     

Selenium deficiency impairs corticosterone and leptin responses to adrenocorticotropin in the rat

Selenium deficiency causes oxidative stress and impairs steroidogenesis in vitro. Leptin is closely related to the hypothalamo-pituitary-adrenal (HPA) axis. Leptin inhibits the HPA axis at the central level while corticosteroids have been shown to stimulate leptin secretion in most studies. We hypothesized that oxidative stress impairs adrenal steroidogenesis and decreases leptin production in vivo. The goal of this study was to investigate in rats the effects of selenium deficiency and oxidative stress on adrenal function and on leptin concentrations. Weanling rats were fed a selenium-deficient (Se-) or selenium-sufficient (Se+) diet for 4-10 weeks. Selenium deficiency caused a marked decrease in liver (> or = 99%) and adrenal (> or = 81%) glutathione peroxidase (GPx) activities. Selenium deficiency did not affect basal and short-term adrenocorticotropin (ACTH) stimulated corticosterone or leptin concentrations. In contrast, after long-term ACTH stimulation, selenium deficiency caused a doubling in adrenal isoprostane content and blunted the increase in corticosterone and leptin concentrations observed in Se+ animals. Plasma leptin concentrations were 50% lower in Se- compared to Se+ animals following long-term ACTH. Our results suggest that oxidative stress causes a decrease in circulating corticosterone in response to ACTH, and, as a consequence, a decrease in plasma leptin concentrations.     

Adrenal function of rats in hypokinesia

Histological and biochemical examinations of the adrenals and plasma of rats for 3 months exposed to hypokinesia have shown that low motor activity led to a decrease in blood corticosterone level in spite of adrenal cortex hypertrophy. The decreased corticosterone blood level was not indicative of adrenal exhaustion, as the adrenals produced a greater amount of corticosterone in response to additional stress stimulus (5-hour immobilisation of animals in an extended state), as compared to the control. The increased production of corticosterone in response to stress stimulus caused no structural transformations or delipoidization of the cortical substance. This indicated that the reserve potentials of the adrenals increased with the animal adaptation to hypokinesia. The major morphological indication of higher adrenal functional activity in hypokinetic animals was an enhanced destruction of lymphocytes in the thymus cortex, the target organ for corticosteroids produced by the adrenals in response to an additional stress stimulus.     

Dehydroepiandrosterone and dehydroepiandrosterone sulfate production in the human adrenal during development and aging.

Dehydroepiandrosterone (DHEA) is produced in prodigious quantities by the human adrenal, principally as the 3-sulfoconjugate DHEA sulfate (DS) during intrauterine life. The fetal zone and neocortex cells of the fetal adrenal express large amounts of DHEA sulfotransferase and minimal amounts, at least until very near the end of gestation, of 3beta-hydroxysteroid dehydrogenase. This pattern of enzyme expression favors substantial secretion of DHEA/DS with minimal cortisol produced; the DHEA/DS serves as the major precursor for placental estrogen formation in human pregnancy. Aside from adrenocorticotropin, other physiologic regulators of growth and steroidogenesis in the fetal adrenal have been postulated to exist, but have yet to be identified. Whereas intrauterine stressors may activate adrenal cortisol secretion, the fetal adrenal responds to many pregnancy conditions by suppressing DHEA/DS formation. After birth, the human adrenal undergoes reorganization whereby the large, inner fetal zone regresses, and DHEA/DS production is diminished. Just prior to gonadal maturation, the human adrenal undergoes morphologic and functional changes (adrenarche) that give rise to a prominent zona reticularis that is characterized by the presence of DHEA sulfotransferase, the absence of 3beta-hydroxysteroid dehydrogenase, and an enhancement of DHEA/DS production. The adrenal of the adult responds to stress in many instances like that of the fetus: increased cortisol secretion and diminished DHEA/DS secretion. The mechanisms for this divergence in the adrenocortical pathway is unknown. With aging, there is suppression of DHEA/DS secretion, possibly as the consequence of an involution of the zona reticularis, but corticosteroid production continues unabated.     

盐胁迫下烟草愈伤组织内源活性氧及乙烯的产生与交替途径发生,？…

This paper reported firstly the dynamic changes of the alternative pathway and the cytochrome pathway in tobacco callus under different concentration of salt. The production rate of endogenous ethylene, the contents of active oxygen species (O2-., .OH and H2O2) and the activities of related enzyme (SOD and CAT) were also investigated simultaneously. The results indicated that the actual operation of the alternative pathway (rho Valt) increased gradually and reached the maxima at 0.75% salt concentration, then declined, while the capacity of the alternative pathway (Valt) didn't exhibit the same change pattern with rho Valt and the cytochrome pathway (rho' Vcyt) changed contrary to rho Valt. At the same time, H2O2 and O2-. accumulated rapidly and reached their peak value at about 0.5% and 0.75% salt concentration respectively, while the content of .OH increased consistently. The production rate of endogenous ethylene increased rapidly and reached its maxima at about 0.5% salt concentration. These data demonstrated that changes of Valt in tobacco callus were associated with a parallel production of H2O2 and endogenous ethylene and a opposite production of .OH, while rho Valt changed parally with the production of O2-.. On the basis of above results, it was deduced that the changes of the development and operation of the alternative pathway in tobacco callus under salt stress might be correlated with the production of endogenous ethylene and the active oxygen species. The possible participation of the alternative pathway in response to salt stress was also discussed.     

Synergistic enhancement of ethylene production and germination with kinetin and 1-aminocyclopropane-1-carboxylic Acid in lettuce seeds exposed to salinity stress

Relief of salt (0.1 molar NaCl) stress on germination of lettuce (Lactuca sativa L., cv Mesa 659) seeds occurred with applications of 0.05 millimolar kinetin (KIN) and 1 to 10 millimolar 1-aminocyclopropane 1-carboxylic acid (ACC). Treatment with KIN enhanced the pregermination ethylene production under saline condition. A synergistic or an additive enhancement of pregermination ethylene production and germination occurred under saline condition in the presence of KIN and a saturating dose (10 millimolar) of ACC. No KIN-ACC synergism was noted in ethylene production or germination under nonsaline condition. Addition of 1 millimolar aminoethoxyvinylglycine (AVG) inhibited the KIN-enhanced pregermination ethylene production (85 to 89%) and germination (58%) under saline condition but not the synergistic effect of KIN + ACC on ethylene production. Under nonsaline condition, AVG had no effect on germination even though ethylene production was strongly inhibited. Alleviation of salt stress by KIN was inhibited in a competitive manner by 2,5-norbornadiene (NBD) (0.02-0.2 milliliter per liter), and the addition of ACC and/or ethylene reduced this inhibition. An increase in the pregermination ethylene production and germination occurred also by cotylenin E (CN) under saline condition. However, neither AVG (1 millimolar) nor NBD (0.02 to 0.2 milliliter per liter) prevented the relief of salt stress by CN. Thus, KIN may alleviate salt stress on germination by promoting both ACC production and its conversion to ethylene. Rapid utilization of ACC may be the basis for the synergistic or the additive effect of KIN plus ACC. The need for ethylene production and action for the relief of salt stress is circumvented by a treatment with CN.     

植物盐胁迫应答转录因子的研究进展

盐胁迫会导致植物受到初级的渗透胁迫和离子毒害以及次级的氧化胁迫和营养胁迫,严重制约了农业生产.植物盐胁迫应答转录因子能够通过调节下游靶基因的表达减轻盐胁迫对植物造成的伤害.文中基于土壤盐渍化及其对植物的危害、转录因子在植物盐胁迫信号转导网络中的中枢调节作用,综述了盐胁迫应答转录因子参与的盐胁迫信号转导途径、通过形成同源...     

盐胁迫环境下植物促生菌的作用机制研究进展

盐胁迫是限制干旱和半干旱地区作物生产的主要非生物胁迫之一,严重影响作物的生长发育,植物促生菌(Plant growth-promoting bacteria,PGPB)可有效减轻植物的盐胁迫损伤,合理施用PGPB是盐胁迫下促进作物生长的重要途径。本文从盐胁迫环境下PGPB在调节植物激素内稳态、促进养分吸收和诱导植物产生系统耐受性等方面的作用阐述了PGPB提高植物耐盐性、减轻植物胁迫损伤的作用机制。讨论了能够在植物根际稳定定殖并在盐生环境下稳定保持PGP活性的功能菌株对未来农业的可持续发展的重要意义,同时,对该研究方向的重难点和未来的发展趋势作出展望。     

Chronic stress induces adrenal hyperplasia and hypertrophy in a subregion-specific manner

The adrenal gland is an essential stress-responsive organ that is part of both the hypothalamic-pituitary-adrenal axis and the sympatho-adrenomedullary system. Chronic stress exposure commonly increases adrenal weight, but it is not known to what extent this growth is due to cellular hyperplasia or hypertrophy and whether it is subregion specific. Moreover, it is not clear whether increased production of adrenal glucocorticoid after chronic stress is due to increased sensitivity to adrenocorticotropic hormone (ACTH) vs. increased maximal output. The present studies use a 14-day chronic variable stress (CVS) paradigm in adult male rats to assess the effects of chronic stress on adrenal growth and corticosterone steroidogenesis. Exogenous ACTH administration (0-895 ng/100 g body wt) to dexamethasone-blocked rats demonstrated that CVS increased maximal plasma and adrenal corticosterone responses to ACTH without affecting sensitivity. This enhanced function was associated with increased adrenal weight, DNA and RNA content, and RNA/DNA ratio after CVS, suggesting that both cellular hyperplasia and hypertrophy occurred. Unbiased stereological counting of cells labeled for Ki67 (cell division marker) or 4,6-diamidino-2-phenylindole (nuclear marker), combined with zone specific markers, showed that CVS induced hyperplasia in the outer zona fasciculata, hypertrophy in the inner zona fasciculata and medulla, and reduced cell size in the zona glomerulosa. Collectively, these results demonstrate that increased adrenal weight after CVS is due to hyperplasia and hypertrophy that occur in specific adrenal subregions and is associated with increased maximal corticosterone responses to ACTH. These chronic stress-induced changes in adrenal growth and function may have implications for patients with stress-related disorders.     

Production of corticosterone in male homozygous Brattleboro rats

Plasma concentration, metabolic clearance rate and in vitro adrenal production of corticosterone were measured in Brattleboro male rats homozygous for diabetes insipidus (DI) and in Long-Evans male rats (LE) as controls in resting conditions, under stress caused by pentobarbitone anesthesia and surgery and after three days water deprivation. In resting animals, plasma concentrations and in vitro adrenal production of corticosterone were higher in DI rats than in LE rats. Under pentobarbitone anesthesia and surgery, plasma concentrations and metabolic clearance rate of corticosterone were slightly but not statistically lower in DI rats; however, the in vivo production rate of corticosterone was significantly lower. After three days water deprivation, increasing plasma corticosterone level was consistently higher in DI than in Le rats. These results are not in favour of a reduced glucocorticoid activity of the adrenal of DI rats and of an important role played by vasopressin on the stimulation of the hypothalamopituitary adrenal activity at least in resting conditions; its role may depend upon stressful circumstances.