Effect of acute and prolonged mineralocorticoid receptor blockade on spontaneous and stimulated hypothalamic-pituitary-adrenal axis in humans

From Ligands to Behavioral Outcomes: Understanding the Role of Mineralocorticoid Receptors in Brain Function

Stress is a normal response to situational pressures or demands. Exposure to stress activates the hypothalamic-pituitary-adrenal (HPA) axis and leads to the release of corticosteroids, which act in the brain via two distinct receptors: mineralocorticoid receptors (MR) and glucocorticoid receptors (GR). Persistent HPA axis overactivation or dysregulation can disrupt an individual's homeostasis, thereby contributing to an increased risk for mental illness. On the other hand, successful coping with stressful events involves adaptive and cognitive processes in the brain that render individuals more resilient to similar stressors in the future. Here we review the role of the MR in these processes, starting with an overview of the physiological structure, ligand binding, and expression of MR, and further summarizing its role in the brain, its relevance to psychiatric disorders, and related rodent studies. Given the central role of MR in cognitive and emotional functioning, and its importance as a target for promoting resilience, future research should investigate how MR modulation can be used to alleviate disturbances in emotion and behavior, as well as cognitive impairment, in patients with stress-related psychiatric disorders.

Glucocorticoid Negative Feedback in Regulation of the Hypothalamic-Pituitary-Adrenal Axis in Rhesus Monkeys With Various Types of Adaptive Behavior: Individual and Age-Related Differences

The study of the mechanisms underlying the increased vulnerability of the individual to stressful environmental factors in different age periods is of great relevance for prevention and effective treatment of stress-dependent diseases that are widespread in the population of aging individuals. The purpose of our study was to investigate the individual and age-related features of the glucocorticoid negative feedback in regulation of the hypothalamic-pituitary-adrenal (HPA) axis, the key adaptive neuroendocrine system, in experiments with physically healthy young and old female rhesus monkeys with administration of mineracorticoid receptor (fludrocortisone) and glucocorticoid receptor (dexamethasone) agonists. We studied the monkeys with increased trait anxiety and depression-like behavior (DAB) characterized, as previously was shown, by the increased vulnerability to acute stress and the animals with normal standard behavior (SB) as the control. The pronounced individual differences in the reaction of HPA axis to fludrocortisone and dexamethasone in young animals were found. Young animals with DAB showed a lower sensitivity of HPA axis to the inhibitory effect of both fludrocortisone and dexamethasone compared with young animals with SB. At the same time, there were no significant intergroup differences in the concentration of ACTH and cortisol in response to placebo injection, i.e., in basal conditions. The old individuals with DAB demonstrated the essential relative resistance of HPA axis to fludrocortisone test and higher basal plasma levels of cortisol and ACTH in the evening (the period of HPA axis low circadian activity) compared to old SB animals. In the same time, the intergroup differences in the response of HPA axis to dexamethasone administration were leveled due to age-related increase in sensitivity of HPA axis to dexamethasone in animals with DAB. These data testify the pronounced intergroup and age differences in the feedback regulation of HPA axis, presumably resulting from unequal individual, and age-related changes in the activity of mineralcorticoid and glucocorticoid receptors in the brain structures supporting the functions of HPA axis. The maximum age disorders in functioning of the negative feedback mechanism in the regulation of HPA axis are characteristic of animals with DAB, which, apparently, underlie the increased vulnerability of these animals to stress exposure.

Differential effects of imipramine and CORT118335 (Glucocorticoid receptor modulator/mineralocorticoid receptor antagonist) on brain-endocrine stress responses and depression-like behavior in female rats

Depression is commonly associated with hypothalamic-pituitary adrenal (HPA) axis dysfunction that primarily manifests as aberrant glucocorticoid secretion. Glucocorticoids act on Type I mineralocorticoid (MR) and Type II glucocorticoid receptors (GR) to modulate mood and endocrine responses. Successful antidepressant treatment normalizes HPA axis function, in part due to modulatory effects on MR and GR in cortico-limbic structures. Although women are twice as likely to suffer from depression, little is known about how antidepressants modulate brain, endocrine, and behavioral stress responses in females. Here, we assessed the impact of CORT118335 (GR modulator/MR antagonist) and imipramine (tricyclic antidepressant) on neuroendocrine and behavioral responses to restraint or forced swim stress (FST) in female rats (n=10-12/group). Increased immobility CORT118335 in the FST is purported to reflect passive coping or depression-like behavior. CORT118335 dampened adrenocorticotropic hormone (ACTH) and corticosterone responses to the FST, but did not affect immobility. Imipramine suppressed ACTH, but had minimal effects on corticosterone responses to FST. Despite these marginal effects, imipramine decreased immobility, suggesting antidepressant efficacy. In an effort to link brain-endocrine responses with behavior, c-Fos was assessed in HPA axis and mood modulatory regions in response to the FST. CORT118335 upregulated c-Fos expression in the paraventricular nucleus of the hypothalamus. Imipramine decreased c-Fos in the basolateral amygdala and hippocampus (CA1 and CA3), but increased c-Fos in the central amygdala. These data suggest the antidepressant-like (e.g., active coping) properties of imipramine may be due to widespread effects on cortico-limbic circuits that regulate emotional and cognitive processes.

The Arcuate Nucleus: A Site of Fast Negative Feedback for Corticosterone Secretion in Male Rats

Variations in circulating corticosterone (Cort) are driven by the paraventricular nucleus of the hypothalamus (PVN), mainly via the sympathetic autonomic nervous system (ANS) directly stimulating Cort release from the adrenal gland and via corticotropin-releasing hormone targeting the adenohypophysis to release adrenocorticotropic hormone (ACTH). Cort feeds back through glucocorticoid receptors (GRs). Here we show in male Wistar rats that PVN neurons projecting to the adrenal gland do not express GRs, leaving the question of how the ANS in the PVN gets information about circulating Cort levels to control the adrenal. Since the arcuate nucleus (ARC) shows a less restrictive blood-brain barrier, expresses GRs, and projects to the PVN, we investigated whether the ARC can detect and produce fast adjustments of circulating Cort. In low Cort conditions (morning), local microdialysis in the ARC with type I GR antagonist produced a fast and sustained increase of Cort. This was not observed with a type II antagonist. At the circadian peak levels of Cort (afternoon), a type II GR antagonist, but not a type I antagonist, increased Cort levels but not ACTH levels. Antagonist infusions in the PVN did not modify circulating Cort levels, demonstrating the specificity of the ARC to give Cort negative feedback. Furthermore, type I and II GR agonists in the ARC prevented the increase of Cort after stress, demonstrating the role of the ARC as sensor to modulate Cort release. Our findings show that the ARC may be essential to sense blood levels of Cort and adapt Cort secretion depending on such conditions as stress or time of day.

Mineralocorticoid receptor function in depressed patients and healthy individuals

BACKGROUND

Many studies have shown disturbed glucocorticoid receptor (GR) in depressed patients. In contrast, only few studies targeted mineralocorticoid receptor (MR) function with inconclusive results. We examined the effects of the MR antagonist spironolactone on cortisol secretion in depressed patients and healthy individuals.

METHODS

Forty-eight unmedicated depressed patients (mean age 41.6years) and 45 age- and sex-matched healthy participants (40.7years) received the MR antagonist spironolactone (300mg) or placebo with three days apart in a randomized, double-blind, within-subject cross-over design. We measured salivary cortisol before ingestion of study medication (baseline) as well as +60min, +90min, +120min, +150min and 180min after baseline.

RESULTS

Repeated-measures ANOVA for area under the curve (AUCg) cortisol revealed a treatment effect with higher cortisol after spironolactone and a treatment by group interaction. Post-hoc analyses revealed higher cortisol in depressed patients compared to healthy participants in the placebo condition. In the spironolactone condition, the cortisol levels were not significantly different.

CONCLUSIONS

Potentially, impaired MR or GR signaling could be responsible for higher cortisol levels in depressed patients in the placebo condition. However, after MR blockade that increased cortisol secretion across groups leading to higher GR occupation, we found no differences between depressed patients and healthy controls. Thus, our results argue for depression-associated alterations in MR signaling rather than disturbed GR-mediated feedback inhibition.

The acute effect of a mineralocorticoid receptor agonist on corticotrope secretion in Addison's disease

PURPOSE

Mineralocorticoid receptors (MR) in the hippocampus display an important role in the control of hypothalamic-pituitary-adrenal (HPA) axis, mediating the ''proactive'' feedback of glucocorticoids (GC). Fludrocortisone (FC), a potent MR agonist, has been shown to decrease HPA activity through a hippocampal mechanism. Since it has been demonstrated that FC shows a significant inhibition of the HPA axis response to hCRH stimulus in normal subjects, also at doses usually administered as replacement therapy in patients with Addison's disease, an FC effect at MRs in human pituitary or a GR-pituitary agonism stronger than believed until now has been postulated.

METHODS

Ten patients affected by autoimmune Addison's disease received: (1) placebo p.o. + placebo i.v., (2) hydrocortisone (H) 10 mg p.o. + placebo i.v., (3) FC 0.1 mg p.o. + placebo i.v., (4) FC 0.1 mg and H 10 mg p.o. + placebo i.v. to verify a possible GR FC-mediated effect that might display a repercussion on the GC-replacement therapy.

RESULTS

H reduced ACTH (p < 0.01) and increased cortisol levels (p < 0.01) with respect to the placebo session, while FC did not affect either ACTH or cortisol levels compared to placebo, and higher ACTH and lower cortisol levels (p < 0.03 and p < 0.01) were observed compared with the H session; furthermore the co-administration of FC + H showed ACTH and cortisol profiles similar to that observed during H alone.

CONCLUSIONS

Our study showed a lack of FC effect on corticotrope secretion in Addison's disease, thus making unlikely the hypothesis of its GR pituitary agonism and the risk of glucocorticoid excess in primary adrenal insufficiency.

The Mineralocorticoid Agonist Fludrocortisone Promotes Survival and Proliferation of Adult Hippocampal Progenitors

Glucocorticoid receptor (GR) activation has been shown to reduce adult hippocampal progenitor cell proliferation and neurogenesis. By contrast, mineralocorticoid receptor (MR) signaling is associated with neuronal survival in the dentate gyrus of the hippocampus, and impairment of hippocampal MR has been linked to pathological conditions, such as depression or neurodegenerative disorders. Here, we aimed to further clarify the protective role of MR in adult hippocampal neurons by studying the survival and proliferative effects of the highly potent MR agonist fludrocortisone (Fludro) in adult rat hippocampal progenitor cells (AHPs), along with the associated signaling mechanisms. Fludro, which upregulated MR but not GR expression, increased survival and proliferation and prevented apoptosis in AHPs cultured in growth factor-deprived medium. These effects were blunted by the MR antagonist spironolactone and by high doses of the GR agonist dexamethasone. Moreover, they involved signaling through cAMP/protein kinase A (PKA)/cAMP response element-binding protein, phosphoinositide 3-kinase (PI3K)/Akt and its downstream targets glycogen synthase kinase-3β (GSK-3β) and mammalian target of rapamycin. Furthermore, Fludro attenuated the detrimental effects of amyloid-β peptide 1-42 (Aβ1-42) on cell survival, proliferation, and apoptosis in AHPs, and increased the phosphorylation of both PI3K/Akt and GSK-3β, which was reduced by Aβ1-42. Finally, Fludro blocked Aβ1-42-induced hyperphosphorylation of Tau protein, which is a main feature of Alzheimer's disease. Overall, these results are the first to show the protective and proliferative role of Fludro in AHPs, suggesting the potential therapeutic importance of targeting MR for increasing hippocampal neurogenesis and for treating neurodegenerative diseases.

Two Japanese patients with the renal form of pseudohypoaldosteronism type 1 caused by mutations of NR3C2

Pseudohypoaldosteronism type 1 (PHA1) is a disease characterized by neonatal salt loss due to aldosterone resistance. Two types of PHA1 are known: an autosomal recessive systemic form and an autosomal dominant renal form. The cause of the renal form of PHA1 is heterozygous mutations in NR3C2, which encodes the mineralocorticoid receptor (MR). We encountered two female Japanese infants with the renal form of PHA1 and analyzed NR3C2. The two patients had poor weight gain, and one was developmentally delayed. Genetic analysis identified one novel mutation (c.492_493insTT, p.Met166LeufsX8) and one previously reported mutation (p.R861X). The two produced a premature stop codon, resulting in haploinsufficiency of the MR. In conclusion, genetic analysis of NR3C2 is useful for diagnosis and planning therapeutic strategies.

Hypothalamic-pituitary-adrenal (HPA) axis and aging

Human aging is associated with increasing frailty and morbidity which can result in significant disability. Dysfunction of the hypothalamic-pituitary-adrenal (HPA) axis may contribute to aging-related diseases like depression, cognitive deficits, and Alzheimer's disease in some older individuals. In addition to neuro-cognitive dysfunction, it has also been associated with declining physical performance possibly due to sarcopenia. This article reviews the pathophysiology of HPA dysfunction with respect to increased basal adrenocorticotropic hormone (ACTH) and cortisol secretion, decreased glucocorticoid (GC) negative feedback at the level of the paraventricular nucleus (PVN) of the hypothalamus, hippocampus (HC), and prefrontal cortex (PFC), and flattening of diurnal pattern of cortisol release. It is possible that the increased cortisol secretion is secondary to peripheral conversion from cortisone. There is a decline in pregnolone secretion and C-19 steroids (DHEA) with aging. There is a small decrease in aldosterone with aging, but a subset of the older population have a genetic predisposition to develop hyperaldosteronism due to the increased ACTH stimulation. The understanding of the HPA axis and aging remains a complex area with conflicting studies leading to controversial interpretations.

Overnight suppression of HPA axis after mineraolocorticoid receptor stimulation: A sleep endocrine study

Nocturnal hyperactivity of hypothalamic-pituitary-adrenal axis (HPA) indicates decreased feedback inhibition with stress-related conditions such as major depression and sleep disorders. To characterize the role of mineralocorticoid (MR) in regulation of HPA axis activity during nocturnal sleep and involvement in sleep architecture, we investigated sleep endocrine effects of the MR agonist fludrocortisone in healthy men after pretreatment with metyrapone to minimize the impact of endogenous cortisol. Subjects (n=8) were treated on three occasions in a single-blinded design in random order with a) metyrapone, b) fludrocortisone after metyrapone, and c) placebo. Polysomnography was recorded and blood samples were drawn for determination of adrenocorticotropic hormone (ACTH) and cortisol during the entire night. After metyrapone administration ACTH was significantly enhanced, while overall nocturnal cortisol secretion remained largely unchanged. Whereas administration of fludrocortisone induced a significant inhibitory effect on basal ACTH and cortisol secretion, no considerable effects on sleep pattern were detectable. While the involvement of MR in sleep regulation needs further study, endocrine findings underline the role of MR in tonic regulation of HPA axis during nocturnal sleep and demonstrate the ability of fludrocortisone to further suppress HPA axis activity overnight. Additional studies would be required to evaluate endocrine and clinical fludrocortisone effects in depressive patients showing HPA hyperactivity.

The brain mineralocorticoid receptor and stress resilience

Stress exposure activates the HPA-axis and results in the release of corticosteroids which bind to two receptor types in the brain: the mineralocorticoid receptor (MR) and the glucocorticoid receptor (GR). While the role of the GR in stress reactivity has been extensively studied, the MR has received less attention. Nevertheless, pioneering in-depth studies over the past two decades have shown the importance of the brain MR in the processing of stressful information. Moreover, a membrane-bound MR mediating the rapid effects of cortisol was recently discovered. This review summarizes how the MR may play a role in stress resilience. Both preclinical and clinical studies suggest that the MR is an important stress modulator and influences basal as well as stress-induced HPA-axis activity, stress appraisal, and fear-related memories. These MR effects are mediated by both genomic and non-genomic MRs and appear to be at least partially sex-dependent. Moreover, the majority of studies indicate that high MR functionality or expression may confer resilience to traumatic stress. This has direct clinical implications. First, increasing activity or expression of brain MRs may prevent or reverse symptoms of stress-related depression. Second, individuals with a relatively low MR functionality may possess an increased stress susceptibility for depression. Nevertheless, the number of clinical MR studies is currently limited. In conclusion, the recent emergence of the MR as a putative stress resilience factor is important and may open up new avenues for the prevention and treatment of psychiatric disorders.

Activation of the hypothalamic-pituitary-adrenal axis in adults with mineralocorticoid receptor haploinsufficiency

CONTEXT

Mineralocorticoid receptors (MRs) contribute to the negative feedback of the hypothalamic-pituitary-adrenal (HPA) axis in rodents. Studies with MR antagonists suggest a similar role in humans.

OBJECTIVE

The objective of the study was to establish whether loss-of-function mutations in NR3C2, encoding MR, cause activation of the HPA axis.

DESIGN AND SETTING

This was a case-control study in members of pedigrees from the PHA1.NET cohort, comprising patients with pseudohypoaldosteronism type 1 (PHA1) who are heterozygous for loss-of-function mutations in NR3C2 and healthy controls who are unaffected family members.

PARTICIPANTS

Twelve adult patients with PHA1 (six men, six women) and 20 age-matched healthy controls (seven men, 13 women) participated in the study.

RESULTS

Patients with PHA1 had higher morning plasma cortisol (816 ± 85 vs 586 ± 50 nmol/L, P = .02) and increased 24-hour urinary excretion of cortisol metabolites (985 ± 150 vs 640 ± 46 μg/mmol creatinine, P = .03), independently of gender. After adjustment for gender, age, PHA1 diagnosis, and percentage body fat, higher plasma cortisol was associated with higher plasma renin, lower serum high-density lipoprotein-cholesterol, and higher waist circumference but not with blood pressure, carotid intima-media thickness, or echocardiographic parameters.

CONCLUSIONS

Haploinsufficiency of MR in PHA1 causes HPA axis activation, providing genetic evidence that MR contributes to negative feedback in the human HPA axis. With limited sample size, initial indications suggest the resulting hypercortisolemia is related to the severity of MR deficiency and has adverse effects mediated by glucocorticoid receptors on liver lipid metabolism and adipose tissue distribution but does not adversely affect cardiac and vascular remodeling in the absence of normal signaling through the MR.

The acute effect of fludrocortisone on basal and hCRH-stimulated hypothalamic--pituitary--adrenal (HPA) axis in humans

Mineralocorticoid receptors (MR) in the hippocampus display an important role in the control of hypothalamic-pituitary-adrenal (HPA)-axis, mediating the "proactive"-feedback of glucocorticoids. Fludrocortisone (FC), a potent MR agonist, has been shown to decrease HPA activity through a mechanism placed at hippocampal level. In order to clarify the effects of MR agonism on HPA function in humans, we studied the effects of FC, in a dose-related manner, on both basal and CRH-stimulated HPA axis during the quiescent phase. 8 young women were studied. ACTH, cortisol and aldosterone levels were evaluated every 15', from 1600 to 2000 hours, in randomized sessions: (1) placebo p.o. + placebo i.v., (2) 0.3 mg FC p.o. + placebo, (3) 0.1 mg FC. + placebo, (4) 0.075 mg FC + placebo, (5) 0.05 mg FC + placebo, (6) placebo + hCRH (2.0 μg/kg iv-bolus), (7) 0.3 mg FC + hCRH, (8) 0.1 mg FC + hCRH, (9) 0.075 mg FC + hCRH, (10) 0.05 mg FC + hCRH. FC induced a dose-related trend toward a further decrease of the ACTH and cortisol levels, while it showed a significant and dose-dependent inhibition of the hormonal response to hCRH (p < 0.05 for the doses of 0.3, 0.1 and 0.075 mg). Conversely, 0.05 mg FC did not modify the CRH-stimulatory effect on both ACTH and cortisol secretion. Aldosterone levels were not modified by FC administration. Fludrocortisone inhibits corticotrope and adrenal response to hCRH in humans, in a dose-dependent manner. The 0.075 mg FC seems the lowest active while 0.05 mg the first neutral dose on HPA activity. These data suggest a possible hypophysial MR-mediated inhibiting effect of FC, although its pituitary glucocorticoid-mediated effect cannot be excluded. The interplay between fludrocortisone and hypophysial glucocorticoid receptors needs to be clarified in order to define better the clinical consequences of the hormonal replacement therapy of patients with primary adrenal insufficiency.

The interface of hypothalamic-pituitary-adrenocortical axis and circulating brain natriuretic peptide in prediction of cardiopulmonary performance during physical stress

Brain natriuretic peptide (NT-pro-BNP) was implicated in the regulation of hypothalamic-pituitary-adrenocortical (HPA) responses to psychological stressors. However, HPA axis activation in different physical stress models and its interface with NT-pro-BNP in the prediction of cardiopulmonary performance is unclear. Cardiopulmonary test on a treadmill was used to assess cardiopulmonary parameters in 16 elite male wrestlers (W), 21 water polo player (WP) and 20 sedentary age-matched subjects (C). Plasma levels of NT-pro-BNP, cortisol and adrenocorticotropic hormone (ACTH) were measured using immunoassay sandwich technique, radioimmunoassay and radioimmunometric techniques, respectively, 10min before test (1), at beginning (2), at maximal effort (3), at 3rdmin of recovery (4). In all groups, NT-pro-BNP decreased between 1 and 2; increased from 2 to 3; and remained unchanged until 4. ACTH increased from 1 to 4, whereas cortisol increased from 1 to 3 and stayed elevated at 4. In all groups together, ΔNT-pro-BNP2/1 predicted peak oxygen consumption (B=37.40, r=0.38, p=0.007); cortisol at 3 predicted heart rate increase between 2 and 3 (r=-0.38,B=-0.06, p=0.005); cortisol at 2 predicted peak carbon-dioxide output (B=2.27, r=0.35, p<0.001); ΔACTH3/2 predicted peak ventilatory equivalent for carbon-dioxide (B=0.03, r=0.33, p=0.003). The relation of cortisol at 1 with NT-pro-BNP at 1 and 3 was demonstrated using logistic function in all the participants together (for 1/cortisol at 1 B=63.40, 58.52; r=0.41, 0.34; p=0.003, 0.013, respectively). ΔNT-pro-BNP2/1 linearly correlated with ΔACTH4/3 in WP and W (r=-0.45, -0.48; p=0.04, 0.04, respectively). These results demonstrate for the first time that HPA axis and NT-pro-BNP interface in physical stress probably contribute to integrative regulation of cardiopulmonary performance.

Role of mineralocorticoid receptors on the hypothalamus-pituitary-adrenal axis in humans

This clinical review will summarize the available data regarding the role of mineralocorticoid receptors (MRs) on the hypothalamus-pituitary-adrenal (HPA) axis control in physiological and pathological conditions and in the memory processes involved in the control and appraisal of a stress event. MRs are predominantly expressed in the limbic structures, with the hippocampus being the main localization, although MRs are also found at the hypothalamic level. It is known that hyppocampal MRs control the proactive feedback involved in the maintenance of the basal HPA activity, mainly at the nadir of the circadian rhythm. In physiological conditions, the administration of pharmacological doses of both MR antagonists and agonists is able to interact with the HPA activity, modifying the quiescent phase-nadir of the circadian rhythm, although some data in the literature do not support these observations. Also, in a physiological condition such as aging, an enhanced HPA axis activity is found in the time window, when MRs are predominantly occupied by cortisol circulating levels, possibly reflecting an MR impairment in this period of life. In pathology, major depression has been correlated to MR qualitative-quantitative alterations which could reflect differences on psychological and physiological responses, possibly predicting psychopathologies. Most of the remarks reported in this review seem to indicate, in agreement with animal data, a role played by MRs in the delicate control of the HPA axis in humans and the possible predisposition to the development of pathologies in case of their alterations.

A randomized trial on mineralocorticoid receptor blockade in men: effects on stress responses, selective attention, and memory

Corticosteroids, released in high amounts after stress, exert their effects via two different receptors in the brain: glucocorticoid receptors (GRs) and mineralocorticoid receptors (MRs). GRs have a role in normalizing stress-induced effects and promoting consolidation, while MRs are thought to be important in determining the threshold for activation of the hypothalamic-pituitary-adrenal (HPA) axis. We investigated the effects of MR blockade on HPA axis responses to stress and stress-induced changes in cognitive function. In a double-blind, placebo-controlled study, 64 healthy young men received 400 mg of the MR antagonist spironolactone or placebo. After 1.5 h, they were exposed to either a Trier Social Stress Test or a non-stressful control task. Responses to stress were evaluated by hormonal, subjective, and physiological measurements. Afterwards, selective attention, working memory, and long-term memory performance were assessed. Spironolactone increased basal salivary cortisol levels as well as cortisol levels in response to stress. Furthermore, spironolactone significantly impaired selective attention, but only in the control group. The stress group receiving spironolactone showed impaired working memory performance. By contrast, long-term memory was enhanced in this group. These data support a role of MRs in the regulation of the HPA axis under basal conditions as well as in response to stress. The increased availability of cortisol after spironolactone treatment implies enhanced GR activation, which, in combination with MR blockade, presumably resulted in a decreased MR/GR activation ratio. This condition influences both selective attention and performance in various memory tasks.

Differential effects of mineralocorticoid blockade on the hypothalamo-pituitary-adrenal axis in pregnant and nonpregnant ewes

During pregnancy, plasma ACTH and cortisol are chronically increased; this appears to occur through a reset of hypothalamo-pituitary-adrenal (HPA) activity. We have hypothesized that differences in mineralocorticoid receptor activity in pregnancy may alter feedback inhibition of the HPA axis. We tested the effect of MR antagonism in pregnant and nonpregnant ewes infused for 4 h with saline or the MR antagonist canrenoate. Pregnancy significantly increased plasma ACTH, cortisol, angiotensin II, and aldosterone. Infusion of canrenoate increased plasma ACTH, cortisol, and aldosterone in both pregnant and nonpregnant ewes; however, the temporal pattern of these responses differed between these two reproductive states. In nonpregnant ewes, plasma ACTH and cortisol transiently increased at 1 h of infusion, whereas in pregnant ewes the levels gradually increased and were significantly elevated from 2 to 4 h of infusion. MR blockade increased plasma aldosterone from 2 to 4 h in the pregnant ewes but only at 4 h in the nonpregnant ewes. In both pregnant and nonpregnant ewes, the increase in plasma aldosterone was significantly related to the timing and magnitude of the increase in plasma potassium. The results indicate a differential effect of MR activity in pregnant and nonpregnant ewes and suggest that the slow changes in ACTH, cortisol, and aldosterone are likely to be related to blockade of MR effects in the kidney rather than to effects of MR blockade in hippocampus or hypothalamus.