The effect of potent CYP2D6 inhibition on the pharmacokinetics and safety of deutetrabenazine in healthy volunteers.

PURPOSE: Deutetrabenazine is a deuterated form of tetrabenazine with a confirmed lower rate of CYP2D6 metabolism of the active metabolites, α- and ß-HTBZ. In this study, we assessed the effect of paroxetine, a potent CYP2D6 inhibitor, on the pharmacokinetics and safety of deutetrabenazine and its metabolites. METHODS: In this open-label sequential drug-drug-interaction study, 24 healthy adults who were CYP2D6 extensive or intermediate metabolizers received a single deutetrabenazine 22.5-mg oral dose on days 1 and 11 and a single paroxetine 20-mg oral daily dose on days 4-12. Pharmacokinetics of deutetrabenazine and its metabolites were assessed on days 1-4 and 11-14. Paroxetine trough concentrations were obtained pre-dose on days 9-13. Safety examinations occurred throughout the study. RESULTS: Paroxetine administered under steady-state conditions, increased exposure of the deuterated active metabolites, α-HTBZ (1.2-fold Cmax and 1.8-fold AUC0-∞) and ß-HTBZ (2.1-fold Cmax and 5.6-fold AUC0-∞), and correspondingly, 1.6-fold Cmax and threefold AUC0-∞ for total (α + ß)-HTBZ. Sixteen subjects reported 45 adverse events and most were mild. Headache was the most common AE reported 8 times by 7 subjects (5 following paroxetine alone; 2 following deutetrabenazine + paroxetine). CONCLUSIONS: Paroxetine-induced increases in exposure to the active deutetrabenazine metabolites were less than those previously reported for tetrabenazine, a finding expected to reduce the burden of drug interaction. In addition, single doses of 22.5 mg deutetrabenazine, when given alone or in the presence of steady-state paroxetine (20 mg daily), were safe.

A comparative study of anticoagulant control in patients on long-term warfarin using home and hospital monitoring of the international normalised ratio.

BACKGROUND: Capillary whole-blood point-of-care prothrombin-INR (PT-INR) testing at home is an alternative to hospital-based monitoring for patients on lifelong warfarin. AIM: To retrospectively assess the safety and efficacy of home point-of-care testing for children on long-term warfarin. METHOD: All patients who had been on point-of-care home monitoring for at least 6 months were included in the study. Their warfarin control was assessed while on home monitoring and compared to that achieved in a similar period before changing from hospital monitoring. RESULTS: Thirty-seven patients were studied for a mean of 1.0 year on clinic monitoring and 1.07 years on home monitoring. The clinic monitoring tests were within a therapeutic range for a median 70.0 (inter-quartile range 34.5) and the home monitoring were within range for median 75.0 (inter-quartile range 44.5). There were no major haemorrhagic or thrombotic complications in either group during the study period. Only 2.3% of all tests had an INR greater than 6.0 with no statistical differences seen between the clinic and home monitoring groups. CONCLUSION: Home point-of-care testing in children on lifelong warfarin is safe, effective and offers a number of advantages to the child and family. Ongoing training and support for the families is essential for this service.

Histaminergic control of sleep-wake cycles: recent therapeutic advances for sleep and wake disorders.

The role of histaminergic neurotransmission in the promotion of waking has been extensively studied in preclinical species. Appreciation for the role of histamine continues to expand with increasing understanding of the interaction of histamine within the broad network of neuromodulators that regulate sleep and wake. The effects of histamine on waking are transduced through the H(1) and the H(3) receptors in the central nervous system. Brain penetrant over-the-counter antihistamines comprised of antagonist actions at H(1) receptors as well as varying degrees of antimuscarinic properties are marketed as sleep aids, based on their well-known daytime drowsiness side effects. The data supporting their use as sedatives, however, are not consistent. H(3) receptors are presynaptic receptors that limit histamine release as well as that of monoamine neurotransmitters thought to participate in the maintenance of waking. In this review, we discuss the existing studies on various antihistamines and antagonists of the H(1) receptor in the regulation of sleep in preclinical studies, normal subjects and in subjects with sleep disorders. In addition, we review the current data available on the use of ligands at H(3) receptors for the modulation of sleep and wake.

Metabotropic glutamate receptor 5 antagonist-induced stimulation of hypothalamic-pituitary-adrenal axis activity: interaction with serotonergic systems.

The mGluR5 antagonist 2-methyl-6-(phenylethynyl) pyridine (MPEP) produces anxiolytic or antidepressant effects in several rodent models through incompletely described mechanisms. Anxiolytics and antidepressants share several neuroendocrine features, including acute activation of the hypothalamic-pituitary-adrenal (HPA)-axis, desensitization of neuroendocrine responses with repeated dosing, and desensitization of the HPA axis to 5-HT1A agonist stimulation. We characterized these neuroendocrine parameters in rats treated systemically with MPEP and compared them to those induced by the anxiolytic buspirone. Acutely, MPEP dose-dependently (0.1-10 mg/kg i.p.) increased plasma corticosterone concentrations. These responses were blocked by 50% with the 5-HT1A antagonist WAY100635. The corticosterone responses to both 3 mg/kg MPEP and buspirone were decreased by 80% after 5 days of twice-daily injections. Repeated injection with MPEP decreased HPA-axis sensitivity to buspirone challenge by 75%. This desensitization was not associated with changes in mGluR5 or 5-HT1A receptor binding properties, expression of G-protein subunits coupled to these receptors, or in 5-HT-stimulated binding of [(3)H]-GTPgammaS to membranes. We conclude that MPEP acutely disinhibits the HPA axis, in part through uncharacterized changes in serotonergic signaling. Desensitization of 5-HT1A responses after repeated MPEP administration may indicate that, like other anxiolytics and antidepressants, plasticity in 5-HT signal transduction pathways has occurred.

Chromaffin cell function and structure is impaired in corticotropin-releasing hormone receptor type 1-null mice.

Corticotropin-releasing hormone (CRH) is both a main regulator of the hypothalamic-pituitary-adrenocortical axis and the autonomic nervous system. CRH receptor type 1 (CRHR1)-deficient mice demonstrate alterations in behavior, impaired stress responses with adrenocortical insufficiency and aberrant neuroendocrine development, but the adrenal medulla has not been analyzed in these animals. Therefore we studied the production of adrenal catecholamines, expression of the enzyme responsible for catecholamine biosynthesis neuropeptides and the ultrastructure of chromaffin cells in CRHR1 null mice. In addition we examined whether treatment of CRHR1 null mice with adrenocorticotropic hormone (ACTH) could restore function of the adrenal medulla. CRHR1 null mice received saline or ACTH, and wild-type or heterozygous mice injected with saline served as controls. Adrenal epinephrine levels in saline-treated CRHR1 null mice were 44% those of controls (P<0.001), and the phenylethanolamine N-methyltransferase (PNMT) mRNA levels in CRHR1 null mice were only 25% of controls (P <0.001). ACTH treatment increased epinephrine and PNMT mRNA level in CRHR1 null mice but failed to restore them to normal levels. Proenkephalin mRNA in both saline- and ACTH-treated CRHR1 null mice were higher than in control animals (215.8% P <0.05, 268.9% P <0.01) whereas expression of neuropeptide Y and chromogranin B did not differ. On the ultrastructural level, chromaffin cells in saline-treated CRHR1 null mice exhibited a marked depletion in epinephrine-storing secretory granules that was not completely normalized by ACTH-treatment. In conclusion, CRHR1 is required for a normal chromaffin cell structure and function and deletion of this gene is associated with a significant impairment of epinephrine biosynthesis.

Modulation of urocortin-induced hypophagia and weight loss by corticotropin-releasing factor receptor 1 deficiency in mice.

Intracerebroventricular injection of CRF or urocortin (Ucn) reduces appetite and body weight. CRFR1 and CRFR2, the receptors for CRF and Ucn, are expressed in neurons associated with appetite-control and metabolism, but their relative contributions in mediating CRF- or Ucn-induced hypophagia and weight loss are not known. We used homozygous mice lacking CRFR1 (CRFR1-/-) and wild-type littermates to determine the role of CRFR1 in mediating the changes in food intake and body weight following intracerebroventricular administration of Ucn. CRFR1-/- mice, which are glucocorticoid deficient, were given corticosterone in their drinking water to induce diurnal variations in circulating corticosterone. A 7-day intracerebroventricular infusion of Ucn transiently suppressed ad libitum food intake equally in CRFR1-/- and wild-type mice. Body weight reduction during Ucn infusion paralleled food intake in wild-type mice, but persisted throughout the infusion in CRFR1-/- mice. After food-deprivation, acute intracerebroventricular injection of Ucn suppressed food intake for 1.5 h in wild-type mice. By contrast, CRFR1-/- mice did not respond to Ucn 1.5 h after injection. At later time points, Ucn suppressed food intake equally in both genotypes. The distinct time courses of CRF-receptor-induced hypophagia suggest that separate pathways act cooperatively to adjust food intake during challenges to homeostasis.

Regulation of corticotropin-releasing factor receptor type 2 beta messenger ribonucleic acid in the rat cardiovascular system by urocortin, glucocorticoids, and cytokines.

CRF receptor type 2 (CRF R2) messenger RNA (mRNA) expression in the rodent heart is modulated by exposure to both the bacterial endotoxin lipopolysaccharide (LPS) and glucocorticoids. In this study we examined the roles of glucocorticoids, cytokines, and CRF R2beta ligands in the regulation of CRF R2beta expression in the cardiovascular system both in vivo and in vitro. Using ribonuclease protection assays, we found that, in addition to the injection of LPS or corticosterone, physical restraint caused a decrease in CRF R2beta mRNA levels in the rat heart and aorta. Adrenalectomy with corticosterone replacement at constant levels partially blocked LPS-induced decreases in CRF R2beta mRNA expression in the heart. Thus, elevations of endogenous circulating corticosterone could contribute to the down-regulation of CRF R2beta mRNA expression in heart. To identify other putative modulating factors, we examined CRF R2beta expression in the aorta-derived A7R5 cell line. Incubation with CRF R2 ligands or dexamethasone reduced CRF R2beta mRNA levels. In addition, incubation with a variety of cytokines, proteins released during immune challenge, also reduced CRF R2beta mRNA expression. The multifactorial regulation of CRF R2beta mRNA expression in the cardiovascular system may serve to limit the inotropic and chronotropic effects of CRF R2 agonists such as urocortin during prolonged physical or immune challenge.

Urocortin messenger ribonucleic acid: tissue distribution in the rat and regulation in thymus by lipopolysaccharide and glucocorticoids.

Urocortin (Ucn), a new mammalian member of the CRF family, is a candidate endogenous ligand for type 2 CRF receptors. In a survey of peripheral tissues from adult male rats, we found that Ucn messenger RNA (mRNA) was abundant in the gastrointestinal tract and immune tissues such as thymus and spleen. We next tested the hypothesis that levels of Ucn mRNA levels in thymus and spleen would be altered after immune activation. As measured by ribonculease protection assay, lipopolysaccharide (LPS) induced a 2-fold time-dependent increase in thymic Ucn mRNA levels within 6 h. By contrast, splenic Ucn mRNA levels decreased after LPS. Because LPS activates the hypothalamus-pituitary-adrenal (HPA) axis, we examined whether the effects of LPS on Ucn mRNA might be mediated through changes in HPA axis hormones. Ucn mRNA in thymus, but not spleen, was significantly increased after ACTH injection; however, LPS did not increase Ucn expression in the thymus of adrenalectomized rats with corticosterone replacement, despite substantial increases in ACTH. Finally, sc injection of corticosterone stimulated Ucn mRNA comparably to that of LPS. Together, these results suggest that Ucn mRNA expression can increase after immune activation in a corticosterone-dependent manner, and that such changes in Ucn mRNA may be an additional consequence of HPA axis activation.

Effects of adrenalectomy and subsequent corticosterone replacement on rat sleep state and EEG power spectra.

Individual effects of corticotropin-releasing hormone (CRH) and glucocorticoids on sleep have been difficult to discern due to the feedback effects each hormone exerts on the other. In addition, it is not known whether hypothalamic-pituitary-adrenal axis hormones alter sleep homeostasis or circadian influences on sleep propensity. We therefore analyzed sleep architecture and electroencephalographic (EEG) power in freely moving rats before and after removal of corticosterone (thus elevating endogenous CRH) by surgical adrenalectomy. Adrenalectomy reduced the amplitude of the diurnal rhythms of maximal and average sleep bout lengths (P < 0.004). After adrenalectomy, power from 1 to 4 Hz decreased (P < 0.042), whereas power from 9 to 12 Hz increased in the power spectra of the EEG recording (P = 0.001). Administration of physiological corticosterone replacement reversed some of these effects. Supraphysiological corticosterone replacement in adrenalectomized rats reduced the amount of non-rapid-eye-movement sleep in the 24-h cycle (P = 0.001). During each endocrine condition, rats were sleep deprived for 6 h. Endocrine status did not alter the subsequent homeostatic response to sleep deprivation. Thus ADX and supraphysiological corticosteroid replacement each altered sleep architecture without a demonstrable effect on sleep homeostasis.

Serotonin-containing fibers in the suprachiasmatic hypothalamus attenuate light-induced phase delays in mice.

Photic and non-photic stimuli phase shift and entrain circadian rhythms through distinct but interacting mechanisms which impinge on the suprachiasmatic nucleus (SCN), the circadian pacemaker. Our understanding of this mechanism is incomplete. Serotonin (5-HT) injected locally at the SCN reduces light-induced glutamate release and decreases the expression of c-fos, a marker of photic transduction. Furthermore, in SCN slices, 5-HT application reduces field potentials after optic nerve stimulation. We therefore predicted that 5-HT-terminal destruction restricted to the SCN would augment phase shifts of circadian rhythms induced by light exposure. To investigate this possibility, we compared photic phase delays and Fos-like immunoreactivity in mice which had previously received bilateral infusions directed at the SCN containing either the selective 5-HT neurotoxin 5,7-dihydroxytryptamine (DHT, n = 16) or vehicle (VEH, n = 12). Phase delays after a light pulse given during the mid-subjective night (30 lux, 30 min starting at circadian time (CT) 12-20) in DHT-mice were 50% greater than in VEH-mice (P = 0.017). DHT mice (n = 5) had 76% larger Fos responses to a mid-subjective night light pulse than VEH-mice (n = 5) (P = 0.029). We conclude that 5-HT at or near the SCN in mice reduces photic phase shifts and modulates the magnitude of the photic phase response in the mouse.

Corticosterone decreases nonshivering thermogenesis and increases lipid storage in brown adipose tissue.

Brown adipose tissue (BAT) contains glucocorticoid receptors; glucocorticoids are required for maintaining differentiated BAT in culture. These studies were performed to determine the effects of corticosterone on BAT thermogenic function and lipid storage. Rats were adrenalectomized and given subcutaneous corticosterone pellets in concentrations that maintained plasma corticosterone constant across the range of 0-20 micrograms/dl or were sham adrenalectomized. All variables were examined 5 days after surgery and corticosterone replacement. Measures of BAT function-thermogenic capacity [guanosine 5'-diphosphate (GDP) binding and uncoupling protein (UCP; a BAT-specific thermogenic protein)] and storage (BAT wet wt, protein, and DNA levels) were made. Plasma hormones (corticosterone, adrenocorticotropic hormone, insulin, 3,3',5-triiodothyronine, and thyroxine were measured. Corticosterone significantly affected BAT thermogenic measures: UCP content and binding of GDP to BAT mitochondria decreased with increasing corticosterone; GDP binding characteristics in BAT from similarly prepared rats examined by Scatchard analysis showed that maximum binding (Bmax) and dissociation constant (Kd) decreased with increasing corticosterone dose. BAT DNA was increased by adrenalectomy and maintained at intact levels with all doses of corticosterone; BAT lipid storage increased dramatically at corticosterone values higher than the daily mean level in intact rats. Histologically, the number and size of lipid droplets within BAT adipocytes increased markedly with increased corticosterone. White adipose depots were more sensitive to circulating corticosterone concentrations than were BAT depots and increased in weight at levels of corticosterone that were at or below the daily mean level of intact rats. We conclude that, within its diurnal range of concentration corticosterone acts to inhibit nonshivering thermogenesis and increase lipid storage.(ABSTRACT TRUNCATED AT 250 WORDS)

The diurnal rhythm in adrenocorticotropin responses to restraint in adrenalectomized rats is determined by caloric intake.

There is a diurnal rhythm in ACTH responses to stressors that peaks, in nocturnally feeding rats, at the time of lights on, in the morning (AM). To determine whether this rhythm is subordinate to the rhythm in food intake, we tested the effects of removing food during the night or the day on ACTH responses in the AM or evening (PM) to the stimulus of restraint in 5-day-adrenalectomized rats. An overnight fast reduced the ACTH response to restraint with tail blood sampling in the AM to the low magnitude observed in the PM in rats fed ad libitum; by contrast, a fast of equivalent duration imposed during the day had no effect on the ACTH response to the stressor in the PM. Short term fasts did not alter the normal AM-PM rhythm in basal ACTH levels. The fasts did, however, significantly decrease the pituitary ACTH concentration at both times of day, suggesting that lack of food had stimulated ACTH secretion during the preceding 14 h. Providing calories by either gavage or manipulation of food presentation increased ACTH responses to restraint in fasted adrenalectomized rats in both the AM and PM. Although four of four experiments showed that provision of calories to fasted rats resulted in increased ACTH responses to the stimulus of restraint, none of the manipulations of caloric intake fully restored ACTH responses in fasted rats to the high amplitude observed in ad libitum fed rats in the AM. We conclude that 1) unlike the circadian rhythm in basal activity in the hypothalamic-pituitary-adrenalocortical (HPA) system, the diurnal rhythm in ACTH responsiveness to stimuli is tightly coupled to the endogenous rhythm in energy intake; and 2) caloric deprivation per se appears to activate the HPA system at some time during the 14- to 17-h fast, but does not produce the normal facilitation in the AM response to acute restraint that is induced by chronic or prior stimulation of the HPA axis.

Roles of type I and II corticosteroid receptors in regulation of basal activity in the hypothalamo-pituitary-adrenal axis during the diurnal trough and the peak: evidence for a nonadditive effect of combined receptor occupation.

Negative feedback regulation of basal activity in the hypothalamo-pituitary-adrenal (HPA) axis requires less corticosterone (B) at the trough (morning) than at the peak (evening) of the diurnal rhythm. It has been hypothesized that in the morning in rats, occupation of the high affinity, type I corticosteroid receptors is sufficient to inhibit adrenalectomy (ADX)-induced increases in plasma ACTH secretion, whereas in the evening, regulation occurs through the occupation of the lower affinity type II corticosteroid receptors. To examine this hypothesis, the sensitivity of ACTH to inhibition by two different doses of B or of dexamethasone (DEX) were compared in ADX rats killed in the morning or the evening (B has a higher affinity for type I receptors in vitro and in vivo; in vivo, DEX has a higher affinity for type II receptors). The requirement for greater concentrations of corticosteroids to inhibit ACTH secretion in the evening was verified. The effect of these treatments on the number of neurons immunoreactive for vasopressin (AVP) and on the expression of AVP messenger RNA (mRNA) in the parvocellular portion of the paraventricular nuclei was also examined. In the morning, plasma concentrations of B equivalent to the IC50 for the reduction of plasma ACTH in the morning reduced the amount of AVP mRNA, but not immunoreactive AVP cell number as compared with ADX rats. DEX reduced plasma ACTH in the morning but did not prevent high levels of expression of AVP mRNA or protein. AVP mRNA was more sensitive to B in the morning than in the evening. Antagonist to the type I receptor (spironolactone) given chronically to ADX rats treated with B increased plasma ACTH secretion at both times of day, even though the plasma B concentrations suggested occupancy of a large proportion of the type II receptors. To test the hypothesis that an interaction between the type I and II receptor is necessary for the control of HPA activity at the peak of the diurnal rhythm, ADX rats were given B or DEX, alone or in combination. DEX reduced evening plasma ACTH only in the presence of very low concentrations of B, suggesting that for full potency, type II receptor occupation requires type I receptor occupation. In summary, these results demonstrate that occupation of type I corticosteroid receptors is capable of controlling basal activity in the HPA axis in the morning and that in the evening, type I receptor occupation potentiates the inhibition of plasma ACTH by occupation of type II receptors.

Lesions of the hippocampal efferent pathway (fimbria-fornix) do not alter sensitivity of adrenocorticotropin to feedback inhibition by corticosterone in rats.

The hypothalamic-pituitary-adrenal (HPA) axis controls the diurnal and stress-induced release of adrenal corticosteroids into the general blood circulation. In turn, corticosteroids inhibit the HPA axis under basal conditions and during stress through occupation of their receptors (types I and II) in the brain by closing a negative feedback loop. The primary site in the brain at which corticosteroids act to inhibit the HPA axis has not been identified. High concentrations of both types of receptors are found in neurons of the hippocampal formation, a structure which has been reported by some, but not others, to control activity within the HPA axis by serving as a major negative feedback site. In many of these past studies, blood was collected after extensive handling or exposure to ether, conditions which do not favor the detection of basal hormone concentrations. To address these controversies, we tested the feedback sensitivity of the anterior pituitary hormone responsible for corticosteroid production, adrenocorticotropin (ACTH), to corticosterone (B), the main corticosteroid in rats, in total fornix- and, as controls, cortex-lesioned rats. All rats were given vascular catheters to avoid any handling-induced differences in plasma B or ACTH when sampling blood. In some experiments, fornix- and cortex-lesioned rats were adrenalectomized and given 1 of 3 doses of exogenous B provided in a subcutaneous pellet to ensure that plasma B was equal in different lesion groups. We hypothesized that if the hippocampal formation were an important site of B-mediated inhibition of the HPA axis, fornix-lesioned rats would have higher plasma B as a result of increased endogenous secretion in the morning or the evening compared to cortex-lesioned rats in rats with adrenal glands. In addition, we hypothesized that adrenalectomized fornix-lesioned rats given the same low to moderate levels of exogenous constant B would have higher basal and stress-induced ACTH than cortex-lesioned rats. Diurnal plasma B was not affected by fornix lesions in intact rats. Moreover, basal ACTH measured in the morning and the evening and stress-induced ACTH was the same in adrenalectomized fornix- and cortex-lesioned rats with constant exogenous B. We conclude, therefore, that information about occupancy of B receptors in the hippocampus carried by the fornix primarily subserves functions which do not directly regulate activity in the HPA axis.

Glucocorticoid deficiency increases phospholipase A2 activity in rats.

An important mechanism for the antiinflammatory effect of pharmacological doses of glucocorticoids is the inhibition of arachidonic acid release from phospholipids by phospholipase A2 (PLA2). As a corollary, one might predict that low endogenous concentrations of glucocorticoids favor inflammatory disease states. Indeed, clinical and experimental observations revealed an association between glucocorticoid deficiency and disease states caused by immunological and/or inflammatory mechanisms. The purpose of the present investigation was to study the regulation of PLA2 mRNA, protein, and enzyme activity in adrenalectomized (ADX) rats where glucocorticoid concentrations were below physiological levels. The mRNA of group I and II PLA2 were measured by PCR. Group II PLA2 mRNA was increased by 126 +/- 9% in lung tissue of ADX rats, whereas group I PLA2 was increased only by 27 +/- 1.5%. The increase in group II mRNA in ADX rats was reflected by a corresponding increase of group II PLA2 protein (70-100%) in lung, spleen, liver, and kidney. This increase was reversed by the administration of exogenous corticosterone. After ADX, the percentage increase in total PLA2 activity was higher than that of mRNA or PLA2 protein, suggesting that the activity of the enzyme was modulated by inhibitors or activators. The concentration of lipocortin-I, an inhibitor of PLA2 enzyme was strongly correlated with the activity of PLA2 in the tissues (lung, spleen, liver, and kidney). In all these tissues, the concentrations of lipocortin-I declined after ADX. Thus upregulation of PLA2 enzyme and downregulation of lipocortin-I might account for the enhanced inflammatory response in hypoglucocorticoid states.

Feast and famine: critical role of glucocorticoids with insulin in daily energy flow.

The hypothesis proposed in this review is that normal diurnal rhythms in the hypothalamic-pituitary-adrenal (HPA) axis are highly regulated by activity in medial hypothalamic nuclei to effect an interaction between corticosteroids and insulin such that optimal metabolism results in response to changes in the fed or fasted state of the animal. There are marked diurnal rhythms in function of the HPA axis under both basal and stress conditions. The HPA axis controls corticosteroid output from the adrenal and, in turn, forward elements of this axis are inhibited by feedback from circulating plasma corticosteroid levels. Basal activity in the HPA axis of mammals fed ad lib peaks about 2 h before the peak of the diurnal feeding rhythm, and is controlled by input from the suprachiasmatic nuclei. The rhythm in stress responsiveness is lowest at the time of the basal peak and highest at the time of the basal trough in the HPA axis activity. There are also diurnal rhythms in corticosteroid feedback sensitivity of basal and stress-induced ACTH secretion which peak at the time of the basal trough. These rhythms are all overridden when feeding, and thus insulin secretion, is disrupted. Corticosteroids interact with insulin on food intake and body composition, and corticosteroids also increase insulin secretion. Corticosteroids stimulate feeding at low doses but inhibit it at high doses; however, it is the high levels of insulin, induced by high levels of corticosteroids, that may inhibit feeding. The effects of corticosteroids on liver, fat, and muscle cell metabolism, with emphasis on their interactions with insulin, are briefly reviewed. Corticosteroids both synergize with and antagonize the effects of insulin. The effects of stress hormones, and their interactions with insulin on lipid and protein metabolism, followed by some of the metabolic effects of injury stress, with or without nutritional support, are evaluated. In the presence of elevated insulin stimulated by glucocorticoids and nutrition, stress causes less severe catabolic effects. In the central nervous system, regulation of function in the HPA axis is clearly affected by the activity of medial hypothalamic nuclei that also alter feeding, metabolism, and obesity in rats. Lesions of the arcuate (ARC) and ventromedial (VMN) paraventricular (PVN) nuclei result in obesity and hyperactivity in the HPA axis. Moreover, adrenalectomy inhibits or prevents development of the lesion-induced obesity. There are interactions among these nuclei; one mode of communication is via inputs of neuropeptide Y (NPY) cells in the ARC to the VMN, dorsomedial nuclei, and PVN.(ABSTRACT TRUNCATED AT 400 WORDS)

Feedback sensitivity of the rat hypothalamo-pituitary-adrenal axis and its capacity to adjust to exogenous corticosterone.

Chronic stress causing elevated morning (AM) corticosterone (B) concentrations of 2-8 micrograms B/dl does not appear to inhibit subsequent activity in the hypothalamic-pituitary-adrenal (HPA) axis, a surprising finding in view of the known depression in AM basal ACTH by only 3 micrograms B/dl in adrenalectomized rats. To distinguish between the possibilities that either intact rats are less sensitive to B feedback than adrenalectomized rats, or that chronic stress facilitates responses in the HPA axis, we elevated basal B levels in young male rats with slow-release B pellets in the absence of stress. Between 4-6 days after implantation of B pellets at three doses that elevated basal AM (diurnal trough) plasma B to approximately 1.2, 4, and 10 micrograms/dl, we studied basal ACTH and B at trough (AM) and peak evening (PM) times of the diurnal cycle, as well as the responses to the stress of restraint and blood collection from the tail at each time of day. We also determined mean daily plasma B, insulin, and glucose from samples collected at six intervals during the day. Adrenal, thymus, and body wts were measured as were transcortin (CBG) and adrenal phenylethanolamine-N-methyl transferase activity. Compared to controls implanted with wax pellets, all doses of B inhibited adrenal wt and AM stress responses and tended to inhibit pituitary ACTH content and adrenal phenylethanolamine-N-methyl transferase activity. Inhibition with the middle dose B pellet was close to maximally effective for these endpoints. Plasma glucose and thymus wt were significantly decreased and insulin was significantly increased in the middle and highest B pellet groups, with significantly greater effects at the highest dose. The gain in body wt and transcortin concentrations were significantly decreased only in the highest dose groups, in which mean daily plasma B was approximately 10 micrograms/dl, a level that clearly overwhelmed the capacity of the adrenocortical system to respond to any stimulus tested. By contrast, rats with low and middle dose B pellets appeared to adjust HPA axis function by decreasing the peak diurnal increase in B, so that 24-h mean B levels did not differ from control, and were maintained at approximately 5 micrograms/dl. Both of these groups also had inhibited ACTH responses to stress applied during the diurnal trough (AM). By contrast, neither group had inhibited ACTH responses to stress applied during the diurnal peak (PM). We conclude that: 1) The HPA axis of intact rats is extremely sensitive to exogenous B.(ABSTRACT TRUNCATED AT 400 WORDS)

Feedback and facilitation in the adrenocortical system: unmasking facilitation by partial inhibition of the glucocorticoid response to prior stress.

Previously stressed animals remain responsive to subsequent stressors, despite secreting an adequate corticosteroid signal during the first stress which should act to damp the response to a second stress. We have previously postulated that stress acts to facilitate subsequent responses in the adrenocortical system, and that this facilitation is balanced by the corticosteroid feedback signal. To test this hypothesis directly, we treated young male rats with cyanoketone (CK) to partially block the adrenal capacity to synthesize corticosterone (B). Subsequently, groups of CK- or vehicle (VEH)-treated rats were exposed to the FIRST stress of 30-min restraint with small blood samples collected at 0, 15, and 30 min. The FIRST stress was given to subgroups of rats 12, 9, 6, or 3 h before lights off (12 h) or lights on (24 h). At 12 or 24 h, rats were again restrained with blood samples at 0 ("basal") and 30 min (SECOND stress). Control groups were stressed for the first time when the experimental groups received their SECOND stress. Plasma ACTH and B concentrations were measured. Although in the absence of stress, basal B concentrations were normal in CK-treated compared to VEH-treated rats throughout the day, the B response to the FIRST stress was reduced by 60% in the CK- compared to the VEH-treated group. When the FIRST stress was performed during the time of lights on, "basal" plasma ACTH was elevated in CK groups at 12 h (lights off) compared to levels in both previously stressed VEH groups and unstressed CK controls. There was no difference at this time of day in the magnitude of the ACTH response to the SECOND stress in CK rats compared to that in CK rats receiving their only stress (controls) or that in VEH-treated rats receiving the SECOND stress. When first stress was performed during the time of lights off, "basal" plasma ACTH at 24 h (lights on) in CK and VEH rats were not different compared to levels in their respective unstressed controls. The ACTH response to the SECOND stress at 24 h was elevated in all previously stressed CK groups compared to that in either CK control or VEH groups. At neither time of day were SECOND stress ACTH concentrations in VEH rats different from those in control VEH rats. At 12 h (lights off), but not at 24 h (lights on), "basal" ACTH was significantly elevated in VEH rats above the unstressed VEH control values.(ABSTRACT TRUNCATED AT 400 WORDS)