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PubMed2006

ACTH therapy for generalized seizures other than spasms.

PURPOSE: We reviewed our experience with ACTH for the treatment of intractable generalized seizures other than spasms. METHODS: Efficacy and adverse effects of ACTH against intractable generalized seizures other than spasms were retrospectively investigated in 15 patients treated between 1991 and 2003. The median age of the patients at ACTH therapy was 42 months. The targeted type of seizure was brief tonic in 6, atypical absence in 6, atonic in 2, and myoclonic in 1. The dose of ACTH was 0.01-0.015 mg/kg in most patients. The effect of ACTH was determined at the end of ACTH therapy, and 3 months and 1 year after ACTH therapy. RESULTS: Seizure freedom was obtained in 13 of 15 patients. However, 6 of them had a recurrence of seizures within 3 months after ACTH therapy. ACTH was the most effective in patients with atypical absence seizures. Statistical analysis showed that the number of injection and total dose of ACTH were smaller in patients with atypical absence seizures than in those with brief tonic seizures. Adverse effects were frequent but serious one was not observed. CONCLUSION: ACTH therapy was effective in patients with intractable generalized seizures other than spasms. However, its efficacy was often transient. ACTH can be useful for generalized seizures other than spasms but its limitation should be considered.

Adrenocorticotropic Hormone↗
PubMed1998

Modulation of adrenal cell functions by cadmium salts. 4. Ca(2+)-dependent sites affected by CdCl2 during basal and ACTH-stimulated steroid synthesis.

In previous studies, nonlethal CdCl2 concentrations apparently inhibited basal Y-1 mouse adrenal tumor cell endogenous mitochondrial cholesterol conversion to pregnenolone. In addition, CdCl2 inhibited all agents stimulating both plasma membrane-dependent cAMP synthesis and 20 alpha-hydroxy-4-pregnen-3-one (20DHP) secretion. Bypassing the plasma membrane using dibutyryl-cAMP (dbcAMP) stimulated cytoplasmic cholesterol metabolism and 20DHP secretion in the presence of CdCl2. Since CdCl2 competed at metabolic steps requiring Ca2+ in other tissues, experiments were designed to examine Cd2+ competition with Ca2+ during steroidogenesis. Sets of cells incubated with either medium or adrenocorticotropin (ACTH) with or without CdCl2 were also treated with 0, 1.0, 5.0 or 10.0 mmol/L CaCl2 in the presence or absence of EGTA, a relatively specific Ca2+, but not Cd2+, chelating agent. Another experimental cell set incubated with either medium or ACTH, with or without CdCl2, was treated with or without 1 mmol/L A23187, an ionophore specifically facilitating extracellular Ca2+ transfer across plasma membranes. Besides determining Ca2+ involvement in steroidogenesis using steroid secretion as an endpoint, we directly measured Ca2+ concentrations using intracellular fura-2 fluorescence. Following loading with 2 mumol/L fura-2, cells remained untreated or medium was infused with CdCl2, ACTH, ACTH/CdCl2 or ACTH followed after 50 s by CdCl2. Using Ca(2+)-supplemented media, we observed that Cd2+ inhibition of ACTH-stimulated 20DHP secretion was completely reversed. Standard Ca(2+)-containing medium supplemented with Ca2+ also enhanced maximally stimulated 20DHP secretion by ACTH. 20DHP secretion by ACTH-treated and ACTH/Cd(2+)-treated cells was only reduced by EGTA, when Ca2+ was not supplemented. The ionophore A23187 increased basal and ACTH-stimulated 20DHP secretion by Cd(2+)-treated cells, suggesting that extracellular Ca2+ resources may compete against Cd2+ effects on plasma membrane cAMP synthesis and on basal cholesterol metabolism by mitochondria. No time-dependent change in Ca2+ concentrations occurred within untreated cell suspensions. ACTH stimulation caused a 25 s burst in Ca2+ concentrations before returning to basal, steady-state levels. Cd2+ also stimulated intracellular fura-2 fluorescence. Untreated cell suspensions infused with Cd2+ exhibited a continuous rise in intracellular fluorescence. ACTH/CdCl2-treated cells exhibited a hyperbolic rise in intracellular fluorescence over the 300 s study period. Cells treated with Cd2+ 50 s after ACTH treatment initially exhibited the 25 s fluorescence burst followed by a Cd(2+)-induced hyperbolic rise in intracellular Cd2+. These fluorescence measurements suggested that cytoplasmic Ca2+ changes do not appear to be necessary for basal 20DHP synthesis and secretion; only a 25 s burst in intracellular Ca2+ is necessary to a slightly higher plateau level for stimulated 20DHP synthesis and secretion. Cd2+ freely enters the cell under basal conditions and Cd2+ entry is accelerated by ACTH stimulation. Data were consistent with Ca2+ being required for optimal stimulated steroid production and Cd2+ probably competing with Ca2+ during basal mitochondrial cholesterol metabolism and plasma membrane ACTH-stimulated cAMP generation.

17-alpha-Hydroxypregnenolone↗
PubMed2004

ACTH stimulates the release of alkaline phosphatase through Gi-mediated activation of a phospholipase C and the release of inositol-phosphoglycan.

We have previously reported that ACTH activates a phospholipase C that hydrolyzes glycosylphosphatidylinositol (GPI), which would release inositolphosphoglycan (IPG) to the extracellular medium, and that an IPG purified from Trypanosoma cruzi is able to inhibit ACTH-mediated steroid production in adrenocortical cells. In the present paper, it was found that anti-inositolphosphoglycan antibodies (anti-CRD) increased ACTH-mediated corticosterone production, which indicates that an endogenous IPG is a physiological inhibitor of ACTH response. On the other hand, we investigated the release to the extracellular medium of the GPI-anchored enzyme, alkaline phosphatase, by ACTH. We found that: (a) the released enzyme appeared in the aqueous phase after Triton X-114 partitioning, consistent with loss of the GPI, (b) the phospholipase C inhibitor, U73122, impaired the release of the enzyme by the hormone and (c) two inhibitors of IPG uptake, inositol 2-monophosphate and 2 M NaCl, increased the amount of alkaline phosphatase in the extracellular medium. These results suggest that ACTH releases alkaline phosphatase by activation of a phospholipase C. Dibutyryladenosine-3',5'-cyclic monophosphate (db-cAMP) was able to increase the release of alkaline phosphatase from adrenocortical cells and this effect was inhibited by U73122, suggesting that cAMP is involved in the activation of phospholipase C. In addition, it was found that a pertussis-toxin sensitive G-protein is required for ACTH- and db-cAMP-mediated release of alkaline phosphatase and that incorporation of anti-Gi antibodies in adrenocortical cells inhibited the release of alkaline phosphatase by ACTH. Our results suggest that ACTH increases the release of alkaline phosphatase by activation of a phospholipase C through cAMP and Gi which would contribute to produce IPG It was also found that the two inhibitors of IPG uptake, inositol-2-monophosphate and 2 M NaCl, increased the amount of alkaline phosphatase in the extracellular medium of ACTH-treated cells more than in control cells, indicating that ACTH also stimulates the uptake of IPG These data support a role of GPI and the involvement of Gi in ACTH action.

Adrenal Glands↗
PubMed1995

Responses of plasma adrenocortical steroids to low dose ACTH in normal subjects.

OBJECTIVE: The standard ACTH test in clinical use employs a pharmacological dose of ACTH which assesses the maximum secretory capacity of the adrenal cortex. We have investigated the responses of plasma adrenocortical steroids including cortisol, aldosterone and dehydroepiandrosterone (DHEA) to physiological doses of ACTH (ACTH 1-24, tetracosactide, Cortrosyn) and determined the minimal dose which induces a response equivalent to that induced by a pharmacological dose of ACTH. DESIGN: Rapid ACTH tests at various physiological (0-1, 0.5, 1 and 5 micrograms) and standard pharmacological (250 micrograms) intravenous doses. SUBJECTS: Seven healthy normal volunteers. MEASUREMENTS: Plasma cortisol, aldosterone and DHEA were measured. Peak value and the increment from basal value were used as indices of responses. RESULTS: Each steroid responded to physiological doses of ACTH in a dose dependent manner. The minimum dose inducing an equivalent response to 250 micrograms ACTH was 0.5 micrograms for peak and incremental values in cortisol and DHEA, while that for aldosterone was 0.1 microgram. The time to peak for each steroid was delayed as the dose increased. Plasma aldosterone and DHEA peaked significantly earlier than plasma cortisol in 1-5 micrograms and 0.5-5-micrograms ACTH tests, respectively. CONCLUSIONS: These results suggest that the sensitivity of secretion to physiological doses of ACTH in descending order is aldosterone > DHEA = cortisol. When peak and incremental values are used, sufficient doses of ACTH are 0.1 microgram for plasma aldosterone and 0.5 microgram for plasma cortisol and DHEA in the rapid ACTH test.

Adrenal Cortex Hormones↗
PubMed2004

A new less-invasive and more informative low-dose ACTH test: salivary steroids in response to intramuscular corticotrophin.

OBJECTIVE: The intravenous low-dose ACTH test has been proposed as a sensitive tool to assess adrenal function through circulating steroids. The aims of this study were to: (a) find the minimal intramuscular ACTH dose that induced serum and salivary cortisol and aldosterone responses equivalent to those obtained after a pharmacological dose of ACTH; and (b) define the minimum normal salivary cortisol and aldosterone responses in healthy subjects to that dose of ACTH. We also compared the performances of the standard- and low-dose ACTH intramuscular tests to screen patients with known hypothalamo-pituitary-adrenal impairments. DESIGN: Rapid ACTH tests were performed in individuals using various intramuscular doses (12.5, 25 and 250 microg) at 2-week intervals. SUBJECTS: Twenty-one healthy volunteers and 19 patients with primary (nine cases) and secondary (10 cases) adrenal insufficiency. MEASUREMENT: Serum and salivary cortisol and aldosterone concentrations were measured at baseline and after ACTH. Serum cortisol > or = 552.0 nmol/l and aldosterone > or = 555.0 pmol/l concentrations at 30 min after 250 microg of ACTH were defined as normal responses. RESULTS: In healthy volunteers cortisol and aldosterone responded to ACTH in a dose-dependent manner. The time to peak in saliva for each steroid was delayed as the dose of ACTH increased. The minimum ACTH dose that produced equivalent steroid responses at 30 min to 250 microg of ACTH (standard-dose test; SDT) was 25 microg (low-dose test; LDT). Saliva collection 30 min after LDT and SDT showed cortisol and aldosterone concentrations of at least 20.0 nmol/l and 100.0 pmol/l, respectively. These values were defined as normal steroid responses. Blunted salivary steroid responses to LDT and SDT were found in all patients with primary adrenal insufficiency. Subnormal salivary cortisol levels in response to LDT and SDT were found in all patients with secondary adrenal insufficiency. In five patients full recovery of adrenal function was demonstrated by both tests after steroid withdrawal. In the follow-up of four patients studied during the recovery period, subnormal SAF response after LDT and normal after SDT was demonstrated. Preservation of the adrenal glomerulosa was found in all the patients with secondary adrenal insufficiency through the normal rise in salivary aldosterone after both LDT and SDT. CONCLUSIONS: Adrenal function can be accurately investigated with simultaneous measurements of salivary cortisol and aldosterone in response to 25 microg of corticotrophin injected into the deltoid muscle. Our data suggest that this may become a useful and relatively noninvasive clinical tool to detect subclinical hypoadrenal states.

Adrenal Insufficiency↗
PubMed1996

Lack of effect of desmopressin on ACTH and cortisol responses to ovine corticotropin-releasing hormone in anorexia nervosa.

Both arginine vasopressin (AVP) and corticotropin-releasing hormone (CRH) are involved in the release of ACTH in man. Desmopressin (DDAVP), a synthetic analogue of AVP, has been shown to have a CRH-like action (able to promote ACTH and cortisol release) in animals but not in normal man. Nevertheless, DDAVP is able to release ACTH and cortisol in ACTH-dependent Cushing's disease. We studied eight anorexia nervosa (AN) patients [as AN is a condition in which chronic activation of the hypothalamic-pituitary-adrenal (HPA) axis is commonly reported] in a refeeding phase of the disease, to evaluate whether, after weight gain, ACTH and cortisol response to ovine corticotropin-releasing hormone (oCRH) [1 microgram i.v. DDAVP alone and as pretreatment to oCRH (1 microgram kg-1 BW i.v.)-induced secretion of ACTH and cortisol. We studied six normal women as control subjects. No significant differences in ACTH and cortisol responses to oCRH were found between AN patients and control subjects. DDAVP was not able to stimulate ACTH or cortisol release in AN patients or in control subjects, but in the latter it was able to significantly enhance (P < 0.05) ACTH [area under curve (AUC): 590.0 +/- 104.4 pmol L-1 120 min-1] and cortisol (AUC: 28899.0 +/- 6935.2 nmol L-1 120 min-1) responses to oCRH (ACTH AUC: 325.7 +/- 101.7 pmol L-1 120 min-1, cortisol AUC: 14197.4 +/- 2930.0 nmol L-1 120 min-1). The present data show that DDAVP does not stimulate ACTH and cortisol in AN patients or, as previously reported, in normal subjects. However, DDAVP is able to enhance ACTH and cortisol release after oCRH administration in normal subjects but not in AN patients. This finding could be due to a down-regulation of hypophyseal DDAVP V3 receptors in AN as a direct consequence of the hypercortisolaemic status usually present.

Adolescent↗
PubMed1988

Neonatal capsaicin treatment of rats reduces ACTH secretion in response to peripheral neuronal stimuli but not to centrally acting stressors.

1. Plasma adrenocorticotrophic hormone (ACTH) concentrations were measured in rats following exposure to anaesthetic agents, after stimulation of peripheral sensory nerves, and during psychological stress. 2. In rats, kept in their home cages, the i.p. injection of sodium pentobarbitone did not cause an increase in plasma ACTH, whereas injection of urethane increased plasma ACTH several times. In rats transferred to a glass dessicator and inhaling oxygen, plasma ACTH was more than 3 fold higher than in rats in their home cage. Exposure to nitrous oxide, halothane or ether in a glass dessicator produced significantly higher plasma ACTH concentrations when compared to exposure in the home cage. 3. In rats anaesthetized with pentobarbitone, the electrical stimulation of large myelinated afferents in the sciatic nerve did not trigger a measurable increase in ACTH secretion, whereas stimulation of afferent A delta- and C-fibres significantly elevated plasma ACTH concentrations. Rats treated as neonates with capsaicin showed an attenuated ACTH response to A and C-fibre stimulation. 4. Similarly, capsaicin pretreatment reduced the increase in ACTH secretion during morphine withdrawal; a similar effect was produced by clonidine. 5. ACTH secretion following open field exposure, ether stress or hypoglycaemia was not changed by capsaicin pretreatment. 6. It was concluded that capsaicin-sensitive afferents are involved in the secretion of ACTH elicited by somatosensory forms of stress. Centrally evoked ACTH release is not affected by capsaicin pretreatment.

Adrenocorticotropic Hormone↗
PubMed1995

ACTH does not control neonatal seizures induced by administration of exogenous corticotropin-releasing hormone.

ACTH has been used extensively for treatment of massive infantile spasms (MIS) and other intractable seizures. The mechanisms by which ACTH exerts anticonvulsant effects are unknown. ACTH is a neuropeptide with both endocrine and neuromodulatory properties; its efficacy against MIS could derive from intrinsic anticonvulsant properties or from hormonal effects, either directly or through glucocorticoids. We tested ACTH activity against exogenous corticotropin-releasing hormone (CRH)-induced seizures in the infant rat model. CRH was administered into the cerebral ventricles of 85 infant rats aged 5-13 days. ACTH was used either 20-60 min before CRH administration or "chronically" (pretreatment with four doses of ACTH every 6 h, before CRH administration). In a separate group of rat pups, we measured plasma corticosterone to ascertain ACTH availability. Administration of CRH, an age-specific endogenous convulsant, resulted in a prolonged series of seizures after 2- to 55-min latency. There was no difference in latency between controls (9.5 +/- 1.2 min) and ACTH-treated rats (12.4 +/- 2.8 min for combined acute and chronic groups). CRH-induced seizure duration (88.2 +/- 9 vs. 74.7 +/- 9.4 min) and severity of seizures was also unchanged by ACTH treatment. ACTH reached the circulation and caused significant increase in plasma glucocorticoids. ACTH does not block the convulsant action of exogenous CRH in infant rats. An alternative mechanism for the anticonvulsant effect of ACTH may be suppression of synthesis and secretion of an endogenous convulsant, i.e., CRH.

Adrenocorticotropic Hormone↗
PubMed2003

Downregulation of CYP2D16 by ACTH in the guinea pig adrenal cortex: time course, reversibility, and mechanism of action.

Studies were done to investigate the actions of ACTH on the expression of CYP2D16 in the guinea pig adrenal cortex. Guinea pigs were treated with ACTH for 1, 3, or 7 days. In addition, some animals received ACTH for 7 days and were then untreated for an additional 3 or 7 days to test for reversibility of ACTH actions. ACTH treatment caused a time-dependent decrease in the rates of adrenal microsomal bufuralol metabolism, a CYP2D-catalyzed reaction; hepatic bufuralol metabolism was unaffected by ACTH. Adrenal enzyme activity was significantly reduced by ACTH within 1 day and decreased by 80% after 7 days. Western blotting and in situ hybridization analyses revealed corresponding declines in adrenal CYP2D16 protein and mRNA concentrations. Nuclear runoff assays indicated that ACTH treatment inhibited CYP2D16 expression at the transcriptional level. Adrenal 17 alpha-hydroxylase activities were increased by ACTH treatment, but CYP17 protein concentrations were not affected. Following cessation of ACTH administration, the rates of adrenal bufuralol metabolism and CYP2D16 protein and mRNA concentrations returned to control levels within 7 days. The results demonstrate that ACTH has a relatively rapid and reversible effect to inhibit adrenal CYP2D16 transcription, thereby decreasing adrenal xenobiotic metabolism. Thus, the actions of ACTH on CYP2D16 expression are opposite to those on other adrenal p450 isozymes, indicating unique regulatory mechanisms.

Adrenal Cortex↗
PubMed1983

Origin of immunoreactive ACTH in brain sites outside the ventral hypothalamus.

Immunoreactive adrenocorticotropin (IR-ACTH) is widely distributed throughout the brain. Highest concentrations have been localized in the ventral hypothalamus, a recognized site of origin of IR-ACTH containing neuronal cell bodies. To determine whether IR-ACTH arises in other brain sites, we determined the effect on the concentration of IR-ACTH in several regions of rat brain after intracerebroventricular injection of colchicine, an agent that inhibits axoplasmic transport and leads to an accumulation of neuronal secretory products within cell bodies. Three regions (ventral hypothalamus, dorsal hypothalamus, amygdala) showed a significant increase in concentration of IR-ACTH after colchicine, whereas the hippocampus and preoptic area did not. Because neuropeptides, in general, undergo posttranslational processing during axoplasmic transport, it could be predicted that inhibition of transport would lead to a relative increase in 'large', precursor forms of hormone in regions containing cells of origin of neuropeptide tracts. Therefore, the effect of colchicine on the processing of molecular forms of IR-ACTH was also examined. In brain regions showing a significant increase in IR-ACTH after colchicine, the proportion of 'big' ACTH and ACTH1-39 (relative to total IR-ACTH) increased and the proportion of 'small' ACTH (less than 4,500 daltons) declined. In contrast, size distribution of IR-ACTH species in other areas were either the opposite or were unchanged. These studies indicate that in addition to the ventral hypothalamus, IR-ACTH also originates in the dorsal hypothalamus and the amygdala, and that decreased axoplasmic peptide transport is associated with decreased processing of molecular forms.

Adrenocorticotropic Hormone↗
PubMed1992

Histamine- and stress-induced secretion of ACTH and beta-endorphin: involvement of corticotropin-releasing hormone and vasopressin.

Histamine (HA) stimulates the release of the pro-opiomelanocortin (POMC)-derived peptides ACTH, beta-endorphin (beta-END), beta-lipotropin and alpha-melanocyte-stimulating hormone, and HA is involved in the mediation of the stress-induced release of these peptides. The effect of HA is indirect and may involve the hypothalamic regulating factors, corticotropin-releasing hormone (CRH) and/or arginine-vasopressin (AVP). We studied the effect of immunoneutralization with specific antisera against CRH or AVP on the response of ACTH and beta-END to HA, restraint stress, CRH, AVP or a posterior pituitary extract in male rats. Intracerebroventricular infusion of HA (34-540 nmol) increased the plasma levels of ACTH and beta-END immunoreactivity (beta-ENDir) in a dose-dependent manner. Pretreatment with antiserum to CRH or AVP prevented the ACTH response to 270 nmol HA and inhibited the beta-ENDir response by 30-60%. One to five minutes of restraint stress caused an increase in the plasma levels of ACTH and beta-ENDir. The increase was dependent on the duration of stress exposure. Pretreatment with CRH antiserum abolished the ACTH response to 5 min of restraint stress and inhibited the beta-ENDir response by 60%. Immunoneutralization with AVP antiserum had only half the inhibitory effect of that seen with CRH antiserum. CRH (100 pmol i.v.) increased the plasma levels of ACTH and beta-ENDir. This effect was abolished by pretreatment with CRH antiserum, whereas pretreatment with AVP antiserum prevented the CRH-induced ACTH release and inhibited the beta-ENDir response by 50%. AVP (24-800 pmol i.v.) stimulated ACTH and beta-ENDir in a dose-dependent manner. CRH and AVP antisera each prevented the effect of AVP (800 pmol) on ACTH secretion, whereas the beta-ENDir response to AVP was only inhibited by about 60% by the antisera. An extract of the posterior pituitary gland administered in a dose corresponding to 0.15 or 0.5 pituitary equivalents had no effect on ACTH secretion, while 1.0 pituitary equivalent increased the ACTH concentration in plasma. This effect was abolished by AVP antiserum. The posterior pituitary extract caused a dose-dependent rise in plasma beta-ENDir which might be due to an unavoidable contamination of the posterior pituitary extract by a small amount of beta-END from the intermediate lobe. Consistent with this view, AVP antiserum had no effect on the rise in the plasma concentration of beta-ENDir following administration of the posterior pituitary extract.(ABSTRACT TRUNCATED AT 400 WORDS)

Adrenocorticotropic Hormone↗
PubMed1981

Presence of ACTH-potentiating factors in rat anterior pituitary glands.

High molecular weight ACTH fractions, obtained through gel filtration of boiled rat anterior pituitary extract, induced a marked increase in corticosterone production from isolated rat adrenal cells in the presence of low concentrations of ACTH-(1-24). This indicates the presence of heat-stable factors augmenting the steroidogenic action of ACTH in the rat anterior pituitary. We also noted that these factors potentiated the activity not only of ACTH-1(1-24) but also of ACTH-(1-8). The ACTH-potentiating factors in rat anterior pituitary extract are possibly present in heterogeneous forms according to their molecular weights (8,000, 10,000 and 15,000), their mobility in ion-exchange chromatography and their content in RIA-ACTH activity. Of these three forms, the former comigrated with biological ACTH activity. The remaining two forms were free of it. Since the effect of potentiating factors on modified ACTH-(1-9), shown to be less susceptible to proteolytic degradation from ACTH-(1-24), was similar to the effect on ACTH-(1-24), it is suggested that potentiation was not due to an inhibition of ACTH proteolysis.

Adrenal Glands↗
PubMed1985

Adrenocorticotrophic hormone in the anterior and neurointermediate lobes of the rat during the perinatal period: polymorphism, biological and immunological activities of ACTH.

When acid extracts (0.1 N HCl) of the anterior or neurointermediate lobes of fetal and newborn rat pituitary were subjected to gel filtration on Sephadex G-50 fine columns, polymorphism of ACTH was revealed by radioimmunoassay. At every stage of pregnancy and after birth three main ACTH forms were observed. The first form ('big' ACTH) eluted near the void volume of the column; its apparent molecular weight was 45,000. The second form ('little' ACTH) coeluted with synthetic human ACTH1-39 and 125I human ACTH. As the latter marker eluted more slowly than the former, 'little' ACTH, which showed an apparent molecular weight near 5,000, could not be a single entity. The third form ('intermediate' ACTH) eluted between 'big' and 'little' ACTH; its apparent molecular weight was near 13,000. During the perinatal period, the relative proportions between these different molecular forms of ACTH changed in both anterior and neurointermediate lobes. Thus the gradual increase of 'intermediate' and 'little' forms was accompanied by a decrease of 'big' ACTH. The perfusion of fetal adrenal glands with the same immunological quantities of 'big', 'intermediate' and 'little' ACTH showed that the 'little' and 'intermediate' forms have greater biological potency in eliciting corticosterone secretion than the 'big' ACTH form.

Adrenocorticotropic Hormone↗
PubMed1984

Corticosteroid inhibition of ACTH secretion.

Corticosteroid feedback inhibits the brain-hypothalamo-pituitary units of the adrenocortical system. Naturally occurring corticosteroids may have their primary actions in vivo at brain and hypothalamic sites of feedback, whereas synthetic glucocorticoids that do not bind to transcortin may act primarily on corticotropes and regions of brain outside the blood-brain barrier. There appear to be three major time frames of corticosteroid action: fast, intermediate and slow. These time frames probably are the consequence of three separate mechanisms of corticosteroid action at feedback-sensitive sites. The rapidity of occurrence of fast feedback is not compatible with a nuclear site of corticosteroid action, and protein synthesis is not required. The action of CRF on ACTH release may be inhibited by a rapid effect of corticosteroids at the cell membrane. Since stimulated, but not basal, ACTH and CRF release are inhibited in vitro, the corticosteroids may inhibit some event in stimulus-secretion coupling (e.g., cAMP production). Intermediate feedback also decreases ACTH release in response to stimulation of the corticotrope, but does not affect ACTH synthesis; CRF synthesis and release both appear to be affected by the intermediate corticosteroid action. The mechanism of intermediate feedback requires the presence of a protein whose synthesis is corticosteroid-dependent; however, the role of this protein is unknown. Intermediate feedback, like fast feedback, apparently does not involve inhibition of total ACTH stores or the releasable pool of ACTH since basal secretion of ACTH is also not inhibited in vitro within this time domain. On the other hand, slow feedback apparently involves the classical genomic steroid mechanism of action; slow feedback reduces pituitary ACTH content by decreasing levels of mRNA encoding for POMC, the ACTH precursor molecule. Slow feedback, therefore, inhibits basal as well as stimulus induced ACTH secretion. Corticosteroid-induced inhibition of basal ACTH secretion has been shown to occur within 2 h in vivo but not in vitro. The time course and sensitivity of this feedback effect is different than that demonstrated for stimulus induced secretion. This difference suggests that basal secretion is activated by different pathways to (CRF and) ACTH secretion. There is some evidence that suggests that whereas comparator elements are not reset during stress, a comparator element is reset during the course of the circadian rhythm so that different basal levels of steroid are achieved.(ABSTRACT TRUNCATED AT 400 WORDS)

Adrenal Cortex Hormones↗
PubMed1993

Ovine anterior pituitary proopiomelanocortin gene expression is not increased by ACTH secretagogues in vitro.

Recent reports have demonstrated that the secretion of ACTH from sheep anterior pituitary primary cultures is markedly stimulated by arginine vasopressin (AVP) but not by CRF, and that AVP-stimulated ACTH secretion is potentiated by CRF. It has also been reported that AVP increases total ACTH content (secreted plus intracellular ACTH), suggesting that AVP stimulates POMC biosynthesis in the ovine anterior pituitary. These observations differ from the rat, in which CRF is the most potent of the ACTH-releasing factors and the only ACTH secretagogue which stimulates POMC gene expression and biosynthesis. The second messenger pathways which mediate CRF- and AVP-stimulated ACTH release (protein kinase A and protein kinase C, respectively) are the same in sheep and rat corticotrophs. The present studies were undertaken to determine if ovine POMC gene expression, unlike the rat POMC gene, is stimulated by AVP via the protein kinase C pathway. A 295 base pair portion of the ovine POMC gene was isolated using polymerase chain reaction and sequenced. Ovine POMC messenger RNA (mRNA) levels were quantitated using this partial complementary DNA clone in a solution hybridization/nuclease protection assay with cytoplasmic RNA from sheep anterior pituitary primary cultures which had been treated with various combinations of ACTH secretagogues or with glucocorticoids for 18 h. Treatment with AVP, alone or with CRF, greatly increased total and secreted ACTH levels; however, the amount of POMC mRNA in these cells was not significantly increased. Treatments which stimulated secretion to a lesser extent and did not alter total ACTH levels (CRF alone, cAMP alone, or with phorbol ester) were associated with a decrease in POMC mRNA levels relative to untreated cells. Glucocorticoid treatment decreased both total ACTH and POMC mRNA levels. Taken together, the data demonstrate a lack of secretagogue-induced stimulation of POMC mRNA levels concomitant with increased total ACTH levels, an unexpected result given the close association between secretion of POMC-derived peptides and POMC gene expression in other mammalian corticotroph systems.

Adrenocorticotropic Hormone↗
PubMed1975

A sensitive bioassay for the determination of human plasma ACTH levels.

A sensitive bioassay for the measurement of plasma ACTH is presented. The use of silicic acid adsorption of plasma, with a subsequent acid wash and aqueous acetone desorption, was successful in removing those substances which had interfered with the steroidogenic response of dispersed adrenal cells when unextracted plasma was employed. This extraction procedure extracted 72-76% of ACTH present in plasma. Two pg ACTH1-39 could be consistently detected. Alpha-hACTH1-39 and alpha-pACTH1-39 exhibited equal potencies. Beta-MSH was ineffective at dosage levels up to 2 x 10(8) pg. One x 10(8) pg of ACTH1-10, ACTH4-10, or alpha-MSH had a steroidogenic effect equivalent to that of 40 pg ACTH1-39. ACTH 17-39 and ACTH 11-24 were incapable of stimulating steroid production at doses of 1 x 10(8) pg. Excesses of the latter, but not of the former appeared to be able to antagonize the steroidogenic effect of ACTH1-39. Plasma from normal subjects, bioassayed by this extraction procedure, contained 12-186 pg/ml ACTH at 0400-0800: 14-93 pg/ml ACTH at 1000-1300, and less than 10-34 pg/ml ACTH at 1600-2200. Hypoglycemia and vasopressin administration were followed by increases in plasma ACTH concentratrations. Plasma ACTH concentrations in untreated patients with Cushing's disease (sampled over the period 0900-1300) ranged from 65-220 pg/ml. Three patients with Addison's disease (untreated or 12 h following replacement steroid withdrawal) had ACTH concentrations of 223, 370 and 1226 pg/ml. Markedly elevated ACTH concentrations were observed in a patient with Nelson's syndrome (391 and 835 pg/ml). Bioassayable ACTH was not detected in 2 patients with panhypopituitarism.

Acetone↗
PubMed1995

Elevated levels of adrenocorticotropin (ACTH) precursors in post-adrenalectomy Cushing's disease and their regulation by glucocorticoids.

The ACTH precursor pro-opiomelanocortin (POMC) undergoes specific endoproteolytic cleavages in the anterior pituitary gland to give ACTH-(1-39). ACTH precursors circulate in normal subjects and are high both in the ectopic ACTH syndrome and in patients with aggressive pituitary adenomas. This study examines plasma levels of ACTH precursors and ACTH in 24 patients with post-adrenalectomy Cushing's disease, in 10 of whom computed tomography showed evidence of tumor progression. ACTH precursors were higher in post-adrenalectomy Cushing's disease (median 97.5 pmol/L, range 26-647 pmol/L) than in untreated Cushing's disease (median 29 pmol/L, range 9-104 pmol/L) and normal controls (5-40 pmol/L) (P < 0.001) and were significantly higher in patients with larger tumors (median 175 pmol/L, range 52-647 pmol/L) than in the remainder (median 41 pmol/L, range 26-510 pmol/L) (P = 0.02). Surprisingly, pro-opiomelanocortin (POMC) processing to ACTH was enhanced in post-adrenalectomy patients (ratio 1 +/- 0.5) compared with Cushing's disease (5.6 +/- 0.8) and normal subjects (5.3 +/- 0.9). After hydrocortisone ACTH precursors rose in 36% of post-adrenalectomy patients (increase 15-78%) and remained within 10% of basal levels in 46%. Six patients had a rise in precursors and a fall in ACTH suggesting differential regulation of these peptides. In conclusion, whereas ACTH precursors are high in post-adrenalectomy Cushing's disease and higher levels correlate with tumor progression, processing of precursors to ACTH is enhanced.

Adolescent↗
PubMed1984

Effect of alpha 1- and alpha 2-adrenoceptor agonists and antagonists on ACTH secretion in intact and in hypothalamic deafferentated rats.

The effect of systemically injected alpha 1- and alpha 2-adrenoceptor agonists and antagonists on ACTH secretion was studied in rats. Epinephrine, norepinephrine, phenylephrine, clonidine, B-HT933, and B-HT920 caused a significant and dose-related increase of the ACTH concentration in the serum. The order of median effective dose (ED50) of these drugs on ACTH secretion was as follows: epinephrine not equal to norepinephrine less than B-HT920 less than clonidine less than phenylephrine much less than B-HT933. Isoproterenol, a beta-adrenoceptor agonist, had no effect on ACTH secretion. ACTH secretion induced by epinephrine or phenylephrine was significantly inhibited by alpha-adrenoceptor antagonists, phentolamine and phenoxybenzamine. However, propranolol, a beta-adrenoceptor antagonist, had no effect on ACTH secretion induced by epinephrine. Prazosin, an alpha 1-antagonist, and yohimbine, an alpha 2-antagonist, significantly blocked ACTH secretion induced by phenylephrine, an alpha 1-agonist, and B-HT933, an alpha 2-agonist, respectively. ACTH secretion induced by norepinephrine or a low dose of clonidine was inhibited by both prazosin and yohimbine. However, ACTH secretion induced by a high dose of clonidine was blocked only by prazosin. In rats with complete deafferentation of the medial basal hypothalamus (MBH), ACTH secretion induced by epinephrine, norepinephrine, and clonidine was significantly blocked, as compared with intact rats. These results suggest that both peripheral alpha 1- and alpha 2-adrenoceptors are involved in ACTH secretion induced by systemically injected adrenergic drugs in rats, and intact neural pathways entering the MBH are necessary for this ACTH releasing action.

Adrenergic alpha-Agonists↗