Daily ACTH Research Articles

Attenuated corticosterone response to chronic ACTH stimulation in hepatic lipase-deficient mice: evidence for a role for hepatic lipase in adrenal physiology

Hepatic lipase (HL), a liver-expressed lipolytic enzyme, hydrolyzes triglycerides and phospholipids in lipoproteins and promotes cholesterol delivery through receptor-mediated whole particle and selective cholesterol uptake. HL activity also occurs in the adrenal glands, which utilize lipoprotein cholesterol to synthesize glucocorticoids in response to pituitary ACTH. It is likely that the role of adrenal HL is to facilitate delivery of exogenous cholesterol for glucocorticoid synthesis. On this basis, we hypothesized that HL deficiency would blunt the glucocorticoid response to ACTH. Furthermore, because exogenous cholesterol also is derived from the LDL receptor (LDLR) pathway, we hypothesized that LDLR deficiency would blunt the response to ACTH. To test these hypotheses, we compared the corticosterone response to eight daily ACTH injections in HL-deficient (hl-/-), LDLR-deficient (Ldlr-/-), and HL- and LDLR-doubly deficient (Ldlr-/- hl-/-) mice with that in wild-type (WT) mice. Plasma corticosterone levels were measured on days 2, 5, and 8. Differences in plasma corticosterone levels between genotypes were analyzed by Kruskal-Wallis one-way ANOVA on ranks and pairwise multiple comparisons by Dunn's test. Our results demonstrate a trend toward reductions in plasma corticosterone levels on day 2 and significant reductions on day 5 and day 8 in the knockout models. Thus, on day 5, plasma corticosterone levels were reduced by 57, 70, and 73% (all P < 0.05) and on day 8 by 76, 59, and 63% (all P < 0.05) in hl-/-, Ldlr-/-, and Ldlr-/- hl-/- mice, respectively. These results demonstrate that HL deficiency, like LDLR deficiency, blunts the adrenal response to chronic ACTH stimulation and suggest a novel role for HL in adrenal physiology.

ACTH 1-24 inhibits proliferation of adrenocortical tumors in vivo

Although several lines of evidence suggest that the overall effects of the ACTH receptor, melanocortin 2 receptor (MC2-R), mediated signal transduction on adrenocortical growth and tumorigenesis are anti-proliferative, activation of MC2-R induces mitogens like jun, fos, and myc and activates the MAPK pathway. In vivo, potential effects of endogenous ACTH on adrenal tumori-genesis can not be separated from effects of other POMC derived peptides. Murine adrenocortical tumor cells that lack MC2-R expression (Y6(pcDNA)) and Y6 cells stablely transfected with MC2-R (Y6(MC2-R)) were generated. Presence of functional MC2-R was demonstrated by RT-PCR and Western blot using an antibody for phosphorylated CREB. As a syngenic tumor model, LaHeF1/J mice simultaneously received 10(7) Y6(MC2-R) and Y6(pcDNA) subcutaneously, giving rise to MC2-R positive and negative tumors within the same animal. Animals were treated for 3 weeks in groups of 12 according to the following schedule: group A, control animals receiving saline injection; group B, animals receiving 5.7 ng/injection of a slow release formula of ACTH 1-24 administered i.p. three times a week (aiming at a low physiologic dose); and group C, animals receiving 57 ng/injection of ACTH 1-24 (high physiological dose). Twenty days of ACTH 1-24 treatment did not significantly affect corticosterone levels, endogenous ACTH levels or adrenal and thymus weight compared with saline injection. However, ACTH 1-24 treatment of group B and C mice significantly reduced tumor weight in MC2-R positive tumors in a dose dependent manner (P = 0.03), while no significant difference in tumor mass was observed in MC2-R negative tumors. PCNA and TUNEL staining, together with morphological characterization, demonstrated that these in vivo effects were due to reduced proliferation, while apoptosis and cellular hypertrophy within the tumor remained unchanged. MC2-R expression is associated with a less aggressive adrenal tumor phenotype and anti-proliferative effects can be amplified through stimulation with physiological doses of ACTH.

Reversible Changes in Adrenocorticotropin (ACTH)-Induced Adrenocortical Steroidogenesis and Expression of the Peripheral-Type Benzodiazepine Receptor during the ACTH-Insensitive Period in Young Rats

We previously demonstrated decreased adrenal content of a mitochondrial cholesterol transporter [peripheral-type benzodiazepine receptor (PBR)] during the first postnatal week in rats, when ACTH-inducible steroidogenesis is low. Here we report that the expression of PBR protein and mRNA increases throughout the neonatal/juvenile period in rats in parallel with ACTH-inducible steroidogenesis in vitro. We also previously reported that chronic stimulation of rat pups with daily ACTH injections augmented the steroidogenic response of the developing adrenal cortex. We therefore tested the hypotheses that the change in phenotype induced by ACTH was permanent, and that the effects of ACTH were mediated by increased PBR expression. Pups were injected with ACTH or saline from postnatal d (pd) 2-8 or 2-14. Another group of pups received ACTH from pd 2-7, followed by saline from pd 8-14. On the final day, all pups were challenged with a test injection of ACTH or saline. Exposure to ACTH, but not saline, for 1 wk significantly increased adrenal mass, the corticosterone response to ACTH, and the expression of PBR protein and mRNA. Continued ACTH treatment for a second week maintained adrenal mass, steroidogenesis, and PBR mRNA expression. When ACTH was withdrawn after 1 wk and replaced with daily saline injections, however, adrenal mass, ACTH-inducible steroidogenesis, and PBR expression returned to levels comparable to those in age-matched saline controls (i.e. animals that had not received ACTH injections during the first 2 wk). Thus, although ACTH was capable of inducing increased steroidogenic capacity of the juvenile rat adrenal, its effects were only manifest when pups were exposed regularly to high plasma ACTH levels. ACTH, therefore, has significant, but reversible, effects on the development of adrenocortical function, possibly mediated in part by increased expression of PBR.

Corticotropin-releasing hormone and arginine vasopressin gene transcription in the hypothalamic paraventricular nucleus of unstressed rats: daily rhythms and their interactions with corticosterone.

To drive the daily ACTH secretory rhythm from anterior pituitary corticotropes signals from the circadian clock schedule CRH and, to lesser extent, arginine vasopressin (AVP) release from neuroendocrine terminals. In turn, releasable pools of CRH and AVP in neuroendocrine terminals are sustained by synthetic mechanisms in the medial parvicellular paraventricular nucleus, a critical component of which involves transcribing primary (heteronuclear (hn)) RNA transcripts from their cognate genes. To determine the fundamental daily patterns of ACTH secretagogue gene transcription in unstressed rats, we measured CRH and AVP hnRNA levels at 1- to 4-h intervals throughout the day using in situ hybridization. Crh gene transcription is readily detectable throughout the day, and shows a pronounced rhythm that is temporally correlated with CRH mRNA levels, but is uncoupled from ACTH release. However, avp gene transcription is barely detectable and shows no discernable rhythm. We then performed similar experiments in adrenalectomized rats with or without corticosterone replacement. Corticosterone-dependent mechanisms regulate CRH hnRNA levels at the nadir and peak as well as the onset of nocturnal crh gene transcription. A prominent rhythm of avp hnRNA seen in adrenalectomized animals was dampened by corticosterone. This study shows, first, CRH synthesis in intact animals is maintained by a nocturnal episode of crh gene transcription, parameters of which are modulated by corticosterone-dependent mechanisms; second, circulating corticosterone is sufficient to completely inhibit a daily rhythm of avp gene transcription present in adrenalectomized rats; third, the neural systems that activate crh gene transcription can be uncoupled from those driving ACTH release.

Dose effect of adrenocorticotropin on aldosterone and cortisol biosynthesis in cultured bovine adrenal glomerulosa cells: in vitro correlate of hyperreninemic hypoaldosteronism.

In some critically ill patients, aldosterone secretion is diminished despite hyperreninemia. These same patients demonstrate appropriately elevated plasma ACTH and cortisol levels. In addition, infusion of ACTH or angiotensin-II (AII) fails to elicit the normal aldosterone response, implying that the defect is at the level of the zona glomerulosa (ZG) cell. To test the hypothesis that elevated ACTH levels induce this defect, Percoll-purified bovine ZG cells were plated in serum-free defined medium and cultured for 5 days. On days 1-4, cells were exposed to various concentrations of ACTH for 1 h. On the fifth day of culture, half of the wells pretreated with ACTH were treated for 1 h with AII (10(-7) M); the other half of the wells received another dose of ACTH for 1 h. Additionally, cells were exposed to daily 1-h pulses of AII (10(-7) M) alone or in combination with ACTH (10(-8) M) for 5 days. Acutely dispersed bovine ZG cells showed dose-dependent increases in aldosterone when incubated with ACTH, potassium, or AII, with minimal cortisol production. Acutely dispersed bovine fasciculata cells produced no aldosterone, but demonstrated a dose-dependent cortisol response to ACTH and AII, but not potassium. On day 1 of culture, the ZG cells demonstrated a significant (P less than 0.001 in all cases) dose-related increase in aldosterone secretion in response to ACTH. However, continued daily pulsation with ACTH resulted in a dose-dependent decrease in aldosterone secretion, with a concomitant dose- and time-related rise in cortisol production. Indeed, ACTH-induced cortisol production in ZG became similar to ACTH-induced cortisol production in zona fasciculata cells. The addition of AII to the daily ACTH pulse did not significantly alter the aldosterone or cortisol response patterns to ACTH alone. In contrast, ZG cells treated with AII alone for 5 days showed a minimal change in cortisol production and no reduction in aldosterone production until day 4. Northern blot analysis of total RNA isolated from ZG cells pulsed with ACTH for 5 days demonstrated a parallel dose-dependent increase in 17 alpha-hydroxylase mRNA, which did not occur in cells pulsed with AII alone. These in vitro results suggest that elevated ACTH levels over time induce 17 alpha-hydroxylase activity in ZG cells, thereby shifting steroid biosynthesis from an aldosterone-producing to a cortisol-producing pathway. It is likely that the chronically elevated ACTH levels in critically ill patients induce a similar change in ZG cell biosynthesis, resulting in their hyperreninemic hypoaldosterone state.

Stimulation of adrenocorticotropin secretion by insulin-induced hypoglycemia in the developing rat involves arginine vasopressin but not corticotropin-releasing factor.

In the neonatal rat, the response of the hypothalamo-pituitary-adrenal axis to stressful stimuli is markedly decreased during the first 2 weeks of life. This peculiar period was named "stress hyporesponsive period." In this report, we studied the effect of insulin-induced hypoglycemia, known as a strong stimulator of the corticotroph function in the adult rat. Rats (8- or 20-day-old) were injected ip with 3 IU/kg synthetic insulin and were killed at various times. In 20-day-old rats, hypoglycemia induced a rapid drop in blood glucose concentrations accompanied by a stimulation of ACTH and corticosterone secretion which reached maximal values within 30 min. On the opposite, in 8-day-old rats, despite a rapid decrease in blood glucose levels, insulin injection induced a gradual rise of plasma ACTH and corticosterone concentrations which peaked at 90 min. This delayed response of the hypothalamo-pituitary-adrenal axis to hypoglycemia in the youngest rats does not seem to be due to a difference of sensitivity to insulin-induced hypoglycemia since injection of increasing doses of insulin (0.3, 0.75, or 3 IU/kg body wt) induced a dose-related decrease of blood glucose concentrations and a rise in plasma ACTH and corticosterone levels, comparable in the two age group studied. Basal or hypoglycemia-stimulated absolute corticosterone values were much lower in 8-day-old rats than in 20-day-old animals, suggesting an immaturity of the adrenal glands in the youngest animals. Daily ACTH injection, starting 3 days before the experiment, had a trophic effect on the adrenal glands leading to a more important increase of corticosterone levels after hypoglycemia in 8-day-old rats. Our results confirm that there is an immaturity of the adrenal glands in young rats, probably due to the low plasma ACTH levels during the neonatal period. To determine the respective role of the two major hypothalamic ACTH secretagogues, we studied the effect of passive immunization against CRF or arginine vasopressin (AVP) on plasma ACTH response after hypoglycemia. Passive immunization against AVP decreased significantly hypoglycemia-stimulated ACTH secretion in both 8- and 20-day-old rats, while no change of plasma ACTH response to insulin injection was observed after passive immunization against CRF. This results suggest that CRF does not seem to be involved in the regulation of ACTH secretion after hypoglycemia in the young rat while AVP seems to be the main hypothalamic stimulatory factor for anterior pituitary corticotrophs response to hypoglycemia during the postnatal period.(ABSTRACT TRUNCATED AT 400 WORDS)

Combination Treatment of High‐Dose Pyridoxal Phosphate and Low‐Dose ACTH in Children with West Syndrome and Related Disorders

Combination therapy of high-dose pyridoxal phosphate (PAL-P, 40-50 mg/kg/day) and low-dose ACTH beta 1-24-Z (tetracosactide acetate-Zn, Cortrosyn Z, 0.01 mg/kg/day) was instituted in 26 children suffering from West syndrome and related disorders--pretreated without success with high-dose PAL-P alone; 18 with West syndrome (14 with symptomatic and 4 with cryptogenic types), 2 with symptomatic Lennox-Gastaut syndrome, 5 with cerebral palsy with hypsarhythmia or diffuse slow spike-waves and one with myoclonic seizures (secondary generalized epilepsy). Clinical, electroencephalographic and neurochemical investigations were carried out. The results were summarized as follows. 1) Only one of 27 children with West syndrome and related disorders pretreated using high-dose PAL-P alone before ACTH showed a clinically excellent response. 2) Clinical seizures were completely suppressed in 19 of 21 children who initially had seizures (90%) after this combination therapy. 3) Twenty-one of the total 26 children (80%) had disappearance of hypsarhythmia or diffuse slow spike-waves in EEG after this therapy. 4) During PAL-P treatment alone transient increases in liver enzymes occurred in 37 percent. The brain shrinkage of CT and the significant rise in CSF NSE were seen in 95% and 78% after ACTH, respectively. 5) Twenty-three children have been followed for one to 29 months after tapering off of ACTH. No relapses were experienced in 11 of 18 who initially had seizures (61%) and 13 of 23 with hypsarhythmia or diffuse slow spike-waves (57%). 6) Postictal PRL elevations were suppressed during high-dose PAL-P. 7) No significant changes in the CSF levels of HVA and 5-HIAA were seen during this combination therapy. The CSF levels of HVA were significantly lower than the controls. 8) Daily ACTH therapy transiently suppressed the secretion of anterior pituitary hormones (GH, TSH, PRL, LH and FSH) and thyroid hormones (T3 free T3, T4 and free T4). It is recommended that the combination therapy of high-dose PAL-P and low-dose ACTH is a promising new method and should be tried in children with West syndrome and related disorders. The mechanism of action of this combination therapy remains obscure although some information has been obtained from our investigations.

Effect of sodium depletion on pressor responsiveness in ACTH-induced hypertension in man.

1. Pressor responsiveness to angiotensin II (AII) and phenylephrine (PHE) was measured before and after 5 days of ACTH (1 mg i.m. daily) in six normal men maintained on low sodium diet (15 mmol daily). 2. ACTH caused a significant increase in systolic blood pressure of 9 mmHg. 3. There was no change in pressor responsiveness to AII with ACTH. 4. ACTH increased pressor responsiveness to PHE for both systolic and diastolic blood pressure, with a fall in the threshold for response from 0.9 to 0.6 micrograms/kg per min. 5. Increased pressor sensitivity to catecholamines during ACTH administration in man is not sodium-dependent.

Comparison of the adrenal sensitivity to ACTH of laying hens with immobilization and plasma baseline levels of corticosterone

The effects of mammalian ACTH (0.01–10.0 IU/kg) given intraarterially on plasma corticosterone levels in laying hens were determined. A rectilinear dose-response relationship was found, y = 24.545 + 8.691 x. Daily ACTH injections of 0.1 IU/kg on 3 successive days showed a good reproducibility in response in plasma corticosterone levels. Immobilization by hand also increases plasma corticosterone to a plateau level of about 4 ng/ml. The effects of ACTH and immobilization in individual birds showed a good correlation ( r = 0.87). A rather low correlation ( r = 0.49) existed between individual baseline levels of plasma corticosterone and adrenal sensitivity for ACTH. The adrenal sensitivity for ACTH was nearly two times higher in the morning than in the evening. A diurnal pattern, however, could not be shown in the corticosterone response to immobilization.

Pressor responsiveness in steroid-induced hypertension in man.

Pressor responsiveness to angiotensin II (AII) and phenylephrine (PE) was examined before and after 5 days of ACTH (1 mg, i.m., daily) or hydrocortisone (200 mg, orally, daily) in six normotensive men. Pulse pressure was higher prior to PE than AII infusion, presumably due to feeding. Systolic blood pressure (SBP) was increased by both ACTH and hydrocortisone treatment, but more by ACTH. There were no significant changes in AII pressor responsiveness with either ACTH or hydrocortisone. ACTH increased pressor responsiveness to PE at 1.35 and 2 micrograms/kg per min, and hydrocortisone at 0.6-2 micrograms/kg per min, with falls in pulse rate at 0.3-0.9 micrograms/kg per min. Changes in pressor responsiveness do not explain ACTH hypertension.

Pituitary-adrenal responsiveness to corticotropin-releasing hormone in patients receiving chronic, alternate day glucocorticoid therapy.

We examined the responsiveness of the pituitary-adrenal axis to ovine corticotropin-releasing hormone (oCRH) in 14 women with systemic lupus erythematosus receiving chronic, alternate day glucocorticoid therapy with prednisone. Testing was done twice and in a random order (at 2000 h) on the day when the steroid was taken (12 h after the last dose) and on the day when no glucocorticoid was administered (36 h after the last dose). Plasma ACTH and cortisol responses were markedly blunted on the day of treatment and mildly blunted on the day off treatment compared to those in normal subjects. Altered metabolic clearance of exogenous oCRF was not responsible for this difference, since the plasma disappearance curves of immunoreactive oCRH were similar on both days. The degree of suppression was dependent on the dose of prednisone, and the amount of cortisol secreted during the oCRH test was directly proportional to the logarithm of the concurrent plasma ACTH level. Thus, the cortisol response to ACTH was normal in all patients. These data suggest that the blunting of responsiveness to oCRH on both days of testing represents prednisolone suppression of the corticotroph cell. Despite this, the adrenal glands retain normal responsiveness to ACTH, suggesting that moderate decreases in daily ACTH secretion are compatible with sustaining normal adrenal function. Hence, the site of the mild suppression of the hypothalamic-pituitary-adrenal axis during chronic, alternate day treatment with glucocorticoids is central, whereas the adrenal glands appear to remain functionally unaffected.

Blood pressure responses to ACTH and adrenaline infusions in dogs.

The hypothesis that interactions between adrenaline and adrenal cortical hormones may increase arterial blood pressure has been examined in trained dogs with chronically indwelling aortic and venous catheters. The dogs received continuous infusions for 4 days of ACTH (400 micrograms/day), or adrenaline (8 mg/day) or both ACTH and adrenaline, or saline vehicle. Compared to pre-infusion control values, ACTH raised mean arterial pressure by 14.9 +/- 2.2 mmHg by the 4th day of infusion, adrenaline infused alone had no effect (-0.2 +/- 3.9 mmHg), and ACTH and adrenaline infused together raised pressure 13.1 +/- 3.2 mmHg (not significantly different to ACTH alone). ACTH increased water consumption, Na+ and K+ excretion and creatinine clearance by the 4th day of infusion and these effects were not significantly altered when adrenaline was also infused. Thus adrenaline did not potentiate the hypertension produced by ACTH administration.

Brain shrinkage and subdural effusion associated with ACTH administration

Sequential computed tomographic (CT) studies of 11 patients (aged five months to seven years) with intractable epilepsy treated with synthetic ACTH-Z showed brain shrinkage in all cases. Brain shrinkage started to appear on daily ACTH injections for seven days, reached the maximum within four weeks of administration (14 injections every day and then 7 injections every other day), and almost returned to the original status in seven out of nine cases which were followed up for one to three months after the therapy. The subjects aged less than two years showed more remarkable brain shrinkage than did those aged more than five years. Furthermore, two other cases were complicated by subdural effusion after ACTH therapy. It is the authors' assumption that both of these phenomena are caused by the high concentration of corticosteroid through a change of the water and electrolyte contents in the brain.

Interactive effects or ACTH and growth hormone on adrenocortical hormone secretion

The effects of ACTH and growth hormone (GH) on adrenocortical hormone secretion were studied in a 13-year-old girl with GH and thyrotropin deficiency but normal ACTH function. Cortisol secretion was measured by the sum of the urinary excretions of tetrahydrocortisol(THF), allotetrahydrocortisol(ATHF), and tetrahydrocortisone(THE). Adrenal androgen secretion was measured by the sum of androsterone(A) and etiocholanolone(E). The patient took a constant daily dose of desiccated thyroid(150mg) during 5 successive periods: 3-day control, 3 days of IM ACTH (0.5mg/kg daily), 12-day post-ACTH control, 6 days of IM human GH (3.5mg daily), and 3 days of ACTH + GH at the previous doses. Control excretion of THF + ATHF + THE was 6.0mg/g creatinine and of A+E was 2.9mg/g creatinine; these values confirm normal endogenous ACTH function. Taking these levels as 100, excretion of ccrtisol and androgen metabolites rose to 240 and 190 respectively during ACTH and decreased to 107 and 105 respectively during the last 3 days of the post-ACTH control period. During the GH period, they fell to 66 and 72 respectively. When ACTH was added to GH, they rose to 170 and 103 respectively. Thus GH given alone depressed secretion of both cortisol and adrenal androgens; this could be due to depression of endogenous ACTH secretion or to interference with the effect of ACTH on the adrenal. The data from the combined GH-ACTH period are compatible with either mechanism.

448 INTERACTIVE EFFECTS OF ACTH AND GROWTH HORMONE ON ADRENOCORTICAL HORMONE SECRETION

The effects of ACTH and growth hormone (GH) on adrenocortical hormone secretion were studied in a 13-year-old girl with GH and thyrotropin deficiency but normal ACTH function. Cortisol secretion was measured by the sum of the urinary excretions of tetra-hydrocortisol (THF), allotetrahydrocortisol (ATHF), and tetra-hydrocortisone (THE). Adrenal androgen secretion was measured by the sum of androsterone (A) and etiocholanolone (E). The patient took a constant daily dose of desiccated thyroid (150 mg) during 5 successive periods: 3-day control, 3 days of I.M. ACTH (0.5 mg/kg daily), 12-day post-ACTH control, 6 days of I.M. human GH (3.5 mg daily),and 3 days of ACTH + GH at the previous doses. Control excretion of THF + ATHF + THE was 6.0 mg/g creatinine and of A + E was 2.9 mg/g creatinine; these values confirm normal endogenous ACTH function. Taking these levels as 100, excretion of cortisol and androgen metabolites rose to 240 and 190 respectively during ACTH and decreased to 107 and 105 respectively during the last 3 days of the post-ACTH control period. During the GH period, they fell to 66 and 72 respectively. When ACTH was added to GH, they rose to 170 and 103 respectively. Thus GH given alone depressed secretion of both cortisol and adrenal androgens; this could be due to depression of endogenous ACTH secretion or to interference with the effect of ACTH on the adrenal. The data from the combined GH-ACTH period are compatible with either mechanism.

Effect of cyproterone acetate on structure of adrenal cortex in hypophysectomized, ACTH treated mice.

Hypophysectomized adult male C57BL/6J mice injected with 0.08 mg/g of cyproterone acetate showed large aggregates of cellular lipid as well as nodular formations in the zona fasciculata of the adrenal cortex. Daily ACTH injections (10 IU) reversed the atrophic changes noted above. At the ultrastructural level, the zona fasciculata and zona reticularis cells exhibited decreased cellular lipid content, proliferated profiles of rough endoplasmic reticulum, an increase in polyribosomes, and an active Golgi apparatus. It is believed that cyproterone acetate inhibited adrenocortical steroidogenesis by interfering with pituitary release of ACTH.

Effects of ACTH and 3?,5?-cyclic purine nucleotides on the morphology and metabolism of normal adult human adrenocortical cells in primary tissue culture

Stereological studies showed that treatment of normal adult human adrenocortical cells in primary culture with ACTH or cyclic-AMP for 2 days results in similar increases in the volume of cells, of the mitochondrial and "membrane space" compartments and of the surface area of the smooth endoplasmic reticulum and mitochondrial cristae, and decrease in the lipid content of the cells. These changes were more marked after 8 days of treatment. Treatment for 2 days with cyclic-GMP had no striking effects on cell ultrastructure, whereas an 8-day treatment led to ultrastructural changes similar to those obtained after 2 days of ACTH- or cyclic-AMP-treatment. A discrete population of untreated cortical cells maintained a slow proliferation that was not effected by exposure to cyclic-GMP, but was significantly increased in cultures treated with ACTH or cyclic-AMP. Radioimmunological studies showed that untreated cortical cells kept secreting progesterone and cortisol and that ACTH, but neither cyclic nucleotide, increased the secretion rate per cell of both hormones. These results assign a major role to cyclic-AMP and a minor one to cyclic-GMP in the mediation of the differentiation-promoting and trophic effects, but not in the steroidogenic effects of ACTH on the human adrenal cortex.

Investigations on the turnover of adrenocortical mitochondria

The effects of chronic administration of ACTH and dexamethasone on the morphology of mitochondria in zona glomerulosa cells of the rat adrenal cortex were investigated by stereological techniques. It was found that the volume of the mitochondrial compartment as well as the surface of the outer and inner mitochondrial membranes were significantly increased or decreased in relation to the number of days of ACTH- or dexamethasone-treatment. In ACTH-administered rats, the average volume of individual mitochondria decreased significantly up to the 6th day of treatment and then showed a conspicuous increase from the 6th to the 15th day, whereas in dexamethasone administered animals this parameter, after a small increase during the first 6 days of treatment, displayed a significant decrease. The number of mitochondria per cell showed a dramatic increase during the first 6 days of treatment with ACTH and continued to increase, but only slightly, with the subsequent treatment. In contrast, this parameter showed a parabolic decrease as a function of the duration of treatment in animals receiving dexamethasone. In the light of evidence showing that dexamethasone blocks ACTH-release, these findings are discussed and interpreted to indicate that ACTH is involved in the maintenance and stimulation of the growth and proliferative activity of mitochondria in rat adrenal zona glomerulosa.

ADRENOCORTICAL RESPONSE UPON REPEATED STIMULATION WITH CORTICOTROPHIN IN PATIENTS LACKING ENDOGENOUS CORTICOTROPHIN SECRETION

ABSTRACT The role played by a normal endogenous corticotrophin secretion in the mechanism by which adrenocortical steroidogenic response to ACTH increases as a result of previous administration of the peptide, was assessed by repeated ACTH administration in 25 patients under prolonged cortico-therapy and in 13 patients with anterior hypophyseal insufficiency. The response to ACTH (250 μg tetracosapeptide iv over 8 h) was evaluated on the basis of changes in plasma cortisol and in the urinary excretion of cortisol and 17-ketogenic steroids. The steroidogenic response to the first ACTH infusion was markedly reduced in these patients when compared to control subjects, or even to subjects on short-term dexametasone. However, in these patients as in normals, acute ACTH administration was followed by a phase, lasting for 3 days at least, during which the steroidogenic response to further ACTH stimulation was increased. When ACTH was infused repeatedly on 4 consecutive days in patients on long-term cortico-therapy, adrenocortical responsiveness was rapidly restored to normal. By contrast, when ACTH was administered every fourth day, a less pronounced enhancement of adrenocortical responsiveness occurred, the secretory activity returning to previous hypo-adrenal state between each stimulation.. These data indicate that the mechanism of amplified adrenocortical response to ACTH does not require continuous endogenous corticotrophin secretion. They further suggest that intermittent corticotrophin therapy may be more adequate in promoting recovery of adrenocortical function on steroid withdrawal than a schedule consisting of daily ACTH administration, since the latter is thought to slow down hypothalamic-pituitary activity because of concomitant sustained enhancement of steroidogenesis.

Role of Adrenal 5a-Reductase Activity in Determining the Responsiveness of Hypophysectomized Rats to ACTH

Studies were conducted to examine the contribution of adrenal 5alpha-reductase to the phenomenon of diminished adrenal "responsiveness" to ACTH after hypophysectomy in rats. Rats hypophysectomized for 1 week secreted small amounts of corticosterone (B), 5alpha-dihydrocorticosterone (DHB) and 3beta,5alpha-tetrahydrocorticosterone (R) acutely after ACTH. Adrenal reductase activity in vitro at that time was high. After replacement with ACTH for 24 h, B,DBH, and R secretion increased slightly. Reductase activity remained high. Treatment with ACTH for 2 days further stimulated secretion of DHB and R but not B. Reductase activity was unaffected. Enzyme activity declined at 3 days concomitant with a proportionately greater increase in B than DHB and R secretion. Only after 7 days of ACTH did B secretion exceed DHB and R output. At that time, reductase activity was still lower. The results establish the functional significance of 5alpha-reductase activity as a regulatory site for the action of ACTH in determining the composition of adrenocortical secretory products in hypophysectomized rats.