Proteolysis of His-Phe-Arg-Trp-Pro-Gly-Pro in the blood and brain of rats in vivo.

The kinetics of the content of His-Phe-Arg-Trp-Pro-Gly-Pro (ACTH (6-9)PGP) and its hydrolysis products in the blood and brain of rats in the case of intranasal administration and intravenous injection of tritiated ACTH(6-9)PGP was studied. The parameters of bioavailability of ACTH(6-9)PGP administered intranasally were higher, indicating certain prospects in the intranasal application in clinical practice. We also found that the factor that determines ACTH(6-9)PGP proteolysis in experiments both in vivo and in vitro is aminopeptidases. The main products of ACTH(6-9)PGP during its metabolism in rats are short peptides and amino acids.

Intranasal application of the melanocortin 4 receptor agonist MSH/ACTH(4-10) in humans causes lipolysis in white adipose tissue.

OBJECTIVE: The melanocortin system has a highly significant role in the hypothalamic regulation of body weight and energy expenditure. In animals, intracerebroventricular infusion of melanocortin receptor 4 (MCR-4) agonists increases basal metabolic rate through activation of the sympathetic nervous system and subsequently reduces food intake. In humans, direct access of MCR-4 agonists to the central nervous system can be achieved by a transnasal route, which leads to weight loss with chronic administration. In the present study, we aimed at investigating the effects of intranasally administered MC4-R agonist MSH/ACTH(4-10) on lipolysis and sympathetic nervous system activity in healthy humans. DESIGN: Healthy normal weight, male volunteers (n=10) received either 10 mg MSH/ACTH(4-10) or placebo intranasally in a double-blinded randomized crossover design. Interstitial glycerol release was assessed by microdialysis in abdominal white adipose tissue (WAT) and in skeletal muscle (SM) of the forearm. Local blood flow, systemic blood pressure, heart rate and muscle sympathetic nerve activity (MSNA) within the superficial peroneal nerve were recorded at rest and after nitroprusside infusion. RESULTS: At 45 min after MSH/ACTH(4-10) administration WAT glycerol concentrations increased by 53.4±19.3% compared with baseline conditions (P<0.05) and remained significantly higher throughout the experiment when compared with placebo (P<0.05) while local glycerol release in SM was not significantly affected. Resting MSNA was not altered by MSH/ACTH(4-10) administration; however, sympathoexcitation by intravenous nitroprusside was markedly elevated (MSH/ACTH(4-10) 569±69% increase to baseline; placebo: 315±64%; P<0.01). CONCLUSION: Intranasally administered MCR-4 agonist MSH/ACTH 4-10 increases both subcutaneous WAT lipolysis and MSNA, which suggests a direct central nervous peptide effect in humans on key factors of human energy metabolism.

Penetration of model hormones through the pericardium in simulated conditions in vivo.

The process of penetration of selected protein-peptide substances including insulin (INS), corticotropin (ACTH), prolactin (PRL) and albumin (reference protein) through the model membrane - pig pericardium was traced. These substances show a wide spectrum of therapeutic effects and diverse physicochemical properties (molecular weight, pI). The model substances penetrated the pericardium in simulated in vivo conditions from 1.0 mg / ml solutions. Based on the results obtained, pharmacokinetic parameters of the permeation process were determined - permeation rate (k), half-life (t50%) and their pharmaceutical availability (AUC [0-24 h]). All tested model substances penetrate the pericardium to different degrees. Within 24 h, they penetrate from 16.8% of albumin to 98.9% of insulin. Corticotropin penetrates 43.8% and PRL 34.2%. The highest availability is achieved with insulin, followed by ACTH, PRL and the lowest content of albumin. The results obtained suggest that the higher molecular weight of model protein-peptide substances, the lower the pericardial penetration (R2 = - 0.700) and availability (R2 = - 0.600), and the longer the half-life (R2 = 0.948).

Physiological and behavioural effects of an intracerebroventricular injection of corticotropin releasing hormone in goats.

This study investigated the effects of an intracerebroventricular (ICV) injection of corticotropin releasing hormone (CRH) on physiological and behavioural responses in goats. In Experiment 1, saline (control) or saline plus 25 microg of ovine CRH was injected into the third ventricle of castrated male goats. CRH increased plasma cortisol (Cor) levels markedly within 15 min, but had little effect on plasma glucose (Glu). Compared with saline injected goats, CRH decreased the total duration of lying behaviour but increased its frequency, and suppressed rumination and self-grooming. In Experiment 2, the effects of an intravenous (IV) injection of human adrenocorticotropic hormone (ACTH) (1-24) (0.1mg) were examined and an IV injection of saline was used as control. ACTH increased plasma Cor levels markedly, but did not change any behaviour compared with controls. It was concluded that CRH mediated the response of the hypothalamus-pituitary-adrenal (HPA) axis and behaviour following stress in goats, although the CRH-induced behavioural changes were independent of the HPA axis and seemed to be the result of direct action within the central nervous system.

Levels of plasma and fecal glucocorticoid metabolites following an ACTH challenge in male and female coyotes (Canis latrans).

Knowledge of endocrine stress responses can be advantageous for understanding how animals respond to their environment. One tool in wildlife endocrinology is to measure the adrenocortical activity as a parameter of disturbance of animals. Fecal glucocorticoid metabolites (GCMs) provide a noninvasive assessment of adrenocortical activity. Using an adrenocorticotropic hormone (ACTH) challenge administered to 28 captive coyotes (Canis latrans), we measured the levels of plasma cortisol, and fecal cortisol and corticosterone metabolites (i.e., GCMs). Our goal was to determine the dose-response in the plasma and fecal samples following the injection and determine if there were effects of sex, age, and time of day. Specifically, animals were anesthetized for ~ 90 min with treatment animals intravenously injected with exogenous ACTH and control animals receiving saline. We collected blood samples prior to injection and at 4 different time points post-injection. We also collected fecal samples 2 days pre- and 2 days post-injection to measure fecal GCMs and determine if an endocrine stress response could be detected in fecal samples. We found a definite response in cortisol levels in the plasma for coyotes to the ACTH challenge. There was a response in fecal corticosterone 1 day post-injection, but the control males showed a similar response indicating a handling effect. Fecal cortisol levels did not indicate a response to the ACTH challenge, and were significantly lower than corticosterone concentrations. We also found significant sex, but not age or diurnal, differences in fecal GCMs. Radioimmunoassays for fecal corticosterone levels appeared to be a reliable indicator of physiological stress in coyotes.

Repository corticotropin injection in multiple sclerosis: an update.

Relapse management is a crucial component of multiple sclerosis care. Acute relapses are defined as new neurological symptoms or worsening of existing symptoms persisting for >24 h that are not attributable to heat, overexertion, or infection. The most commonly used treatment for multiple sclerosis relapse is a 3-5-day course of corticosteroids, primarily intravenous methylprednisolone with or without oral steroid taper. Repository corticotropin injection is also the US FDA-approved option for managing acute relapse, particularly in the patients with inadequate response, intolerability or allergy to corticosteroid treatment; poor venous access; or limited ability to receive home or clinic infusions.

Impaired arginine-vasopressin-induced aldosterone release from adrenal gland cells in mice lacking the vasopressin V1A receptor.

We examined aldosterone release in response to stimulation with arginine-vasopressin (AVP) using adrenal gland cells. AVP caused a significant increase in aldosterone release from the dispersed adrenal gland cells of wild-type mice (V1AR+/+) at concentrations from 0.1 microM to 1 microM. In contrast, AVP-induced aldosterone release was impaired in adrenal gland cells from mice lacking the vasopressin V1A receptor (V1AR-/-), while adrenocorticotropic hormone (ACTH)-induced aldosterone release in V1AR-/- mice was not significantly different from that in V1AR+/+ mice. In addition, a vasopressin V1A receptor-selective antagonist 1-[1-[4-(3-acetylaminopropoxy)benzoyl]-4-piperidyl]-3,4-dihydro-2(1H)-quinolinone (OPC-21268) potently inhibited AVP-induced aldosterone release. Thus, our study clearly demonstrates that AVP-induced aldosterone release from adrenal gland cells is mediated via the vasopressin V1A receptor in mice.

Biological Variability in Serum Cortisol Concentration Post-adrenocorticotropic Hormone Stimulation in Healthy Dogs.

BACKGROUND: The ACTH stimulation has low sensitivity for the diagnosis of hypercortisolism possibly as a result of biological and analytical variability. HYPOTHESIS/OBJECTIVES: To report the components of biological and analytical variability in serum cortisol concentration post-ACTH stimulation ([cortisol]) in healthy dogs. ANIMALS: Fourteen healthy harrier hound dogs. METHODS: The data were extracted from a separate, prospective, randomized, double-blinded, controlled discovery study in which dogs treated with vehicle control and 4 different doses of cortisone acetate (CA) for 7 days had an ACTH stimulation test performed to confirm the dose-dependent effect of CA. The index of individuality (IoI), the critical difference between sequential measurements (CD ), and the number of measurements required to assess the homeostatic set point (HSP) of [cortisol] with confidence intervals (CI) of 90 and 95% were estimated. RESULTS: The IoI was equal to 1.1 and the CD was 3.3 µg/dL (92 nmol/L). The number of measurements required to assess the HSP of [cortisol] with CI of 90 and 95% were 3 and 15, respectively. Additionally, mean [cortisol] was higher in males than in females (13.3 ± 4 µg/dL [366 ± 114 nmol/L] vs. 11.5 ± 2.5 µg/dL [318 ± 65 nmol/L], respectively; P = .046). As expected, treatment with CA resulted in a dose-dependent suppression of [cortisol]. CONCLUSIONS AND CLINICAL IMPORTANCE: False-negative test results in hypercortisolism could occur when [cortisol] is outside of the individual's HSP and within the reference interval. The large CD emphasizes the importance of assessing clinically relevant parameters in the diagnosis and monitoring of HC.

Adrenocorticotropic hormone protects learning and memory function in epileptic Kcna1-null mice.

ACTH, a member of the melanocortin family of peptides, is often used in the treatment of the developmental epileptic encephalopathy spectrum disorders including, Ohtahara, West, Lennox Gastaut and Landau-Kleffner Syndromes and electrical status epilepticus of sleep. In these disorders, although ACTH is often successful in controlling the seizures and/or inter-ictal EEG abnormalities, it is unknown whether ACTH possesses other beneficial effects independent of seizure control. We tested whether ACTH can ameliorate the intrinsic impairment of hippocampal-based learning and memory in epileptic Kcna1-null (KO) mice. We found that ACTH - administered in the form of Acthar Gel given i.p. four times daily at a dose of 4 IU/kg (16 IU/kg/day) for 7days - prevented impairment of long-term potentiation (LTP) evoked with high-frequency stimulation in CA1 hippocampus and also restored spatial learning and memory on the Barnes maze test. However, with this treatment regimen, ACTH did not exert a significant effect on the frequency of spontaneous recurrent seizures. Together, our findings indicate that ACTH can ameliorate memory impairment in epileptic Kcna1-null mice separate from seizure control, and suggest that this widely used peptide may exert direct nootropic effects in the epileptic brain.

The adrenocorticotropin stimulation test: contribution of a physiologically based model developed in horse for its interpretation in different pathophysiological situations encountered in man.

The present study aimed to characterize the adrenal response to ACTH. A model was developed that coupled the nonlinear disposition of cortisol with a physiologically based model for cortisol secretion by the adrenals. It was assumed that the response to ACTH resulted from two mechanisms: a stimulation of the cortisol secretion rate and control of the duration of the secretion. Seven dose levels of ACTH were tested in horses, a species similar to man as regards adrenal function. The main result was that the secretion rate of the adrenal gland can be modelized by a zero order process that is maximal for a relatively low dose of ACTH (0.1 microg/kg). Beyond this dose, the increasing adrenal gland response is only due to the prolongation of the time of its secretion. The consequences of these different features were explored by simulation to reproduce classical pathophysiological situations encountered in man. Our model was able to reproduce and simply explain many adrenal gland responses that are dimmed by the different nonlinearities of the system.

Intramuscular administration of a low dose of ACTH for ACTH stimulation testing in dogs.

OBJECTIVE: To compare adrenal gland stimulation achieved following administration of cosyntropin (5 microg/kg [2.3 microg/lb]) IM versus IV in healthy dogs and dogs with hyperadrenocorticism. DESIGN: Clinical trial. Animals-9 healthy dogs and 9 dogs with hyperadrenocorticism. PROCEDURES: In both groups, ACTH stimulation was performed twice. Healthy dogs were randomly assigned to receive cosyntropin IM or IV first, but all dogs with hyperadrenocorticism received cosyntropin IV first. In healthy dogs, serum cortisol concentration was measured before (baseline) and 30, 60, 90, and 120 minutes after cosyntropin administration. In dogs with hyperadrenocorticism, serum cortisol concentration was measured before and 60 minutes after cosyntropin administration. RESULTS: In the healthy dogs, serum cortisol concentration increased significantly after administration of cosyntropin, regardless of route of administration, and serum cortisol concentrations after IM administration were not significantly different from concentrations after IV administration. For both routes of administration, serum cortisol concentration peaked 60 or 90 minutes after cosyntropin administration. In dogs with hyperadrenocorticism, serum cortisol concentration was significantly increased 60 minutes after cosyntropin administration, compared with baseline concentration, and concentrations after IM administration were not significantly different from concentrations after IV administration. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that in healthy dogs and dogs with hyperadrenocorticism, administration of cosyntropin at a dose of 5 microg/kg, IV or IM, resulted in equivalent adrenal gland stimulation.

[Kinetics of Semax penetration into the brain and blood of rats after its intranasal administration].

The radioactive peptide analogue Semax corresponding to the ACTH(4-10) sequence (Met-Glu-His-Phe-Pro-Gly-Pro) with a molar radioactivity of 56 Ci/mmol labeled with tritium at the C-terminal Pro was prepared. The labeled peptide was used for studying the kinetics of Semax penetration into rat brain and blood after its intranasal administration (50 microg/kg, 20 microl of solution) to nonbred white rats of body mass 200-250 g. It was demonstrated that 0.093% of the total introduced radioactivity per gram can be found in the rat brain 2 min after the administration, 80% of this radioactivity belonged to Semax, and the rest, to its metabolites. The peptide undergoes rapid enzymatic degradation, with the tripeptide Pro-Gly-Pro prevailing in biological samples relative to the total content of Semax and its metabolites.

[Evenly tritium-labeled peptides and their in vivo and in vitro biodegradation].

Biologically active peptides evenly labeled with tritium were used for studying the in vitro and in vivo biodegradation of the peptides. Tritium-labeled peptides with a specific radioactivity of 50-150 Ci/mmol were obtained by high temperature solid phase catalytic isotope exchange (HSCIE) with spillover tritium. The distribution of the isotope label among all amino acid residues of these peptides allows the simultaneous determination of practically all possible products of their enzymatic hydrolysis. The developed analytical method includes extraction of tritium-labeled peptides from organism tissues and chromatographic isolation of individual labeled peptides from the mixture of degradation products. The concentrations of a peptide under study and the products of its biodegradation were calculated from the results of liquid scintillation counting. This approach was used for studying the pathways of biodegradation of the heptapeptide TKPRPGP (Selank) and the tripeptide PGP in blood plasma. The pharmacokinetics of Selank, an anxiolytic peptide, was also studied in brain tissues using the intranasal in vivo administration of this peptide. The concentrations of labeled peptides were determined, and the pentapeptide TKPRP, tripeptide TKP, and dipeptides RP and GP were shown to be the major products of Selank biodegradation. The study of the biodegradation of the heptapeptide MEHFPGP (Semax) in the presence of nerve cells showed that the major products of its biodegradation are the pentapeptide HFPGP and tripeptide PGP. The enkephalinase activity of blood plasma was studied with the use of evenly tritium-labeled [Leu]enkephalin. A high inhibitory effect of Semax on blood plasma enkephalinases was shown to arise from its action on aminopeptidases. The method, based on the use of evenly tritium-labeled peptides, allows the determination of peptide concentrations and the activity of enzymes involved in their degradation on a tg scale of biological samples both in vitro and in vivo.

Use of compounded adrenocorticotropic hormone (ACTH) for adrenal function testing in dogs.

Serum cortisol concentrations were measured in five healthy dogs in response to five adrenocorticotropic hormone (ACTH) preparations. Cortisol concentrations were similar at time 0 (pre-ACTH) and at 30 and 60 minutes after injection of all forms of ACTH. However, at 90 and 120 minutes post-ACTH, serum cortisol concentrations were significantly lower following injection of two compounded forms of ACTH. The data showed that injection of four compounded forms of ACTH caused elevations in serum cortisol concentrations of a similar magnitude as cosyntropin in samples collected 60 minutes after administration; but concentrations at later times varied, depending on the type of ACTH used.

Rhesus monkey model for concurrent analyses of in vivo selectivity, pharmacokinetics and pharmacodynamics of aldosterone synthase inhibitors.

INTRODUCTION: In vivo profiles of aldosterone synthase inhibitors (ASIs) have been investigated utilizing various rodent models. Due to lack of CYP17 activity, rodents produce corticosterone rather than cortisol as that of humans, which raised concern to their effectiveness in translational pharmacological characterization of ASI. METHODS: A rhesus monkey model that combines a low sodium diet with adrenocorticotropin (ACTH) treatment was developed. Plasma concentrations of steroid metabolites associated with reactions catalyzed by CYP11B2 and CYP11B1 were measured concurrently by a UPLC/MS method. RESULTS: Plasma concentration of aldosterone in regular diet fed rhesus monkeys was low at 109pg/mL. Aldosterone concentrations were increased to 252pg/mL when animals were maintained on a low sodium diet for 3weeks, and to 300pg/mL with ACTH treatment at 0.3mg/kg. The combination of low sodium diet with ACTH treatment further increased plasma concentration of aldosterone to 730pg/mL and other steroid metabolites at various levels. Intravenous administration of ASI, fadrozole (0.001-1mg/kg) or LCI699 (0.003-3mg/kg), led to dose-dependent reductions in aldosterone and 18-hydroxycorticosterone, increases in 11-deoxycorticosterone and 11-deoxycortisol, and bell-shaped changes in cortisol and corticosterone. In vivo selectivity of CYP11B2/CYP11B1 for fadrazole was 26-fold and LCI-699 was 27-fold, which was consistent with relative selectivity using in vitro values from recombinant cells transfected with rhesus monkey CYP11B2 and CYP11B1. DISCUSSION: This model enables concurrent characterization of pharmacokinetics, pharmacodynamics and selectivity of CYP11B2 over CYP11B1 inhibition in the same animal. It may be used as a translational model for pharmacological characterization of ASI.

Adrenocorticotropin stimulation of aldosterone: prolonged continuous versus pulsatile infusion.

Continuous iv administration of ACTH leads to a sustained stimulation of cortisol but a transient stimulation of aldosterone followed by a decline to prestimulation levels by 72 h. Since CRH and ACTH are released in a pulsatile pattern in man, this study sought to investigate whether pulsatile administration of alpha-cosyntropin-(1-24) would lead to the maintenance of aldosterone stimulation over time. Eight normal male subjects on a 10-meq sodium, 100-meq potassium diet received both a continuous and a pulsatile (0.33 U ACTH/pulse over 15 min, pulsed every 2 h) infusion of cosyntropin (4 U/24 h) for 48 h (n = 4) or 72 h (n = 4). Aldosterone and cortisol were sampled every 6 h, and PRA and angiotensin-II every 24 h. Continuous infusion led to a stimulation of aldosterone followed by a progressive decline to preinfusion levels by 72 h [preinfusion 29 +/- 5 ng/dL (810 +/- 139 pmol/L); 72 h, 38 +/- 10 ng/dL (1054 +/- 277 pmol/L); P = 0.40]. Pulsatile infusion led to a stimulation of aldosterone which was maintained up to 72 h [preinfusion 33 +/- 7 ng/dL (915 +/- 194 pmol/L); 72 h, 85 +/- 13 ng/dL (2358 +/- 361 pmol/L); P less than 0.05]. Regression analysis of aldosterone (y) over time (x) from the peak level at 18 h for the continuous infusion showed a significant negative relation (r = 0.63; P = 0.001), indicating a progressive decline in aldosterone. However, for the pulsatile infusion, there was no relation (r = 0.02; P = 0.85), indicating maintenance of aldosterone levels. There were no significant differences in sodium, potassium, PRA, angiotensin-II, or cortisol between infusions to explain these differences in aldosterone levels. Therefore, pulsatile infusion of cosyntropin maintains aldosterone secretion over time.

Lipoxygenase products as common intermediates in cyclic AMP-dependent and -independent adrenal steroidogenesis in rats.

Aldosterone secretion from adrenal glomerulosa cells can be stimulated by angiotensin II (AII), extracellular potassium and ACTH. Mitochondria from these cells respond to intracellular factors generated by AII (cyclic AMP (cAMP)-independent steroidogenesis) and ACTH (cAMP-dependent steroidogenesis), suggesting that the two-signal-transduction mechanisms are linked by a common intermediate. We have evaluated this hypothesis by stimulating mitochondria from the unstimulated zona glomerulosa with a subcellular post-mitochondrial fraction (PMF) obtained from the zona glomerulosa after stimulation with AII or from the fasciculata gland after stimulation with ACTH; the subcellular fractions were also tested on mitochondria from fasciculata cells. PMFs obtained after incubation of adrenal zona glomerulosa with or without AII (0.1 microM) or ACTH (0.1 nM) were able to increase net progesterone synthesis 4.5-fold in mitochondria isolated from unstimulated rat zona glomerulosa. AII-pretreated PMFs from the zona glomerulosa also stimulated steroidogenesis by mitochondria from zona fasciculata cells. Separate experiments showed that inhibitors of arachidonic acid release and metabolism (bromophenacyl bromide, nordihydroguaiaretic acid, caffeic acid or esculetin) blocked corticosterone production in fasciculata cells stimulated with ACTH, suggesting that arachidonic acid could be the common intermediate in the actions of AII and ACTH on steroid synthesis. Evidence to support this concept was obtained from experiments in which the formation of an activated PMF by treatment of zona fasciculata with ACTH was blocked by the presence of the same inhibitors. Moreover, the inhibitory effects of these substances on PMF activation by ACTH were overcome by exogenous arachidonic acid and, in addition, arachidonic acid release was stimulated by ACTH.(ABSTRACT TRUNCATED AT 250 WORDS)

Nasal administration of an ACTH(4-9) peptide analogue with dimethyl-beta-cyclodextrin as an absorption enhancer: pharmacokinetics and dynamics.

1. The systemic absorption and the neurotrophic effect of the metabolically stabilized ACTH (4-9) analogue, Org2766, were investigated following intranasal (i.n.) administration. 2. Without additives the nasal bioavailability of the peptide was in the order of 15 and 10% in rats and rabbits, respectively. The absorption could be improved by addition of a variety of absorption enhancers to the nasal preparation. The beta-cyclodextrin derivative, dimethyl-beta-cyclodextrin (DM beta CD) at a concentration of 5% (w/v) improved the absorption in rats about 5 fold from 13 +/- 4% (mean +/- s.d.) for administration of the peptide alone to 65 +/- 21%, and in rabbits 1 to 2 fold, from 10 +/- 6% to 17 +/- 8%. 3. The increased permeability of the rat nasal mucosa for Org2766 caused by DM beta CD in rats reversed substantially within 1 h. However, the nasal absorption had not yet completely returned to the level without enhancer. 4. S.c. administered Org2766 accelerated the functional recovery from peripheral nerve damage in rats. However, the peptide did not facilitate nerve repair following i.n. administration with DM beta CD, in spite of the fact that Org2766 was well absorbed. I.v. injection of Org2766 was also ineffective.

Kinetics of radiolabeled adrenocorticotropin hormone in infant and weanling rats.

Unlike the adult animal, the developing rat has a diminished ability to activate and inhibit the hypothalamic pituitary adrenal axis. In general, a gradual ACTH and corticosterone response to stressors appear after postnatal day 10 and is well established to adult level by weaning age. Although at this age the peak ACTH level is comparable to that of the adult, ACTH levels remain elevated for a longer period of time. The purpose of this study was to investigate the possibility that ACTH metabolism can, in part, explain this prolonged ACTH elevation after a challenge. The plasma half life of disappearance (t1/2, the apparent volume of distribution and metabolic clearance rate (MCR) were determined after injection of a tracer dose of 3-I125-Iodotyrosyl23 ACTH1-39 in rats at 14 and 25 days of age. An adult animal group (65 days old) was used for comparison. The t1/2 for ACTH decreases with age (14 day old = 7.47 +/- 0.9 min; 25 day old = 6.48 +/- 0.4 min; adult = 4.46 +/- 0.2 min) while the volume of distribution remains constant. The MCR is also decreased in the young animals (14 day old = 1.5 +/- 0.19 min; 25 day old = 1.6 +/- 0.18 min; adult = 3.0 +/- 0.56 min). For the first time, it is established that the young animals require longer to clear ACTH from an equivalent volume of blood when compared to the adult. Thus, the kinetic properties of ACTH are different in the developing animal and this partly explains the prolonged ACTH elevation observed after stress challenges.

Brain transfer of a new neuromodulating ACTH analog, ebiratide, in rats.

The transfer of ebiratide into the brain was examined in rats. Its brain levels after intravenous administration (2-20 mg/kg), determined by radioimmunoassay, peaked at 5 min and declined almost in parallel with the plasma levels. Brain/plasma ratios (B/P) were constantly about 0.05 ml/g at all doses. Brain distribution study at 5 min after 125I-ebiratide at an effective dose (0.4 microgram/kg) revealed that unchanged ebiratide had larger B/P than the metabolites and region selectivity. The combined use with unlabeled ebiratide resulted in marked decreases in B/P, particularly in the hippocampus, suggesting a specific uptake of this peptide.