ACTH 1-14 (Adrenocorticotropic Hormone Fragment 1-14)

Chronic adrenocorticotrophic hormone treatment alters tricyclic antidepressant efficacy and prefrontal monoamine tissue levels

Several animal models are currently utilised in the investigation of major depressive disorder; however, each is validated by its response to antidepressant pharmacotherapy. Few animal models consider the notion of antidepressant treatment resistance. Chronic daily administration of adrenocorticotropic hormone (ACTH) or corticosterone can alter behavioural responses to antidepressants, effectively blocking antidepressant efficacy. Herein, we demonstrate that ACTH-(1-24) (100μg/day; 14 days) blocks the immobility-reducing 'antidepressant' effects of a single dose of imipramine (10mg/kg) in the forced swim test. This finding was accompanied by altered monoamine tissue levels in the prefrontal cortex (PFC) 1h after exposure to the acute stress of the forced swim test. PFC tissue from ACTH pre-treated animals contained significantly higher serotonin, noradrenaline and adrenaline concentrations relative to saline pre-treated controls. Conversely, dopamine levels were significantly decreased. Altered plasma corticosterone responses to ACTH injections were observed over the treatment course. Measures were taken on treatment days 1, 4, 8, 11, 14 and 15. ACTH administration initially enhanced plasma corticosterone levels, however, these normalised to levels consistent with control animals by day 14. No differences in corticosterone levels were observed across the treatment time course in saline-treated animals. Taken together these results indicate that pre-treatment with ACTH (100μg/day; 14 days) blocks the antidepressant effects of imipramine (10mg/kg), significantly alters key PFC monoamine responses to stress and downregulates glucocorticoid responses. These results suggest that chronic ACTH treatment is a promising paradigm for elucidation of mechanisms mediating antidepressant treatment resistance.

alpha-Melanocyte-stimulating-hormone precursors in the pig pituitary

The occurrence of intermediates from the processing of ACTH-(1-39) [adrenocorticotropic hormone-(1-39)] to alpha-melanocyte-stimulating hormone was investigated in normal pig pituitaries by the use of sensitive and specific radioimmunoassays for ACTH-(1-13), ACTH-(1-14), ACTH-(1-13)-NH2 and ACTH-(1-39). Fractionation by reverse-phase h.p.l.c. revealed ACTH(1-17) and their acetylated analogues. The intermediate lobe contained NO-diacetyl-ACTH-(1-13)-NH2, N-acetyl-ACTH-(1-13)-NH2 and ACTH-(1-13)-NH2. In addition, the corresponding ACTH-(1-14) peptides (the glycine-extended precursor of the amidated peptides) were detected in lower amounts in both the intermediate lobe and the anterior lobe. ACTH-(1-17), ACTH-(1-13) and their acetylated analogues could not be detected in the anterior lobe or the intermediate lobe. The results suggest that an endopeptidase initially cleaves ACTH-(1-39) at the Lys-16-Arg-17 bond. ACTH-(1-16) is then processed by a pituitary carboxypeptidase to ACTH-(1-14) and ACTH-(17-39) by the aminopeptidase to ACTH-(18-39).

The actions of N-terminal fragments of corticotrophin on steroidogenesis in dispersed rat adrenal cells in vitro

The finding that the rat adrenal zona glomerulosa cell shows specific sensitivity to stimulation by alpha-MSH and related peptides has been confirmed both in vivo and in vitro, raising the possibility that alpha-MSH may have a physiological role in the control of glomerulosa function and aldosterone secretion. To define more closely the structural features which confer teh specificity of the glomerulosa response, other ACTH derived peptides have been tested for their specificity of actions on rat adrenal cells in vitro. The peptides tested were ACTH(5-24), ACTH(1-12), ACTH(1-14), ACTH(1-15), ACTH(1-16) and ACTH(1-17). Their actions were compared with those of alpha-MSH and ACTH(1-24). All of the ACTH-derived peptides stimulated glomerulosa corticosterone production with sensitivities similar to that of alpha-MSH; minimum effective concentration was 10 nmol/l. Also, like alpha-MSH, the shorter ACTH peptides stimulated aldosterone production only relatively weakly in these cells from animals on normal sodium intake. Only ACTH(5-24), ACTH(1-16) and ACTH(1-17) stimulated fasciculata/reticularis cells at concentrations up to 1 mumol/1. The actions of all of the shorter peptides were thus unlike those of ACTH(1-24) which stimulates both cell types with approximately equal sensitivity, and which furthermore strongly stimulates aldosterone production. The data suggest that the 18-24 region of the ACTH molecule contains the signal for a fasciculata/reticularis response, and the region 1-13 that for glomerulosa specificity. They confirm the view that, in the rat, alpha-MSH itself may be the specific pituitary glomerulosa-stimulating agent which much experimental work has predicted. They also indicate that synthetic ACTH(1-17) analogues should be used with caution.

Alpha-amidated peptides derived from pro-opiomelanocortin in normal human pituitary

Normal human pituitaries were extracted in boiling water and acetic acid, and the alpha-amidated peptide products of pro-opiomelanocortin (POMC), alpha-melanocyte-stimulating hormone (alpha MSH), gamma-melanocyte-stimulating hormone (gamma 1MSH), and amidated hinge peptide (HP-N), as well as their glycine-extended precursors, were characterized by sequence-specific radioimmunoassays, gel-chromatography, h.p.l.c. and amino acid sequencing. alpha MSH and gamma 1MSH constituted 0.27-1.32% and 0.10-5.10%, respectively, of the POMC-derived products [calculated as the sum of adrenocorticotropic hormone (ACTH)-(1-39), ACTH-(1-14) and alpha MSH immunoreactivity]. alpha MSH and ACTH-(1-14) were only present in non- or mono-acetylated forms. Only large forms of gamma 1MSH and gamma 2MSH were present in partly glycosylated states. The hinge peptides were amidated to an extent two to three orders of magnitude greater than alpha MSH and gamma 1MSH. Most (99%) of the HP-N was of low molecular mass and consisted mainly of HP-N-30. The remaining part was high-molecular-mass HP-N, probably HP-N-108, although the presence of HP-N-44 could not be completely excluded. These results show that all the possible amidated POMC-related peptides are present in normal human pituitary. It also shows that cleavage in vivo at all dibasic amino acids but one, takes place at the N-terminal POMC region; the exception is at the POMC-(49-50) N-terminal of the gamma MSH sequence. The pattern of peptides produced suggests that the generation of amidated peptides is mainly regulated at the endopeptidase level.

Alpha-amidated peptides derived from pro-opiomelanocortin in human pituitary tumours

Human pituitary tumours, obtained at surgery for Cushing's disease and Nelson's syndrome, were extracted and the content and molecular forms of pro-opiomelanocortin (POMC)-derived peptides determined by radioimmunoassay, gel chromatography, reversed-phase high-performance liquid chromatography (HPLC) and sequence analysis. In the tumours from patients with Cushing's disease the mean concentrations of amidated peptides relative to the total amount of POMC were as follows: alpha-MSH, 1.7%; amidated gamma-MSH (gamma 1-MSH), 8.5% and the peptide linking gamma-MSH and ACTH in the precursor (hinge peptide or joining peptide) in its amidated form (HP-N), 17.1%. The same relative concentrations in the tumours from patients with Nelson's syndrome were 8.5% (alpha-MSH), 7.5% (gamma 1-MSH) and 12.2% (HP-N). More than 95% of the ACTH(1-39) immunoreactivity eluted as synthetic ACTH(1-39) by gel chromatography and HPLC. The remaining ACTH(1-39) immunoreactivity eluted as partly glycosylated high molecular weight forms. All the alpha-MSH and its glycine-extended precursor ACTH(1-14) were of low molecular weight, mainly non- or mono-acetylated forms, but significant amounts of diacetylated analogues were also present. gamma 1-MSH and gamma 2-MSH immunoreactivities eluted as high molecular weight forms and were partly glycosylated. No low molecular weight forms of gamma 1-MSH or gamma 2-MSH could be detected in the pituitary tumours. Amidated hinge peptide was mainly of the 30 amino acid form. In conclusion, all the molecular forms of the amidated peptides detected in tumours from patients with Cushing's disease and Nelson's syndrome were similar to the molecular forms found in the normal human pituitary. The main difference between the tumours and the normal pituitary was the greater amount of peptides produced, particularly alpha-MSH and gamma 1-MSH.