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

A new endogenous form of PYY isolated from canine ileum: Gly-extended PYY(1-36)

We purified and identified the peptide YY (PYY) forms present and determined their levels from a portion of the canine ileum directly adjacent to the cecum by a new extraction method designed to prevent and evaluate degradation of endogenous peptides. We used three reverse phase chromatography steps with radioimmunoassay of fractions for PYY-like-immunoreactivity (PYY-LI). The purified fractions underwent intact protein/peptide mass spectrometry identification and sequencing (i.e. "top-down" MS analysis). This analysis confirmed the identity of a new form of PYY, PYY(1-36)-Gly, which co-elutes with PYY(1-36)-NH(2) through all three of separation steps used. The PYY(1-36)-Gly form represents approximately 20% of the total PYY found in this region of the canine intestine. In addition, we also found that the PYY(3-36)-NH(2) form represents 6% of the total PYY in the canine ileo-cecal junction. The physiological implication of the Gly-extended form of PYY(1-36) warrants further investigation.

Adrenocorticotropic hormone secretion in rats induced by stimulation with serotonergic compounds. hsj@mfi.ku.dk

The serotonin receptors involved in the secretion of adrenocorticotropin hormone (ACTH) were investigated in conscious adult male rats. Administration of serotonin (5-HT), 5-hydroxytryptophan (5-HTP) in combination with the serotonin reuptake inhibitor fluoxetine (Flx), or of the 5-HT agonists 8-OH-DPAT (5-HT1A), 5-carboxamido-tryptamine (5-HT1A+1B+5A+7), RU 24969 (5-HT1B+1A), DOI (5-HT2A+2c), S-alpha-methyl-5-HT (5-HT2A+2B+2c), MK212 (5-HT2B+2c), or methyl-chlorophenyl-piperazine (5-HT2A+2c) dose-dependently stimulated ACTH secretion. The 5-HT3 agonist 2-methyl-5-HT had no effect. Administration of a 5-HT1 agonist in combination with any of the 5-HT2 agonists DOI, S-alpha-methyl-5-HT or MK212 had an additive effect on the plasma concentration of ACTH. The ACTH stimulating effect of each of the 5-HT agonists was inhibited by pretreatment with antagonists with corresponding 5-HT receptor affinity. The ACTH response to 5-HT or 5-HTP/Flx was inhibited by injection with the 5-HT1A+2A+2c+5A+7 antagonist methysergide, the 5-HT2A antagonist ketanserine and the 5-HT2C+2A antagonist LY 53857. The 5-HT1A antagonist WAY 100635 enhanced 5-HT- and 5-HTP/Flx-induced ACTH secretion, suggesting a presynaptic 5-HT1A autoreceptor effect of the drug. The 5-HT3 antagonist ondansetrone had no effect on the either of the 5-HT agonists. The 5-HT3+4 antagonist tropisetrone attenuated the effect of 5-HTP/Flx, which may suggest a stimulation of ACTH secretion via 5-HT4 receptors. It is concluded that 5-HT1A, 5-HT2A+2C, and to a lesser extent 5-HT1B receptors, but not 5-HT3 receptors are involved in the effects of serotonin agonists on ACTH secretion. Furthermore, an involvement of the 5-HT5A and the 5-HT7 receptor is possible.

Serotonergic involvement in stress-induced ACTH release

We investigated the involvement of serotonin (5-HT) and 5-HT receptors in mediation of stress-induced ACTH secretion in adult male rats, which were pretreated by 5-HT antagonists before restraint-, ether-, cold swim-stress or endotoxin. All stressors potently increased plasma ACTH. Lesion of 5-HT neurons with 5, 7-dihydroxytryptamine injected intracerebroventricularly, into the paraventricular nucleus or into the raphe nuclei, inhibited the restraint stress-induced ACTH response by 50%. Restraint increased the content of 5-HT and its metabolite 5-hydroxyindole acetic acid, in the raphe nuclei, whereas the other stressors had no such effect. Pretreatment with the 5-HT1A receptor antagonist WAY 100635 inhibited the restraint stress- and endotoxin-induced ACTH secretion by 50%. The 5-HT1+2 antagonist methysergide or the 5-HT2 antagonist ketanserin inhibited the restraint- or ether stress-induced ACTH response, and eliminated the endotoxin-induced ACTH response. The 5-HT2 receptor antagonist LY 53857 blocked only the endotoxin-induced ACTH response. Pretreatment with the 5-HT3 receptor antagonist ondansetrone had no effect on stress-stimulated ACTH secretion. The 5-HT3+4 receptor antagonist tropisetrone inhibited the restraint- and ether stress-induced response. The ACTH response to swim stress was not affected by any of the antagonists used. It is concluded that the 5-HT1A, the 5-HT2A and the 5-HT2C receptor, but not the 5-HT3 receptor are involved in the stress-induced ACTH secretion. An involvement of the 5-HT4 receptor is possible. Furthermore, that serotonergic neurons in the raphe nuclei are activated during restraint stress, and that these neurons and neurons in PVN of the hypothalamus, are important for the mediation of the restraint stress-induced ACTH response.

Evidence for the paracrine action of islet-derived corticotropin-like peptides on the regulation of insulin release

In view of recent evidence for the endogenous synthesis of proopiomelanocortin (POMC) by pancreatic islets, we have assessed (1) the release of POMC-derived corticotropin (ACTH)-like peptides (ACTH-LP) from isolated perifused rat islets, and (2) the potential paracrine modulatory effect on insulin output of these putative secretagogues. Islets perifused at a glucose concentration of 3.3 mmol/L secreted ACTH-LP at 0.15 +/- 0.005 ng/islet/10 min, which was increased by 17-fold at 16.7 mmol/L glucose. Islets statically incubated with different concentrations of medium glucose plus synthetic 1-39ACTH at 55 pmol/L showed a significant increase of insulin release at 8 (by 79%) and 16 (by 119%) mmol/L glucose, but not at 4 mmol/L. To determine the possible cis-directed effects of these endogenously released islet ACTH-LP on insulin secretion, we either blocked their biological action by immunoneutralization with an ACTH-specific antiserum or prevented their receptor interaction by addition of the ACTH-inhibiting polypeptide (CIP) to the incubation medium. In the presence of 16.7 mmol/L glucose, the rate of insulin output decreased by approximately 25% upon exposure to the antiserum and by approximately 50% in the presence of CIP. The foregoing observations would therefore suggest that both (1) the elaboration of ACTH-LP by isolated perifused islets and (2) the stimulation of islet insulin release by exogenous 1-39ACTH in static incubation occur as a function of glucose concentration in the incubation medium, and that (3) the newly-secreted endogenous ACTH-LP operate in a cis mode to enhance islet insulin output in a manner analogous to that of exogenously added ACTH species. These results strongly support the view that islet-elaborated ACTH-LP are important physiological paracrine modulators of insulin secretion.

Glucose-induced secretion of ACTH-like products by rat pancreatic islets

This work was performed to study the release of proopiomelanocortin (POMC)-derived peptides from isolated pancreatic islets and the effect of ACTH--a member of that peptide family--on insulin secretion. Islets were incubated with 3,3 and 16.6 mM glucose and insulin and ACTH-like products (ACTH-LP) were measured by radioimmunoassay. Glucose stimulated the simultaneous release of insulin and ACTH-LP, the ACTH-LP concentration being higher when assayed with an antibody reacting with the N-terminus of ACTH. However, the increment in this release in the presence of the higher glucose concentration was larger when measured with an antibody against the ACTH mid-portion. Thus, although the islets would release more of a smaller ACTH-LP, 16.6 mM glucose would selectively increase the release of peptides of larger molecular size. Islets incubated with different concentrations of synthetic ACTH (50-500 pg/ml) increased the release of insulin in a dose-dependent manner. These results suggest that the release of endogenous ACTH-LP could contribute to the paracrine regulation of insulin secretion.

Autonomic nervous system function in patients with functional abdominal pain. An experimental study

Functional abdominal pain--that is, pain without demonstrable organic abnormalities--has often been associated with psychologic stress. The aim of the present study was to investigate whether sympathetic nervous system response to laboratory stress and basal parasympathetic neural activity were disturbed in 22 patients with functional abdominal pain (functional group) as compared with 14 healthy controls (healthy group) and 26 patients with organic abdominal pain (organic group) due to duodenal ulcer (DU), gallstones, or urinary tract calculi. Plasma adrenocorticotrophic hormone (ACTH) and serum cortisol measurements were included, to assess the pituitary-adrenocortical axis. Heart rate, systolic blood pressure, and plasma adrenaline increased significantly in all groups in response to a stress test (mental arithmetic). Plasma noradrenaline increased in the DU patients only, and plasma ACTH and serum cortisol did not increase at all in any of the groups. As a measure of parasympathetic neural activity, independent of sympathetic neural activity, the beat-to-beat variation of the heart rate was calculated. The functional patients had a significantly higher beat-to-beat variation expressed as the mean square successive differences of the R-R intervals (MSSD), indicating a higher basal parasympathetic neural activity (mean MSSD +/- SEM = 64 +/- 6 msec in the functional group, 46 +/- 6 msec in the healthy group, and 49 +/- 6 msec in the organic group; P = 0.03). A reduced sympathetic neural response as indicated by a lesser stress-induced increment in heart rate, was seen in both patient groups (functional, 13 +/- 2 beats/min; organic, 10 +/- 2 beats/min) as compared with the healthy group (19 +/- 2 beats/min; P = 0.003).(ABSTRACT TRUNCATED AT 250 WORDS)

Endocrine function in patients with Cushing's disease before and after treatment

OBJECTIVE

To estimate the value of some commonly used tests in diagnosing Cushing's disease and to assess the outcome after treatment.

DESIGN

Follow-up of a consecutive group of patients for 4.1 to 109.6 months, median 34.4.

PATIENTS

Forty-six patients assumed to have ACTH dependent hypercorticism (of 50 patients with Cushing's syndrome) were included. Forty-five underwent transsphenoidal neurosurgery. Ten were treated preoperatively with radiotherapy.

MEASUREMENTS

Pituitary, adrenal, thyroid and gonadal function, radiology and pituitary histology were evaluated.

RESULTS

One main finding was a significant correlation between the urinary excretion of cortisol before and during administration of dexamethasone. Thus patients with modestly elevated urinary cortisol excretion had an apparently normal suppression. The urinary cortisol values during the dexamethasone test were significantly related to the peak plasma cortisol concentrations at the 30-minute ACTH tests. Computed tomography failed to identify an adenoma in 10 of the 19 patients who were histologically proved to harbour a corticotroph adenoma. At 6 months after radiotherapy, clinical and biochemical improvement was noted in none. Cure was achieved in 36 after neurosurgery. Eventually, adrenalectomy was needed in eight patients. Sixteen patients developed persisting adrenal insufficiency after neurosurgery so that the total number of patients on permanent steroid substitution was 24. Post-operative thyroid and gonadal insufficiency (in men and women of fertile age) was found in 36 and 49%, respectively.

CONCLUSIONS

The diagnostic value of measuring the cortisol excretion during dexamethasone administration appears doubtful. The outcome after neurosurgical treatment for Cushing's disease is not entirely satisfactory. Further studies are needed to decide whether adrenalectomy as the first line of therapy should be considered relevant in some patients with Cushing's disease.

Autonomic response to an experimental psychological stressor in healthy subjects: measurement of sympathetic, parasympathetic, and pituitary-adrenal parameters: test-retest reliability

A mental arithmetic test (the stressor; 15 min) significantly increased systolic and diastolic blood pressure, heart rate and plasma adrenaline by 11%, 12%, 28% and 152% respectively, with a prompt return to resting values after the test. Plasma noradrenaline and serum cortisol did not increase significantly during the 15 min of stress. Afterwards, however, the concentrations of both hormones increased, resulting in a total and significant increase averaging 19% and 23%, respectively. Plasma adrenocorticotrophic hormone (ACTH) did not rise significantly, but it was only measured before and at the end of the stressor. As a measure of parasympathetic nervous function, the beat-to-beat variation of heart rate, expressed as the mean successive square difference (MSSD), was employed. Four to 14 months later, the investigation was repeated, and resting values of all measures were found to be stable. The increments in systolic blood pressure and heart rate were significantly lower at retest. MSSD at stress, but not at rest, was significantly lower at retest. The mental arithmetic stress test as described here produces a sufficient autonomic response to make it viable for laboratory stress research. However, if repeated examinations are desired, the lower response at retest should be taken into consideration.

Amidated joining peptide in the human pituitary, gut, adrenal gland and bronchial carcinoids. Immunocytochemical and immunochemical evidence

The distribution of the proopiomelanocortin-derivated amidated joining peptide (JP-N) was examined in the human pituitary gland, adrenal gland, gut and in three bronchial carcinoids. Double immunostaining showed coexistence of immunoreactive JP-N and other proopiomelanocortin derivatives, e.g., ACTH, beta-endorphin, Pro-tau-MSH, in the pituitary gland and adrenal medulla. The JP-N immunoreactive cells in the adrenal medulla were identified as a subpopulation of adrenaline-producing cells by means of an antiserum against phenylethanolamine N-methyltransferase. In the gut immunoreactive JP-N was costored with somatostatin in endocrine cells. Using radioimmunoassay, JP-N was found in higher concentrations than ACTH and alpha-MSH in the gut but not in the adrenal gland. Gel chromatography of gastric antrum and adrenal gland extracts showed three and two dominating components of immunoreactive JP-N, respectively, but under reduced conditions most of the immunoreactive material appeared as of low molecular weight in both extracts. In conclusion, immunoreactive JP-N is a major product from the processing of proopiomelanocortin in human extrapituitary tissues. The molecular forms of immunoreactive JP-N correspond to previous findings in the human pituitary gland.

Alpha-melanocyte-stimulating hormone immunoreactivity in human melanoma metastases extracts

Seven human melanoma metastases were extracted in order to check the possible presence of any alpha-melanocyte stimulating hormone (MSH) immunoreactivity. The aim of that study was to provide some explanation for, mainly, two observations that we have already made and reported: 1) increased plasma alpha-MSH levels in melanoma of tumour-bearing patients as compared with tumour-free patients; 2) the presence of specific alpha-MSH receptors on human melanoma cells in culture. We could measure large amounts of immunoreactive alpha-MSH in all tumours ranging from 0.31 to 4.27 pmoles per g of wet tissue. Further identification of the extracted material by high-performance liquid chromatography revealed compounds of higher molecular weight and more hydrophobic than synthetic alpha-MSH. In addition, purified extracts could also displace 125I-labelled alpha-MSH from its cellular binding sites in an alpha-MSH specific radio-receptor binding assay. Our findings would suggest a possible presence of some hormone precursor(s) inside the melanoma tumours.

The trophic responses of avian sensory ganglia in vitro to N-acetylated and des-acetyl forms of alpha-melanocyte stimulating hormone (alpha-MSH) are qualitatively distinct

alpha-Melanocyte-stimulating hormone (alpha-MSH) accelerates the regrowth of peripheral nerve axons in the rat following their transection (Verhaagen et al., Expl Neurol. 92, 451-454, 1986). The cellular mechanisms of this trophic response were investigated for several naturally occurring derivatives of alpha-MSH using Nerve Growth Factor (NGF)-stimulated quail sensory ganglion explants in vitro in which both neurite outgrowth and non-neuronal cell behaviour could be more reliably observed and quantified. Neurite outgrowth was determined with a semi-quantitative scoring assay. Glial migration into the outgrowth was quantified using a monoclonal antibody, GTE-52, which labels the nuclei of Schwann cells. Des-acetyl alpha-MSH caused a marginal increase in the neurite outgrowth density which was significant at concentrations of 0.04 and 0.1 microgram/ml. The response to acetylated (N-acetyl, N,O-diacetyl) forms of alpha-MSH was characterized by fascicle formation by neurites which resulted in an apparent decrease in the neurite score, and by the outgrowth of non-neuronal cells. Using monoclonal antibody GTE-52, which recognizes a glial nuclear antigen, these cells were identified as Schwann cells. N-Acetyl, but not des-acetyl alpha-MSH increased the number of GTE-52-labelled cells in the NGF-stimulated neurite outgrowth and stimulated their migration in the absence of neurites when NGF was omitted from the culture medium. Exposure of growing explants to two polyclonal antibodies against alpha-MSH resulted in an increased neurite outgrowth density. The results support the hypothesis that alpha-MSH peptides stimulate peripheral nerve growth by modulating the neurite sprouting response, and demonstrate that the nature of the neurotrophic response to naturally occurring melanotropins depends on the existence of acyl substitution at the N-terminal amino acid residue. A possible role of endogenous melanotropin peptides in the regulation of sensory nerve growth is discussed.

Proline residues in the maturation and degradation of peptide hormones and neuropeptides

The proteases involved in the maturation of regulatory peptides like those of broader specificity normally fail to cleave peptide bonds linked to the cyclic amino acid proline. This generates several mature peptides with N-terminal X-Pro-sequences. However, in certain non-mammalian tissues repetitive pre-sequences of this type are removed by specialized dipeptidyl (amino)peptidases during maturation. In mammals, proline-specific proteases are not involved in the biosynthesis of regulatory peptides, but due to their unique specificity they could play an important role in the degradation of them. Evidence exists that dipeptidyl (amino)peptidase IV at the cell surface of endothelial cells sequesters circulating peptide hormones which are then susceptible to broader aminopeptidase attack. The cleavage of several neuropeptides by prolyl endopeptidase has been demonstrated in vitro, but its role in the brain is questionable since the precise localization of the protease is not clarified.

Pro-opiomelanocortin-derived peptides in the pig pituitary: alpha- and gamma 1-melanocyte-stimulating hormones and their glycine-extended forms

Pro-opiomelanocortin (POMC)-related peptides in extracts of anterior and neurointermediate pituitary lobes from pigs were characterized by gel chromatography, reversed-phase chromatography and radioimmunoassays. The peptide content was ca. 3-fold greater in the anterior lobe compared to the neurointermediate lobe (19.8 nmol POMC/anterior lobe vs 7.0 nmol/neurointermediate lobe). In the neurointermediate lobe 93% of POMC was processed to alpha-melanocyte-stimulating hormone (alpha-MSH) and analogs exclusively of low molecular weight. Most of the remaining adrenocorticotropic hormone (ACTH)-related material consisted of the glycine-extended intermediate ACTH-(1-14) and analogs. In contrast only one fourth to one third of the N-terminal part of POMC (N-POMC) was processed to amidated gamma-MSH and its C-terminal glycine-extended precursor. The relative amount of amidated gamma-MSH was the same as alpha-MSH and analogs (94%). However, more than 95% of these peptides were of high molecular weight. In the anterior lobe 2.3% of N-POMC was processed and 94% was amidated gamma-MSH of only high molecular weight. These results show that gamma-MSH and alpha-MSH are amidated to the same extent and that gamma 1-MSH and gamma 2-MSH immunoreactivity are present in both the anterior lobe and the neurointermediate lobe. The results suggest that the production of amidated peptides is not regulated by the amidation process itself but at an earlier step (e.g. at the proteolytic cleavage).

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.