Failure of cyclo (His-Pro) to exhibit natriuretic activity

Administration of exogenous cyclo (His-Pro) to dogs has been reported to elicit natriuresis. In contrast, our data fail to show any natriuretic activity of cyclo (His-Pro) in dogs or rats. The possible reasons underlying this discrepancy are discussed.     

Increased cerebrospinal fluid cyclo(His-Pro) content in schizophrenia.

Cyclo(His-Pro) (CHP) is a peptide endogenous to human brain and cerebrospinal fluid (CSF). In animal studies administration of exogenous CHP augments dopaminergic neurotransmission. To explore the role of this peptide in schizophrenia, a disease characterized by a hyperdopaminergic state, we have measured CSF CHP levels in control, never-medicated schizophrenics and medicated schizophrenics. Our data show a 53% increase in CSF levels of CHP in never-medicated schizophrenics (p = 0.015), and a 25% increase in medicated schizophrenics when compared to controls. We speculate that CHP may contribute to the expression of hyperdopaminergic symptoms in schizophrenia.     

Could dietary proteins serve as cyclo(His-Pro) precursors?

Cyclic dipeptides or diketopiperazines are readily generated during in vitro hydrolysis of proteins and polypeptides. This led us to examine whether cyclo(His-Pro) (CHP), a diketopiperazine containing histidine and proline, could be formed in vivo from dietary proteins. The data presented here show that at least in rat, neither urinary nor plasma concentration of CHP is elevated by consumption of a diet rich in proteins. Several dietary supplements derived from casein and/or soy protein hydrolysates, however, contain high levels of CHP-LI. Oral intake of one such supplement led to a sharp increase in the plasma level of CHP-LI.     

Distribution and characterization of cyclo (His-Pro)-like immunoreactivity in the human gastrointestinal tract

Cyclo (His-Pro) [C(HP)] has been measured by radioimmunoassay in perchloric acid extracts of human gastrointestinal (GI) tract structures derived from autopsy sources and fresh colonic biopsies. C(HP) was identified in all regions of the human GI tract, ranging in concentrations from 599 +/- 102 pg/mg protein in stomach, to 127 +/- 26 pg/mg protein in esophagus. The mean concentration of C(HP) from colonic biopsies was 335 +/- 30 pg/mg protein, statistically similar to values derived from postmortem sources. Since C(HP) concentrations are within the range of other gut peptide modulators, cyclo (His-Pro) is speculated to play a role as a new paracrine modulator of human GI tract function(s).     

Fasting and feeding-associated changes in cyclo(His-Pro)-like immunoreactivity in the rat brain

This study examined the efflux of endogenous serotonin and substance P-like immunoreactive material into in vivo superfusates of the rat spinal cord under quiescent conditions and during the addition of either capsaicin or p-chloroamphetamine to the superfusate. Using a method which permitted concurrent measurement of serotonin and substance P-like immunoreactive material in the same sample of superfusate, it was found that capsaicin increased the efflux of substance P-like immunoreactive material from the spinal cord but did not alter the efflux of serotonin. Conversely, the addition of p-chloroamphetamine caused the efflux of serotonin from the spinal cord to increase, but did not affect the efflux of substance P-like immunoreactive material.     

Neuropeptide-dopamine interactions. I. Dopaminergic mechanisms in cyclo(His-Pro)-mediated hypothermia in rats

Administration of cyclo(His-Pro) to rats produces a dose-dependent hypothermia that is attenuated by dopaminergic antagonists. Chronic treatment with cyclo(His-Pro) potentiates hypothermia induced by apomorphine. These results suggest that cyclo(His-Pro) acts via a dopaminergic mechanism to modulate body temperature.     

The distribution of Histidyl-Proline Diketopiperazine [cyclo(His-Pro)] in discrete rat hypothalamic nuclei

The distribution of Histidyl-Proline Diketopiperazine [cyclo(His-Pro)], a metabolite of thyrotropin-releasing hormone (TRH), was determined by specific RIA in Palkovits micropunch pools derived from discrete hypothalamic nuclei. Highest concentrations of cyclo(His-Pro) were identified in the anterior nucleus (3.5 ng/mg protein) and the paraventricular nucleus (2.95 ng/mg protein), while lower concentrations of cyclo(His-Pro) were seen in the other 6 nuclei. In contrast, TRH concentrations were highest in the ventromedial nucleus pars medialis (3.2 ng/mg protein) and arcuate nucleus (2.7 ng/mg protein). This qualitatively different distribution of cyclo(His-Pro) from that of TRH suggests that not all of cyclo(His-Pro) is derived exclusively from TRH.     

Effects of two diketopiperazines, cyclo (His-Pro) and Cyclo (Asp-Phe), on striatal dopamine: A microdialysis study

The effects of two diketopiperazines, Cyclo (His-Pro) (CHP) and Cyclo (Asp-Phe) (CAP), on striatal extracellular levels of dopamine (DA), dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), and 5-hydroxyindoleacetic acid (5-HIAA) were examined using in vivo microdialysis in anaesthetized rats. Treatment with neither CHP (0.1–10 mg/kg IP and 0.3 mg/kg IV) nor CAP (0.1–10 mg/kg IP and 10 mg/kg PO) significantly changed the efflux of DA, DOPAC, HVA, or 5-HIAA when compared to the effects of treatment with saline. Our results suggest that systemic administration of CHP or CAP alone does not modify striatal dopaminergic neurotransmission. The previous findings of enhanced DA release by systemic administration of thyrotropin releasing hormone (TRH) are probably not explained by formation of CHP from TRH.     

Distribution of histidyl-proline diketopiperazine [cyclo (His-Pro)] and thyrotropin-releasing hormone (TRH) in the primate central nervous system

The concentrations of cyclo (His-Pro) and its precursor, thyrotropin-releasing hormone (TRH) were measured in 47 different loci of monkey brain using specific radioimmunoassays. Cyclo (His-Pro) concentrations were higher than those of TRH in all loci excepting the hypothalamus, where TRH concentration was found to be the highest of all the loci and twice those of cyclo (His-Pro). The high levels of cyclo (His-Pro) were seen within the cerebellar system (inferior olivary nucleus>nucleus interpositus>fastigial nucleus>posterior vermis). The great variations in TRH-cyclo (His-Pro) ratios among different loci suggest that other factors in addition to TRH concentration must play roles in determining the unique distribution pattern of cyclo (His-Pro) in the primate brain.     

Acute tetrodotoxin-induced neurotoxicity after ingestion of puffer fish

This study documents the effects of puffer-fish poisoning on peripheral nerve. Excitability measurements investigated membrane properties of sensory and motor axons in four patients. The median nerve was stimulated at the wrist, with compound muscle potentials recorded from abductor pollicis brevis and compound sensory potentials from digit 2. Stimulus-responses, strength-duration time constant (tau(SD)), threshold electrotonus, and current-threshold relations were recorded. The urine of each patient tested positive for tetrodotoxin. Compared with controls, axons were of higher threshold, compound muscle action potentials and compound sensory nerve action potentials were reduced in amplitude, latency was prolonged, and tau(SD) was reduced. In recovery cycles, refractoriness, superexcitability, and late subexcitability were decreased. Threshold electrotonus of motor axons exhibited distinctive abnormalities with less threshold decline than normal on depolarization and greater threshold increase on hyperpolarization (p < 0.0005 for each patient). The changes in excitability were reproduced in a mathematical model by reducing sodium (Na(+)) permeabilities by a factor of two. This study confirms that the neurotoxic effects of puffer-fish poisoning can be explained by tetrodotoxin blockade of Na(+) channels. It demonstrates the ability of noninvasive nerve excitability studies to detect Na(+) channel blockade in vivo and also the utility of mathematical modeling to aid interpretation of altered excitability properties in disease.     

Hormone and metabolite plasma levels after oral glucose in bulimia and healthy controls

Bulimia patients claim to crave sweets and since as clinical evidence suggests that the food consumed during eating binges often contains large amounts of carbohydrates, hormones involved in carbohydrate metabolism might be affected in bulimia. We therefore performed a 4-hr glucose tolerance test (GTT), using 100 g oral glucose and inquired about attitudes toward sweets. Thirteen female patients, with a mean age of 23.3 years, who had had bulimia from 3 to 7 years but whose binge-eating/vomiting behavior was largely controlled at the time of testing, were compared to 14 age-matched healthy female controls with a mean age of 24.4 years. All bulimic patients and most controls had liked sweets as children and still liked sweets. Significantly more bulimic patients than controls stated they overate on sweets and avoided sweets. Glucose utilization and the insulin, glucagon, growth hormone (GH), and pancreatic polypeptide (PP) response curves in the bulimic patients were within the normal range. Fasting plasma levels of glucose, insulin, glucagon, GH, cortisol, free fatty acids (FFA), and PP were not different from controls. There was a trend in bulimic patients to have lower plasma FFA levels and higher plasma cortisol levels during the GTT than controls. The findings suggest that, given body weight maintenance and adequate nutrition, patients with bulimia nervosa have normal glucose tolerance and normal hormonal responses following an oral glucose load.     

Acute neurotoxicity after trichloroethylene ingestion. Case report

Trichloroethylene (TCE), a solvent widely used in the chemical industry, in dry cleaning because of its degreasing action and as a household grease remover, is known to have a toxic action, especially on the nervous system. Cases of intoxication, acute and chronic, due to inhalation, are reported. We report a case, certainly an unusual one, of acute oral intoxication.

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Sommario Viene presentato un caso di intossicazione acuta da ingestione orale di tricloroetilene. Sintomi da interessamento del Sistema Nervoso Centrale sono comparsi a distanza di 2–3 ore. In prima giornata si documentavano anche turbe della conduzione cardiaca e in seconda giornata l'esame EMG dimostrava la presenza di una polineuropatia assonale distale.

     

Acute encephalopathy after ingestion of "sugihiratake" mushroom]

An outbreak of acute encephalopathy has occurred among patients with renal dysfunction after ingestion of "sugihiratake" mushroom (angel's wings mushroom) in the northern area of Japan between the end of September and the middle of October in 2004. Most of the patients had varying degree of renal dysfunction. Patients initially presented with asthenia in legs, shaking limbs, and difficulty in ambulation. Several days later, tremor-like involuntary movements or myoclonus developed, which were frequently followed by intractable status epilepticus. Eleven patients were dead. CSF examination showed elevated protein levels without pleocytosis. Brain CT and MRI studies revealed abnormal signal intensities in bilateral external capsule and claustrum, and in the cortical white matter. All of the patients had a history to have ingested sugihiratake in varying quantities and frequencies prior to the onset of the illness. Although no similar patients have been reported in the past, this edible mushroom must have induced acute toxic encephalopathy. The characteristic features of clinical signs and symptoms, and laboratory findings of this encephalopathy were briefly summarized.     

Time course of saliva and serum melatonin levels after ingestion of melatonin

Abstract Salival and serum melatonin levels after melatonin ingestion were measured by gas chromatography-mass spectrometry. Ingestion of 3 mg melatonin caused a marked increase in serum melatonin (3561 ± 1201 pg/mL) within 20 min, followed by a gradual decrease, but the level still remained higher than the basal level at 240 min after the ingestion. The saliva melatonin 60 min after the ingestion showed the highest level (1177 ± 403 pg/mL) which was one-third of the plasma level. The saliva melatonin level was highly correlated with the serum level throughout the experimental period ( r = 0.82, P = 0.0001). These data indicate that the measurement of saliva melatonin level may be a suitable indicator for the melatonin secretion into general circulation.     

Cyclo (His-Pro): Mapping hypothalamic sites for its hypothermic action

Hypothalamic loci of Sprague-Dawley rats were individually injected with cyclo (His-Pro) to determine the sites where that metabolite of thyrotropin-releasing hormone acts to produce hypothermia. There was almost always a positive hypothermic response in the preoptic-anterior hypothalamic area (POA/AHA); injection into the posterior or middle hypothalamic areas or into the hippocampus caused no significant decrease in core temperature. The fact that only injection into the POA/AHA evoked hypothermia suggests that this area is a major hypothalamic site of action of cyclo (His-Pro) in modulating thermoregulation in the rat.     

Regional alterations in glucose consumption and metabolite levels during postischemic recovery in cat brain

Local CMRgl (LCMRgl) and metabolite levels were measured in the same tissue samples following 4 h of recirculation after 1 h of occlusion of the middle cerebral artery in the cat. The rate of glucose utilization was calculated using direct measurement of tissue deoxyglucose-6-phosphate and using a "lumped" constant corrected in each sample for alterations in tissue glucose. Increased LCMRgl (compared with that in sham-operated animals) occurred in regions with only minor alterations in levels of lactate and phosphocreatine. By contrast, LCMRgl was markedly depressed in regions with major changes in lactate and high-energy phosphates. Interestingly, tissue levels of glucose and unphosphorylated deoxyglucose were abnormally elevated in regions with profound energy failure. These results indicate an inhibition of glucose utilization in regions damaged by ischemia, despite the persistent elevation of tissue lactate. Increased glucose metabolism at 4 h post ischemia was detected only in areas with minor anaerobic alteration of metabolite levels.     

Cyclo(His-Pro): its distribution, origin and function in the human

Cyclo(His-Pro), or histidyl-proline diketopiperazine, is a cyclic dipeptide endogenous to blood, cerebrospinal fluid (CSF), semen, brain, spinal cord, and gastrointestinal tract of humans. Although a part of cyclo(His-Pro) clearly appears to be derived from the limited proteolysis of thyrotropin-releasing hormone by Pyroglutamate aminopeptidase, the biosynthetic origin of the remainder of the peptide can only be speculated. The levels of this peptide in blood and CSF fluctuate in health and disease in a manner appropriate for a physiologically active endogenous molecule.