Concentration-dependent stimulation of cholinergic motor nerves or smooth muscle by [Nle13]motilin in the isolated rabbit gastric antrum.

In man, rabbit and cat, the effects of motilin and motilides are neurally mediated in vivo, whereas in vitro binding and contractility studies suggest the presence of a smooth muscular receptor. The aim of this study was to investigate in vitro interactions of motilin with the enteric excitatory neurotransmission in the gastric antrum of the rabbit. Circular muscle strips from the pre-pyloric antrum were subjected to electrical field stimulation (1 ms, 1-32 Hz, 10 s train) and muscle twitch responses were recorded isometrically. Induced twitch responses were frequency dependent (1-32 Hz) and entirely neurogenic (tetrodotoxin sensitive). [Nle13]motilin dose-dependently (10[-9]-10[-8] M) enhanced the amplitude of, atropine sensitive, evoked contractions. At 4 Hz the response, expressed as a % of the response to 32 Hz, increased from 15.5 +/- 4.1% (control) to 28.1 +/- 5.8% (motilin 10[-9] M), and to 45.8 +/- 3.6% (motilin 10[-8.5] M) (P < 0.05). This effect was not inhibited by hexamethonium (10[-3.3] M) but was abolished by the motilin receptor antagonist GM-109 (10[-5] M). In unstimulated strips, motilin induced phasic-tonic contractions with a threshold concentration of 10[-8] M and an pEC50 of 7.48, which were also inhibited by GM-109 (10[-5] M) but not by tetrodotoxin (10[-5.5] M). The maximal tension, frequency and dose-dependency of carbachol-induced contractions were not influenced by motilin (pEC50, carbachol: 6.48 +/- 0.06 (control), 6.49 +/- 0.07 (motilin)). In conclusion, motilin enhances contractions induced by electrical field stimulation in the rabbit antrum by a post-ganglionic interaction with the cholinergic neurotransmission in vitro at low doses and interacts directly with antral smooth muscle at high doses. This model is an accurate reflection of the in vivo effects of motilin and provides a tool to study neurogenic and myogenic actions of motilin and motilides in vitro.

Pentachlorophenol concentrations in human cerebrospinal fluid.

Pentachlorophenol (PCP) is a widely applied insecticide and fungicide, particularly in wood preservation. Significant amounts of this compound have been reported in human serum, adipose tissue and urine. PCP is even found in people not occupationally exposed to this toxin or not living in PCP-treated log-houses. Substantial concentrations of this possible neurotoxic agent were detected in the cerebrospinal fluid (CSF) of 16 neurologic patients as measured by a high resolution gas chromatographic method using electron capture detection. This is the first report on PCP levels in (human) CSF. The observed level in CSF ranged from 0.24 up to 2.03 micrograms/L (ppb), with an average value of 0.75 +/- 0.49. The cerebrospinal fluid level did not correlate with the serum PCP concentration nor with the protein level of the cerebrospinal fluid.

Quantitative determination of nitroglycerin by capillary gas chromatography-electron capture detection.

A rapid and sensitive capillary gas chromatographic method based on the one described by Noonan et al. [1] was used to evaluate the nitroglycerin content in serum samples of healthy volunteers, who had orally received a special preparation of the drug (Nisconitrine 6.5, Bio-Therabel). Concentrations were monitored up to 12 h after administration. In accordance with other literature data [2], no detectable amounts of the mother compound were found (limit of detection: 50 pg ml-1). Yet, significant amounts of the active metabolites, 1,2- and 1,3-dinitroglycerine could be demonstrated. Due to the low mass spectrometric response (electron impact ionization) of the different nitroglycerins, positive confirmation of the results with GC-MS was not possible. However, the concentrations reported here do agree with literature data [2], i.e. the ng ml-1 level.

On the de novo synthesis of polychlorinated dibenzo-p-dioxins and dibenzofurans.

Some possible intermediates or by-products in the synthesis of polychlorodibenzo-p-dioxins and dibenzofurans in municipal waste incinerators are presented. In stack gas samples from two different incinerators, the following compounds were tentatively identified: polychloromonobenzofurans, polychloromonobenzodioxins, monobromo-polychlorobenzenes and polychlorothiophenes. The occurrence of complete series of homologues and isomers with an increasing degree of chlorination suggests an analogous formation mechanism with common precursors. The presence of these compounds in the vapour phase, the non-regiospecific character of these reactions and the high reaction temperature and speed confirm a radical mechanism of formation.

Positive confirmation of identity of doping agents using gas chromatography-mass spectrometry with Fourier transform infrared spectrometry.

During the past two decades, the use of retention times in gas chromatography has been augmented by mass spectrometric data. By providing both the retention indices and spectrometric data, this technique has greatly improved gas chromatographic identification analysis. However, although gas chromatography-mass spectrometry has become pre-eminent, several drawbacks still remain. The mass spectral library often gives erroneous identifications when concentrations near the detection limit are analysed, when gas chromatographically interfering substances are present, or when structural isomers or compounds exhibiting identical retention behaviour are analysed. Linked with gas chromatography-mass spectrometry, Fourier transform infrared spectroscopy can be a powerful complementary technique in peak identification analysis. Some spectral data to illustrate this point are presented.

Patterns of gas and liquid reflux during transient lower oesophageal sphincter relaxation: a study using intraluminal electrical impedance.

BACKGROUND: Belching has been proposed as a major mechanism underlying acid gastro-oesophageal reflux in normal subjects. However, the presence of oesophageal gas has not been measured directly but only inferred from manometry. AIMS: To investigate, using intraluminal electrical impedance, the patterns of gas and liquid reflux during transient lower oesophageal sphincter (LOS) relaxations, the main mechanism of acid reflux in normal subjects. METHODS: Impedance changes associated with the passage of gas were studied in vitro, and in vivo in cats. Oesophageal manometry, pH, and intraluminal electrical impedance measurements were performed in 11 normal subjects after a meal. RESULTS: Gas reflux caused a sudden increase in impedance that propagated rapidly to the proximal oesophagus whereas liquid reflux induced a retrogressively propagated fall in impedance. Impedance showed gas or liquid reflux during most (102/141) transient LOS relaxations. When acid reflux occurred, impedance showed evidence of intraoesophageal retrograde flow of liquid in the majority (78%) of events. Evidence of gas retroflow was found in almost half (47%) of acid reflux episodes. When present together, however, liquid preceded gas on 44% of occasions. Overall, gas reflux occurred as the initial event in only 25% of acid reflux episodes. CONCLUSIONS: These findings suggest that in upright normal subjects, although belching can precipitate acid reflux, most acid reflux occurs as a primary event.

Acetylation of melanocyte-stimulating hormone and beta-endorphin in the pars intermedia of the perinatal pituitary gland in the mouse.

This report concerns ontogenetic aspects of the production and in vitro release of NH2-terminally acetylated forms of melanocyte-stimulating hormone (alpha-MSH) and beta-endorphin by the pars intermedia of the pituitary gland of the mouse. In vitro biosynthetic analysis and radioimmunoassay revealed that approximately 12 h before birth most of the MSH in the fetal pars intermedia is present as des-N alpha-acetyl alpha-MSH. The same non-acetylated peptide is at this stage also the major release form of melanotropin. In 1-day-old mice the level of alpha-MSH and diacetylated alpha-MSH had increased considerably, although des-N alpha-acetyl alpha-MSH remained the major form. Five days after birth alpha-MSH and its diacetylated form constitute the major tissue and release form of the peptide, a situation very similar to that in adult mice. Acetylation of beta-endorphin appeared to occur earlier in development, N alpha-acetyl beta-endorphin (1-31) being the major form of endorphin already in the fetal pars intermedia. It is concluded that in the mouse acetylation of melanotropin and acetylation of beta-endorphin are not necessarily concomitant events. It could be established that the ability of the pars intermedia cells for cleaving N alpha-acetyl beta-endorphin (1-31) to yield C-terminally shortened forms of beta-endorphin develops after birth.

Region-specific antiproliferative effect of VIP and PACAP-(1-38) on rabbit enteric smooth muscle.

The ability of neuropeptides to modulate enteric smooth muscle proliferation was examined in primary explant cultures of rabbit gastric antrum and colon smooth muscle. Cell proliferation was determined by [3H]thymidine incorporation measurements and cell counting. Subcultured rabbit antrum and colon myocytes (passages 2-6) preserved a smooth muscle phenotype, as verified by immunohistochemistry for alpha-smooth muscle actin and electron microscopy. Both vasoactive intestinal polypeptide (VIP) and pituitary adenylate cyclase-activating peptide-(1-38) [PACAP-(1-38)] concentration dependently (10(-10) to 10(-6) M) inhibited the serum-induced [3H]thymidine incorporation [in colon, 48.2 +/- 5.8 and 55.6 +/- 9.3% of control with 10(-6) M VIP and 10(-7) M PACAP-(1-38)] and inhibited increase in cell numbers in cultures derived from the colon but not in those from the antrum. Effects of VIP and PACAP-(1-38) were mimicked by forskolin (10(-7) to 10(-6) M) but not by 8-bromo-cGMP, whereas theophylline enhanced the effects of VIP. Inhibition of nitric oxide synthase with NG-nitro-L-arginine methyl ester (10(-3.5) M) did not alter the effects of VIP. Substance P, motilin, calcitonin gene-related peptide, and somatostatin had no effect. A single class of 125I-labeled VIP binding sites was found in antrum and colon myocyte cultures with an equal affinity for VIP and PACAP-(1-38) [dissociation constant (Kd) in antrum = 3.4 +/- 0.8 nM for VIP and 2.0 +/- 1.0 nM for PACAP-(1-38); Kd in colon = 2.0 +/- 1.0 nM for VIP and 2.8 +/- 1.6 nM for PACAP-(1-38)]. Density of binding sites in the antrum was higher than in the colon. In disease states such as inflammatory bowel disease, inhibition of myocyte proliferation by VIP and PACAP may serve to control smooth muscle hyperplasia in the colon but not in the antrum.