Early investigations on the effect of methyl mercuric chloride upon DMN-acute hepatotoxicity

Acute toxicity induced by DMN was partially prevented by previously administering methyl mercuric chloride (MMC), a chemical inhibitor of the drug metabolizing enzyme system (DMES). We have studied the early changes occurring during the course of DMN-intoxication, namely disaggregation of polysomal profiles and necrosis, evaluated morphologically and by the release of S-GPT.     

Effects of imidazoline derivatives on cholinergic motility in guinea-pig ileum: involvement of presynaptic alpha2-adrenoceptors or imidazoline receptors?

The present study investigates the possibility that imidazoline receptors mediate modulation of cholinergic motor functions of the guinea-pig ileum. For this purpose, the effects of a series of compounds with known affinity for alpha2-adrenoceptors and/or imidazoline recognition sites were examined on the cholinergic twitch contractions evoked by electrical field stimulation (0.1 Hz) of longitudinal muscle-myenteric plexus preparations. Additional experiments were carried out on ileal strips preincubated with [3H]choline, superfused with physiological salt solution containing hemicholinium-3, and subjected to electrical field stimulation (1 Hz). The stimulation-induced outflow of radioactivity was taken as an index of endogenous acetylcholine release. Alpha-methyl-noradrenaline, noradrenaline, clonidine, medetomidine, oxymetazoline and xylazine caused a concentration-dependent inhibition of twitch responses (IC50 from 0.13 to 1.05 microM; Emax from 85.9 to 92.5%). Rilmenidine and agmatine were less potent in reducing the twitch activity, and the latter compound acted also with low intrinsic activity (IC50=44.9 microM; Emax=35.5%). In interaction experiments, the inhibitory action of clonidine on twitch responses was competitively antagonized by RX 821002 (2-(2-methoxy-1,4-benzodioxan-2-yl)-2-imidazoline), idazoxan, rauwolscine, yohimbine and BRL 44408 (2-[2H-(1-methyl-1,3-dihydroisoindole)-methyl] -4,5-dihydroimidazoline), whereas prazosin (10 microM), ARC 239 (2-(2,4-(O-methoxy-phenyl)-piperazin-1-yl)-ethyl-4,4-dimethyl- 1,3-(2H,4H)-isoquinolindione; 10 microM) and BRL 41992 (1,2-dimethyl-2,3,9,13b-tetrahydro-1H-dibenzo[c,f]imidazol[1,5-a]a zepine; 10 microM) were without effect. Rauwolscine antagonized the inhibitory effects of various agonists on ileal twitch activity in a competitive manner and with similar potency. Agmatine and idazoxan did not significantly modify the twitch contractions when tested in the presence of alpha2-adrenoceptor blockade by rauwolscine (3 microM) or RX 821002 (1 microM). Linear regression analysis showed that the affinity values of antagonists correlated with their affinity at the alpha2A and alpha2D binding sites as well as at previously classified alpha2A/D adrenoceptor subtypes, whereas no significant correlation was obtained when comparing the potency estimates of agonists and antagonists with the affinity at I1 or I2 binding sites. When tested on the electrically induced outflow of tritium, alpha-methyl-noradrenaline, noradrenaline, clonidine, medetomidine, oxymetazoline, xylazine and rilmenidine yielded inhibitory concentration-response curves which were shifted rightward to a similar extent in the presence of rauwolscine (3 microM). In the absence of further drugs, agmatine significantly reduced the evoked tritium outflow at the highest concentrations tested (10 and 100 microM), whereas idazoxan (up to 100 microM) was without effect. When RX 821002 (1 microM) was added to the superfusion medium, neither agmatine nor idazoxan modified the evoked outflow of radioactivity. The results argue against modulation by imidazoline receptors of acetylcholine release from myenteric plexus nerve terminals. They provide evidence that compounds endowed with imidazoline-like structures affect the cholinergic motor activity of the guinea-pig ileum by interacting with presynaptic alpha2-adrenoceptors belonging to the alpha2D subtype.     

Early aspects of the intrarenal distribution of mercury after the intravenous administration of mercuric chloride

It is generally considered that the clinical manifestations of human and canine systemic lupus erythematosus (SLE) are similar in many respects. However, there are differences in serological markers of SLE between the two species, which has led to much discussion on which immunopathological criteria might be appropriate in the diagnosis of the canine disorder. Further studies on canine SLE will need to address these issues, so that definitive diagnostic indices may be employed. Areas which require to be re-assessed, in particular, include the applicability of assays for antibodies to double-stranded DNA--a hallmark of human SLE, a re-evaluation of the anaemia associated with canine SLE and an index of the clinical activity of the disease process.     

Effects of physostigmine and electrical stimulation on the acetylcholine content of the guinea-pig ileum

Incubation with physostigmine (7.7 muM) caused an approximately 2 fold increase in the acetylcholine content of the myenteric plexus--longitudinal muscle preparation of the guinea-pig ileum. This effect was due mainly to an increase in 'free' acetylcholine, which was directly assayable in either the homogenate after removal of cell debris or the supernatant fraction (100,000 g for 60 min) after subcellular fractionation. Acetylcholine output during stimulation at 0.017, 0.1 or 1 Hz was maintained for 60 min at a rate 2--4 times greater than the non-stimulated output; there was no change in content. At 10 HZ, output was high at the start of stimulation and then decreased continuously; there was a proportionate loss of mainly 'free' acetylcholine from the tissue. Mn2+, hexamethonium, morphine and noradrenaline, which depressed acetylcholine output during stimulation at 0.1 HZ, had no effect on the acetylcholine content nor did they affect the increase in acetylcholine content during incubation with physostigmine.     

Reduced mercury excretion with feces in germfree mice after oral administration of methyl mercury chloride

When methyl mercury chloride was administered orally the amount of mercury excretion with feces of germfree mice was noticeably lower than that of the control mice. Germfree mice excreted 24 percent of the administered mercury within 10 days of administration while the control mice excreted 46 percent. Mercury retention in the organs of germfree mice was slightly higher than in the control mice. These results suggest that the existence of microorganisms in animal intestines are concerned with mercury excretion in the animal body.     

Effects of cadmium and lead on adrenergic neuromuscular transmission in the rabbit

The effects of inorganic lead (PbCl2) and cadmium (DdCl2) on the pressor response of rabbit saphenous arteries produced by sympathetic nerve stimulation were examined. A 1- to 3-cm length of artery was removed, placed in a bath containing mammalian Ringer solution, and perfused with the same solution at a constant rate sufficient to maintain a 40-60 mmHg perfusion pressure. Increases in perfusion pressure resulting from electrical stimulation -f periarterial nerve endings were reduced or completely blocked by the addition of 5-20 muM lead or cadmium to the bathing solution for a period of 15-30 min. Responses to norepinephrine or to direct electrical stimulation of the muscle remained relatively unaffected. During lead or cadmium blockade, the response to nerve stimulation could be restored by a fourfold increase in calcium concentration. It is concluded that lead and cadmium reduce the response to sympathetic nerve stimulation primarily through an effect on presynaptic nerve terminals.     

Metal-induced genotoxic adaptation in barley (Hordeum vulgare L.) to maleic hydrazide and methyl mercuric chloride

Presoaked seeds of barley, Hordeum vulgare L., were exposed for 2 h to maleic hydrazide (MH), 5 x 10(-2) M or methyl mercuric chloride (MMCl), 10(-4) M with or without a prior conditioning with MH, 5 x 10(-3) M; MMCl, 10(-5) M; cadmium sulfate (CdSO4), 10(-4) M or zinc sulfate (ZnSO4), 10(-1) M; the interexposure time was 2 h. Subsequently as the seeds germinated a number of endpoints were measured that included mitotic index, mitotic chromosome aberrations and micronuclei (MNC) in embryonic shoot cells fixed at 32, 36, 40, 44, 48 and 52 h of recovery, and seedling height on day 7. The results demonstrated that prior conditioning exposure to MH or metals induced genotoxic adaptation to the subsequent challenge exposure to MH and MMCl. Cadmium-induced genotoxic adaptation against either MH or MMCl challenge exposure was, however, significantly prevented when the presoaked seeds were pre-exposed to buthionine sulfoximine, 10(-3) M for 2 h, thereby providing evidence that the underlying mechanism of genotoxic adaptation possibly involved phytochelatins.     

The kinetics of competitive antagonists on guinea-pig ileum

Echo-encephalographic examinations were performed in 144 patients after subarachnoid hemorrhage. Ninety-three of the patients received antifibrinolytic treatment (AMCA). The width of the third ventricle could be measured in all the patients, and lateral ventricle measurements were obtained in 94 patients. Third ventricular dilatation developed in 78 patients (54 per cent), and lateral ventricle enlargement was seen in 55 patients (58 per cent of those examined). The incidence of third ventricle dilatation was higher in the AMCA-treated group (62.5 per cent) than in the non-treated group (39.2 per cent), and this difference was statistically significant (P less than 0.05). The hydrocephalus in most cases developed 2-3 weeks after the bleeding, and reached its peak within the first 2-3 months, with subsequent complete or partial normalization of the ventricular size. At later follow-up examinations 1-4 years after the bleeding, only nine patients had persisting dilatation of moderate or pronounced degree. There was no indication that the dilatation was more severe or pronounced degree. There was no indication that the dilatation was more severe or protracted in the AMCA-treated group than in the non-treated group. In 11 patients the hydrocephalus required a shunt-operation, but the frequency of shunt-operations was not significantly different in the two groups. It is concluded that although AMCA-treated patients in comparison with non-treated patients are exposed to a somewhat higher risk of complicating hydrocephalus after subarachnoid hemorrhage, this risk cannot at present be considered as any serious contraindiction to this sort of treatment.     

Neurochemical classification of myenteric neurons in the guinea-pig ileum

A strategy has been developed to identify and quantify the different neurochemical populations of myenteric neurons in the guinea-pig ileum using double-labelling fluorescence immunohistochemistry of whole-mount preparations. First, six histochemical markers were used to identify exclusive, non-overlapping populations of nerve cell bodies. They included immunoreactivity for the calcium binding proteins calbindin and calretinin, the neuropeptides vasoactive intestinal polypeptide, substance P and somatostatin, and the amine, 5-hydroxytryptamine. The sizes of these populations of neurons were established directly or indirectly in double-labelling experiments using a marker for all nerve cell bodies. Each of these exclusive populations was further subdivided into classes by other markers, including immunoreactivity for enkephalins and neurofilament protein triplet. The size of each class was then established directly or by calculation. These distinct, neurochemically-identified classes were related to other published work on the histochemistry, electrophysiology and retrograde labelling of enteric neurons and to the simple Dogiel morphological classification. A classification scheme, consistent with previous studies, is proposed. It includes 14 distinct classes of myenteric neurons and accounts for nearly all neurons in the myenteric plexus of the guinea-pig ileum.     

Effects of L-NG-nitro arginine on cholinergic transmission in the gastric muscle of the rabbit

In the circular muscle of the rabbit gastric corpus, the nitric oxide-synthesis inhibitor L-NG-nitro arginine (L-NOARG), enhanced the neurally-induced cholinergic responses evoked by electrical field stimulation (EFS) and ganglionic stimulating agents (nicotine, dimethylphenyl piperazinium iodide). The muscular contractions caused by acetylcholine (Ach) and methacholine were not influenced by the nitric oxide-synthesis inhibitor. The nitric oxide-releasing compound sodium nitroprusside (SNP) did not affect the Ach-induced muscular responses. Our results suggest that L-NOARG enhances gastric cholinergic responses by removing an inhibitory influence exerted at the prejunctional level in the nerve-muscle pathway.     

Effects of muscle electrical activity on the transmission of developing neuromuscular junction

A prospective cohort study in a neonatal intensive care unit (ICU) was carried out to evaluate whether the incidence of infection in neonates receiving intestinal decolonization was reduced in comparison to those who did not. This study was performed after controling possible confounding infection risk factors. A total of 536 babies were screened in our ICU during the 27-month study period. Neonates were admitted to the ICU for different reasons: low weight, respiratory distress syndrome, acute fetal suffering, surgery, etc. The doctor in charge decided whether the baby should be decolonized or not, so this experimental study was non-random. Thus more of the babies with a greater risk of infection were decolonized more often than the other babies who were not so much at risk. In this study, babies were classified by type of decolonization given: a well-performed Selective Intestinal Decolonization (SID) was done (early and with three oral drugs: E polymyxin, tobramycin and nystatin): 10.8% of the babies; Incorrect SID (was begun late and/or less than three drugs were used): 16.7% of the babies; and Without SID (72.9%). Total nosocomial infection (NI) was 11.2%, catheter-associated sepsis was 42% of the total NI. When the NI incidence was directly compared among groups, it was lower in the group without SID, but infants with decolonization initially had more infection risk factor than the first group. For this reason, multiple logistic regression was used in order to stratify factors by infection probability, and correcting the existing bias.(ABSTRACT TRUNCATED AT 250 WORDS)     

Histamine H3 receptor desensitization in the guinea-pig ileum

Histamine H3 receptor ligands are usually tested in guinea-pig intestine preparations. A possible desensitization of agonist-induced twitch inhibition was studied in longitudinal muscle-myenteric plexus from ileal segments. A cumulative concentration-response curve for R-alpha-methylhistamine was made; when a second curve was made 30 min afterwards, a marked decrease of pD2 and a more modest decrease of Emax were observed without changes in tissue sensitivity to electrical stimulation or morphine inhibition. At 120 min, pD2 and Emax were not different from those for the first curve. Receptor desensitization seems homologous and reversible and could interfere with repetitive testing of histamine H3 receptor ligands.     

Guanidines as analogs of histamine and antihistamines on the isolated guinea-pig ileum

The present work describes the interaction of phenylguanidine and cyclohexylguanidine with receptor structures of the isolated guinea-pig ileum. It is suggested that phenylguanidine in the range of 0.2-2 mM, acts in a way similar to histamine. At lower concentrations in the bath, phenylguanidine and cyclohexylguanidine, behave as competitive antagonists of histamine, with Ki values close to 0.1 mM and 0.4 mM, respectively. At higher concentrations phenylguanidine acts as agonist with a Kn near 0.3 mM; the Kn for histamine was found to be 0.127 muM, in agreement with previous data from the literature. The agonistic action of phenylguanidine is inhibited by promethazine and atropine, which have Ki values of 0.342 muM and 0.575 muM, respectively. Cyclohexylguanidine is devoid of spasmogenic activity, and this was attributed to the lack of aromatic character and to the bulkiness of the cyclohexyl side chain.     

Excitatory transmission to the circular muscle of the guinea-pig ileum: evidence for the involvement of cannabinoid CB1 receptors

1. The effect of cannabinoid drugs has been investigated on cholinergic and non-adrenergic non-cholinergic (NANC) contractile responses to the circular smooth muscle of guinea-pig ileum elicited by electrical field stimulation (EFS). 2. The cannabinoid receptor agonist WIN 55,212-2 (1-1000 nM) and the putative endogenous ligand anandamide (0.1-100 microM) both produced a concentration-dependent inhibition of the cholinergic (9-57% and 1-51% inhibition) and NANC (9 55% and 2-57% inhibition) contractile responses. WIN 55,212-2 and anandamide did not modify the contractions produced by exogenous acetylcholine or substance P. 3. Apamin (30 nM), a blocker of Ca2+-activated K+ channels, reduced the inhibitory effect of WIN 55,212-2 on cholinergic, but not NANC, contractile response. NG-nitro-L-arginine methyl ester (100 microM), an inhibitor of nitric oxide synthase, or naloxone (1 microM), an opioid receptors antagonist, did not modify the inhibitory effect of WIN 55,212-2 on both cholinergic and NANC contractions. 4. The inhibitory effects of WIN 55,212-2 and anandamide on both cholinergic and NANC contractile response was competitively antagonized by the cannabinoid CB1 receptor antagonist SR 141716A (10-1000 nM). 5. In absence of other drugs, SR 141716A (1-1000 nM) enhanced cholinergic (1-45% increase) and NANC (2-38% increase) contractile responses elicited by electrical stimulation, but did not modify the contractions produced by acetylcholine or substance P. 6. It is concluded that activation of prejunctional cannabinoid CB1 receptors produces inhibition of cholinergic and NANC excitatory responses in the guinea-pig circular muscle. The inhibition of cholinergic (but not NANC) transmission involves activation of apamin-sensitive K+ channels. In addition, an endogenous cannabinoid ligand could inhibit cholinergic and NANC transmission in the guinea-pig ileal circular muscle.     

Pathophysiology on the disorder of neuromuscular transmission defects

Neuromuscular transmission defects are often puzzling but challenging diseases for the pediatric and adult neurologists. Some of these disorders entail severe or even life-threatening disability: Most are treatable, but effective therapy requires precise diagnosis sometimes difficult to make especially in congenital defects. The diagnosis rests on the combination of clinical data, the electromyogram and additional studies that may include microelectrode analysis of neuromuscular transmission, ultrastructural and cytochemical studies of neuromuscular junction (NMJ) and biochemical/molecular genetic studies on muscle specimens. Understandably, these studies often depend on the collaboration of several investigators. In each myasthenic disorder, an abnormality affects neuromuscular transmission directly or causes secondary derangements that eventually affects transmission. Namely, lesions of both the presynaptic and/or postsynaptic area manifest a variety of clinical findings. Here was discussed the pathophysiology on myasthenia gravis and Lambert-Eaton myasthenic syndrome of abnormal autoimmunity, congenital myasthenic syndromes of a chromosomal defect, and poisoning of organophosphorus, botulism and some other toxins.     

Effects of neuromuscular blocking agents on excitatory transmission and gamma-aminobutyric acidA-mediated inhibition in the rat hippocampal slice

BACKGROUND: Although neuromuscular blocking agents do not cross the blood-brain barrier, they may penetrate the central nervous system under particular circumstances and eventually cause neurotoxic consequences. METHODS: The effects of neuromuscular blocking agents on excitatory and inhibitory transmission in area CA1 of rat hippocampal slices were investigated using extracellular and intracellular recording techniques. RESULTS: Application of atracurium in the perfusion medium resulted in a dose-dependent enhancement of excitatory synaptic responses averaging 48.7 +/- 4.3% at a concentration of 10 nM. This effect was correlated with an increase in the size of the presynaptic fiber volley. Laudanosine, but not pancuronium bromide or vecuronium bromide, produced similar changes. In addition, atracurium and laudanosine blocked inhibitory transmission and reduced intracellularly recorded gamma-aminobutyric acidA receptor-mediated potentials. These effects were observed only at concentrations >1 microM and were not reproduced by pancuronium bromide and vecuronium bromide. CONCLUSIONS: Atracurium and its metabolite, laudanosine, contrary to pancuronium bromide and vecuronium bromide, produce two distinct effects on hippocampal slices. They enhance excitatory transmission and neuronal excitability and they block inhibitory gamma-aminobutyric acidA-mediated synaptic responses.