Toxic polyneuropathy produced by methyl N-butyl ketone.

A polyneuropathy affecting a large number of workers was recently observed at a plant producing plastic-coated and color-printed fabrics. Epidemiological data suggested strongly that methyl N-butyl ketone (MBK) was responsible for the outbreak. This hypothesis is now supported by the development of a peripheral neuropathy in chickens, rats, and cats exposed to MBK at atmospheric concentrations of 200 to 600 parts per million, 24 hours per day, 7 days per week. Although the animals were exposed continuously and the affected workers were exposed intermittently, the averages of the total number of hours of exposure for development of the peripheral neutropathy in the animals and workers were remarkably close.

Effect of atropine and acetylcholine on nerve stimulated output of noradrenaline and dopamine-beta-hydroxylase from isolated rabbit and guinea pig hearts.

The role of a cholinergic muscarinic inhibitory mechanism in sympathetic neurotransmission was investigated in isolated rabbit and guinea pig hearts with intact sympathetic nerves. The effect of varying frequencies of stimulation (2.5, 5 and 10 Hz) on the concentration of noradrenaline (NA) and dopamine-beta-hydroxylase (DBH) released into the perfusate was investigated. Stimulation in the presence of atropine sulfate (3.4 micrometer) resulted in an augmented outflow of NA at all three frequencies while DBH outflow was significantly incrreased only at 5 and 10 Hz. d-Tubocurarine (2.0 micrometer) attenuated the augmenting effect of atropine on NA release at all frequencies of stimulation whereas it negated the significant effect of atropine on DBH release. Nerve stimulation in the presence of acetylcholine (0.55 micrometer) resulted in a significant decrease in the concentrations of NA and DBH in the perfusate. It is suggested that atropine augments NA outflow in part by blocking an "intrinsic" muscarinic inhibitory mechanism. Acetylcholine's inhibitory effect on NA release is reflected in a similar decrease in DBH release and, therefore, may function in vivo via an effect on exocytosis at the adrenergic nerve ending.

Subacute reserpine treatment reveals preferential coupling between the M3 muscarinic receptor subtype and phosphatidylinositol turnover.

Muscarinic receptors in the rat cerebral cortex, cardiac atria and vas deferens were identified, quantitated, and characterized relative to phosphatidylinositol (PI) turnover as the functional response to stimulation of specific receptor subtypes. Receptor densities as determined by 3H-QNB binding were ranked: cerebral cortex greater than vas deferens greater than heart. Using displacement of 3H-QNB binding by the selective M1 and M2 muscarinic receptor antagonists pirenzepine and 11[[2-[(diethylamino)methyl]-1-piperidinyl]acetyl]-5,11-dihydro- 6H-pyrido [2,3-b] [1,4] benzodiazepine-6-one (AF-DX 116) respectively, heterogeneous populations were found in the cerebral cortex and vas deferens. The M1 receptor subtype predominated in the former and the M2 predominated in the latter. An homogeneous M2 receptor population was present in the heart. Methacholine-stimulated accumulation of 3H inositol-1-phosphate was greater in the vas deferens than in the cerebral cortex, whereas PI turnover was not enhanced in cardiac atria. Reserpine treatment of rats (0.5 mg kg-1 day-1 for 7 days) increased muscarinic receptor density in the vas deferens coincident with a shift in the low affinity pKi for AF-DX 116 to a value comparable to high affinity binding, and abolished the enhanced PI hydrolysis. In the cerebral cortex, reserpine treatment shifted only the early portion of the methacholine dose-response curve to the right. These results are judged to be supportive of preferential coupling between the M3 muscarinic receptor subtype and PI turnover.

Reserpine-induced post-receptor reduction in muscarinic-mediated airway smooth muscle contraction.

Radioligand binding was conducted on airways of the rat and human, surgically subdivided into trachea, lung airways, and parenchyma. 3H-QNB bound uniformly to receptors in separate sections of the rat and human airway. Receptor densities generally were ranked: lung airways greater than trachea greater than parenchyma. Receptor subtypes were identified mostly by pirenzepine displacement of bound 3H-QNB. The rat trachea, and rat and human lung airways had a uniformly low affinity for pirenzepine while rat and human parenchyma demonstrated both high and low affinity pirenzepine binding. Inhibition of methacholine-stimulated smooth muscle contraction by the M1 receptor antagonist, pirenzepine, and M2 receptor antagonist, gallamine, was studied in rat trachea and bronchus in vitro. Schild plot pA2 values were compatible with low potency antagonism, thereby favoring the presence of M3 receptors at these smooth muscle sites. Reserpine treatment of rats (0.5 mg kg-1 day-1 for 7 days) produced a decrease in peak tension in response to methacholine without changing the muscarinic receptor character (Kd 3H-QNB), population density (Bmax in fmol mg-1 protein), or function (methacholine EC50). These results indicate that muscarinic receptor heterogeneity exists in the airway of both laboratory rat and man. While the muscarinic receptor subserving airway smooth muscle contraction appears to be the M3 subtype, decreased contractile responses to methacholine by trachea and bronchus from reserpine-treated rats were receptor independent.

gamma-Aminobutyric acid antagonism produced by an organophosphate-containing combustion product.

Results from [35S]t-butylbicyclophosphorothionate (TBPS) binding and gamma-aminobutyric acid (GABA)-dependent 36Cl- uptake indicated that the pyrolysis product of liquid trimethylol propane (TMP) containing organic phosphates interacts with the GABA/benzodiazepine receptor chloride ionophore complex (GBRC) producing a receptor-mediated reduction in 36Cl- flux. The pyrolysate-ligand interaction was competitive and directly proportional to the trimethylol propane phosphate (TMPP) content of the combustion product. TBPS displacement demonstrated that TMPP had less affinity than did TBPS and picrotoxin, but greater affinity than GABA, racemic dimethylbutyl barbituric acid (DMBB), clonazepam, and phenobarbital for their respective recognition sites. Addition of exogenous GABA was a necessary condition for demonstrating clonazepam-induced ligand displacement, thus being indicative of an allosteric interaction. The same rank order held for altering GABA-dependent 36Cl- uptake with the caveat of inhibitors vs enhancers, and noting that pentobarbital was less potent than DMBB. Concentration-dependent ligand displacement by GBRC agonists and antagonists quantitatively correlated with alterations in GABA-dependent 36Cl- uptake. The median convulsant dose (CD50) of pyrolysate TMPP was higher than that of synthetic TMPP. The presence of combustion by-products altering the dispositional kinetics of the former is felt to be the reason for this difference. Under our experimental conditions, phenobarbital was the most effective antidote for pyrolysate (TMPP) toxicity. The inhalant convulsant, flurothyl, was found not to displace [35S]TBPS binding, not to affect GABA-dependent 36Cl- uptake, and not to respond to the anticonvulsants in a manner consistent with a strict GABAA receptor phenomenon.

A mechanism of tolerance to the antihypertensive effect of ganglionic blocking agents in rats.

Functional tolerance was demonstrated to the antihypertensive effect of chlorisondamine Cl (Ecolid), a noncompetitive autonomic ganglion blocking agent, when administered chronically in increasing doses to spontaneously hypertensive rats (SHR), and normotensive Wistar-Kyoto (WKY) rats. Concomitant administration of atropine SO4 restored the hypotensive response to chlorisondamine without increasing its serum concentration. Atropine had no effect on the blood pressure of chlorisondamine-naive animals. No qualitative differences in therapeutic response were observed between the SHR and WKY rats. The results support the hypothesis that tolerance to the antihypertensive action of ganglionic blocking agents may be mediated by an activation of an alternate compensatory sympathetic ganglionic muscarinic pathway. It is speculated that this secondary pathway does not contribute to the hypertension in the SHR model.

The effect of pancuronium and gallamine on muscarinic transmission in the superior cervical ganglion.

Pancuronium enhanced contraction of the nictitating membrane elicited via ganglionic muscarinic pathways in the superior cervical ganglion of the cat. In order to elucidate this phenomenon, recordings of the superior cervical ganglion surface potential were made which demonstrated that pancuronium and gallamine reduced and haloperidol enhanced ganglionic hyperpolarization without significantly altering the ganglionic slow depolarization. Pancuronium reversed the effects produced by haloperidol, whereas the latter drug was unable to antagonize those induced by pancuronium. These results allow the speculation that pharmacologically distinct muscarinic receptors reside in sympathetic ganglia, one of which is susceptible to blockade by pancuronium or gallamine.

Distinct muscarinic mediation of suspected dopaminergic activity in sympathetic ganglions.

The competitive neuromuscular blocking agents, gallamine and pancuronium, enhanced the nictitating membrane contraction, in the cat, resulting from muscarine ganglionic transmission. Inhibition of ganglionic muscarinic hyperpolarization, in response to short tetanic bouts of preganglionic cervical sympathetic stimulation, was an associated event and is considered by us to be causally related. The neuroleptic drug, haloperidol, enhanced ganglionic hyperpolarization under similar stimulatory conditions, and reduced the nictitating membrane contraction elicited via ganglionic muscarine pathways, effects opposite to those produced by the skeletal muscle relaxants. Apomorphine reduced both ganglionic hyperpolarization and the ganglionic muscarinic-induced nictitating membrane contractions. The action of gallamine and pancuronium conforms to a speculative cholinergic antagonism at the specific muscarinic receptors, termed Mi, on the ganglionic dopaminergic interneuron. Haloperiodol and apomorphine are anticipated to be exerting distinct antagonistic and agonistic actions, respectively, on prejunctional dopamine receptors of the ganglionic interneuron. Ganglionic slow depolarization mediated through the muscarinic receptors, termed Me, was unaltered by any of the agents studied.

Potentiation of 2,5-hexanedione neurotoxicity by methyl ethyl ketone.

Chronic oral administration of a combination of 2.2 mmol methyl ethyl ketone (MEK) and 2.2 mmol 2,5-hexanedione (2,5-HD)/kg/day, 5 days/week resulted in more rapid onset of motor deficits than did chronic dosing with 2.2 mmol 2,5-HD/kg/day alone. In kinetic studies blood time courses of 2,5-HD were determined in rats in the presence and absence of MEK. Concomitant administration of MEK reduced blood 2,5-HD clearance and increased the area under the curve (AUC) for the blood 2,5-HD. In companion experiments with 2,5-[1,6-14C]HD as a tracer, neural and nonneural tissues were examined 72 hr following the last treatment at Weeks 1, 2, and 3 of chronic administration of 2,5-HD alone or in combination with an equimolar dose of MEK. Rats treated with 2,5-[14C]HD alone or in combination with MEK demonstrated no difference in total or trichloroacetic acid-precipitable radioactivity in blood, in liver homogenates, or in neurofilament-enriched fractions from sciatic nerve and spinal cord. The data support a suggestion that the potentiation of hexacarbon neurotoxicity by MEK is the result of the persistence of the neurotoxic metabolite in the blood and not the enhanced metabolism of parent hexacarbon to 2,5-HD.