Effects of halothane and other chlorinated hydrocarbons on alpha 2-adrenoceptors in the mouse cortex.

A number of general anaesthetics and organic solvents were tested for their ability to inhibit the binding of 3H-clonidine to alpha 2-adrenoceptors in mouse cerebral cortex membranes. The order of potency of the tested agents was: chloroform greater than halothane greater than trichloroethylene greater than carbon tetrachloride greater than dichloromethane. Of these agents halothane was tested further. When saturation curves of 3H-clonidine were constructed, halothane (25 mmol/l added directly to the assay) was found to induce a proportionally greater inhibition at low 3H-clonidine concentrations than at high. Computer modelling these saturation curves indicated that halothane reduced the apparent affinity of 3H-clonidine; Kd = 4.2 nmol/l in the absence of halothane and Kd = 6.0 nmol/l in its presence. Gassing the cortex membranes with 3% halothane induced a practically identical reduction in the affinity for 3H-clonidine; Kd = 4.6 nmol/l for the control versus Kd = 10.7 nmol/l for halothane. The effects of halothane was compared to that of the non-hydrolyzable GTP analog Gpp(NH)p. Gpp(NH)p in the concentration range 10(-8)-10(-3) mol/l dose-dependently reduced the binding of 1 nmol/l 3H-clonidine, the effect being essentially maximal at 10(-4) mol/l. Computer modelling of saturation curves of 3H-clonidine indicated that 0.1 mmol/l Gpp(NH)p reduced the apparent affinity of 3H-clonidine; Kd = 5.4 nmol/l in the absence of Gpp(NH)p and Kd = 9.3 nmol/l in its presence. In addition Gpp(NH)p caused some reduction in the apparent number of 3H-clonidine binding sites. The effect of halothane on 3H-clonidine binding was tested both in the absence and presence of 0.1 mmol/l 1 Gpp(NH)p. During these conditions halothane was slightly more potent in the presence of Gpp(NH)p (IC50 of halothane = 17 mmol/l) than in its absence (IC50 = 41 mmol/l).(ABSTRACT TRUNCATED AT 250 WORDS)

Trichloroethylene and halothane inhibit uptake and metabolism of 5-hydroxytryptamine in rat lung slices.

The effect of exposure to organic solvents on uptake and metabolism of 5-HT was studied in rat lung slices. It was found that under control conditions 5-HT was both taken up and metabolized to 5-HIAA. When halothane (35,000 ppm) or trichloroethylene (18,000 ppm) were equilibrated with the incubation medium the uptake of 5-HT decreased by approximately 50% after 30 min of incubation, and the production of 5-HIAA was inhibited by approximately 70% and 80%, respectively. The results are consistent with earlier studies using a much more elaborate technique, in which halothane and trichloroethylene were found to depress 5-HT uptake in isolated perfused rat lungs. Our results demonstrate that the simpler technique employing lung slices can also be used, to investigate factors affecting pulmonary uptake of endogenous amines, and, potentially, the uptake of other compounds as well.

Trichloroethylene inhibits uptake of 3H-5-hydroxytryptamine but not uptake of 3H-zimeldine or 3H-propranolol in isolated perfused rat lungs.

Pulmonary uptake of 5-hydroxytryptamine (5-HT), zimeldine and propranolol were studied using the isolated perfused rat lung model. The 5-HT uptake was found to be attenuated by approximately 50 per cent in comparison to the control, when the lungs were ventilated with air containing 5,000 p.p.m. trichloroethylene. In experiments in which the active uptake of 5-HT was blocked with the selective 5-HT uptake inhibitor zimeldine (5 X 10(-6) M), the uptake of 5-HT decreased by 70 +/- 1.7 per cent (mean +/- S.E.M.). When trichloroethylene (5,000 p.p.m. and 18,000 p.p.m.) was added, no further decrease in uptake was noted. The uptake of 3H-zimeldine (10(-6) M) and 3H-propranolol (10(-6) M) was unaffected by ventilating the lungs with trichloroethylene. It is concluded that trichloroethylene inhibits the active uptake of 5-HT from the pulmonary circulation, but that it has no effect on the uptake of zimeldine or propranolol, which are taken up predominantly by passive diffusion.

Lysophosphatidylcholine increases airway and capillary permeability in the isolated perfused rat lung.

The effects of lysophosphatidylcholine (lysoPC) on airway and capillary permeability in the isolated perfused rat lung were investigated. We determined the influence of lysoPC on the passage of different-sized (326-722 dalton) polyethylene glycols (PEGs), both from the airways to the pulmonary circulation and from the pulmonary circulation into the lung. We found that 1 mM lysoPC increased the overall passage of PEGs from the airways to the pulmonary circulation, and that 80 microM lysoPC increased the overall passage from the circulation into the lung. In both cases, the passage of the larger (502-722 dalton) PEGs increased more than the passage of the smaller (326-458 dalton) PEGs. We also found that the presence of lysoPC in the circulation increased the pulmonary arterial pressure, whereas deposition of lysoPC in the trachea did not. The pressure increase was blocked by indomethacine, BW755C, and quinacrine, inhibitors of arachidonic acid metabolism. These findings suggest that higher concentrations of lysoPC increase the airway permeability to larger molecules, and that lower concentrations of lysoPC increase the capillary permeability. The increase in capillary permeability may be due to a rise in capillary pressure mediated by arachidonic acid metabolites. The possibility that formation and accumulation of lysoPC is of importance for mediating inflammatory reactions in the lung is inferred.

Effect of a homologous series of halogenated methanes on pulmonary uptake of 5-hydroxytryptamine in isolated perfused rat lung.

The potency of halogenated methanes to inhibit uptake of 5-hydroxytryptamine (5-HT) from the pulmonary circulation was studied using an isolated, perfused and ventilated rat lung preparation. The agents were vaporized and mixed with the inlet air. The results indicate that the degree of chlorination is the most important factor for potency of the methanes to inhibit lung uptake of 5-HT. When hydrogen was substituted with fluorine the potency was decreased dramatically. Bromine seemed to have the opposite effect. The data also suggested that the degree of chlorination was more important rather than hydrophobic/hydrophilic balance of the solvent molecule. These effects seem to be correlated with the narcotic effects of the substances studied.

Effect of general anaesthetics and organic solvents on alpha 1-adrenoceptors in the myometrium.

The alpha 1 selective radioligand 3H-prazosin was used to assay alpha 1 receptors in membranes prepared from the rabbit myometrium. 3H-Prazosin was found to bind to a single high affinity site in these membranes which was the presumed alpha 1 receptor. A series of general anaesthetics and organic solvents were tested for their ability to inhibit 3H-prazosin binding. The order of potency of the tested agents to inhibit the binding was: chloroform=halothane=trichloroethylene greater than carbon tetrachloride greater than dichloromethane. The depression of 3H-prazosin binding seemed to be induced on the alpha 1 receptor since non-specific radioligand binding was not affected as revealed by a saturation experiment with 3H-prazosin where halothane was used as inhibiting agent. Computer analysis of the latter experiment also showed that halothane depressed mainly the affinity of 3H-prazosin for the alpha 1 receptor. The ability of the general anaesthetics and organic solvents to inhibit contractions elicited by alpha 1 stimulation with phenylephrine in the rabbit uterus was also investigated. In these tests the order of potency for the inhibition of the contractile response was: carbon tetrachloride greater than or equal to halothane=chloroform greater than trichloroethylene greater than dichloromethane. The mechanism of action for alpha 1 receptor and myometrial depression is discussed.

Uptake of zimelidine and inhibition of uptake of 5-hydroxytryptamine in the isolated, ventilated and perfused rat lung.

Uptake of zimelidine from the perfusate in isolated perfused rat lung was concentration-dependent. Accumulated zimelidine was released from the lung according to a two-compartment model and lidocaine injected as a bolus did partially displace zimelidine. The properties of the displacement curves indicated, however, that the affinity to the lung tissue was greater for zimelidine than lidocaine. Uptake of 5-hydroxytryptamine added to the perfusion buffer was inhibited by zimelidine. The displacement of zimelidine by lidocaine did not, statistically, significantly alter the extraction of 5-hydroxytryptamine.

Trichlorethylene and halothane inhibit uptake of 5-hydroxytryptamine in the isolated perfused rat lung.

Lung uptake of 5-hydroxytryptamine (5-HT) was determined in isolated perfused and ventilated rat lung, and was found to decrease with time according to a two-compartmental model. When the lungs were exposed to either trichlorethylene (TRI) or halothane, the uptake of 5-HT was drastically reduced. Both TRI and halothane gave log dose inhibition curves, which were superimposed, i.e. they were equally potent to inhibit lung uptake of 5-HT. At a concentration TRI of 18,000 ppm, the extraction of 5-HT was inhibited by 80 +/- 2 (X +/- S.E.M.) per cent, at 8500 ppm the inhibition was 65 +/- 6 per cent and 25 +/- 1 per cent at 3000 ppm. When the lungs were exposed to halothane, the inhibition was 85 +/- 6 per cent at 40,000 ppm, 48 +/- 1 per cent at 6000 ppm, and 15 +/- 0.3 per cent at 2000 ppm. When exposure to the solvent was discontinued, extraction of 5-HT was rapidly normalized. There was no detectable displacement of [3H]-5-HT from lungs saturated with the amine when they subsequently were exposed to solvent-containing atmosphere. This inhibition of lung uptake of 5-HT from the circulation is therefore postulated as to be an effect dependent on concentration solvent in the tissue, and is probably due to a reversible membrane stabilization of the endothelium.

Characterization of 5-hydroxytryptamine uptake in sliced rat lung.

Slices of rat lung were incubated with tritiated 5-hydroxytryptamine and the tissue uptake of tritium was studied after separating the free and bound radioactivity by filtration on glass fiber filters. At 37 degrees a rapid uptake occurred during the first 10 min. After that time the uptake was less marked but it was still present after 60 min. The uptake was moderately potentiated by the MAO inhibitor iproniazid (3 micrometers) after 30-60 min. incubation. The 5-hydroxytryptamine uptake was inhibited by some uptake inhibitors, their order of potency beeing: clomipramine greater than imipramine greater than or equal to nortriptyline greater than or equal to cocaine greater than or equal to desipramine greater than maprotiline. At 0 degrees the uptake of 5-hydroxytryptamine was negligible. Non-linear regression analysis of uptake data indicated that 5-hydroxytryptamine was taken up by two different mechanisms. One of the uptake processes was saturated by high concentrations of 5-hydroxytryptamine and showed an apparent Km of 8 X 10(-7) M. The other uptake was linearly related to the 5-hydroxytryptamine concentration and could not be saturated even by concentration up to 5 X 10(-5) M of the amine.