Application of low-temperature autoradiography to studies of the uptake and metabolism of volatile anesthetics in the mouse: II. Diethyl ether

Distribution in female rats of an anaesthetic intravenous dose of 14C-propofol

1. Bolus i.v. doses of 14C-propofol (9 mg/kg) were administered to female rats for measurement of tissue levels of total 14C and propofol from 2 min to 24 h post-dose; whole-body autoradiography was studied at 6 min, 2 h and 24 h post-dose, and also involved 15-day pregnant rats. 2. The blood propofol concentration-time profile was fitted by a tri-exponential function corresponding to a three-compartment open model. Data show rapid distribution during the mixing period into highly perfused tissues and muscle, comprising the central compartment, and slower uptake into less well-perfused skin and adipose tissues comprising the deeper compartments. 3. The initial decline in blood propofol concentration was associated with redistribution (t1/2 4 min), the second decline (15-240 min post-dose) was associated with metabolism (t1/2 33 min) and the third decline reflected slow depletion of drug from deep tissue compartments (t1/2 6.4 h). 4. Blood and brain propofol concentrations on waking (at 7 min post-dose) were 4 micrograms/ml and 9 micrograms/g respectively; the model shows that, at this time, 30% of the dose was lost from the central compartment by redistribution and a similar amount by metabolism. 5. Tissue profiles of total 14C and propofol diverged for highly perfused tissues (other than brain) because of slow clearance of metabolites, accentuated by enterohepatic recirculation.

Application of whole-body autoradiography in toxicology

Whole-body autoradiography enables the drugs and toxicants to be distributed throughout the animal. Good results are obtained with this technique. However, certain artifacts can occur that could lead to misinterpretation, and these must be known. These artifacts are described. From the metabolic point of view, autoradiography provides data on the distribution kinetics of a compound and the elimination of radioactivity in various organs. These data are a guide for quantitative research into the metabolism of a compound. From the toxicological point of view, it must be admitted that the main purpose of this technique is to reveal the sites of retention of radioactivity. Such specific organ retention could be the consequence of the activation of a minor metabolite into a very reactive compound. If this is so, it is a specific organ effect which could not be studied by other techniques and could lead the way to a more specific organ effect which could not be studied by other techniques and could lead the way to a more appropriate line of research in the study of chronic toxicity. However, it must be recalled that the fact that a compound is retained by a specific organ does not always mean that the compound exerts a toxic effect upon the said organ. With this technique, distribution study can be performed on pregnant animals, and it provides us with more data concerning the transplacental passage of radioactive metabolites. All these aspects of the technique clearly indicate that whole-body autoradiography should be insisted upon during the early stages of development of new molecules. Successive experiments could then lead to selecting the best experimental conditions for metabolic pharmacokinetics and studies in toxicology.

Application and results of whole-body autoradiography in distribution studies of organic solvents

With the growing concern for the health hazards of occupational exposure to toxic substances attention has been focused on the organic solvents, which are associated with both deleterious nervous system effects and specific tissue injuries. Relatively little is known about the distribution of organic solvents and their metabolites in the living organism. Knowledge of the specific tissue localizations and retention of solvents and solvent metabolites is of great value in revealing and understanding the sites and mechanisms of organic solvent toxicity. Whole-body autoradiography has been modified and applied to distribution studies of benzene, toluene, m-xylene, styrene, methylene chloride, chloroform, carbon tetrachloride, trichloroethylene and carbon disulfide. The high volatility of these substances has led to the development of cryo-techniques. Whole-body autoradiographic techniques applicable to the study of volatile substances are reviewed. The localizations of nonvolatile solvent metabolites and firmly bound metabolites have also been examined. The obtained results are discussed in relation to toxic effects and evaluated by comparison with other techniques used in distribution studies of organic solvents and their metabolites.

Formation of acetaldehyde from diethyl ether in man

Diethyl ether anaesthesia caused detectable blood acetaldehyde levels in 15 patients. The average acetaldehyde concentration was 21 micro M which approximates the level found after intake of ethanol. No acetaldehyde could be found in patients anaesthetised without ether.

The biochemical basis of anesthetic toxicity

The inhalational anesthetics reversibly inhibit mitochondrial electron transport from NADH-linded substrates at the level of the enzyme NADH-dehydrogenase. The effect of this inhibition on ATP production is probably not the basis of the anesthetic state, as the level of high-energy phosphate in the brain does not decrease during anesthesia. Anesthetics, therefore, interfere with brain energy untilization, in addition to brain energy production. Inhibition by anesthetics of mitochondrial calcium uptake, which results from the inhibition of electron transport, may be an important anesthetic effect if it raises the intracellular calcium level. Other areas of investigation which have not been discussed here include the effects of anesthetics on glycolytic and other enzyme systems, ion fluxes, neurotransmitter synthesis and release, and on the structure of natural and artificial membranes. It is now appreciated that most of the inhalational anesthetics are metabolized by the endoplasmic reticulum of hepatocytes. The biotransformation of several anesthetics can be increased by drugs which induce hepatic microsomal enzymes. The organ toxicities of chloroform, trichloroethylene, fluroxene, methoxyflurane, and possibly of halothane and enflurane are related to their intermediary or final metabolites. It is of anesthetic drugs for an individual patient.