Bo Karlén

Acetylcholine and choline in mouse brain--influence of peripherally acting cholinergic drugs.

Abstract The effects of muscarinic drugs on levels of choline (Ch) in brain and blood and on levels and turnover of acetylcholine (ACh) in brain were studied in mice by means of a pulse injection of 2H6-Ch and analysis of Ch and ACh by mass fragmentography. Oxotremorine (OT) increased the levels of Ch and ACh and reduced the turnover of ACh. Muscarine, which is supposed not to penetrate into brain increased Ch but not ACh levels and reduced ACh turnover. Methylatropine had no effect by itself but when given before OT it abolished the increase in blood Ch and counteracted the OT effect on levels and turnover of ACh. The results demonstrate, that the concentration of ACh does not solely regulate its turnover and that apart from the central actions of OT its peripheral actions play an important role for the turnover of ACh and levels of ACh and Ch in brain.

Effects of oxotremorine on synthesis of acetylcholine in striatum and whole brain of mice killed by various techniques

Abstract Levels of acetylcholine (ACh) and choline (Ch) and turnover of ACh have been studied in whole brain and striatum of mice by mass fragmentography, employing either spinal dislocation or microwave irradiation to kill the animals. Oxotremorine (OT) was found to increase levels of ACh and Ch both in whole brain and striatum regardless of the way of killing. In whole brain turnover of ACh was decreased after OT independently of the way of killing, but in striatum a decrease was observed only if microwave irradiation was used, which is in contrast to previous findings. The discrepancy between whole brain and striatum may be explained by the preserving effect of microwave irradiation on a very fast turning-over pool of ACh in striatum.

Enzymic Oxidation α to the Acetylenic Group in the Metabolism of N-(5-Pyrrolidinopent-3-ynyl)- Succinimide (BL 14) in vitro

1. The product of alpha-acetylenic oxidation of N-(5-pyrrolidinopent-3-ynyl)-succinimide (BL 14) by rat liver preparations was identified as N-(5-pyrrolidino-2-hydroxypent-3-ynyl)succinimide, by mass spectral analysis of metabolites of deuterium-labelled and non-labelled substrate. 2. The synthesis and physicochemical characteristics of the metabolite are reported. 3. Substantial amounts of the metabolite were obtained in preparations from phenobarbital-treated rats, while only minute amounts were formed by non-induced preparations. 4. Evidence for the involvement of an inducible cytochrome P-450 system in effecting this alpha-acetylenic oxidation is presented.

EVIDENCE FOR BINDING OF LIDOCAINE TO TWO CATALYTICALLY DIFFERENT SITES OF LIVER MICROSOMAL CYTOCHROME P-450

ABSTRACT Addition of lidocaine to liver microsomes results in biphasic type I spectral titration curves. A high-affinity and a low-affinity binding phase exist. In this study we have found that microsomes from female rats have a marked high affinity phase, which can hardly be observed with microsomes from female guinea-pigs. Male rats were intermediate. On incubation of lidocaine at concentrations of 1 μM or less with female rat liver microsomes a larger fraction of the drug was aromatically hydroxylated than deethylated. The opposite was true for guinea-pig liver microsomes, and microsomes from male rats were intermediate. The ratio between the formation of deethylated and hydroxylated metabolite increases with the amount of added lidocaine in all microsomes. These data suggest that the two spectral phases represent different binding sites of cytochrome P-450 with a certain “catalytic specificity” – the “high affinity site” catalyzing aromatic hydroxylation and the “low affinity site” deethylation. Observed differential effects of pH and MgCl2 concentration on aromatic hydroxylation and deethylation further strengthens the view that these reactions are catalyzed by different entities of cytochrome P-450.