András Schaefer

The effects of a soluble factor and of catecholamines on the activity of adenosine triphosphatase in subcellular fractions of rat brain

Abstract The ATPase activity in the presence of K + , Na + , Mg 2+ , total ATPase activity of several subcellular fractions of rat brain was studied. The particle bound ATPase activity is lower in the presence of the soluble fraction. Noradrenaline, dopamine and their α-methylated analogues, adrenaline, isoprenalin and DOPA stimulate ATPase activity. The presence of the soluble fraction is essential for the enzyme stimulating effect. The ATPase stimulating action seems to depend on the catecholamine structure. The soluble fraction inhibits and the catecholamines stimulate both the ouabain sensitive and insensitive parts of the total ATPase activity. A heatstable dialysable factor is responsible both for inhibition and stimulation of the enzymes. The stimulating effect of catecholamines may occur as a reaction to the inhibition.

Lipid peroxidation as the cause of the ascorbic acid induced decrease of adenosine triphosphatase activities of rat brain microsomes and its inhibition by biogenic amines and psychotropic drugs

Abstract The inhibitory effect of ascorbic acid on microsomal Na + , K + -ATPase and Mg 2+ -ATPase activities of rat brain and the ability of several mediator substances and of many drugs acting on the nervous system to antagonize this inhibition was studied. The maximal effect of ascorbic acid on ATPase activities was completely antagonized by catecholamines, apomorphine, oxypertine, reserpine, tetrabenazine, phenothiazines (chlorpromazine and promethazine) and yohimbine at a concentration of 10 −4 M or below. Apomorphine proved to be the most effective compound, fully antagonizing the effect of ascorbic acid at a concentration of 10 −6 M. A partial inhibition of the effect of ascorbic acid was induced by 10 −4 M serotonin, desipramine, imipramine and LSD. During the incubation of the microsomes for ATPase activity determinations in the presence of ascorbic acid, a significant amount of lipid peroxide was formed. Compounds which antagonized the effect of ascorbic acid on the ATPase activities inhibited at the same concentrations the lipid peroxide formation. The well-known inhibitors of lipid peroxidation eliminated the effect of ascorbic acid on the ATPase activities. It has been established that the inhibition of ATPase activities by ascorbic acid is a consequence of lipid peroxidation. The mechanism of action of the antagonizing compounds is discussed.

Protective role of brain ascorbic acid content against lipid peroxidation.

The high ascorbic acid concentration in the brain inhibits lipid peroxidation induced by various agents in rat brain microsomes. The physiological importance of the fact is discussed.

Effects of biogenic amines and psychotropic drugs on endogenous prostaglandin biosynthesis in the rat brain homogenates

Abstract Phenylalkylamine and indolalkylamine derivatives, as well as several drugs acting on the central nervous system, were tested for their effects on endogenous prostaglandin, (PG) biosynthesis in the rat brain homogenates. In the particulate suspension obtained by the removal of the soluble fraction from the rat brain homogenates PG-biosynthesis could be stimulated by noradrenaline. dopamine, adrenaline, serotonin, tryptamine and to a slight extent by tyramine. Isoprenaline, DOPA. α-methyl noradrenaline, α-methyl dopamine, α-methyl tryptamine and 5-hydroxy tryptophan were ineffective. PG-biosynthesis stimulated by catecholamines or indolalkylamines responsively could be inhibited by compounds with monoamine oxidase blocking properties. In the total rat brain homogenates another type of PG-biosynthesis could be demonstrated in the absence of catecholamine or indolalkylamine that could not, or but to a slight extent, be inhibited by monoamine oxidase blocking agents. Apomorphine, oxypertine, α-methyl noradrenaline, promethazine, DOPA, reserpine, chlorpromazine, desipramine, yohimbine and tetrabenazine inhibited this type of PG-biosynthesis, though they failed to influence PG-formation stimulated by catecholamine or indolalkylamine. A correlation could be established between the PG-formation inhibitory and lipid peroxidation antagonizing effects of these compounds. Non-steroidal anti-inflammatory agents, such as indomethacin, acetylsalicylic acid and dipyrone, inhibited both types of PG-biosynthesis. The results permit the conclusion that psychotropic drugs exert their effects on endogenous PG biosynthesis in the rat brain homogenates by inhibiting various activation processes.

On the mechanism of the involvement of monoamine oxidase in catecholamine-stimulated prostaglandin biosynthesis in particulate fraction of rat brain homogenates: Role of hydrogen peroxide

Abstract: The mechanism of involvement of monoamine oxidase (MAO) in catecholamine‐stimulated prostaglandin (PG) biosynthesis was studied in the particulate fraction of rat brain homogenates. High concentrations of either noradrenaline (NA) or dopamine (DA) stimulated effectively PGF2α formation. The same amount of 2‐phenylethylamine (PEA) acted similarly, provided that it was administered together with a catecholamine analogue or metabolite possessing the 3,4‐dihydroxyphenyl nucleus–3, 4‐dihydroxyphenylalanine (DOPA), 3,4‐dihydroxyphenylacetic acid (DOPAC), 3,4‐dihydroxyphenyl‐glycol (DOPEG), 3,4‐dihydroxyphenylacetaldehyde (DOPAL), or α‐methylnoradrenaline (α‐met‐NA)–or with SnCl2. In the absence of PEA, these compounds were ineffective with regard to stimulation of PGF2α formation. Catalase, pargyline, or indomethacin abolished completely PGF2α formation elicited either by catecholamines or by PEA plus a 3,4‐dihydroxyphenyl compound or SnCl2. With regard to the stimulation of PGF2α formation in the presence of α‐met‐NA, PEA could be replaced by H2O2, generated by the glucose oxidase(GOD)‐glucose system. The effect of H2O2 was inhibited by indomethacin or catalase, but pargyline was ineffective. It is assumed that catecholamines play a dual role in the activation of PG biosynthesis in brain tissue. During the enzymatic decomposition of catecholamines MAO produces H2O2, which stimulates endoperoxide synthesis. Simultaneously, catecholamines as hydrogen donors promote the nonenzymatic transformation of endoperoxides into PGF2α. The possible physiological importance of these findings is discussed.

The role of monoamine oxidase in catecholamine-stimulated prostaglandin biosynthesis of rat brain homogenates

Baldessarini, R. J., Kula, N. S., Walton, K. G. (1977) Psychopharmacology 53 : 45-53 Costall, B., Naylor, R. J., Nohria, V. (1978) Eur. J. Pharmacol. 50: 39-50 Ezrin-Waters, C., Muller, P., Seeman, P. (1976) Can. J. Physiol. Pharmacol. 54: 516-519 Friedman, A,, Everett, G. M. (1964) in: Garattini, S., Shore, P. A. (eds) Advances in Pharmacology. Vol. 3 Academic Press, New York, pp 83-127 Goldensohn, E. S., Hardie, J., Borea, E. (1962) J. Am. Med. Assoc. 180: 840-842 Marsden, C. D. (1975) in: Williams, D. (ed) Modern Trends in Neurology. Vol. 6 Butterworths, London,

Effects of tetrabenazine and of chlorpromazine on submitochondrial adenosine triphosphatases of rat brain in the presence of the soluble fraction

Abstract The effects of tetrabenazine and of chlorpromazine on Na + -K + -ATPase and Mg 2+ -ATPase in two submitochondrial fractions prepared from rat brain were studied. The soluble fraction inhibits the ATPases in the two particulate fractions. Tetrabenazine, like the catecholamines, counteracts the inhibition by the soluble fraction. Chlorpromazine inhibits differently the ATPases in the two fractions. In the presence of the soluble fraction chlorpromazine can reduce both the inhibition by the soluble fraction and the stimulation by dopamine or tetrabenazine. It is suggested that an endogenous inhibitor and the catecholamines regulate the ATPase activity of certain membrane structures of the rat brain. Drugs like tetrabenazine and chlorpromazine might affect this regulation.

Inhibition of the sodium and potassium-stimulated adenosine triphosphatase activity during autooxidation of apomorphine

Apomorphine acts fairly selectively to stimulate the dopaminergic receptors (Andtn, Rubenson & others, 1967; Ernst, 1967). Owing to this property it represents an important pharmacological tool in the examination of dopaminergic systems. As a result of an ever more intensive interest in the dopaminergic receptors in the central nervous system an increasing number of papers have discussed also the in vitro biochemical effects of apomorphine (e.g. Goldstein, Freedman & Backstrom, 1970; Kebabian, Petzold & Greengard, 1972; Di Chiara, Balakleevsky & others, 1974; Ferris, Tang & Russell, 1975; Bucher & Schorderet, 1975; Miller, Kelly & Neumeyer, 1976). However, the experiments now reported clearly show that in in vitro systems apornorphines oxidation results in inhibition of Na+, K+-ATPase activity that might lead to the formation of various artifacts. Moreover, this in vitro effect of apomorphine might be of value in studying the inhibitory mechanisms of Na+, K+-ATPase activity. CFE rats of either sex, 150-250 g, were used. From the whole brains a Na+, K+-ATPase rich fraction was obtained by the cell fractionation procedure of Skou (1962) with the alterations of Schaefer, Seregi & Komlos (1974). Samples of the particulate suspension containing 20-30 pg of protein were assayed for ATPase activity in 1 ml incubation mixtures. The standard incubation system for determination of the total ATPase activity contained 50 mrvl tris-HCI buffer pH 7.4, 3 mM MgCI,, 100 mM NaCI, 30 mM KCI, 3 mM Na,ATP (Sigma, St. Louis). Mg2+-ATPase activity was measured in a similar reaction mixture with the omission of NaCl and KC1 and containing 0.5 mM ouabain (Fluka, Buchs). Various amounts of apomorphine hydrochloride (Ph. Hg. VI.) were tested for their effect on ATPase activities in the presence or absence of 0.1 mM of L-ascorbic acid (Merck, Darmstadt) or Lcysteine (Reanal, Budapest) and 0.2 mM of EDTA (Reanal, Budapest). Determination of the ATPase activity was based on the measurement of inorganic phosphate liberated from ATP. The method of Fiske & Subbarow (1925) was adopted to measure inorganic phosphate. Incubations were carried out and the enzyme activities were calculated as described previously (Schaefer, Seregi & Pfeifer, 1973). Protein was determined according to Lowry, Rosebrough & others (1951). Fig. 1 shows the ATPase activities of the partially Purified Na+, K+-ATPase preparation, isolated from rat brain, in the presence of various amounts of