Björn E. Svensson

Different effects on the responses of functional pre- and postsynaptic 5-HT1A receptors by repeated treatment of rats with the 5-HT1A receptor agonist 8-OH-DPAT.

The effects of repeated treatment of rats with 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT), 1.0 mg/kg, subcutaneously, twice daily for 7 days, on the stimulation of post- and presynaptic 5-HT1A receptors were examined. The postsynaptic responses, hypothermia and inhibition of the cage-leaving response, evoked by 0.05 mg/kg 8-OH-DPAT, were measured 48 hr after the final injection. Another postsynaptic response, the 5-HT syndrome (flat body posture and forepaw treading) was observed after the third injection of 8-OH-DPAT (1.0 mg/kg s.c.). One presynaptic response examined was the 8-OH-DPAT-induced decrease in the concentration of 5-hydroxyindoleacetic acid (5-HIAA), that indicates a decrease in turnover of 5-HT, due to stimulation of 5-HT receptors on the cell bodies and measured as the ratio of 5-HIAA to 5-HT in the hippocampus, hypothalamus and medulla oblongata. Another presynaptic response was the 8-OH-DPAT-induced decrease in the accumulation of 5-hydroxytryptophan (5-HTP) in the hippocampus and hypothalamus, after inhibition of L-aromatic amino acid decarboxylase by 3-hydroxybenzylhydrazine (NSD 1015), that is due to stimulation of autoreceptors on the 5-HT cell bodies. The kinetic properties of 5-HT1A receptors in the cerebral cortex and hippocampus, hippocampus alone, hypothalamus and medulla oblongata were determined with [3H]8-OH-DPAT. It was found that the postsynaptic effects were markedly attenuated after the treatment, the hypothermic effect already after a single dose.(ABSTRACT TRUNCATED AT 250 WORDS)

Thiols as peroxidase substrates

The abilities of haem peroxidases to catalyse the oxidation of various thiols were studied using the spin-trapping electron spin resonance (ESR) technique. Myeloperoxidase, a neutrophil and monocyte enzyme, catalysed the oxidation of cysteamine, cysteine methyl, and ethyl ester and to some extent 2-mercaptoethanol and thioglycollic acid. This peroxidase poorly catalysed the oxidation of cysteine, N-acetylcysteine, penicillamine, and glutathione under the same conditions. The dependence on pH of peroxidase-catalysed thiol oxidation may indicate that the thiolate anion form is the actual peroxidase substrate. Another leucocyte peroxidase, eosinophil peroxidase, had similar catalytic properties toward thiols as myeloperoxidase. Lactoperoxidase (found in milk, saliva, and tears) and the plant horseradish peroxidase were, however, different from the aforementioned leucocyte peroxidases in their abilities to catalyse the oxidation of thiols.

Involvement of cysteine, serotonin and their analogues in peroxidase-oxidase reactions

Myeloperoxidase-oxidase reactions with close to physiological concentrations of thiols and phenols were studied. Cysteine was shown to be a myeloperoxidase-oxidase substrate when catalytic amounts of serotonin were added as cosubstrate. Penicillamine could be substituted for cysteine and acetaminophen could be substituted for serotonin. The properties of these peroxidase-oxidase reactions, e.g. the dependence on substrate and myeloperoxidase concentration, reduced oxygen species, metal ions and pH, were studied. Also, eosinophil, lacto- and horseradish peroxidase could catalyse these reactions.

Biochemical and behavioural effects of isamoltane, a β-adrenoceptor antagonist with affinity for the 5-HT1B receptor of rat brain

SummaryThe biochemical and behavioural effects of isamoltane, a \-adrenoceptor and 5-HT1B receptor antagonist that has higher affinity for 5-HT1B receptors than for 5-HTIA receptors, on 5-HT neurotransmission in the rat brain were examined. In binding experiments isamoltane was found to be about five times more potent as a ligand for the 5-HT1B receptor than for the 5-HT1A receptor (Ki values 21 and 112 nmol/l, respectively). Isamoltane increased the K+-evoked overflow of 3H from 3H-5-HT loaded slices of rat occipital cortex at 0.1 μmol/l, consistent with inhibition of the terminal 5HT autoreceptor. In vivo, isamoltane significantly increased the concentration of 5-hydroxyindoleacetic acid in hypothalamus and hippocampus indicating an increased 5-HT turnover with a maximal effect at 3 mg/kg s.c. A higher dose produced a less pronounced effect. This effect did not seem to be due to the β-adrenoceptor blocking action of isamoltane since the β-adrenoceptor antagonists, (−)-alprenolol, betaxolol or ICI 118,551 had no significant effects on 5-HT turnover at 5 mg/kg s.c. Isamoltane at 3 mg/kg s.c. induced the wet-dog shake response which was blocked by the tryptophan hydroxylase inhibitor p-chlorophenylalanine. In contrast, the same response induced by the 5-HT2 receptor agonist quipazine was not blocked by pretreatment with p-chlorophenylalanine. The wet-dog shakes evoked by isamoltane and quipazine were blocked by ritanserin, which indicates that 5-HT2 receptors are involved in their expression. These observations indicate that isamoltane, by inhibiting the terminal 5-HT autoreceptors, increased the synaptic concentration of 5-HT to a level that induced a behavioural response.

C8-substituted derivatives of 2-(dipropylamino)tetralin: Palladium-catalyzed synthesis and interactions with 5-HT1A-receptors

Abstract A series of C8-modified analogues of 8-OH-DPAT (1) have been prepared by facile palladium-catalyzed reactions of the triflates of the enantiomers of 1. Several of the new compounds have high affinity for 5-HT1A-receptors and some are potent agonists.

Synergism between substrate and non-substrate thiols in peroxidase-oxidase reactions

Cysteamine and reduced glutathione were shown to act synergistically as peroxidase-oxidase substrates as measured by oxygen consumption and Nitro Blue Tetrazolium reduction. Cysteine methyl ester could be substituted for cysteamine and N-acetylcysteine and penicillamine could be substituted for glutathione. The involvement of reduced oxygen species and the effects of pH and chloride were studied. A possible mechanism of peroxidase-oxidase oxidation of cysteamine and glutathione is proposed. These studies show that peroxidase oxidase reactions can occur with close to physiological concentrations of peroxidase and thiols.

C8-Substituted derivatives of 2-(dipropylamino)tetralin: exploration of the effect of C8-aryl and heteroaryl substituents on the interaction with 5-HT1A-receptor

Summary In order to further explore the structure—activity relationships of serotonergic 2-aminotetralin derivatives, a total of 12 aryl and heteroaryl substituents have been introduced in the C8-position of 2-(dipropylamino)tetralin. The affinity of the compounds was studied by competition experiments with [ 3 H]-8-OH-DPAT in rat-brain tissue. In addition, the effects of the compounds were assessed in vivo using biochemical and behavioral tests in rats. Although all the novel derivatives had fairly high affinities for the 5-HT 1A receptors, several compounds failed to produce biochemical or behavioral effects indicative of 5-HT 1A receptor stimulation. In addition, they did not appear to be 5-HT 1A -receptor antagonists. Hence, the apparent inactivity in vivo may be due to pharmacokinetic factors such as extensive metabolism or poor ability to pass the blood—brain barrier. However, a few compounds in the present series, such as ( S )-8-(2-furyl)-2-(dipropylamino)tetralin, did produce most of the in vivo pharmacological actions typical of 5-HT 1A receptor agonists.

(Z)-3-(4-Bromophenyl)-3-(3-pyridyl)allylamine as substrate for studies of myeloperoxidase activity

(Z)-3-(4-Bromophenyl)-3-(3-pyridyl)allylamine (CPP 200) is transformed to the corresponding chloroimine by hypochlorite ion (ClO-) formed in the presence of myeloperoxidase. A scheme for this transformation is given. The influence of various compounds on this process has been studied. Cysteamine, cysteine and 6-chloro-3-hydrazino-pyridazine inhibited the transformation of CPP 200, while some p-hydroxyphenyl derivatives increased the rate of transformation of CPP 200. The increase seen on addition of the p-hydroxyphenyl derivatives is not a chloride-dependent reaction. Various mechanisms for the inhibiting effect as well as for the activating effect on the transformation of CPP 200 are discussed.