1. A simple in vitro system was developed to study the effect of gamma-hydroxybutyrate on nerve cell depolarization-induced release of labelled dopamine, noradrenaline and 5-hydroxytryptamine from brain slices.2. The release of (3)H-dopamine formed in rat striatal slices incubated with (3)H-tyrosine was followed either by transferring the slices through successive media or by using a superfusion system. A one to three minute exposure to K(+) (53 mM) caused up to a thirty fold increase in the release of newly synthesized (3)H-dopamine. This K(+)-induced release was antagonized when gamma-hydroxybutyrate (1 x 10(-3)M) was present in the medium.3. Potassium (53 mM) increased (eighteen to thirty fold) the release of (3)H-dopamine from striatal slices initially loaded by preincubation with (3)H-dopamine. However, the K(+)-induced release of this pool of dopamine was not antagonized by gamma-hydroxybutyrate.4. Potassium (53 mM) also increased the release from striatal slices of (3)H-5-hydroxytryptamine newly synthesized from (3)H-tryptophan. This K(+)-induced release of 5-hydroxytryptamine was also not inhibited by gamma-hydroxybutyrate.5. The release of newly synthesized (3)H-noradrenaline from hypothalamic slices was also increased by K(+). This K(+)-induced release, however, unlike that of 5-hydroxytryptamine, was antagonized when gamma-hydroxybutyrate was present in the superfusion medium.6. Removal of Ca(++) had no effect on K(+)-induced release of (3)H-dopamine when followed by transferring the slices through successive media. This K(+)-induced release was abolished, however, when Mg(++) (12 mM) was present in the medium.7. The removal of Ca(++) from the superfusion medium abolished almost completely the K(+)-induced release from striatal slices of either newly synthesized (3)H-dopamine or preloaded (3)H-dopamine. This is presumably due to a more effective washout of tissue Ca(++) by the superfusion technique.8. The ability of gamma-hydroxybutyrate to antagonize the K(+)-induced release of monoamines from brain slices does not appear to be unique to the release of newly synthesized dopamine from the striatum.

Amines↗

PubMed1972

Acceleration of catecholamine biosynthesis in sympathetically innervated tissues by angiotensin-II-amide..

1. The effect of angiotensin-II-amide on the biosynthesis of catecholamines (CA) has been studied in a number of isolated tissues in vitro.2. Angiotensin increased the synthesis of CA from (14)C-tyrosine in guinea-pig atria and portal vein, in rat vasa deferentia and the rabbit portal vein.3. Angiotensin had no effect on synthesis of CA from (14)C-labelled DL-DOPA.4. The conditions required to demonstrate an increased synthesis were critical with respect to incubation time and angiotensin concentration. Effects were most readily apparent after incubation for 1 h with concentrations of angiotensin ranging from 10(-9) to 10(-7)M. Higher concentrations caused a significant reduction in synthesis.5. An increased release of newly synthesized CA into the incubation medium was sometimes seen in the presence of angiotensin. However, there was no correlation between increased synthesis and release of CA.6. Angiotensin was rapidly destroyed when incubated with guinea-pig or rat tissues in Krebs solution. The increase in CA synthesis was only apparent at a time when the incubation medium could have contained only a fraction of the original angiotensin activity.7. It is concluded that the effect of angiotensin is not due to increased release of noradrenaline (NA) or to inhibition of NA uptake into nerves. It is possible that angiotensin may influence the activity of tyrosine hydroxylase or its cofactors by an as yet unknown mechanism.

Angiotensin II↗

PubMed1972

Effect of drugs on the synthesis of noradrenaline in guinea-pig vas deferens.

1. Reserpine in vitro (10(-5)M) caused a profound inhibition (>85%) of the formation of both (14)C-catecholamine ((14)C-CA) and (14)C-dihydroxyphenylalanine ((14)C-DOPA) (in the presence of the amino acid decarboxylase inhibitor brocresine) from (14)C-tyrosine in guinea-pig vas deferens. The magnitude of the inhibition was similar for both (14)C-CA and (14)C-DOPA suggesting that the inhibition occurred primarily at the tyrosine hydroxylase step.2. One hour after in vivo treatment with reserpine (1 mg/kg) when tissue stores of noradrenaline (NA) were depleted by 50%, there was a significant inhibition of the formation of (14)C-DOPA. Twenty-four hours after such treatment, when endogenous NA could no longer be detected, synthesis of (14)C-DOPA was indistinguishable from untreated controls. However a 45% inhibition of (14)C-DOPA synthesis from (14)C-tyrosine could be produced in tissues which had been depleted of NA for 24 h or 48 h by the addition of reserpine, 10(-5)M, to the incubation medium.3. Addition of pteridine cofactor, 2-amino-6,7,-dimethyl-4-hydroxy-5,6,7,8-tetrahydropteridine, to the incubation medium in a concentration of 5 x 10(-3)M enhanced the formation of both (14)C-CA and (14)C-DOPA from (14)C-tyrosine in guinea-pig vas deferens. In 52 mM KCl Krebs-Henseleit medium (14)C-CA formation increased from 2.58+/-0.20 (nmol/g)/h to 6.35+/-0.47 (nmol/g)/h whilst (14)C-DOPA formation increased from 5.04+/-0.88 (nmol/g)/h to 11.29+/-0.59 (nmol/g)/h.4. Pteridine cofactor (5 x 10(-3)M) did not reverse the inhibition of (14)C-DOPA formation seen with reserpine (10(-5)M) in previously untreated tissues or in vasa deferentia from animals pretreated with reserpine 1 mg/kg for 24 hours. However, the inhibition did disappear in the presence of pteridine cofactor when treatment with reserpine was prolonged to 48 h and included two doses of reserpine of 2 mg/kg.5. Tyramine (5.8 x 10(-5)M) and bretylium (10(-5)M) in vitro inhibited the formation of (14)C-CA and (14)C-DOPA from (14)C-tyrosine to the same extent in guinea-pig vas deferens again indicating that their major site of action is on tyrosine hydroxylase. The inhibitory effects were reversed by pteridine cofactor.6. Synthesis of (14)C-NA from (14)C-tyrosine in calf splenic nerve was not increased by incubating the tissue in 52 mM KCl-Krebs-Henseleit solution.

Animals↗

PubMed1972

Interaction of atropine-like drugs with dopamine-containing neurones in rat brain.

1. A variety of atropine-like drugs effective in the treatment of drug-induced extrapyramidal syndromes have been investigated with regard to their interaction with dopamine-containing neurones in rat brain.2. Under some conditions benztropine, trihexyphenidyl, atropine and ethopropazine significantly antagonized the chlorpromazine-induced increase in subcortical concentrations of homovanillic acid.3. Most of the atropine-like drugs investigated also decreased the turnover of dopamine in the subcortex as measured by following the disappearance of dopamine after administration of alpha-methyl-p-tyrosine.4. These findings are suggestive that an imbalance between a dopaminergic and cholinergic system might be closely linked to the pathogenesis of extra-pyramidal movement disorders.

Animals↗

PubMed1972

Effect of -hydroxybutyrate on the release of monoamines from the rat striatum.

A simple in vitro system was developed to study the effect of gamma-hydroxybutyrate on nerve cell depolarization-induced release of labelled DA and 5-hydroxytryptamine. The release of (3)H-dopamine formed in rat striatal slices incubated with (3)3H-tyrosine was followed. A three minute exposure to K+ (53.0 mM) caused a thirty-fold increase in the release of newly synthesized (3)H-dopamine. This K + -induced release was antagonized when gamma-hydroxybutyrate (1 mM) was present in the medium. Potassium (53.0 mM) increased (eighteen-fold) the release of (3)H-dopamine from striatal slices initially loaded by preincubation with (3)H-dopamine. The K + -induced release of this pool of DA was, however, not antagonized by gamma-hydroxybutyrate.Potassium (53.0 mM) also increased the release from striatal slices of (3)H-5-hydroxytryptamine (5-HT) newly synthesized from (3)H-tryptophan. This K + -induced release of 5-HT was also not inhibited by gamma-hydroxybutyrate. The ability of gamma-hydroxybutyrate to antagonize only the K + -induced release of newly formed DA may explain why this agent causes a rapid and selective increase in brain dopamine.

Animals↗

PubMed1972