Biomedical subjects

G M Tyce

Publications and source records attributed to G M Tyce.

At least 91 records · Page 5Linked to original sources

PubMed1985

Effects of L-dopa and L-tyrosine on release of free and conjugated dopamine, homovanillic acid and dihydroxyphenylacetic acid from slices of rat striatum.

Conjugation (presumably with sulfate) is a demonstrable metabolic pathway for 3, 4-dihydroxyphenylethylamine (dopamine, DA) in brain. Studies were done to determine whether conjugation becomes of increased significance in the presence of precursors of DA. The effects of 3, 4-dihydroxyphenylalanine (L-DOPA) and L-tyrosine on the efflux of free and conjugated DA, 3, 4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid from slices from striatum in rats were studied under quiescent conditions and during release evoked by 40 mM K+ or by 5 X 10(-5) M phenylethylamine (PEA). Conjugated DA was present in the basal efflux from striatal slices and the amounts present were increased during evoked release. More conjugated DA was present in superfusate during K+-evoked release than during PEA-evoked release. L-Tyrosine (5 X 10(-4) M or 5 X 10(-5) M) had little effect on the efflux of conjugated DA, but decreased the amounts of free DA released by PEA, and attenuated the increase in DOPAC that occurred during K+-evoked release of transmitter. L-DOPA (5 X 10(-5) M) increased the formation of conjugated DA, but to a lesser extent than that of free DA or of DOPAC. Thus even after the addition of precursors, conjugation remains a minor metabolic pathway for DA relative to O-methylation or oxidative deamination. The data also suggest that conjugation of DA occurs chiefly outside of the dopaminergic neurons in striatum.

3,4-Dihydroxyphenylacetic Acid↗

PubMed1985

The effects of ethanol on the efflux and release of norepinephrine and 5-hydroxytryptamine from slices of rat hypothalamus.

Studies were done to determine the effects of ethanol on release of norepinephrine, dopamine and 5-hydroxytryptamine from nerve terminals in the central nervous system. Superfused slices of rat hypothalamus were used in these studies and endogenous amines in the superfusate were quantitated using HPLC with electrochemical detection. In these experiments 'release' of transmitters was studied in the presence of amitriptyline to block neuronal uptake of amines, whereas 'efflux' was measured in its absence. A highly intoxicating concentration of ethanol (69.6 mM, 320 mg%) increased the K+-evoked release of norepinephrine, dopamine and serotonin without affecting basal release. Since this concentration of ethanol increased the basal efflux but not the basal release of 5-hydroxytryptamine, it appeared that neuronal uptake of 5-hydroxytryptamine under basal conditions may also be inhibited by intoxicating levels of ethanol.

Affective Disorders, Psychotic↗

PubMed1985

Free and conjugated amines in human lumbar cerebrospinal fluid.

Significant amounts of acid-hydrolyzable conjugates of 3,4-dihydroxyphenylethylamine, norepinephrine, and 5-hydroxytryptamine were detected in lumbar CSF from 22 awake unpremedicated healthy individuals. In the CSF samples, the amounts of conjugated amines almost always exceeded the amounts of free amines, but were less than the amounts of the acid metabolites 3,4-dihydroxyphenylacetic acid, homovanillic acid, and 5-hydroxyindoleacetic acid.

3,4-Dihydroxyphenylacetic Acid↗

PubMed1985

Efflux of 5-hydroxytryptamine and noradrenaline into spinal cord superfusates during stimulation of the rat medulla.

High pressure liquid chromatography with electrochemical detection was used to quantify the efflux, in the same sample, of endogenous 5-hydroxytryptamine (5-HT), noradrenaline (NA), and 5-hydroxyindoleacetic acid (5-HIAA) into superfusates of the rat spinal cord in vivo. The efflux of these three agents was measured prior to, and during, electrical stimulation of the nucleus raphe magnus (n.r.m.) and nucleus reticularis paragigantocellularis (n.r.p.g.), two medullary nuclei implicated in antinociception. In untreated rats, basal efflux of 5-HT and NA was 0.21 and 0.12 ng/ml of superfusate respectively; the basal efflux of 5-HIAA was 18.17 ng/ml. Stimulation of the n.r.m. and n.r.p.g. in these animals increased the efflux of 5-HT and 5-HIAA, but did not alter the efflux of NA. 60 min after administration of fluoxetine (10 mg/kg, I.P.), a 5-HT uptake inhibitor, basal efflux of 5-HT and NA was unaltered, but the basal efflux of 5-HIAA was decreased. In these rats, stimulation of the n.r.m. and n.r.p.g. increased the efflux of 5-HT and of NA. The efflux of 5-HIAA was not altered. In rats pre-treated with both fluoxetine and desipramine (10 mg/kg, I.P.), the basal efflux of NA was increased while that of 5-HIAA was decreased; the basal efflux of 5-HT was not affected. The efflux of NA, but not of 5-HT, was increased in these animals during stimulation of the n.r.m. and n.r.p.g. The efflux of 5-HIAA was not changed by stimulation. Addition of fluoxetine alone or with desipramine to the superfusate in high concentrations greatly increased basal efflux of 5-HT. Failure of stimulation of the ventromedial medulla to increase the efflux of 5-HT in these animals may be related to feed-back inhibition of release by the high concentration of 5-HT initially present in the superfusate. These results indicate that electrical stimulation of the n.r.m. and n.r.p.g. increases the efflux of endogenous 5-HT and NA from the spinal cord. These stimulation sites are coincident with brain-stem sites at which stimulation produces antinociception by activation of spinal serotonergic and noradrenergic receptors. Thus, the ability of stimulation at these sites to evoke the spinal release of the probable neurotransmitters further supports the hypothesis that the antinociceptive effect is mediated by activation of serotonergic and noradrenergic neurones projecting to the spinal cord.

Animals↗

PubMed1985

Uptake and metabolism of norepinephrine by endothelium of dog pulmonary artery.

The contribution of endothelium of dog pulmonary artery to the extraneuronal metabolism of norepinephrine was determined. Pulmonary artery was cut into helical strips; the endothelium was removed from half of the strips by gently stroking them with a wooden applicator stick. All strips were immersed in l-[3H]norepinephrine (2 X 10(-7) M) and mounted for superfusion. Superfusate was collected continuously before, during, and after electrical stimulation (10 V, 2 ms, 2 Hz). Column chromatography was used to separate [3H]norepinephrine and its radiolabeled metabolites in superfusate. Quantitation was by liquid scintillation spectrometry. Previous studies have established that 3,4-dihydroxyphenylglycol is of neuronal origin and that O-methylated metabolites are of extraneuronal origin. Since cocaine prevented neuronal uptake of norepinephrine, the reduction in metabolites of norepinephrine of extraneuronal origin in arteries with endothelium removed represented the contribution of endothelium to extraneuronal metabolism. O-Methylated metabolites were decreased from 3.50 to 2.17 X 10(3) dpm/2 ml of superfusate during basal conditions preceding electrical stimulation and from 11.16 to 6.94 X 10(3) dpm/2 ml of superfusate during electrical stimulation when endothelium had been removed. Decreases in extraneuronal metabolite production continued throughout the basal periods following stimulation. These studies suggest that in small pulmonary artery a substantial amount of the total norepinephrine that is released at the neuroeffector junction may be metabolized following uptake into endothelium.

Animals↗

PubMed1985

The effect of etidocaine on spontaneous and evoked release of norepinephrine from rat brain synaptosomes.

Local anesthetics have been shown to have an effect on neurotransmission. In this study we examined the effect of a local anesthetic, etidocaine, on the uptake, efflux, and release of norepinephrine (NE) from central nerve terminals. The studies were performed on synaptosomes and vesicles prepared from rat brains. Etidocaine 10(-4) M inhibited synaptosomal accumulation of [3H]NE and did not significantly effect vesicular accumulation of this neurotransmitter. This concentration of etidocaine also augmented efflux of norepinephrine from synaptosomal preparations. This augmented efflux was primarily due to an increase in the deaminated metabolite 3,4-dihydroxyphenylglycol (DOPEG). The presence of etidocaine did not significantly alter the release of NE from synaptosomes superfused with high potassium (40 mM), a calcium-dependent exocytotic release process. These results indicate that in the central nervous system, as previously demonstrated in the peripheral nervous system, high concentrations of etidocaine alter vesicular storage of NE, resulting in more NE leaking into the cytoplasm where it is metabolized to an inactive metabolite.

Acetanilides↗

PubMed1984

Effects of estradiol on the basal and evoked efflux of norepinephrine and 5-hydroxytryptamine from slices of rat hypothalamus.

17-beta-Estradiol, at a concentration (100 ng/ml) approaching plasma levels found in pregnant women, inhibited the K+-evoked efflux of endogenous norepinephrine from superfused slices of rat hypothalamus. The same concentration of estradiol increased slightly the basal efflux of serotonin. Since estradiol crosses the blood-brain barrier with ease it is suggested that the inhibition of norepinephrine release from central neurons may contribute to the depression and emotional lability sometimes associated with estradiol therapy.

Animals↗

PubMed1984

Conjugates of dopamine and serotonin in ventriculocisternal perfusates of the cat.

The in vivo formation of acid-hydrolyzable conjugates of dopamine and of serotonin (presumably dopamine-O-sulfate and serotonin-O-sulfate) in ventriculocisternal perfusions of the cat is described. Small amounts of these amine conjugates were detected under quiescent conditions and during evoked release of the parent amines. The amounts of conjugated dopamine in perfusate were increased during and immediately after the period in which release of dopamine was evoked, but were not affected by inhibition of monoamine oxidase. In contrast, the efflux of serotonin conjugate during the evoked release of serotonin was not increased unless monoamine oxidase was inhibited. The data suggest that conjugation of amines in the CNS may be of functional importance in their disposition either under conditions of augmented release or during inhibition of oxidative deamination.

3,4-Dihydroxyphenylacetic Acid↗

PubMed1984

Evidence that halothane inhibits norepinephrine release from sympathetic nerve endings in dog saphenous vein by stimulation of presynaptic inhibitory muscarinic receptors.

Studies were done to determine the mechanism whereby halothane inhibits the release of norepinephrine from postganglionic sympathetic nerve endings. Helical strips of dog saphenous vein were mounted for superfusion and measurement of isometric contractile tension in the presence or absence of halothane (1.2 or 2.5%). Endogenous norepinephrine overflowing in response to electrical stimulation (10 V, 2 Hz for 15 min), and the content of norepinephrine remaining in the veins after stimulation, were measured by liquid chromatography with electrochemical detection. The data indicate that halothane decreased the stimulation-evoked release of norepinephrine by stimulation of prejunctional inhibitory muscarinic receptors. Evidence was also obtained that halothane may impair clearance of norepinephrine from the synaptic cleft.

Animals↗

PubMed1984

Increased conjugated dopamine in plasma after exercise training.

To evaluate the effect of endurance exercise on plasma catecholamines, we exercise trained eight dogs (group T) by treadmill running for 8 weeks. Six sedentary dogs constituted a nontrained control group (group NT). Heart rate response to a graded submaximal stress test was reduced in group T dogs (p less than 0.05), but mean resting aortic blood pressure (NT, 84 +/- 5 mm Hg; T, 82 +/- 4 mm Hg) and heart rate (NT, 87 +/- 1 bpm; T, 84 +/- 2 bpm) were unchanged by exercise, and no cardiac hypertrophy occurred after exercise. Plasma norepinephrine and epinephrine levels were reduced in group T at rest and during a fixed exercise workload. Plasma conjugated dopamine showed a marked increase in group T dogs (NT, 1398 +/- 130 pg/ml; T, 11346 +/- 1291 pg/ml; p less than 0.01) at rest, and no change in conjugated dopamine occurred in either group after short-term exercise stress. No intergroup differences were noted in resting coronary flow or coronary arteriovenous oxygen, or in myocardial oxygen consumption. The data verify previous findings of lower plasma levels of norepinephrine and epinephrine after training, and indicate that a marked rise in conjugated dopamine occurs after training. These findings suggest that norepinephrine and epinephrine metabolism is shifted toward conjugated dopamine by exercise training, thereby reducing active catecholamines in plasma, but retaining a large pool of usable metabolite.

Animals↗

PubMed1983

Drug-induced alterations in the efflux of 5-hydroxytryptamine and of 5-hydroxyindoleacetic acid into superfusates of the rat spinal cord.

The effect of dl-p-chloroamphetamine, fluoxetine and probenecid on the efflux of endogenous 5-hydroxytryptamine (5HT) and 5-hydroxyindoleacetic acid (5HIAA) into superfusates of the spinal cord of anesthetized rats was examined. Mean basal efflux of 5HT and 5HIAA was 0.27 and 15.56 ng/ml superfusate, respectively. The addition of dl-p-chloroamphetamine to the superfusate produced a dose-dependent increase in the efflux of 5HT into the superfusate, but did not increase the efflux of 5HIAA. Probenecid (200 mg/kg i.p.) increased the basal efflux of both 5HT and 5HIAA as compared to control values. When administered systemically, fluoxetine (10 mg/kg i.p. or s.c.) decreased the basal efflux of 5HIAA, but did not alter the basal efflux of 5HT as compared to control values. In contrast, when administered in the superfusate, fluoxetine produced a dose-dependent increase in the basal efflux of 5HT, but did not alter the basal efflux of 5HIAA. The release of 5HT produced by the addition of 2.5 X 10(-4) M dl-p-chloroamphetamine to the superfusate was not prevented in rats pretreated systemically with fluoxetine, although when administered in the superfusate fluoxetine inhibited the dl-p-chloroamphetamine-induced release of 5HT.

Animals↗

PubMed1983

Glucose and amino acid metabolism in rat brain during sustained hypoglycemia.

The metabolism of glucose in brains during sustained hypoglycemia was studied. [U-14C]Glucose (20 microCi) was injected into control rats, and into rats at 2.5 hr after a bolus injection of 2 units of insulin followed by a continuous infusion of 0.2 units/100 g rat/hr. This regimen of insulin injection was found to result in steady-state plasma glucose levels between 2.5 and 3.5 mumol per ml. In the brains of control rats carbon was transferred rapidly from glucose to glutamate, glutamine, gamma-aminobutyric acid and aspartate and this carbon was retained in the amino acids for at least 60 min. In the brains of hypoglycemic rats, the conversion of carbon from glucose to amino acids was increased in the first 15 min after injection. After 15 min, the specific activity of the amino acids decreased in insulin-treated rats but not in the controls. The concentrations of alanine, glutamate, and gamma-amino-butyric acid decreased, and the concentration of aspartate increased, in the brains of the hypoglycemic rats. The concentration of pyridoxal-5'-phosphate, a cofactor in many of the reactions whereby these amino acids are formed from tricarboxylic acid cycle intermediates, was less in the insulin-treated rats than in the controls. These data provide evidence that glutamate, glutamine, aspartate, and GABA can serve as energy sources in brain during insulin-induced hypoglycemia.

Amino Acids↗

PubMed1983

Excretion of amines and their metabolites by two patients in hepatic coma treated with L-dopa.

Two patients in hepatic coma were treated with L-dopa. The first patient showed clear clinical improvement, but the second patient did not. Analyses of urinary metabolites indicated that L-dopa was not absorbed by the second patient. There was evidence that L-dopa had the following beneficial effects in the first patient: (1) increased production of urine, which could have been accompanied by increased excretion of toxins; (2) displacement of tyramine from transmitter sites (because increased excretion of p-hydroxyphenylacetic acid, a major metabolite of tyramine, occurred during L-dopa treatment in patient 1); (3) replenishment of dopamine, and to a much lesser extent, norepinephrine, at central or peripheral neuroeffector junctions; and (4) scavenging of methyl groups by L-dopa, because ratio of methylated amines to catecholamines was higher than normal in both comatose patients before L-dopa treatment, and this ratio decreased during L-dopa treatment in patient 1.

Dopamine↗

PubMed1983

Norepinephrine content and disposition in large and small pulmonary artery of dog.

Comparisons were made between large and small pulmonary arteries in 1) the content of norepinephrine (NE) and 2) the disposition of released NE. Endogenous NE was measured by liquid chromatography with electrochemical detection. The disposition of NE was studied using superfused strips of arteries previously incubated in l-[3H]NE. Superfusate was collected continuously before, during, and after electrical stimulation. 3,4-Dihydroxyphenylglycol (DOPEG) was shown to be of neuronal, and O-methylated metabolites to be of extraneuronal, origin. Thus extraneuronal uptake was estimated directly by measuring the O-methylated metabolites in the superfusate, and neuronal uptake followed by metabolism was estimated by measuring [3H]DOPEG. The magnitude of the neuronal uptake fraction entering vesicles for reuse was estimated from the compensatory increases in [3H]NE and O-methylated metabolites when neuronal uptake was blocked. The predominant route of disposition for NE was neuronal uptake in the small arteries (41% of released NE) but was extraneuronal uptake or NE overflow in the large vessels (35 and 37% of released NE, respectively). Recapture of NE by storage vesicles was greater in small than in large vessels (22 and 7%, respectively, of released NE).

Animals↗

PubMed1983

Effects of hypoxia on norepinephrine release and metabolism in dog pulmonary artery.

The effect of low O2 tensions on the release and metabolism of norepinephrine during resting conditions and in response to electrical stimulation was studied in isolated superfused segments of dog pulmonary artery. Liquid chromatography with electrochemical detection was used to measure the release and overflow of endogenous norepinephrine and the content of norepinephrine remaining in the tissue after stimulation. In other preparations, norepinephrine stores were labeled with [3H]norepinephrine, and measurements were made of [3H]norepinephrine and its metabolites (separated by column chromatography) in superfusates. Radiolabeled metabolites of norepinephrine produced intraneuronally (3,4-dihydroxyphenylglycol) and extraneuronally (O-methylated) were quantitated by liquid scintillation spectrometry and the relative importance of neuronal uptake, extraneuronal uptake and of norepinephrine overflow in the disposition of norepinephrine calculated. Hypoxia increased the release and overflow of endogenous norepinephrine. In hypoxic conditions 41% of released norepinephrine was disposed of by overflow from the cleft compared with 27% during normoxia. Neuronal uptake of released norepinephrine was reduced during hypoxia and the intraneuronal metabolism of norepinephrine by monoamine oxidase was almost eliminated.

Animals↗

PubMed1983

Contractions of canine vascular smooth muscle cells caused by ouabain are due to release of norepinephrine from adrenergic nerve endings.

Experiments were performed to determine whether the contractions of isolated canine blood vessels caused by ouabain are due solely to the release of endogenous norepinephrine. The response of segments of splenic arteries and veins and strips of splenic capsules to ouabain were compared before and after surgical sympathectomy. Successful denervation was demonstrated by absence of a contractile response to electrical stimulation, supersensitivity to exogenous norepinephrine, an extremely low content of endogenous norepinephrine, reduced accumulation of 3H-norepinephrine, and inability of electrical stimulation and tyramine to augment the overflow of 3H-norepinephrine. Ouabain augmented the overflow of 3H-norepinephrine from control but not from denervated splenic capsule. It caused contraction of control but not of denervated splenic arteries, veins, and capsules. Studies were also conducted in the same tissues and in segments of mesenteric and femoral arteries and of circular and longitudinal segments of the portal mesenteric vein before and after chemical sympathectomy with 6-hydroxydopamine. In these tissues, the contractile responses to electrical stimulation but not exogenous norepinephrine and prostaglandin F2 alpha were abolished. In the control tissues, ouabain caused strong contractions, whereas, in the denervated tissues, only a weak or no response to the glycoside occurred. The study demonstrates that, in isolated canine blood vessels, ouabain causes contraction of smooth muscle cells by virtue of its ability to release norepinephrine from the sympathetic nerves.

Adrenergic Fibers↗

PubMed1982

Conjugated dopamine in superfusates of slices of rat striatum.

An acid-hydrolyzable conjugate of 3,4-dihydroxyphenylethylamine (dopamine, DA) was detected in superfusates from slices from rat striatum. The concentrations of endogenous free and conjugated DA, and of the acid metabolites (3,4-dihydroxyphenylacetic acid [DOPAC] and homovanillic acid [HVA]) in superfusates were measured using HPLC with electrochemical detection. Conjugated DA in superfusates represented 10-20% of the free DA under basal conditions and during release evoked by p-tyramine (5 X 10(-6) M to 5 X 10(-4) M); much smaller amounts of conjugated DA overflowed into superfusate when DA was released by equimolar concentrations of beta-phenylethylamine. Surprisingly, inhibition of monoamine oxidase by the inhibitors N-methyl-N-propargyl-3-(2,4-dichlorophenoxy)propylamine hydrochloride (clorgyline) or N-methyl-N-2-propynylbenylamine (pargyline) had little effect on the amounts of conjugated DA present in superfusate. Under basal conditions, the amounts of conjugated DA in superfusate were always less than the amounts of DOPAC but quite similar to the amounts of HVA. However, during release of DA evoked by p-tyramine the concentrations of conjugated DA in superfusate showed much more pronounced increases than those of the acidic metabolites.

3,4-Dihydroxyphenylacetic Acid↗

PubMed1982

Regulation of norepinephrine levels in synaptic clefts of dog vascular tissue.

The overflow of endogenous norepinephrine (NE) from superfused dog pulmonary artery and saphenous vein in response to electrical stimulation and the content of NE remaining in the tissue after stimulation were measured using liquid chromatography with electrochemical detection. Overflow of NE was 0.15-0.22 and 0.14 to 0.30 ng/min in pulmonary artery and saphenous vein, respectively, during stimulation. Release of NE (measured in the presence of cocaine and corticosterone to block removal of NE from the synaptic cleft) was greater in the pulmonary artery (0.50-0.87 ng/min) than in saphenous vein (0.39-0.51 ng/min). NE overflow decreased after the first 4 min of continuous stimulation in saphenous vein but not in pulmonary artery. As only 2.26% of the NE content of vein overflowed during stimulation, depletion of NE or deterioration of the preparation seemed unlikely. Presynaptic alpha- or beta-receptor blockade did not change the pattern of NE overflow. Thus in the saphenous vein, but not in the pulmonary artery, removal of NE from the synaptic cleft appears to be facilitated during electric stimulation. This suggests the existence of a new mechanism, possibly related to enhanced catechol methyltransferase activity, which regulates NE levels in the synaptic cleft in saphenous vein but not in pulmonary artery.

Animals↗