Role of duodenal serotonin in the pharmacological effects of DOPA and dopamine in the isolated rat duodenum]

We have studied the responsibility of tissue serotonin reserves in the excito-motor effects induced by DOPA and dopamine on the isolated rat duodenum in vitro in certain experimental conditions. Two groups of experiments have been performed: first the determination of serotonin endogenous stores after administration of repeated high doses of DOPA and dopamine in the organ bath, secondly the evaluation of motor effects of DOPA and dopamine on rat duodenums experimentally depleted of their endogenous serotonin stores. Serotonin levels were lowered after DOPA and the excito-motor effect of this compound was suppressed in serotonin-depleted duodenums. After dopamine, serotonin tissue levels were not significantly lowered, and the excito-motor effect was observed whatever the serotonin stores may be, depleted or not. Our results are consistent with a relationship between the excito-motor effects of DOPA and serotonin release from endogenous stores; but, concerning dopamine, experimental proofs supporting this hypothesis have not been obtained.     

Effect of DOPA and dopamine on the motility of isolated rat duodenum in vitro]

The motor effects of DOPA and Dopamine on the isolated rat duodenum in vitro have been studied by establishing successive dose- response curves. These effects are either excitatory or inhibitory according to the concentrations used. In every case they are of small amplitude. The inhibitory effects do not exist in the presence of alpha, and beta blocking agents. The excitatory effects are suppressed by using a serotoninergic blocking agent.     

Research on the mechanism of the motor action of dopamine on in vitro isolated rat duodenum]

The study of the direct action of dopamine on the rat duodenum serotoninergic receptors and the parallelism of the results obtained with the motricity curves of this organ in vitro allows us to conclude that dopamine recognizes serotoninergic receptors : the excito- motor effect observed with certain dopamine concentrations on the isolated rat duodenum may be attributed to this action of dopamine on serotoninergic receptors. These results seem in agreement with the observations of other authors.     

Fasciola hepatica: the effects of neuropharmacological agents upon in vitro motility

The effects of a wide range of neuropharmacological agents on the motility in vitro of Fasciola hepatica have been determined using an isometric transducer system. The neuromuscular blocking agents tubocurarine and decamethonium cause a long-term stimulation of the basal activity of the fluke. Acetylcholine causes an inhibition of activity. This effect is mimicked by the cholinergic agonists carbachol and nicotine, antagonised by the cholinergic blocking agents atropine and mecamylamine, and potentiated by eserine, a cholinesterase inhibitor. With nicotine and atropine the effects are accompanied by an increase in muscle tone at a concentration of 1 X 10(-2) M. Noradrenaline and adrenaline also cause some inhibition of activity, an effect antagonised by guanethidine, which blocks the release of noradrenaline. In contrast, dopamine stimulates fluke motility, whilst its antagonist dihydroergotamine causes an inhibition of activity. The monoamine oxidase inhibitors iproniazid and p-chloromercuribenzoic acid induce a stimulation of activity; with the latter there is an increase in muscle tone at a concentration of 1 X 10(-3) M. The amine depleting agents chloroamphetamine and reserpine, and the monoamine uptake inhibitors desipramine and nortriptyline produce an inhibition of fluke activity, as does the serotonin uptake inhibitor fluoxetine. High concentrations of chloroamphetamine (1 X 10(-2) M) and the uptake inhibitors (1 X 10(-3) M and above) also induce an increase in muscle tone. Serotonin causes a marked stimulation of motility. The pharmacological evidence is consistent with a neurotransmitter role of acetylcholine (inhibitory), dopamine (excitatory), and noradrenaline (inhibitory). The status of serotonin is discussed.     

Effect of 7-(3-[4-(2,3-dimethylphenyl)piperazinyl]propoxy)- 2(1H)-quinolinone (OPC-4392), a newly synthesized agonist for presynaptic dopamine D2 receptor, on tyrosine hydroxylation in rat striatal slices

The effects of a newly synthesized compound, 7-(3-[4-(2,3-dimethylphenyl)piperazinyl]propoxy)-2(1H)-quinolinone (OPC-4392), on tyrosine hydroxylation in situ and in vitro were studied using rat striatal slices and tyrosine hydroxylase (TH) purified from bovine adrenal medulla, respectively. OPC-4392 dose-dependently inhibited L-dihydroxyphenylalanine (DOPA) formation in rat striatal slices with IC50 values of about 10(-6) M. The inhibitory effect of OPC-4392 on in situ DOPA formation was dose-dependently reversed by addition of sulpiride, a dopamine D2 receptor antagonist, whereas no change was observed by addition of nomifensine (5 X 10(-6) M), a blocker of dopamine uptake. From in vitro experiment using purified TH, OPC-4392 affected neither the enzymatic activity nor the Km value for 6-methyl-5,6,7,8-tetrahydropterin (6MPH4). These results suggest that OPC-4392 impairs in situ DOPA formation by stimulating presynaptic dopamine D2 receptor as a dopamine agonist, and not by directly inhibiting the TH activity.     

Effect of 3,4-dihydroxyphenylalanine on Cu(2+)-induced inactivation of HDL-associated paraoxonasel and oxidation of HDL; inactivation of paraoxonasel activity independent of HDL lipid oxidation

Paraoxonase1 (PON1), one of HDL-asssociated antioxidant proteins, is known to be sensitive to oxidative stress. Here, the effect of endogenous reducing compounds on Cu²⁺-mediated inactivation of PON1 was examined. Cu²⁺-mediated inactivation of PON1 was enhanced remarkably by catecholamines, but not by uric acid or homocysteine. Furthermore, catecholamines such as 3,4-dihydroxyphenylalanine (DOPA), dopamine or norepinephrine were more effective than caffeic acid or pyrocatechol in promoting Cu²⁺-mediated inactivation of PON1, suggesting the importance of dihydroxybenzene group as well as amino group. DOPA at relatively low concentrations showed a concentration-dependent inactivation of PON1 in a concert with Cu²⁺, but not Fe²⁺. The DOPA/Cu²⁺-induced inactivation of PON1 was prevented by catalase, but not hydroxyl radical scavengers, consistent with Cu²⁺-catalyzed oxidation. A similar result was also observed when HDL-associated PON1 (HDL-PON1) was exposed to DOPA/Cu²⁺. Separately, it was found that DOPA at low concentrations (1-6 μM) acted as a pro-oxidant by enhancing Cu²⁺-induced oxidation of HDL, while it exhibited an antioxidant action at ≥10 μM. In addition, Cu²⁺-oxidized HDL lost the antioxidant action against LDL oxidation. Meanwhile, the role of DOPA/Cu²⁺-oxidized HDL differed according to DOPA concentration; HDL oxidized with Cu²⁺ in the presence of DOPA (60 or 120 μM) maintained antioxidant activity of native HDL, in contrast to an adverse effect of DOPA at 3 or 6 μM. These data indicate that DOPA at micromolar level may act as a pro-oxidant in Cu²⁺-induced inactivation of PON1 as well as oxidation of HDL. Also, it is proposed that the oxidative inactivation of HDL-PON1 is independent of HDL oxidation.     

Simultaneous Determination of 3,4-Dihydroxyphenylalanine, 5-Hydroxytryptophan, Dopamine, 4-Hydroxy-3-Methoxyphenylalanine, Norepinephrine, 3,4-Dihydroxyphenylacetic Acid, Homovanillic Acid, Serotonin, and 5-Hydroxyindoleacetic Acid in Rat Cerebrospinal Fluid and Brain by High-Performance Liquid Chromatography with Electrochemical Detection

A method using reversed-phase ion-pair high-performance liquid chromatography with electrochemical detection for the simultaneous determination of tryptophan (TRP), 3,4-dihydroxyphenylalanine (DOPA), and their metabolites in whole brain, small-brain parts, and cerebrospinal fluid of rats has been developed. The sample preparation requires only homogenization in perchloric acid and centrifugation before injection onto the column. With a LiChrosorb RP-18 (10 micrometer) column and a mobile phase consisting of a phosphate (NaH2PO4, 0.1 M)-methanol mixture with octylsulfonate (2.6 x 10(-3) M) at pH 3.35 and 26 degrees C, the separation of DOPA, dopamine, norepinephrine, 3,4-dihydroxyphenylacetic acid, homovanillic acid, 4-hydroxy-3-methoxyphenylalanine, TRP, 5-hydroxytryptophan (5-HTP), serotonin, and 5-hydroxyindoleacetic acid was achieved. The method has been applied to study the effect of alpha-monofluoromethyldopa alone and in combination with L-DOPA or L-5-HTP, on the catechol and 5-OH indole levels in brain and CSF of the rat.     

Effect of 3,4-dihydroxyphenylalanine on Cu2+-induced Inactivation of HDL-associated Paraoxonase1 and Oxidation of HDL; Inactivation of Paraoxonase1 Activity Independent of HDL Lipid Oxidation

Paraoxonase1 (PON1), one of HDL-asssociated antioxidant proteins, is known to be sensitive to oxidative stress. Here, the effect of endogenous reducing compounds on Cu²⁺-mediated inactivation of PON1 was examined. Cu²⁺-mediated inactivation of PON1 was enhanced remarkably by catecholamines, but not by uric acid or homocysteine. Furthermore, catecholamines such as 3,4-dihydroxyphenylalanine (DOPA), dopamine or norepinephrine were more effective than caffeic acid or pyrocatechol in promoting Cu²⁺-mediated inactivation of PON1, suggesting the importance of dihydroxybenzene group as well as amino group. DOPA at relatively low concentrations showed a concentration-dependent inactivation of PON1 in a concert with Cu²⁺, but not Fe²⁺. The DOPA/Cu²⁺-induced inactivation of PON1 was prevented by catalase, but not hydroxyl radical scavengers, consistent with Cu²⁺-catalyzed oxidation. A similar result was also observed when HDL-associated PON1 (HDL-PON1) was exposed to DOPA/Cu²⁺. Separately, it was found that DOPA at low concentrations (1-6 μM) acted as a pro-oxidant by enhancing Cu²⁺-induced oxidation of HDL, while it exhibited an antioxidant action at ≥10 μM. In addition, Cu²⁺-oxidized HDL lost the antioxidant action against LDL oxidation. Meanwhile, the role of DOPA/Cu²⁺-oxidized HDL differed according to DOPA concentration; HDL oxidized with Cu²⁺ in the presence of DOPA (60 or 120 μM) maintained antioxidant activity of native HDL, in contrast to an adverse effect of DOPA at 3 or 6 μM. These data indicate that DOPA at micromolar level may act as a pro-oxidant in Cu²⁺-induced inactivation of PON1 as well as oxidation of HDL. Also, it is proposed that the oxidative inactivation of HDL-PON1 is independent of HDL oxidation.     

PAF antagonists: different effects on platelets, neutrophils, guinea pig ileum and PAF-induced vasodilation in isolated rat lung

The effects of structurally different PAF receptor blockers were investigated in platelets, neutrophils, guinea pig ileum, rat isolated lung and rat isolated pulmonary artery. PAF caused serotonin release from platelets and a characteristic shape change and adhesion of neutrophils. The antagonists (CV 3988, alprazolam, 48740 RP and Merck-Sharp and Dohme L-652, 731) inhibited platelet serotonin release but not neutrophil shape change adhesion or lysosomal enzyme release. The antagonists in high concentrations (10(-5)-10(-4)M) inhibited nonspecifically the PAF-induced (10(-8)M) guinea pig ileum contraction, but were ineffective at concentrations which inhibited platelet responses. In the rat lung the compounds, in high concentrations, partially inhibited the low dose PAF-induced pulmonary vasodilation and the high dose PAF induced pulmonary vasoconstriction and edema. Our data indicate that some platelet PAF antagonists may be ineffective in blocking the action of PAF on neutrophils and smooth muscle preparations and suggest either PAF-receptor independent actions of PAF or different classes of PAF receptors.     

Effect of various adenine derivatives on gastric acid secretion in the isolated rat stomach

The adenine derivatives adenosine 5'-triphosphate (ATP), adenosine 5'-diphosphate (ADP), adenosine 5'-monophosphate (AMP) and adenosine (AD), in concentrations of 10(-3)M and 10(-4)M caused significant and dose-related modifications in the basal acid secretion from isolated whole rat stomach. The first three purine derivatives, ATP, ADP and AMP significantly increased the spontaneous acid secretion. On the other hand, AD caused a significant reduction in the basal acid secretion. When ATP, ADP, AMP and AD were assayed in the presence of the adrenergic and cholinergic blocking agents, ergotamine, 10(-6)M, propranolol, 5 X 10(-7)M and atropine, 10(-6)M, all these purine derivatives, including AD, caused a significant increase in the basal acid secretion.     

Changes in the Turnover of Monoamines in Prefrontal Cortex of Rats Fed on Vitamin E-Deficient Diet

Turnover of noradrenaline (NA), dopamine (DA), serotonin (5-HT), and their metabolites has been measured after a 15-day vitamin E-deficient diet in adult rat prefrontal cortex. Turnover rates of 3,4-dihydroxyphenylacetic acid, homovanillic acid, and 5-hydroxy-3-indoleacetic acid have been assayed from the disappearance rates after blocking by pargyline inhibition of monoamine oxidase. NA, DA, and 5-HT turnover rates have been measured as accumulation rates of NA, DA, and 5-HT after pargyline inhibition of monoamine oxidase. No change was found in the turnover rate of NA between control and experimental animals. In contrast, turnover rates of DA and homovanillic acid significantly increased in the animals fed on a low-vitamin E diet. However, the most striking results were found on the serotoninergic system. Levels of 5-HT and its main metabolite, 5-hydroxy-3-indoleacetic acid, and their respective turnover rates were lower in the vitamin E-deficient diet. These results could indicate that vitamin E is necessary for the normal functioning of the serotoninergic neurons in the rat prefrontal cortex. The involvement of vitamin E in preventing the formation of free radicals is well known. Therefore, this lack of protective effect after a 15-day vitamin E-deficient diet could be responsible for the neuronal damage to the serotoninergic system. The opposing results found in DA (increase) and 5-HT (decrease) turnover could provide further evidence for an inhibitory control of the serotoninergic ascending pathways to the dopaminergic system in the prefrontal cortex.     

Receptors and neurotransmitters involved in the dual modulation of prolactin release by the serotoninergic system in pregnant and lactating rats

The receptors and neurotransmitter pathways that may participate in the inhibitory action of 5-hydroxytryptamine (5HT) on prolactin release during late pregnancy and lactation in rats were studied. Administration of the 5HT synthesis inhibitor, p-chlorophenylalanine, to late pregnant rats induced a significant increase in serum prolactin concentrations at 17:00 h on day 19 of pregnancy that was partially blocked by injections of the 5HT precursor, 5-hydroxytryptophan, or the 5HT agonists, 8-hydroxy-2-(di-n-propylamino)-tetralin hydrobromide (S1a), 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (S2) and N-(3-chlorophenyl)imidodicarbonimide diamide HCl (S3), but not by RU 24969 (S1b) or 1-meta-(chlorophenyl)-piperazine-2-HCl (S1a-2c). The 5HT neurotoxins, fenfluramine and p-chloroamphetamine, which selectively destroy fine axon serotoninergic fibres but not coarse ones, prevented the increase in circulating prolactin observed at 18:00 h on pro-oestrus and on day 21 of pregnancy, but did not modify serum prolactin concentrations at 17:00 h on day 19 of pregnancy. Administration of the adrenergic antagonists, metoprolol or prazosin, also prevented the stimulatory effects of p-chlorophenylalanine or ketanserin in pregnant rats on day 19 (17:00 h) or on days 10-12 (16:30 h) in lactating rats separated from their litters. Administration of p-chlorophenylalanine to pregnant rats on day 19 reduced dopamine concentrations in the arcuate nucleus and in the anterior hypothalamus and noradrenaline concentrations in the anterior hypothalamus and the suprachiasmatic nucleus. These results indicate that the inhibitory actions of 5HT on prolactin release in pregnant and lactating rats are mediated by S1a, S2a and S3 receptors and by the coarse axon serotoninergic fibres. In addition, the inhibitory actions of 5HT may modulate the action of a stimulatory adrenergic pathway, as well as the concentrations of noradrenaline and dopamine in different hypothalamic areas, which, in turn, particularly arcuate nucleus dopamine, regulate prolactin release.     

Effects of Handling or Immobilization on Plasma Levels of 3,4-Dihydroxyphenylalanine, Catecholamines, and Metabolites in Rats

In conscious animals, handling and immobilization increase plasma levels of the catecholamines norepinephrine (NE) and epinephrine (EPI). This study examined plasma concentrations of endogenous compounds related to catecholamine synthesis and metabolism during and after exposure to these stressors in conscious rats. Plasma levels of 3,4-dihydroxyphenylalanine (DOPA), NE, EPI, and dopamine (DA), the deaminated catechol metabolites 3,4-dihydroxyphenylglycol (DHPG), and 3,4-dihydroxyphenylacetic acid (DOPAC), and their O-methylated derivatives methoxyhydroxyphenylglycol (MHPG) and homovanillic acid (HVA) were measured using liquid chromatography with electrochemical detection at 1, 3, 5, 20, 60, and 120 min of immobilization. By 1 min of immobilization, plasma NE and EPI levels had already reached peak values, and plasma levels of DOPA, DHPG, DOPAC, and MHPG were increased significantly from baseline, whereas plasma DA and HVA levels were unchanged. During the remainder of the immobilization period, the increased levels of DOPA, NE, and EPI were maintained, whereas levels of the metabolites progressively increased. In animals immobilized briefly (5 min), elevated concentrations of the metabolites persisted after release from the restraint, whereas DOPA and catecholamine levels returned to baseline. Gentle handling for 1 min also significantly increased plasma levels of DOPA, NE, EPI, and the NE metabolites DHPG and MHPG, without increasing levels of DA or HVA. The results show that in conscious rats, immobilization or even gentle handling rapidly increases plasma levels of catecholamines, the catecholamine precursor DOPA, and metabolites of NE and DA, indicating rapid increases in the synthesis, release, reuptake, and metabolism of catecholamines.     

Pharmacological induction of larval settlement and metamorphosis in the blue mussel Mytilus edulis L

The blue mussel Mytilus edulis L. is an important aquaculture and fouling species in northern seas. Although the general role of chemical cues for settlement of larvae of the blue mussel has been proposed, few studies have focused on induction of settlement and metamorphosis by pharmacological agents. In this study, the induction of larval settlement of the blue mussel by pharmacological compounds was investigated through a series of laboratory experiments with an aim of identifying artificial cues for laboratory bioassay systems in fouling and antifouling research. Gamma-aminobutiric acid (GABA), dihydroxyphenyl L-alanine (DOPA), isobutyl methylxanthine (IBMX) and acetylcholine chloride (ACH) at 10(-7)-10(-2) M as well as KCl at 10-40 mM K+ in excess of the level in normal seawater were tested for their inductive effect on larval settlement. In filtered seawater (FSW) < 9% of the larvae settled after 48 h. Elevated K+ and GABA levels had no effect on larval settlement and metamorphosis. DOPA at 10(-5) M and IBMX at 10(-6)-10(-4) M induced 41-83% larval settlement and ACH at 10(-7)-10(-5) M induced < 40% larval settlement. While the highest settlement rates were observed after 48 h exposure to the chemical, most of the larvae settled within 24 h. Compounds at concentrations of 10(-3)-10(-2) M were either toxic to larvae or retarded the growth of the post-larvae shell. Juveniles resulting from induction by lower concentrations of chemicals had a very high survival rate, completed metamorphosis and grew as well as the juveniles that metamorphosed spontaneously. IBMX at 10(-6)-10(-4) M and L-DOPA at 10(-5) M are effective agents for induction of settlement and metamorphosis for future studies using juvenile M. edulis.     

7-[3-(4-[2,3-Dimethylphenyl]piperazinyl)propoxy]-2(1H)-quinolinone (OPC-4392), a presynaptic dopamine autoreceptor agonist and postsynaptic D2 receptor antagonist

7-[3-(4-[2,3-dimethylphenyl]piperazinyl)propoxy]-2(1H)-quinolinone (OPC-4392), was synthesized in our laboratories and compared with apomorphine, 3-(3-hydroxyphenyl)-N-n-propylpiperidine (3-PPP) and dopamine antagonists in a series of tests designed to characterize dopamine receptor activation and inhibition. The assertion that OPC-4392 acts as an agonist at presynaptic dopamine autoreceptors is supported by the following behavioral and biochemical observations: OPC-4392, 3-PPP and apomorphine inhibited the reserpine-induced increase in DOPA accumulation in the forebrain of mice and in the frontal cortex, limbic forebrain and striatum of rats. In addition, the gamma-butyrolactone (GBL)-induced increase in DOPA accumulation in the mouse forebrain was also inhibited by OPC-4392, 3-PPP and apomorphine. Haloperidol antagonized the inhibitory effect of OPC-4392 in both instances. The inhibitory effect of OPC-4392 on GBL-induced DOPA accumulation lasted for at least 8 hours after oral administration to mice, while that of 3-PPP and apomorphine disappeared in 4 hours after subcutaneous injection. OPC-4392 failed to increase spontaneous motor activity in reserpinized mice, enhance spontaneous ipsilateral rotation in rats with unilateral striatal kainic acid (KA) lesions, induce contralateral rotation in rats with unilateral striatal 6-hydroxydopamine (6-OHDA) lesions and inhibit 14C-acetylcholine (Ach) release stimulated by 20 mM KCl in rat striatal slices. In addition, OPC-4392 appears to block postsynaptic D2 receptors since OPC-4392, as well as dopamine antagonists, was able to inhibit stereotyped behavior and climbing behavior induced by apomorphine in mice, displace the 3H-spiroperidol binding to rat synaptosomal membranes in vitro and reverse the inhibitory effect of apomorphine on Ach release in rat striatal slices. These results suggest that OPC-4392 acts as a dopamine agonist at presynaptic autoreceptors related to dopamine synthesis and acts as dopamine antagonist at postsynaptic D2 receptors.     

Triazine‐based tyrosinase inhibitors identified by chemical genetic screening

As most of the available depigmenting agents exhibit only modest activity and some exhibit toxicities that lead to adverse side effects after long‐term usage, there remains a need for novel depigmenting agents. Chemical genetic screening was performed on cultured melanocytes to identify novel depigmenting compounds. By screening a tagged‐triazine library, we identified four compounds, TGH11, TGD10, TGD39 and TGJ29, as potent pigmentation inhibitors with IC₅₀ values in the range of 10 μM. These newly identified depigmenting compounds were found to function as reversible inhibitors of tyrosinase, the key enzyme involved in melanin synthesis. Tyrosinase was further confirmed as the cellular target of these compounds by affinity chromatography. Kinetic data suggest that all four compounds act as competitive inhibitors of tyrosinase, most likely competing with l ‐3,4‐dihydroxyphenylalanine (l ‐DOPA) for binding to the DOPA‐binding site of the enzyme. No effect on levels of tyrosinase protein, processing or trafficking was observed upon treatment of melanocytes with these compounds. Cytotoxicity was not observed with these compounds at concentrations up to 20 μM. Our data suggest that TGH11, TGD10, TGD39 and TGJ29 are novel potent tyrosinase inhibitors with potential beneficial effects in the treatment of cutaneous hyperpigmentation.     

Enhanced [3H]DOPA and [3H]Dopamine Turnover in Striatum and Frontal Cortex In Vivo Linked to Glutamate Receptor Antagonism

Abstract: We tested the hypothesis that blockade of NMDA glutamate receptors in brain enhances dopamine turnover. We blocked this class of glutamate receptors in the rat brain in vivo with dizocilpine (MK-801) and measured the accumulation of radiolabeled DOPA and its metabolites as functions of time after intravenous bolus injection. Using the time courses of the accumulated metabolites, we calculated the turnover constants of enzymes mediating dopamine synthesis and catabolism. Dizocilpine treatment for 8 days enhanced the rates of DOPA decarboxylation and dopamine oxidation (monoamine oxidation) 4- and 16-fold, respectively, in neostriatum and 10- and 3-fold, respectively, in frontal cortex. The findings are not inconsistent with the hypothesis that the psychotomimetic properties of dizocilpine may be the manifestation of denervation hypersensitivity linked to activation of key enzymes of dopamine turnover in striatum.     

Axoplasmic transport of dopamine in nigro-striatal neurons

The possibility that dopamine is transported in the nigro-striatal system was investigated by the stereotaxic injection of labelled tyrosine or l -DOPA into the substantia nigra of tranylcypromine-pretreated rats. At various intervals thereafter (2-48 h), significant quantities of labelled material were recovered from the ipsilateral substantia nigra, globus pallidus and caudate-putamen, The activity in the substantia nigra consisted of DOPA, dopamine, methoxytyramine, acid metabolites and other unidentified metabolites. In the caudate-putamen, however, nearly all of the activity (85 per cent) was recovered in the dopamine fraction, the remainder being distributed among some of the metabolites. No DOPA was recovered from the caudate-putamen. On the basis of time-course studies after the injection of [¹⁴C]DOPA into the substantia nigra, we calculated the transport rate of dopamine in the nigro-striatal bundle to be 0.8 mm/h. Electrolytic lesions of the nigrostriatal bundle at the level of the lateral hypothalamus, pretreatment with 6-hydroxydopamine, or injections of [¹⁴C]DOPA dorsal to the substantia nigra each produced profound reductions in the amount of activity subsequently recovered from the caudate-putamen. These data suggest that the activity recovered from the caudate-putamen after injections of [¹⁴C]DOPA into the or substantia nigra reflected axonal transport rather than other processes such as diffusion or transport via the circulation. Pretreatment with the DOPA decarboxy-lase inhibitor, R_o 4-4602, significantly reduced the amount of activity recovered in the caudate-putamen, an indication that decarboxylation of DOPA to dopamine was a prerequisite for transport. Pretreatment with reserpine also severely reduced the transport of dopamine in the nigro-striatal bundle, an observation suggesting that dopamine was transported by binding to the amine storage granules. There was no evidence of retrograde transport of dopamine in the nigrostriatal bundle. Injections of larger than tracer quantities of labelled tyrosine into the substantia nigra did not produce the degree of transport of dopamine that was obtained after injections of DOPA, a result suggesting that the amine storage granules may not normally be filled during axonal transport.     

Adrenomedullary Secretion of DOPA, Catecholamines, Catechol Metabolites, and Neuropeptides

Abstract: Catecholamines and their metabolites have been proposed as markers of sympathetic nervous system stimulation. However, the adrenal medulla is a rich source of catecholamines and catecholamine metabolites and may play a significant role in plasma levels of these compounds. In addition to adrenal catecholamine metabolite efflux, the role of the catecholamine precursor 3,4-dihydroxyphenylalanine (DOPA) has not been fully evaluated. The simultaneous effluxes of catecholamines, metabolites, DOPA, and neuropeptides were measured in perfusates from isolated dog adrenals. The relative abundance of compounds detected consistently during unstimulated conditions was epinephrine ≫ norepinephrine > 3,4-dihydroxyphenylglycol > metanephrine > normetanephrine > dopamine > 3,4-dihydroxyphenylacetic acid > 3-methoxy-4-hydroxyphenylglycol ≥ DOPA ≫ [Met]enkephalin ≫ neuropeptide Y. Effluxes of analytes were not affected by cocaine and the ratios of catecholamines to metabolites increased dramatically with carbachol stimulation, consistent with negligible reuptake into adrenal cells. Thus, most of the 3,4-dihydroxyphenylglycol is expected to be derived from epinephrine and norepinephrine subsequent to translocation from chromaffin vesicles into the cytosol. The efflux of DOPA increased dramatically during stimulation with 30 µ M carbachol in a calcium-dependent manner. Efflux of DOPA during the initial stabilization period of the perfusion preparation declined exponentially, in parallel with the effluxes of the catecholamines and neuropeptides but not with metabolites. Evoked release of DOPA was Ca²⁺-dependent. These data suggest that DOPA can be stored and released exocytotically from chromaffin granules.     

Biogenic amines and their metabolites in Trichostrongylus colubriformis, a nematode parasite of ruminants

The following biogenic amines (BA) and BA metabolites were identified via HPLC in homogenates prepared from adults of Trichostrongylus colubriformis (Nematoda) recovered from the intestines of goats: N-acetyldopamine, DOPA, dopamine, epinephrine, epinine, 5-hydroxyindoleacetic acid, 4-hydroxy-3-methoxy-phenylglycol, 3-(p-hydroxyphenyl) proprionic acid, metanephrine, O-methyl-DOPA, 3-methoxytyramine, norepinephrine, normetanephrine, octopamine, p-hydroxymandelic acid, serotonin, synephrine, tyramine and vanillylmandelic acid. The mean concentrations of these compounds in groups of worms collected from different goats did not differ significantly with sex, but between the groups variance was high with probable components of both host and nematode origin.