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PubMedDate not supplied

Cellular distributions and functions of histamine, octopamine, and serotonin in the peripheral visual system, brain, and circumesophageal ring of the horseshoe crab Limulus polyphemus.

The data reviewed here show that histamine, octopamine, and serotonin are abundant in the visual system of the horseshoe crab Limulus polyphemus. Anatomical and biochemical evidence, including new biochemical data presented here, indicates that histamine is a neurotransmitter in primary retinal afferents, and that it may be involved in visual information processing within the lateral eye. The presence of histamine in neurons of the central nervous system outside of the visual centers suggests that this amine also has functions unrelated to vision. However, the physiological actions of histamine in the Limulus nervous system are not yet known. Octopamine is present in and released from the axons of neurons that transmit circadian information from the brain to the eyes, and octopamine mimics the actions of circadian input on many retinal functions. In addition, octopamine probably has major functions in other parts of the nervous system as octopamine immunoreactive processes are widely distributed in the central nervous system and in peripheral motor nerves. Indeed, octopamine modulates functions of the heart and exoskeletal muscles as well as the eyes. A surprising finding is that although octopamine is a circulating neurohormone in Limulus, there is no structural evidence for its release into the hemolymph from central sites. The distribution of serotonin in Limulus brain suggests this amine modulates the central processing of visual information. Serotonin modulates cholinergic synapses in the central nervous system, but nothing further is known about its physiological actions.

Animals↗
PubMed1991

Immunocytochemical localization of octopamine in the central nervous system of Limulus polyphemus: a light and electron microscopic study.

We have determined the distribution and localization of the monoamine octopamine in the prosomal central nervous system of the horseshoe crab, Limulus polyphemus, by light and electron microscopic immunocytochemistry. Sixteen discrete clusters of octopamine-like immunoreactive neurons are situated bilaterally in the tritocerebrum and circumesophageal ring of fused thoracic ganglia. Two pairs of anterior clusters are located laterally in the cheliceral and first pedal ganglia; the remaining six pairs of clusters are located ventromedially in the second through fifth pedal ganglia, chilarial ganglia, and opercular ganglia. The immunoreactive somata range from about 40 to 100 microns in diameter and occur in clusters of 12-24 cells. There is extensive distribution of octopamine-immunoreactive nerve fibers in Limulus; dense fiber tracts course anteroposteriorly through the central nervous system, and most neuropil regions are innervated by immunoreactive processes and terminals. This wide distribution of octopamine-like immunoreactivity provides an anatomical basis for the several effects of octopamine in Limulus. We determined the subcellular localization of octopamine by postembedding immunoelectron microscopy. The immunogold-labelled terminals are morphologically unique; they contain large, distinctively shaped dense-core granules, typically cylindrical with a prominent indentation in one end. These large granules are 100-150 nm in diameter and range from 150-400 nm in length. The dense labelling of these unusual granules with immunogold particles indicates that octopamine is sequestered in or associated with the granules.

Animals↗
PubMed1992

A new specific antibody reveals octopamine-like immunoreactivity in cockroach ventral nerve cord.

An antiserum was raised in rabbits immunized with octopamine conjugated to thyroglobulin. The specificity of this antiserum for octopamine is shown by dot blot immunoassay analysis. The antiserum does not crossreact with dopamine, noradrenaline, and serotonin, but slight crossreactivity with the amine tyramine at high concentrations was observed. The tyramine crossreactivity could be eliminated by preabsorption with a tyramine-glutaraldehyde-BSA conjugate. Using this antiserum, we describe the topographical distribution of octopamine-immunoreactive (ir) neuronal elements in wholemounts and paraffin sections of the ventral nerve cord of the American cockroach. The pattern of octopamine immunostaining is completely different from that obtained with an antidopamine serum, and can be blocked by preabsorbing the antioctopamine serum with BSA-conjugated octopamine. Cell bodies and dendritic processes of putatively octopaminergic dorsal (DUM) and ventral (VUM) unpaired median neurons were clearly octopamine-ir in all ganglia examined. The numbers of stained DUM somata in the mesothoracic, metathoracic, and terminal ganglion of females correspond to those of peripherally projecting DUM cells revealed previously by retrograde tracing (Gregory, Philos Trans R Soc Lond [Biol] 306:191, 1984; Tanaka and Washio, Comp Biochem Physiol 91A:37, 1988; Stoya et al., Zool Jb Physiol 93:75, 1989). In addition, various, previously unknown, paired cells with octopamine-like immunoreactivity were found in all ventral ganglia except abdominal ganglia 3-6. Some of these probably project intersegmentally.

Animals↗
PubMed1975

Occurrence, transport, and storage of octopamine in human thrombocytes.

3H-octopamine was found to be accumulated in human platelets, achieving a maximum concentration gradient of 30:1. Its accumulation was partially inhibited by reserpine, imipramine, serotonin, ouabain, dinitrophenol, and iodoacetate. When octopamine was added to platelet preparations, it led to a decrease of both endogenous and 14C-serotonin. To determine whether octopamine accumulates in human platelets in vivo, preparations from 6 patients receiving monoamine oxidase inhibitors and 17 control subjects were assayed enzymatically for octopamine. Octopamine was detectable in all of the drug-treated patients, averaging 0.45 +/- 0.06 ng/mg protein, while only 4 of the 17 control subjects had detectable (greater than 0.05 ng/mg protein) platelet octopamine. Although much lower than platelet serotonin levels, these octopamine levels are in the range of those reported for platelet norepinephrine and epinephrine.

Biological Transport↗
PubMed1987

Presynaptic modulation by octopamine at a single neuromuscular junction in the mealworm (Tenebrio molitor).

The effect of octopamine on the neuromuscular junction of the mealworm (Tenebrio molitor) was examined. Octopamine potentiated excitatory junctional potentials (EJPs) recorded intracellularly and extracellularly from ventral longitudinal muscle fibers. The potentiating action of octopamine was blocked in the presence of the alpha-adrenergic blocking agent, phentolamine, but not in the presence of another alpha-blocker, phenoxybenzamine, or the beta-blockers propranolol and dichloroisoproterenol. The resting membrane potential, membrane input resistance, reversal potential of EJP, glutamate potentials, and spontaneous miniature EJPs were found to be unaffected by octopamine. In contrast, quantal contents estimated by the extracellularly recorded EJP failures were greatly increased by octopamine. These results suggest that octopamine acted on the presynaptic terminals via alpha-adrenoceptor-like receptors (octopamine receptors) at the Tenebrio neuromuscular junctions to enhance the transmitter release associated with the motor nerve impulses.

Animals↗
PubMed1989

The release of 3H-noradrenaline by p- and m-tyramines and -octopamines, and the effect of deuterium substitution in alpha-position.

The 3H-noradrenaline-releasing effects of p- and m-tyramines and -octopamines, either deuterated or not, were studied in isolated vasa deferentia of the rat (COMT inhibited and calcium-free solution in all experiments). Km for uptake1 was higher for octopamines than for tyramines, but not increased by the introduction of deuterium in alpha-position, except for (probably contaminated) deuterated p-octopamine. Other tissues were preloaded with 3H-noradrenaline. After inhibition of vesicular uptake and MAO equi-releasing concentrations of the eight amines were strictly correlated with Km, they were 6 to 7 times higher for unsubstituted octopamines than for corresponding tyramines. When only MAO (but not vesicular uptake) was inhibited, this difference decreased to about 4-fold, but the releasing potency of the deuterated amines (relative to their parent amines) remained unchanged (except for p-octopamine). When vesicular uptake and MAO were intact, unsubstituted octopamines were only 1.5 to 2.2 times less potent than the corresponding tyramines. Analysis of the efflux of 3H-DOPEG confirmed that this gain in the relative potencies of octopamines is due to their increased ability to mobilize vesicular 3H-noradrenaline; moreover, deuterated amines as well were then better mobilizers than were their parent amines. It is concluded that, provided vesicular uptake is intact, the introduction of a beta-OH-group enhances the ability of indirectly acting sympathomimetic amines to mobilize vesicular noradrenaline; the introduction of deuterium in alpha-position, on the other hand, enhances this mobilizing effect exclusively when MAO is intact.

2-Hydroxyphenethylamine↗
PubMed2000

Octopamine modulates the sensitivity of silkmoth pheromone receptor neurons.

Effects of octopamine and its antagonist epinastine on electrophysiological responses of receptor neurons of Antheraea polyphemus specialised to the pheromone components (E,Z)-6,11-hexadecadienyl acetate and (E,Z)-6,11-hexadecadienal were investigated. Injections of octopamine and epinastine into the moths had no effect on the transepithelial potential of the antennal-branch preparation nor on the spontaneous nerve impulse frequency in either type of receptor neuron. However, in the presence of continuous low-intensity pheromone stimulation, octopamine significantly increased the nerve impulse frequency in the acetate receptor neuron, but not in the aldehyde receptor neuron. Octopamine and epinastine had no significant effect on the receptor potential amplitudes elicited in both receptor neuron types by pheromone stimulation. However, the peak nerve impulse frequency in the response of both receptor neuron types to pheromone was significantly affected: decreased by epinastine and increased by octopamine over a broad range of pheromone concentrations. In control experiments, injection of physiological saline did not significantly alter the peak nerve impulse frequency. The effect of octopamine was established within 1 h after injection and persisted for about 4 h. The possibility of a direct action of octopamine on the nerve impulse generation by the receptor neurons is discussed.

Animals↗
PubMed1986

Octopamine and cyclic AMP mediate release of adipokinetic hormone I and II from isolated locust neuroendocrine tissue.

Octopamine serves as a neurotransmitter in the glandular lobe of the locust corpus cardiacum where it regulates adipokinetic hormone (AKH) secretion from intrinsic neurosecretory cells. Two AKHs (AKH I and II) from the corpus cardiacum of Locusta have been sequenced and synthesized. We have now demonstrated that octopamine mediates release of both AKH I and II from Locusta corpora cardiaca in vitro. Octopamine, IBMX, and forskolin have previously been shown to elevate levels of cAMP in the glandular lobe. In this paper we demonstrate that IBMX and forskolin mediate secretion of AKH I and AKH II thus mimicking the effects of octopamine in this tissue. The cAMP analogs dibutyryl cAMP and 8-bromo cAMP also elicit release of AKH and a subthreshold concentration of IBMX potentiates the effects of octopamine. These observations demonstrate that cAMP participates in regulating AKH release and support the hypothesis that octopamine mediates hormone release at least in part via changes in intracellular levels of cAMP. The release of AKH I and AKH II is apparently regulated by similar mechanisms. The hyperlipemic activity of AKH II released into the perfusates following stimulation by octopamine and agents which elevate cAMP levels is significantly lower than that of AKH I. This differential response is probably due both to the reduced lipid-mobilizing effect of AKH II relative to AKH I, as well as to the release of greater amounts of AKH I.

Animals↗
PubMed2000

Octopamine is the synaptic transmitter between identified neurons in the buccal feeding network of the pond snail lymnaea stagnalis.

We report the pharmacological properties of synaptic connections from the three octopamine-containing OC interneurons to identified buccal feeding neurons in the pond snail, Lymnaea stagnalis. Intracellular stimulation of an OC interneuron evokes inhibitory postsynaptic potentials in the B3 motoneurons and N2 (d) interneurons, while the synapse between OC and N3 (phasic) interneurons has two components: an initial electrical excitation followed by chemical inhibition. All synaptic responses persist in a saline with elevated calcium and magnesium suggesting that the connections are monosynaptic. Local perfusion of 10(-4) M octopamine produces the same inhibitory membrane responses from these buccal neurons as OC stimulation. These responses also persist in high Mg(2+)/Ca(2+) saline indicating direct membrane effects. The similarities in reversal potentials for the synaptic hyperpolarization evoked on B3 neurons after OC stimulation (-89.0 mV, S.E.M.=14.1, n=10) and the octopamine response of the B3 neurons (-84.7 mV, S.E.M.=6.6, n=6) indicate that increased K(+)-conductance underlies both responses. Bath application of the octopaminergic drugs phentolamine (10(-6) M), epinastine (10(-6) M) or DCDM (10(-4) M) blocks the inhibitory synapse onto B3 or N2 neurons and the chemical component of the N3 response. They also block the octopamine-evoked inhibition of B3, N2 and N3 neurons. NC-7 (2x10(-5) M) has a hyperpolarizing agonist effect (like octopamine) on these neurons and also blocks their chemical synaptic input from the OC interneurons. These results provide pharmacological evidence that the neurotransmitter between the octopamine-immunopositive OC interneurons and its followers is octopamine. This is the first example of identified octopaminergic synaptic connections within the snail CNS.

Action Potentials↗
PubMed1979

Determination of plasma octopamine and its level in renal disease.

A radioenzymatic assay method for the estimation of octopamine levels in plasma was developed. Preparation of the enzyme, phenylethanolamine-N-methyl transferase, dilution of the plasma sample, preparation of a suitable blank, and the assay conditions were found to have a significant effect on the sensitivity of the assay. Plasma octopamine levels were measured in a population of 33 normal individuals ranging in age from 19 to 94 years. Significantly higher plasma octopamine levels were found in the age group 70-90 years. Excluding those individuals over the age of 70 years, no significant differences in plasma octopamine levels were found for males or females, the range of values was 0 to 0.68 ng per ml, with a mean value of 0.23 ng per ml (n = 25). Examination of plasma octopamine levels in patients with severe renal disease requiring hemoperfusion dialysis, revealed a significantly higher level of plasma octopamine in renal disease (1.9 ng per ml), and an increase in plasma octopamine during dialysis; the mean level post dialysis being 2.7 ng per ml.

Adult↗
PubMed2002

Intracerebroventricular administration of octopamine stimulates food intake of chicks through alpha(2)-adrenoceptor.

Octopamine, known to be an important neurotransmitter in invertebrates, has been noted to have several similarities to noradrenaline (NA) in mammals. The present study was done to elucidate whether central injection of octopamine enhances the feeding behavior of chicks and to investigate the interaction of octopamine with both alpha(1)- and alpha(2)-adrenoceptors. We found that the intracerebroventricular injection of octopamine significantly stimulated food intake of neonatal chicks during 30 min postinjection, but not thereafter. Moreover, this octopamine-induced eating response was attenuated by the alpha(2)-antagonist yohimbine, but not by the alpha(1)-antagonist prazosin. These results suggest that the action of octopamine on the feeding behavior of the neonatal chick is similar to that of NA, since octopamine regulates food intake through the alpha(2)-adrenoceptor.

Adrenergic alpha-2 Receptor Agonists↗
PubMed2000

Developmental changes in the response of larval Manduca sexta fat body glycogen phosphorylase to starvation, stress and octopamine.

Fasting or starvation of 1(st)- and 2(nd)-day fifth instar Manduca sexta larvae leads to rapid activation of fat body glycogen phosphorylase. Under feeding conditions, 21-29% of the phosphorylase was found in the active form. However, after only one hour of starvation, the active form increased to 55-65%. In larvae on the 3(rd)-day there was a slower increase in the activation, requiring three hours of starvation to reach a maximum of 60-65%. No activation was observed in 4(th)-day larvae after three hours of starvation. When 1(st)- or 2(nd)-day larvae were decapitated, the time-course of activation of glycogen phosphorylase was very similar to that observed in intact insects. However, activation of glycogen phosphorylase following decapitation was only observed in 1(st)- and 2(nd)-day larvae. In 2(nd)-day larvae, octopamine promoted activation of glycogen phosphorylase and 100-pmol of octopamine promoted maximum activation. Higher amounts of injected octopamine caused a decrease in activation. The injection of 100 pmol of octopamine caused a 50-55% activation of phosphorylase within 30 minutes. The simultaneous injection of the alpha-adrenergic receptor antagonist phentolamine with octopamine blocked the octopamine effect in 1(st)- and 2(nd)-day feeding larvae. However, the activation of glycogen phosphorylase observed in ligated/decapitated larvae on the 1(st)- and 2(nd)-day was not abolished by injection of phentolamine. All of these data suggest that factors other than adipokinetic hormone and octopamine may be involved in the activation of glycogen phosphorylase during fasting or starvation in the early part of the fifth larval stage of M. sexta.

Animals↗
PubMedDate not supplied

Octopamine--a neurohormone with presynaptic activity-dependent effects at crayfish neuromuscular junctions.

Octopamine, the phenol analogue of noradrenaline, is a neurosecretory product found in many vertebrate and invertebrate species. In the American lobster, octopamine produces an increase in muscular tension during activation of the motor nerve and may induce spontaneous contractions at concentrations of 10(-7) M (refs 1,2). In the lobster, postsynaptic mechanisms, including a change in Ca2+ conductance of the muscle membrane, are thought to be responsible for potentiation of contraction. In contrast, studies on insects have implicated both pre- and postsynaptic effects: for example, O'Shea and Evans reported that neuromuscular transmission in the locust leg extensor muscle is modulated by octopamine released from a specific neurosecretory neurone which acts on high-affinity octopamine receptors located both on the muscle and on excitatory nerve terminals. The presynaptic receptors mediate an increase in frequency of spontaneous miniature postsynaptic potentials recorded in the muscle. In view of the apparent discrepancy between insect and crustacean results, we have re-examined the effects of octopamine on neuromuscular transmission in a crustacean muscle and report here that enhanced postsynaptic potentials produced by very low levels of octopamine (10(-10) -10(-7) M) are largely attributable to a presynaptic effect which increases quantal release of transmitter. Also, this effect is more pronounced and longer lasting when octopamine is applied to active neuromuscular preparations. This system provides a model for selective consolidation of active synapses by neurohormonal mechanisms. Such an effect could be of general significance in the nervous system, as it would provide a mechanism for selective neurohormonal regulation and strengthening of pathways used during specific activities.

Animals↗
PubMed1997

Selective inhibition of adenylyl cyclase by octopamine via a human cloned alpha 2A-adrenoceptor.

1. In this study we have compared the abilities of the enantiomers of the structural isomers of the phenolamines, octopamine and synephrine, and the catecholamines, noradrenaline and adrenaline, to couple selectively a human cloned alpha 2A-adrenoceptor, stably expressed in a Chinese hamster ovary (CHO) cell line, to G-protein linked second messenger pathways mediating an increase and a decrease in cyclic AMP production. 2. The catecholamines couple the alpha 2A-adrenoceptor to both an increase and a decrease in the rate of cyclic AMP production. In the absence of pertussis toxin pretreatment both catecholamines tested showed a dose-dependent decrease with a maximum at 100 nM. After pertussis toxin pretreatment they both produced a dose-dependent increase in cyclic AMP production with a maximum at 10 microM. 3. The phenolamines, octopamine and synephrine were only able to couple the alpha 2A-adrenoceptor to a dose-dependent decrease in cyclic AMP production at concentrations up to 1 mM, with the synephrine isomers being more potent than the corresponding octopamine isomers. The meta-isomers of both phenolamines were more potent than the corresponding para-isomers and the (-)-enantiomers were more potent than the (+)-enantiomers. Thus, (-)-meta-synephrine [(-)-phenylephrine] was the most effective isomer tested with an observable decrease occurring between 100 nM and 1 microM. 4. The effects of octopamine and the catecholamines on the decrease in cyclic AMP production were additive at submaximal concentrations, whilst octopamine reduced the stimulant effect of submaximal concentrations of noradrenaline on cyclic AMP production after pertussis toxin pretreatment. 5. The time courses of the inhibitory effects of both meta-octopamine and noradrenaline were parallel and peaked after a 1 min exposure to the agonist. In contrast, the stimulant effects of noradrenaline after pertussis toxin pretreatment were of a much slower time course with a maximum effect occurring after a 5 min incubation period. 6. Since octopamine and synephrine occur naturally in, and are co-released with catecholamines from, mammalian tissues, the results of the present study suggest that the human cloned alpha 2A-adrenoceptor can be coupled selectively by different endogenous agonists to G-protein pathways mediating the regulation of adenylyl cyclase activity.

Adenylyl Cyclase Inhibitors↗
PubMed1977

Serum octopamine, coma, and charcoal haemoperfusion in fulminant hepatic failure.

Serum octopamine levels were significantly higher in twenty patients with fulminant hepatic failure (FHF) during the first 48 h of grade IV coma than in health control subjects (3.38 +/- 0.20 ng/ml and 1.75 +/- 0.19 ng/ml respectively, P less than 0.001). Serial measurements in five patients who died without regaining consciousness showed serum octopamine to remain raised, and concentrations in the cerebrospinal fluid at death reflected serum levels. In five patients who regained consciousness, improvement in encephalopathy was associated with a significant reduction in serum octopamine. Renal failure in patients with FHF was found to contribute to raised serum octopamine but could not alone account for the observed levels. Patients given neomycin therapy did not have significantly lower serum octopamine levels than an untreated group. There was, however, a significant correlation between elevated serum octopamine and the occurrence of gestrointestinal bleeding during the previous 24 h. Charcoal haemoperfusion did not appreciably reduce serum octopamine levels.

Charcoal↗
PubMed2005

A family of octopamine [corrected] receptors that specifically induce cyclic AMP production or Ca2+ release in Drosophila melanogaster.

In invertebrates, the biogenic-amine octopamine is an important physiological regulator. It controls and modulates neuronal development, circadian rhythm, locomotion, 'fight or flight' responses, as well as learning and memory. Octopamine mediates its effects by activation of different GTP-binding protein (G protein)-coupled receptor types, which induce either cAMP production or Ca(2+) release. Here we describe the functional characterization of two genes from Drosophila melanogaster that encode three octopamine receptors. The first gene (Dmoa1) codes for two polypeptides that are generated by alternative splicing. When heterologously expressed, both receptors cause oscillatory increases of the intracellular Ca(2+) concentration in response to applying nanomolar concentrations of octopamine. The second gene (Dmoa2) codes for a receptor that specifically activates adenylate cyclase and causes a rise of intracellular cAMP with an EC(50) of approximately 3 x 10(-8) m octopamine. Tyramine, the precursor of octopamine biosynthesis, activates all three receptors at > or = 100-fold higher concentrations, whereas dopamine and serotonin are non-effective. Developmental expression of Dmoa genes was assessed by RT-PCR. Overlapping but not identical expression patterns were observed for the individual transcripts. The genes characterized in this report encode unique receptors that display signature properties of native octopamine receptors.

Amino Acid Sequence↗
PubMed2005

Identification and characterization of a novel family of Drosophila beta-adrenergic-like octopamine G-protein coupled receptors.

Insect octopamine receptors carry out many functional roles traditionally associated with vertebrate adrenergic receptors. These include control of carbohydrate metabolism, modulation of muscular tension, modulation of sensory inputs and modulation of memory and learning. The activation of octopamine receptors mediating many of these actions leads to increases in the levels of cyclic AMP. However, to date none of the insect octopamine receptors that have been cloned have been convincingly shown to be capable of directly mediating selective and significant increases in cyclic AMP levels. Here we report on the identification and characterization of a novel, neuronally expressed family of three Drosophila G-protein coupled receptors that are selectively coupled to increases in intracellular cyclic AMP levels by octopamine. This group of receptors, DmOct beta1R (CG6919), DmOct beta2R (CG6989) and DmOct beta3R (CG7078) shows homology to vertebrate beta-adrenergic receptors. When expressed in Chinese hamster ovary cells all three receptors show a strong preference for octopamine over tyramine for the accumulation of cyclic AMP but show unique pharmacological profiles when tested with a range of synthetic agonists and antagonists. Thus, the pharmacological profile of individual insect tissue responses to octopamine might vary with the combination and the degree of expression of the individual octopamine receptors present.

Adrenergic Agents↗
PubMed1983

The metabolism and biosynthesis of (+/-)-o-octopamine and (+/-)-o-synephrine in the rat.

The metabolism of (+/-)-o-octopamine and (+/-)-o-synephrine by rats was studied quantitatively by a gas chromatography-mass spectrometry-selected ion monitoring (g.c.-m.s.-s.i.m.) method using deuterated internal standards. When o-octopamine was injected intraperitoneally into rats four metabolites were excreted in the urine: (i) unconjugated o-hydroxymandelic acid (OHMA) (16%), (ii) unconjugated o-hydroxyphenylglycol (OHPG) (4.5%), (iii) an acid-hydrolysable conjugate of OHPG (28%) and (iv) unconjugated o-octopamine (10%). When o-synephrine benzoate was similarly administered six metabolites were excreted in urine: (i) unconjugated OHMA (13.5%), (ii) unconjugated OHPG (3.3%), (iii) an acid-hydrolysable conjugate of OHPG (15.6%), (iv) unconjugated o-synephrine (10%), (v) an acid-hydrolysable conjugate of o-synephrine (8.5%) and (vi) unconjugated o-octopamine (0.3%). Adult rats normally excreted OHMA (1.0 micrograms day-1) but OHPG, o-octopamine and o-synephrine could not be detected in urine. After the administration of a monoamine oxidase inhibitor, unconjugated o-octopamine (0.3 micrograms day-1) was excreted in urine but OHPG and o-synephrine could not be detected. o-Tyramine given to rats afforded urinary o-octopamine (75 ng day-1) and this was increased 10-fold upon co-administration of a monoamine oxidase inhibitor and o-tyramine.

Animals↗