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At least 19 recordsLinked to original sources
PubMed1985

Phenyliminoimidazolidines. Characterization of a class of potent agonists of octopamine-sensitive adenylate cyclase and their use in understanding the pharmacology of octopamine receptors.

Octopamine, a major aminergic neurotransmitter in invertebrates, exerts many of its actions through receptors which are associated with the activation of adenylate cyclase. The present study defines and characterizes a new class of potent octopamine agonists, the substituted phenyliminoimidazolidines (PIIs). Approximately 30 of these derivatives were examined for agonist and antagonist effects on the highly enriched and specific octopamine-sensitive adenylate cyclase present in the firefly light organ, as well as on adenylate cyclases present in other invertebrate and vertebrate tissues. Several derivatives were extremely active and some (e.g. 2,6-diethyl-PII) had potencies exceeding those of any previously described agonists of octopamine-sensitive adenylate cyclase. Stimulation by the potent PIIs was reversible, nonadditive to that caused by octopamine, and could be antagonized by antagonists such as cyproheptadine (Ki = 4 microM), phentolamine (Ki = 23 microM), and propranolol (Ki = 72 microM). These inhibitory constants agreed well with those for inhibiting octopamine stimulation. Certain PII derivatives acted as partial agonists and some as antagonists of octopamine stimulation. Structure-activity relationships revealed, among other things, that short-chain alkyl substitution in the 2- and 6-phenyl positions enhanced activity, as did further substitution of 4-halo, 4-methyl, or 4-hydroxy substituents. 4-Amino or N-alkyl substitution decreased activity. Structurally related benzylimidazoline derivatives such as tolazoline and naphazoline were partial octopamine agonists, generally less active than the PIIs. Comparison, in three invertebrate species, of the effects of the PIIs and two other chemical classes of octopamine agonists demonstrated clearcut differences in species responsiveness. Other comparative studies revealed that the agonist activity of the potent PIIs was specific for tissues containing an octopamine-sensitive adenylate cyclase; adenylate cyclases activated by dopamine or by beta 1- or beta 2-adrenergic agonists were unaffected by these compounds. Evaluation of the relative binding affinities of various PIIs for mammalian alpha-adrenergic receptors, as well as the ability of various antagonists to block PII binding, strongly suggested that the active PIIs are affecting a class of octopamine receptors distinct from mammalian alpha 1- or alpha 2-adrenergic receptors. These octopamine receptors also appeared distinct from mammalian 5-HT1 and 5-HT2 receptors. Correlative physiological studies in insects revealed that the active PIIs mimicked octopamine and were potent activators of light emission in the firefly light organ.(ABSTRACT TRUNCATED AT 400 WORDS)

Adenylyl Cyclases↗
PubMed1985

m-Octopamine: normal occurrence with p-octopamine in mammalian sympathetic nerves.

The development of a radiochemical enzyme assay for p-octopamine in 1969 led to its identification in a large number of invertebrate nerve systems and in mammalian sympathetic nerves. The original method by which p-octopamine was measured has now been found to be nonspecific; however, modifications of this procedure can determine both m- and p-octopamine. We recently developed a new specific method for the unequivocal identification and quantitative determination in tissue of the six octopamine and synephrine isomers. With this method--negative chemical ionization gas chromatography-mass spectrometry--the more physiologically active m-octopamine has been found in association with p-octopamine in 10 organs of the rat. m-Octopamine is present in concentrations equal to those of p-octopamine in heart, spleen, and liver and in concentrations from 30 to 60% of p-octopamine in adrenals, vas deferens, brain, kidney, large intestine, bladder, and lungs. In vivo inhibition of monoamine oxidase markedly increased the concentrations of both m- and p-octopamine in all organs examined. Both amines were virtually absent from all organs except the adrenals following chemical sympathectomy with 6-hydroxydopamine, thereby establishing that m- and p-octopamine are localized within sympathetic nerve endings.

2-Hydroxyphenethylamine↗
PubMed1989

A possible new class of octopamine receptors coupled to adenylate cyclase in the brain of the dipterous Ceratitis capitata. Pharmacological characterization and regulation of 3H-octopamine binding.

Octopamine exerts its effects in insects through interaction with at least two classes of receptors, designated octopamine-1 and octopamine-2. Octopamine-2 receptors are positively coupled to adenylate cyclase, while octopamine-1 receptors are not coupled to this enzyme system. Ceratitis capitata brain appears to have octopamine receptors as unique aminergic receptors coupled to adenylate cyclase. These receptors show some pharmacological analogies with respect to octopamine-2 receptors, however they should constitute a new class of octopamine receptors. C. capitata brain octopamine receptors have also been characterized by [3H]octopamine-binding studies, exhibiting similar regulatory mechanisms to other receptors coupled to adenylate cyclase activation.

Adenylyl Cyclase Inhibitors↗
PubMed1985

Characterization of octopamine-sensitive adenylate cyclase: elucidation of a class of potent and selective octopamine-2 receptor agonists with toxic effects in insects.

Octopamine-2 receptors, associated with activation of adenylate cyclase, mediate a number of the important hormonal and neurotransmitter functions of octopamine in invertebrates. By utilizing the highly enriched octopamine-sensitive adenylate cyclase present in the firefly light organ, it has been possible to pharmacologically characterize octopamine-2 receptors and to define a new class of highly potent and selective octopamine-2 agonists. At low concentrations, these substituted phenyliminoimidazolidines stimulate light emission when injected into fireflies. At somewhat higher concentrations, these compounds, when ingested by tobacco hornworms, cause disruption of motor and feeding behavior, leading to insect death. The effects of these compounds are markedly potentiated by phosphodiesterase inhibitors and mimicked by other activators of octopamine-sensitive adenylate cyclase, including octopamine itself. Because octopamine-2 receptors appear to be present primarily in invertebrates, these findings, together with other data, raise the possibility that potent and selective octopamine agonists could be useful as insect toxins with low toxicity in vertebrates.

Adenylyl Cyclases↗
PubMed1987

Is octopamine a 'false transmitter'? Regional distribution and serial changes in octopamine and noradrenaline following locus coeruleus lesions.

The effects of electrolytic lesions of the locus coeruleus (LC) on endogenous octopamine and noradrenaline levels were observed at various temporal intervals. Noradrenaline was assayed from halved tissue samples by high-performance liquid chromatography (HPLC) while octopamine was determined from the other halves of the brain samples by radioenzymatic assay methods accompanied by chromatographic separation. Brains were dissected into 8 regions: cerebellum, anterior and posterior cortex, hippocampus, hypothalamus, medulla/pons, midbrain and striatum. Assays were performed at postlesion intervals of 4, 8, 13 and 18 days. The rates of depletion of noradrenaline at the tested intervals roughly matched those of octopamine in the anterior cortex, posterior cortex and striatum. In the cerebellum, hypothalamus, hippocampus and pons/medulla, levels of octopamine diminished later than those of noradrenaline, at times showing an initial increase within the first week after the LC lesion. In the midbrain however, this pattern was reversed, octopamine levels initially decreasing in parallel with noradrenaline but subsequently recovering to significantly higher values. The results do not unequivocally support the hypothesis that octopamine is present in the brain solely as a 'false transmitter' in noradrenergic neurones. Neither, however, do they provide clear support for earlier contentions that octopamine is likely to play a role in central neurones as a synaptic transmitter, independent of the noradrenergic system.

Animals↗
PubMed1976

Octopamine neurons in lobsters: location, morphology, release of octopamine and possible physiological role.

Octopamine cells are found along second thoracic roots, where they serve as neurosecretory neurons capable of releasing octopamine at two distinct points: one into the hemolymph immediately before it enters the gills; one into the hemolymph immediately after it leaves the gills. The octopamine cells receive a cholinergic synaptic input. We presume that this input is from processes of peripheral sensory cells bringing information to the CNS. Octopamine can increase the strength of contraction of exoskeletal muscles and, at higher concentrations, can induce contractures in these muscles. These effects can be interpreted as a resetting of the level of ionized calcium within muscle fibers (the contracture) to a higher value or a possible enhanced entry of calcium ions during nerve stimulation (increased strength of contraction). The observed effects are of a prolonged duration, outlasting the time of application of octopamine by some 20-40 minutes. We do not know if this effect on muscle tension production is the normal physiological role of octopamine. Other possible roles will be explored in the future. The pathway involving the octopamine neurons in lobsters may provide a model neurohumoral system that can be studied and understood in detail from the level of sensory input to the level of behavioral output.

Animals↗
PubMed1992

A new octopamine receptor class in locust nervous tissue, the octopamine 3 (OA3) receptor.

The insect neuronal 3H-octopamine binding site represents a new type of octopamine receptor. This receptor has pharmacological features that are characteristic for all known octopamine receptors, but it is possible to distinguish this receptor class from all others using either agonists or antagonists. The quantitative determination of the pharmacological relationships to the other octopamine receptor classes could demonstrate greatest homology with both class 2 (OA2A and OA2B) receptors. Therefore, the neuronal octopamine receptor should be named a class 3 receptor (OA3). A new and simple classification scheme for octopamine receptors which enables classification of the new receptor class is established using antagonists.

Adrenergic Agonists↗
PubMed1989

A probe for octopamine receptors: synthesis of 2-[(4-azido-2,6-diethylphenyl)imino]imidazolidine and its tritiated derivative, a potent reversible-irreversible activator of octopamine-sensitive adenylate cyclase.

In order to develop an irreversible ligand for octopamine receptors, a highly potent azido-substituted 2-(phenyl-imino)imidazolidine (NC-5Z, 8) and its tritiated derivative (3H-NC-5Z, 11) have been designed and synthesized. Under reversible-binding conditions, NC-5Z is 50-100-fold more potent than octopamine in activating octopamine-sensitive adenylate cyclase in a variety of tissues. After photolysis, 3H-NC-5Z binds irreversibly to cell membranes, and this binding is reduced by preincubation with octopamine agonists and antagonists but not by norepinephrine, dopamine, serotonin, or histamine. NC-5Z should be useful both as a potent reversible octopamine agonist and as an affinity probe for characterizing and isolating octopamine-receptor proteins.

Adenylyl Cyclases↗
PubMed1979

Age variation in the increase of hypothalamic and brain stem contents of phenylethanolamine m-octopamine and p-octopamine in spontaneously hypertensive rats (SH Kyoto).

Phenylethanolamine, m-octopamine and p-octopamine contents were determined as a function of age in the hypothalamus and brain stem of spontaneously hypertensive rats and controls Wistar Kyoto. In hypothalamus, the content of the 3 amines was 2--4-fold greater for the SH rats. In the brain stem, the phenylethanolamine and p-octopamine contents were 2--3-fold greater in SH rats but 5--6-fold higher in the case of m-octopamine. The difference appears at 3 weeks and correlates the blood pressure with the increase of age. The significance of these findings is discussed.

2-Hydroxyphenethylamine↗
PubMed1978

[Increased contents of phenylethanolamine, m-octopamine and p-octopamine in the hypothalamus and brain stem of spontanously hypertensive rats (S.H.R. Kyoto)].

Phenylethanolamine, p-octopamine and m-octopamine contents were determined in the hypothalamus and the brain stem of spontaneously hypertensive Rats (S.H.R. Kyto) and the corresponding controls (Wistar Kyoto). In three-week-old Rats, phenylethanolamine and p-octopamine are found to be present in S.H.R. hypothalamus and brain stem at concentrations twice as high as compared to Wistar Kyoto Rats. The amount of m-octopamine is 5-fold higher in the brain stem of S.H.R. Rats as compared to Wistar Kyoto Rats.

2-Hydroxyphenethylamine↗
PubMed1973

Octopamine-sensitive adenylate cyclse: evidence for a biological role of octopamine in nervous tissue.

An adenylate cyclase that is activated specifically by very low concentrations of octopamine has been identified both in homogenates and in intact cells of the thoracic ganglia of an insect nervous system. This enzyme appears to be distinct from two other adenylate cyclases present in the same tissue, which are activated by dopamine and by 5-hydroxytryptamine, respectively. The data raise the possibility of a role of octopamine-sensitive adenylate cyclase in the physiology of synaptic transmission.

Adenylyl Cyclases↗
PubMed1988

Activities of octopamine and synephrine stereoisomers on octopaminergic receptor subtypes in locust skeletal muscle.

The activities of the (-) and (+)- forms of p-, m- and o-octopamine and p- and m-synephrine have been compared on the different subtypes of octopamine receptor present in the extensor-tibiae neuromuscular preparation from the locust hindleg. The rank order of potency of the (-)-forms on the OCTOPAMINE2A receptors was p-synephrine greater than p-octopamine greater than m-octopamine greater than o-octopamine greater than m-synephrine whilst the rank order of the (+)-forms was p-synephrine greater than p-octopamine greater than m-octopamine. (+)-m-Synephrine and (+)-o-octopamine had no effect on this class of receptor when tested up to a concentration of 10(-3) M. The rank order of potency of the (-)-forms on the OCTOPAMINE2B receptors was p-synephrine greater than p-octopamine greater than m-synephrine greater than m-octopamine greater than o-octopamine whilst the rank order of the (+)-forms was p-octopamine greater than p-synephrine greater than m-octopamine greater than o-octopamine. (+)-m-Synephrine again had no effect up to a concentration of 10(-3) M. The rank order of potency of the (-)-forms on the OCTOPAMINE1 receptors was p-synephrine greater than p-octopamine greater than m-synephrine greater than m-octopamine greater than o-octopamine, whilst the rank order of the (+)-forms was p-synephrine greater than p-octopamine greater than o-octopamine greater than m-synephrine greater than m-octopamine.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

Activities of octopamine and synephrine stereoisomers on alpha-adrenoceptors.

1. The activities of the (-)- and (+)-forms of m- and p-octopamine and m- and p-synephrine on alpha 1-adrenoceptors from rat aorta and anococcygeus and alpha 2-adrenoceptors from rabbit saphenous vein were compared with those of noradrenaline (NA). 2. The rank order of potency of the (-)-forms on alpha 1-adrenoceptors from rat aorta and alpha 2-adrenoceptors was NA greater than m-octopamine = m-synephrine greater than p-octopamine = p-synephrine. The two m-compounds were 6 fold less active than NA on alpha 1-adrenoceptors from rat aorta and 150 fold less active on alpha 2-adrenoceptors. The two p- compounds were 1,000 fold less active than NA on both alpha 1-adrenoceptors from rat aorta and alpha 2-adrenoceptors. The rank order of potency of the (-)- forms on alpha 1-adrenoceptors from rat anococcygeus was NA = m-synephrine greater than m-octopamine greater than p-octopamine = p-synephrine. m-Octopamine was 4 fold less active than NA and (-)-m-synephrine. The two p- compounds were 30 fold less active than NA. 3. The rank order of potency of the (+)- forms was NA greater than m-octopamine greater than m-synephrine greater than p-octopamine greater than p-synephrine on both alpha 1- and alpha 2-adrenoceptors. The potency of each (+)- form was 1-2 orders of magnitude less than that of the (-) counterpart, the differences being greater for the stereoisomers of synephrine than for those of octopamine on both alpha 1- and alpha 2-adrenoceptors. 4. The yohimbine diastereoisomer antagonists, rauwolscine and corynanthine, were tested against (-)-NA and (-)-m-octopamine-induced contractions in both preparations. Based upon the known selectivities of these isomers for alpha-adrenoceptor subtypes, it is concluded that the rat aorta contains only alpha 1-adrenoceptors while the rabbit saphenous vein possesses predominantly alpha 2-adrenoceptors. 5. Ligand binding data for the octopamine and synephrine stereoisomers at alpha 1- and alpha 2-binding sites from rat cerebral cortex was also obtained. (-)-Forms were more active than (+)-forms. The rank order of affinity of the (-)-forms for both alpha 1- and alpha 2-binding sites was NA greater than m-octopamine = m-synephrine greater than p-synephrine greater than p-octopamine. The relative affinities of the members of the series against alpha 1-binding sites were very similar to their relative functional activities on rat aorta. However, the affinities of both m- and p-compounds relative to that of ( -)-NA were much greater at the x2-binding sites than were the relative activities in rabbit saphenous vein, possibly suggesting low intrinsic efficacy. Functional antagonist responses to NA by the (-)-octopamine and synephrines could not, however, be demonstrated on rat aorta or rabbit saphenous vein. 6. The activities of m-octopamine and m-synephrine were not significantly different from each other on either a,-adrenoceptors from rat aorta or x2-adrenoceptors; however, m-synephrine is more active than m-octopamine on a,-adrenoceptors from rat anococcygeus. Both m-octopamine and msynephrine can be considered to be naturally occurring x,-selective amines. However, if m- and poctopamine are co-released with NA in amounts proportional to their concentration, it is concluded that their activities on m,- and x2-adrenoceptors are too low to be physiologically significant.

2-Hydroxyphenethylamine↗
PubMed1989

M-octopamine injected into the paraventricular nucleus induces eating in rats: a comparison with noradrenaline-induced eating.

1. The effects on food intake in rats of injection of m- and p-octopamine into the paraventricular nucleus (PVN) of the hypothalamus were examined, and compared to the effects of noradrenaline (NA). 2. m-Octopamine injected into the PVN induced a dose-dependent increase in food intake, with the maximal effect occurring at a dose of 25 nmol. p-Octopamine did not elicit eating unless it was administered to animals pretreated with the monoamine oxidase inhibitor, pargyline. 3. The effects of pretreatment with various adrenoceptor antagonists, injected into the PVN, on the eating responses induced by 25 nmol m-octopamine and NA were examined. The alpha 1-adrenoceptor antagonist, corynanthine, and the beta-adrenoceptor antagonist, propranolol, failed to alter the eating induced by m-octopamine or NA. The effects of these two amines were susceptible to blockade of alpha 2-adrenoceptors. Idazoxan reversed the eating induced by m-octopamine and noradrenaline. However, yohimbine was effective only against the eating induced by m-octopamine. Thus, both m-octopamine and NA appear to act via alpha 2, but not alpha 1 or beta-adrenoceptors. 4. Injection of alpha-methyl-p-tyrosine into the PVN attenuated the effect of m-octopamine, but not of NA. This result suggests that m-octopamine elicits eating, at least in part, by releasing endogenous NA. 5. The NA and octopamine uptake inhibitor, desipramine, significantly potentiated the eating induced by a low dose of m-octopamine. This effect may occur because desipramine would prolong the synaptic activity of released NA. 6. The results indicate that m-octopamine elicits a marked and reliable eating response which is mediated largely by a release of endogenous NA, which acts at alpha 2-receptors. These results are consistent with the view that octopamine may function as a modulator of NA activity in the central nervous system.

Animals↗