Removal of octopamine

High performance liquid chromatography with coulometric electrochemical detection was used to separate and quantify octopamine and N-acetyl octopamine in haemolymph and incubated tissues of the American cockroach, Periplaneta americana. Injected octopamine is rapidly removed from the insect haemocoel and this removal of octopamine occurs concomitantly with elevated haemolymph levels of N-acetyl octopamine. Studies with isolated tissues indicate that the gut, especially the Malpighian tubules, contribute substantially to the removal of octopamine by N-acetylation. The inclusion of the formamidine pesticide, N-demethylchlordimeform in incubations containing octopamine and Malpighian tubules inhibits the N-acetylation of octopamine by the incubated tissue. 

The rate of removal of -octopamine and N-acetyl OA was determined by injecting 5 yl of a solution containing 26 nmoles of the compound in cockroach physiological saline (16) (CPS) into the insect haemocoel and withdrawing 5 yl aliquots of haemolymph at various times after the initial injection Procedures for injection and haemolymph collection have been described previously (17) Each haemolymph sample was transferred immediately to a 1 5 ml polypropylene tube containing 370 yl 0 3 mM EDTA in 0.1 M perchloric acid and vortexed. Following centrifugation at 40,000 g for 30 min, a 5 yl aliquot of the supernatant was injected directly onto the HPLC column for analysis ... 

Table IV. Rate of Removal of -Octopamine and Production of N-Acetyl -Octopamine by Incubated Malpighian Tubules of Periplaneta americana...

Two important pathways for catecholamine metaboHsm are 0-methylation by COMT, which is cytoplasmicaHy localized, and oxidative deamination by the mitochondrial localized enzyme MAO. There are large amounts of MAO in tissues such as the fiver and the heart which are responsible for the removal of most of the circulating monoamine, including some taken in from the diet. Tyramine is found in high concentrations in certain foods such as cheese, and in wine. Normally, this tyramine is deaminated in the fiver. However, if MAO is inhibited, the tyramine may then be converted into octopamine [104-14-37] which may indirecdy cause release of NE from nerve terminals to cause hypertensive crisis. Thus MAO, which is relatively nonspecific, plays an important role in the detoxification of pharmacologically active amines ingested from the diet. 

The stimulation of the octopaminergic nervous system of invertebrates is a proven strategy for the control of important pest species. This has been achieved in the past by the use of octopamine receptor agonists such as formamidine and imidazoline derivatives. However, other potential strategies to achieve this end include the inhibition of cyclic nucleotide phosphodiesterase, inhibition of the neural reuptake of octopamine, and inhibition of octopamine N-acetyltransferase. Using the American cockroach nervous system, formamidines were found to inhibit both the uptake and acetylation of octopamine, but not with a potency comparable to their effect on octopamine receptors. The tricyclic antidepressant, desipramine, and the benzylamine, xylamine, were the most active inhibitors of these octopamine removal systems. The pharmacological profiles for uptake and N-acetylation appear to be quite similar, but differ from that of the adenylate cyclase-linked octopamine receptor. 

Fig. 1, Confirmation that the cell bodies shown to contain octopamine (in Table 1) belong to PM4 neurons. The photomontage shows the major projections of a Lucifer yellow-stained PM4 neuron revealed by anti-Lucifer yellow immunohistochemistry. The cell body is missing because it was removed for biogenic amine analysis. See Note 9 for additional commentary. Scale 100 pm.

The locust CNS contains approx 100 DUM neurons, distributed dorsomedially in the ganglia of the ventral nerve cord. These neurons contain and release p-octopamine (10). It is possible, therefore, to remove and maintain m vitro an approximately homogeneous population of DUM cell bodies to monitor the biosynthesis of p-octopamine (Fig. 2). Because of the stereotyped location and lai ge size of these cells, physiological confirmation of their identity prior to removal is unnecessary... 

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