Differences between the neuronal handling of 3H-7- and 3H-7,8-(-)noradrenaline: implications for the release of the labelled neurotransmitter by nerve stimulation.
Neighbouring rabbit aortic strips were exposed to a tracer concentration of 3H-7- or 3H-7,8-(-)noradrenaline (bearing 30-35% of its label in position 8) and to 0.5 mumol/l unlabelled (-)noradrenaline for 60 min and then washed in amine-free Krebs solution. Catechol-O-methyl transferase and extraneuronal amine uptake were inhibited throughout. After 114 min of wash-out, the tissue contained less tritium when loaded with 3H-7-(-)noradrenaline than when loaded with 3H-7,8-(-)noradrenaline, and the fractional rate of loss of tritium was greater for the former than for the latter tissues. In the presence of cocaine (to prevent neuronal re-uptake), the same percentage of tissue tritium was released by nerve stimulation (six consecutive periods of stimulation at 1 Hz for 5 min each) in spite of the above difference between tissue tritium levels of the two differently labelled amines. In the absence of cocaine, a higher percentage of tissue tritium was released by nerve stimulation (1 or 3 Hz, 5 min each) for 3H-7- than 3H-7,8-(-)noradrenaline. Unchanged 3H-(-)noradrenaline amounted to 35% of tritium in the stimulation-evoked overflow for 3H-7- and to 50% for 3H-7,8-(-)noradrenaline (frequency of stimulation, 1 Hz). When monoamine oxidase (MAO) was inhibited, no differences were observed between the neuronal handling of 3H-7- and 3H-7,8-(-)noradrenaline, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)
D012369:2H-Benzo(a)quinolizin-2-ol, 2-Ethyl-1,3,4,6,7,11b-hexahydro-3-isobutyl-9,10-dimethoxy- / Q000494:pharmacology; D000818:Animals; D003042:Cocaine / Q000494:pharmacology; D004558:Electric Stimulation; D005260:Female; D066298:In Vitro Techniques; D008297:Male; D008996:Monoamine Oxidase Inhibitors / Q000494:pharmacology; D009474:Neurons / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D018377:Neurotransmitter Agents / Q000378:metabolism*; D009638:Norepinephrine / Q000378:metabolism*; D011817:Rabbits
D008996:Monoamine Oxidase Inhibitors; D018377:Neurotransmitter Agents; D012369:2H-Benzo(a)quinolizin-2-ol, 2-Ethyl-1,3,4,6,7,11b-hexahydro-3-isobutyl-9,10-dimethoxy-; D003042:Cocaine; D009638:Norepinephrine