ISSN:
1432-1912
Keywords:
Dental pulp
;
Noradrenaline
;
Extraneuronal uptake1
;
O-methylation
Source:
Springer Online Journal Archives 1860-2000
Topics:
Medicine
Notes:
Summary The extraneuronal removal and disposition of noradrenaline in rabbit dental pulp was examined in view of earlier evidence that the tissue possessed an extra-neuronal uptake process resembling neuronal uptake1. Pulp, which had been depleted of sympathetic nerves by homolateral superior cervical ganglionectomy, was incubated in vitro with 3H-noradrenaline in low concentrations (0.025 or 0.18 μmol/l). When the metabolising enzymes (monoamine oxidase, catechol-O-methyl transferase) were active, 3H retention by the denervated pulp, as indicated by the 3H content after the tissue had been washed for 30 min following incubation with 3H-noradrenaline, was less than 30% of that of the innervated pulp. When the enzymes were inhibited, retention rose to approximately 30% of that of the innervated pulp. Analysis of the time course of the 3H efflux indicated that the 3H-noradrenaline in the denervated pulp had accumulated in a single compartment characterised by a t1/2 for efflux of several hours. Accumulation did not occur under Na+-free conditions, and was inhibited by desipramine (IC50 〈 0.03 μmol/l) and by substrates of neuronal uptake1. Mean IC50, values of the latter were very similar to those for inhibition of neuronal uptake1 and comprised (in μmol/l): (+)amphetamine (0.29), dopamine (0.31), tyramine (0.39), (−)noradrenaline (0.70), (−)adrenaline (1.50), 5-hydroxytryptamine (20) and bretylium (35). Uptake2 inhibitors were less active (O-methyl isoprenaline, IC50 = 60 μmol/l) than uptake1 inhibitors, or were without inhibitory effects at the concentrations tested (hydrocortisone, 210 μmol/l; 2-methoxy oestrone, 10 μmol/l). The effects of Na+ omission, of (+)amphetamine, and of O-methylisoprenaline on 3H-normetanephrine formation (measured in the absence of catechol-O-methyl transferase inhibition) matched their effects on 3H-noradrenaline accumulation. The results provide strong support for the presence in rabbit dental pulp of extraneuronal uptake1 which is linked with catechol-O-methyl transferase in the removal of noradrenaline.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00165298
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