ISSN:
1432-1912
Keywords:
Nerve Stimulation
;
Noradrenaline Metabolites
;
Hydrocortisone
;
Extraneuronal Uptake
;
Normetanephrine
;
Nictitating Membrane
Source:
Springer Online Journal Archives 1860-2000
Topics:
Medicine
Notes:
Summary The metabolism of 3H-noradrenaline released by nerve stimulation in the isolated nerve-muscle preparation of the cat nictitating membrane was determined under control conditions and in the presence of hydrocortisone, 28 μM, a concentration which inhibits the high affinity extraneuronal uptake of noradrenaline in this tissue. in the controls the main fraction in the overflow elicited by stimulation at 10 Hz during 2 min was the deaminated glycol, 3H-DOPEG (3,4-dihydroxyphenylglycol), which accounted for 45.2±2.96% of the total radioactivity. Under these conditions, 3H-noradrenaline represented 30.8±1.92%, while 3H-normetanephrine accounted for 14.5±0.94% of the total overflow of radioactivity. During exposure to hydrocortisone there was a selective inhibition in 3H-normetanephrine formation from 3H-noradrenaline released by stimulation while the other fractions were not affected significantly. In contrast to these results, there were no changes in the spontaneous outflow of 3H-normetanephrine during exposure to hydrocortisone. The results obtained support the view that 3H-normetanephrine in sponteneous release originates from the activity of prejunctional catechol-O-methyltransferase. On the other hand, 3H-normetanephrine formed during transmitter release elicited by nerve stimulation is due to the activity of extraneuronal catechol-O-methyltransferase. Access of 3H-noradrenaline released by nerve stimulation to extraneuronal catechol-O-methyltransferase is mediated through the high-affinity, hydrocortisone-sensitive extraneuronal uptake mechanism.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00501472
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