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Author Allen, J. M. ♦ Mccarron, J. G. ♦ Mchale, N. G. ♦ Thornbury, K. D.
Source PubMed Central
Content type Text
File Format PDF
Language English
Difficulty Level Medium
Subject Domain (in DDC) Technology ♦ Medicine & health
Abstract 1. Isolated segments of bovine mesenteric lymphatic vessels were loaded with [3H]-noradrenaline and its efflux in response to field stimulation examined. Vessels were attached to an isometric force transducer for the simultaneous recording of mechanical activity. 2. Field stimulation at 1, 4 and 8 Hz (0.3 ms pulses, 1 min train) increased spontaneous contraction rate and evoked 3H release up to a maximum of 4.5% of total tissue 3H at 8 Hz. Output per pulse was maximal at 4 Hz. 3. Tetrodotoxin (3 x 10(-6) M) blocked the release of 3H in response to field stimulation although the drug did not attenuate release evoked by high K+ (65 mM) solution. Field-evoked release of 3H was also absent in Ca2+ -free solution containing EGTA (1 mM). 4. When vessels were preincubated with labelled transmitter plus cocaine (5 x 10(-5) M) evoked release of 3H was absent. After preloading with [3H]-noradrenaline, cocaine (10(-6) M) potentiated both the mechanical response to field stimulation and evoked 3H release. 5. The relatively non selective alpha-adrenoceptor antagonist phentolamine (3 x 10(-6) M) and the alpha 2-antagonists yohimbine (10(-8) M) and rauwolscine (10(-6) M) significantly increased evoked 3H release at both of the frequencies examined (1 and 4 Hz). In contrast, the selective alpha 1-antagonist prazosin (10(-6) M) failed to alter 3H release to 4 Hz stimulation although release at 1 Hz was potentiated in the presence of the drug. 6. The postsynaptic excitatory response to field stimulation remained in the presence of prazosin (10(-6) M), but was converted to an inhibitory effect in the presence of phentolamine (3 x 10(-6) M), yohimbine (10(-6) M) or rauwolscine (10(-6) M). 7. Evoked 3H efflux was significantly reduced by clonidine (10(-6) M), xylazine (10(-6) M) and exogenous noradrenaline (5 x 10(-7) M), although phenylephrine (10(-6) M) reduced release only at the lower of the two frequencies tested (1 Hz). 8. These findings suggest that release of 3H by field stimulation reflects endogenous transmitter release and that this is subject to autoinhibition via feedback onto inhibitory prejunctional alpha 2-adrenoceptors. The postjunctional excitatory response is mediated via postjunctional alpha 2-adrenoceptors.
ISSN 00071188
Age Range above 22 year
Educational Use Research
Interactivity Type Expositive
Education Level UG and PG
Learning Resource Type Article
Publisher Date 1988-07-01
Journal British Journal of Pharmacology
Volume Number 94
Issue Number 3
Starting Page 823


Source: PubMed Central