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Presynaptic α 2 ‐adrenoceptor antagonism by verapamil but not by diltiazem in rabbit hypothalamic slices
Author(s) -
Galzin AnneMarie,
Langer S.Z.
Publication year - 1983
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1111/j.1476-5381.1983.tb08817.x
Subject(s) - diltiazem , verapamil , endocrinology , antagonist , medicine , yohimbine , chemistry , stimulation , agonist , inhibitory postsynaptic potential , antagonism , prazosin , pharmacology , receptor , calcium
1 Rabbit hypothalamic slices prelabelled with [ 3 H]‐noradrenaline and superfused with Krebs solution were stimulated electrically at a frequency of 5 Hz. Exposure to verapamil (0.1 to 10 μ m ) significantly increased, in a concentration‐dependent manner, the electrically‐evoked overflow of tritium, without affecting the spontaneous outflow of radioactivity. 2 Exposure to diltiazem in concentrations up to 100 μ m had no effect on the electrically evoked release of [ 3 H]‐noradrenaline, but increased the basal outflow of radioactivity at 10 and 100 μ m . 3 The preferential α 2 ‐adrenoceptor antagonist, yohimbine (0.1 μ m ) significantly antagonized the inhibitory effect of clonidine or adrenaline on [ 3 H]‐noradrenaline overflow elicited by electrical stimulation. Verapamil (3 μ m ) also antagonized this inhibitory effect of the α 2 ‐adrenoceptor agonists on [ 3 H]‐noradrenaline release. In contrast to these results, exposure to diltiazem (10 μ m ) was ineffective in blocking the action of the α 2 ‐adrenoceptor agonist. 4 These results suggest that the two Ca 2+ ‐antagonists verapamil and diltiazem differ in their ability to affect central noradrenergic neurotransmission. While verapamil is a relatively potent α 2 ‐adrenoceptor antagonist, diltiazem is devoid of presynaptic α 2 ‐adrenoceptor antagonist properties.