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p K 1 values of prazosin and idazoxan for receptors stimulated by neuronally released transmitter in the epididymal portion of rat isolated vas deferens
Author(s) -
Mackay D.,
Kengatharan M.
Publication year - 1994
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.1476-5381.1994.tb14048.x
Subject(s) - prazosin , idazoxan , vas deferens , endocrinology , medicine , chemistry , antagonist , biology , receptor
1 A new method has been used to measure p K 1 values of prazosin and idazoxan against neuronally‐released transmitter in the epididymal portion of the rat isolated vas deferens. The most reproducible results were obtained with a prolonged antagonist equilibration time (1 h). 2 Under these conditions the p K 1 of prazosin was practically unaffected by addition of α, β‐methylene‐adenosine‐5′‐triphosphate (10 μ m ) to desensitize purinoceptors. Addition of desmethylimipramine (DMI) (0.3 μ m ) produced a small, but statistically non‐significant, reduction. 3 The same method has been used to measure the p K 1 of prazosin against exogenous noradrenaline. In the latter case addition of DMI (0.3 μ m ) and corticosterone (30 μ m ) together produced a statistically significant reduction in the apparent p K 1 of prazosin. 4 The new method for estimating p K 1 values shows that DMI itself acts either pseudo‐irreversibly or non‐competitively and may be reducing the apparent p K 1 of prazosin. 5 The p K 1 values obtained for prazosin and idazoxan against neuronally‐released transmitter are in good agreement with those obtained by other workers for the actions of these drugs on α‐adrenoceptors.