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Differential effects of calcium antagonists and Bay K 8644 on contractile responses to exogenous noradrenaline and adrenergic nerve stimulation in the rabbit ear artery
Author(s) -
Skärby Tor V. Ch.,
Högestätt Edward D.
Publication year - 1990
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.1476-5381.1990.tb14188.x
Subject(s) - prazosin , phenoxybenzamine , nifedipine , rauwolscine , endocrinology , medicine , diltiazem , verapamil , stimulation , bay k8644 , calcium , chemistry , antagonist , biology , propranolol , receptor
1 The effects of three calcium antagonists (nifedipine, verapamil, diltiazem) and the calcium agonist Bay K 8644 were compared on contractile responses of similar amplitude elicited by noradrenaline (NA) and electrical nerve stimulation (ENS) in the rabbit isolated ear artery. 2 Contractions induced by both NA (3 × 10 −7 m ) and ENS (10 Hz, 10 s) were almost exclusively mediated by α 1 ‐adrenoceptors, since 10 −7 m prazosin abolished (NA) or almost abolished (ENS) the responses, and prazosin was more than three orders of magnitude more potent than rauwolscine on both types of response. 3 ENS‐induced contractions were considerably less inhibited by nifedipine, verapamil and diltiazem than were those elicited by NA. Bay K 8644 enhanced responses to NA more than those to ENS. 4 The inhibitory effect of nifedipine and Ca 2+ deprivation on NA‐induced contractions decreased with increasing NA concentration. Reduction of the NA response by prazosin or phenoxybenzamine increased the nifedipine inhibition. 5 Reduction of the ENS‐induced contractions by prazosin or phenoxybenzamine, or by use of a lower stimulation frequency did not increase the inhibitory effect of nifedipine. 6 In conclusion, the differential effects of the calcium antagonists on NA‐ and ENS‐induced contractions were not related to differences in α‐adrenoceptor subtype (α 1 /α 2 ), receptor reserve or response amplitude, but may rather reflect temporal and spatial differences in α‐adrenoceptor activation between the responses.