Premium
Characterization of postsynaptic α‐adrenoceptors in the arteries supplying the oviduct
Author(s) -
Costa Gonzalo,
Isla Miguel,
GarcíaPascual Angeles,
Jimenez Eugenio,
Recio Paz,
Labadia Alicia,
GarcíaSacristán Albino
Publication year - 1992
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.1476-5381.1992.tb14262.x
Subject(s) - rauwolscine , prazosin , yohimbine , medicine , endocrinology , phenylephrine , postsynaptic potential , chemistry , propranolol , antagonist , receptor , biology , blood pressure
1 In vitro experiments were designed to characterize postjunctional α‐adrenoceptor subtypes in ring segments (1 mm length; outer diameter 300–500 μ m ) from arteries supplying the oviduct of the heifer. 2 Noradrenaline, adrenaline and phenylephrine evoked concentration‐dependent contractile responses. The pD 2 values were 5.67, 5.89 and 5.93, respectively. Medetomidine, clonidine and B‐HT 920 (2‐amino‐6‐allyl‐5,6,7,8‐tetra‐hydro‐4H‐(thiazo)‐4,5‐d‐azepine) were ineffective. 3 The α‐adrenoceptor selective antagonists, prazosin (1 n m −0.1 μ m ) and rauwolscine (0.1–10 μ m ) competitively antagonized the response to noradrenaline. The pA 2 values were 9.38 and 6.83, respectively. 4 The dissociation constant ( K D ) for noradrenaline calculated by use of the irreversible antagonist, dibenamine, was 3.95 (2.09–5.81) μ m . The occupancy‐response relationship was non‐linear. Half‐maximal response to noradrenaline was obtained with 22% receptor occupancy while maximal response required 100% occupancy. 5 B‐HT 920 evoked a biphasic contractile concentration‐dependent response in preparations incubated in a physiological solution containing 20 m m K + , 0.1 μ m prazosin and 1 μ m propranolol. Rauwolscine 0.1 μ m significantly ( P < 0.01) blocked the first component of the B‐HT 920 concentration‐response curve with an apparent pA 2 value of 8.52 (7.86–9.18). 6 These results strongly suggest that α‐adrenoceptors in oviductal arteries are mainly of the α 1 subtype, although a possible role for α 2 ‐adrenoceptors cannot be excluded.