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THE OCCURRENCE OF POSTSYNAPTIC α‐ AND β‐ADRENOCEPTORS IN THE GUINEA‐PIG GALL BLADDER
Author(s) -
DOGGRELL SHEILA A.,
SCOTT G.W.
Publication year - 1980
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.1476-5381.1980.tb10924.x
Subject(s) - isoprenaline , phentolamine , propranolol , postsynaptic potential , endocrinology , medicine , atropine , stimulation , cholinergic , guinea pig , chemistry , acetylcholine , carbachol , biology , receptor
1 Guinea‐pig gall bladder strips were contracted by (–)‐noradrenaline, 10 −5 m , and by field stimulation at 5 Hz (in the absence or presence of 10 −6 m atropine) and relaxed to 10 −5 m (–)‐isoprenaline. (–)‐Adrenaline, 10 −5 m , predominantly contracted, but sometimes relaxed, this preparation. 2 In the presence of 10 −6 m phentolamine, contractions to (–)‐noradrenaline and to (–)‐adrenaline were reversed to relaxations. The relaxations produced by (–)‐isoprenaline were unaltered. In the presence of 10 −6 m propranolol, contractions to (–)‐noradrenaline increased in magnitude, relaxations to (–)‐adrenaline were reversed to contractions, and relaxations to (–)‐isoprenaline were abolished. These results demonstrate the presence of postsynaptic α‐adrenoceptors which mediate contractions, and postsynaptic β‐adrenoceptors which initiate relaxations, in the guinea‐pig gall bladder. 3 The contractile responses to continuous field stimulation for 5 min at 5 Hz in Krebs solution alone were reduced in magnitude by propranolol, 10 −6 m . In the presence of 10 −6 m atropine (added to eliminate the cholinergic component of the response), propranolol, 10 −6 m , had no effect on responses to stimulation at 5 Hz. Thus propranolol reduced the response to cholinergic stimulation in this tissue; the basis of this effect is unclear. In the absence or presence or atropine (10 −6 m ), the responses to 5 Hz were smaller in magnitude in the presence than absence of phentolamine, 10 −6 m . This suggests that the responses to field stimulation of the guinea‐pig gall bladder may, in part, be due to the release of endogenous noradrenaline which acts at postsynaptic α‐adrenoceptors.