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Effects of clonidine and yohimbine on a C‐fibre‐evoked blood pressure reflex in the rat
Author(s) -
Donnerer Josef,
Yan Zhao,
Lembeck Fred
Publication year - 1988
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.1476-5381.1988.tb11596.x
Subject(s) - yohimbine , clonidine , reflex , medicine , blood pressure , capsaicin , anesthesia , spinal cord , reflex bradycardia , withdrawal reflex , endocrinology , baroreflex , heart rate , antagonist , receptor , psychiatry
1 The involvement of α 2 ‐adrenoceptors in a capsaicin‐induced depressor reflex in the rat has been investigated. 2 The reflex fall in blood pressure following an intra‐arterial injection of capsaicin was partially blocked by an intrathecal infusion of clonidine (1 μg) at the spinal cord level L4‐L5, an effect which was abolished by the prior intrathecal infusion of yohimbine (5 μg). 3 Clonidine (1μg) given intracisternally blocked the depressor reflex almost completely; however, it also produced a gradual, prolonged fall in mean carotid pressure. 4 Yohimbine (20 μg) given intracisternally did not change mean blood pressure but had a dual effect on the depressor reflex in response to the capsaicin injection: a short period of enhanced reflex response was followed by a long lasting inhibition of the response. 5 It was concluded that α 2 ‐adrenoceptors in the spinal cord inhibit the capsaicin‐evoked depressor reflex and that pre‐ and postsynaptic α 2 ‐adrenoceptors in the brain stem modulate this reflex.