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Adrenalectomy abolishes antagonism of α‐adrenoceptor‐mediated hypotension by a β‐blocker in conscious rats
Author(s) -
Tabrizchi R.,
Pang C.C.Y.
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.tb12714.x
Subject(s) - phentolamine , propranolol , atenolol , adrenalectomy , endocrinology , medicine , epinephrine , antagonist , mean arterial pressure , blood pressure , bolus (digestion) , chemistry , catecholamine , heart rate , receptor
1 The effects of a single bolus injection of propranolol, atenolol or ICI 118,551, non‐selective β‐, selective β 1 ‐ and selective β 2 ‐adrenoceptor antagonists, respectively, on mean arterial pressure (MAP) and plasma catecholamine concentrations were examined in seven groups of conscious and unrestrained adrenalectomized rats receiving a continuous infusion of the α‐adrenoceptor antagonist phentolamine. In all rats adrenaline was undetectable in the plasma four days after adrenalectomy. 2 In the first three groups, phentolamine significantly decreased MAP and increased the plasma concentrations of noradrenaline. The injection of propranolol, atenolol or ICI 118,551 in Groups I, II and III, respectively, caused a small increase in MAP and a small, but not significant, decrease in plasma noradrenaline concentrations. 3 Groups IV, V and VI were given a continuous infusion of adrenaline for 1 h prior to the infusion of phentolamine, followed by a bolus injection of propranolol, atenolol or ICI 118,551, respectively. Group VII was treated similarly to IV, but was also given daily cortisone replacement after adrenalectomy. Adrenaline slightly, but not significantly, decreased MAP while phentolamine significantly decreased MAP and increased plasma noradrenaline concentrations in all groups. A subsequent injection of a β‐blocker caused a significant increase in MAP in each group and a slight decrease in the plasma level of noradrenaline which reached statistical significance in group VII. The pressor effect of propranolol was significantly greater in the cortisone‐treated rats (Group VII) than in Group IV. 5 The results suggest that adrenaline and adrenocortical steroids are both involved in the antagonism of α‐adrenoceptor‐induced hypotension by a β‐blocker.