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THE EFFECTS OF PARAOXON ON BLOOD PRESSURE IN THE ANAESTHETIZED AND IN THE CONSCIOUS RAT
Author(s) -
NEEF J.H.,
JORDAAN K.M.,
PORSIUS A.J.
Publication year - 1982
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.1476-5381.1982.tb09289.x
Subject(s) - prazosin , phentolamine , yohimbine , paraoxon , phenylephrine , mecamylamine , guanethidine , endocrinology , blood pressure , medicine , atropine , reserpine , reflex bradycardia , hexamethonium , chlorisondamine , chemistry , anesthesia , pharmacology , propranolol , bradycardia , acetylcholinesterase , stimulation , heart rate , antagonist , biochemistry , receptor , enzyme
1 Intravenous administration of paraoxon (150–825 μg/kg) to anaesthetized rats induced long‐lasting, dose‐dependent pressor effects. Only after injection of 825 μg/kg paraoxon was the pressor response followed by a depressor effect and a bradycardia that could be blocked by N‐methylatropine. Intracerebroventricular injection of paraoxon into anaesthetized rats also induced pressor effects. 2 In order to elucidate the mechanism of the pressor action rats were given dexetimide, N‐methylatropine, mecamylamine, phentolamine, prazosin, yohimbine, atenolol and metoprolol. If treatment with these drugs resulted in a low initial blood pressure, vasopressin was infused to elevate blood pressure to normal levels. The influence of adrenalectomy, pretreatment with reserpine and midcollicular transection was also examined. 3 The pressor effect of paraoxon was not influenced by N‐methylatropine or mecamylamine. However, a combination of these drugs as well as dexetimide, phentolamine or prazosin combined with yohimbine, reduced or prevented the pressor effect. 4 In conscious rats the effects of paraoxon and the action of antimuscarinic drugs upon the pressor response were similar to those observed in anaesthetized animals. 5 Acetylcholinesterase activities were measured in various brain regions and in whole blood. Paraoxon concentrations within the CNS were also measured. 6 It is concluded that the pressor effect of paraoxon in anaesthetized and conscious rats is mediated by a central mechanism, although a contribution of peripheral acetylcholinesterase inhibition in sympathetic ganglia to this pressor effect cannot be ruled out.