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The influence of blood gases on α 1 ‐ and α 2 ‐adrenoceptor‐mediated pressor responses in the pithed rat
Author(s) -
Grant T.L.,
McGrath J.C.,
O'Brien J.W.
Publication year - 1985
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.1476-5381.1985.tb09436.x
Subject(s) - phenylephrine , xylazine , alkalosis , endocrinology , medicine , hypocapnia , respiratory alkalosis , agonist , hypercapnia , arterial blood , hypoxia (environmental) , acidosis , diuretic , anesthesia , chemistry , blood pressure , metabolic acidosis , receptor , oxygen , ketamine , organic chemistry
1 The influence of blood gases on α 1 ‐ and α 2 ‐adrenoceptor‐mediated pressor responses was studied in the pithed rat by varying the inspired gas mixture or the ventilation stroke volume. 2 Acidosis favoured the peak responses to the α 2 ‐adrenoceptor agonist, xylazine, while alkalosis favoured the peak responses to the α 1 ‐adrenoceptor agonist, phenylephrine. A combination of hypoxia and hypercapnia greatly depressed the α 1 response to phenylephrine whereas the α 2 response to xylazine remained relatively unaffected. 3 When P aO 2 was varied in either acidotic or alkalotic conditions the response to the phenylephrine increased as P aO 2 increased. 4 To prevent hypoxia in air ventilated rats, large stroke volumes were required. This caused alkalosis and hence decreased responsiveness to xylazine. Consequently, air ventilated pithed rats gave poorer responses to xylazine than did those ventilated on 100% O 2 . 5 The results show that α 1 ‐ and α 2 ‐adrenoceptor‐mediated pressor responses can be differentially affected by blood gases. The relative contribution of α 1 ‐ and α 2 ‐adrenoceptors to vascular tone may be either under‐ or over‐estimated depending on the arterial blood gases.