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Contractile and relaxant responses of the canine isolated spinal artery to vasoactive substances
Author(s) -
Shirai K.,
Kawai Y.,
Ohhashi T.
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.tb12113.x
Subject(s) - chemistry , prazosin , medicine , endocrinology , isoprenaline , contraction (grammar) , yohimbine , phenylephrine , phentolamine , acetylcholine , cromakalim , practolol , adenosine , pharmacology , agonist , propranolol , stimulation , biochemistry , receptor , blood pressure , antagonist
1 Effects of vasoactive substances were investigated in the canine isolated spinal branch of the intercostal artery (SBICA). 2 Addition of angiotensin II (AII), vasopressin, noradrenaline (NA), adrenaline, 5‐hydroxytryptamine (5‐HT), and dopamine each produced concentration‐dependent contraction in the SBICA, whereas prostaglandin F 2α , histamine, and tyramine caused only slight contraction. The decreasing order of the potency of contractile agents was AII ≫ vasopressin = NA > 5‐HT > adrenaline ≫ dopamine. 3 Although the pD 2 value for phenylephrine (5.31 ± 0.36) was smaller than that for NA (6.48 ± 0.13), there was no significant difference in E max value between these two agonists in the SBICA. On the other hand, xylazine produced only a slight contraction, the pD 2 value being 3.59 ± 0.08. Phentolamine (10 −8 –10 −6 m ) and prazosin (10 −8 –10 −6 m ) competitively inhibited the NA‐induced contraction, while yohimbine (10 −8 –10 −6 m )did not. 4 Acetylcholine (ACh), sodium nitroprusside (SNP), ATP, ADP, and adenosine caused concentration‐dependent relaxations in SBICA following contraction with NA. On the other hand, isoprenaline up to 10 −4 m did not produce any relaxation. The decreasing order of potency of the relaxant agents was ACh > SNP ≫ ATP = ADP = adenosine. 5 The ACh‐induced relaxation was competitively inhibited by atropine and was abolished by mechanical removal of the endothelium. Aspirin (5 × 10 −5 m ) did not affect the relaxant response to ACh, while oxyhaemoglobin (10 −5 m ) and methylene blue (10 −5 m ) produced significant attenuation. 6 These results suggest that NA produces contraction of the isolated canine SBICA which is mainly mediated via α 1 ‐adrenoceptors and that ACh causes a relaxation of the SBICA due to release of endothelium‐derived relaxing factor (EDRF) from the endothelial cells.