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The influence of the initial stretch and the agonist‐induced tone on the effect of basal and stimulated release of EDRF
Author(s) -
Dainty I.A.,
McGrath J.C.,
Spedding M.,
Templeton A.G.B.
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.tb14090.x
Subject(s) - acetylcholine , phenylephrine , chemistry , contraction (grammar) , sodium nitroprusside , endothelium derived relaxing factor , isoprenaline , endocrinology , atropine , medicine , agonist , biophysics , stimulation , nitric oxide , biology , biochemistry , blood pressure , receptor
1 The effects of initial stretch and degree of agonist‐induced tone on acetylcholine‐induced relaxations were examined in rings of rat isolated aorta. The relaxation to acetylcholine was antagonized by atropine and almost completely abolished by haemoglobin. Relaxation to sodium nitroprusside was similar in rings with an intact or disrupted endothelium but that to isoprenaline was greater in intact preparations. 2 In preparations with either an intact or disrupted endothelium there was a similar length‐dependent increase in the resting tension of the aortic rings. The size of the contractile response to phenylephrine (1 μ m ) was dependent on the initial length (and hence degree of stretch) of the preparation in both rubbed and unrubbed tissues. The absolute difference in contractile response between rubbed and unrubbed was greatest at 1.8 mm and less at the other lengths tested, including the optimum degree of stretch for contraction i.e. 2.4 mm. 3 The absolute acetylcholine‐induced relaxation (only seen in rings with an intact endothelium) was dependent on the initial length (and hence degree of stretch) of the preparation and was maximum at 2.4 mm. The proportionate relaxation (i.e. expressed as a percentage of induced tone) was also length‐dependent, being optimal at 1.5 mm. 4 The sensitivity of the vessels to acetylcholine varied depending on the level of agonist‐induced tone. When tone was low, acetylcholine sensitivity was high (at [NA] 0.03 μ m : pIC 50 = 7.36 ± 0.07), when the concentration of noradrenaline was increased the tone increased and the acetylcholine sensitivity was low (at [NA] 0.3 μ m : pIC 50 = 6.57 ± 0.07). 5 The absolute sensitivities and maximum relaxations induced by acetylcholine are discussed in relation to the initial degree of stretch (and hence length of the preparation) or the degree of agonist‐induced tone.