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Developmental disappearance of excitatory α 1 adrenoceptor function in the oesophagus of chick embryo
Author(s) -
Miyazaki Hideto,
Taneike Tetsuro,
Ohga Akira
Publication year - 1989
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.1476-5381.1989.tb12009.x
Subject(s) - incubation , prazosin , phentolamine , contraction (grammar) , endocrinology , phenylephrine , carbachol , medicine , isoprenaline , chemistry , propranolol , bethanechol , stimulation , biology , receptor , muscarinic acetylcholine receptor , antagonist , biochemistry , blood pressure
1 Developmental change in the response to noradrenaline (NA) and 5‐hydroxytryptamine (5‐HT) was investigated in the chick oesophagus between 9 and 21 days of incubation and 4 days after hatching. 2 NA (5 μ m ) produced a significant contraction in the oesophagus at 9 days of incubation. The NA‐induced contraction progressively decreased with development and changed to an inhibition of spontaneous contraction or a small relaxation by 17 days of incubation. 3 The NA‐induced contractile response was inhibited by phentolamine (2.7 μ m ) and prazosin (0.55 μ m ). Phenylephrine (5 μ m ) but not clonidine (5–50 μ m ), also induced a contraction at early stages. The relaxation response to NA was sensitive to the β‐receptor blocker, carteolol (3.4 μ m ). 4 Pretreatment with carteolol unmasked the contractile responses to NA in preparations at 17–19 days of incubation. However, even in the presence of carteolol, the contraction produced by NA decreased and disappeared by the time of hatching. This change in response to NA is accompanied by a decline in the pD 2 value. The response to phenylephrine (5 μ m ) followed the same pattern as that to NA. 5 The maximum binding sites of [ 3 H]‐dihydroergocryptine to the crude membrane preparation from oesophagus changed little at 13, 17 and 21 days of incubation. 6 Isoprenaline (Iso, 0.01–20 μ m ) caused a carteolol‐sensitive relaxation in the carbachol‐contracted oesophagus after 13 days of incubation. The sensitivity (pD 2 value) to Iso decreased slightly up to 17 days of incubation. 7 5‐HT (10 μ m ) caused a contraction in the oesophagus after 13 days of incubation and the amplitude of the response increased up to 17 days of incubation. The response to 5‐HT was abolished by methysergide (1 μ m ) but not by tetrodotoxin (0.78 μ m ) or atropine (1 μ m ) at every stage tested. 8 These results suggest that the response to NA changed from an α 1 ‐adrenoceptor‐mediated contraction to a β‐receptor‐mediated relaxation during the embryonic period, resulting partly from the decline and disappearance of excitatory α 1 ‐receptor function in the chick oesophagus.