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EFFECTS OF ENDORPHINS ON DIFFERENT PARTS OF THE GASTROINTESTINAL TRACT OF RAT AND GUINEA‐PIG in vitro
Author(s) -
NIJKAMP F.P.,
REE J.M.
Publication year - 1980
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.1476-5381.1980.tb10849.x
Subject(s) - phentolamine , medicine , endocrinology , enkephalin , hexamethonium , methysergide , guinea pig , endorphins , chemistry , propranolol , ileum , mepyramine , atropine , antagonist , biology , opioid , receptor
1 The spasmogenic and spasmolytic effects of β‐lipotropin (LPH) fragments and one analogue were investigated on different parts of the gastro‐intestinal tract of guinea‐pig and rat in vitro . 2 Changes in muscle tone were observed in colon and rectum and to a lesser extent in jejunum and ileum of both species. Rat colon and rectum contracted to the peptides. Guinea‐pig colon and rectum relaxed after an initial short‐lasting contraction. 3 On the rat rectum ( d ‐ala 2 )met‐enkephalin, leu‐enkephalin, γ‐endorphin, α‐endorphin and β‐LPH 80–91 caused dose‐dependent contractions, their ED 50 values being 0.96 × 10 −12 mol, 1.05 × 10 −11 mol, 1.22 × 10 −11 mol, 1.08 × 10 −10 mol, 2.65 × 10 −10 mol and 6.5 × 10 −9 mol, respectively. 4 Naloxone dose‐dependently shifted the dose‐response curve of met‐enkephalin to the right. Atropine, hexamethonium, burimamide, mepyramine, propranolol and indomethacin did not influence the response to met‐enkephalin. 5 In the presence of tetrodotoxin, the ED 50 for met‐enkephalin and the maximal contractor response induced by met‐enkephalin, appeared to be increased. 6 The 5‐hydroxytryptamine (5‐HT) antagonists, methysergide and cyproheptadine, reduced the contractor response in a non‐competitive manner. The α‐adrenoceptor antagonist phentolamine, in contrast, caused an increase of the maximal response to met‐enkephalin of up to 200%. Noradrenergic and tryptaminergic systems, therefore, might be involved in the changes in muscle tone induced by met‐enkephalin. 7 These results demonstrate that rectum and colon of guinea‐pig and rat are very sensitive to opioid‐like peptides.