Article date: April 1980
By: F.P. NIJKAMP, J.M. REE in Volume 68, Issue 4, pages 599-606
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.
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.
On the rat rectum (d‐ala2)met‐enkephalin, leu‐enkephalin, γ‐endorphin, α‐endorphin and β‐LPH 80–91 caused dose‐dependent contractions, their ED50 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.
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.
In the presence of tetrodotoxin, the ED50 for met‐enkephalin and the maximal contractor response induced by met‐enkephalin, appeared to be increased.
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.
These results demonstrate that rectum and colon of guinea‐pig and rat are very sensitive to opioid‐like peptides.
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.
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.
On the rat rectum (d‐ala2)met‐enkephalin, leu‐enkephalin, γ‐endorphin, α‐endorphin and β‐LPH 80–91 caused dose‐dependent contractions, their ED50 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.
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.
In the presence of tetrodotoxin, the ED50 for met‐enkephalin and the maximal contractor response induced by met‐enkephalin, appeared to be increased.
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.
These results demonstrate that rectum and colon of guinea‐pig and rat are very sensitive to opioid‐like peptides.
DOI: 10.1111/j.1476-5381.1980.tb10849.x
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