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2-Phenylmelatonin: a partial agonist at enteric melatonin receptors
M G Santagostino-Barbone1, E Masoero, V Spelta
1Department of Experimental and Applied Pharmacology, School of Pharmacy, University of Pavia, Italy.
Pharmacology & Toxicology
|November 30, 2000
Summary
2-Phenylmelatonin acts as both a weak contractile agonist and an antagonist of melatonin receptors in guinea-pig colon. This dual action depends on the concentration, with lower doses blocking melatonin effects and higher doses causing contractions.
Area of Science:
- Pharmacology
- Gastroenterology
- Neuroendocrinology
Background:
- Melatonin receptors play a role in gastrointestinal function.
- Understanding melatonin receptor ligands is crucial for developing new therapeutic agents.
Purpose of the Study:
- To investigate the pharmacological effects of 2-phenylmelatonin on isolated guinea-pig proximal colon.
- To determine the concentration-dependent agonist and antagonist properties of 2-phenylmelatonin at melatonin receptors.
Main Methods:
- Isolated guinea-pig proximal colon strips were used to assess contractile responses.
- Concentration-response curves were generated for 2-phenylmelatonin and melatonin.
- The effects of 2-phenylmelatonin as an antagonist of melatonin-induced contractions were evaluated.
- Prazosin, a selective MT3 site antagonist, was used for comparison.
Main Results:
- 2-Phenylmelatonin induced concentration-dependent contractions, with a potency (-log EC50) of 9.3 +/- 1.0.
- At subnanomolar concentrations, 2-phenylmelatonin antagonized melatonin-induced contractions.
- At nanomolar to micromolar concentrations, 2-phenylmelatonin acted as a weak contractile agonist.
- Prazosin showed similar antagonism to low concentrations of 2-phenylmelatonin.
Conclusions:
- 2-Phenylmelatonin exhibits dual pharmacological activity at melatonin receptors in the guinea-pig proximal colon.
- Its effect is concentration-dependent, acting as an antagonist at low concentrations and an agonist at higher concentrations.
- These findings contribute to understanding the complex role of melatonin signaling in the gastrointestinal tract.