Identification of serotonin 5HT2 receptors in bovine pineal gland.
The concentration of serotonin in the pineal gland is extremely high, which prompted speculation that in addition to serving as a precursor of melatonin, serotonin may have an independent function of its own. By using [3H]-spiperone as a ligand, and ketanserine as a selective serotonin 5HT2 receptor antagonist, we have identified 5HT2 receptor in the bovine pineal gland, revealing a single population of binding sites with a dissociation equilibrium constant (Kd) value of 1.26 +/- 0.41 nM and a receptor density (Bmax) value of 193 +/- 38.85 fmol/mg protein. In displacement experiments, the concentrations of the drugs required to inhibit 50% of the specific binding of [3H]-spiperone in descending order of potency were methysergide greater than ritanserin greater than pirenperone greater than pipamperone greater than ketanserin greater than cyproheptadine greater than M-trifluoromethylphenyl-piperazine greater than prazosin greater than 5-methoxy-N-N-dimethyltryptamine hydrogen oxalate greater than 1-(3-chlorophenol) piperazine greater than serotonin. In the rat pineal gland, [3H]-spiperone revealed a low affinity serotonin binding site with a Kd value of 25.77 +/- 10.7 nM and a Bmax value of 1244 +/- 472 fmol/mg protein. The results of these studies are interpreted to indicate that the bovine pineal gland possess serotonin 5HT2 receptor. However, the rat pineal gland possess a serotoninergic binding site of unknown nature.
Govitrapong
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P
Neuro- and Behavioral Biology Center, Mahidol University, Nakorn Pathom, Thailand.
Prapapanich
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V
Ebadi
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M
D000818:Animals; D001665:Binding Sites; D001667:Binding, Competitive; D002417:Cattle; D007650:Ketanserin / Q000378:metabolism; D007700:Kinetics; D008024:Ligands; D010870:Pineal Gland / Q000378:metabolism*; D011985:Receptors, Serotonin / Q000302:isolation & purification* / Q000378:metabolism; D013134:Spiperone / Q000378:metabolism
D008024:Ligands; D011985:Receptors, Serotonin; D013134:Spiperone; D007650:Ketanserin