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Identification and characterization of 2[ 125 I]‐iodomelatonin binding sites in the rat epididymis
Author(s) -
Yu ZongHan,
Chow P. H.,
Pang ShiuFun
Publication year - 1994
Publication title -
journal of pineal research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.881
H-Index - 131
eISSN - 1600-079X
pISSN - 0742-3098
DOI - 10.1111/j.1600-079x.1994.tb00132.x
Subject(s) - epididymis , hamster , medicine , endocrinology , biology , dissociation constant , radioligand , guinea pig , melatonin , binding site , radioligand assay , vas deferens , receptor , sperm , biochemistry , botany
Yu ZH, Chow PH, Pang S‐F. Identification and characterization of 2[ 125 I]iodomelatonin binding sites in the rat epididymis. J. Pineal Res. 1994;17:195–201. Abstract Putative melatonin receptors in different parts of the male reproductive system of rats (Sprague‐Dawley), mice (ICR), hamsters (Syrian) and guinea pigs (Dunkin‐Hartley), rat epididymal sperm, and boar and human semen were studied by a radioreceptor assay using 2[ 125 I]iodomelatonin as the radioligand. There was limited or no detectable binding of 2[ l25 I]iodomelatonin to membrane preparations of rat testis, seminal vesicles, prostate, or sperm from rat, human, and boar. However, significant bindings of 2[ 125 I]iodomelatonin to the epididymides of rat, mouse, hamster, and guinea‐pig were demonstrated. The relative binding capacities of 2[ 125 I]iodomelatonin to the distal epididymal segment in different rodent species was of the order rat mouse hamster guinea pig. The relative number of binding sites was much lower in the proximal segment than in the distal segment of epididymis. 2[ 125 I]iodomelatonin binding to the distal segment of rat epididymis was studied in detail. The binding sites fulfilled all criteria for a receptor site; being stable, saturable, reversible, and of high affinity. The binding had an equilibrium dissociation constant (K d ) of 62.6 ± 7.79 pmol/1 (n = 7) and a density (B max ) of 1.55 ± 0.16 fmol/mg protein (n = 7). The Hill coefficient approached 1. 0, suggesting a single class of 2[ 125 I]iodomelatonin binding sites. Pharmacological studies revealed that these 2[ 125 I]iodome‐latonin binding sites were specific for melatonin receptors. In addition, there was an age‐related change in the 2[ 125 I]iodomelatonin binding sites in the rat distal epididymal segment. The binding increased from a lower value in 1‐month‐old rats to a higher adult value in the l 1 /i‐ to 24‐month‐old animals. The demonstration of 2[ 125 I]iodomelatonin binding sites in the epididymis indicates the presence of melatonin receptors. A high binding level in the distal epididymal segment suggests the possible participation of melatonin in the process of sperm maturation.