Blackwell Publishing Journal Backfiles 1879-2005
Yu ZH, Chow PH, Pang S-F. Identification and characterization of 2[125I]iodomelatonin binding sites in the rat epididymis. J. Pineal Res. 1994;17:195–201.〈section xml:id="abs1-1"〉〈title type="main"〉AbstractPutative 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[125I]iodomelatonin as the radioligand. There was limited or no detectable binding of 2[l25I]iodomelatonin to membrane preparations of rat testis, seminal vesicles, prostate, or sperm from rat, human, and boar. However, significant bindings of 2[125I]iodomelatonin to the epididymides of rat, mouse, hamster, and guinea-pig were demonstrated. The relative binding capacities of 2[125I]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[125I]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 (Kd) of 62.6 ± 7.79 pmol/1 (n = 7) and a density (Bmax) of 1.55 ± 0.16 fmol/mg protein (n = 7). The Hill coefficient approached 1. 0, suggesting a single class of 2[125I]iodomelatonin binding sites. Pharmacological studies revealed that these 2[125I]iodome-latonin binding sites were specific for melatonin receptors. In addition, there was an age-related change in the 2[125I]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 l1/i- to 24-month-old animals. The demonstration of 2[125I]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.
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