2-[125I]iodomelatonin binding sites in the rat vas deferens.

To further understand the mechanism by which melatonin potentiates noradrenergic transmission in the rat vas deferens, we localized and partially characterized 2-[125I]-iodomelatonin-binding sites in tissue sections of the rat vas deferens using quantitative autoradiography. High-affinity 2-[125I]-iodomelatonin-binding sites were localized around the lumen of the prostatic portion, but not in the epididymal portion of the rat vas deferens. The binding of 2-[125I]-iodomelatonin to sections of the prostatic portion was stable, reversible and saturable. Saturation studies revealed a single class of high-affinity binding sites with a dissociation constant (Kd) of 104.2 +/- 23.7 pM (n = 4) and a binding capacity (Bmax) of 2.07 +/- 0.19 fmol/mg of protein (n = 4). These results suggest that melatonin may regulate sympathetic neurotransmission through activation of specific melatonin receptors in the prostatic portion of the rat vas deferens.