Melatonin binding sites in interstitial cells from immature rat testes

Melatonin binding sites in rat testes interstitial cells were identified using 2-[125I]-iodomelatonin. Saturation studies of cells revealed a single class of high affinity binding sites, with an apparent equilibrium dissociation constant (Kd) of 100 +/- 20 pM, and a total binding capacity (B max) of 3.0 +/- 0.2 x 10(3) melatonin molecules per cell. Binding was reversible and inhibited by non radioactive melatonin. These results suggest that interstitial cells from immature rat testes have specific receptors for melatonin.