FIGURE 5.

Effects of melatonin pretreatment on radiation-induced changes on STS and 17β-HSD1 activity and expression in endothelial cells. Melatonin 1 mM or its diluent pretreated endothelial and MCF-7 cells for a week were plated on the co-culture as described in material and methods. (A) When a homogenous monolayer of pre-confluent HUVECs was reached, media were aspirated and changed to serum-free media containing the labeled substrate 20 nM [6,7-³H(N)]-estrone sulfate ammonium salt and radiated. After 24 h of radiation, sulfatase activity was measured as described in material and methods. (C) When a homogenous monolayer of pre-confluent HUVECs was reached, media were aspirated and changed for fresh ones containing 2 nM [2,4,6,7-³H(N)]-estrone (100 Ci/mM) and cells were irradiated. After 30 min of incubation, 17β-HSD1 activity was measured as described in material and methods. (B,D) Control and melatonin pretreated endothelial cells were irradiated and incubated for 4 h. The total cellular RNA was isolated from cells and reverse transcribed. cDNA was subjected to PCR using specific primers for STS, 17β-HSD1 or S14. Data are expressed as the percentage of the control group (Mean ± SEM). C, control; M, melatonin; and R, radiation. a, p < 0.001 vs C; and b, p < 0.001 vs R.