BACKGROUND:With the development of technology,electromagnetic irradiation has been applied in many fields;meanwhile,health of people could be threatened by electromagnetic exposure.Reproductive system of males is the major target of electromagnetic irradiation.But under the condition of electromagnetic exposure,the change of testosterone and its mechanism remain unknown. OBJECTIVE:To study the effect of electromagnetic irradiation on steroidogenic acute regulatory protein(StAR) and cytochrome P450 cholesterol side-chain cleavage(P450scc) in the tissues of the testis of the adult rats,and to preliminarily reveal the molecular mechanism of electromagnetic radiation that affects the synthesis of testosterone. DESIGN:A randomized controlled study. SETTING:Department of Nuclear Medicine and Staff Room of Labour Hygiene, Institute of Field Surgery,Daping Hospital of the Third Military Medical University of Chinese PLA. PARTICIPANTS:The study was completed in the Department of Nuclear Medicine and Staff Room of Labour Hygiene, Institute of Field Surgery,Daping Hospital of the Third Military Medical University of Chinese PLA from June 2003 to May 2004.A total of 75 male Wistar rats of clean degree II,weighing 180 to 220 g,were randomly divided into 5 groups:control group,and groups of 3,6,24,72 hours after electromagnetic irradiation with 15 rats in each group. INTERVENTIONS:The rats were exposed to microwave with the peak power of 90 W/cm2 for 15 minutes successively,and all the rats survived the irradiation.The serum contents of testosterone of rats in the groups of 3,6,24,72 hours after electromagnetic irradiation and control group were measured by using radioimmunoassay(RIA) respectively;meanwhile the levels of the StAR and P450scc mRNA in testis tissue were also determined with RT-PCR. MAIN OUTCOME MEASURES:Serum contents of testosterone in the groups of 3,6,24,72 hours after electromagnetic irradiation and control group;the expression levels of the StAR and P450scc mRNA in testis tissues. RESULTS:The serum contents of testosterone,the StAR and P450scc mRNA levels at the point of 3 hours after electromagnetic irradiation were significantly lower than those in the control group,and they were decreased by 83.1% ,57.3% and 53.6% respectively(P< 0.01).At the point of 6 hours, although those were increased a little, but were still obviously lower than those of the control group, and they were decreased by 52.6%, 17.9% and 29.2% respectively(P< 0.01,0.05) compared with the control group, and were recovered to the normal level at the point of 24 hours, but the contents of testosterone, the StAR and P450scc mRNA levels were significantly reduced again after 72 hours, and they were decreased by 57.6% , 39.5% , 53.5% respectively compared with those in the control group(P< 0.01). CONCLUSION:Electromagnetic irradiation can affect the expression of StAR and P450scc mRNA in the Leydig's cells of the adult rats, thereby decreasing the synthesis of testosterone.