EFFECT OF LIGHT DARK REGIMEN AND ELECTROM AGNETIC-FIELDS ON MAMMARY CARCINOGENESIS IN FEMALE RATS/

Outbred female rats from the age of 1 month were kept at rooms with 12 h light: 12 h dark (LD), 24 h light (LL) and 24 h dark (DD) regimens and 2 weeks later were exposed to 3 weekly i.v. injections of NMU at t he dose of 50 mg/kg and starting in 2 days after first NMU administrat ion - to variable or static magnetic fields (VMF and SMF). Exposure to LL regimen significantly promoted whereas the exposure to DD regimen significantly inhibited NMU-induced mammary carcinogenesis. RIA of ser um samples from rats maintained under different light regimens has sho wn that exposure to LL followed by decrease of melatonin level and inc rease of prolactin level at all of modifying factors (NMU, VMF, SMF). Surgical light deprivation inhibits NMU-indiced mammary carcinogenesis in female rats. The primary role of pineal function in the modifying effects of light/dark regimens and electromagnetic fields on mammary c arcinogenesis are suggested.