Effects of low-frequency magnetic fields on implantation in rats

Effects of 50-Hz sinusoidal magnetic fields (MFs) on embryo implantation, s erum 17 beta -estradiol, progesterone, testosterone, and melatonin levels, and on estrogen receptor (ER) and progesterone receptor (PgR) densities in the uterus were studied during the preimplantation and implantation periods in rats. Pregnant Wistar rats were exposed to magnetic r.m.s. field streng ths of 10 or 100 A/m (13 or 130 muT) or sham-exposed (controls) from day 0 of pregnancy for 24 h/day and killed during light and dark periods between 70 h and 176 h after ovulation. MFs did not influence the mean total number of implantations. The nocturnal mean serum melatonin concentration decreas ed by 34 and 38% at 10 and 100 A/m, respectively. At the same time, the fir st embryos, at an early developmental stage, arrived in the uterus in the M F-exposed groups. Serum estradiol and progesterone levels did not significa ntly change. Nuclear PgR and ER densities in the uterus decreased before im plantation and there was an increased incidence of early stage embryos and fewer hatched embryos were found in the uterus at 100 A/m. During the early implantation period, the uterine cytosolic ER/PgR-ratio was increased at 1 00 A/m and no implants were concomitantly found in uterus. The nuclear ER/P gR-ratio decreased during implantation in both ME-groups due to decreased n uclear ER density. At the same time, 19% and 15% of the embryos (calculated from the corpora luteae) at 10 and 100 A/m, respectively, were yet morulae and not implanted. In summary, the results show that MFs do not impair imp lantation in rats although there may be some borderline changes in the tran sport and development of embryos and associated endocrinologic parameters. (C) 2001 Elsevier Science Inc. All rights reserved.