Exposure to naturally occurring estrogens during critical periods of development can alter morphologic and physiologic markers of sexual differentiation. The current experiment characterizes the effects of in utero treatment with genistein, an isoflavonoid phytoestrogen, on birth weight, anogenital distance (AGD) at birth. GnRH stimulated luteinizing hormone (LH) secretion, volume of the sexually dimorphic nucleus in the preoptic area of the hypothalamus (SDN-POA), puberty onset, and vaginal cyclicity. Pregnant Charles River CD rats were injected sc daily on gestation day 16-20 with either 25,000 micrograms genistein (G25), 5,000 micrograms genistein (G5), 5 micrograms diethylstillbestrol (DES), 50 micrograms estradiol benzoate (E), or corn oil alone for controls. Birth weights and anogenital distance was taken and exposed progeny were subsequently used in two experiments. In Experiment 1 intra-atrial catheters were placed in adult castrated rats, GnRH was given iv, serial blood samples were drawn and sera were assayed for LH by radioimmunoassay (RIA). Brains obtained by subsequent decapitation were saved for histology. In Experiment 2, females were monitored for timing of vaginal opening as a marker of puberty onset, and vaginal smears were taken to monitor cyclicity. G25-treated females and DES- and E-treated animals of both sexes had decreased weights at birth compared with controls. G5- and E-treated animals of both sexes and DES males had smaller AGD than controls. No significant differences in pituitary responsiveness to GnRH were found among treatment groups. There was a nonsignificant decrease in SDN-POA volume in G5-treated females while DES- and E-treated females had increased SDN-POA volume compared with controls. G5-treated females had delayed puberty onset, and DES-treated females had atypical vaginal cycles in comparison with controls. The results confirm that prenatal exposure to estrogens in the environment can influence sexual differentiation. Our previous experiments have demonstrated that castrate female rats exposed as neonates to genistein have decreased pituitary responsiveness to GnRH challenge and enlarged SDN-POA volume in comparison with controls. Prenatal genistein at these dosages did not significantly alter these markers. However, genistein did mimic other estrogens' effects on AGD and birth weight and had a unique influence on puberty onset. Not only are genistein's effects different from other estrogens, but dosage and timing of exposure during development appear to be important factors in genistein's ability to modify these end points.

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The neonatal hormone environment determines the sexually differentiated pattern of brain growth. Estrogens, derived from intracerebral aromatization of testosterone, promote male sexual central nervous system (CNS) development. Developing animals may also encounter estrogens from plant, fungal, and xenobiotic sources (environmental estrogens). The purpose of this study was to assess the effects of environmental estrogens on the physiology and morphology of the hypothalamus and pituitary. Neonatal rats received injections of either corn oil, 0.1 microgram diethylstilbestrol (DES), 100 micrograms genistein (G100), 1000 micrograms genistein (G1000), 100 micrograms zearalenone (Z100), or 1000 micrograms zearalenone (Z1000) on Days 1-10 of life and were castrated on Day 21. On Day 42, right heart catheters were placed, GnRH (50 ng/kg) was administered, and blood was sampled for LH at 0, 5, 10, 15, and 30 min. Females exposed neonatally to DES, G1000, Z100, and Z1000 showed significantly decreased pituitary responsiveness to GnRH, whereas G100 increased GnRH-induced LH secretion. Males exposed neonatally to G100 also showed increased pituitary response to GnRH, and the remaining estrogen-exposed groups of males exhibited either decreased tonic LH or attenuated GnRH-stimulated LH secretion. The animals were killed by decapitation on Day 49. Volumes of the sexually dimorphic nucleus of the preoptic area (SDN-POA) of the exposed groups were compared. In females, DES, G1000, and Z1000 increased SDN volume; Z100 and G100 had no effect. There was no difference in SDN size among the male groups. These data show that exposure to environmental estrogens early in development alters postpubertal pituitary response to GnRH and "androgenizes" the SDN-POA.