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 influences the sexually differentiated patterns of development. Estrogens, derived from intracerebral aromatization, promote male pattern development of the central nervous system. The purpose of this study was to determine the effects of neonatal exposure to environmental estrogens on luteinizing hormone (LH) secretion and development of the sexually dimorphic nucleus of the medial preoptic area (SDN-POA) in castrated adult rats. Neonatal rats of both sexes received injections of either corn oil, 0.1 microgram diethylstilbestrol (DES), 3 micrograms beta-sitosterol (B1), 30 micrograms beta-sitosterol (B2), 0.1 microgram coumestrol (C1), 1 microgram coumestrol (C2), or 10 micrograms coumestrol (C3) on Day 1-10 of life and were castrated on Day 21. Right heart catheters were placed on Day 42, and GnRH (50 ng/kg) was administered. Blood was sampled for LH at 0-, 5-, 10-, 15-, and 30-min intervals. All doses of beta-sitosterol and coumestrol elicited increased basal levels of LH in females. In males, B1, B2, C2, and C3 increased basal levels of LH. The GnRH-induced LH increase was prevented in females treated with diethylstilbestrol and 10 micrograms of coumestrol. Males in all treatment groups exhibited GnRH-induced LH surges. The animals were sacrificed by decapitation on Day 49. Volumes of the SDN-POA of the groups were compared. Treatment with the agents did not result in significantly increased SDN volume in females; nor was there a difference in SDN size among the male groups. These data show that exposure to environmental estrogens early in development alters both postpubertal pituitary response to GnRH and basal LH secretion in females and alters only basal LH secretion in males. No significant enlargement (i.e., masculinization) of the SDN-POA was exhibited.

The effects of neonatal diethylstilbestrol (DES) exposure on the volume of the sexually dimorphic nucleus of the preoptic area of the hypothalamus (SDN-POA) and on GnRH-stimulated LH secretion were investigated in castrated female rats of known anogenital distance (AGD) at birth. The AGD was measured in females on the day of birth, and 0.1 microgram DES or corn oil was injected from Days 1 through 10 of life. The volume of the SDN-POA was significantly larger in animals that had received DES than in those that had received corn oil. The largest SDN-POA volumes were seen in DES-treated animals that had long (> 1.4 mm) AGDs, and smallest volumes in corn oil-treated females that had short (< or = to 1.4 mm) AGDs. Within treatment groups, animals with longer AGDs had significantly larger SDN-POA volumes than those with short AGDs. Within AGD subgroups, the effect of DES was similar in that the percentage increase in SDN-POA volume was equivalent. Pituitary responsiveness to GnRH was greater in corn oil-treated females with long AGD than in similarly treated females with short AGD. DES treatment blunted LH secretion in both AGD subgroups, but the increased LH secretion was preserved in rats with long AGD. The results indicate that the individual effects of the postnatal environment depend on the androgenicity of the intrauterine microenvironment. Further, variations in the individual's response to potential environmental hazards may be predicted by antecedent intrauterine events.