Environmental estrogens and reproductive health: a discussion of the human and environmental data.

Estrogenic activity of certain xenobiotics is an established mechanism of toxicity that can impair reproductive function in adults of either sex, lead to irreversible abnormalities when administered during development, or cause cancer. The concern has been raised that exposure to ambient levels of estrogenic xenobiotics may be having widespread adverse effects on reproductive health of humans and wildlife. The purpose of this review is to evaluate (a) the nature of the evidence supporting this concern, and (b) the adequacy of toxicity screening to detect, and risk assessment procedures to establish safe levels for, agents acting by this mechanism. Observations such as adverse developmental effects after maternal exposure to therapeutic levels of the potent estrogen diethylstilbestrol or male fertility problems after exposure to high levels of the weak estrogen chlordecone clearly demonstrate that estrogenicity is active as a toxic mechanism in humans. High level exposures to estrogenic compounds have also been shown to affect specific wildlife populations. However, there is little direct evidence to indicate that exposures to ambient levels of estrogenic xenobiotics are affecting reproductive health. Reports of historical trends showing decreasing reproductive capacity (e.g., decreased sperm production over the last 50 years) are either inconsistent with other data or have significant methodologic inadequacies that hinder interpretation. More reliable historical trend data show an increase in breast cancer rate, but the most comprehensive epidemiology study to data failed to show an association between exposure to persistent, estrogenic organochlorine compounds and breast cancer. Clearly, more work needs to be done to characterize historical trends in humans and background incidence of abnormalities in wildlife populations, and to test hypotheses about ambient exposure to environmental contaminants and toxic effects, before conclusions can be reached about the extent or possible causes of adverse effects. It is unlikely that current lab animal testing protocols are failing to detect agents with estrogenic activity, as a wide array of estrogen-responsive endpoints are measured in standard testing batteries. Routine testing for aquatic and wildlife toxicity is more limited in this respect, and work should be done to assess the validity of applying mammalian toxicology data for submammalian hazard identification. Current risk assessment methods appear to be valid for estrogenic agents, although the database for evaluating this is limited. In conclusion, estrogenicity is an important mechanism of reproductive and developmental toxicity; however, there is little evidence at this point that low level exposures constitute a human or ecologic health risk. Given the potential consequences of an undetected risk, more research is needed to investigate associations between exposures and effects, both in people and animals, and a number of research questions are identified herein. The lack of evidence demonstrating widespread xenobiotic-induced estrogenic risk suggests that far-reaching policy decisions can await these research findings.

Prenatal delta-9-tetrahydrocannabinol in the rat: effects on postweaning growth.

Either 15 or 30 mg/kg of delta-9-tetrahydrocannabinol (delta-9-THC) was administered from Day 2 through Day 22 of gestation. Pair-fed and nontreated groups served as controls and all treated and control litters were fostered at birth to untreated dams. When weighed at 57-60 days of age, pair-fed controls were significantly heavier than the nontreated, whereas the treated animals were intermediate between the controls. These findings are discussed with respect to nutritional studies that have reported postnatal growth enhancement following prenatal maternal undernutrition and the possibility that prenatal delta-9-THC inhibits this effect.

Structural and functional effects of prenatal cocaine exposure in adult rat brain.

The long-term effects of cocaine exposure early in development on the metabolic function of major central neuronal systems in the rat are reported in this study. Pregnant Wistar rats were administered either 60 mg/kg cocaine or the vehicle from gestation day (G) 8 through 22 via daily gastric intubation. Sixty-day-old male offspring were examined using the quantified deoxyglucose autoradiographic method. Of the 45 structures examined, 2 cortical and 14 subcortical structures showed statistically significant alterations in glucose metabolism compared to controls. The primary somatosensory and motor cortices showed significant decreases. The hypothalamus contained the greatest concentration of nuclei showing significant changes in activity. All of these changes were decreases. The nigrostriatal pathway, the medial forebrain bundle, the hippocampus, septum and amygdala were all significantly less metabolically active in the exposed offspring. The subcortical sensory systems did not appear to be affected at the dose of cocaine studied. Adjacent sections incubated in 1nM [3H]SCH 23390 showed an increase in the concentration of D1 receptors in the substantia nigra, pars reticulata. Forebrain dopaminergic regions which showed decreased glucose metabolism did not appear to have altered SCH 23390 binding. Although size determinations were made on several cortical and subcortical structures, none were significantly affected by prenatal cocaine. Effects of chronic prenatal cocaine exposure on adult brain metabolism in several neuronal systems were identified at doses which had no significant effects on adult brain or body size. These data support the hypothesis that cocaine use during pregnancy produces permanent neurological effects at doses below those which produce growth retardation and terata.

Prenatal phencyclidine in rats: effects on apomorphine-induced climbing.

Either 5 or 10 mg/kg of phencyclidine (PCP) in saline was administered by subcutaneous injection to gravid dams during the last two weeks of gestation. A pair-fed control group was administered the vehicle alone and allowed to eat and drink only the amount consumed by the 10 mg/kg group on the same gestation days. A nontreated control group was left undisturbed during pregnancy. All treated and control litters were fostered at birth to untreated dams. Among the dams receiving 10 mg/kg of PCP, food and water intake was initially reduced to 33-43% of nontreated controls, but then returned to control levels. Surprisingly, after 3 days of drug administration, water intake of PCP-treated dams exceeded that of the nontreated dams by approximately 15%. Compared with the nontreated dams, both PCP groups and pair-fed control dams gained significantly less body weight from conception to term. PCP had no significant effect on number of implantation sites or number of live births, however, PCP produced an apparent selective embryolethal effect on males and body weight reduction in all groups at birth. Prenatal PCP did not alter the sensitivity to apomorphine-induced climbing behavior during the second postnatal week. These results are discussed with respect to published animal and clinical studies of PCP exposure during pregnancy.

Effects of prenatal phencyclidine on 3H-PCP binding and PCP-induced motor activity and ataxia.

Either phencyclidine hydrochloride (PCP) (5, 10, or 20 mg/kg) or saline was administered by subcutaneous injection to gravid CF-1 mice during either Mid (E6-15) or Late (E12-18) gestation. A nontreated control group (UTC) was left undisturbed during pregnancy. All treated and control litters were fostered at birth to untreated dams. Although postnatal challenge of PCP increased motor activity and ataxia in a dose-related manner, prenatal PCP had no effect on postnatal motor activity, ataxia or 3H-PCP binding. However, treatment period did have a significant effect on ataxia and 3H-PCP binding. In response to challenge doses of 5.0 and 7.5 mg/kg PCP, ataxia scores of the Late gestation offspring were significantly greater than the UTC offspring which in turn were significantly greater than the ataxia scores of the Mid gestation group. The results are discussed in relation to other animal and clinical reports of prenatal PCP exposure.

The effects of prenatal exposure to delta-9-tetrahydrocannabinol on the rest-activity cycle of the preweanling rat.

Either 15 or 50 mg/kg of delta-9-tetrahydrocannabinol (delta-9-THC) was administered from Day 2 through Day 22 of gestation. Pair-fed (0 mg/kg) and nontreated groups served as controls and all treated and control litters were fostered at birth to untreated dams. To examine whether delta-9-THC produces effects on the rest-activity cycle of the offspring, groups of 3 littermates from each of the treated and control groups were tested for an 8 hr observation period on electronic activity monitors at 17, 22 and 30 days of age. Whereas all treated and control groups showed age-dependent changes in activity, neither activity level nor the rest-activity pattern were affected by delta-9-THC. These findings are discussed in relation to neurobehavioral studies of activity changes following prenatal exposure to cannabis.

Dopamine autoreceptor agonists attenuate spontaneous motor activity but not spontaneous fighting in individually-housed mice.

The present study was conducted to determine whether or not two behavioral characteristics of individually-housed mice, hyperactivity in a novel environment and intermale fighting, are attenuated by the dopamine (DA) agonists, apomorphine, (+)- and (-)-3-(3-hydroxyphenyl)-N-n-propylpiperidine (3-PPP). Autoreceptor-activating doses of these drugs which reduced spontaneous activity in a novel environment did not inhibit spontaneous fighting with conspecific olfactory bulbectomized males. Individually-housed mice were more active in a novel environment and showed a significant reduction of activity at lower doses of apomorphine, (+)- and (-)-3-PPP than group-housed mice. However, the ED50's for the inhibition of spontaneous activity in a novel environment in group- and individually-housed mice were similar: apomorphine, 0.02 vs. 0.012 mg/kg, SC; (+)-3-PPP, 0.50 vs. 0.51 mg/kg, SC; and (-)-3-PPP, 1.0 vs. 0.56 mg/kg, SC, for group- and individually-housed mice respectively. A significant proportion of individually-housed mice, but not group-housed mice, displayed catalepsy in response to high doses of (-)-3-PPP. These data suggest that DA autoreceptor agonists can modulate the hyperactivity syndrome but not spontaneous fighting behavior in individually-housed mice.

Comparison of oral and subcutaneous routes of cocaine administration on behavior, plasma drug concentration and toxicity in female rats.

Oral and subcutaneous routes of administration of cocaine HCl were investigated in female Wistar rats for food and water consumption, locomotor activity, stereotypic behaviors, plasma drug concentrations and injection site pathology. Animals received either 40 or 80 mg/kg/day by gastric intubation (PO-40 and PO-80 respectively) or 20 or 40 mg/kg/day subcutaneously (SC-20 and SC-40). All groups received the drug or the vehicle for 16 consecutive days. Locomotor activity and stereotypy were evaluated on Days 1, 5, 10, and 15. Plasma drug concentrations and injection site pathology were determined on Day 16. Subcutaneous administration was associated with a sensitization to the effects of cocaine on locomotion and stereotypy, higher blood levels than oral administration at the same dose, and severe dermal lesions. However, there were no differences in any measure between the SC-20 and SC-40 groups. Oral cocaine was also associated with behavioral sensitization. However, unlike the SC route, oral cocaine was characterized by dose-related increases in locomotion and stereotypy in the absence of gastrointestinal pathology. Inasmuch as oral administration resulted in dose-response relationships and low toxicity while subcutaneous administration did not, these factors should be considered in future studies utilizing chronic cocaine administration.

Prenatal cocaine: maternal toxicity, fetal effects and locomotor activity in rat offspring.

Either 30 or 60 mg/kg of cocaine hydrochloride (COC) was administered by gastric intubation to gravid rats during the last two weeks of gestation. A pair-fed control group was administered the vehicle alone and allowed to eat and drink only the amount consumed by the 60 mg/kg group on the same gestation days. A nontreated control group was left undisturbed during pregnancy. All treated and control litters were fostered at birth to untreated dams. None of the treated dams died nor were any gross signs of cocaine toxicity observed. Among the COC-60 dams, there was a reduction in food and water intake at the beginning of treatment; whereas water intake returned to control levels, food intake remained approximately 12% below that of the controls. Compared to the nontreated dams, both COC-treated and pair-fed dams gained significantly less body weight from conception to term. Cocaine had no effect on offspring mortality, birthweight or rate of postnatal growth. Measurement of the ontogeny of motor activity during the first month of life revealed a similar activity pattern for all the groups except for the COC-60 group which showed heightened activity on Days 20 and 23. These findings are discussed in relation to other animal and clinical reports of prenatal cocaine exposure.

Phencyclidine during pregnancy: fetal brain levels and neurobehavioral effects.

Either phencyclidine (PCP) (5, 10, or 20 mg/kg) or saline was administered SC to pregnant CF-1 mice during either MID (E6-E15) or LATE (E12-E18) gestation. Because of the reported prolonged persistence of PCP in adult tissues we first determined its half-life in fetal brain for both treatment periods. PCP appeared rapidly in fetal tissues after maternal administration but was not detected after 8 hours. Then, other treated and control litters were fostered to untreated controls, growth determined and the ontogeny of isolation-induced aggressive behavior examined. Subteratogenic doses of PCP produced mild maternal toxicity without lethality. There was an apparent selective embryolethal effect on males but PCP did not produce an effect on postnatal growth. Prenatal PCP did not alter the ontogeny or intensity of isolation-induced aggressive behavior in male offspring. The results are discussed in relation to other prenatal studies of PCP toxicity and teratogenicity.