Pubertal gonadal hormones in modulating the testosterone dependency of hepatic aryl hydrocarbon hydroxylase in female rats

The responsiveness of the hepatic microsomal aryl hydrocarbon hydroxylase (AHH) to testosterone enanthate (TE; 2.5 mumol/kg/day for 9 days) was sex-dependent in adult rats, the enzyme being very resistant to TE in normal adult or ovariectomized females. Administration of testosterone propionate or diethylstilbestrol (1.45 mumol) to neonatal female rats at 1 and 3 days of age did not increase the responsivity to TE in adulthood. However, exposure of female rats to TE (5.0 mumol/kg/day) during the peripubertal period (35-50 days old) resulted in increased sensitivity to TE (+55.2%) when tested in adulthood. The responsivity was further potentiated (+109.3%) if the animals were ovariectomized at 28 days of age. Prepubescent ovariectomized females which received corn oil or estradiol benzoate (1.5 mumol/kg on alternate days) during puberty were not able to respond to TE significantly. These results suggest that the refractoriness of the hepatic AHH to testosterone in adult female rats is determined by the absence of testosterone, as well as the presence of estrogens, during puberty.     

Imprinting of hepatic microsomal cytochrome P-450 enzyme activities and cytochrome P-450IIC11 by peripubertal administration of testosterone in female rats.

The influence of peripubertal exposure to physiological doses of testosterone on the adult androgen responsiveness of hepatic microsomal cytochrome P-450 was investigated. Male and female Sprague-Dawley rats were sham-operated or gonadectomized before puberty, at 25 days of age. They were injected subcutaneously with testosterone enanthate (5 mumol/kg/day) during the pubertal time period, on days 35-49. Responsiveness to this same dose of testosterone was tested by administering the compound during adulthood, on days 81-89. The females provided a model that had not been exposed to neonatal androgen imprinting, in contrast to the males. Testosterone 2 alpha-hydroxylase activity and cytochrome P-450IIC11, which are normally expressed only in adult males, were expressed in the gonadectomized females administered testosterone during puberty with no further exposure to the hormone for the next 40 days. The levels found were similar to those in the gonadectomized male group. When the combined pubertal and adult testosterone regimen was used, a synergistic effect was produced; the 2 alpha-hydroxylase activity reached control male levels in both gonadectomized and sham-operated females and, in addition, cytochrome P-450IIC11 attained control male levels in the gonadectomized females. Testosterone 6 beta-hydroxylase and erythromycin N-demethylase activities were used as indicators of the cytochrome P-450IIIA subfamily. These activities were significantly increased only in the females treated with testosterone during both the pubertal and adult periods, reaching control male levels of 6 beta-hydroxylation. A similar effect, but in the opposite direction, was found with testosterone 7 alpha-hydroxylase, an enzyme activity indicative of cytochrome P-450IIA1. A decrease in this enzyme was produced in the females administered testosterone during both time periods, resulting in levels equivalent to those found in control males. In general, a highly significant interaction was found between the pubertal and adult treatment periods for the females, indicating a chronic effect of the pubertal exposure. The experiments with castrated males did not result in synergistic interactions, although there was some evidence of an additive effect. The results of this study support the hypothesis that the peripubertal period is a time during which testosterone imprinting of both increased basal levels and adult androgen responsiveness of some hepatic cytochrome P-450 enzymes can occur in the female rat.     

Effect of flutamide on hepatic cytosolic methyltrienolone (R1881) binding kinetics and testosterone responsive hepatic drug and steroid metabolism in the adult male rat

Flutamide was used to investigate the mechanism involved in androgen responsive hepatic microsomal drug and steroid metabolism. We compared the antiandrogenic action of flutamide on the prostate to its effect on testosterone responsive hepatic microsomal benzo[a]pyrene hydroxylase (BPH) and testosterone reductase (TR) activities. Male Wistar rats, castrated as adults, were treated with 5 mumoles.kg-1.day-1 of testosterone enanthate subcutaneously for 10 days. Co-administration of increasing doses of flutamide caused a dose-dependent reduction in prostate to body weight ratios and, in the same animals, caused significant alterations in adult male hepatic microsomal BPH and TR activities. These doses of flutamide did not affect the serum testosterone levels. To test the possibility that the action of flutamide on androgen responsive hepatic microsomal drug and steroid metabolism may be similar to that occurring in the prostate, a tissue which contains an androgen receptor, we also studied the effect of flutamide on the binding kinetics of the high affinity hepatic cytosolic [3H]R1881 binding protein in vivo. Scatchard analysis of [3H]R1881 binding data revealed a reduction in the binding capacity of the hepatic cytosolic androgen binding protein in castrated animals treated with a combination of flutamide and testosterone enanthate at doses capable of maximally altering hepatic microsomal drug and steroid metabolism. No alteration in binding affinity occurred in this treatment group. However, a decreased binding affinity was found when flutamide alone was given. The binding kinetics of the hepatic cytosolic androgen binding protein were not altered in the castrated adult male with or without testosterone treatment. When flutamide was injected daily into the intact adult female rat, no effect was observed on either hepatic microsomal BPH or TR activities. Taken together, these data indicate that flutamide reduces hepatic cytosolic R1881 binding in the adult male rat, and this may explain some of the effects of this antiandrogen on testosterone-sensitive hepatic microsomal drug and steroid metabolism.     

Testosterone is required for corticosteroid-binding globulin upregulation by morphine to be fully manifested

We previously reported that morphine increases the concentration of corticosteroid-binding globulin (CBG) in blood of male, but not female, rats. This pronounced sexual dimorphism suggested that CBG upregulation by morphine might be androgen-dependent. In the current studies, we found that castration, whether performed just before or just after puberty or in adulthood, increased the concentration of CBG in adult male rats. Naltrexone did not prevent this increase and, therefore, it does not appear to be attributable to the release of endogenous opioids. Exposure to morphine for 1 week in adulthood increased ( approximately 100%) the concentration of CBG in intact, i.e., sham-castrated, males. The CBG levels of castrated rats treated with morphine did not differ from those of intact rats treated with morphine. However, because castration increased the concentration of CBG, the difference between the placebo and morphine groups decreased with time after castration. At 4 weeks after castration, the difference between the morphine and placebo groups (19%) was no longer statistically significant. Testosterone replacement prevented the rise in CBG levels following castration and maintained the magnitude of the difference between placebo and morphine-treated rats within the normal range. Thus, testosterone appears necessary for morphine effects on CBG to be fully manifested.     

Growth hormone regulation and developmental expression of rat hepatic CYP3A18, CYP3A9, and CYP3A2

The present study investigated the role of growth hormone (GH) in hepatic CYP3A18 and CYP3A9 expression in prepubertal and adult male rats. For comparison, the effects of GH on CYP3A2 expression were also measured. Initial experiments demonstrated that CYP3A18 mRNA levels were greater during puberty and adulthood than during the prepubertal period, CYP3A9 mRNA was not expressed until puberty and its expression increased in adulthood, and CYP3A2 mRNA levels were relatively constant from prepuberty to adult life. Hypophysectomy, which results in the loss of multiple pituitary factors including GH, increased CYP3A2 and CYP3A18 mRNA expression 3- to 4-fold, but it did not affect CYP3A9 mRNA levels or CYP3A-mediated testosterone 2beta- or 6beta-hydroxylase activity in adult rats. GH administered as twice daily s.c. injections (0.12 microg/g body weight) to hypophysectomized or intact adult rats did not affect CYP3A18 or CYP3A9 mRNA expression. The same treatment decreased CYP3A2 mRNA and protein and testosterone 2beta- and 6beta-hydroxylase activity levels in intact but not hypophysectomized rats. However, in intact prepubertal rats, intermittent GH administration decreased CYP3A18 and CYP3A2 mRNA levels, but a higher dosage (3.6 microg/g) was required to suppress CYP3A2. Overall, the present study demonstrated that: (a) the constitutive expression of CYP3A18, CYP3A9, and CYP3A2 does not require the presence of GH, (b) CYP3A18 is more sensitive than CYP3A9 to GH modulation in adult rats; and (c) CYP3A2 is less sensitive to the suppressive influence of GH during the prepubertal period than during adult life.     

Pre- and postnatal toxicity of the commercial glyphosate formulation in Wistar rats

Glyphosate is the active ingredient and polyoxyethyleneamine is the surfactant present in the herbicide Roundup formulation commercialized in Brazil. The aim of this study was to assess the reproductive effects of glyphosate-Roundup on male and female offspring of Wistar rats exposed during pregnancy and lactation. Dams were treated orally with water or 50, 150 or 450 mg/kg glyphosate during pregnancy (21-23 days) and lactation (21 days). These doses do not correspond to human exposure levels. The results showed that glyphosate-Roundup did not induce maternal toxicity but induced adverse reproductive effects on male offspring rats: a decrease in sperm number per epididymis tail and in daily sperm production during adulthood, an increase in the percentage of abnormal sperms and a dose-related decrease in the serum testosterone level at puberty, and signs of individual spermatid degeneration during both periods. There was only a vaginal canal-opening delay in the exposed female offspring. These findings suggest that in utero and lactational exposure to glyphosate-Roundup may induce significant adverse effects on the reproductive system of male Wistar rats at puberty and during adulthood.     

Effect of dietary administration of genistein, nonylphenol or ethinyl estradiol on hepatic testosterone metabolism, cytochrome P-450 enzymes, and estrogen receptor alpha expression.

The objective of this study was to examine effects of estrogenic agents of varying potencies (genistein, p-nonylphenol, and ethinyl estradiol) on hepatic testosterone metabolism, cytochrome P-450 (CYP450) enzymes, and ERalpha expression. These endpoints were examined as potential biomarkers of, and contributors to, endocrine disruptive activity. Exposure occurred during critical developmental periods, from gestational day 7 through weaning via the mothers' diet. Thereafter, rats were exposed via their diet to the compounds until puberty (postnatal day 50). Testosterone hydroxylase and 5alpha-reductase activities, CYP2C and CYP3A levels were determined. In general, the compounds were more active in male rats than female rats. The only effect observed in female rats was at the 250 ppm genistein dose, in which an approximately 40% increase in 5alpha-reductase activity was observed. In male rats, genistein treatment had mixed effects on testosterone metabolism. The 1250 ppm dose decreased both CYP2C and CYP3A protein levels. Nonylphenol had the most profound effects on testosterone metabolism and CYP450 expression in male rats, with effects occurring at doses as low as 25 ppm. An increase in 5alpha-reductase activity and a decrease in the formation of 16alpha-OH-, 2alpha-OH-testosterone metabolites, CYP2C and CYP3A protein were observed. EE2 decreased the formation of several testosterone metabolites and CYP2C protein. All compounds had some effect on hepatic ERalpha expression, although a consistent effect was not observed. This study demonstrates that the test compounds can influence hepatic testosterone hydroxylase activity and CYP450 expression, as well as ERalpha expression, although these activities cannot be directly related to estrogenic activity.     

Atrazine disrupts the hypothalamic control of pituitary-ovarian function.

The chloro-S-triazine herbicides (i.e., atrazine, simazine, cyanazine) constitute the largest group of herbicides sold in the United States. Despite their extensive usage, relatively little is known about the possible human-health effects and mechanism(s) of action of these compounds. Previous studies in our laboratory have shown that the chlorotriazines disrupt the hormonal control of ovarian cycles. Results from these studies led us to hypothesize that these herbicides disrupt endocrine function primarily through their action on the central nervous system. To evaluate this hypothesis, we examined the estrogen-induced surges of luteinizing hormone (LH) and prolactin in ovariectomized Sprague-Dawley (SD) and Long-Evans hooded (LE) rats treated with atrazine (50-300 mg/kg/day, by gavage) for 1, 3, or 21 days. One dose of atrazine (300 mg/kg) suppressed the LH and prolactin surge in ovariectomized LE, but not SD female rats. Atrazine (300 mg/kg) administered to intact LE females on the day of vaginal proestrus was without effect on ovulation but did induce a pseudopregnancy in 7 of 9 females. Three daily doses of atrazine suppressed the estrogen-induced LH and prolactin surges in ovariectomized LE females in a dose-dependent manner, but this same treatment was without effect on serum LH and prolactin in SD females. The estrogen-induced surges of both pituitary hormones were suppressed by atrazine (75-300 mg/kg/day) in a dose-dependent manner in females of both strains evaluated after 21 days of treatment. Three experiments were then performed to determine whether the brain, pituitary, or both organs were the target sites for the chlorotriazines. These included examination of the ability of (1) the pituitary lactotrophs to secrete prolactin, using hypophyosectomized females bearing pituitary autotransplants (ectopic pituitaries); (2) the synthetic gonadotropin-releasing hormone (GnRH) to induce LH secretion in females treated with high concentrations of atrazine for 3 days; and (3) atrazine (administered in vivo or in vitro) to suppress LH and prolactin secretion from pituitaries, using a flow-through perifusion procedure. In conclusion, the results of these studies demonstrate that atrazine alters LH and prolactin serum levels in the LE and SD female rats by altering the hypothalamic control of these hormones. In this regard, the LE female appeared to be more sensitive to the hormone suppressive effects of atrazine, as indicated by the decreases observed on treatment-day 3. These experiments support the hypothesis that the effect of atrazine on LH and prolactin secretion is mediated via a hypothalamic site of action.     

EFFECTS ON PUBERTAL GROWTH AND REPRODUCTION IN RATS EXPOSED TO LEAD PERINATALLY OR CONTINUOUSLY THROUGHOUT DEVELOPMENT

The reproductive, endocrine, and growth effects of developmental lead exposure were assessed using a rat model in which 0.6% lead acetate (w/v) was administered in the drinking water ad libitum during different developmental periods to determine if lead actions were a result of direct effects of continuous exposure to the metal ion or secondary to disrupted neonatal "endocrine imprinting." Sprague Dawley rats were exposed to lead: (1) from gestational d 5 through birth; (2) during pregnancy and lactation; (3) during lactation only; (4) from birth through adulthood; or (5) from gestational d 5 through adulthood. Lead effects were measured on the development of aspects of the reproductive system, adult sex steroid levels, and growth rates in both male and female animals. The relative weights of male secondary sex organs in adult offspring were not significantly affected in any of the lead-treated groups. In contrast, female pups exposed to lead from birth through adulthood or from gestational day 5 through adulthood were observed to have significantly delayed vaginal opening and disrupted estrus cycling. These effects on female reproductive physiology were not observed in animals where lead exposure was confined only to pregnancy or lactation. Significant suppression of adult mean serum testosterone levels was only observed in male pups exposed to lead continuously from gestational age 5 d throughout life. Lead decreased birth weight in all animals exposed in utero and mean body weights were significantly decreased in all lead-treated groups up to weaning. Analysis of growth curves revealed that all lead-treated groups had significantly reduced growth rates during lactation. However, in addition, in male pups exposed to lead during pregnancy and lactation, from birth or from gestational age 5 d, growth rates were also significantly reduced during puberty. Postpubertal growth rates were unaffected in any lead-treated group. Thus, delayed female reproductive development and suppression of adult male serum testosterone concentration required continuous exposure to the heavy metal. Little evidence was observed for an alteration of "endocrine imprinting" by lead on either reproductive or growth parameters. Exposure during early development (pregnancy and lactation) resulted in no permanent effects in this model other than small (10%) decreases in the body weight of pups postpuberty.     

Modulation of hepatic CYP2A1, CYP2C11, and CYP3A9 expression in adult rats by neonatal administration of tamoxifen.

To examine the effect of neonatal administration of tamoxifen on adult expression of hepatic cytochrome P-450 (CYP) enzymes and steroid 5alpha-reductase, male and female Sprague-Dawley rats were injected s.c. with tamoxifen (20 microg) or peanut oil (control) once daily at days 1 to 5 of age and sacrificed at 3 months of age. Neonatal tamoxifen treatment did not affect b.wt. or liver weight of adult male and female rats, but decreased testicular weight by approximately 40% in adult male rats. Neonatal administration of tamoxifen decreased hepatic microsomal testosterone 6beta- and 7alpha-hydroxylase activities in adult female rats whereas it did not alter steroid 5alpha-reductase activity. The same treatment increased testosterone 7alpha-hydroxylase activity, but did not affect testosterone 6beta-hydroxylase or steroid 5alpha-reductase activity in adult male rats. Immunoblot analysis indicated that neonatal tamoxifen treatment decreased CYP2C11 protein level by 26% and increased CYP2A1 protein content by 2.6-fold in adult male rats, whereas it had no effect on CYP3A or CYP2B protein expression. The reduction in the CYP3A-mediated testosterone 6beta-hydroxylase activity in adult female rats was accompanied by a decrease in CYP3A9 mRNA expression. Analysis of serum hormone levels indicated that neonatal exposure to tamoxifen resulted in a decrease in serum 17beta-estradiol concentration in adult female rats, whereas it did not alter serum testosterone concentration in adult male rats. In summary, treatment of neonatal rats with tamoxifen produced a long-lasting effect on hepatic CYP2A1, CYP2C11, and CYP3A9 expression in addition to testicular weight and serum 17beta-estradiol concentration.     

Hypophagic,endocrine and subjective responses to m-chlorophenylpiperazine in healthy men and women

We studied the effect of the 5-HT receptor agonist, m-chlorophenylpiperazine (mCPP) (0.4 mg orally), on food intake, plasma prolactin and subjective state in 24 healthy male and female volunteers, using a double-blind, placebo-controlled design. mCPP lowered food intake, and increased plasma prolactin to the same extent in both sexes. Increased anxiety ratings, however, occurred more in females. Other mCPP-induced subjective changes in nausea, light-headedness and hunger did not distinguish the sexes. There was no significant correlation between the decrease in food intake produced by mCPP and any of the subjective ratings. Overall, the data indicate that mCPP produces significant hypophagia in both men and women. The greater anxiogenic effect of mCPP in female subjects is of interest in view of the increased prevalence of clinical anxiety disorders in women.     

Androgen deprivation from pre-puberty to peripuberty interferes in proteins expression in pubertal and adult rat epididymis

Few studies have focused on experimental testosterone deprivation in immature animals. Therefore, this study used sexually immature rats aiming to evaluate the testes and epididymis histology and proteins expression in these organs on PND50 and 75, after premature antiandrogen exposure, from PND21 to 44. Although the androgen deprivation from pre-puberty up to peripuberty did not alter the histological organization of the testes and epididymis either at puberty or at adulthood, the treatment impaired the expression of specific proteins in epididymal tissue at puberty and adulthood (androgen receptor, calmodulin, Rab11A). These changes may be related to impaired epididymal function, sperm quality and fertility capacity as observed in a previous study. Further studies are necessary to better investigate the molecular mechanisms involved in the impairment on reproductive competence of male rats after precocious hormonal injury.     

Chronic morphine exposure during puberty decreases postpartum prolactin secretion in adult female rats

Opiate use in teenage populations has been increasing in recent years. The potential impact of exposure to high levels of opiates at a time when reproductive systems are maturing has not been well studied, especially in females. The present study used an animal model of adolescent opiate abuse in females to examine the potential impact of high levels of opiates during puberty on several reproductive parameters, including suckling-induced prolactin secretion. Two groups of juvenile female rats were administered increasing doses of morphine sulfate or saline (s.c.) from age 30-50 days, beginning with a dose of 2.5 mg/kg and achieving a maximal dose of 50 mg/kg. As adults, these females were mated and reared either their own or foster pups. On either postpartum day 5 or 10, following a 4 h separation, suckling-induced prolactin secretion was measured. In addition, on postpartum day 5 maternal behavior latencies were determined. The results demonstrate reduced suckling-induced prolactin secretion on postpartum day 5 in females previously exposed to morphine during pubertal development. These effects were observed in females rearing either their own or fostered pups. These effects were not due to any differences in maternal behavior latencies, as retrieval or crouching latencies were unaffected. In summary, chronic morphine exposure during puberty results in changes in the regulation of prolactin secretion during early lactation, which are observed several weeks after cessation of drug treatment. These data suggest that prior opiate use during puberty can continue to affect the regulation of prolactin secretion into adulthood.     

Gonadal steroids mediate the opposite changes in cocaine-induced locomotion across adolescence in male and female rats

Evidence from both human studies and animal models indicates that cocaine elicits more behavioral stimulation in females than males. The present study sought to determine whether sex-specific responses to cocaine emerge during adolescence and to determine if gonadal steroid action during puberty affects adult responsiveness to cocaine. We administered cocaine using an escalating dose model in male and female rats at ages postnatal (PN) 28, 42, and 65 days. To assess the effects of pubertal gonadal steroid action, we compared the effects of binge cocaine administration on intact and prepubertally gonadectomized male and female rats in adulthood. Cocaine responses changed in opposite directions in males and females as they progressed through adolescence. At most doses, adolescent males were more responsive than adult males whereas adult females were more responsive than adolescent females. Ambulatory activity was age-dependent in males whereas non-ambulatory activity was age-dependent in females. Prepubertal gonadectomy increased behavioral responsiveness to the highest dose of cocaine in males whereas it decreased behavioral responsiveness to lower doses of cocaine in females. We conclude that sex differences in behavioral responses to cocaine arise during adolescence from a concurrent decrease in male responsiveness and increase in female responsiveness. Our results suggest that gonadal steroids exert lasting and opposing effects on the sensitivity of males and females to psychostimulants during development.     

Reproductive disorders in female rats after prenatal exposure to sodium arsenite

Arsenic is a metalloid widely found in the environment in organic and inorganic forms. Exposure to inorganic arsenic forms via drinking water has been associated with an increased incidence of negative health effects, including reproductive disorders and dysfunction of the endocrine system. However, the impact of arsenic exposure on female reproductive development is still unclear. Therefore, in the present study, we evaluated the effects of prenatal exposure to arsenic on the initial sexual development and puberty onset, and in the morphology of the female reproductive organs, estrous cycle regularity and fertility parameters during adulthood. To do that, pregnant female Wistar rats were exposed to 10 mg/L sodium arsenite via drinking water from gestational day (GD) 1 until GD 21 and the female offspring was evaluated in different postnatal days. Our results showed that prenatal arsenic exposure induced a decrease of litter weight and morphological masculinization in females at postnatal day 1. Moreover, these females had a delay in the age of puberty onset and alteration in estrous cycle number and length. During adulthood, females from the sodium arsenite group showed an increase in endometrium, myometrium and perimetrium areas, and an imbalance in uterine antioxidant enzyme activity. These animals also presented an increase in post-implantation loss and reabsorption number, leading to reduced viable fetus number. In conclusion, prenatal arsenic exposure in rats was able to promote female masculinization, alter sexual development and impair reproductive performance.     

Repeated binge ethanol administration during adolescence enhances voluntary sweetened ethanol intake in young adulthood in male and female rats

Binge alcohol consumption is a rising concern in the United States, especially among adolescents. During this developmental period alcohol use is usually initiated and has been shown to cause detrimental effects on brain structure and function as well as cognitive/behavioral impairments in rats. Binge models, where animals are repeatedly administered high doses of ethanol typically over a period of three or four days cause these effects. There has been little work conducted aimed at investigating the long-term behavioral consequences of repeated binge administration during adolescence on later ethanol-induced behavior in young adulthood and adulthood. The repeated four-day binge model may serve as a good approximate for patterns of human adolescent alcohol consumption as this is similar to a “bender” in human alcoholics. The present set of experiments examined the dose-response and sex-related differences induced by repeated binge ethanol administration during adolescence on sweetened ethanol (Experiment 1) or saccharin (Experiment 2) intake in young adulthood. In both experiments, on postnatal days (PND) 28-31, PND 35-38 and PND 42-45, ethanol (1.5, 3.0 or 5.0 g/kg) or water was administered intragastrically to adolescent rats. Rats underwent abstinence from PND 46-59. Subsequently, in young adulthood, ethanol and saccharin intake were assessed. Exposure to any dose of ethanol during adolescence significantly enhanced ethanol intake in adulthood. However, while female rats had higher overall g/kg intake, males appear to be more vulnerable to the impact of adolescent ethanol exposure on subsequently increased ethanol intake in young adulthood. Exposure to ethanol during adolescence did not alter saccharin consumption in young adulthood in male or female rats. Considering that adolescence is the developmental period in which ethanol experimentation and consumption is usually initiated, the present set of experiments demonstrate the importance of elucidating the impact of early binge-pattern ethanol exposure on the subsequent predisposition to drink later in life.     

Exposure of prepubertal female rats to inhaled di(2-ethylhexyl)phthalate affects the onset of puberty and postpubertal reproductive functions.

We evaluated the effects of inhaled di(2-ethylhexyl)phthalate (DEHP) on the onset of puberty and on postpubertal reproductive functions in prepubertal female rats. DEHP was administered by inhalation at doses of 0, 5, and 25 mg/m3 to groups of female rats for 6 h/day, 5 contiguous days/week from postnatal days (PNDs) 22 to 41 and to PND 84. The onset of puberty was determined by daily examination for vaginal opening (VO) and first estrous cycle. Reproductive function was evaluated by observing estrous cyclicity from PNDs 49 to 84. Upon completion of exposure, the rats were sacrificed at PND 42 and PNDs 85-88 during the diestrous stage. DEHP exposure advanced the age of VO and first estrous cycle, and serum cholesterol, luteinizing hormone, and estradiol levels were significantly elevated in the 25-mg/m3 DEHP group. Irregular estrous cycles were observed more frequently in DEHP-exposed rats, and serum cholesterol decreased in DEHP-exposed rats in adulthood; RT-PCR showed that the expression of aromatase mRNA, encoding a rate-limiting enzyme that catalyzes the conversion of testosterone to estradiol, was elevated in the 25-mg/m3 DEHP group. These data suggest that inhaled DEHP may advance the onset of puberty and alter postpubertal reproductive functions.     

Adolescent vs. adult-onset nicotine self-administration in male rats: duration of effect and differential nicotinic receptor correlates

Adolescence is the life stage when tobacco addiction typically begins. Adolescent neurobehavioral development may be altered by nicotine self-administration in a way that persistently potentiates addiction. Previously, we showed that female adolescent rats self-administer more nicotine than do adults and that the increased nicotine intake then persists through the transition to adulthood [E.D. Levin, A. Rezvani, D. Montoya, J. Rose, H. Swartzwelder, Adolescent-onset nicotine self-administration modeled in female rats, Psychopharmacology 169 (2003) 141-149.]. In the current study, male Sprague-Dawley rats were given access to nicotine via the standard operant IV self-administration procedure (nicotine bitartrate dose of 0.03 mg/kg/infusion). One group of male rats started during adolescence the other group started in young adulthood. After the end of the four-week period of self-administration brain regions of the rats were assessed for alpha4beta2 nicotinic receptor binding. We found that male rats, like females, show higher nicotine self-administration when starting during adolescence as compared to starting in adulthood (p<0.001). Indeed, the effect in adolescent males was even greater than that in females, with more than triple the rate of nicotine self-administration vs. the adult-onset group during the first 2 weeks. The adolescent onset nicotine-self-administering rats also had significantly greater high affinity nicotinic receptor binding in the midbrain and the striatum, whereas hippocampal binding did not differ between the age groups. Striatal values significantly correlated with nicotine self-administration during the first 2 weeks in the adult-onset group but not the adolescent-onset rats, suggesting that the differences in self-administration may depend in part on underlying disparities in synaptic responses to nicotine. After the initial 2 weeks, nicotine self-administration in male rats declined toward adult-like levels, as the adolescent rats approached adulthood. This study showed that adolescent male rats self-administer significantly more nicotine than do male adult rats, but that adolescent-onset nicotine self-administration in male rats declines over weeks of continued use to approach adult-onset levels. In a previous study, we found that female rats also show greater nicotine self-administration with adolescent onset vs. adult onset, but that the females continued higher rates of self-administration into adulthood. Our results thus reinforce the concept that the adolescent brain is unusually receptive to the effects of nicotine in a manner that reinforces the potential for addiction.     

Reproductive effects in male and female rats of neonatal exposure to genistein

Sprague-Dawley rats were administered genistein orally at doses of 12.5, 25, 50, or 100 mg/kg on postnatal days 1 through 5 to examine its effects on reproductive function after puberty. In addition, preputial separation and vaginal opening as endpoints of sexual maturation, estrous cycling, sperm count, serum testosterone concentration, and histopathologic changes of reproductive organs of male and female rats were examined. Body weights of male and female rats exposed to genistein at any dose level examined were lower than those of controls. Timing of preputial separation in males and timing of vaginal opening were not affected by genistein treatment. The number of females showing estrous cycle irregularities was increased by genistein treatment. The fertility of female rats exposed neonatally to genistein at 100 mg/kg was disrupted, while neonatal exposure to genistein did not affect male fertility. Neither sperm counts nor serum testosterone concentration were changed by neonatal exposure to genistein. Female rats exposed neonatally to genistein at 100 mg/kg showed histopathologic changes in the ovaries and uterus, while male rats showed no histopathologic alterations in the gonads. The results of this study indicate that early neonatal exposure to genistein caused dysfunction of postpubertal reproductive performance as well as abnormal development of gonads in female but not in male rats.