Effects Of Neonatal Androgenization Research Articles

Pituitary leptin gene expression is reduced by neonatal androgenization of female rats.

We have previously reported evidence of leptin gene expression (ob mRNA) in adult rat brain and pituitary gland. We have also shown that ob mRNA levels in female rat brain and pituitary are regulated in an age- and tissue-dependent fashion. In view of the known sexual dimorphism in adipose tissue leptin expression, we have extended our original work to include an assessment of ob mRNA levels in brain, pituitary and fat of developing male and female rats. In addition we determined the effects of neonatal androgenization of female rat pups with testosterone propionate. Leptin (ob) mRNA expression was evaluated using semi-quantitative RT-PCR analysis. Leptin mRNA levels were developmentally regulated in the pituitary and cortex of male rats, paralleling the changes previously observed in female rats. In the pituitary, leptin expression was significantly higher during the early postnatal period and dropped abruptly by postnatal day (PD) 22. In the cortex, leptin expression was lowest at PD 4 and rose significantly by PD 14. In addition gender differences, most notably in the pituitary, were also observed. In pituitary gland, ob mRNA was significantly higher in female rats than in males at PD 14 (+60%; p < 0.05) but there were no sex differences at PD 4 and PD 22. Testosterone treatment of neonatal female rats profoundly reduced ob mRNA at PD 14 (3.5-fold; p < 0.01) and PD 22 (3-fold; p = 0.05). In subcutaneous adipose tissue and hypothalamus we observed no sex difference in ob mRNA levels nor an effect of testosterone. We conclude that leptin gene expression in rat pituitary gland is sexually dimorphic and sensitive to neonatal manipulation of sex steroid levels.

Effect of neonatal androgenization on the circadian rhythm of feeding behavior in rats

The effect of neonatal androgenization with testosterone propionate (TP) on growth, food intake, and feeding circadian and ultradian rhythms was studied in male and female rats. TP-female rats but not TP-male rats weighed more and ate more in adulthood than control animals injected with oil. TP administration to male rats induced few changes in the circadian organization of food intake and meal size. However, neonatal androgenization of female rats produced an approach of feeding parameters to those showed by male rats: diminished meal number and increased meal size and food intake. Moreover, the spectral analysis of meal frequency revealed that TP induced in female rats an enlargement in the 4.8 h ultradian component. Although hormone secretions produced in adult animals contribute to sexual dimorphism, it is noticeable that androgen presence during the organizational period is largely responsible for differences between sexes.

Effects of neonatal androgenization on the chromatofocusing pattern of anterior pituitary FSH in the female rat

Anterior pituitary glands were removed from neonatally androgenized (100 micrograms testosterone propionate) female rats and normal controls at 5, 10, 18, 21, 30, 60 and 90 days of age, and the multiple forms of FSH present within them were separated by chromatofocusing (pH range 7.5-4.0). Additional pituitary glands from intact adult males (90 days old) were also studied for comparative purposes. All animal groups exhibited multiple forms of immunoactive FSH within a pH range of 7.5-4.0, as well as an additional FSH form obtained after the addition of 1.0 mol NaCl/l to the chromatofocusing column (salt peak). In animals 5-30 days old (controls and androgenized) the majority of FSH applied to the chromatofocusing columns was recovered within the salt peak (45-85% of total FSH immunoactivity recovered). However, as the animals aged, more FSH immunoactivity focused within less acidic regions (isoelectric point (pI) 5.9-5.0); pituitaries from animals 60 days old contained the greatest proportion of FSH focused within this pH range (controls, 39.2 +/- 0.6%; androgenized, 23.1 +/- 0.9% of total immunoactivity recovered; P less than 0.03 vs animals 30 days old for both experimental groups). This shift towards less acidic FSH was attenuated in androgenized animals compared with the controls (P less than 0.01). In control adult rats, the chromatofocusing distribution pattern of pituitary FSH varied according to the day of the oestrous cycle. Pituitary extracts from control rats decapitated during the morning of pro-oestrus, oestrus and day 1 of dioestrus exhibited the highest proportion of immunoactive FSH (23.2-28.8% of total) focused within a pH range of 5.9-5.0, whilst only 10.4-11.6% of FSH from androgenized rats and those on day 1 of dioestrus was recovered within this pH range (P less than 0.05). In control animals decapitated during the morning of pro-oestrus and oestrus, 10-26% of FSH focused within the most alkaline region (pI 7.5-6.0); the chromatofocusing pattern of pituitary FSH from the neonatally androgenized animals was characteristic, in that no more than one peak (1.5 +/- 0.5% of total) was detected in this alkaline region. In the adult male rats, the majority of pituitary FSH eluted from the chromatofocusing columns within a pH of 4.9-4.0 (52.4 +/- 1.2% of total FSH immunoactivity) and the salt peak (pH less than 4.0) (33.1 +/- 2.4 of total). All FSH isoforms obtained after chromatofocusing represented alpha and beta dimers as disclosed by size exclusion chromatography.(ABSTRACT TRUNCATED AT 400 WORDS)

Augmentation of the Sterilizing Effect of Neonatal Androgenization with Tropolone, a Catechol-O-Methyltransferase Inhibitor, in Female Rats

The influence of tropolone, a catechol-O-methyltransferase (COMT) inhibitor, on the sterilizing effect of neonatal testosterone propionate (TP) has been studied in Wistar female rats. Tropolone-induced changes in COMT activity and noradrenaline (NA) and dopamine (DA) contents in the hypothalamus have been evaluated. Inhibition of COMT activity was maximal 3 h after a single injection of 0.6 mg tropolone on postnatal day 5. An increase in DA level was observed 6 h after drug injection, whereas the NA content was elevated 24 h after tropolone administration. A sexual dimorphism in hypothalamic NA content in rats was found on postnatal day 10: it was higher in males than in females. The rise of catecholamines in the hypothalamus of 10-day-old female rats induced by COMT inhibition with tropolone (0.3 mg on postnatal days 5 and 7) was unable to masculinize developing neuroendocrine regions responsible for sexual cyclicity. At the same time, combined administration of tropolone (0.1 mg daily on postnatal days 4-10) and TP (0.025 mg on day 4) enhanced the sterilizing effect of the androgen. An anovulatory sterility appeared in all experimental animals. It is suggested that a cooperative interaction occurs between catecholamines and sex steroids as determinants of brain sexual differentiation.

Effect of Neonatal Androgenization on the Testosterone Feedback Sensitivity in Adult Rats in Two Lighting Conditions

Neonatally androgenized and intact adult male Wistar rats received daily, during 1 week, either testosterone propionate or sesame oil injections in periodic or constant light. Serum and pituitary gonadotropins and hypothalamic LHRH were measured. In periodic light, neonatal androgenization did not change the serum concentration or pituitary contents of gonadotropins, or the hypothalamic content of LHRH. Testosterone injections decreased serum concentration and pituitary content of gonadotropin of intact rats but failed to decrease the pituitary gonadotropin content of neonatally androgenized rats. In constant light, serum FSH was decreased in neonatally androgenized rats. Testosterone injections decreased both serum LH and FSH concentrations of intact rats but only serum LH of androgenized rats. Pituitary gonadotropin and hypothalamic LHRH contents remained unchanged. We conclude that neonatal androgenization renders the male rat hypothalamo-pituitary axis more resistant to changes of testosterone concentration in adulthood. Constant light did not sensitize the neonatally androgenized rats to testosterone, but on the contrary, testosterone injections were less effective in constant than in periodical light.

Effect of neonatal androgenization on positive feedback in female mice.

Exposure of female mice to androgens within 5 days of birth impairs fertility. Such treatment in rats results in a post-pubertal acyclic state of persistent vaginal cornification and in an inability, when ovariectomized, to show normal positive feedback on luteinizing hormone (LH) release in response to steroid challenge. In the present study, we explored whether neonatally androgenized mice demonstrate positive feedback. Female mice were administered 100 micrograms of testosterone propionate (TP) on either Day 1 (TP1) or Day 5 (TP5) after birth, or vehicle on Day 1 (SO1). Androgen-treated mice had a statistically significant advance in onset of vaginal opening as compared with vehicle-treated mice. All mice that received TP entered constant vaginal estrus, whereas those given vehicle showed variable cytology. All mice were ovariectomized at 7 wk of age and received Silastic capsules containing a priming dose of 17 beta-estradiol. When all mice were challenged 1 wk later with sequential administration of estradiol benzoate and progesterone, a significant increase in plasma LH level was present only in the vehicle-treated mice. We conclude that neonatal androgenization defeminizes the neuroendocrine mechanisms controlling gonadotropin release.

Sexual differentiation of oxytocin stress responsiveness: effect of neonatal androgenization, castration and a luteinizing hormone-releasing hormone antagonist.

The plasma OT increment following stress in rats is sexually dimorphic, females exhibiting greater responses than males. We have investigated the role of neonatal androgen secretion in determining the sex-typical level of response. Castration of male pups either surgically or functionally (GnRH antagonist treatment) within either 2 h or 5 days of birth did not elevate the OT responses of adult males. In contrast, androgenization of female pups (testosterone, 1.25 mg/pup) within 5 days of birth markedly reduced the OT stress responses of adults to a level insignificantly different to males. The results show that neonatal androgens can exert organizational effects on OT regulatory mechanisms. Since neonatal castration was ineffective it would appear that a prenatal defeminization or masculinization event determines OT stress responsiveness in males.

Social play soliciting by male and female juvenile rats: Effects of neonatal androgenization and sex of cagemates.

Male and female juvenile rats were individually exposed to nonplayful juvenile social stimuli in a novel test of play-soliciting behavior to examine hormonal and experiential determinants of sex differences. In Experiment 1, neonatally androgenized females engaged in play soliciting at a level equal to that of male controls and greater than that of nonandrogenized female controls. In Experiment 2, males and females were reared in unisexual and bisexual groups in order to compare long-term sex-related social experience effects on juvenile play soliciting. Males exposed only to other young males engaged in greater play soliciting than males exposed to both sexes; females, in contrast, were unaffected by sex of cagemates. Within rearing conditions, however, males engaged in greater play soliciting than females. The combined results suggest that perinatal gonadal androgen exposure effects on social play are prepotent and contribute essentially to sex differences in the initiation of social play behavior.

Social play soliciting by male and female juvenile rats: Effects of neonatal androgenization and sex of cagemates.

Social play soliciting by male and female juvenile rats: Effects of neonatal androgenization and sex of cagemates.

Effect of neonatal androgenization on induction of sarcomas of the uterus by 1,2-dimethylhydrazine in CBA mice

Effect of neonatal androgenization on induction of sarcomas of the uterus by 1,2-dimethylhydrazine in CBA mice

Effect of neonatal androgenization on the LHRH response of dispersed pituitary cell cultures.

To determine if neonatal androgenization affects pituitary luteinizing hormone releasing hormone (LHRH) response, female rats were androgenized 24-48 hr following birth. Intact male and female litter mates were maintained for comparison. At 83 days of age, randomly selected males and androgenized females were gonadectomized. At 90 days of age, pituitary cell cultures were begun. On day 3 the cells were challenged with LHRH. Gonadotropin response was determined by radioimmunoassay (RIA). Basal gonadotropin release from androgenized female cells was similar to male cells, while the pattern and magnitude of the LHRH response was similar to intact female cells. After castration, the pattern and magnitude of the LHRH response of the androgenized female pituitary was most like the male. Androgenized female cells exhibited mixed male and female LHRH response.

Induction of Mammary Dysplasia and Mammary Carcinoma in Neonatally Androgenized Female Rats by 7,12-Dimethylbenz[a]anthracene2

Effects of neonatal androgenization on 7,12-dimethylbenz[a]anthracene (DMBA)-induced mammary tumorigenesis infemale noninbred Sprague-Dawley rats are reported. Testosterone propionate (1.25 mg) was injected sc into 29 2-day-old rats. At 50 days of age, all rats were given 20 mg of DMBA through a stomach tube. In these androgenized rats, no corpora lutea were found in the ovaries and the induction of mammary carcinoma by DMBA was strongly suppressed, whereas the induction of mammary dysplasia was significantly accelerated in comparison with the neonatally intact controls. Mammary dysplasia in the androgenized group varied widely, with two kinds of macroscopically detectable tumor-forming lesions (solid and cystic) and with microscopic characteristics of acinar adenosis, fibrotic adenosis, fibrosis, intraductal papillary proliferative lesions, and epithelial cysts. The earliest lesions of mammary dysplasia observed were acinar adenosis nodules and microcysts, both of which appeared as multifocal phenomena as early as 25 days after administration of DMBA.

The effects of neonatal androgenization on the in vivo transport of alpha-aminoisobutyric acid into specific regions of the rat brain

The purpose of the present study was to determine if the administration of testosterone propionate (TP) to neonatal rats is followed in vivo by alterations in the transport of the non-metabolizable amino acid, α-aminoisobutyric acid (AIB), into specific regions of the brain. Forty-eight hours after birth, male and female rats were injected s.c. with either 1.25 mg TP or an equivalent volume of vehicle. Five, 10 and 17 days after birth, control and TP-treated rats were decapitated at intervals of 2, 5, 60 and 300 min after the i.p. injection of 0.25 μCi [1- 14C]α-aminoisobutyric acid/g body weight. Twelve brain regions, i.e., amygdala, cerebellum, corpora quadrigemina, frontal cortex, hypothalamus, medulla, occipital cortex, olfactory bulbs, olfactory tubercles, parietal cortex, pons, pyriform cortex and samples of serum were analyzed in terms of disint./min/mg tissue and as tissue/serum (T/S) ratios. At the end of 300 min there was a significant increase in the active transport of AIB in all brain regions of the 5-day-old TP-treated rats. Similarly, by 300 min, the active transport of AIB was significantly increased in all brain regions except cerebellum and pons of the 10-day-old TP-treated rats. The administration of TP to neonatal rats did not alter the accumulation and/or active transport of AIB in brain regions of the 17-day-old rat at any of the tested intervals. These data indicate that (1) neonatally administered TP enhanced (either directly or indirectly) the transport and/or accumulation of AIB in specific brain regions of 5- and 10-day-old rats and (2) the effectiveness of the steroid decreased with the age of the rat.

Effect of neonatal androgenization on hypothalamic biogenic monoamines and pituitary function in rats

Injection of testosterone propionate into female Wistar rats on the 2nd–4th day after birth did not change the serotonin concentration but sharply reduced the noradrenalin and dopamine conconcentrations in the hypothalamus of the animals at the age of 3.5 months. This was accompanied by an increase in the prolactin content in the adenohypophysis despite preservation of normal somatotropic activity. The results of this investigation point to a role of catecholamines in the pathogenesis of anovulatory sterility and give greater precision to modern views on the regulation of pituitary gonadotropic function.

Neonatal modification of endocrine functions and mammary carcinogenesis in the rat.

Effects of neonatal androgenization or neonatal ovariectomy in female rats on endocrine functions and mammary tumourigenesis are examined. Pituitary gonadotrophin contents (both LH and FSH) are significantly lower in neonatally androgenized rats (TT) and significantly increased in neonatally ovariectomized rats (NO) when compared with controls of the same age. Plasma and pituitary prolactin levels are higher in TT rats than in the control rats of the same age, but the difference is not significant. Mammary tumours developing in TT rats after DMBA treatment are predominantly fibroadenomata, and lactogenesis in TT rats occurs almost entirely in those receiving DMBA treatment. Neonatal ovariectomy in female rats protects against subsequent induction of mammary cnacer by DMBA. The relationship between neonatal modification of endocrine functions and mammary tumourigenesis is discussed.

Sex-Related Differences in the Regulation of Cytoplasmie Estrogen Receptor Levels in Responsive Tissues of the Rat

Cytoplasmic estrogen receptors were measured in the anterior pituitary and hypothalamus of intact adult Holtzman male and female rats at various time intervals following injection of 10 mug of 17beta-estradiol. Following equivalent depletion of receptors at 1 h in either sex, replenishment of cytosol receptor levels progressed at a greater rate and to a higher level in the male than in the female. Cycloheximide only partially inhibited replenishment, and its blocking effect was similar in males and females. The administration of 5 mug of 17beta-estradiol to adult males elicited less depletion than did 10 mug, and a completely cycloheximide-sensitive replenishment phase. Patterns of depletion and replenishment in immature rats following 0.1 mug of 17beta-estradiol were the same for males and females. In an analysis of the effects of neonatal androgenization, Charles River rats were used and it was initially demonstrated that no sex differences in receptor levels existed between normal males and females. After an injection of an androgenizing level of testosterone propionate on day 3 of age, a full normal complement of receptors was found in estrogen-responsive tissues at 90--100 days of age. The functional dynamics of receptor depletion and replenishment under the influence of exogenous estrogen, however, indicated that the anterior pituitary of the androgenized female responded differently from that of the untreated female, and similarly to that of the male. The hypothalamic receptor dynamics in the male were unaltered by early androgen administration, but estrogen-induced depletion of receptors in the female hypothalamus was considerably less extensive in the androgenized animal than in the untreated control. Whereas cytoplasmic estrogen receptor levels are essentially independent of sex in the rat, the present results indicate a sex-linked difference in the dynamics of receptor turnover in the anterior pituitary and hypothalamic response to 17beta-estradiol.