Coordination of growth and differentiation in the fetal lung

The male fetal lung begins to synthesize surfactant later in gestation than the female. This delay appears to be caused by androgens. We hypothesized that male fetal lung differentiation is delayed as a consequence of an extended phase of growth which is elicited by androgens. We observed that in vivo fetal lung protein synthesis relative to DNA synthesis peaked earlier in gestation in the female fetal lung and that this event was synchronous with the onset of differentiation. Pregnant rats were treated with dihydrotestosterone (DHT) during pregnancy, and fetal lung growth parameters were measured. Lung wet weight, dry weight, and DNA and protein concentrations were significantly elevated by DHT treatment. Type II cells and fibroblasts were isolated from lungs of DHT-treated fetuses. The number of total cells recovered was increased by 30%; the number of type II cells recovered was increased by 87%; and the number of fibroblasts recovered was increased by 42%. The type II cells which were recovered exhibited increased incorporation of [3H]thymidine into DNA and a reduced ratio of radiolabeled protein to radiolabeled DNA compared to that of cells from control lungs. Further studies were done in vitro with fibroblasts and type II cells isolated from untreated fetal rat lungs. Treatment of the fibroblasts with DHT during culture caused an increase in thymidine incorporation into DNA. This effect was not blocked by simultaneous treatment with cortisol, which normally causes reduced DNA synthesis and induces fibroblast differentiation. Treatment of the type II cells with DHT in culture caused a dose-dependent increase in cell number but a decrease in synthesis of disaturated phosphatidylcholine. These studies provide more direct evidence of the interrelationships between the control of growth and the control of differentiation in the fetal lung. DHT, a signal which delays the onset of expression of differentiation, also induces growth. We conclude that the controls of growth and of differentiation of the fetal lung are reciprocally linked.     

Testosterone regulation of sex differences in fetal lung development.

Fetal lung development, in particular surfactant synthesis, exhibits a sexual dimorphism. Dihydrotestosterone (DHT) has been shown to delay fetal pulmonary surfactant production, but the potential role for testosterone is unknown. Both testosterone and DHT are potent masculinizing hormones, yet in some instances, an end organ specificity for DHT is present. We hypothesized that the delay in fetal lung surfactant production is dependent upon DHT such that inhibition of the synthesis of DHT from the precursor hormone testosterone would eliminate the sex difference by allowing the male fetus to produce surfactant at the female level. We tested this hypothesis using 17 beta-N,N-diethylcarbamoyl-4-aza-4-methyl-5-alpha-androstane-3-one (4-MA), a potent inhibitor of the enzyme 5 alpha-reductase, which converts testosterone into DHT. First, studies were performed in vivo. 4-MA (20 mg/kg/day) or an equivalent volume of vehicle was injected into pregnant rabbits from Day 12 through Day 26 of gestation. On Day 26, the fetuses were delivered, the lungs were lavaged, and fetal sex was noted. Treatment with 4-MA resulted in a lack of any male-female difference in the anogenital distance and no DHT was detected in the serum of any treated fetus. Phosphatidylcholine (PC), saturated phosphatidylcholine (SPC), and sphingomyelin (S) were measured in the lung lavage, and were expressed as the ratios of PC to sphingomyelin (PC:S) and SPC to sphingomyelin (SPC:S). Sex differences in the PC to sphingomyelin ratio of 4-MA-treated fetuses (female PC:S ratio, 1.43 +/- 0.14; male PC:S ratio, 1.00 +/- 0.13 [mean +/- SE]; P = 0.04) and in the SPC:S ratio of the 4-MA-treated group (female SPC:S ratio, 0.68 +/- 0.10; male SPC:S ratio, 0.35 +/- 0.10; P = 0.03) were present after treatment with 4-MA. The effect of testosterone and of 4-MA on fibroblast pneumonocyte factor (FPF) production was studied in vitro. Fetal rat lung fibroblasts were cultured to confluence with either no added androgen, DHT, testosterone, or testosterone plus 4-MA, and conditioned media for FPF were prepared. Conditioned media were added to fetal Type II cell cultures and FPF activity was measured as the degree of stimulation of the incorporation of [3H] choline into SPC. The conversion of radiolabeled testosterone to DHT by the fibroblasts was inhibited by 4-MA (10(-5) M). Conditioned media from untreated female fibroblasts stimulated with cortisol exhibited significant FPF activity ([3H]choline incorporation into SPC, 140 +/- 17% of control).(ABSTRACT TRUNCATED AT 400 WORDS)     

Development of fibroblast-type-II cell communications in fetal rabbit lung organ culture.

The development of the fetal lung is regulated by fibroblast-type-II cell communications which involve fibroblast pneumonocyte factor (FPF). FPF production is positively regulated by glucocorticoids and negatively regulated by dihydrotestosterone (DHT) and transforming growth-factor beta (TGF-beta). We studied whether DHT or TGF-beta affected other steps in the process of lung maturation, by studying how the developing lung in organ culture would respond to exogenously supplied FPF after DHT or TGF-beta exposure. Fetal rabbit (day 19 of gestation) lung organ cultures were prepared and cultured in the presence of cortisol, DHT or TGF-beta. After seven days, the media were replaced with serum-free medium containing either cortisol or FPF conditioned medium. The incorporation of [14C]glycerol into surfactant lamellar body DSPC was studied over 24 h as the index of surfactant synthesis. Results were compared to simultaneous control cultures. Treatment had no significant effect on tissue protein concentration or on the efficiency of lamellar body recovery. Cortisol stimulated baseline incorporation of glycerol into DSPC. This was inhibited by DHT, such that DHT plus cortisol treatment was no different from untreated controls. FPF stimulated the incorporation of glycerol into DSPC, and did so even after culture treatment with DHT. Cultures treated with TGF-beta exhibited glycerol incorporation similar to untreated controls. After TGF-beta exposure, FPF did not stimulate glycerol incorporation into DSPC. We conclude that DHT interferes with progression of lung development by delaying the appearance of FPF production by the fibroblast. TGF-beta, on the other hand, inhibits other elements of lung maturation besides FPF production. We speculate that TGF-beta interferes with type-II cell development such that the cell cannot respond to FPF.     

Epidermal growth factor influences the developmental clock regulating maturation of the fetal lung fibroblast

Growth factors may play a significant role in regulating the orderly progression of organ growth and differentiation during fetal development. We hypothesized that epidermal growth factor (EGF) would help regulate the development of surfactant synthesis in the fetal lung by influencing fibroblast-epithelial cell interactions. The effect of EGF (10 ng per ml) on the ability of the fetal lung fibroblast to produce fibroblast pneumonocyte factor (FPF) was studied in sex-specific fibroblasts cultured from day 16, day 17 or day 18 fetal mouse lungs. FPF which is normally not produced by day 16 fibroblasts, is found only in female fibroblasts on day 17, and then in both males and females on day 18. EGF advanced this pattern such that female fibroblasts produced activity on day 16 and fibroblasts from both sexes produced FPF activity on day 17 and day 18. Fibroblasts from an androgen receptor-deficient mouse model confirmed that the effect of EGF was sex-specific and related to the state of development of the fetal lung. We conclude that EGF advances the fetal lung fibroblast through specific stages of development. It appears, therefore, to help control the timing of the clock regulating fetal lung maturation.     

Effects of exogenous steroids on androgen receptors in fetal guinea pig brain

We treated pregnant guinea pigs on Day 50 of gestation with 10 mg testosterone propionate (TP), obtaining fetuses 2, 4, 8, or 18 h later as well as after 5 days of treatment. In a second group of pregnant guinea pigs, dihydrotestosterone propionate (DHTP), estradiol benzoate (E2B), progesterone (P), or cortisol was given 2 h before obtaining fetuses. Although TP treatment elevated fetal serum T (p less than 0.05), brain cytosolic androgen receptor (ARc) content was unchanged in fetuses of either sex. In female fetuses, nuclear androgen receptors (ARn) increased 10-fold in medial-basal hypothalamus (MBH) and preoptic area (POA) at 2 and 4 h (respectively) after treatment, while fetal male ARn content was unchanged. Maternal injection of other steroids (E2B, P, or cortisol, but not DHTP) significantly increased these hormones in the fetus 2 h later (p less than 0.05). Only androgens affected fetal androgen receptor (AR) content. While TP increased ARn in female MBH, DHTP decreased ARc in fetal anterior pituitary of both sexes. In this latter case, a metabolite of DHT may mediate the effects. We conclude that T crosses the guinea pig placenta and activates ARn in POA and MBH of female fetuses; male ARn appear to be maximally occupied by endogenous T. Steroids of other classes do not induce AR responses in fetal guinea pig brain. These AR changes may represent an initial cellular mechanism in brain sexual differentiation.     

Sexually dimorphic gene expression that overlaps maturation of type II pneumonocytes in fetal mouse lungs

Background  

In human, respiratory distress of the neonates, which occurs in prematurity, is prevalent in male. Late in gestation, maturation of type II pneumonocytes, and consequently the surge of surfactant synthesis are delayed in male fetuses compared with female fetuses. Although the presence of higher levels of androgens in male fetuses is thought to explain this sex difference, the identity of genes involved in lung maturation that are differentially modulated according to fetal sex is unknown. We have studied the sex difference in developing mouse lung by gene profiling during a three-day gestational window preceding and including the emergence of mature PTII cells (the surge of surfactant synthesis in the mouse occurs on GD 17.5).     

Interaction between prostacyclin and cortisol in fetal lung cells: effects on cAMP production.

Glucocorticoids secreted by the fetal adrenal, or administered for therapeutic reasons, stimulate fetal lung maturation in the human and other species. Prostacyclin, produced within the lung may be another agent with maturational effects. In this investigation we have demonstrated that glucocorticoids interact with lung cells and increase their response to a prostacyclin analogue (Iloprost, PGIp). This agent stimulates adenylate cyclase activity in fetal lung fibroblasts, fetal lung epithelial cells and in neonatal vascular smooth muscle cells. The cAMP response to PGIp in fibroblasts and epithelial cells occurred in the range 3nM-1 microM. When fibroblasts were pretreated with cortisol before PGIp, cAMP was increased 2-3 fold (p less than 0.01). There was a similar increase in cAMP after cortisol pretreatment in response to PGIp by fetal lung epithelial cells, but not with smooth muscle cells. The action of cortisol was blocked by an inhibitor of RNA synthesis (Actinomycin D) but not by an inhibitor of DNA synthesis (5-fluorodeoxy-uridine). Additional experiments with cholera and pertussis toxins, and with forskolin suggest that cortisol principally increases the quantity or activity of the adenylate cyclase sub-unit in fetal lung fibroblasts and, in doing so, increases the cAMP response to PGIp.     

Sexual dimorphism of growth plate prehypertrophic and hypertrophic chondrocytes in response to testosterone requires metabolism to dihydrotestosterone (DHT) by steroid 5-alpha reductase type 1

Rat costochondral growth plate chondrocytes exhibit sex-specific and cell maturation dependent responses to testosterone. Only male cells respond to testosterone, although testosterone receptors are present in both male and female cells, suggesting other mechanisms are involved. We examined the hypothesis that the sex-specific response of rat costochondral cartilage cells to testosterone requires further metabolism of the hormone to dihydrotestosterone (DHT). Resting zone (RC) and growth zone (GC, prehypertrophic and upper hypertrophic zones) chondrocytes from male and female Sabra strain rats exhibited sex-specific responses to testosterone and DHT: only male cells were responsive. Testosterone and DHT treatment for 24 h caused a comparable dose-dependent increase in [3H]-thymidine incorporation in quiescent preconfluent cultures of male GC cells, and a comparable increase in alkaline phosphatase specific activity in confluent cultures. RC cells responded in a differential manner to testosterone and DHT. Testosterone decreased DNA synthesis in male RC cells but DHT had no effect and alkaline phosphatase specific activity of male RC cells was unaffected by either hormone. Inhibition of steroid 5alpha-reductase activity with finasteride (1, 5, or 10 microg/ml), reduced the response of male GC cells to testosterone in a dose-dependent manner, indicating that metabolism to DHT was required. RT-PCR showed that both male and female cells expressed mRNAs for steroid 5alpha-reductase type 1 but lacked mRNAs for the type 2 form of the enzyme. Male cells also exhibited 5alpha-reductase activity but activity of this enzyme was undetectable in female cells. These observations show that sex-specific responses of rat growth zone chondrocytes to testosterone requires the further metabolism of the hormone to DHT and that the effect of DHT in the male growth plate is maturation-state dependent. Failure of female chondrocytes to respond to testosterone may reflect differences in testosterone metabolism, since these cells possess greater ability to aromatize the hormone to estradiol.     

Stimulation of aromatase activity by dihydrotestosterone in human skin fibroblasts

In order to study the regulation of aromatase activity by androgens in cultured fibroblasts derived from genital skin of normal prepubertal boys, aromatase activity was evaluated in the presence of various concentrations of non-aromatizable androgen DHT(5 alpha-dihydrotestosterone). The estrogen formation was assayed by an enzymatic method, after 24 h incubation of the cells with 10(-6) M androstenedione. Aromatase activity was stimulated 3- to 20-fold by DHT at concentrations 10(-10) and 10(-9) M. It was necessary to preincubate the cells with DHT for 48 h in order to bring about this stimulation. The stimulatory effect was not significant after preincubation for only 24 h. The basal value of aromatase activity was in the range of 8 +/- 1.2 pmol/mg protein/day (mean +/- SEM), while the maximal stimulation 1043 +/- 46 pmol/mg protein/day was obtained at the concentration of 10(-8) M DHT. This stimulation was partially blocked with cyproterone acetate at level of 20 +/- 4 pmol/mg protein/day; stimulation of aromatase activity by DHT could thus be mediated by the androgen receptor. This stimulatory effect was prevented by incubation of the cells with cycloheximide or actinomycin D, suggesting that DHT acts to increase aromatase activity in cultured fibroblasts by inducing the synthesis of new proteinaceous material. In vitro regulation of aromatase activity by androgens could contribute to a new approach to the extraglandular formation of estrogen.     

Tissue androgens and androphilic proteins in rat epididymis during sexual development

The appearance of the epididymal 8s cytoplasmic receptor in the rat during sexual development was followed and correlated with the endogenous concentrations of three biologically active androgens in the epididymis, testosterone (T), dihydrotestosterone (DHT)and 5α-androstane-3α, 17β-diol (Diol).The results indicate that receptors could not be evidenced in the 10-day-old animal in which androgens were undetectable. The 8s receptor was first detected in the 20 day-old rat, coincidently with a rise in the concentration of DHT (0,24 ng/ epididymis) while T and Diol remained too low to be measured. At the 26th day of life a peak of androgen binding activity, sedimenting at approximately 4S, was seen and probably corresponds to ABP. This pattern of two binding peaks (8 and 4S) remained constant through adulthood. The association constant (Ka) of the 8s receptor from 35-, 45- and 60-day-old rats was found to be similar.T became detectable in the epididymides of the 35 day-old rat (0.03 ng/ep.) and increased with sexual maturation. However, DHT concentrations were higher than those of T at all ages studied and Diol could not be detected at any age.These results raise the possibility that the synthesis or availability of receptors in the developing animals is under androgenic control.     

Androgen regulation of secretory component synthesis by lacrimal gland acinar cells in vitro

This study sought to determine whether androgens directly stimulate the production of secretory component (SC) by acinar cells from the rat lacrimal gland. Homogeneous populations of acrinar cells were isolated from lacrimal tissues by serial enzymatic digestion and Ficoll gradient centrifugation and then cultured on reconstituted basement membranes in supplemented, serum-free medium. Acinar cell exposure in vitro to dihydrotestosterone (DHT) resulted in a significant increase in cellular SC output. This hormone action was dose dependent and androgen specific. Testosterone, but not 17 beta-estradiol, progesterone, dexamethasone, or aldosterone, also induced a considerable elevation in acinar cell SC production. The effect of testosterone may not require intracellular enzymatic conversion to DHT. The impact of androgens on SC output was associated with enhanced cellular synthesis and secretion and did not involve variations in acinar cell viability or density. Moreover, the SC response to DHT occurred irrespective of whether lacrimal gland acinar cells were obtained from young adult male or female rats. In contrast, the androgen-related rise in SC production was significantly reduced in acinar cells isolated from tissue of orchiectomized and hypophysectomized rats. In summary, these findings demonstrate that androgens directly increase the synthesis of SC by lacrimal gland acinar cells in vitro. This effect, however, may be significantly altered by prior changes in the endocrine environment of acinar cells in vivo.     

Prolactin levels during the periparturitional period in the biparental cotton-top tamarin (Saguinus oedipus): interactions with gender, androgen levels, and parenting

Unlike biparental bird and rodent species, mating and parenting occur simultaneously in cotton-top tamarins, Saguinus oedipus, providing a unique model for examining endocrine interactions. This study was designed to determine the relationship of prolactin to testicular androgens during parenting and mating. Specifically we examined (1) the patterns of postpartum prolactin excretion in male and female tamarins with and without infant survival; (2) the relationship between androgen and prolactin levels during the periparturitional period in male tamarins; and (3) male hormonal response to the postpartum mating that occurs simultaneously with paternal care. All females showed an elevation in prolactin during the first week postpartum and when infants died, female prolactin levels decreased significantly. Infant survival during the first 15 days did not influence male levels of prolactin, cortisol, or the testicular androgens testosterone and dihydrotestosterone (DHT). Prolactin did not show an inverse relationship with any of the androgens (testosterone, DHT) studied during the postpartum period. No significant differences in hormones were found between prepartum levels and the first, second, and third 5-day blocks postpartum for all 10 males. Males who had infant-care experience showed an increase in testosterone during the first 5 days postpartum and prolactin levels correlated with the number of previous births a male had experienced. However, the most significant changes in testosterone occurred in males whose mates ovulated during the first 15 days following birth in contrast to males whose mates ovulated later than 15 days. These results indicate that unlike females, male tamarins are not showing hormonal changes in response to infants. Urinary androgens did not show an inverse relationship to prolactin in male tamarins, but were elevated concurrent with the female's fertile period.     

The role of isoacceptor transfer RNAs in regulation of age-related changes in the rate of protein synthesis

In cell-free protein-synthesizing systems containing an S30 extract from liver and brain cortex tissues of 22-day-old fetuses and of male WAG rats (1-900 days old), the minimal rate of protein synthesis was observed in the fetuses, while the maximal one - in 7-day-old animals. The difference in the rates of protein synthesis correlated with the minimal concentration of total tRNA in the former group and with its maximal concentration in the latter. In fetal tissues, an addition to cell-free systems of total tRNA isolated from homologous tissues of 7-day-old animals augmented protein synthesis up to a level observed in 7-day-old animals, whereas in the tissues of animals belonging to other age groups total tRNA had a far less pronounced stimulating effect which decreased with age. Fractionation of total tRNA and analysis of effects of individual tRNAs on protein synthesis demonstrated that the stimulating influence was induced by tRNA(2Arg), tRNA(4Arg) and tRNA(2Val) from brain cortex and by tRNA(2Leu), tRNA(5Leu), tRNA(2Val), tRNA(1Met) and tRNA(2Met) from liver.     

Glucocorticoids affect the synthesis of pulmonary fibroblast-pneumonocyte factor at a pretranslational level

Glucocorticoids accelerate fetal lung maturation by acting on the fetal lung fibroblast to induce the synthesis of fibroblast-pneumonocyte factor which in turn stimulates pulmonary surfactant synthesis by the alveolar type II cell. We have studied the site of glucocorticoid regulation of fibroblast-pneumonocyte factor synthesis in primary cultures of fetal rat lung fibroblasts. Conditioned media from fetal rat lung fibroblasts exposed to cortisol stimulate [Me-3H]choline incorporation into saturated phosphatidylcholine by primary cultures of fetal rat lung alveolar type II cells. This effect is blocked by the presence of actinomycin D during the first, but not the second, 24 h of incubation of the fibroblasts with cortisol. Cycloheximide blocks this effect if present during either the first or second 24 h of incubation. We fractionated mRNA from fetal rat lung fibroblasts incubated in the presence or absence of dexamethasone and observed that cell-free translation products from a fraction of approximately 500 bases possess biological activity in the bioassay. Such activity is only present in cell-free translation products of mRNA isolated from fibroblasts treated with dexamethasone. These results suggest that glucocorticoids act at a pretranslational level to induce production of fibroblast-pneumonocyte factor and that the primary translation products are biologically active.     

Sex-specific effects of 17β-estradiol and dihydrotestosterone (DHT) on growth plate chondrocytes are dependent on both ERα and ERβ and require palmitoylation to translocate the receptors to the plasma membrane

Rat costochondral cartilage growth plate chondrocytes exhibit cell sex-specific responses to 17β-estradiol (E₂), testosterone, and dihydrotestosterone (DHT). Mechanistically, E₂ and DHT stimulate proliferation and extracellular matrix synthesis in chondrocytes from female and male rats, respectively, by signaling through protein kinase C (PKC) and phospholipase C (PLC). Estrogen receptors (ERα; ERβ) and androgen receptors (ARs) are present in both male and female cells, but it is not known whether they interact to elicit sex-specific signaling. We used specific agonists and antagonists of these receptors to examine the relative contributions of ERs and ARs in membrane-mediated E₂ signaling in female chondrocytes and DHT signaling in male chondrocytes. PKC activity in female chondrocytes was stimulated by agonists of ERα and ERβ and required intact caveolae; PKC activity was inhibited by the E₂ enantiomer and by an inhibitor of ERβ. Western blots of cell lysates co-immunoprecipitated for ERα suggested the formation of a complex containing both ERα and ERß with E₂ treatment. DHT and DHT agonists activated PKC in male cells, while AR inhibition blocked the stimulatory effect of DHT on PKC. Inhibition of ERα and ERβ also blocked PKC activation by DHT. Western blots of whole-cell lysates, plasma membranes, and caveolae indicated the translocation of AR to the plasma membrane and specifically to caveolae with DHT treatment. These results suggest that E₂ and DHT promote chondrocyte differentiation via the ability of ARs and ERs to form a complex. The results also indicate that intact caveolae and palmitoylation of the membrane receptor(s) or membrane receptor complex containing ERα and ERβ is required for E₂ and DHT membrane-associated PKC activity in costochondral cartilage cells.     

Androgen receptors in fetal rabbit lung and the effect of fetal sex on the levels of circulating hormones and pulmonary hormone receptors

High affinity (KD = 0.2 nM), low capacity (3.6-5.0 fmol/mg protein), androgen-specific binding proteins with characteristics typical of androgen receptors were identified in the lungs of rabbit fetuses between the 26 and 29th day of gestation and in the lungs of adult rabbits. While androgen receptor concentrations increased significantly from late gestation to adulthood (P less than 0.01), no sex-related differences were observed in either the binding affinities or concentrations of the receptors at any age tested. Similarly, no sex-related differences were found in the levels of progesterone, cortisol and cortisone in the fetal circulation, or in the levels of progesterone receptors, glucocorticoid receptors and beta-adrenergic receptors in the fetal lung at 26 days of gestation. It is concluded that the fetal lung interacts directly with circulating androgens via specific androgen receptors and that the suggested male disadvantage with respect to lung maturation in the perinatal period does not appear to be associated with sex-related differences in the levels of pulmonary androgen, glucocorticoid, progesterone or beta-adrenergic receptors.     

Manipulation of androgens causes different energetic responses to cold in 60- and 40-day-old male rats

Previous studies suggested that adults respond differently than pubertal male rats to cold stress. To test the role of androgens in this difference, we adrenalectomized and replaced with corticosterone either 60- or 40-day-old male rats, then sham gonadectomized (Intact), gonadectomized (GDX), or GDX and replaced with testosterone (T; GDX+T) or dihydrotestosterone (DHT). One-half remained at room temperature (RT), and one-half lived in cold for 5 days. Cold reduced T in adult but not in pubertal Intacts. In 60-day-old rats, GDX with or without T replacement had minor effects on body weight (BW) and food intake (FI) at RT and cold. In 40-day-old rats at RT, androgens had slight effects; however, androgens affected almost all variables in cold. Separation of 40-day-old T-treated rats into two groups (moderate T levels, 1.4 ng/ml; high T levels, 1.9 ng/ml) revealed major differences between the groups. Moderate T (and DHT) prevented cold-induced loss of BW and increased FI. No T and high T induced decreased BW and FI in cold. We conclude that at 40 days of age, partial resistance to stress-induced reduction of T and high sensitivity to small changes in T have markedly positive effects on threatened energy balance.     

Androgen receptor in rat liver: characterization and separation from a male-specific estrogen-binding protein

Many liver processes are sexually dimorphic. In particular, the microsomal content of specific enzymes and the synthesis of specific proteins are under sex steroid hormone control. Because the liver of male rats is strikingly androgen responsive, we sought evidence for an androgen receptor in this tissue. We detected and characterized both cytosolic and nuclear androgen-binding proteins. Both forms bind [3H]R1881 (methyltrienolone, 17 beta-hydroxy-17 alpha-methyl-4,9,11-estratriene-3-one) with the high affinity, low capacity, and specificity for androgens and antiandrogens characteristic of androgen receptors. No high-affinity binding of [3H]DHT could be detected in unfractionated cytosol because of the rapid metabolism of this ligand; however, binding of a DHT metabolite to the high-capacity male-specific estrogen binder (MEB) of cytosol was observed. Both gel filtration and heparin-Sepharose affinity chromatography separate the cytosolic androgen receptor from MEB. Incubation of cytosol in the absence of sodium molybdate resulted in androgen-binding activity which was retained by DNA-cellulose. Castration of male rats results in a time-dependent loss of both cytosolic and nuclear androgen binding, as well as a loss in MEB activity. Androgen-binding activity is low in livers from female rats, but can be induced by testosterone treatment. An intact pituitary is necessary for maintenance of androgen-binding activity, as hypophysectomy results in complete loss of activity.     

Molecular mechanisms involved in the differential effects of sex steroids on the reproduction and infectivity of Taenia crassiceps

The in vitro exposure of Taenia crassiceps cysticerci to 17-beta estradiol (E2) and progesterone (P4) stimulated their reproduction and infectivity. Testosterone (T4) and dihydrotestosterone (DHT) inhibited their reproduction and reduced their motility and infectivity. E2 and P4 increased, whereas T4 and DHT reduced, the expression of parasite c-fos and c-jun and DNA synthesis. In vitro exposure of cysticerci to sex steroids before their inoculation into recipient noninfected mice resulted in large parasite loads when pretreated with E2 and P4 and in smaller loads when pretreated with T4 and DHT To determine the possible molecular mechanisms by which sex steroids affect T. crassiceps, sex steroid receptors were amplified. Taenia crassiceps expressed estrogen receptors (both alpha and beta isoforms) and androgen receptors but no P4 receptors. These results demonstrate that sex steroids act directly on parasite reproduction by binding to a classic and specific sex steroid receptor on the parasite. The differential response of cysticerci to sex steroids may also be involved in their ability to grow faster in the murine female or feminized male host. This is the first report of direct sex steroid effects on the parasite possibly through sex steroid receptors in the cysticerci.