Development of gonadotropes may involve cyclic transdifferentiation of growth hormone cells

The cyclic rise in expression of anterior pituitary gonadotropins coincides with the appearance of cells sharing gonadotropic and somatotropic phenotypes. To learn more about possible factors that regulate the origin of this cell type, we studied the time of appearance of cells that co-expressed growth hormone (GH) and gonadotropins and estrogen receptors during the estrous cycle and compared this timing with known changes in regulatory hormones or their receptors. The first event in this cell population is an increase in expression of estrogen receptor (ER)beta by GH cells from estrus to metestrus suggesting that estrogen may mediate this early change. Expression of GH mRNA rises rapidly from metestrus to mid-cycle. The rise is seen first in GH cells and then in cells with luteinizing hormone (LH) antigens. These data suggest that, early in the cycle, cells bearing GH and growth hormone releasing hormone (GHRH) receptors begin to produce LH and gonadotropin releasing hormone (GnRH) receptors. Early in proestrus, there is an increase in cells with GH and follicle-stimulating hormone (FSH) suggesting that this set of multipotential cells develops later than GH-LH cells. This fits with earlier studies showing the later rise in expression of FSH mRNA. Collectively these data suggest that the anterior pituitary contains a subset of GH cells that have the capacity to respond to multiple releasing hormones and support more than one system.     

Pituitary alpha subunit mRNA amounts during the sheep estrous cycle. Assessment by cDNA hybridizations

Pituitary glycoprotein hormones exhibit a dimeric structure consisting of a common alpha subunit and similar beta subunits. In this study, alpha subunit mRNA amounts have been examined in sheep pituitaries during defined times of the normal estrous cycle. These times were designed to include events prior to, and including the beginning of, the preovulatory luteinizing hormone surge. Criteria such as serum and pituitary luteinizing hormone, serum progesterone, and ovarian morphology were used to classify the groups as: 1) Day 12 of the cycle; 2) 24 h before behavioral estrus (E-24); and 3) 5 h after estrus (E + 5). RNA was extracted from the pituitaries and amounts of alpha subunit mRNA quantitated using cell-free translations and cDNA hybridizations. Both Northern transfers and RNA dot blots were used. The amount of alpha subunit mRNA in the Day 12 group was the lowest of the three groups and was similar to that seen in the pituitary from an anestrous ewe. The amount observed in the E-24 animals was only slightly increased over the Day 12 (approximately 2-fold); however, a greater increase was observed when the E + 5 group was examined (approximately 4-8-fold). These results suggest that the amount of alpha subunit mRNA increases during the time of the preovulatory luteinizing hormone surge in the normal estrous cycle of the sheep and thus probably plays a role in the important physiological event.     

Cellular turnover in the rat uterine cervix and its relationship to estrogen and progesterone receptor dynamics

Histoarchitectural changes of the uterine cervix allow its successful adaptation to different physiological conditions. In this study, we evaluated cell turnover in each cellular compartment of the uterine cervix in association with steroid hormone receptor expression in order to establish the range of physiological changes. Proliferation, apoptosis, and progesterone receptor (PR) and estrogen receptor alpha (ERalpha) expression were evaluated in cycling, pregnant, and postpartum rats. In estrus and diestrus II, ERalpha and PR expression exhibited variations according to the region evaluated. Proliferation and apoptosis showed a reciprocal pattern, the epithelium being the region with higher cell turnover. High apoptotic index (AI) in estrus was associated with the lowest ERalpha and the highest PR scores. During pregnancy, proliferation of the epithelium was the predominant event and AI was low. On Postpartum Day 1 (PPD1), proliferation decreased while apoptosis increased. As described for the estrous cycle, during pregnancy and PPD1, AI and ERalpha were negatively correlated. In the fibroblastic stroma, low proliferation was observed throughout pregnancy; however, there was a net increase in cell number because very few cells underwent apoptosis. No difference in ERalpha was observed in fibroblastic cells during pregnancy and postpartum; however, a great decrease of this receptor in the epithelial compartment was observed after delivery. Unlike cervical epithelium, PR was highly expressed in stromal cells. At term, a dramatic increase in epithelial PR was observed. While epithelial PR remained high on PPD1, a decrease was observed in muscle stroma. These results show that, in all stages studied, 1) ERalpha and PR have different patterns of expression with differential responses to signals that modulate proliferation and/or apoptosis depending on the cellular compartment, and 2) even though the epithelium is the region with the highest cell turnover, the fibroblastic and muscle stroma are active regions that have their own patterns of behavior.     

Effects of estrogen on serum leptin levels and leptin mRNA expression in adipose tissue in rats

OBJECTIVE: In this study, we examined changes in serum leptin levels during the estrus cycle and the role of estrogen in these changes. METHODS: We measured serum leptin levels during normal estrus cycles in intact rats and estradiol-17beta (E2)-induced artificial estrus cycles in ovariectomized rats. RESULTS: Serum leptin levels increased 1.6-fold from 4.2 +/- 0.2 ng/ml during diestrus stage 2 to 6.7 +/- 0.9 ng/ml during proestrus stage during the 4-day estrus cycle. During the E2-induced estrus cycle, serum leptin levels increased 2.3-fold from 2.3 +/- 0.1 ng/ml at estrus to 5.4 +/- 1.2 ng/ml at proestrus. E2 also increased serum leptin concentrations and leptin mRNA expression in adipose tissue of immature rats. DISCUSSION: These findings suggest that increased serum leptin induced by estrogen during proestrus may trigger the preovulatory release of luteinizing hormone. Furthermore, our findings indicate that estrogen has a positive effect on leptin production in adipose tissue.     

Estrus induction in the bitch using a combination diethylstilbestrol and FSH-P

The purpose of the study was to induce estrus and ovulation in normal bitches using a combination of diethylstilbestrol (DES) and follicle stimulating hormone of porcine pituitary origin (FSH-P). Thirteen mature mongrel female dogs were divided into two groups, the first group was treated for estrus induction during late anestrus and the second group during mid-anestrus. The dogs were monitored by teasing, vaginal cytology, and hormonal assay during the induced (n = 13) and the previous spontaneous estrous cycle (n = 9). Six of eight and three of five bitches came into standing estrus in the first and second group, respectively. Of the bitches that came into estrus, three conceived in the first group and one in the second. The average induced litter size was 7.0 versus 7.5 for the colony. Based on vaginal cytology the induced proestrus and estrus lasted 1.7 (0 to 3) and 12.9 (4 to 24) d, respectively, while the spontaneous proestrus and estrus lasted 5.8 (0-17) and 12.8 (9-15) d, respectively. Progesterone profiles were similar between the induced and spontaneous estrous cycles, although the progesterone peak was higher during the spontaneous cycle. The preovulatory luteinizing hormone (LH) surge was observed in only one induced estrous cycle. Modest results were obtained with this therapy. However, the litter sizes were normal and the induced cycles were very similar to the physiologic ones. No side effects were seen with the oral form of DES.     

Pituitary and ovarian luteinizing hormone releasing hormone receptors during the estrous cycle, pregnancy and lactation in the rat

Female Sprague-Dawley rats were decapitated at various stages of the estrous cycle, pregnancy, lactation and following ovariectomy. Anterior pituitary and ovarian tissues were collected and assayed to quantify luteinizing hormone releasing hormone (LHRH) receptors. No changes were noted in receptor affinity either between tissues or physiological stages studied. Pituitary LHRH receptor concentrations and content were greater (P less than 0.05) during diestrus II and proestrus than during estrus. Pituitary LHRH receptor concentrations and content during pregnancy were not different from those during estrus, however, a significant decrease was noted in pituitary LHRH receptor content and concentrations during lactation compared to estrus. Ovarian LHRH receptor content did not change with stage of reproduction (P less than 0.05). There was, however, a decrease (P less than 0.05) in ovarian LHRH receptor concentrations at Week 3 of pregnancy and Week 1 of lactation which was possibly due to the increase ovarian weight noted at both these physiological stages. There was no correlation (P less than 0.1) between ovarian and pituitary LHRH receptor numbers (r = 0.096). These findings suggest that the internal mechanisms which control changes in pituitary LHRH receptor numbers do not control ovarian LHRH receptor numbers.     

白细胞介素2对大鼠垂体前叶细胞雌激素受体蛋白含量和基因表达的影响

采用原代无血清细胞培养技术结合免疫组织（细胞）化学和半定量反转录－ＰＣＲ方法,观察白细胞介素２（ＩＬ－２）对大鼠垂体前叶雌激素受体（ＥＲ）蛋白含量和基因表达的影响,以探讨ＩＬ－２和ＥＲ在大鼠重体前叶的相互关系。结果显示：在大鼠垂体前叶细胞有ＩＬ－２受体表达。在无血清培养条件下,ＩＬ－２能增加ＥＲα蛋白含量,促进ＥＲα基因表达,而对ＥＲβ的作用正好相反,ｒｈＩＬ－２（１０μｇ／Ｌ）作用４８ｈ后,ＥＲ     

The induction of divergent gonadotropin secretion in vitro by variations in luteinizing hormone releasing hormone pulse regimen

The effects of luteinizing hormone releasing hormone (LHRH) pulse amplitude, duration, and frequency on divergent gonadotropin secretion were examined using superfused anterior pituitary cells from selected stages of the rat estrous cycle. Cells were stimulated with one of five LHRH regimens. With low-amplitude LHRH pulses (regimen 1) in the presence of potentially estrogenic phenol red, LH response in pituitary cells from proestrus 1900, estrus 0800, and diestrus 1,0800 were all significantly larger (P less than 0.05) than the other stages tested. In the absence of phenol red, responsiveness at proestrus 1900 was significantly larger than proestrus 0800, proestrus 1500, and estrus 0800 (P less than 0.01, 0.05, and 0.05, respectively); other cycle stages tested were smaller. No significant differences were observed between cycle stages for follicle-stimulating hormone (FSH) secretion in the presence or absence of phenol red. Because pituitary cells at proestrus 1900 were the most responsive to low-amplitude 4 ng LHRH pulses, they were also used to study the effects of LHRH pulses of increased amplitude or duration and decreased frequency. Increasing the amplitude (regimen 2) or the duration (regimens 3 to 5) increased FSH secretion; this effect was greatest with regimens 3 and 5. When regimens 3 and 5 were studied in pituitary cells obtained at proestrus 1500, FSH was significantly increased by both regimes, but most by regimen 5; furthermore, LH release was significantly reduced. When regimens 3 and 5 were studied in pituitary cells obtained at estrus 0800, FSH release was elevated most significantly by regimen 5. Thus, variations in LHRH pulse regimen were found to be capable of inducing significant divergence in FSH release from superfused anterior pituitary cells derived from specific stages of the estrous cycle.     

Regulation of leptin mRNA and protein expression in pituitary somatotropes.

Leptin, the ob protein, regulates food intake and satiety and can be found in the anterior pituitary. Leptin antigens and mRNA were studied in the anterior pituitary (AP) cells of male and female rats to learn more about its regulation. Leptin antigens were found in over 40% of cells in diestrous or proestrous female rats and in male rats. Lower percentages of AP cells were seen in the estrous population (21 +/- 7%). During peak expression of antigens, co-expression of leptin and growth hormone (GH) was found in 27 +/- 4% of AP cells. Affinity cytochemistry studies detected 24 +/- 3% of AP cells with leptin proteins and growth hormone releasing hormone (GHRH) receptors. These data suggested that somatotropes were a significant source of leptin. To test regulatory factors, estrous and diestrous AP populations were treated with estrogen (100 pM) and/or GHRH (2 nM) to learn if either would increase leptin expression in GH cells. To rule out the possibility that the immunoreactive leptin was bound to receptors in somatotropes, leptin mRNA was also detected by non-radioactive in situ hybridization in this group of cells. In estrous female rats, 39 +/- 0.9% of AP cells expressed leptin mRNA, indicating that the potential for leptin production was greater than predicted from the immunolabeling. Estrogen and GHRH together (but not alone) increased percentages of cells with leptin protein (41 +/- 9%) or mRNA (57 +/- 5%). Estrogen and GHRH also increased the percentages of AP cells that co-express leptin mRNA and GH antigens from 20 +/- 2% of AP cells to 37 +/- 5%. Although the significance of leptin in GH cells is not understood, it is clearly increased after stimulation with GHRH and estrogen. Because GH cells also have leptin receptors, this AP leptin may be an autocrine or paracrine regulator of pituitary cell function.     

Messenger RNA levels of estrogen receptors alpha and beta and progesterone receptors in the cyclic and inseminated/early pregnant sow uterus

The aim of the present study was to investigate differences in the expression of mRNAs for ERalpha, ERbeta and PR in the sow uterus at different stages of the estrous cycle as well as in inseminated sows at estrus and during early pregnancy by use of solution hybridization and in relation to plasma levels of estradiol and progesterone. Uterine samples were collected at different stages of the estrous cycle and after insemination/early pregnancy. In the endometrium, the expression of ERalpha mRNA and PR mRNA was similar for cyclic and early pregnant groups. Both were highest at early diestrus/70 h after ovulation and ERalpha mRNA was lowest at late diestrus/d 19 while PR mRNA was lowest at diestrus and late diestrus/d 11 and d 19. The expression of endometrial ERbeta was constantly low during the estrous cycle but higher expression was found in inseminated/early pregnant sows at estrus and 70 h after ovulation. In the myometrium, high expression of ERalpha mRNA and PR mRNA was observed at proestrus and estrus in cyclic sows and at estrus in newly inseminated sows. Higher expression of myometrial ERbeta mRNA was found in inseminated/early pregnant sows compared with cyclic sows, although significant only at estrus. In conclusion, the expression of mRNAs for ERalpha, ERbeta and PR in the sow uterus differed between endometrium and myometrium as well as with stages of the estrous cycle and early pregnancy. In addition to plasma steroid levels, the differences between cyclic and inseminated/early pregnant sows suggest that other factors, e.g. insemination and/or the presence of embryos, influence the expression of these steroid receptor mRNAs in the sow uterus.     

Expression of estrogen receptors alpha and beta in the corpus luteum and uterus from non-pregnant and pregnant llamas

Because estrogen may be involved in maternal recognition of pregnancy and embryonic migration in llamas, expression of estrogen receptor subtypes alpha (ERalpha) and beta (ERbeta) was evaluated in corpus luteum (CL), endometrium, and uterus using relative RT-PCR. Tissues were recovered from sterile-mated (SM) and pregnant (PG) females during Days 7-11 and 7-13 (Day 0 = day of mating), respectively, and follicular phase and juvenile females. Luteal expression of ERalpha and beta was similar (P > 0.10) in SM and PG females and within Days 7-11, however, expression of ERalpha in ovarian tissue from follicular phase females was greater (P < 0.05) than Days 7 and 9 CL. Uterus expressed less ERalpha and beta compared to endometrium (P = 0.07 and P < 0.01, respectively). Expression of ERalpha was greater (P < 0.05) in Day 7 and follicular phase uteri than Days 9 and 11, Day 13 PG and juvenile uteri. Uterine ERbeta expression was greater (P = 0.09) in PG versus SM females and in mated compared to follicular phase females (P < 0.05). Endometrial expression of ERalpha and beta did not differ (P > 0.10) between SM and PG females or by day. The presence of luteal ER during this period may mean a role for estradiol in maternal recognition of pregnancy. Observed increases in uterine ER expression with no changes in endometrium suggest expression increased in myometrium and/or perimetrium. Upregulation of myometrial ERbeta in PG females may be involved in supporting uterine migration of the embryo.     

Effects of the intensity of the suckling stimulus and ovarian steroids on pituitary gonadotropin-releasing hormone receptors during lactation

These studies examined whether the decrease in pituitary responsiveness to gonadotropin-releasing hormone (GnRH) observed during lactation in the rat results from a change in pituitary GnRH receptors. GnRH binding capacity was determined by saturation analysis using D-Ala6 as both ligand and tracer. During the estrous cycle, the number of GnRH binding sites increased from 199 +/- 38 fmol/mg protein on estrus to 527 +/- 31 fmol/mg protein on the morning of proestrus, whereas there was no change in receptor affinity (Ka, 6-10 X 10(9) M-1), During lactation, females nursing 8 pups on Days 5 or 10 postpartum had 50% fewer GnRH receptors (109-120 fmol/mg protein) than observed during estrus or diestrus 1 (199-242 fmol/mg protein) although receptor affinity was similar among all the groups. No deficits in pituitary GnRH receptors were observed in females nursing 2 pups on Day 10 postpartum. Removal of the 8-pup suckling stimulus for 24 or 48 h resulted in a dramatic increase in GnRH receptor capacity by 24 h from 120 +/- 16 to 355 +/- 39 fmol/mg protein. The rise in GnRH receptors after pup removal was accompanied by an increase in serum luteinizing hormone (LH) and estradiol concentrations. To assess the role of ovarian steroids in determining GnRH receptor capacity during lactation, females were ovariectomized (OVX) on Day 2 postpartum. Suckling of a large litter (8 pups) completely blocked the postcastration rise in serum LH and in pituitary GnRH receptors on Day 10 postpartum (OVX+ 8, 77 +/- 12 fmol/mg protein; OVX+ 0, 442 +/- 38 fmol/mg protein).(ABSTRACT TRUNCATED AT 250 WORDS)     

Inhibin secretion during the rat estrous cycle: relationships to FSH secretion and FSH beta subunit mRNA concentrations

Serum inhibin and FSH and FSH beta subunit mRNA levels were measured at 3h intervals throughout the 4 day estrous cycle in female rats and hourly between 1000 and 2400 h of proestrus. On proestrus, serum inhibin concentrations fell during the late morning-early afternoon, then increased transiently during the late afternoon gonadotropin surges. Inhibin levels decreased during the late evening of proestrus, coincident with the FSH surge-related rise in FSH beta mRNA levels. Serum inhibin remained relatively stable during estrus and early metestrus, but rose during the late evening of metestrus and remained elevated until early diestrus. FSH beta mRNA levels were elevated on late estrus and early metestrus and declined during the evening of metestrus as serum inhibin levels increased. These data show that concentrations of serum inhibin change during the estrous cycle and that a general inverse relationship exists between serum inhibin and FSH levels and FSH beta mRNA concentrations in the pituitary. This suggests that inhibin may inhibit FSH beta gene expression and FSH secretion during the 4 day cycle in female rats.     

Estrogen receptor-alpha mediates the effects of estradiol on telomerase activity in human mesenchymal stem cells

Sex steroid hormone receptors play a central role in modulating telomerase activity, especially in cancer cells. However, information on the regulation of steroid hormone receptors and their distinct functions on telomerase activity within the mesenchymal stem cell are largely unavailable due to low telomerase activity in the cell. In this study, the effects of estrogen (E2) treatment and function of estrogen receptor alpha (ERalpha) and estrogen receptor beta (ERbeta) on telomerase activity were investigated in human mesenchymal stem cells (hMSCs). Telomerase activity and mRNA expression of the catalytic subunit of telomerase (hTERT) were upregulated by treatment of the cells with E2. The protein concentration of ERalpha was also increased by E2 treatment, and enhancement of ERalpha accumulation in the nucleus was clearly detected with immunocytochemistry. When ERalpha expression was reduced by siRNA transfection into hMSCs, the effect of E2 on the induction of hTERT expression and telomerase activity was diminished. In contrast, the transient overexpression of ERalpha increased the effect of E2 on the expression of hTERT mRNA. These findings indicate that the activation of hTERT expression and telomerase activity by E2 in hMSCs depends on ERalpha, but not on ERbeta.     

Actions of acetyl-L-carnitine on the hypothalamo-pituitary-gonadal system in female rats.

Acetyl-L-carnitine (ALC) is known to affect several aspects of neuronal activity. To evaluate the neuroendocrine actions of this compound, several endocrinological parameters were followed in ALC-treated and control animals during recovery from dark-induced anestrus. In treated animals, serum luteinizing hormone (LH) and prolactin levels were higher than those of controls during the proestrous and estrous phases of the cycle, and serum estradiol levels were higher during estrus. No significant changes were observed in serum levels of follicle-stimulating hormone and progesterone. Uterine weight was increased in ALC-treated rats during proestrus and estrus, but not in diestrus. The basal release of gonadotropin-releasing hormone (GnRH) from perifused hypothalamic slices of ALC-treated animals was elevated at proestrus and diestrus, and GnRH release elicited by high K+ was higher during all three phases of the cycle. The basal release of LH from perifused pituitaries of treated animals was elevated in diestrus, and the LH response to GnRH was higher in estrus and diestrus I. Depolarization with K+ caused increased LH secretion during proestrus and estrus in treated animals. In contrast to these effects of ALC treatment in vivo, no direct effects of ALC were observed during short- or long-term treatment of cultured pituitary cells. These results indicate that ALC treatment influences hypothalamo-pituitary function in a cycle stage-dependent manner, and increases the secretory activity of gonadotrophs and lactotrophs. Since no effects of ALC on basal and agonist-induced secretory responses of gonadotrophs were observed in vitro, it is probable that its effects on gonadotropin release are related to enhancement of GnRH neuronal function in the hypothalamus.