Regulation of ovine follicle-stimulating hormone beta-chain mRNA by 17 beta-estradiol in vivo and in vitro

Understanding the pathological manifestations of aromatase excess syndrome: lessons for clinical diagnosis

CYP19A1

Aromatase excess syndrome is characterized by pre- or peripubertal onset of gynecomastia due to estrogen excess because of a gain-of-function mutation in the aromatase gene (CYP19A1). Subchromosomal recombination events including duplication, deletion, and inversion has been identified. The latter two recombinations recruit novel promoters for CYP19A1 through a unique mechanism. Gynecomastia continues for life, and although the general condition is well preserved, it may cause psychological issues. Minor symptoms (variably advanced bone age and short adult height), if present, are exclusively because of estrogen excess. Serum estradiol levels are elevated in 48% of affected males, but are not necessarily useful for diagnosis. Molecular analysis of CYP19A1 mutations is mandatory to confirm aromatase excess syndrome diagnosis. Furthermore, the use of an aromatase inhibitor can ameliorate gynecomastia.

Molecular bases and phenotypic determinants of aromatase excess syndrome

Aromatase excess syndrome (AEXS) is a rare autosomal dominant disorder characterized by gynecomastia. This condition is caused by overexpression of CYP19A1 encoding aromatase, and three types of cryptic genomic rearrangement around CYP19A1, that is, duplications, deletions, and inversions, have been identified in AEXS. Duplications appear to have caused CYP19A1 overexpression because of an increased number of physiological promoters, whereas deletions and inversions would have induced wide CYP19A1 expression due to the formation of chimeric genes consisting of a noncoding exon(s) of a neighboring gene and CYP19A1 coding exons. Genotype-phenotype analysis implies that phenotypic severity of AEXS is primarily determined by the expression pattern of CYP19A1 and the chimeric genes and by the structural property of the fused exons with a promoter function (i.e., the presence or the absence of a natural translation start codon). These results provide novel information about molecular mechanisms of human genetic disorders and biological function of estrogens.

17β-Estradiol transcriptionally represses human insulin receptor gene expression causing cellular insulin resistance

In this study, we demonstrate that 17beta-estradiol (E(2)) inhibits human insulin receptor (IR) gene expression in a dose- and time-dependent manner in U-937 human promonocytic cells. Using cells transfected with the -1819 to -271 bp fragment of the human IR promoter (wild type promoter) and treated with E(2), we show that this repression is regulated at the transcriptional level. The steroid was also found to diminish the insulin responsiveness of the cells in terms of cell survival, DNA synthesis, glucose transport, and glucose oxidation, this last effect possibly involving reduced phosphatidylinositol 3-kinase (PI3-kinase) activity. These data provide new information on the molecular mechanisms of estrogen-inducing insulin resistance in human cells.

Influence of estradiol, progesterone, and nutrition on concentrations of gonadotropins and GnRH receptors, and abundance of mRNA for GnRH receptors and gonadotropin subunits in pituitary glands of beef cows

Nutritionally induced anovulatory cows (n = 28) were used to determine the effect of steroids on regulation of synthesis and secretion of gonadotropins. Anovulatory cows were ovariectomized and received intravaginal inserts containing estradiol (E2), progesterone (P4), E2 and P4 (E2P4), or a sham intravaginal insert (C) for 7 d. Concentrations of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) were quantified in serum and E2 and P4 were quantified in plasma. Cows were exsanguinated within 1 to 2 h after removal of intravaginal inserts and pituitary glands were collected and stored at -80 degrees C until messenger ribonucleic acid (mRNA) for gonadotropin-releasing hormone receptor (GnRH-R) and gonadotropin subunits, pituitary content of GnRH-R, and LH and FSH were quantified. Pituitary glands from five proestrous cows were harvested to compare gonadotropin characteristics between ovariectomized, anovulatory cows and intact cows. Plasma concentrations of E2 were greater (P < 0.05) in E2-treated cows than in sham-treated cows. Concentrations of P4 were greater (P < 0.05) in cows treated with P4 than in sham-treated cows. Mean serum concentrations of LH and FSH were not significantly influenced by steroid treatments. However, frequency of LH pulses of ovariectomized, nutritionally induced anovulatory cows was increased (P < 0.05) by treatment with E2 and amplitude of LH pulses was greater (P < 0.05) in cows treated with E2 or P4 than in cows treated with E2P4 or sham-treated. Quantity of mRNA for LHbeta in the pituitary gland was greater when cows were treated with P4. Concentrations of LH in the pituitary gland were not affected by steroid treatments; however, pituitary concentrations of FSH were less (P < 0.1) in E2 cows than in sham-treated cows. The number of GnRH-R was increased (P < 0.05) in cows treated with E2, but P4 treatment did not influence the number of GnRH-R. Abundance of mRNA for GnRH-R, common alpha-subunit, and FSHbeta were not affected by treatments. Pituitary concentrations of LH were greater (P < 0.05) and concentrations of FSH were less (P < 0.05) in proestrous cows than in ovariectomized, anovulatory cows treated with or without steroids. Abundance of mRNA for GnRH-R, common alpha-subunit, LHbeta and FSHbeta were similar for proestrous and anovulatory cows. We conclude that treatment of nutritionally induced anovulatory cows with progesterone and estradiol may cause pulsatile secretion of LH.

Molecular characterization of LH-beta and FSH-beta subunits and their regulation by estrogen in the goldfish pituitary

The gonadal steroids, along with gonadotropin-releasing hormone (GnRH) are involved in the regulation of gonadotropin (GtH) production in vertebrates. Goldfish have an annual reproductive cycle, characterized by seasonal fluctuations in the circulating levels of the reproductive hormones, including 17beta-estradiol (E2). The purpose of the present study was to investigate the effect of E2 on basal and GnRH-induced GtH subunit (alpha, FSH-beta and LH-beta) gene expression in the goldfish pituitary. Northern analyses were performed to determine changes in steady state mRNA levels. Both in vivo and in vitro treatment with E2 resulted in a stimulation of all three GtH subunit mRNA levels, although a higher concentration was required for the stimulation of the FSH-beta subunit mRNA levels. The effect of E2 on GnRH-induced GtH mRNA level was also investigated and demonstrated that E2 influences the GnRH-induced GtH subunit mRNA levels in a seasonally dependent manner. Overall, the present results indicate that E2 stimulates GtH subunit mRNA levels directly at the level of the pituitary in a seasonally dependent manner in goldfish.

Steroidogenic factor-1 (SF-1) and the regulation of expression of luteinising hormone and follicle stimulating hormone b-subunits in the sheep anterior pituitary in vivo

Luteinising hormone (LH) and follicle stimulating hormone (FSH) comprise a common alpha-subunit and hormone-specific beta-subunit, are expressed in gonadotroph cells of the anterior pituitary and during the sheep oestrous cycle, are regulated by gonadotrophin releasing hormone (GnRH), ovarian peptides and steroids. Transcription factor steroidogenic factor-1 (SF-1) transactivates the common alpha-subunit and LH beta subunit in other species. We investigated whether SF-1 regulates beta-subunit expression and the regulation of SF-1 expression in vivo in sheep. Immunocytochemistry co-localised SF-1, LH and FSH to sheep pituitary gonadotrophs and electrophoretic mobility shift assays (EMSA) demonstrated that SF-1 bound to the LH beta promoter in vitro. No SF-1 DNA binding site was found in the FSH beta promoter. No difference in mean levels of SF-1, FSH beta, LH beta and GnRHr mRNA was measured between the luteal and follicular phases of the oestrous cycle. However SF-1 mRNA levels were correlated to those of LH beta in individual luteal phase animals (r = 0.88, p < 0.05), when the transcription rate of LH beta was significantly higher (p < 0.01). GnRH antagonist treatment of luteal animals did not produce a significant reduction in mRNA levels of LH beta, SF-1 and FSH beta. Administering oestradiol benzoate with GnRH antagonist reduced levels of SF-1 and FSH beta mRNA from luteal values (p < 0.005). We conclude that: (1) expression of SF-1 is not solely dependent on GnRH and is downregulated by oestradiol; (2) the LH beta transcription rate is increased during the luteal phase but is not related to levels of LH beta or SF-1 mRNA; and (3) SF-1 does not appear to directly regulate expression of FSH beta, but may regulate expression indirectly.

Assessment of gene expression and peptide secretion from individual cells

We have developed an assay that allows one to monitor gene expression in and peptide secretion from individual cells. By combining the reverse hemolytic plaque with in situ hybridization, investigators can quantitate simultaneously the level of gene expression and the level of secretion of a peptide. The method can be used in any system in which an appropriate antibody for the reverse hemolytic plaque assay and probes complementary to the mRNA of interest are available. It can be used to monitor the level of mRNA and secretion of the peptide product, or expression of one gene and the secretion of another peptide. In this paper we will describe the major steps of the method. We have used the pituitary lactotroph as a model to demonstrate the power of this technique. However, we believe that this method may be an important approach to answer many questions regarding the cellular and molecular mechanisms that regulate the coupling of peptide secretion and gene expression at the single cell level.

Differential regulation of anterior pituitary prodynorphin and gonadotropin-subunit gene expression by steroid hormones

Prodynorphin is expressed by neurons of the hypothalamus and gonadotrophs of the anterior pituitary gland (AP) and plays a role in the negative feedback regulation of the reproductive neuroendocrine axis. The present study examined whether gonadal steroid hormones are capable of modulating pituitary prodynorphin expression in immature, female rats. Steroids were administered via subcutaneous Silastic implants and rats were killed at 29 days of age. Northern blot analysis was used to measure AP prodynorphin, luteinizing hormone-beta (LH beta), follicle-stimulating hormone-beta (FSH beta), and common alpha-subunit mRNA levels (normalized to 18S ribosomal RNA). Treatment groups (n = 5-6) consisted of control (CNT; empty implants), estradiol (E2; 4 days), E2 + progesterone (E2 + P4; 8 days and 4 days, respectively), and dihydrotestosterone (DHT; 4 days). Pituitary prodynorphin mRNA was significantly suppressed in only the DHT-treated animals (26 +/- 10% of CNT, p < 0.01). LH beta mRNA was suppressed by all steroid treatments (p < 0.01), FSH beta was lower in only the E2 group, and alpha-subunit was reduced in both the E2 + P4 and DHT groups (p < 0.01). Serum LH was suppressed by all steroid treatments but FSH was reduced in only the E2 and E2 + P4 groups (p < 0.01). Treatment of prepubescent rats with continuous high levels of gonadal steroids is known to severely reduce endogenous hypothalamic gonadotropin releasing hormone (GnRH) release and this is supported by our observation of reduced gonadotropin-subunit gene expression.(ABSTRACT TRUNCATED AT 250 WORDS)

Estradiol and progesterone effects on relative luteinizing hormone and follicle stimulating hormone release induced from superfused anterior pituitary cell cultures by defined LHRH pulse regimens

These studies examined the capacity of estradiol and progesterone to modulate relative luteinizing hormone (LH) and follicle stimulating hormone (FSH) secretion from superfused anterior pituitary cells when stimulated with luteinizing hormone releasing hormone (LHRH) pulse regimens of specific amplitude, duration and frequency. There was particular interest in whether such steroid and LHRH treatments induced evidence of divergent LH or FSH secretion. Pituitaries were recovered from adult, 2 week ovariectomized rats and cultured for 48 h with collagen coated Cytodex microcarrier beads. Cultures were preincubated either with or without estradiol (1 or 10 nM) for 48 h and were subsequently incubated for 3,6 or 12 h with 100 nM progesterone. All groups were then pulsed with 1 of 3 LHRH regimens; regimen 1 delivered 8 ng in a single 100 microliters bolus once/h; regimen 2 divided the 8 ng dose of regimen 1 into 3 equal doses administered at 4 min intervals thereby maintaining the 8 ng mass of regimen 1 while extending the duration of exposure; regimen 3 was the same as regimen 2 except that the 3 equal doses were administered at a pulse frequency of 1 per 2 h rather than 1 per h thereby not only maintaining the duration of exposure as in regimen 2 but also reducing the pulse frequency. 1 nM estrogen alone for 48 h had no effect on LHRH stimulated LH release regardless of regimen; however, FSH was increased when hourly pulses of increased duration were applied (regimen 2). When estrogen was increased to 10 nM, regardless of regimen, LH was predominantly inhibited while FSH was unaffected. When 1 nM estrogen was followed by progesterone, both LH and FSH were elevated at 6 h progesterone in response to regimen 2; with 10 nM estrogen however, a divergent response was observed in that LH release was elevated at 6 h while FSH was elevated at 3 h in response to regimens 2 and 3. These results first of all confirm that progesterone in combination with estrogen is capable of exerting both inhibitory and stimulatory effects on gonadotropin secretion; secondly, these studies show that, as a direct pituitary effect, the LHRH regimen and the gonadal steroid milieu are capable of interacting to significantly influence the relative secretion of LH and FSH. The data therefore suggest that the divergent gonadotropin secretion seen in various physiological states in vivo is due likely in part to a combination of estrogen and progesterone priming in combination with the hypothalamic LHRH secretory pattern.

Molecular cloning of the rhesus glycoprotein hormone alpha-subunit gene

A rhesus monkey genomic library was screened with a cDNA for the glycoprotein hormone alpha-subunit. Genomic clones hybridizing with exon-specific probes were selected and the DNA sequences were determined for 1.6 kb of 5'-flanking DNA, all four exons, the second and third introns, all exon-intron junctions, and 357 bp of 3'-flanking DNA. Comparison with the 236 bp of 5'-flanking sequence data available for the human alpha gene indicates an overall homology of 95%. Primer extension analysis of rhesus placental and pituitary mRNA demonstrated that transcription initiation is identical to that in the human placenta. The rhesus gene contains an element nearly identical (21/22 bases) to the placental tissue-specific element described for the human alpha gene. The rhesus gene has only one copy of the cAMP-response element (CRE), which is present as a direct repeat in the human gene. The rhesus CRE contains the consensus core sequence TGACG-TCA with the cytosine in the fourth position that is essential for placental expression of the human gene. The 5'-flanking region also has elements highly homologous to the consensus estrogen and progesterone/glucocorticoid response elements, as well as thyrotrope-specific and Pit-1-like binding sites described in rodent genes. The nucleotide sequence of four exons (predicted mRNA) have an aggregate homology of 92.7% with the human sequence. However, a 12-bp insertion to the second exon results in the addition of 4 amino acids to the amino-terminal end of the protein; these are homologous with the proteins of nonprimates but are lacking in the human alpha-subunit. The amino acid sequence of the deduced protein was slightly more homologous with the bovine than the human protein (91.6% vs. 89.6%). Thus, the rhesus glycoprotein alpha-subunit gene codes for a protein whose structure somewhat more closely resembles that of lower species, but the 5'-flanking DNA of the gene has gained the elements necessary for transcription in the placental syncytiotrophoblast which distinguishes the primate placenta from the other species examined.

[Focus on the biogenesis of hypophyseal gonadotropins]

We have studied the regulation of the biosynthesis of pituitary gonadotropins in the rat by gonadal steroids and a hypothalamic hormone, GnRH. The methodology used for studying the action of steroids, was either cell-free translation of pituitary messenger RNAs, or hybridization (Northern blot) with synthetic oligodeoxynucleotides (ODN), and for studying the effect of GnRH, primary anterior pituitary cell culture. Our results show that gonadectomy increases and injection of gonadal steroids into gonadectomized rats diminishes the rate of synthesis of the gonadotropin subunit precursors. Progesterone acts only after induction of its pituitary receptors in ovariectomized rats with estradiol benzoate. Thyroxine modulates the action of steroids. Hybridization experiments suggest that gonadal steroids act on the expression of genes encoding the precursors of gonadotropin subunits. GnRH significantly increases incorporation of the labeled amino acids into polypeptide chains of both alpha and LH beta subunits. Intracellular mediators of hormone action, such as cyclic AMP and diacylglycerols, mimic the stimulatory action of GnRH on the synthesis of LH subunits. However, we have no evidence that these products intervene in the effect of GnRH on the LH subunit synthesis. In conclusion, the synthesis of LH and FSH subunits is regulated, with opposite effects, by gonadal steroids which exert their negative control at the genomic level and by GnRH which proceeds via different, yet unknown mechanisms.

Isolation and characterization of the gene encoding the beta-subunit of rat follicle-stimulating hormone

Follicle-stimulating hormone (FSH) is a pituitary glycoprotein hormone that is comprised of two dissimilar subunits, alpha and beta, encoded by separate genes. We have isolated the gene encoding the beta-subunit of rat FSH by screening a rat genomic DNA-library by filter hybridization with bovine FSH-beta cDNA. Southern blot analysis of rat genomic DNA suggests that there is a single copy of the FSH-beta gene per haploid genome in the rat. The nucleotide sequence of the rat FSH-beta gene was determined and the amino acid sequence of the subunit was deduced. The gene is composed of three exons and two introns. The predicted amino acid sequence reveals that there is a 20-amino-acid signal peptide followed by a mature protein of 110 amino acid residues. Exons I, II, and III are 36, 187, and 1221 bp, respectively. Intron 1 (640 bp) interrupts the 5'-untranslated (UT) region (61 bp) and intron 2 (approximately 1 kb) interrupts the coding region between amino acid residues +34 and +35. Comparison of the amino acid sequence to those of the human and bovine FSH-beta subunits reveals 80% similarity to both species. The "CAGY" sequence, or the Cys-Ala-Gly-Tyr quartet of amino acids encoded by exon II is present in every other glycoprotein beta-subunit sequenced thus far, is altered in rat FSH-beta, with the Ala residue replaced by Glu. Primer extension analysis demonstrated that there is a single transcriptional start site. The nucleotide sequence of the 5'-flanking region (1 kb) was determined and compared to the nucleotide sequences of corresponding regions in the bovine and human genes. This analysis revealed that there are three regions in the 5'-flanking region of the rat FSH-beta gene that display greater than 80% sequence similarity to regions in the bovine and human genes. The second of these regions also shares similarity to segments within the 5'-flanking regions of the rat alpha- and LH beta-subunit genes. The characterization of the rat FSH-beta gene will enable further study of the regulation of rat FSH using in vitro systems.

Pituitary gonadotropin content in gonadectomized rats. Immunoassay measurements influenced by extraction solvent and testosterone replacement

Increasing interest in events regulating gonadotropin synthesis and secretion led to the reexamination, by radioimmunoassay (RIA), of the pituitary content of luteinizing hormone (LH) and follicle stimulating hormone (FSH). In a preliminary experiment, the importance of the composition of the solvent used to homogenize pituitaries on the detection of LH and FSH was demonstrated by RIA. Experiment 1 demonstrated that a drop in pituitary FSH occurred acutely following gonadectomy in males, but not in females. Experiment 2 tested whether this decline resulted from loss of testosterone or inhibin. Males were castrated and treated daily with oil or testosterone propionate, porcine follicular fluid, porcine serum, or testosterone plus follicular fluid for 2 to 14 days. Castration lowered pituitary FSH at 2, 4, and 6 days. Follicular fluid suppressed serum FSH, but not LH, and did not prevent the fall in pituitary FSH. Testosterone blocked the rise of serum LH and FSH and prevented the decline in pituitary FSH.

Dual role of glucocorticoids in regulation of pituitary content and secretion of gonadotropins

To verify the inhibitory effect of cortisol (F) on secretion of luteinizing hormone (LH) 24 h postorchidectomy, we implanted cholesterol (C) or F subcutaneously into male rats, and 4 days later orchidectomized or sham orchidectomized them under ether anesthesia. We injected gonadotropin-releasing hormone (GnRH) or saline into these rats 24 h postorchidectomy, collected blood 30 min later, and measured LH and follicle-stimulating hormone (FSH) in serum and pituitaries. F inhibited GnRH-induced secretion of LH without affecting secretion of FSH. We then implanted C, corticosterone (B), or F into rats, performed the same surgeries, and collected pituitaries 24 h after surgery for quantitation of receptors for GnRH. Neither F nor B affected the number of receptors for GnRH or their affinity for a GnRH analogue. Suppression of LH in serum occurred without decreased pituitary content of LH. In contrast, F increased pituitary content of FSH. Implantation of progesterone in a similar experiment did not affect circulating concentrations or pituitary contents of FSH or LH. These data suggest that glucocorticoids may inhibit responsiveness to GnRH by some mechanism distal to the receptor for GnRH that affects only LH.

Nucleotide sequence of the bovine gene for follicle-stimulating hormone beta-subunit

The gene for the beta-subunit of follicle-stimulating hormone (FSH-beta) was isolated from a library of bovine DNA fragments cloned in bacteriophage gamma and the complete nucleotide sequence of the gene was determined. The bovine FSH-beta gene contains approximately 4000 nucleotides and consists of three exons separated by two intervening sequences. The transcription initiation site of the gene was mapped by nuclease protection experiments. Analysis of RNA species present in pituitary mRNA demonstrated the presence of a 4.0-kb RNA containing FSH-beta sequences, which is the appropriate size for the primary transcript of the gene. Comparison of nucleotide sequence of the 5'-flanking sequence of the FSH-beta gene to the 5'-flanking regions of other pituitary glycoprotein hormone genes reveals little sequence similarity.

Measurement of the amount of mRNA for gonadotropins during an estradiol-induced preovulatory-like surge of LH and FSH in ovariectomized ewes

The amount of messenger RNA (mRNA) for luteinizing hormone beta-subunit (LH beta), follicle-stimulating hormone beta-subunit (FSH beta) and alpha-subunit was measured during estradiol-17 beta (E) positive feedback in ovariectomized (OVX) ewes. During the anestrous season, OVX ewes were given an i.m. injection of E (25 micrograms: n = 5) or oil (control; n = 4) and hourly blood samples were collected for 16 hr. After blood collection, ewes were killed and anterior pituitary glands were removed for analysis of hormone and mRNA content. Preovulatory-like increases in serum concentrations of LH and FSH were measured in E-treated OVX ewes. In two E-treated OVX ewes the serum concentrations of LH and FSH were still increasing, whereas in the remaining three E-treated OVX ewes, serum concentrations of LH were on the decreasing portion of the E-induced preovulatory-like surge. Pituitary content of LH was lower (P less than .10) in E-treated OVX ewes when serum concentrations of LH were decreasing than that measured in control ewes or E-treated OVX ewes in which serum concentrations were still increasing. Pituitary content of FSH and prolactin were similar (P greater than .05) among all groups. The amount of mRNA for LH beta-subunit was similar (P greater than .05) in ewes in which serum concentrations of LH were increasing and in control ewes, but was lower (P less than .05) in ewes with decreasing levels of LH. The amount of mRNA for FSH beta-subunit was lower (P less than .05) in all E-treated OVX ewes (independent of whether serum concentrations of FSH were increasing or decreasing) than that measured in control ewes. There was no difference (P greater than .05) in the amount of mRNA for alpha-subunit among any groups. Thus, amounts of mRNA for the beta-subunits of gonadotropins are reduced, while amounts of mRNA for alpha-subunit are unchanged during estradiol positive feedback in OVX ewes.

Naturally occurring antihormones: secretion of FSH antagonists by women treated with a GnRH analog

Follicle-stimulating hormone (FSH) is a glycoprotein essential for gonadal development and steroidogenesis. Recent studies suggest that deglycosylation of FSH results in the formation of antagonistic proteins that are capable of binding to gonadal receptors but that are devoid of bioactivity. Treatment of hypogonadal women with an antagonist of gonadotropin-releasing hormone substantially decreased serum FSH bioactivity with minimal changes in immunoreactivity. Chromatofocusing and size fractionation of the serum samples indicated the secretion of immunoreactive FSH isoforms that are devoid of bioactivity but that are capable of blocking FSH action in ovarian granulosa cells. These findings provide the first demonstration of naturally occurring circulating antihormones. These FSH antagonists may play an important role in the physiology and pathophysiology of the gonads.

Organization and expression of gonadotropin genes

We have examined the question of how hormones regulate the biosynthesis of gonadotropins. In particular we have studied the effects of gonadal sex steroid hormones on the regulation of LH subunit gene expression to determine whether they may occur at the pre-translational level. Success in the molecular cloning of cDNAs in genes encoding the subunits of LH has allowed such studies. It is now known that the subunit genes are located in separate genes on separate chromosomes in man and mouse. These genes must be coordinately expressed in a tissue-specific fashion in gonadotropes to yield subunit mRNAs which are ultimately translated to form the protein backbones of the subunits. It is clear that the gonadal sex steroid hormones in both castration and castration-replacement experimental paradigms negatively regulate the subunit mRNAs in vivo in a rapid and effective manner. Also, it is interesting to note that alpha-subunit RNA is regulated to a lesser extent than the LH beta. This observation is reminiscent of those previously observed in the studies of the biosynthesis of TSH in which the subunit mRNA is less well controlled than the TSH beta mRNA. These studies were performed initially using thyrotropic tumor which lacked confounding gonadotropes. However, studies have also been performed in the pituitary gland of the hypothyroid mouse with similar results. Hence, it appears that the alpha subunit gene is also under regulation by hormones but to a lesser extent than the LH beta. These findings provide hope that future studies will allow us to understand further the molecular mechanisms involved in the regulation of these genes by various hormonal influences.

Minimal quantities of FSH beta subunit are released by rat anterior pituitary cells in primary culture

FSH beta in the medium and extracts of cultured rat anterior pituitary cells was quantitated with a heterologous radioimmunoassay utilizing anti-rFSH beta and hFSH beta as the standard and tracer. After 4 days in culture, extracts were prepared from washed cells, cells incubated for 6 h or 24 h in fresh medium or cells incubated for 6 h in the presence of 10(-7) M GnRH. FSH beta/rFSH molar ratios were approximately 0.05, 0.04, 0.21 and 0.35, respectively. The elevation in FSH beta/rFSH molar ratios in 24 h basal and GnRH-treated cultures was due in part to an increase in intracellular FSH beta. Both unstimulated and GnRH-treated cultures contained non-detectable quantities of FSH beta in the medium (less than 0.063 ng/100 000 cells; FSH beta/rFSH molar ratio less than 0.024). Thus, it appears that cultured rat anterior pituitary cells contain a small amount of uncombined FSH beta but that minimal quantities are released. Furthermore, GnRH may increase intracellular quantities of FSH beta but does not induce its release.

Luteinizing hormone beta-subunit mRNA amounts increase during the preovulatory surge of luteinizing hormone in the ewe: the highest levels are observed at the completion of the peak

Amounts of mRNA for luteinizing hormone (LH) beta-subunit were assessed during selected times in the normal estrous cycle of sheep. These times spanned the luteal phase through the preovulatory LH surge, and included groups designated as: (i) day 12 of the cycle (day 12); (ii) 24 hr before the onset of the expected behavioral estrus (E - 24); and (iii) 5, 15, and 25 hr after the onset of behavioral estrus (E + 5, E + 15 and E + 25). These groups were characterized by criteria such as serum and pituitary LH concentrations, serum progesterone, and ovarian morphology. Specific LH beta-subunit mRNA was evaluated by Northern transfers, using a specific bovine LH beta cDNA probe. Slopes were determined using a linear regression analysis and then expressed as fold stimulation relative to the values for the day 12 group. The results indicate that LH beta mRNA amounts increase after day 12, reaching a value of approximately 12-fold by E + 25. When correlated with serum and pituitary LH amounts, it is observed that the amounts of beta mRNA increase in a fashion parallel to serum and pituitary LH concentrations through the time E + 5. After this time, LH beta mRNA amounts continue to increase despite a dramatic fall in both serum and pituitary LH. These results suggest that LH beta mRNA amounts are regulated during the LH preovulatory surge.

Effect of gonadectomy on pituitary levels of mRNA encoding gonadotropin subunits and secretion of luteinizing hormone

Using cell-free translation of pituitary mRNAs we have investigated how, following gonadectomy in rats, the translational capacity of the specific messages encoding precursors to gonadotropin subunits alpha, LH-beta and FSH-beta increases with time. In parallel, serum LH was assayed in order to compare release and synthesis patterns. We observed a rapid rise in the rate of synthesis of all three precursors, with a significant increase already detectable 4 days after gonadectomy, and a plateau reached after 21 days. The kinetics were similar in both males and females, but maximal translational values for alpha-subunit were slightly higher in males. During the same time period, serum LH rapidly increased in the males, while in the females the rise of circulating LH was somewhat delayed. Although no direct correlation seems to exist between synthesis and release processes of gonadotropins, it is evident from our previous findings and the present data that both phenomena are dependent on gonadal steroids. In this respect, estradiol has been shown to regulate negatively, via different routes, the synthesis as well as the secretion of pituitary gonadotropins.

In vitro translation of distinct mRNAs coding for the precursors of porcine LH subunits

Conditions are described to characterize and estimate the precursors of porcine LH alpha and beta subunits and indirectly their specific mRNAs. Poly(A) RNAs extracted from castrated male pig anterior pituitaries were translated in a wheat-germ system in the presence of [35S] cysteine and [35S] methionine. The translation products were precipitated by antisera directed against reduced and carboxymethylated LH alpha and beta subunits and analyzed by high resolution electrophoresis. It is shown that the precursors of pLH alpha and beta subunits are located in two distinct congruent to 15 K proteins and represent--on the basis of the incorporation of the [35S] labeled aminoacids into proteins--congruent to 0.12% and 0.05% respectively of the total translation products. It is suggested that in the pig, as in other species, the LH alpha and beta subunits are encoded by two distinct mRNAs, and at variance with other species the leader sequence of LH alpha mRNA is longer than that of LH beta mRNA.

Hormonal regulation of androgen production by the Leydig cell

The control of androgen production by the Leydig cell is dependent upon the episodic secretion of hormone (LH), which is released from the anterior pituitary gland in pulses of high biological activity. This mode of episodic LH secretion supports steroidogenic enzyme activity in the testis through interaction with LH receptors and stimulation of the adenylate cyclase/protein kinase sequence, leading to phosphorylation of key intermediates in the steroid biosynthetic pathway. The plasma membrane events that are rapidly activated by the specific interaction of LH or hCG with Leydig cell receptors include increased binding of guanyl nucleotide, and stimulation of cAMP-independent, Ca2+-dependent phosphorylation of a 44,500 Mr protein, with the characteristics of the adenylate cyclase nucleotide regulatory unit. Hormonal activation of adenylate cyclase is affected by Ca2+ with the same concentration-dependence, suggesting that nucleotide-induced phosphorylation is related to activation of the catalytic cyclase unit. In addition to the characteristic increases in pregnenolone synthesis and androgen production, gonadotropin-stimulated Leydig cells show prominent changes in LH receptor content and steroidogenic activity that modify their subsequent responses to hormonal signals. Thus, after exposure to increased LH and hCG levels in vivo and in vitro, LH receptors show an initial transient increase (up-regulation) followed by a marked decrease (down-regulation) and a prolonged depletion of LH receptor sites. Large doses of hCG cause "early" (prior to pregnenolone) and "late" steroidogenic lesions (17 alpha-hydroxylase, 17-20 desmolase) that are independent of receptor loss. The early lesion is partly due to reduced activity of HMG CoA reductase, and is mainly attributable to the increased activity of an inhibitory protein factor that modulates the activity of cholesterol side chain cleavage enzyme in Leydig cell mitochondria. In contrast, the late steroidogenic lesion is related to the nuclear actions of E2 produced during hormonal action. After hCG stimulation, an increase in nuclear E2 binding was accompanied by an early rise of RNA polymerase activities within 45 min coincident with the maximal increases in circulating testosterone and estradiol levels. These events were followed by the emergence of an E2-induced protein of Mr 27,000 at 3-6 h, and by reduction in the activity of 17 alpha-hydroxylase/17-20 desmolase, and a decrease in microsomal cytochrome P-450.(ABSTRACT TRUNCATED AT 400 WORDS)

Estradiol regulates mRNAs encoding precursors to rat lutropin (LH) and follitropin (FSH) subunits

Anterior pituitary mRNA was prepared using a microscaled method and translated in a wheat-germ cell-free system in the presence of [35S] labeled cysteine and methionine. Translation products, immunologically related to LH beta, FSH beta and the common subunit alpha, were isolated as precursors with antisera to denatured subunits and characterized by SDS-polyacrylamide gel electrophoresis and fluorography. The radioactive bands were excised from the gel and counted for quantitative evaluation. Our data show that translation of pituitary mRNAs from ovariectomized (ovx) rats results in precursor levels increased by 10 fold for alpha and 14 fold for LH beta as compared to the levels in normal rats. The increase in FSH beta precursor was impossible to evaluate as a specific immunoprecipitation product was undetectable in the case of normal rats. Estradiol, but not progesterone, administered in vivo to ovariectomized rats, reversed the stimulatory effect of ovariectomy on the expression of mRNAs coding for gonadotropin subunit precursors 48 h after injection. These results suggest that estradiol, but not progesterone, negatively regulates the synthesis of the pituitary gonadotropins in the female rats via changes in specific mRNA levels. This hormonal control probably occurs at the transcriptional level.