Molecular genetic analysis of AKR1C2-4 and HSD17B6 genes in subjects 46,XY with hypospadias

BACKGROUND

The formation of the male urethra depends to enzyme-mediated testosterone (T) conversion into 5α-dihydrotestosterone (DHT). Two metabolic pathways could be operating in the fetal testis to synthesize androgens: 1) the "classic" route (T→DHT) mediated by SRD5A2 and 2) a "backdoor" pathway in which DHT is synthesized by aldo-keto reductase family 1, member C2 (AKR1C2), AKR1C3, and AKR1C4 enzymes without formation of a T intermediate.

OBJECTIVE

We studied four genes of the "backdoor" pathway in karyotypic males with hypospadias to ascertain whether gene defects in AKRs impair urethral DHT formation that result in hypospadias.

DESIGN AND PATIENTS

The coding regions of the AKR1C2-4 and HSD17B6 genes were analyzed by PCR-SSCP and sequencing in a cohort of 25 Mexican patients (0.3-9 year-old-children) with 46,XY-hypospadias. Chi-squared tests was performed to evaluate the distribution of genotypes, alleles, and the Hardy-Weinberg (H-W) equilibrium. The effect of the genetic variants was investigated by in silico studies.

RESULTS

Screening studies revealed distinct genotypic patterns at different exons of AKR1C2-4 whereas HSD17B6 presented a wild-type sequence. The DNA analyses detected two synonymous variants (c.327C>T, c.666T>C/unreported) in AKR1C2. The AKR1C3 had two variants (c.15C>G, c.230A>G), two unreported variants (c.538T>C, c.596G>A), and one silent variant (c.312G>A). Two variants (c.434C>G, c.931C>G) were identified in AKR1C4. All variants were in H-W equilibrium without structural changes.

DISCUSSION

Hypospadias have been associated with defects that alter androgen biosynthesis in the human fetal testis, specifically 5α-DHT. We selected four candidate genes involved in the "backdoor" pathway for the formation of 5α-DHT. Molecular assays of the AKR1C2, AKR1C3, and AKR1C4 genes revealed a total of nine genetic single nucleotide variants. Several variants in the AKR1C genes have been associated with a variety of human pathologies. However, our studies suggest that active steroid biosynthesis via AKR1C might not be involved in hypospadias. Additionally, genetic research suggests a low involvement in the "backdoor" 5α-DHT pathway during human sexual development, specifically, the differentiation of male external genitalia.

CONCLUSION

These results indicate that substitutions in AKR1C2-4 are polymorphisms and all genetic variants lacks deleterious significant association with hypospadias. The data suggest that inactivating mutations in the AKR1C2-4 and HSD17B6 genes are an infrequent cause of hypospadias, which might weaken the contribution of the "backdoor" pathway to embryonic urethral masculinization.

Mutational analysis of SRD5A2: From gene to functional kinetics in individuals with steroid 5α-reductase 2 deficiency

Human steroid 5α-reductase 2 (SRD5A2) plays a determinative role in the masculinization of external genitalia. To date, approximately 114 different mutations of the SRD5A2 gene have been reported; however, little information is available about their impact on catalytic function or their three-dimensional (3D) structures. We determined the effect of point mutations on the testosterone-depend kinetic constants (K_m,app and V_max,app) and structural characteristics of SRD5A2 from Mexican patients with 46,XY-steroid 5α-reductase 2 deficiency. PCR-SSCP assays identified ten distinct gene variants and sequencing analysis identified missense mutations [p.V3I, p.S14R, p.A52T, p.F118L, p.R145W, p.R171S, p.L226P, p.F229S, p.S245Y, and p.A248V]. Mutations were re-created by site-directed mutagenesis and expressed in HEK293 cells. Functional studies demonstrated that 8 variants led to partial (K_m,app = 0.16-2.6 μM; V_max,app = 224-2640 pmol/mg P/min) or complete losses of activity compared to the wild-type enzyme (K_m,app = 0.7 μM; V_max,app = 4044 pmol/mg P/min). All the mutations were assessed using multiple software tools and the results predicted that all of the mutations were associated with disease or damage. Mapping mutations on the model of a 3D structure of SRD5A2 demonstrated alterations in contact sites with their proximal amino acids. Our data show that mutations affect the catalytic efficiency (V_max/K_m) or result in residual enzymatic activity, which could be due to erroneous interactions between amino acid residues, the substrate testosterone, or NADPH.

Isolation and sex steroid effects on the expression of the ATP-binding cassette transporter ABCB6 in Harderian glands of hamster (Mesocricetus auratus)

ATP-Binding Cassette, subfamily B, member 6 (ABCB6) is a transporter that is upregulated by elevated intracellular porphyrin concentrations. In the Harderian gland (HG), the synthesis of porphyrins appears to be under the influence of gonadal steroids and to exhibit a dimorphic pattern. To explore whether ABCB6 is also influenced by sex steroids, we isolated its specific cDNA sequence and investigated its mRNA levels in the HGs of hamsters. ABCB6's cDNA sequence presents an open reading frame (ORF) of 2529 bp that encodes a predicted 842-amino acid (aa) protein with a molecular weight of 93 kDa. Multiple sequence alignments showed that ABCB6's aa sequence is highly conserved and shares the highest homology (93%) with mouse ABCB6. RT-qPCR analysis indicated that ABCB6 is expressed in all the tissues examined, exhibiting high expression levels in the liver, adrenal glands, and testis. The mRNA concentrations of ABCB6 in HGs were very similar between males and in females; similarly, gonadectomy and treatment with sex steroids appear to scarcely affect ABCB6 mRNA levels. The intraglandular content of ABCB6 mRNA showed discrete, though non-significant, variations through the estrous cycle. The results provide evidence that gonadal steroids have a minimal physiological role on the regulation of ABCB6 expression and might indicate that this transporter has a small effect on porphyrin trafficking in the HGs of hamsters.

Hamster SRD5A3 lacks steroid 5α-reductase activity in vitro

According to current knowledge, two steroid 5α-reductases, designated type 1 (SRD5A1) and type 2 (SRD5A2), are present in all species examined to date. These isozymes play a central role in steroid hormone physiology by catalyzing the reduction of 3-keto-4-ene-steroids into more active 5α-reduced derivatives, including the conversion of testosterone (T) to dihydrotestosterone (DHT). A third 5α-reductase (SRD5A3, -type 3), which is overexpressed in hormone-refractory prostate cancer cells, has been identified; however, its enzymatic characteristics are practically unknown. Here, we isolated a cDNA encoding hamster Srd5a3 (hSrd5a3) and performed functional metabolic assays to investigate its biochemical properties. The cloned cDNA encodes a 330 amino acid protein that is 87% identical to the homologous protein in mice and 78% to that in humans. However, hSrd5a3 exhibits low sequence homology with its counterparts hSrd5a1 (19%) and hSrd5a2 (17%). A fusion protein consisting of hSrd5a3 and green fluorescent protein provided evidence for cytoplasmic localization in transfected mammalian cells. Real-time PCR analysis revealed that, Srd5a3 mRNA was present in nearly all hamster tissues, with high expression in the cerebellum, Harderian gland and testis. Functional assays expressing hSrd5a3 cDNA in HEK-293 cells revealed that this isozyme is unable to reduce T into DHT. Further expression assays confirmed that similar to testosterone, progesterone, androstenedione and corticosterone are not reduced by hSrd5a3 or human SRD5A3. Together, these results indicate that hSrd5a3 lacks the catalytic activity to transform 3-keto-4-ene-compounds; therefore 5α-reductase type 3 may not be involved in 5α-reduction of steroids.

The influence of sex steroid hormones on ferrochelatase gene expression in Harderian gland of hamster (Mesocricetus auratus)

Ferrochelatase (protohaem ferrolyase, EC 4.99.1.1), the terminal enzyme of the haem biosynthetic pathway, catalyses the insertion of ferrous iron into protoporphyrin IX to form protohaem. The Syrian hamster Harderian gland (HG) is known for its ability to produce and accumulate large amounts of protoporphyrins. In this species, the female gland contains up to 120 times more porphyrin than the male gland. Data from biochemical studies suggest that this gland possesses the enzymatic complex for haem biosynthesis but lacks ferrochelatase activity. The abundance of intraglandular haem proteins does not support this idea. To gain more insight into this process, we isolated cDNA for ferrochelatase from hamster liver, using the 5'- and 3'- rapid amplification of complementary DNA ends (RACE), and investigated its expression in HG from males and females. The full-length cDNA comprises an open reading frame of 1269 bp encoding a polypeptide of 422 amino-acid residues. Hamster DNA sequence exhibits 92% identity to mouse and 87% identity to human sequences. The predicted hamster enzyme was shown to have structural features of mammalian ferrochelatase, including a putative NH2- terminal presequence, a central core of about 330 amino-acid residues and an extra 30-50-amino-acid stretch at the carboxyl-terminus. RNA blotting experiments indicated that this cDNA hybridized to a liver mRNA of about 2.1 kb, while a weak hybridization signal was observed with mRNA from HG preparations. RT-PCR assays confirmed the expression of specific transcripts in both tissues. Male glands contained approximately twofold more enzyme mRNA than female glands. Likewise, the intraglandular content of mRNA varied during the oestrous cycle, with the highest levels found in the oestrous phase. These cyclic variations were less evident in liver. Ovariectomy plus treatment with progesterone or 17beta-oestradiol plus progesterone increased ferrochelatase mRNA of the gland. In HG of short- or long-term castrated males, the administration of testosterone did not affect the ferrochelatase mRNA concentration. Based on mRNA expression levels, we conclude that Harderian ferrochelatase may play an active role in maintaining the physiological pool of haem required for processing cytochromes and other glandular haem proteins. Likewise, the sex-steroid hormones appear to have only a modest influence upon Harderian ferrochelatase.

A heterozygous mutation in the desert hedgehog gene in patients with mixed gonadal dysgenesis

Aetiology of mixed gonadal dysgenesis (MGD) has not been completely elucidated. Molecular analyses have failed to demonstrate the presence of mutations in sex-determining region on Y chromosome (SRY); it has been suggested that these individuals may bear mutations in other genes involved in the testis-determining pathway. Desert hedgehog's (DHH) importance regarding male sex differentiation has been demonstrated in various studies we describe here, for the first time, two cases of MGD in which a monoallelic single base deletion in DHH is associated with the disorder. Genomic DNA was isolated from paraffin-embedded gonad tissue from 10 unrelated patients with MGD and three controls; in addition to, DNA from peripheral blood leukocytes in 100 controls. Coding sequence abnormalities in DHH were assessed by exon-specific PCR, single-stranded conformation polymorphism (SSCP) and direct sequencing. In two patients, a heterozygous 1086delG in exon 3 was found. Comparing previously described mutations in DHH to the one observed in this study, we can affirm that the phenotypic spectrum of patients with gonadal dysgenesis due to mutations in DHH is variable. This study continues to demonstrate the importance that DHH has in mammalian male sexual differentiation, providing extended evidence that DHH constitutes a key gene in gonadal differentiation.

Polymorphic changes in the KAL1 gene: not all of them should be classified as polymorphisms

The KAL1 gene has a closely related nonfunctional pseudogene on the Y chromosome; a high degree of X-Y sequence similarity is observed. Some individuals present a T to C substitution at position 1833 (exon 12). Because this nucleotide differs in the X (thymine) and in the Y (cytosine) chromosome, we investigated if this was truly a polymorphism, or if in some cases the Y sequence had been amplified. The complete sequence of exon 12 of KAL1 was analyzed in 11 Kallmann Syndrome (KS) males, in 50 normal males, in 50 normal females, and in 16 patients with Ullrich-Turner Syndrome (UTS). Nucleotide 1833 was found in a heterozygous or a homozygous state in KS, normal males and normal females; UTS patients were always homozygous. Of the 61 males, 17 were heterozygous, while 11 were TT and 33 were CC. With these observations we can not assure whether these patients present a "real" polymorphism. Besides, all males were heterozygous in nucleotides 1678, 1694, 1699, 1708 and 1825, whilst females were homozygous; and in these positions, KAL1 also differs from its pseudogene. These results indicate that we are identifying the X and the Y nucleotide and these variants are not polymorphisms. Sequence variations may be pseudogene products rather than true polymorphisms, so we should always determine if the position where the variation is located differs between KAL1 and its pseudogene, because it has been suggested that the presence of various polymorphisms in affected individuals could be the cause of KS.

Evaluation of the pituitary-testicular function during experimental nephrosis

To investigate the pituitary-testicular function in nephrotic rats, a sequence of experiments was undertaken in adult male rats after a single dose of puromycin aminonucleoside (PAN). Endocrine modifications were evaluated chronologically throughout the experimental disease in order to determine the appearance of hormone alterations which lead to the axis dysfunction. Serum concentration of LH, FSH, androstenedione, total and free testosterone, estradiol as well as urine testosterone were measured by specific RIAs on days 3, 7 and 10 after treatment on nephrotic and control groups. Prolactin was also evaluated on day 10. Likewise, total weight of various androgen responsive tissues from both groups was recorded, and the number of androgen receptor (AR) binding sites were determined. To know the functional status of the hipophyseal-testicular unit, groups of nephrotic and control rats were stimulated with LHRH (300 ng/100 g b.w.) or with one or four doses of hCG (8 UI), respectively. Additionally, the relative in vitro biological activity of FSH from nephrotic and control rats before and after LHRH stimulus was determined. The results from the hormonal profile revealed clear endocrine disorders characterized by a progressive diminution of all serum hormones except prolactin and urine testosterone, which remained unmodified. The weight of the main androgen responsive tissues, the ventral prostate and the seminal vesicle, decreased parallelly to androgen diminution. The binding analysis of AR shows a significant elevation of the available androgen sites in all analyzed tissues except kidney and hypothalamus. The secretion of LH and FSH from nephrotic animals after LHRH administration was lower than that from intact animals at the registered times. Interestingly, the biological activity of FSH from nephrotic rats was not detectable at both, before and after LHRH administration. Testicular response to hCG stimuli, in terms of testosterone synthesis was not significantly different in the two groups analyzed with respect to the intact animals. By contrast, no response was observed in terms of estradiol production at either one or four doses of hCG. On the whole, the results presented herein allow us to conclude that experimental nephrosis has a harmful effect on the pituitary-testicular axis, and strongly suggests that the endocrine dysfunction is initiated at the hypophyseal level; even though a specific testicular damage is also present.

The cDNA cloning and tissue expression of the cytochrome P450scc from Syrian hamster (Mesocricetus auratus)

In this study we report the cloning and sequencing of a cDNA for cholesterol side chain cleavage cytochrome P450scc from Syrian hamster adrenal glands. Isolation of P450scc mRNA was carried out with degenerate primer PCR together with 5' and 3' RACE protocol. The full-length cDNA comprises an open reading frame of 1563 bp encoding a polypeptide of 520 amino acid residues. The predicted protein sequence exhibits well-preserved heme- and steroid-binding domains and shares 89% amino acid sequence identity with rat and mouse enzymes. Transient transfection of HEK-293 cells with the cloned cDNA leads to the formation of pregnenolone from 25-hydroxycholesterol. Northern blot analysis showed expression of mRNAs for P450scc in the major steroidogenic tissues, namely, the adrenal cortex, testis, and ovary. In addition, tissue distribution analysis using the coupled reaction of RT-PCR and Southern blotting revealed that the mRNA of the enzyme is also expressed in various nonendocrine tissues, including the epididymis, Harderian gland, and lungs. The relative abundance of specific transcripts at these novel sites suggests that P450scc could potentially play an important role in regulating local steroid hormone synthesis.

Eight novel mutations of the androgen receptor gene in patients with androgen insensitivity syndrome

Androgen insensitivity syndrome (AIS) is an X-linked genetic disorder of male sexual differentiation caused by mutations in the androgen receptor (AR) gene. A reliable genotype-phenotype correlation in these patients does not exist as yet. Here we report the molecular studies performed on eight individuals with AIS. Exon-specific polymerase chain reaction (PCR), single-strand conformation polymorphism, and sequencing analyses, were performed in exons 2 to 8 of the AR gene. In one case, total cellular RNA was extracted from genital skin fibroblasts and reverse transcriptase-PCR was performed. Six different point mutations leading to amino acid substitutions (P682T, Q711E, G743E, F827V, H874R, D879Y), one splice-junction mutation (g-->c at +5, exon 6/intron 6), and a missense mutation without amino acid substitution (S888S) were identified. All mutations, including a de novo mutation, were previously undescribed on the steroid binding domain. Of the eight mutations identified, four led to a complete female phenotype (codons 743, 827, 874 and the donor splice site +5), two were detected in phenotypic females with partial virilization (codons 682 and 711), and two were present in phenotypic male subjects with undervirilized external genitalia, thus indicating that all of these sites determine AR functional activity.

Novel molecular defects in the androgen receptor gene of Mexican patients with androgen insensitivity

The androgen insensitivity syndrome (AIS) is an X-linked form of male pseudohermaphroditism caused by mutations in the androgen receptor (AR) gene. In the present study, we analyzed the AR gene in 8 patients, 4 sporadic and 2 familial cases with the syndrome, using exon-specific polymerase chain reaction, single-stranded conformational polymorphism and sequencing analysis and identified six new single base mutations, including one nonsense mutation at the hinge region of the receptor. These molecular lesions occurred in the steroid-binding domain (SBD) and all but one affected the first nucleotide of their respective codons. A nonsense mutation in exon 4, which converts a glutamine into a premature termination signal (Q657stop), a missense mutation changing arginine instead of glycine (G743R) and a conservative substitution of leucine with valine at amino acid 830 (L830V) were detected in patients with CAIS. Three other missense mutations located in exons 4 (L701I), 5 (A765S), and 6 (Q802R) were present in individuals bearing a partial form of AIS. These data allow us to reaffirm the view that nonsense mutations in the AR results almost invariably in a CAIS phenotype and underly the importance of the SBD for the AR functional activity.

Follicle-stimulating hormone regulates steroidogenic enzymes in cultured cells of the chick embryo ovary

This investigation addresses the potential regulation of enzymes involved in the biosynthesis of steroid hormones during early stages of gonadal development by follicle-stimulating hormone (FSH). Gonadal cells of 10-day-old chick embryo and cells of the left ovary of 18-day-old chick embryo were cultured for 60 h in a defined medium with or without the addition of FSH (2.0 IU/ml). At the end of the culture, cells were recovered and evaluated by biotransformation of tritiated steroid precursors and mRNA levels were evaluated by RT-PCR. The production of estrone from androstenedione was increased in the FSH-treated cells, both human FSH (hFSH) and recombinant human FSH (rhFSH), indicating a stimulatory effect on aromatase (P450arom). Similarly, the intensity of the band corresponding to P450arom mRNA was higher in hFSH and rhFSH than in control and chorionic gonadotropin (hCG) groups. The P450arom stimulation was observed in the ovary of 10- and 18-day-old chick embryo. The transformation of dehydroepiandrosterone to androstenedione was taken as evidence of 3beta-hydroxysteroid dehydrogenase function. This enzyme was stimulated in the cultured ovarian cells of 18-day-old chick embryos treated with hFSH and rhFSH compared with controls. The production of pregnenolone in the mitocondrial fraction of 18-day-old chick embryo ovary was increased when cultured with hFSH and rhFSH. This observation together with the increase in the band intensity corresponding to mRNA of P450 cholesterol side-chain cleavage indicates stimulation by FSH treatment; hCG produced a similar effect. Somatic cells of the medullary cords are proposed to be FSH target cells in the ovary of the chick embryo.

Uniparental disomy in steroid 5alpha-reductase 2 deficiency

Steroid 5alpha-reductase 2 deficiency is an autosomal recessive form of male pseudohermaphroditism caused by mutations in the SRD5A2 gene. In this study, we performed DNA analyses in two unrelated subjects bearing the enzyme deficiency and found differences in the mode of transmission for the disease. The data showed that in both families the fathers were carriers for an E197D mutation, whereas the mothers were carriers for a P212R mutation. Patient 1 was identified as compound heterozygote because he had both alterations (E197D/P212R). On the contrary, patient 2 was found to be homozygous, but only for the paternal mutation. Because this finding could not be explained on the basis ofnonpaternity or a chromosomal abnormality, the presence of uniparental disomy was suggested. The reduction to homozygosity for the E197D mutation, as confirmed by restriction analysis, supported this view. The results of our study give evidence of the first case of 5alpha-reductase deficiency resulting from uniparental disomy and also disclose an alternate mechanism whereby this enzymatic disorder can derive from a single parent.

Identification of a 25-hydroxyvitamin D3 1alpha-hydroxylase gene transcription product in cultures of human syncytiotrophoblast cells

Although accumulating data show that placenta is able to synthesize 1,25-dihydroxyvitamin D3, the presence of cytochrome P(450) enzyme capable of converting 25-hydroxyvitamin D3 (250HD(3)) to the biologically active form of vitamin D in this tissue, has not been yet clearly established. In this study, we have investigated the presence of 25-hydroxyvitamin D3 1alpha-hydroxylase (1alpha-(OH)ase) gene expression products in cultured human syncytiotrophoblast. Total RNA was isolated from cultured placental cells and subjected to Northern blots or RT-PCR by using 1alpha-(OH)ase-specific primers. The amplified complementary DNA fragments were analyzed by gel electrophoresis and nucleotide sequencing. Total RNA from kidney HEK 293 cells was subjected to reverse transcriptase reaction, and a 298-bp complementary DNA 1alpha-(OH)ase probe was generated by PCR. Primary cultures of human syncytiotrophoblasts exhibited 1alpha-(OH)ase activity, and a transcript for this gene could be demonstrated in these cells. Northern blot analysis revealed the presence of a 2.5-kb product, similar in size to that previously reported in kidney. RT-PCR analysis demonstrated the presence of a single transcript with nucleotide sequence identical to that previously reported for human 1alpha-(OH)ase complementary DNA clones. In addition, data are presented which suggest that differentiation of cytotrophoblast to the syncytial state was not necessary for this gene to be expressed, which may indicate a role of this enzyme all through pregnancy. The overall results of this study provide evidence for the presence of 1alpha-(OH)ase in the human placenta, suggesting that conversion of 25OHD(3) to 1,25-dihydroxyvitamin D3 in the trophoblast is most probably attributed to an enzymatic 1alpha-hydroxylation reaction.

Identification of a 25-hydroxyvitamin D3 1alpha-hydroxylase gene transcription product in cultures of human syncytiotrophoblast cells

Although accumulating data show that placenta is able to synthesize 1,25-dihydroxyvitamin D3, the presence of cytochrome P(450) enzyme capable of converting 25-hydroxyvitamin D3 (250HD(3)) to the biologically active form of vitamin D in this tissue, has not been yet clearly established. In this study, we have investigated the presence of 25-hydroxyvitamin D3 1alpha-hydroxylase (1alpha-(OH)ase) gene expression products in cultured human syncytiotrophoblast. Total RNA was isolated from cultured placental cells and subjected to Northern blots or RT-PCR by using 1alpha-(OH)ase-specific primers. The amplified complementary DNA fragments were analyzed by gel electrophoresis and nucleotide sequencing. Total RNA from kidney HEK 293 cells was subjected to reverse transcriptase reaction, and a 298-bp complementary DNA 1alpha-(OH)ase probe was generated by PCR. Primary cultures of human syncytiotrophoblasts exhibited 1alpha-(OH)ase activity, and a transcript for this gene could be demonstrated in these cells. Northern blot analysis revealed the presence of a 2.5-kb product, similar in size to that previously reported in kidney. RT-PCR analysis demonstrated the presence of a single transcript with nucleotide sequence identical to that previously reported for human 1alpha-(OH)ase complementary DNA clones. In addition, data are presented which suggest that differentiation of cytotrophoblast to the syncytial state was not necessary for this gene to be expressed, which may indicate a role of this enzyme all through pregnancy. The overall results of this study provide evidence for the presence of 1alpha-(OH)ase in the human placenta, suggesting that conversion of 25OHD(3) to 1,25-dihydroxyvitamin D3 in the trophoblast is most probably attributed to an enzymatic 1alpha-hydroxylation reaction.

A mutation in the 5' non-high mobility group box region of the SRY gene in patients with Turner syndrome and Y mosaicism

In Ullrich-Turner syndrome (UTS) patients, the presence of a Y-chromosome or Y-derived material has been documented in frequencies ranging from 4-61%. Mutations of SRY (testis-determining gene) constitute the cause of XY sex reversal in approximately 10-15% of females with pure gonadal dysgenesis. Most of these mutations have been described in the HMG (high mobility group) box of the gene, which is the region responsible for DNA binding and bending; however, various mutations outside the HMG box have been reported. We carried out molecular studies of the SRY gene in three patients with a UTS phenotype and bilateral streaks; two presented a 45,X/46,XY mosaic, and the third a Y marker chromosome. In two patients a missense mutation, S18N, was identified in the 5' non-HMG box region in DNA from blood and both streaks; this mutation was not identified in 75 normal males. Sequencing of the DNA region of interest was normal in the father and older brother of patient 1, demonstrating that in this patient the mutation was de novo. A previous report of a 46,XY patient with partial gonadal dysgenesis who presented the same mutation as our patients indicates the probable existence of a hot spot in this region of the SRY gene and strengthens the possibility that all gonadal dysgeneses constitute part of a spectrum of the same disorder. It also demonstrates that a single genetic abnormality can result in a wide range of phenotypic expression.

Identification of missense mutations in the SRD5A2 gene from patients with steroid 5alpha-reductase 2 deficiency

BACKGROUND AND OBJECTIVE

Mutations of the steroid 5alpha-reductase type 2 (SRD5A2) gene in karyotypic males result in a spectrum of external genitalia phenotypes ranging from complete female to nearly complete male. Here we performed genomic DNA analyses from individuals bearing the enzyme deficiency in order to detect the molecular abnormalities.

PATIENTS

Four unrelated 46,XY patients of Mexican origin with ambiguous external genitalia were studied. A fertile, phenotypically normal male was also included.

MEASUREMENTS

Coding sequence abnormalities of the SRD5A2 gene were assessed by exon-specific polymerase chain reaction, single-stranded conformational polymorphism and sequencing analysis.

RESULTS

Five different missense mutations (two of them novel mutations) were identified. Three subjects presented homozygous single base mutations. These were located at exon 2 (G115D), exon 4 (P212R) and exon 5 (R246Q), and such changes have been described previously. The fourth patient was a compound heterozygote who presented two mutations located in exons 1 and 2. We found a hitherto unreported G --> A transition at the second nucleotide of codon 85 in exon 1 (GGC --> GAC), substituting glycine for aspartic acid (G85D). This patient also presented an identical alteration at codon 115 of exon 2, which was carried by his father (G115D). Finally, in another subject who was included originally as a control, we found a C --> A transversion (yet undescribed) at codon 245 in exon 5 (S245Y).

CONCLUSIONS

Four different single base mutations that cause amino acid substitutions were detected in the steroid 5alpha-reductase type 2 gene of affected individuals. One patient and a normal control had two previously undescribed mutations. Although in the latter individual we cannot exclude the possibility that the base change is a genetic polymorphism, the molecular screening of 100 chromosomes suggests strongly that the change at codon 245 does represent a heterozygous mutation. Further studies, including the recreation of the mutations, will help to reveal the biochemical consequences resulting from these changes.

Reproductive function in male rats with chronic nephrosis

Endocrine dysfunction has been associated with renal diseases. The present study was conducted to explore reproductive function in male rats with chronic nephrosis. Experimental chronic nephrosis was induced by the administration of 7.5, 5.0 and 5.0 mg per 100 g body weight of puromycin aminonucleoside on days 0, 21 and 35, respectively. Reproductive function was evaluated on the basis of hormonal concentrations, mass of accessory sex organs and fertility during an 84 day period. Circulating LH, FSH, testosterone and oestradiol concentrations were measured by specific radioimmunoassays, while fertility was estimated by the rate of pregnancy induction. Samples were collected on days 7, 14, 28, 56 and 84. The results showed an important endocrine dysfunction characterized by low concentrations of LH and FSH during the first month, after which concentrations were similar to control values or even increased on days 56 and 84. Testosterone and oestradiol decreased significantly at all time points evaluated. The mass of the testes did not alter. However, the mass of the prostate and seminal vesicle decreased only during the first 2 weeks, and became essentially normal thereafter. The reproductive capacity of nephrotic males was eliminated on day 7, whereas on day 14, 16% of the group was able to mate successfully and subsequently most animals recovered their normal reproductive function. This study demonstrates for the first time that rats with experimental chronic nephrosis develop an important endocrine dysfunction, characterized mainly by persistent reduction in testosterone concentrations, which impairs reproductive capacity only transiently.

Evidence for estrogen receptor expression in germ cell and somatic cell subpopulations in the ovary of the newly hatched chicken

Estrogens are involved in the gonadal morphogenesis of vertebrates, and almost all hormonal effects of 17beta-estradiol are mediated through specific receptors. At the time of sexual differentiation in the chicken, or even before, there is evidence of the presence of estrogen receptors and the secretion of 17beta-estradiol. However, no information is available regarding the cellular types that express the estrogen receptor in the immature chick ovary. The present study analyzes estrogen receptor expression in germ and somatic cells of the ovary in the newly hatched chicken. Highly purified cell subpopulations of germ and somatic cells were evaluated for specific 17beta-estradiol nuclear binding. In addition, the estrogen receptor was localized at the ultrastructural level by the immunogold technique. Finally, reverse transcription and polymerase chain reaction procedures detected a steady-state level of mRNA for the estrogen receptor. Somatic cells including typical steroidogenic cells showed specific 17beta-estradiol nuclear binding, displayed the estrogen receptor, and possessed estrogen receptor transcripts. The same result was observed in primary oocytes, together with the ultrastructural localization of estrogen receptor in extended chromatin filaments. Our experimental data support the hypothesis that estrogens are involved in the function of somatic and germ cells subpopulations in the immature chicken ovary.

Synthesis of steroids in pancreas: evidence of cytochrome P-450scc activity

In pancreas, the activities of several sex steroid-transforming enzymes have been reported. Data have been obtained in perfused organs, total tissue homogenates, and subcellular organelles. These data, concurrent with the description of the presence of ligand-regulated steroid receptors, as well as the sexually dimorphic behavior of some pancreatic tumors, are clear evidence in support of the participation of steroid hormones in the pancreatic function. In this study, the steroidogenic ability of the pancreas was demonstrated by two different methods: (a) in tissue homogenates, by the identification of cytochrome P-450scc gene (CYP11A) transcripts after reverse transcription-polymerase chain reaction amplification (RT-PCR); and (b) in isolated mitochondria by the glutethimide-dependent inhibition of cholesterol-pregnenolone biotransformation. The results obtained in a series of independent experiments showed that (a) the pancreatic tissue possessed transcriptional activity of the CYP11A gene, although to a lesser extent than the typical steroidogenic tissues, and (b) isolated mitochondria obtained from the pancreas were able consistently to synthesize pregnenolone; furthermore, the addition of the specific inhibitor aminoglutethimide (AMG) blocked its synthesis. On the whole, these findings are interpreted as clear evidences of the activity of the cytochrome P-450scc enzymatic complex (P450scc), responsible for the transformation of cholesterol into pregnenolone and considered the first and limiting step in steroid biosynthesis.

Transient alteration of the reproductive function in nephrotic rats

The reproductive function of male and female rats with induced nephrotic syndrome was examined by assessing hormonal levels, the estrous cycle pattern and fertility. Measurements were carried out on day 10 (nephrotic stage) and on day 30 (remission stage) after treatment (a single s.c. dose of puromycin aminonucleoside 15 mg/100 g body wt.). Serum concentrations of luteinizing hormone (LH), follicle-stimulating hormone (FSH) and progesterone (P4) from both sexes as well as 17beta-estradiol (E2) in females and total testosterone (tT) in males were assayed at both phases of the illness by specific radioimmunoassays; free and urine testosterone (fT, uT) was also determined in male rats on day 10. The estrous cycle was followed alongside the study through vaginal smears, while fertility was estimated by the rate of pregnancies (females) or pregnancy induction (males), and by the litter size. The results showed that most serum hormone levels, except FSH in females, were significantly reduced at the nephrotic stage of the illness, returning to their normal values after 30 days. Besides, on day 10, fT was found reduced in nephrotic males, while uT concentrations remained unmodified. The ovulatory cycle of nephrotic rats was disrupted on day 3 and not restored until day 23; nevertheless, the reproductive function, measured as a fertility index, was fully reinstalled at the remission stage. Interestingly, the capacity of fertilization of the nephrotic males was not entirely abolished during the acute phase, since 37% of the animals were fertile. Moreover, on day 30 the reproductive function in nephrotic males was totally recovered. The data from this study show the existence of reversible endocrine disorders in rats bearing nephrotic syndrome; such changes are manifested during the acute phase of the illness as a temporary cessation of the reproductive processes.

Codon 89 polymorphism of the human 5alpha-steroid reductase type 2 gene

The existence of a genetic polymorphism within the coding region of the human 5alpha-steroid reductase type 2 (5alpha-SR2) gene is reported in a Mexican population. Genotypic variation was assessed in 100 unrelated, healthy volunteers (50 males; 50 females), using single-stranded conformational polymorphism and direct sequencing analysis. Examination of exon 1 DNAs disclosed the presence of sequences encoding for valine (GTA) or leucine (CTA) at codon 89 of the gene. Of the subjects screened, 45% were homozygous for GTA (89Val), 50% had a heterozygous pattern GTA/CTA (89Val/89Leu) and the remaining 5% were homozygous for CTA (89Leu). These data support the view that the G/C condition at codon 89 of the 5alpha-SR2 gene represents a silent polymorphism which does not alter phenotypical development in the human.

Molecular analysis of the 5 alpha-steroid reductase type 2 gene in a family with deficiency of the enzyme

This report describes the identification of a point mutation in the 5 alpha-reductase type 2 (5 alpha-SR2) gene from a family in which both sibs (6 and 3 years old) have steroid 5 alpha-reductase 2 deficiency. The five exons of the gene were individually amplified by the polymerase chain reaction (PCR) and analysed for single-strand conformation polymorphisms (SSCP) to detect mutations. Direct sequencing of the mutant PCR products demonstrated a single C-->T mutation, within exon 4, changing codon 227 from CGA (Arg) to TGA (premature termination signal). Both patients were homozygous for the mutation, but their parents were heterozygous. These results suggest that the mutation at codon 227 impairs normal 5 alpha-SR2 function, thus leading to the phenotypical expression of this rare enzymatic defect.

Mutations of the 5 alpha-reductase type 2 gene in eight Mexican patients from six different pedigrees with 5 alpha-reductase-2 deficiency

BACKGROUND AND OBJECTIVE

Male pseudohermaphroditism due to 5 alpha-reductase deficiency was originally described in 1974. Recently, 5 alpha-reductase Type 2 gene defects have been found generally to be due to point mutations within the 5 exons of the 5 alpha-reductase-2 gene. In this report, we describe the molecular study of patients with 5 alpha-reductase deficiency.

DESIGN

Previously diagnosed patients with 5 alpha-reductase deficiency were sampled in order to perform molecular studies.

PATIENTS

Eight 5 alpha-reductase deficient individuals from 6 unrelated families.

MEASUREMENTS

Single-strand conformational polymorphism and DNA sequencing were performed after polymerase chain reaction amplification of each of the 5 exons of the gene.

RESULTS

Five different missense mutations were found. In 4 patients a cytosine to guanine substitution was observed at codon 212 in exon 4. Two siblings presented a cytosine to adenine substitution at codon 207 in exon 4. Another patient exhibited a guanine to adenine substitution at codon 34 in exon 1, whilst one individual presented 2 mutations: a guanine to adenine substitution at codon 115 in exon 2 and a guanine to adenine substitution at codon 203 in exon 4 (previously undescribed mutation).

CONCLUSIONS

The presence of the same mutation in 4 patients from 3 families indicates the increased prevalence of this mutation in a particular ethnic group, suggesting a common ancestry for the gene defect in these patients. The existence of hot spots is supported by the mutations in codons 34 and 207 which have also been found in other ethnic groups. Interestingly, the patient who presented 2 different mutations, one of them previously undescribed, was reared as a male and exhibited a more masculine phenotype. Further studies in patients with this and other mutations will be needed to verify genotype-phenotype correlation.

Identification and androgen regulation of a 156-kDa hemeprotein in the harderian gland of the Syrian hamster

An abundant cytosolic protein from hamster Harderian glands was partially purified by ultracentrifugation and analyzed on SDS-PAGE. This 156-kDa protein occurs in male but not in female glands. Castration of adult males for different time periods resulted in a gradual disappearance of the protein over 5 weeks. Daily administration of testosterone, 5 alpha-dihydrotestosterone, 3 alpha- or 3 beta-androstanediol (0.5 mg/day/15 days), to castrated males maintained the levels of the protein. In females, the protein was induced with the same compounds but not with 17 beta-estradiol. These observations indicate an androgen-mediated hormonal regulation. In developing animals, the 156-kDa protein was detectable in glands of 2-week-old males and females; it was not detected in 4-week-old females. Its specific reactions to 3,3',5,5'-benzidine derivatives strongly suggest heme groups associated with this Harderian gland protein.

Molecular interactions of levonorgestrel and its 5 alpha-reduced derivative with androgen receptors in hamster flanking organs

The 5 alpha-reduction of levonorgestrel (LNG) as well as its binding capacity to the androgen receptors of the hamster flank organ were investigated. Furthermore, the effects of LNG and its 5 alpha-reduced metabolite in the flank organ test and on [U-14C]glucose incorporation into lipids by this tissue were determined. Homogenates from female hamster flank organs were incubated in the presence of [3H]LNG at pH 7.4. The radioactive 5 alpha-LNG metabolite was isolated and its purity was assessed. Competition experiments for androgen binding receptors were carried out with 1.38 nM [3H-7 alpha-17 alpha]dimethyl-19- nortestosterone (DMNT), Kd, plus a range of increasing concentrations of the different unlabeled steroid hormones. The flank organ test was performed in vivo, and [U-14C]glucose incorporation into lipids was determined under organ culture conditions. The 5 alpha-LNG had the same binding capacity to androgen receptors (AR) as LNG in male flank organs. The flank organ test demonstrated that 5 alpha-LNG activity was similar to that observed for levonorgestrel and testosterone (T) on gonadectomized male hamster flank organs. Topical applications of LNG or 5 alpha-LNG increased [U-14C]glucose incorporation into lipids in a way similar to that of T. The overall data indicate that LNG and 5 alpha-LNG produced androgenic activity in the lipid pathway of male flank organs, and that 5 alpha-reduction is not essential for the LNG effect on this tissue.

Pituitary-ovarian dysfunction in rats with induced nephrotic syndrome

The reproductive hormonal profile was evaluated in female rats with experimental nephrotic syndrome induced with a single subcutaneous dose of puromycin aminonucleoside (PAN). Serum concentrations of luteinizing hormone (LH), follicle-stimulating hormone (FSH), progesterone (P4), testosterone and 17 beta-estradiol (E2) were determined sequentially in control and experimental groups on days 1, 3, 7 and 10 after PAN administration. Prolactin levels were also assessed on day 10. In both groups, vaginal smears were taken daily throughout the study to evaluate cyclic histological changes. At the end of the experiment the histological appearance of the ovaries was evaluated by light microscopy. Nephrotic rats had a rapid loss of the estrous cycle starting on day 4, which set them at diestrus. At the same time the hormonal evaluation indicated a gradual decrease in E2, LH and P4 concentrations, starting from days 3, 7 and 10, respectively. No significant changes were noted in FSH or testosterone values. Besides, on day 10, prolactin concentrations remained unmodified. Even though most hormonal levels were found low on day 10, all values except E2 (undetectable) corresponded to the interval reported for the diestrus phase. Likewise, histological examination of ovarian tissue from nephrotic rats showed a considerable increase in the number of atretic follicles. These findings indicate that female rats with nephrotic syndrome develop an important endocrine dysfunction that probably involves steroidogenic tissues (ovary and/or adrenal gland), and suggest the existence of a hypothalamic-hypophyseal impairment.

Steroid 5 alpha-reductase activity in the harderian glands of male and female Syrian hamster (Mesocricetus auratus)

The activity of the enzyme steroid 5 alpha-reductase in Harderian glands of adult syrian hamsters was assessed by measuring the conversion of testosterone (T) to 5 alpha-dihydrotestosterone (DHT). The optimal conditions for this reaction were determined in vitro using whole gland homogenates and [3H]testosterone as substrate. Enzyme activity was maximal at pH 5.5. The Michaelis-Menten constant of the Harderian enzyme for T was 4.6 +/- 1.2 x 10(-6) M in females and 4.2 +/- 0.39 x 10(-6) M in males, estimated by Eadie-Hofstee plots. On the basis of relative maximum velocity values, there was 9 or 10 times more 5 alpha-reductase in females (2.8 +/- 0.67 nmol/mg protein/hr) than in males (0.289 +/- 0.029 nmol/mg protein/hr). Consistently, glands of intact male hamsters had lower 5 alpha-reductase activities than those of females. Castration of males significantly increased the enzymatic activity, which within 4 weeks reached female-like values. The levels of 5 alpha-reductase mRNA also increased with castration. There was a direct correlation between activity and mRNA levels of the enzyme in castrated male glands. Further, the administration of T or DHT to ovariectomized hamsters led to intact male values in the enzymatic activity of the gland. The sex differences in 5 alpha-reductase activity may be of relevance to the differential regulation exerted by androgen upon the physiology of male and female glands. The results are consistent with the view that 5 alpha-dihydrotestosterone is the active androgen in the Harderian gland.

Mechanisms of hormonal and antihormonal action of contraceptive progestins at the molecular level

19-Nor synthetic progestins undergo extensive metabolism at the target cells. The resulting metabolic conversion products interact with putative steroid receptors within the cells, and through those interactions, they may exert either agonistic, synergistic and antagonistic hormonal effects. Studies conducted in our laboratories have disclosed that norethisterone (NET) and D-(1) norgestrel (LNG), two widely used contraceptive progestins, are biotransformed to several A-ring reduced (dihydro and tetrahydro) derivatives. The resulting metabolites 5 alpha-dihydro NET (5 alpha-NET) and 5 alpha-dihydro LNG bind with relative high affinity to the progesterone and androgen receptors. To gain insight into the underlying molecular events mediating the mode of action of NET and its neutral metabolites, we have examined the expression of their biological effects at target organs by using the rabbit uteroglobin gene model and the beta-glucuronidase activity of the mouse kidney. The results of a series of experiments seem to indicate that the enzyme-mediated formation of the 5 alpha (trans A/B ring junction) NET derivative results in a significant diminution of its progestational and androgenic potencies. Furthermore, 5 alpha-NET acquire a potent anti-progestational/contragestational effect as assessed in the female rabbit. These results demonstrated that 5 alpha-reduction of 19-nor progestins exerts a paradoxical effect, at least in terms of their hormone-like effects. The overall data are in line with the concept that metabolism of synthetic progestins at hormone-sensitive organs modulates their mechanisms of action.

Mechanism of action of levonorgestrel: in vitro metabolism and specific interactions with steroid receptors in target organs

Levonorgestrel (LNG) is a synthetic steroid that displays potent progestational and androgenic effects but it lacks estrogen-like activity. To examine the mode of action of this progestin, we studied its metabolism in vitro in target organs and the specific interactions of LNG and its metabolites with putative steroid receptors. The results demonstrated that [3H]LNG was efficiently converted to A-ring reduced derivatives when incubated with rat hypothalamus and pituitary. Under optimal incubation conditions, [3H]5 alpha-dihydro LNG (5 alpha-LNG) and [3H]3 alpha,5 alpha-tetrahydro LNG (3 alpha,5 alpha-LNG) were identified as the major metabolic conversion products, while [3H]3 beta,5 alpha-LNG formation occurred to a lesser extent. A-ring reduction of LNG was NADPH-dependent. Assessment of the relative binding affinities of LNG and its derivatives to progesterone (PR), androgen (AR) and estrogen (ER) receptors by displacement analysis revealed that unchanged LNG binds with high affinity to PR and AR but not to ER. 5 alpha-LNG exhibited a diminished though significant interaction with PR and an enhanced binding affinity for AR as compared with LNG, indicating that 5 alpha-reduction of LNG increases its affinity for AR. The most striking finding was that further reduction of the 5 alpha-LNG molecule at C-3 abolished its binding activity to PR, AR, and even to ER. The overall data provides a plausible explanation for the lack of estrogen agonistic action of LNG and for its potent progestational and androgenic effects.

Steroid hormone binding in the Harderian gland of birds: characteristics of the androgen, estrogen, and progestin receptors of Anas platyrhynchos and Gallus domesticus

A series of experiments was carried out in immature female chicks and ducks to establish whether the avian Harderian gland contains specific receptors for sex steroids. Cytosol preparations of Harderian glands were submitted to hormone saturation analysis using radiolabeled estradiol, ORG-2058, and dimethylnortestosterone as ligands. In addition, the sedimentation characteristics of the hormone-receptor complexes were studied by ultracentrifugation of linear sucrose gradients. The presence of high affinity binding sites for estrogens (Kd = 2.4 and 1.6 nM), progestins (0.8 and 1.0 nM), and androgens (1.0 and 1.0 nM) was indicated in the chick and duck glands, respectively. The sedimentation coefficients were 7-7.5 S, 7-8 S, and 8 S for estrogen, progestin, and androgen receptor-ligand complexes, respectively. The concentration of the androgen receptor was significantly higher in chick than in duck Harderian glands whereas the estrogen and progestin receptor concentrations were similar in both species. A striking finding was the presence of progestin receptors, which apparently do not exist in the glands of many mammals. Priming with estrogens did not modify the concentration of ORG-2058 binding sites in either species studied, indicating that gland progestin receptor is not estrogen-regulated. Overall the data suggest intracellular mechanisms whereby circulating gonadal hormones regulate avian Harderian gland function.

Steroid hormone receptors and the sexual phenotype of the Harderian gland in hamsters

To investigate the participation of intracellular steroid hormone receptors in the sexual transformation process of the Harderian gland, a series of experiments were undertaken in adult golden hamsters. The invitro labelling of cytosolic steroid-binding sites with appropriate radioligands revealed the presence of androgen, oestrogen and glucocorticoid but not progestin receptors in the glands from animals of both sexes. The androgen receptor of the female gland was further characterized because it was found to be the predominant intracellular steroid receptor. Studies of binding kinetics using [3H]7 alpha,17 alpha-dimethyl-17 beta-hydroxy-4-oestren-3-one (DMNT) as ligand, demonstrated a high affinity androgen-binding site with an apparent dissociation constant (Kd) of 0.7 nmol/l and maximal saturation binding capacity of 84.0 +/- 3.0 (S.D.) fmol/mg protein. Specificity of the androgen receptor was assessed by displacement analysis; DMNT, 5 alpha-dihydrotestosterone, testosterone and 3 alpha-androstanediol were efficient competitors for the androgen-binding site, while oestradiol-17 beta, progesterone and dexamethasone exhibited very little, if any, competitive potency. The sedimentation coefficient of the androgen receptor in sucrose density gradients was 8-9 S. These data indicate that the physicochemical characteristics of the androgen receptor from the female gland are similar to those previously described in the male gland. The striking observation of a complete lack of oestrogen-inducible and oestrogen-insensitive progestin receptors in glands cytosol, even after stimulation with cholera toxin, adds further support to the concept that the androgen receptor is the key molecule mediating the hormone-induced sexual transformation of the Harderian gland in this species.

The metabolism of 19-nor contraceptive progestins modulates their biological activity at the neuroendocrine level

In this communication, a series of studies from our laboratory dealing with the mechanism of action of 17 alpha-ethinyl derivatives of 19-nor testosterone are reviewed. The administration of norethisterone (NET) to long-term castrated female rats induces the nuclear translocation of pituitary estradiol receptors and is followed by some estrogenic-like effects at the hypothalamic-pituitary unit. It is established that an A-ring reduced metabolite of NET, the 3 beta,5 alpha-tetrahydro NET derivative, is responsible for the observed in vivo estrogenic effects of the parent compound. 3 beta,5 alpha-NET binds to the estrogen receptor and is efficient in inducing the pituitary estrogen-dependent progesterone receptor and in increasing the uterine weight in long-term castrated rats. Furthermore, administration of 3 beta,5 alpha-NET and the 5 alpha-reduced metabolite of NET (5 alpha-NET) are able to inhibit the release of gonadotropins in the castrated animal to a greater extent than NET. Moreover, pretreatment with tamoxifen, an estrogen binding site competitor, results in a significant diminution of the antigonadotropic potency of 3 beta,5 alpha-NET but not of the 5 alpha-NET, which is only inhibited by the administration of cyproterone acetate. These findings underline the importance of the metabolic rate of NET for the expression of its biological effects at the hypothalamic-pituitary unit.

Hormone regulation of the rodent Harderian gland: binding properties of the androgen receptor in the male golden hamster

Studies were conducted in castrated golden hamsters to assess whether sexual dimorphism and sensitivity to sex steroid hormones in the rodent Harderian gland are mediated by an interaction of androgens with specific intracellular receptors. Physical properties, binding kinetics and stereospecificity of the androgen receptor were analysed using [3H]mibolerone as the radioligand. The presence of [3H]mibolerone-androgen receptor complexes with a sedimentation coefficient of 7-8S was demonstrated in Harderian gland cytosol by a linear sucrose gradient ultracentrifugation technique using a vertical rotor. Kinetic analysis revealed an androgen-binding site with an apparent dissociation constant of 0.3 +/- 0.07 (S.D.) nmol/l and a saturation binding capacity of 113 +/- 15 fmol/mg protein. Displacement studies indicated that unlabelled mibolerone, methyltrienolone, 5 alpha-dihydrotestosterone and testosterone were efficient competitors for the androgen-binding sites, while progesterone, 17 beta-oestradiol, dexamethasone, dehydroepiandrosterone, ethiocholanolone and 5 alpha-16-androsten-3-one were not. Experiments in longterm castrated animals revealed that the Harderian gland androgen receptor concentration and sedimentation coefficient remained unmodified. The results of these studies were interpreted as demonstrating the presence of a specific high-affinity intracellular androgen receptor in the male hamster Harderian gland.

A-ring reduction enhances the antigonadotropic potency of norethisterone

To assess whether structural modifications on the A-ring of norethisterone (NET) could modify its antigonadotropic potency, comparative studies using NET, 5 alpha-dihydro NET (5 alpha-NET) and its 3 beta,5 alpha and 3 alpha,5 alpha tetrahydro derivatives in castrated adult rats were undertaken. The antigonadotropic effect of these compounds was evaluated by measuring the serum and pituitary immunoreactive concentrations of LH and FSH following their chronic sc administration to animals depleted of progesterone receptors. The results demonstrated that 3 beta,5 alpha-NET and 5 alpha-dihydro-NET exhibited a significantly greater gonadotropic inhibiting activity as compared with that of their parent compound. The simultaneous administration of tamoxifen with 3 beta,5 alpha-NET resulted in a significant diminution of its antigonadotropic potency, particularly for LH. These data indicate that the potent antigonadotropic effect of 3 beta,5 alpha-NET metabolite was mediated via oestrogen receptors. The LH inhibitory activity of 5 alpha-dihydro-NET was not suppressed by the non-steroidal antioestrogen administration, thus suggesting that 5 alpha-NET might exert its effect via androgen receptors. The overall data were interpreted as demonstrating that metabolic conversion products of NET exhibit potent antigonadotropic effect. The data are consistent with an A-ring enhancement of the antigonadotropic potency of this synthetic progestin and open an alternate approach to the development of fertility regulating agents.

Evidence that a non-aromatizable metabolite of norethisterone induces estrogen-dependent pituitary progestin receptors

Neutral reduced metabolites of norethisterone (NET) specifically interact with intracellular estrogen receptors in target organs. To determine if this interaction can effectively initiate estrogen-dependent cellular responses, the effects of an A-ring-reduced NET derivative upon the induction of cytosol-located pituitary progestin receptors (PR) and uterine growth were studied in adult castrated female rats. Different doses of 17 alpha-ethynyl-5 alpha-estran-3 beta, 17 beta-diol (3 beta, 5 alpha-NET) were s.c. administered to ovariectomized animals for 6 days. 17 beta-Estradiol (E2) and oil-treated rats served as experimental controls. Pituitary PR were labeled in vitro by a post-gradient technique using [3H]ORG-2058 as the ligand. PR binding specificity was determined by the use of an excess of radioinert steroids. The results demonstrated that administration of 3 beta, 5 alpha-NET induced specific 8-9S pituitary cytosol PR in a dose-dependent manner. Binding properties of the 3 beta, 5 alpha-NET-induced progestin binding sites (Kd = 1.0 X 10(-9) M; NBS = 1.2 X 10(-9) M) appear indistinguishable from those induced by E2. In addition, 3 beta, 5 alpha-NET administration resulted in a significant increase in uterine weight at the expense of myometrium and endometrium growth in a similar fashion to that observed in the E2-treated group. When 3 alpha, 5 alpha-epimeric alcohol (3 alpha, 5 alpha-NET) was administered, induction of pituitary PR and uterine growth were also observed although to a lesser extent. Inasmuch as the results demonstrate that neutral non-aromatizable NET metabolites induce biochemical and morphological estrogenic responses, they offer an alternative explanation for the mechanism of estrogen-like action of this synthetic contraceptive progestin.

Stereospecificity of the intracellular binding of norethisterone and its A-ring reduced metabolites

The interaction of norethisterone (NET) and four A-ring reduced metabolites of NET with cytosol receptors for progesterone (PR), androgen (AR), and estrogen (ER) was investigated. Cytosol preparations from: uteri of adult estrogen-primed castrated rats, ventral prostates of adult castrated rats and uteri of immature rats were used as the source of PR, AR, and ER respectively. 3H-Labeled ORG-2058, R-1881, and 17 beta-estradiol were used as the radioligands. The results of competitive studies disclosed that: the most efficient competitor for PR binding sites was NET (Ki = 1.1 X 10(-7) M) followed by 5 alpha-dihydro NET (5 alpha-NET), whereas the 3 alpha,5 alpha; 3 beta,5 alpha and 3 alpha,5 beta-tetrahydro NET derivatives were ineffective the most efficient competitor for AR binding sites was 5 alpha-NET (Ki = 1 X 10(-8), immediately followed by NET, while the three tetrahydro NET derivatives were not competitors and remarkable competition for ER binding sites was only exhibited by the 3 beta,5 alpha-tetrahydro NET derivative (Ki = 4.6 X 10(-8) M) and to a lesser extent by its 3 alpha,5 alpha-epimeric alcohol, while NET and 5 alpha-NET were completely ineffective. These findings demonstrate the stereospecificity of the intracellular binding of NET and its reduced metabolites with cytosol steroid putative receptors, and provide biochemical support to the understanding of the variety of hormone-like effects observed after the in vivo administration of NET.

Interaction of medroxyprogesterone acetate with cytosol androgen receptors in the rat hypothalamus and pituitary

The binding of medroxyprogesterone acetate (MPA) with cytosol androgen receptors from rat pituitary and hypothalamus was studied. The pituitary and hypothalamic cytosol androgen receptors from adult castrated female rats were in vitro labeled using 3H natural (testosterone (T) and 5 alpha-dihydrotestosterone (DHT] and [3H]synthetic (methyltrienolone) androgens as radioligands. The [3H]androgen-receptor complexes sedimented with a coefficient of 8S in linear sucrose gradients. When incubated with an excess of radioinert MPA, specific binding was abolished indicating interaction of MPA with androgen receptors. Furthermore specific [3H]MPA-androgen cytosol receptor complexes could be identified in these neuroendocrine tissues when a post-gradient receptor labeling technique was used in the absence or presence of radioinert MPA, DHT, and triamcinolone acetonide. A study of binding kinetics disclosed that the equilibrium dissociation constant and saturation binding capacity for the MPA binder, were similar to those exhibited by DHT binding to androgen receptors in both studied tissues under identical experimental conditions. The overall results were interpreted as demonstrating that MPA interacts with cytosol steroid receptors other than those of progesterone in the rat hypothalamus and anterior pituitary. The data are consistent with MPA binding to androgen receptors.