Acephate interferes with androgen synthesis in rat immature Leydig cells

Acephate is an organophosphate pesticide. It is widely used. However, whether it inhibits androgen synthesis and metabolism remains unclear. In the current study, we investigated the effect of acephate on the inhibition of androgen synthetic and metabolic pathways in rat immature Leydig cells after 3-h culture. Acephate inhibited basal androgen output in a dose-dependent manner with the inhibition starting at 0.5 μM. It significantly inhibited luteinizing hormone and 8-Br-cAMP stimulated androgen output at 50 μM. It significantly inhibited progesterone-mediated androgen output at 50 μM. Further study demonstrated that acephate down-regulated the expression of Hsd3b1 and its protein at ≥ 0.5 μM, Lhcgr at 5 μM and Star at 50 μM. Acephate directly blocked rat testicular HSD3B1 activity at 50 μM. Acephate did not affect other androgen synthetic and metabolic enzyme activities as well as ROS production, proliferation, and apoptosis of immature Leydig cells. In conclusion, acephate targets LHCGR, STAR, and HSD3B1, thus blocking androgen synthesis in rat immature Leydig cells and HSD3B1 is being the most sensitive target of acephate.

Luteinizing hormone acts at the hippocampus to dampen spatial memory

Luteinizing hormone (LH) rises dramatically during and after menopause, and has been correlated with an increased incidence of Alzheimer's disease and decreased memory performance in humans and animal models. To test whether LH acts directly on the dorsal hippocampus to affect memory, ovariectomized female rats were infused with either the LH-homologue human chorionic gonadotropin (hCG) or the LH receptor antagonist deglycosylated-hCG (dg-hCG). Infusion of hCG into either the lateral ventricle or the dorsal hippocampus caused significant memory impairments in ovariectomized estradiol-treated females. Consistent with this, infusion of the LH antagonist dg-hCG into the dorsal hippocampus caused an amelioration of memory deficits in ovariectomized females. Furthermore, the gonadotropin-releasing hormone antagonist Antide, failed to act in the hippocampus to affect memory. These findings demonstrate a significant role for LH action in the dorsal hippocampus in spatial memory dysfunction.

THE RELATIONSHIP BETWEEN PHYSICAL-CHEMICAL CHARACTERISTICS AND BIOLOGICAL ACTIVITY OF PEPTIDE 562—572 OF LUTEINIZING HORMONE RECEPTOR MODIFIED BY DECANOYL RADICALS AT THE N- AND C-TERMINI

Lipophilic derivatives of peptides corresponding to the cytoplasmic regions associated with the G-protein coupled receptors (GPCRs) are capable of functioning as an intracellular agonist. Previously, we have shown that peptides corresponding to region 562—572 of luteinizing hormone receptor (LHR) and modified by decanoate and palmitate at the C-terminus activate adenylyl cyclase (AC) in the testes of rats. The stimulating effect of peptide 562—572 modified by decanoates at the N- and C-termini (IV) peaked at a concentration of 10(–5) M and then subsequently decreased with increasing concentration. We hypothesized that this may be due to ability of the peptide IV to micelle formation. To test this suggestion, we examined the relationship between biological activity, hydrophobicity and ability to micelle formation for peptide IV and other acylated derivatives of peptide 562—572 including the derivatives containing C-terminal decanoate (III) and palmitate (VI). It has been shown that the stimulating effect of peptide IV at a concentration of 10(–5) M on AC activity in the plasma membranes of rat testes and ovaries is only slightly inferior to that of peptide VI and superior to the corresponding effect of peptide III. The effect of peptide IV at a concentration of 10–3 M was reduced by 20—27 % and amounted to 50—51 and 87—88 % of that of peptides VI and III, respectively. Despite the high hydrophobicity, the peptide IV had abnormally low retention time in reverse-phase HPLC when it was eluted from the Nucleosil C8 column, even lower than that of unmodified peptide 562—572. However, with increasing concentration of trifluoroacetic acid in the eluent from 0.1 to 0.5 % causing the destruction of micelle-like structures, the retention time of the peptide IV was significantly increased, whereas it remained unchanged in the case of the other peptides. Surface tension of aqueous solution of peptide IV insignificantly decreased with the increase of its concentration, but then, at peptide concentration of 710(–6) M, the sharp decline and the plateau were found, which indicates the beginning of the formation of micelles. Thus, at concentration of 10(–5) M and higher the peptide IV forms micelles which prevents its interaction with the receptor. The ability of GPCR-peptides to self-aggregation and micelle formation should be taken into account when developing their membrane-active analogues.

D-Aspartic acid stimulates steroidogenesis through the delay of LH receptor internalization in a mammalian Leydig cell line

PURPOSE

Recent experimental evidence on non-mammalian animal models showed that D-Aspartic acid (d-Asp) administration increases testosterone levels through upregulation of StAR in Leydig cells. In this study, we aimed to investigate in vitro the signaling pathway associated with d-Asp stimulation in MA-10 murine Leydig cells.

METHODS

MA-10 cells were stimulated with different concentrations of d-Asp, in presence or absence of hCG. Then total testosterone (T) levels in the culture medium were evaluated by electrochemiluminescence immunoassay, and StAR and LHR protein expressions were quantified by the means of Western blotting. LHR cellular localization after hormonal stimulation was assessed by immunofluorescence.

RESULTS

Stimulation with the sole d-Asp did not induce any relevant increase of T release from cultured cells. On the other hand, stimulation with hCG induced significant increase of T (P = 0.045). Concomitant stimulation with hCG and d-Asp, at the concentration of 0.1 and 1 nM, induced additional and significant increase of released T (P = 0.03 and P = 0.04, respectively). StAR protein levels increased after concomitant stimulation with hCG and d-Asp 0.1 nM, compared with stimulation with the sole hCG (P = 0.02), whereas no variation in LHR protein expression was observed. Finally, d-Asp attenuated displacement of LHR staining, from cell membrane to cytoplasm, subsequent to hCG stimulation.

CONCLUSIONS

In this study, we confirmed a steroidogenic role for d-Asp, in concert with hCG, on murine Leydig cells, which is mediated by an increase in StAR protein levels. In addition, we showed that the possible mechanism subtending the effect of d-Asp could rely on the modulation of LHR exposure on the cell membrane.

[New achievements in the development and study of the mechanisms of action of the low molecular weight agonists of receptors of the thyroid-stimulating and the luteinizing hormones]

Pituitary glycoprotein hormones, luteinizing (LH) and thyroid-stimulating (TSH), exert their regulatory effects on cells through the G protein-coupled receptors, specifically binding to their extracellular domain. There is an alternative way of activation of LH and TSH receptors, when low molecular weight organic molecules bind to an allosteric site of the receptors which is localized within their transmembrane channel. Low molecular weight agonists have many advantages over glycoprotein hormones, among them a high efficiency not only in the case of the parenteral but also in the oral administration, low immunogenicity, chemical stability, and a low cost. Unlike pituitary glycoprotein hormones with the agonistic activity, low molecular weight compounds may be either agonists or inverse agonists and neutral antagonists. Recently it was shown that low molecular weight agonists of LH receptor are able to stimulate its mutant forms by restoring the processing of receptor in a cell, and by increasing its sensitivity to LH, which is important for the treatment of reproductive dysfunctions caused by mutations in the LH receptor. This review summarizes the recent achievements that are linked with the development of low molecular weight regulators of TSH and LH receptors and the study of their mechanisms of action. It also presents the author' data concerning the creation of new low molecular weight agonists of LH receptor based on the thienopyrimidine structure, which are effective both in vitro, and in vivo in different ways of administration.

Use of hecate-chorionic gonadotropin beta conjugate in therapy of lutenizing hormone receptor expressing gonadal somatic cell tumors

Improvement of cancer treatment is a major challenge of medical research. Despite the immense efforts made in the improvement of diagnosis and treatment, cancer remains a major concern and cause of morbidity and mortality. Most of the modern anti-neoplastic therapies have severe side effects, and tumor cells often develop drug resistance. There is promise in the new generation of treatments (gene therapy, immunotherapy, vaccines, etc.) that are under development, but the efficacies and side effects of such therapies have so far been disappointing. Receptor-based therapies are not new, but many normal cells also present the same receptors reducing the specificity of such approaches. Several lytic peptides have been investigated because of they appear to kill cancer cells due to changes of their membrane potential. Thus, linking receptor-specific ligands to lytic peptides is expected to augment the specificity of targeting and decrease the toxicity of lytic peptides on normal cells. One such polypeptide is hecate (an analogue to the bee venom main component, melittin) that preferentially kills cancer cells at low doses. When this peptide is fused with the 81-95 amino acid fragment of chorionic gonadotropin-beta (CGbeta) subunit (hecate-CGbeta), it targets cells expressing luteinizing hormone receptor (LHR), even at very low doses, or when LHR is expressed at low level. Our recent data showed that this peptide conjugate is efficient in destroying LHR-positive cells in xenografts and more importantly in transgenic mouse models developing LHR-positive somatic cell tumors in gonads. The mechanism of action of hecate-CGbeta after binding to LHR is destruction of cell membranes resulting in rapid cell death by necrosis with minimal side effects. This review summarizes our findings on the action of this novel peptide and considers the future potential of this family of targeting peptides in the treatment of neoplasias.

Manganese acts centrally to activate reproductive hormone secretion and pubertal development in male rats

Manganese (Mn) is an important element for normal growth and reproduction. Because Mn accumulates in the hypothalamus and is capable of stimulating puberty-related hormones in female rats, we assessed whether this metal could cause similar effects in male rats. We have demonstrated that MnCl2, when administered acutely into the third ventricle of the brain, acts dose dependently to stimulate luteinizing hormone (LH) release. Furthermore, there was a dose dependent stimulation in the secretion of LH-releasing hormone (LHRH) from the medial basal hypothalamus in vitro, and administration of an LHRH receptor antagonist in vivo blocks Mn-induced LH release. To assess potential chronic effects of the metal, male pups were supplemented with 10 or 25 mg MnCl2 per kg by gastric gavage from day 15 until days 48 or 55, at which times developmental signs of spermatogenesis were assessed. Results demonstrate that while significant effects were not observed with the 10 mg/kg dose, the animals receiving the 25 mg/kg dose showed increased LH (p<0.05), FSH (p<0.01) and testosterone (p<0.01) levels at 55 days of age. Furthermore, there was a concomitant increase in both daily sperm production (p<0.05) and efficiency of spermatogenesis (p<0.05), demonstrating a Mn-induced acceleration in spermatogenesis. Our results suggest Mn is a stimulator of prepubertal LHRH/LH secretion and may facilitate the normal onset of male puberty. These data also suggest that the metal may contribute to male precocious pubertal development should an individual be exposed to low but elevated levels of Mn too early in life.

Targeted ablation of prostate carcinoma cells through LH receptor using Hecate-CGbeta conjugate: functional characteristic and molecular mechanism of cell death pathway

A Hecate-CGbeta conjugate (lytic peptide and beta-chorionic gonadotropin) selectively destroyed cells possessing LH receptors. This study described functional characteristics of the conjugate and the molecular mechanism of the cell death pathway in prostate cancer cells. Based on in vitro studies, we conclude that the conjugate kills cells possessing luteinizing hormone receptors (LHR) faster than Hecate alone. Competitive studies have shown that blocking of LHR by preincubation with chorionic gonadotropin (100 ng/ml) reduced toxicity of the conjugate in low concentrations. Further studies have also shown that the conjugate in treated cells both did not induce internucleosomal DNA fragmentation and did not induce morphological changes in cells characterized as having apoptotic features. These results proved that cells died by necrosis rather than apoptosis after the conjugate treatment.

3-(2-Aminoalkyl)-1-(2,6-difluorobenzyl)-5- (2-fluoro-3-methoxyphenyl)-6-methyl- uracils as Orally Bioavailable Antagonists of the Human Gonadotropin Releasing Hormone Receptor

Uracils possessing N-3 side chains derived from various amino alcohols were designed and synthesized as potent human gonadotropin releasing hormone receptor antagonists. The compounds herein presented displayed superior metabolic stability than their predecessor molecules. Selected compounds from this series featured good oral bioavailability in mice and cynomolgus monkeys.

Development of a fluorescence based high throughput assay for antagonists of the human chorionic gonadotropin receptor extracellular domain: analysis of peptide inhibitors

A simple method for prompt fluorescent detection of inhibitors of human chorionic gonadotropin (hCG) binding to the extracellular domain of the human luteinizing hormone/chorionic gonadotropin (hLH/CG) receptor was developed for high throughput screening (HTS). Construction and analysis of a recombinant phage that displays the extracellular binding domain of the hLH/CG receptor on its surface and specifically binds hCG was previously described. To facilitate the identification of molecules that disrupt the interaction of hCG with its receptor, a method for prompt fluorescent detection of these phage bound to hCG was developed. This technique is extremely sensitive and employs fluorescent labels (PBXL dyes) that are derived from red and blue-green algae. Antibodies labeled with PBXL dye were able to specifically detect phage that display the extracellular domain of the hLH/CG receptor when bound to hCG immobilized in 96-well microplates. Decreases in fluorescence correlate with the concentration of exogenous hCG or hCG antagonists in the assay. This prompt fluorescence detection assay was optimized in a 96-well format as a model system for HTS applications that target the receptors for the group of hormones known as the gonadotropins. Low-affinity molecules that disrupt binding of the phage-displayed receptor extracellular domain to hCG can be rapidly identified in this high throughput screen.

Desensitization of the luteinizing hormone/choriogonadotropin receptor in ovarian follicular membranes is inhibited by catalytically inactive ARNO(+)

We have investigated the participation of endogenous ADP-ribosylation factor (ARF) nucleotide-binding site opener (ARNO) in desensitization of the luteinizing hormone/choriogonadotropin (LH/CG) receptor, independent of receptor internalization, using a cell-free plasma membrane model. We recently showed that the addition of recombinant ARNO promotes binding of beta-arrestin1 to the third intracellular (3i) loop of the active LH/CG receptor, thereby reducing the ability of the receptor to activate the stimulatory G protein and signal to adenylyl cyclase. In the present report we determined whether ARNO is detectable in follicular membranes and whether the catalytically inactive E156K ARNO mutant, containing a mutation in the Sec7 domain, can act in a dominant negative manner to block LH/CG receptor desensitization. Results show that ARNO is readily detected in follicular membranes and that levels of membrane-associated ARNO increase with follicular maturation. The addition of catalytically inactive E156K ARNO blocks both the release of beta-arrestin1 from its membrane docking site, based on Western blot analysis, and development of LH/CG receptor desensitization. We also investigated whether a point mutation in the pleckstrin homology (PH) domain of ARNO (R280D), which blocks binding of phosphoinositides like phosphatidylinositol 3,4,5-trisphosphate and phosphatidylinositol 4,5-bisphosphate (PIP(2)) but not catalytic activity, disrupts LH/CG receptor desensitization. R280D ARNO neither promotes nor inhibits LH/CG receptor desensitization, consistent with a requirement of the PH domain of ARNO for its association with the plasma membrane. LH/CG receptor activation of ARNO is not mediated by activation of phosphatidylinositol 3-kinase (PI 3-kinase) or by G protein beta gamma subunits. Taken together, these results suggest that LH/CG receptor promotes beta-arrestin1 release from its membrane docking site to bind to the 3i loop of the LH/CG receptor via activation of membrane delimited endogenous ARNO. As ARNO activation is independent of PI 3-kinase and G beta gamma, our results are consistent with a role for PIP(2) in receptor-stimulated ARNO activation.

Circulating luteinizing hormone receptor inhibitor(s) in boys with chronic renal failure

Patients with chronic renal failure frequently have hypogonadism. To elucidate the molecular mechanisms involved, we tested the ability of serum from these patients to inhibit recombinant human luteinizing hormone receptors. Using a cell line expressing functional human luteinizing hormone receptors, we found that adenosine 3'5'-monophosphate (cAMP) production was markedly inhibited by sera from the patients, but not by sera from healthy subjects. Inhibition of cAMP production was associated with inhibition of 125I-human chorionic gonadotropin binding. Inhibition of LH receptors by sera from patients correlated with the glomerular filtration rate and after renal allograft transplantation, decreased. Fractionation of serum samples indicated the receptor-inhibiting activity in proteins of molecular weights from 30,000 to 60,000 Daltons. When characterized and purified, the factor responsible may well be a new LH receptor antagonist of clinical significance.

Rat luteinizing hormone receptor messenger ribonucleic acid expression and luteolysis: inhibition by prostaglandin F2 alpha

To elucidate the mechanisms by which prostaglandin F2 alpha (PGF2 alpha) permanently inhibits LH-dependent steroidogenesis during luteolysis, we investigated the effect on luteal LH receptor mRNA levels of the stable PGF2 alpha analogue cloprostenol injected into adult pseudopregnant rats on different days during the luteal period. After treatment, LH receptor mRNA expression was determined by RNase protection assay. Twelve hours after cloprostenol injection on Day 8 of pseudopregnancy, the luteal LH receptor mRNA levels were drastically reduced (0.95 +/- 0.18 fmol mRNA/microgram DNA, p < 0.01) as compared with those in untreated controls (12.3 +/- 1.3 fmol mRNA/microgram DNA) or in corresponding controls given an injection of saline (8.8 +/- 0.7 fmol mRNA/microgram DNA) (n = 6-8 per group). At 24 h the levels rose to 4.3 +/- 0.8 fmol mRNA/ microgram DNA but were still significantly decreased compared to control values. Forty-eight hours after cloprostenol injection, the luteal LH receptor mRNA levels were not significantly different from control levels; but if the rats received an injection every twelfth hour, levels were significantly decreased compared to those in controls. When PGF2 alpha was injected, LH receptor mRNA levels were reduced in the same manner as seen after cloprostenol injection. LH receptor mRNA of young corpora lutea (CL) (Day 3) was more resistant to down-regulation by cloprostenol than that of CL of the mid (Day 8)-or late (Day 11) luteal phase. On the eighth day of pseudopregnancy, serum progesterone levels were decreased at 0.5 h after cloprostenol injection and fell further at 3 h; serum 20 alpha-dihydroprogesterone levels were first increased at 7 h after cloprostenol injection. We conclude that luteal LH receptor mRNA expression is under direct regulatory control by PGF2 alpha in a both time-and dose-dependent manner and thereby may decisively contribute to the inhibition of LH responsiveness during luteolysis.

Identification of luteinizing hormone receptor binding inhibitor in bovine corpora lutea

A 7000 g supernatant, obtained during the purification of luteinizing hormone (LH) receptor from bovine corpora lutea homogenate, was concentrated by ultrafiltration. The filtrate, containing < 50,000 molecular weight material, exhibited LH receptor binding inhibitor (LH-RBI) activity. The filtrate was ultrafiltered sequentially through Amicon PM-10, PM-30 and UM-2 filters to yield a LH-RBI-containing fraction in the higher molecular weight range of 30,000-10,000 and a LH-RBI-containing fraction in the lower molecular weight range of 10,000-1000. The higher molecular weight LH-RBI fraction was purified on Sephadex G-25 and the lower molecular weight LH-RBI fraction was purified on Sephadex G-50. Both the high- and the low-molecular-weight LH-RBI species inhibited the binding of 125I-labeled human chorionic gonadotropin (hCG) to bovine corpora lutea and to rat Leydig cell membrane receptors. Similarly, the production of testosterone by hCG-stimulated rat Leydig cells was inhibited in a dose-response manner by both the high- and the low-molecular-weight LH-RBI species. The LH-RBI activity in the low-molecular-weight species was stable at 4 degrees C for up to 6 months and at temperatures up to 90 degrees C for 15 mins, whereas the LH-RBI activity of the high-molecular-weight species was stable at 4 degrees C for 15 months and unstable at 60 degrees C after 15 min. The 7000 g supernatant provided a much-needed source to obtain larger than previously reported quantities of LH-RBI for isolation as well as for structure and function studies.

Metal chelators reverse the action of hydrogen peroxide in rat luteal cells

In rat luteal cells hydrogen peroxide (H2O2) interferes with the functional coupling of the luteinizing hormone (LH) receptor and blocks cAMP-dependent progesterone production. To test if this action of H2O2 is dependent on the generation of hydroxyl radicals, the effects of metal chelators and hydroxyl radical scavengers were evaluated. The heavy metal chelator o-phenanthroline prevented H2O2 inhibition of LH-sensitive cAMP and progesterone accumulation and depletion of ATP. Tetrakis(2-pyridylmethyl)ethylenediamine (TPEN) partially reversed inhibition of cAMP accumulation by H2O2 and completely prevented H2O2-induced ATP depletion, but had no effect on H2O2 inhibition of progesterone synthesis. Three other heavy metal chelators, deferoxamine, bathocuproinedisulfonic acid (BA) and penicillamine, as well as hydroxyl radical scavengers ethanol, thiourea and N-(2-mercaptopropionyl)glycine (MPG), had no effect on the luteolytic actions of H2O2. Differential effects of the chelators were probably due to differences in their cell permeability and subcellular compartmentalization. We conclude that metal chelators block the luteolytic actions of H2O2 by a mechanism probably linked to inhibition of hydroxyl radical generation.

Tyrphostins inhibit follicle-stimulating hormone-mediated functions in cultured rat ovarian granulosa cells

FSH induces the expression of cholesterol side-chain cleavage cytochrome P450 (P450scc) in rat ovarian granulosa cells. The present study reveals that the tyrphostin AG18, a member of novel protein tyrosine kinase inhibitors, can arrest the FSH-induced synthesis of P450scc with an apparent IC50 of 30 microM. Total inhibition of P450scc expression was achieved at 80 microM AG18. AG18-mediated inhibition of P450scc was also observed when the enzyme was induced by prostaglandin E2, forskolin, or 8-bromo-cAMP. Studies examining functional LH receptors showed that the tyrphostin inhibits the expression of FSH-induced LH receptors. The drug did not affect FSH-induced cAMP accumulation, suggesting that it may interfere with the flow of FSH signal transduction at a site distal intracellular accumulation of cAMP. Control experiments demonstrated that the inhibitory action of AG18 was reversible, did not hamper total protein synthesis in the cells, and did not change the adenine nucleotide (ATP:ADP:AMP) ratio or their levels in the treated cells. A cell-free assay of cAMP-dependent protein kinase showed that the tyrphostin AG18 does not affect this enzyme activity up to concentrations above 200 microM. These results suggest that a putative tyrosine kinase activity is involved in the gonadotropin signal transduction pathway leading to expression of functional genes in ovarian cells.

Isolation of luteinising hormone receptor binding inhibitor from bovine corpus luteum

A luteinising hormone receptor binding inhibitor (LHRBI) has been purified from bovine corpus luteum (CL). Steroid-free extract of the CL was subjected to successive chromatographies on Sephadex G-50, Q-Sepharose, Orange A dye and metal chelate affinity columns followed by high performance-reverse phase and gel filtration columns. Purification was monitored by the ability of the fractions to inhibit the binding of 125I-human chorionic gonadotropin (hCG) to porcine granulosa cells in vitro. The final isolate showed an 8000-fold enrichment of activity. It was also capable of inhibiting porcine granulosa cell secretion of estradiol and progesterone (P) in vitro. Administration of LHRBI into follicle-stimulating hormone (FSH)-stimulated, immature rats strongly inhibited the ovarian ovulatory response to hCG as revealed by decreased P levels and the number of ova released. The M(r) of LHRBI as assessed by sodium dodecyl sulphate-polyacrylamide gel electrophoresis was ca. 15 kDa and the pI was between 5.0 and 5.5.

Biological mimicry of gonadotropin action by antiidiotypic antibodies to luteinizing hormone: characterization and biological properties

High affinity polyclonal rabbit antibodies to ovine (o) pituitary LH [anti-oLH-immunoglobulin G (IgG) Ab1] were used to immunize young Southdown lambs. Their serum samples as well as those from controls receiving normal rabbit IgG were studied for the presence of anti-Ab1 antibodies. In RIAs using [125I]oLH and affinity-purified Ab1, sera from experimental sheep showed high activity, as expressed in oLH equivalents. These sera also showed ability to compete with [125I]oLH for binding to receptor on pig ovarian and testicular membranes. The antiidiotypic antibodies (Ab2) in experimental sheep sera were purified by successive affinity chromatography on immobilized rabbit normal IgG and immobilized oLH-IgG columns. Ab2-IgG eluted from the latter mimicked oLH in RIAs and RRAs. These purified Ab2 antibodies were also of a stimulatory type, because they elicited progesterone production in rat granulosa cells and collagenase-dispersed rat Leydig cells. This stimulatory action was counteracted by coincubation with anti-oLH-IgG, which would also terminate (oLH) hormone action in a similar manner. The Ab2 antibodies had no effect on oFSH RIA or on the binding of [125I]oFSH to pig ovarian receptors, indicating specificity with respect to LH antigenic structure and function. As can be expected from the choice of the immunogen (polyclonal anti-oLH-IgG), only a small percentage of the true Ab2 population could display biological mimicry of the original antigen (oLH). Their presence in circulation during 6-8 months had no effect on testicular size or body growth. The formation of Ab2 antibodies to rabbit anti-oLH-IgG was also demonstrated in male rats, but these were not purified. In this instance also there was no effect on testicular weight after 6 months of immunization. These results show the feasibility of producing antiidiotypic antibodies that stimulate gonadal function in a manner much like the pituitary gonadotropin (oLH).

Inhibition of luteinizing hormone-human chorionic gonadotropin binding by retinoids in a Leydig cell line

Treatment of K9 mouse Leydig cells with 3 x 10(-6) M retinol (R) and retinoic acid (RA) resulted in 75% and 65% reduction of 125I-labeled hCG binding respectively, when assayed at 35 degrees C. This effect was dose-dependent and was first detected 12 h after initiation of treatment: it was maximal at 48 h for RA. R and RA had no significant effect on the rate of internalization and degradation of 125I-hCG as measured by disappearance of acid-releasable (i.e. surface-bound) radioactivity from the cells and by the appearance of trichloracetic acid-soluble label in the medium. When exposed to increasing concentrations of hCG for 24 h, both retinoid-treated and control cells 'down-regulated' their gonadotropin receptors with the same dose-dependent pattern. The kinetics of reappearance of the receptors was similar for retinoid-treated and control cells, but for treated cells the maximal number of receptors reinitiated at 24 h never exceeded 40% of the values observed with control cells. Scatchard plot analysis confirmed a decrease in hCG receptor number from approximately 26,000 to approximately 6400 and approximately 3500 sites per cell after R and RA treatment. Kd values for 125I-hCG binding were 2 x 10(-10) M, 7.3 x 10(-11) M and 6.9 x 10(-11) M for control, R- and RA-treated cells respectively. On the basis of our data it is likely that retinoid-induced reduction in 125I-hCG binding to K9 Leydig cells is due to decreased receptor synthesis.