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M Luconi

Publications and source records attributed to M Luconi.

17 recordsLinked to original sources
PubMed1999

Identification and characterization of a novel functional estrogen receptor on human sperm membrane that interferes with progesterone effects.

The presence of a novel functional estrogen receptor on the human sperm surface has been demonstrated by using different experimental approaches. Ligand blot analysis of sperm lysates, using peroxidase-conjugated estradiol as probe, identified a specific estradiol-binding protein of approximately 29-kDa apparent molecular mass. The same protein band was also revealed by using alphaH222 antibody, which is directed against the steroid binding domain of the genomic estrogen receptor. The biological effects of estrogen receptor were investigated by analyzing calcium fluxes, tyrosine phosphorylation, and acrosome reaction (AR) in response to 17beta-estradiol (17betaE2) and by measuring the steroid influence on calcium and AR in responses to progesterone (P), a well-known physiological stimulus for human spermatozoa. Our results demonstrate that 17betaE2 induces a rapid and sustained increase of intracellular calcium concentrations ([Ca2+]i). This effect is totally dependent on the presence of extracellular calcium, because it is completely abolished in a calcium-depleted medium. The dose-response curve for calcium increase to 17betaE2 is biphasic with a first component in the nanomolar range (effective concentration 50 = 0.60 +/- 0.12 nmol/L) and a second component in the micromolar range (EC50 = 3.80 +/- 0.26 micromol/L). 17BetaE2 stimulates tyrosine phosphorylation of several sperm proteins, including the 29-kDa protein band, and determines a reduction of calcium response to P, finally resulting in inhibition of P-stimulated sperm AR. Conversely, no direct effect of 17betaE2 is observed on AR. 17BetaE2 effects on calcium are clearly mediated by a membrane receptor, because they are reproduced by the membrane-impermeable conjugate of the hormone BSA-E2 and reduced by sperm preincubation with alphaH222 antibody. Taken together, our results clearly show the presence of a functional surface estrogen receptor, of 29 kDa, on human spermatozoa. This receptor may play a role in the modulation of nongenomic action of P in these cells during the process of fertilization.

Acrosome Reaction↗
PubMed1998

Nongenomic effects of progesterone on spermatozoa: mechanisms of signal transduction and clinical implications.

Progesterone (P) is one of the physiological stimuli of human sperm acrosome reaction. It is present in high levels at the site of fertilization (cumulus oophorus) and has been describe to affect several sperm functions including motility, capacitation and acrosome reaction. The effects of the steroid, which is present in high levels in the cumulus matrix that surrounds the oocyte, are mediated by an increase of intracellular calcium concentrations, efflux of chloride, stimulation of activity of phospholipases and phosphorylation of proteins. These effects are due to activation of a rapid/nongenomic pathway. Two different types of receptors for P, distinct from the genomic ones, have been recently identified on the surface of human spermatozoa. The affinities of P for these receptors are respectively in the nano- and in the micromolar range. Sperm responsiveness to progesterone is impaired in subfertile patients and is strictly correlated to the ability of fertilize the oocyte. In addition, the determination of sperm responsiveness is predictive of fertilizing ability with a positive predictive value of 90% and can be clinically useful for the preliminary assessment of the male partner to select the appropriate assisted reproductive technique.

Calcium↗
PubMed1998

Progesterone stimulates p42 extracellular signal-regulated kinase (p42erk) in human spermatozoa.

Mitogen-activated protein kinases (MAPK), also known as extracellular signal-regulated kinases (ERKs) are cytoplasmic and nuclear serine/threonine kinases involved in signal transduction of several extracellular effectors. Recently, we have demonstrated that ERKs are present in spermatozoa and are involved in the regulation of the process of capacitation. We report here the effect of progesterone, a well-known inducer of the acrosome reaction in mammalian spermatozoa, on the immunolocalization, phosphorylation and activity of ERKs in capacitated human spermatozoa. We demonstrated that short-term incubation of spermatozoa with progesterone induces phosphorylation and activation of ERKs, resulting in redistribution of the proteins from the post-acrosomal region to the equatorial segment within the sperm head. To investigate the role of ERKs on the biological effects of progesterone, we used the MAPK cascade inhibitor PD098059, which strongly inhibited progesterone-induced activation of ERK-2. This compound did not inhibit progesterone-induced acrosome reaction, although it prevented redistribution of the enzyme to the equatorial region of the sperm head. These results suggest that the two processes, although temporally related, are independent. In conclusion, we provide new insight into the signal transduction pathways involved in the non-genomic action of progesterone in spermatozoa and suggest a possible involvement of ERKs in the process of fertilization.

Acrosome↗
PubMed1998

Extracellular signal-regulated kinases modulate capacitation of human spermatozoa.

Recent evidence indicates the presence of p21 Ras and of a protein with characteristics similar to mitogen-activated protein kinases (MAPKs), also known as extracellular signal-regulated kinases (ERKs), in mammalian spermatozoa, suggesting the occurrence of the Ras/ERK cascade in these cells. In the present study we investigated the subcellular localization of ERKs and their biological functions in human spermatozoa. Immunohistochemistry, immunofluorescence, confocal microscopy, and immunoelectron microscopy demonstrated localization of ERKs in the postacrosomal region of spermatozoa. After stimulation of acrosome reaction with the calcium ionophore A23187 and progesterone, ERKs were mostly localized at the level of the equatorial region, indicating redistribution of these proteins in acrosome-reacted spermatozoa. Two proteins of 42 and 44 kDa that are tyrosine phosphorylated in a time-dependent manner during in vitro capacitation were identified as p42 (ERK-2) and p44 (ERK-1) by means of specific antibodies. The increase in tyrosine phosphorylation of these proteins during capacitation was accompanied by increased kinase activity, as determined by the ability of ERK-1 and ERK-2 to phosphorylate the substrate myelin basic protein. The role of this activity in the occurrence of sperm capacitation was also investigated by using PD098059, an inhibitor of the MAPK cascade. The presence of this compound during in vitro capacitation inhibits ERK activation and significantly reduces the ability of spermatozoa to undergo the acrosome reaction in response to progesterone. Since only capacitated spermatozoa are able to respond to progesterone, these data strongly indicate that ERKs are involved in the regulation of capacitation. In summary, our data demonstrate the presence of functional ERKs in human spermatozoa and indicate that these enzymes are involved in activation of these cells during capacitation, providing new insight in clarifying the molecular mechanisms and the signal transduction pathways of this process.

Acrosome↗
PubMed1998

Identification and characterization of functional nongenomic progesterone receptors on human sperm membrane.

The presence of functional nongenomic progesterone (P) receptors in human spermatozoa has been investigated by equilibrium binding studies in intact spermatozoa, ligand blot and Western blot analysis of sperm lysates, as well as determination of the effects of the steroid on sperm intracellular Ca2+ concentrations. Binding experiments were performed using progesterone-11alpha-glucuronide-[125I]iodotyramine as tracer. Computer analysis of competition curves using different steroids as competitors indicated the presence of two distinct binding sites for P. The high affinity site (Kd in the nanomolar range) appears to be specific for P, whereas the low affinity one (Kd in the micromolar range) binds with equal affinity 11beta-hydroxyprogesterone (11betaOHP) and 17alpha-hydroxyprogesterone (17alphaOHP). A significant correlation exists among affinity constants (as determined by binding studies) and EC50 values for the effects of P, 11betaOHP, and 17alphaOHP on intracellular Ca2+ in fura-2-loaded spermatozoa, strongly indicating the involvement of P-binding sites in the biological effect of the steroid. In particular, dose-response curves for P were biphasic, with an EC50 in the nanomolar range and another in the micromolar range. Conversely, curves for 11betaOHP and 17alphaOHP were monophasic, with an EC50 just in the micromolar range. Ligand blot analysis of sperm total lysates performed with peroxidase-conjugated P revealed the presence of two binding proteins of 54 and 57 kDa that were specific for P. Indeed, peroxidase-conjugated P binding was blocked by the simultaneous presence of the unconjugated steroid. Using alpha c262 antibody, which is directed against the P-binding domain of genomic receptor, we detected two proteins of similar molecular mass (54 and 57 kDa), whereas using antibodies directed against the DNA-binding and N-terminal domains of the genomic P receptors, the two proteins were not detected. In addition, p54 and p57 appear to be mostly localized in sperm membranes and virtually absent in the cytoplasm. The involvement of these proteins in the biological effects of P is indicated by the strong inhibitory effect of alpha c262 on P-induced acrosome reaction of capacitated human spermatozoa.

Acrosome↗
PubMed1997

Protein tyrosine kinase, mitogen-activated protein kinase and protein kinase C are involved in the mitogenic signaling of platelet-activating factor (PAF) in HEC-1A cells.

We have recently demonstrated that the phospholipid platelet-activating factor (PAF) mediates an autocrine proliferative loop in the endometrial adenocarcinoma cell line HEC-1A. In the present study we investigated the signaling pathways involved in PAF-mediated increase of proliferation in these cells. In particular, we studied the effect of PAF on protein tyrosine phosphorylation and mitogen-activated protein kinase (MAPK) activity, as well as the effect of protein tyrosine kinase (PTK) and protein kinase C (PKC) inhibition on PAF-induced increase of c-fos gene expression and thymidine incorporation in HEC-1A cells. We found that PAF induced a rapid, time- and dose-dependent increase of tyrosine phosphorylation of a subset of proteins of 42, 44, 78, 99, and 150 kDa molecular weight. We also found that PAF increased tyrosine phosphorylation and activity of p42 MAPK, suggesting the involvement of this important intermediary enzyme in the proliferative effect of PAF. The effect of PAF on c-fos gene expression was not prevented by pre incubation with the PTK inhibitors genistein or methyl-2,5-dihydroxycinnamate, whereas was strongly affected by PKC down regulation after long term incubation with PMA or by PKC inhibition with sangivamycin. We also found that genistein and methyl 2,5-dihydroxycinnamate decreased both basal and PAF-stimulated [3H]thymidine uptake in these cells. Similar results were obtained with PD 098059, a specific inhibitor of MAP kinase cascade. PAF-stimulated [3H]thymidine uptake was also prevented by PKC down regulation after long term exposure to PMA and PKC inhibition with the two inhibitors sangivamycin and bis-indolylmaleimide. In conclusion, our results indicate that PAF-induced mitogenesis in HEC-1A cells is mediated by the activation of multiple signaling pathways, involving PTK, MAPK, and PKC activation.

Adenocarcinoma↗
PubMed1996

Human sperm activation during capacitation and acrosome reaction: role of calcium, protein phosphorylation and lipid remodelling pathways.

Two processes, namely capacitation and acrosome reaction, are of fundamental importance in the fertilization of oocyte by spermatozoon. Physiologically occurring in the female genital tract, capacitation is a complex process, which renders the sperm cell capable for specific interaction with the oocyte. During capacitation, modification of membrane characteristics, enzyme activity and motility property of spermatozoa render these cells responsive to stimuli that induce acrosome reaction prior to fertilization. Physiological acrosome reaction occurs upon interaction of the spermatozoon with the zona pellucida protein ZP3. This is followed by liberation of several acrosomal enzymes and other constituents that facilitate penetration of the zona and exposes molecules on the sperm equatorial segment that allows fusion of sperm membrane with the oolemma. The molecular mechanisms and the signal transduction pathways mediating the processes of capacitation and acrosome reaction are only partially defined, and appear to involve modifications of intracellular calcium and other ions, lipid transfer and phospholipid remodelling in sperm plasma membrane as well as changes in protein phosphorylation. The human and mouse sperm receptor for ZP3 has been recently sequenced and cloned. This receptor exhibits sequence homology with proto-oncogenes that mediate proliferation and differentiation in somatic cells. This review summarizes the main signal transduction pathways involved in capacitation and acrosome reaction.

Acrosome Reaction↗
PubMed1996

Platelet-activating factor enhances production of insulin-like growth factor binding proteins in a human adenocarcinoma cell line (HEC-1A)

We have recently demonstrated the existence of an autocrine growth loop driven by platelet-activating factor (PAF) in the human endometrial adenocarcinoma. cell line HEC-1A. To investigate a possible cooperation between PAF and the insulin-like growth factor (IGF) system in this cell line, the effect of PAF on insulin-like growth factor binding protein (IGFBP) production as well as binding and biological activities of IGF-I, IGFv-II, and the analog Des(1-3)IGF-I have been evaluated. Analysis of self- and cross-displacement curves of [125I]IGF-I binding to HEC-1A cells indicates the presence of a single class of binding sites, with affinity constants of 1-4 nM for IGF-I and IGF-II and 70 nM for Des(1- 3)IGF-I, which binds to IGFBPs with lower affinity. Insulin does not apparently bind to this binding site. Moreover, the addition of increasing concentrations of IGF-I leads to a paradoxical increase of binding. These results indicate a similarity of this binding site to IGFBPs. The presence of IGFBPs has been demonstrated by Western ligand blot analysis of HEC-1A conditioned medium which shows the presence of two bands of 32-34 and 40-45 kDa. By Western immunoblotting analysis, the two bands were respectively identified as IGFBP-2 and IGFBP-3. Incubation with PAF (1 microM) highly increases the release of the two IGFBPs from the cells. Such an effect is inhibited by the PAF receptor antagonist L659,989, by the PKC inhibitor sangivamycin, and by the tyrosine kinase inhibitor genistein. PAF also induces a time-dependent increase of mRNA expression for IGFBP-3, suggesting an effect on synthesis of this protein. IGF-I and IGF-II (0.1-100 nM) are almost ineffective in inducing [3H]thymidine incorporation, whereas a slight proliferative effect is observed with Des(1-3)IGF-I which also increases PAF synthesis. These data demonstrate a modulatory action of PAF on IGFBP secretion in HEC-1A cells and indicate that the IGF system plays a minor, if any, modulatory role on proliferation of this cell line.

Adenocarcinoma↗
PubMed1996

Two functional assays of sperm responsiveness to progesterone and their predictive values in in-vitro fertilization.

We have recently reported, in a small cohort of subjects, that acrosome reaction (AR) and intracellular free calcium ([Ca2+]i) increase in response to progesterone were significantly correlated with in-vitro fertilization (IVF) rate. In the present study we extended these results to 90 subjects undergoing IVF. We confirm that both parameters were highly significantly correlated with the fertilization rate (P < 0.001). In particular, significantly lower responses to progesterone were detected in subjects with a fertilization rate < 50%, further enlightening the functional significance of sperm responsiveness to progesterone with respect to the process of fertilization. Moreover, we report here that both tests are highly discriminant of fertilization success, with positive predictive values > 90% for [Ca2+]i values which increase by > 1.2-fold and AR inducibility > 7% (cut-off values). Conversely, AR following challenge with the calcium ionophore A23187 was less significantly correlated with the percentage fertilization rate (P < 0.05), and showed lower predictive values than response to progesterone. All these tests ([Ca2+]i increase in response to progesterone, AR in response to progesterone and to A23187) appear highly sensitive and moderately specific. The positive predictive value may rise to > 95% when the combination of two tests ([Ca2+]i and inducibility of AR in response to progesterone) is considered. No correlation with fertilization rate has been found for spontaneous AR or basal [Ca2+]i. In conclusion, we propose that assessment of human sperm responsiveness to progesterone may be clinically useful in predicting fertilizing ability in vitro.

Acrosome↗
PubMed1996

Extracellular calcium negatively modulates tyrosine phosphorylation and tyrosine kinase activity during capacitation of human spermatozoa.

Capacitation of spermatozoa, a complex process occurring after sperm ejaculation, is required to obtain fertilization of the oocyte in vivo and in vitro. Although most of the biochemical/ biophysical events that occur during capacitation in vitro have been characterized, the molecular mechanisms underlying these complex events are still obscure. Increases of intracellular free Ca2+ concentrations ([Ca2+]i) and protein tyrosine phosphorylation have previously been demonstrated during in vitro capacitation of human spermatozoa. In the present study we investigated the relationship between extracellular/intracellular Ca2+, protein tyrosine phosphorylation, and tyrosine kinase and phosphatase activities during sperm capacitation. We report that the increase in tyrosine phosphorylation of several protein bands that occurs during sperm capacitation is independent of the presence of Ca2+ in the external medium and, at least partially, of the increase in [Ca2+]i occurring during the process. Indeed, the spontaneous increase in phosphorylation was still present in Ca(2+)-free/EGTA-containing-medium and in the presence of the intracellular Ca2+ chelator BAPTA/AM. Moreover, phosphorylation of proteins and protein tyrosine kinase (PTK) activity was enhanced if spermatozoa were incubated in Ca(2+)-free medium, suggesting the presence of Ca(2+)-inhibited tyrosine kinase(s) in human sperm. This hypothesis is further substantiated by the lower tyrosine phosphorylation observed after incubation with the ionophore A23187 and the endoplasmic Ca(2+)-ATPase inhibitor thapsigargin, which promote Ca2+ influx in human sperm. The ability of the cells to undergo acrosome reaction in response to progesterone, which can be considered a functional endpoint of capacitation, was highly compromised when spermatozoa were incubated in Ca(2+)-free medium or in the presence of EGTA, confirming that Ca2+ is required for sperm capacitation. Conversely, in the presence of erbstatin, a inhibitor of tyrosine kinase activity, which blunts tyrosine phosphorylation during capacitation, response to progesterone was maintained, suggesting that tyrosine phosphorylation must be kept at a low level (physiologically by the presence of Ca2+ in the external medium, or pharmacologically by the presence of erbstatin) in order to obtain response to progesterone. This mechanism may be important in vivo during sperm transit in the female genital tract to ensure appropriate timing of full capacitation in the proximity of the oocyte.

Acrosome↗
PubMed1995

Tyrosine kinase inhibition reduces the plateau phase of the calcium increase in response to progesterone in human sperm.

Progesterone (P) has previously been shown to induce a rapid increase in [Ca2+]i as well as tyrosine phosphorylation of proteins in human spermatozoa. Both these effects are essential for induction of the acrosome reaction by P. We investigated a possible relationship between the P-induced calcium increase and tyrosine kinase activation, by evaluating the effect of the tyrosine kinase inhibitor genistein on these two effects. We found that preincubation with genistein abolished P-induced tyrosine phosphorylation of two sperm proteins of 97 and 75 kDa molecular weight and significantly inhibited the plateau phase of P-induced [Ca2+]i increase without affecting the peak phase. Conversely, the plateau phase was enhanced by the tyrosine phosphatase inhibitor Na3VO4. The effect of genistein was specific for P, since no inhibition was observed on the [Ca2+]i increase induced by thapsigargin, an inhibitor of endoplasmic Ca(2+)-ATPase previously shown to mobilize Ca2+ in spermatozoa. These results indicate that tyrosine kinase activation is involved in the generation of the plateau phase of Ca2+ influx induced by P, and suggest the possibility that two different pathways are involved in the induction of Ca2+ entry by P in human sperm.

Biological Transport↗
PubMed1995

Stimulation of protein tyrosine phosphorylation by platelet-activating factor and progesterone in human spermatozoa.

Tyrosine phosphorylation of proteins is involved in several sperm functions, including capacitation, motility, and acrosome reaction of spermatozoa. This study was undertaken to determine changes of tyrosine phosphorylation during 'in vitro' capacitation as well as the ability of platelet-activating factor (PAF) and progesterone (P), two known activators of sperm functions, to stimulate tyrosine phosphorylation of human sperm proteins. Spermatozoa were capacitated in BSA-containing medium and incubated with PAF (10-1000 nM) and progesterone (0.1-1 microgram/ml). After SDS-PAGE, sperm proteins were transferred to nitrocellulose and tyrosine phosphorylated proteins immunodetected by reacting with anti-phosphotyrosine antibody. The antibody mainly reacted with two proteins of approximately 97 and 75 kDa. The level of phosphorylation increased in these two proteins as a function of capacitation time, with a maximum between 120 and 180 min. In addition, phosphorylation in these two proteins was increased in capacitated spermatozoa by treatment with progesterone and PAF and was greatly reduced by pre-incubation with the tryosine kinase inhibitor erbstatin. Furthermore, pre-incubation with the two tyrosine kinase inhibitors erbstatin and genistein inhibited the induction of acrosome reaction by progesterone and, partially, by PAF. Our results suggest a role for tyrosine kinase(s) in the mechanism of capacitation and activation of human spermatozoa by PAF and progesterone.

Acrosome↗
PubMed1995

Actions of progesterone on human sperm: a model of non-genomic effects of steroids.

Non-genomic actions of steroids have been extensively studied in the last few years. Among these actions, the non-genomic effect of progesterone (P) on human spermatozoa appears to be very promising, in view of the dramatic effect of this steroid on intracellular calcium, activation of tyrosine kinase, and induction of acrosome reaction. We have shown that the ability of spermatozoa to respond to P increases during the process of capacitation and is not counteracted by the P-receptor antagonist RU486 nor by the GABAA antagonists bicuculline and picrotoxin. We have also shown that P increases tyrosine phosphorylation of a sperm protein of about 97 kDa, suggesting activation of tyrosine kinase(s). In addition, we found that P induces a perturbation of sperm membrane phospholipid metabolism resulting in an increase of synthesis of platelet-activating factor and liberation of arachidonic acid. Results of these biochemical studies indicate that P is able to stimulate several signal transduction pathways in human sperm. We have also investigated responsiveness to P in sperm of oligozoospermic subjects as well as of men undergoing an in vitro fertilization (IVF) program. Our results show that the percentage increases of intracellular calcium and acrosome reaction in response to P is significantly reduced in oligozoospermic men as well as in subjects with reduced fertilization rate. Moreover, in the latter subjects response to P is highly significant correlated to fertilization rate of oocytes. These studies indicate that a biochemical alteration of sperm in their capacity to respond to P might be responsible for reduced fertilizing ability.

Acrosome↗
PubMed1995

Intracellular calcium increase and acrosome reaction in response to progesterone in human spermatozoa are correlated with in-vitro fertilization.

In this study we have investigated responsiveness to progesterone in spermatozoa from a group of unselected male partners of couples undergoing in-vitro fertilization (IVF). We evaluated progesterone-stimulated intracellular Ca2+ ([Ca2+]i) and percentage increase in acrosome reaction in the same sperm sample used for oocyte inseminations. [Ca2+]i was measured with a fluorimetric method, while the acrosome reaction was assessed using a fluorescent probe (fluorescein isothiocyanate-labelled peanut lectin). The average percentage [Ca2+]i as well as the rate of increase in the frequency of acrosome reaction following progesterone challenge were significantly lower (P < 0.005) in the group of patients with a fertilization rate < 50%. In addition, significant correlations between the fertilization rate and the progesterone-stimulated [Ca2+]i and acrosome reaction increases (r = 0.78 and r = 0.79 respectively) were observed. Furthermore, in cases of fertilization failure, no increase of [Ca2+]i or acrosome reaction was observed in response to progesterone with the exception of one case. Our results indicate that [Ca2+]i and acrosome reaction increases in response to progesterone can be of value in the prediction of sperm fertilizing ability. As the two parameters were significantly correlated to each other (r = 0.86), the two assays have similar IVF predictive value and might be used interchangeably as a diagnostic tool in the assignment of male patients to the different kinds of assisted fertilization techniques.

Acrosome↗
PubMed1994

Platelet-activating factor in human endometrium.

Platelet-activating factor (PAF) is a phospholipid actively produced by human endometrium and deeply involved in the processes of ovoimplantation and labor. We recently found that PAF represents a new autocrine growth factor for a human adenocarcinoma cell line, HEC-1A. Indeed, biologically active PAF is synthesized by HEC-1A cells, under progesterone control. In HEC-1A cells, PAF regulates intracellular calcium concentration ([Ca2+]), DNA synthesis and expression of early oncogenes. All these effects are blocked by the receptor antagonist L659,989. However, while nanomolar concentrations of PAF mobilize [Ca2+], only micromolar concentrations affect cell growth, suggesting heterogeneity of PAF receptors or signaling. Two distinct populations of PAF receptors are present in HEC-1A cells, which bind PAF in nanomolar and micromolar concentrations, respectively. Since HEC-1A cells are producing elevated concentrations of PAF and micromolar concentrations of the PAF antagonist L659,989 inhibit cell proliferation, an autocrine role for PAF is suggested in HEC-1A cells.

Adenocarcinoma↗
PubMedDate not supplied

Nongenomic progesterone receptor on human spermatozoa: biochemical aspects and clinical implications.

Progesterone (P) is a physiological stimulus of human sperm functions. It is present in high levels at the site of fertilization (cumulus oophorus) and has been described to affect several sperm functions, including motility, capacitation, acrosome reaction, and the ability to bind and to respond to zona proteins. The effects of the steroid are mediated essentially by an increase of intracellular calcium concentrations, stimulation of activity of phospholipases, phosphorylation of proteins, efflux of chloride. These effects are due to activation of a rapid, nongenomic pathway. Whether the effects of progesterone are mediated or not by specific interactions with sperm membrane proteins is questioned. By using an antibody directed against the C-terminal region (P-binding region) of the genomic receptor, we have recently identified two sperm proteins with molecular weights distinct from the classic genomic receptors. In addition, ligand blot analysis with peroxidase-conjugated P demonstrated that P specifically binds these two proteins. Classical ligand binding experiments demonstrated the presence of two specific binding sites with affinity in the nanomolar and in the micromolar range, respectively. The involvement of progesterone in the physiological process leading to fertilization of the oocyte is suggested by several studies. In particular, the demonstration that sperm responsiveness to progesterone is impaired in subfertile patients and that is strictly correlated to the ability of fertilizing the oocyte represents a further indication of the participation of the steroid in this process. In addition, the determination of sperm responsiveness may be predictive of fertilizing ability with a positive predictive value of 90% and can be clinically useful for the preliminary assessment of the male partner to select the appropriate assisted reproductive technique.

Humans↗