Beta-endorphin, Met-enkephalin, and calcitonin in human semen: evidence for a possible role in human sperm motility

THERAPY OF ENDOCRINE DISEASE: Amylin and calcitonin - physiology and pharmacology

Type 2 diabetes is a common manifestation of metabolic dysfunction due to obesity and constitutes a major burden for modern health care systems, in concert with the alarming rise in obesity worldwide. In recent years, several successful pharmacotherapies improving glucose metabolism have emerged and some of these also promote weight loss, thus, ameliorating insulin resistance. However, the progressive nature of type 2 diabetes is not halted by these new anti-diabetic pharmacotherapies. Therefore, novel therapies promoting weight loss further and delaying diabetes progression are needed. Amylin, a beta cell hormone, has satiating properties and also delays gastric emptying and inhibits postprandial glucagon secretion with the net result of reducing postprandial glucose excursions. Amylin acts through the six amylin receptors, which share the core component with the calcitonin receptor. Calcitonin, derived from thyroid C cells, is best known for its role in humane calcium metabolism, where it inhibits osteoclasts and reduces circulating calcium. However, calcitonin, particularly of salmon origin, has also been shown to affect insulin sensitivity, reduce the gastric emptying rate and promote satiation. Preclinical trials with agents targeting the calcitonin receptor and the amylin receptors, show improvements in several parameters of glucose metabolism including insulin sensitivity and some of these agents are currently undergoing clinical trials. Here, we review the physiological and pharmacological effects of amylin and calcitonin and discuss the future potential of amylin and calcitonin-based treatments for patients with type 2 diabetes and obesity.

Paracrine signalling by cardiac calcitonin controls atrial fibrogenesis and arrhythmia

Atrial fibrillation, the most common cardiac arrhythmia, is an important contributor to mortality and morbidity, and particularly to the risk of stroke in humans¹. Atrial-tissue fibrosis is a central pathophysiological feature of atrial fibrillation that also hampers its treatment; the underlying molecular mechanisms are poorly understood and warrant investigation given the inadequacy of present therapies². Here we show that calcitonin, a hormone product of the thyroid gland involved in bone metabolism³, is also produced by atrial cardiomyocytes in substantial quantities and acts as a paracrine signal that affects neighbouring collagen-producing fibroblasts to control their proliferation and secretion of extracellular matrix proteins. Global disruption of calcitonin receptor signalling in mice causes atrial fibrosis and increases susceptibility to atrial fibrillation. In mice in which liver kinase B1 is knocked down specifically in the atria, atrial-specific knockdown of calcitonin promotes atrial fibrosis and increases and prolongs spontaneous episodes of atrial fibrillation, whereas atrial-specific overexpression of calcitonin prevents both atrial fibrosis and fibrillation. Human patients with persistent atrial fibrillation show sixfold lower levels of myocardial calcitonin compared to control individuals with normal heart rhythm, with loss of calcitonin receptors in the fibroblast membrane. Although transcriptome analysis of human atrial fibroblasts reveals little change after exposure to calcitonin, proteomic analysis shows extensive alterations in extracellular matrix proteins and pathways related to fibrogenesis, infection and immune responses, and transcriptional regulation. Strategies to restore disrupted myocardial calcitonin signalling thus may offer therapeutic avenues for patients with atrial fibrillation.

Delta and kappa opioid receptors on mouse sperm cells: Expression, localization and involvement on in vitro fertilization

The endogenous opioid peptides have been reported to be involved in the regulation of reproductive physiology. Many of the studies conclude with sentences around the harmful effect of opioids in male fertility but, actually, there is only one study regarding the real fertility potential of spermatozoa that have been exposed to mu specific opioids. The aim of the present study was to see if the modulation of delta (OPRD1) and kappa (OPRK1) opioid receptors in mouse sperm during capacitation was able to vary the embryo production after in vitro fertilization (IVF). The presence of OPRD1 and OPRK1 in mouse mature spermatozoa was analyzed by RT-PCR and immunofluorescence. Incubating the sperm with, on one hand, the delta specific agonist DPDPE and/or antagonist naltrindole, and, on the other hand, the kappa specific agonist U-50488 and antagonist nor-binaltorphimine, we analyzed the involvement of OPRD1 and OPRK1 on IVF and preimplantational embryo development. We verified the presence of OPRD1 and OPRK1 in mouse mature spermatozoa, not only at the mRNA level but also at protein level. Moreover, the sperm incubation with DPDPE, before the IVF, had an effect on the fertilization rate of sperm and reduced the number of reached blastocysts, which was reverted by naltrindole. Instead, the use of the kappa agonist U-50488 and the antagonist nor-binaltophimine did not have any effect on the amount and the quality of the achieved blastocysts. Although nowadays the pure delta or kappa opioid ligands are not used for the clinic, clinical trials are being conducted to be used in the near future, so it would be interesting to know if the modulation of these receptors in sperm would generate any consequence in relation to fertilization capacity.

Mu opioid receptor expression and localisation in murine spermatozoa and its role in IVF

The endogenous opioid peptides are reported to be involved in the regulation of reproductive physiology. Many of the studies conclude with statements on the harmful effect of opioids on male fertility but, in fact, there are no studies regarding the real fertilisation potential of spermatozoa that have been exposed to opioids. The aim of the present study was to examine if modulation of mu opioid receptor (OPRM1) in murine spermatozoa during capacitation influenced embryo production after IVF. The presence of OPRM1 in murine mature spermatozoa was analysed by reverse transcription-polymerase chain reaction and immunofluorescence. We analysed the involvement of OPRM1 on IVF and pre-implantational embryo development by incubating the spermatozoa with the opioid agonist morphine and/or antagonist naloxone. We verified the presence of OPRM1 in murine mature spermatozoa, not only at the mRNA level but also the protein level. Moreover, incubation of the spermatozoa with morphine, before IVF, had an effect on the fertilisation rate of the spermatozoa and reduced the numbers of blastocysts, which was reversed by naloxone. Considering that opioids are widely used clinically, it is important to take into account their effect, via OPRM1, on the fertility of patients.

Heparin binding carboxypeptidase E protein exhibits antibacterial activity in human semen

Carboxypeptidase E (CPE) cleaves basic amino acid residues at the C-terminal end and involves in the biosynthesis of numerous peptide hormones and neurotransmitters. It was purified from human seminal plasma by ion exchange, heparin affinity and gel filtration chromatography followed by identification through SDS-PAGE and MALDI-TOF/MS analysis, which was further confirmed by western blotting. CPE was characterized as glycoprotein by Periodic Acid Schiff (PAS) staining and treating with deglycosylating enzyme N-glycosidase F. The interaction of CPE with heparin was illustrated by surface plasmon resonance (SPR) and in silico interaction analysis. The association constant (KA) and dissociation constant (KD) of CPE with heparin was determined by SPR and found to be 1.06 × 10(5)M and 9.46 × 10(-6)M, respectively. It was detected in human spermatozoa also by western blotting using mouse anti-CPE primary antibody. 20-100 μg/ml concentration of CPE was observed as highly effective in killing Escherichia coli by colony forming unit (CFU) assay. We suggest that CPE might act not only in the innate immunity of male reproductive tract but also regulate sperm fertilization process by interacting heparin.

Enkephalin-Degrading Enzymes in Normal and Subfertile Human Semen

Opioid peptides have been reported to have important functions in human reproduction. Indeed, very high concentrations of enkephalins and their degrading enzymes have been reported in human semen. In the present paper, we compare the activity of two enkephalin-degrading enzymes, aminopeptidase N and neutral endopeptidase 24.11, in different fractions of semen from normozoospermic, fertile men and from subfertile patients with different abnormalities revealed by spermiogram analysis (asthenozoospermia, necrozoospermia, and teratozoospermia). High levels of activity of aminopeptidase N were found in the soluble and particulate sperm fractions of semen from patients presenting asthenozoospermia with necrozoospermia. In contrast, lower aminopeptidase N activity was measured in the soluble sperm fraction of asthenozoospermic semen. The percentage of dead spermatozoa was positively correlated with aminopeptidase N activity in both soluble and particulate sperm fractions. In contrast, the percentage of immobile spermatozoa was negatively correlated with aminopeptidase activity in soluble and particulate sperm, and in prostasome fractions. Levels of activity of neutral endopeptidase were found to be unaltered among the different conditions. In summary, the results of the present study indicate that alterations in the activity of aminopeptidase N may be one of the molecular components that contribute to male human subfertility.

Regulation of human sperm motility by opioid receptors

The endogenous opioid system has been reported to have important functions in human reproduction. Practically all the components of this peptide system have been discovered in human sperm cells, but their functions in these cells are far from being well understood. In the present work, we report the effects of opioid agonism and antagonism on human sperm motility, a parameter which is crucially associated with male fertility. Morphine (10(-7) M), a μ- opioid receptor agonist, decreased both the percentage of motile progressive sperm and three measured velocities without altering the linearity, straightness or vigour of sperm cells. This effect was reversed by naloxone. Higher doses of morphine did not have further effects on the measured parameters. The incubation of sperm cells with the δ-opioid receptor agonist D-penicillamine (2,5)-enkephalin did not affect sperm cell motility. However, naltrindole, a specific δ-receptor antagonist, reduced the linear and curvilinear velocities, as well as linearity, straightness and the amplitude of head displacement, and beat frequency. In summary, our results indicate that the endogenous opioid system may regulate opioid motility in vitro. These finding suggest that the endogenous opioid system could be useful as a biochemical tool for the diagnosis and treatment of male infertility.

Regulation of male fertility by the opioid system

Endogenous opioid peptides are substances involved in cell communication. They are present in various organs and tissues of the male and female reproductive tract, suggesting that they may regulate some of the processes involved in reproductive function. In fact, the opioid system that operates as a multi-messenger system can participate in the regulation of reproductive physiology at multiple levels, for example, at the levels of the central nervous system, at the testes level and at sperm level. A better understanding of the implication of the opioid system in reproductive processes may contribute to clarifying the etiology of many cases of infertility and the effect of opiate abuse on fertility. Indeed, a novel biochemical tool for the diagnosis and treatment of male infertility could be based upon components of the opioid system. The presence of the opioid system in sperm cells also represents a novel opportunity for reproductive management, for either enhancing the probability of fertilization or reducing it through the development of novel targeted contraceptives.

Expression and localization of delta-, kappa-, and mu-opioid receptors in human spermatozoa and implications for sperm motility

CONTEXT

Endogenous opioid peptides signal through delta-, kappa-, and mu-opioid receptors. Some of these peptides such as endorphins and enkephalins are present in the male reproductive tract, but the presence of the corresponding receptors in human sperm cells has not yet been reported.

OBJECTIVE

Our objective was to study the expression and localization of delta-, kappa-, and mu-opioid receptors on human spermatozoa and the implication in sperm motility.

METHODS

The expression of receptors was studied by RT-PCR, Western blot, and immunofluorescence techniques. We evaluated the effects of activation of each opioid receptor by specific agonist and antagonist.

RESULTS

Human spermatozoa express delta-, kappa-, and mu-opioid receptors. These receptors were located in different parts of the head, in the middle region, and in the tail of the sperm. Progressive motility of spermatozoa, an important parameter to evaluate male fertility, was found to be significantly reduced after incubation with the mu-receptor agonist morphine, whereas this effect was antagonized in the presence of the corresponding antagonist naloxone. The delta-receptor antagonist naltrindole significantly reduced progressive motility immediately after its addition. However, the delta-receptor agonist DPDPE had no significant effect. Finally, neither the kappa-receptor agonist U50488 nor its antagonist nor-binaltorphimine significantly affected the progressive motility of human spermatozoa.

CONCLUSION

We report for first time the presence of functional delta-, kappa-, and mu-opioid receptors in human sperm membranes. These findings are indicative of a role for the opioid system in the regulation of sperm physiology.

Beta-endorphin in serum and seminal plasma in infertile men

AIM

To access beta-endorphin levels in serum as well as seminal plasma in different infertile male groups.

METHODS

Beta-endorphin was estimated in the serum and seminal plasma by enzyme-linked immunosorbent assay (ELISA) method in 80 infertile men equally divided into four groups: non-obstructive azoospermia (NOA), obstructive azoospermia (OA), congenital bilateral absent vas deferens (CBVAD) and asthenozoospermia. The results were compared to those of 20 normozoospermic proven fertile men.

RESULTS

There was a decrease in the mean levels of beta-endorphin in the seminal plasma of all successive infertile groups (mean +/- SD: NOA 51.30 +/- 27.37, OA 51.88 +/- 9.47, CBAVD 20.36 +/- 13.39, asthenozoospermia 49.26 +/- 12.49 pg/mL, respectively) compared to the normozoospermic fertile control (87.23 +/- 29.55 pg/mL). This relation was not present in mean serum level of beta-endorphin between four infertile groups (51.09 +/- 14.71, 49.76 +/- 12.4, 33.96 +/- 7.2, 69.1 +/- 16.57 pg/mL, respectively) and the fertile control group (49.26 +/- 31.32 pg/mL). The CBVAD group showed the lowest seminal plasma mean level of beta-endorphin. Testicular contribution of seminal beta-endorphin was estimated to be approximately 40%. Seminal beta-endorphin showed significant correlation with the sperm concentration (r = 0.699, P = 0.0188) and nonsignificant correlation with its serum level (r = 0.375, P = 0.185) or with the sperm motility percentage (r = 0.470, P = 0.899).

CONCLUSION

The estimation of beta-endorphin alone is not conclusive to evaluate male reproduction as there are many other opiates acting at the hypothalamic pituitary gonadal axis.

Proopiomelanocortin gene expression and β-endorphin localization in the pituitary, testis, and epididymis of stallion

Proopiomelanocortin (POMC) is a precursor protein that contains the sequences of several bioactive peptides including adrenocorticotropin (ACTH), beta-endorphin (beta-EP), and melanocyte-stimulating-hormone (MSH). POMC is synthesized in the pituitary gland, brain, and many peripheral tissues. Immunoreactive POMC-derived peptides as well as POMC-like mRNA have been evidenced in several nonpituitary tissues, thus suggesting that POMC is actively synthesized by these tissues. The present study was aimed at evaluating if also in the case of stallion POMC-derived peptide, beta-EP, is produced locally in the testis, thus playing effects in a paracrine/autocrine fashion. To investigate this hypothesis the POMC gene expression was analyzed using 3' RACE-PCR and Northern Blot approaches in the testis and epididimys of stallion; moreover, immunocytochemical localization for beta-EP was also performed through confocal laser microscopy. The immunofluorescence results showed a positive beta-EP reaction not only in cellular nest of pituitary but also in the testis and genital tract of stallion, which function could be related with sperm mobility. Such role seem not to be no dependent on the peptide synthesized locally, because the molecular biology approach demonstrated the presence of POMC transcript in the pituitary only. In fact the Northern Blot analysis showed the presence of a single POMC transcript in the pituitary while no signal was detected in the testis and epididimys. The same results were obtained by applied 3' RACE-PCR analysis. In conclusion, opioid-derived peptide beta-EP is present in the genital tract of stallion, but is not locally produced as in other mammalian, and nonmammalian models; its possible biological function at testicular level could be linked to a long-loop feed-back mechanisms.

Peptidase activities in human semen

Enkephalins are one of the opioids present in human semen and to date their function in this tissue remains unknown. The present work studies enkephalin-degrading enzyme activities, puromycin-sensitive alanyl aminopeptidase (AAP-S), puromycin-insensitive alanyl aminopeptidase N (Ap N) and neprilysin (NEP) in human seminal fractions. AAP-S activity was not detected in any fractions, whereas Ap N appeared in soluble and particulate sperm fractions in seminal fluid and in prostasome fraction. With regard to NEP activity, this was exclusively located in prostasome membranes. The high activity values observed in the prostasome fraction suggested that these peptidases and their substrates could be involved in seminal physiology.

Substance P and beta-endorphin act as possible chemoattractants of mouse sperm

The effect of beta-endorphin and substance P on mouse sperm motion was examined in an in vitro model. The number of mouse sperm cells migrating to mediuin containing substance P in pharmacological concentrations of 5, 25, and 50 ng/mL were significantly higher than the number migrating to control. This effect was observed after 3 h at a concentration of 5 ng/mL and 1 h at 25 and 50 ng/mL. Demonstrated changes in spermatozoa behavior in the presence of substance P were time and concentration dependent. These effects were interpreted as chemotaxis but not chemokinesis of sperm induced by influence of this tachykinin on membrane receptors. The presence of beta-endorphin in incubation fluid in concentrations of 5, 25, and 50 ng/mL did not cause any visible changes or decrease sperm migration. Substance P contained in follicular fluid played a direct and important role in the process of mammalian fertilization.

Neuroendocrine cells of the verumontanum: a comparative immunohistochemical study

OBJECTIVE

To define the distribution of neuroendocrine (NE) cells in the different compartments of the verumontanum (utricle, ejaculatory ducts, main prostatic ducts) in relation to other areas of the prostate.

MATERIALS AND METHODS

A retrospective study was conducted of 30 radical prostatectomy specimens processed in toto as whole-mount sections. Among these cases, 15 patients had received a preoperative short course of total androgen blockade. The distribution and number of NE cells in the prostatic utricle and in normal areas of the prostate were analysed using chromogranin A (CgA) and serotonin immunohistochemistry; prostate-specific antigen (PSA) immunostaining was performed systematically on a consecutive section. Six cases of endometrioid carcinomas were also investigated using these methods. The vascularization of the verumontanum was assessed by factor VIII immunohistochemistry and examined in relation to vascular endothelial growth factor (VEGF) immunohistochemistry.

RESULTS

There were significantly more NE cells in the prostatic utricle than in the main prostatic ducts of the verumontanum and the peripheral prostatic acini. In the ejaculatory ducts. there were NE cells only in the extreme distal portion. Cells immunoreactive for PSA were present at the level of the utricle and the extreme distal portion of the ejaculatory ducts. The distribution, number and shape of NE cells were unaltered by hormonal treatment. NE cells of the verumontanum were positive for VEGF expression. Factor VIII detected more vessels around the utricle and ejaculatory ducts. NE cells (positive for CgA and serotonin) were observed in three cases of endometrioid carcinoma.

CONCLUSION

The high concentration of NE cells found in the prostatic utricle suggests a possible role for these cells in human fertility. Moreover, neuroendocrine differentiation in endometrioid (large duct) carcinoma, documented for the first time, supports the concept that this cancer type is a variant of a conventional adenocarcinoma.

Metenkephalin in seminal plasma of infertile men

BACKGROUND

Enkephalin is one of the opioids, which is expressed widely in reproductive organs. However, the function of enkephalin in male reproduction is not completely understood. The effect of metenkephalin on sperm motility remains especially controversial. In this study we examined the level of metenkephalin in seminal plasma from men with normal sperm production and patients with asthenospermia, oligospermia, and azoospermia to investigate the role of metenkephalin in seminal plasma on sperm function. We also investigated the effect of metenkephalin on sperm motility in vitro.

METHODS

Sixty nine infertile patients (31 oligospermic, 21 asthenospermic, and 17 azoospermic) were included in this study. The level of metenkephalin in seminal plasma of these men was measured and the effect of the peptide on the motility of human sperm was examined in vitro. Seventeen men with normal seminograms were a control group.

RESULTS

The level of metenkephalin in the seminal plasma of semen from asthenospermic men was significantly lower than that from the controls (P < 0.05). No significant correlations between the level of metenkephalin and the mean pathing or progressive velocity of sperm, or serum hormone levels were observed. In the in vitro study, which used semen from the controls, treatment of sperm with metenkephalin (50-200 pg/mL) maintained sperm motility for 4 hours. On the other hand, motility of sperm incubated without metenkephalin began to decrease at 3 hours. Metenkephalin levels of 50 pg/ mL in seminal plasma is considered to be necessary for maintaining sperm motility.

CONCLUSION

These results suggest that metenkephalin in seminal plasma is an important clue in the investigation of decreased sperm motility.

Neuroendocrine peptides in the prostate

Circulating androgens are required for normal growth and maintenance of function of the prostate. However, the prostate also contains neuroendocrine peptides, found either in nerve terminals or in prostatic neuroendocrine cells, which are likely to regulate prostate growth or function. The neuronal peptides are likely to participate in the regulation of the synthesis and secretion of prostatic secretory products. While the function of the neuroendocrine cells is undefined, there is evidence for growth-regulating effects of several neuroendocrine cell peptides. Since neuroendocrine differentiation has been correlated with tumor grade and poor prognosis in prostate cancer, the peptide products of the neuroendocrine cells may influence cancer cell replication as well. Recent evidence in other tissues suggests that peptide hormone receptor second-messenger systems may interact with steroid receptors to modulate their actions. These findings raise the possibility that prostatic neuroendocrine peptides may modulate the response of prostate to androgens.

Identification of the human seminal TRH-like peptide pGlu-Phe-Pro-NH2 in normal human prostate

Human and rat prostate contain thyrotropin-releasing hormone immunoreactivity (iTRH) including TRH and an uncharged TRH-like peptide. Recently the uncharged TRH-like peptide pGlu-Phe-Pro-NH2 was purified from human semen. To determine whether this peptide was of prostatic origin, human and rat prostate extracts were analyzed by ion-exchange chromatography and reversed-phase HPLC. The predominant uncharged iTRH comigrated exactly with synthetic pGlu-Phe-Pro-NH2 on HPLC and had identical affinity to pGlu-Phe-Pro-NH2 in a TRH radioimmunoassay. We conclude that prostate is a source of this peptide in humans and rats. This amidated TRH-like peptide may play a role in human reproductive physiology.

Characterization of neuroendocrine differentiation in human benign prostate and prostatic adenocarcinoma

BACKGROUND

This report describes an immunohistopathologic analysis characterizing the incidence, pattern of distribution, and hormonal content of neuroendocrine (NE) cells in human benign prostate and prostatic adenocarcinoma.

METHODS

Formaldehyde-fixed, paraffin-embedded material from 15 benign prostates, 31 primary prostatic adenocarcinomas, 16 metastatic lesions, 21 primary tumors treated with short-course diethylstilbestrol (DES), and 10 specimens from hormone-refractory patients were examined. NE cells were identified using silver histochemistry and a panel of immunohistochemical NE markers (chromogranin-A, serotonin, neuron-specific enolase), and specific peptide hormone antibodies.

RESULTS

NE cells were identified in all benign prostates. NE cells were identified in 77% of primary untreated adenocarcinomas with no significant differences with respect to pathologic stage. NE cells were found isolated and dispersed in the tumor, composing the minority of malignant cells. Double-labeling and serial section immunohistochemistry demonstrated the coexpression of prostate-specific antigen (PSA) in NE cells. In addition to serotonin, some tumors expressed multiple hormone immunoreactivities. NE cells were identified in 56% of metastatic deposits, with a similar pattern of distribution. In DES-treated cases, NE cells were found consistently in the adjacent benign epithelium, whereas 52% of tumors contained NE cells. Hormone-refractory tumors contained NE cells in 60% of cases.

CONCLUSIONS

This analysis demonstrates that a significant proportion of primary and metastatic prostatic adenocarcinomas contain a subpopulation of NE cells, the expression of which does not appear to be suppressed with androgen ablation and does not correlate with pathologic stage. Furthermore, NE cells coexpress PSA, suggesting a common precursor cell of origin. The elaboration of biogenic amines and neuropeptides suggests that NE cells dispersed in prostatic carcinoma may play a paracrine growth-regulatory role.

Significance of substance P- and enkephalin-peptide systems in the male genital tract

The plexi of the male reproductive tract have components of both the autonomic and sensory nervous systems. Rat epididymis was found to be a rich source of substance P. Substance P levels in the epididymis were higher by about 2.8 and 19.3 times than those in the prostate and seminal vesicles, respectively. Seminal vesicles were found to be a rich source of enkephalins. They had about 2.9 and 2.6 times higher leucine enkephalin levels than epididymis and prostate, respectively. Human seminal plasma contained about 47 times higher levels of leucine enkephalin than substance P. Using the split ejaculate technique, it has been demonstrated that early fractions of the human ejaculate contain fluids from prostate (and possibly epididymis), whereas later fractions represent seminal vesicle secretions. A low exogenous concentration of substance P (400 nM) increased sperm motility, whereas leucine enkephalin (100 microM) depressed it. Substance P (1-10 micrograms/mL) and muscarinic agonists enhanced the adrenergic transmission of the rat vas deferens to electrical stimulation. Leucine enkephalin (1-10 micrograms/mL) depressed adrenergic transmission and antagonized the effects of substance P and muscarinic agonists. These studies suggest that substance P-like tachykinins may play a role in sperm maturation, in expulsion of fluid from the epididymis, and in initiation of motility, whereas leucine enkephalin-like peptides may contribute to the orgasmic experience and detumescence.

Proenkephalin products are stored in the sperm acrosome and may function in fertilization

Previous studies have shown that spermatogenic cells are a major source of testicular RNA encoding the opioid peptide precursor proenkephalin, suggesting that proenkephalin-derived peptides may function as intratesticular paracrine factors produced by male germ cells. However, direct evidence for the production of proenkephalin by spermatogenic cells has been lacking. In this report, we have used polysome profile analysis, peptide quantitation, and immunocytochemistry to show that proenkephalin products are synthesized during spermatogenesis and are retained within spermatozoa of humans, hamsters, rats, and sheep. We further show that these peptides are stored in the sperm acrosome and are depleted from sperm following the acrosome reaction, an exocytotic event required for fertilization. Proenkephalin products thus may serve a dual function as sperm acrosomal factors released during the fertilization process as well as intratesticular regulators secreted by spermatogenic cells.

Cortisol and transcortin in human seminal plasma and amniotic fluid as estimated by modern specific assays

Cortisol concentrations in human seminal plasma, as estimated by the very specific Amersham 'Amerlite' luminescence immunoassay, were 176 +/- 43 (85-260) nmol/l, that is, 63.7 +/- 15.5 (31-94) ng/ml (mean +/- SD, n = 21). This is about 60% of random levels in blood serum and is the first description of cortisol in seminal fluid. In human amniotic fluid at 16-22 weeks of gestation, cortisol concentrations were lower, at 72.6 +/- 14.6 (63-124) nmol/l, that is, 29.3 +/- 5.3 (23-45) ng/ml (n = 21). Concentrations were about 15% of random maternal serum levels in the second trimester of pregnancy. The cortisol concentrations in both fluids were considerably higher than those reported for saliva, which has a mean of about 10 nmol/l. Transcortin (corticosteroid binding globulin, CBG), has been found in human seminal plasma and amniotic fluid for the first time. Concentrations were low, with values up to 12 micrograms/ml, with no significant difference between the two fluids, when using the IRE-Megenix monoclonal iodinated radioimmunoassay. Transcortin concentrations were about 10% of levels in non-pregnant blood serum, compared with about 0.1% for saliva. The higher concentrations of transcortin could perhaps account for the greater diffusion of cortisol into seminal plasma and amniotic fluid. The presence of beta-endorphin, ACTH and cortisol in amniotic fluid, seminal fluid, ovarian follicular fluid, endometrial fluid and gastric fluid may possibly, indicate the existence of a small paracrine ACTH-cortisol axis in the relevant secretory tissues.

Immunohistochemical localization of growth hormone-releasing hormone in human gonads

Human gonads were examined for the presence of ir growth hormone-releasing-hormone. We demonstrated the presence of immunostainable cells both in ovarian and in testicular tissue using a non-crossreactive anti-GRH antiserum and the immunoperoxidase detection technique. In ovaries from ovulating women, GRH immunoreactivity was localized in the corpora lutea; granulosa cells, theca cells and cells of primary follicles did not stain. In premenopausal ovaries, staining was detectable in scattered luteinized stromal cells. In testes from post-puberal men GRH immunoreactivity was localized in the Leydig cells; cells of the germinal epithelium did not stain. These results demonstrate the presence of GRH in human gonads and suggest that this peptide may exert regulatory function at the testicular and ovarian levels.

Absence of direct effect of beta-endorphin and calcitonin on human sperm motility

Beta-endorphin and calcitonin are found in the male reproductive tract. To elucidate the role of these hormones in reproduction, we studied their effect on sperm motility in vitro. Eight semen specimens were obtained from healthy donors, washed, and incubated with different concentrations of human beta-endorphin and human calcitonin. After 30 min of incubation, percentage of motile sperm (% motility), mean progressive velocity (MPV), and lateral head displacement (LHD) were assessed by a computerized semen analyzer. There were no significant differences in any of the sperm motility parameters between control and treated sperm. There was also no correlation between the concentration of beta-endorphin or calcitonin and any sperm motility parameters. It would appear that beta-endorphin and calcitonin may not directly affect sperm motility parameters in vitro.

The neuroendocrine prostate: characterization and quantitation of calcitonin in the human gland

Calcitonin was extracted from surgically-derived prostate tissue, and quantified using radioimmunoassay. Normal prostatic specimens contained 15.18 +/- 10.03 ng./gm. wet weight (mean +/- S.D., n = 20), with a range of 1.50 to 39.62 ng./gm. The result for the hyperplastic tissue samples (n = 20) averaged 0.63 +/- 0.39 ng./gm. with a range of 0.22 to 1.49 ng./gm. This difference was statistically significant (p less than .0001). Dilution profiles for the prostatic calcitonin and synthetic monomeric human calcitonin were congruent, suggesting that the two peptides are identical. A comparison of calcitonin levels and the number of immunohistochemically derived neuroendocrine cells in contiguous tissue sections showed an empiric correlation. The mean calcitonin level in normal human prostate tissue was found to exceed values previously reported for numerous other organs, with the exception of the thyroid gland, the principal source of circulating calcitonin. We propose that a subpopulation of neuroendocrine cells within the prostate gland produce calcitonin, as is the case in the gastrointestinal tract, lung, and other organs. Our findings also support the hypothesis that the calcitonin found in seminal fluid originates in the prostate. Putative roles for calcitonin in the genitourinary system are discussed.

Presence of immunoreactive beta-endorphin and calcitonin in human seminal plasma, and their relation to sperm physiology

Opioid peptides and calcitonin are found in high concentrations in the male reproductive tract. To further elucidate their role in sperm physiology, we studied semen samples from 49 infertile men and 25 men with proven fertility. beta-endorphin and calcitonin were measured in each sample by radioimmunoassay and then were correlated with seminal plasma testosterone (T) and dihydrotestosterone levels as well as sperm count, total motile sperm/milliliter, and percentage of penetrated hamster eggs. The levels of beta-endorphin (308 +/- 22 pg/ml) and calcitonin (331 +/- 32 pg/ml) in seminal plasma were 10 and 20 times higher than levels found in venous plasma (32 +/- 2 and 14.5 +/- 1.2 pg/ml, respectively) (P less than 0.001). There was no difference between the levels of beta-endorphin and calcitonin in seminal plasma of fertile and infertile men. However, seminal plasma T was significantly higher in fertile than infertile men (19.4 +/- 2 versus 11.5 +/- 1 ng/dl; P less than 0.05). No correlation could be demonstrated between either beta-endorphin or calcitonin and any of the parameters studied. In conclusion, beta-endorphin and calcitonin are produced locally in the male reproductive tract; however, their role in male reproduction remains to be elucidated.

Beta-endorphin and calcitonin in human semen

The levels of beta-endorphin (beta-E) and calcitonin were estimated in 36 samples of seminal plasma from semen of normospermic, oligozoospermic, and azoospermic origins and in pools of isolated sperm. The mean levels in plasma calculated for all samples examined were 192 +/- 224 pg/ml for beta-E and 754 +/- 397 pg/ml for calcitonin. The amounts in sperm were as follows: for beta-E in pools with sperm counts of 0.1-10 x 10(6)/ml, 157.2 +/- 99.7 pg/10(8) and 27.9 +/- 23.6 pg/ml protein; in pools of greater than 10-30 x 10(6)/ml, 71.2 +/- 41.5 pg/10(8) and 6.5 +/- 1.2 pg/mg protein; in pools of greater than 30-200 x 10(6)/ml, 24.9 +/- 9.7 pg/10(8) and 61 +/- 1.9 pg/mg protein. For calcitonin the amounts were: 501.2 +/- 170.8 pg/10(8) and 27.4 +/- 21.5 pg/mg protein, correspondingly. It was suggested that beta-E and calcitonin present in seminal plasma are synthesized mostly in a compartment of the male reproductive system. The high cellular beta-E and calcitonin levels would be involved in the process of motility through their effect on calcium transport.

Isolation and characterization of a basic carboxypeptidase from human seminal plasma

A carboxypeptidase which cleaves the C-terminal arginine or lysine from peptides was purified by a two-step procedure; gel filtration on Sephacryl S-300 and affinity chromatography on arginine-Sepharose. The activity increased 280% after the first step, indicating the removal of an inhibitor from the crude starting material. The activity in the crude seminal plasma eluted from the Sephacryl S-300 column with an apparent Mr 98,000 and after purification with an Mr 67,000, indicating that it binds to another protein in the crude seminal plasma. When analyzed by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate, a single band at Mr 53,000 was seen which was converted to two smaller bands (Mr 32,000 and/or 26,000) after reduction. The seminal plasma carboxypeptidase has a neutral pH optimum, is inhibited by o-phenanthroline and by the inhibitor of carboxypeptidase B-type enzymes, 2-mercaptomethyl-3-guanidinoethylthiopropanoic acid, and can be activated by cobalt. The purified enzyme has a high specific activity (67.8 mumol/min/mg) with the ester substrate benzoyl (Bz)-Gly-argininic acid and readily cleaves Bz-Ala-Lys, Bz-Gly-Arg, and Bz-Gly-Lys. It also hydrolyzes biologically active peptides such as bradykinin (Km = 6 microM, kcat = 43 min-1), Arg6-Met5-enkephalin (Km = 103 microM, kcat = 438 min-1), and Lys6-Met5-enkephalin (Km = 848 microM, kcat = 449 min-1). The seminal plasma carboxypeptidase did not cross-react with antiserum to human plasma carboxypeptidase N; other properties distinguish it from the blood plasma enzyme as well as from pancreatic carboxypeptidase B and granular, acid carboxypeptidase H (enkephalin convertase). The carboxypeptidase could be involved in the control of fertility by activating or inactivating peptide hormones in the seminal plasma. In addition it could contribute to the degradation of basic proteins during semen liquefaction.

Production and exocrine secretion of LHRH-like material by the male rat reproductive tract

Luteinizing hormone-releasing hormone (LHRH)-like immunoreactivity was localized in the male reproductive system of the rat. Epithelial cells of the epididymus, seminal vesicles and coagulation gland showed a strong reaction to anti-LHRH serum. Also the epithelia of the ductus deferens and the prostate gland appeared to be immunoreactive, albeit to a lesser extent. The LHRH-like substances are most likely secreted into the male tract, as can be concluded from the observation that the secretion product in the lumina of the seminal vesicles, coagulation gland and prostate gland was also immunopositive. The functional significance of these phenomena is discussed. No immunostaining was obtained with antisera to FSH, LH or beta-hCG.

Immunohistochemical localization of beta-endorphin in hyperplastic interstitial tissue of the human testis

The immunohistochemical localization of beta-endorphin in the normal testis (two patients) and in the pathologic testis (two cases of Sertoli Cell Only Syndrome, two cases of Klinefelter Syndrome, two cases of post-orchitis tubular sclero-hialinosis) was investigated. No beta-endorphin immunostaining was detected in the normal testis, while positive beta-endorphin immunostaining has been observed in pathologic tissues. These results indicate that, as in animals, beta-endorphin is present in human Leydig cells and may play a local role in regulating male reproductive function.

Expression of opioid genes in bovine seminal vesicles

In seminal vesicles, the organ producing most of seminal plasma in the bovine species, the pro-opiomelanocortin and the proenkephalin genes are transcribed and translated, and their translation products processed into opioid peptides, which are secreted into the seminal plasma. By using a micro-organ preparation of seminal vesicles we found that, after 20 h of incubation with labelled methionine, a multiplicity of opioids was produced. Among these, [Met]enkephalin and beta-endorphin were positively identified, whereas in the newly formed secretion only [Met]enkephalin was detected. This may be correlated to the finding that the concentration of beta-endorphin in an extract of seminal plasma was one order of magnitude lower than that of [Leu]enkephalin and [Met]enkephalin. These findings expand the picture of the presence of opioid peptides in the male reproductive tract, indicating that they should have a role(s) in the physiology of reproduction, not only in the hypothalamus-pituitary-gonadal axis, determining the reproductive potential, but also in the so-termed sex accessory glands, determining the actual events leading to reproduction. To our knowledge this is also the first case studied of opioid peptides produced as exocrine hormones.

Large forms of immunoreactive calcitonin in human seminal fluid exhibit PDN-21 immunoreactivity

Semen samples were obtained from 4 healthy males on two occasions. One of the samples was liquefied at room temperature for 20 min while the other was diluted immediately with buffer to suppress proteolysis. A pool of immunoextracted calcitonin from liquefied and diluted samples, respectively, was subjected to gel chromatography in a separate experiment. In lyophilized samples the majority of immunoreactive calcitonin (CT) had an approximate molecular weight (Mr) of 10 kilodaltons (Kd) and immunoreactive PDN-21 was also present in the fractions. In diluted ejaculates CT was composed of larger species as well as the 10 Kd form. PDN-21 was present in fractions containing the 10 Kd form but could not be detected in the peaks of larger molecular weight, probably because of lower sensitivity of the PDN-21 assay compared to the CT assay. Our finding of CT and PDN-21 in the same fractions after immunoextraction with CT antibodies suggests the presence of proforms of CT in human seminal fluid.