Neuroendocrine control of male reproductive function. The opioid system as a model of control at multiple sites

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.

Lifestyles and sexuality in men and women: the gender perspective in sexual medicine

Sexual health is strictly related with general health in both genders. In presence of a sexual dysfunction, the expert in sexual medicine aims to discover the specific weight of the physical and psychological factors can cause or con-cause the sexual problem. At the same time, a sexual dysfunction can represent a marker of the future development of a Non-communicable diseases (NCDss) as cardiovascular or metabolic diseases.In the evaluation phase, the sexual health specialist must focus on these aspects, focusing especially on the risk and protective factors that could impact on both male and female sexuality.This article presents a review of researches concerning healthy and unhealthy lifestyles and their contribute in the development of sexual quality of life in a gender-dependent manner.Among the unhealthy lifestyle, obesity contributes mostly to the development of sexual dysfunctions, due to its negative impact on cardiovascular and metabolic function. Tobacco smoking, alcohol - substance abuse and chronic stress lead to the development of sexual dysfunction in a med-long term.In order to guarantee a satisfying sexual quality of life, sexual health specialists have the responsibility to guide the patient through the adoption of healthy lifestyles, such as avoiding drugs, smoke and excessive alcohol, practicing a regular physical activity, following a balanced diet and use stress-management strategies, even before proposing both pharmaco- and/or psychotherapies.

Paternal morphine exposure induces bidirectional effects on cocaine versus opioid self-administration

The United States is in the midst of an opioid epidemic and is thus experiencing unprecedented levels of opioid exposure. A growing body of evidence has demonstrated that this may have consequences on multiple generations. The current set of experiments examined the effect of male adolescent opioid exposure on cocaine and opioid self-administration in the F1 generation. Male Sprague Dawley rats were administered increasing doses of morphine (5-25 mg/kg, s.c.) for 10 days during adolescence (P30-39). Rats were then maintained drug free until adulthood (P70-80) at which point they were mated with drug-naïve females. Male and female F1 offspring were first examined for cocaine self-administration during adulthood. Naïve littermates were tested for morphine self-administration acquisition followed by a within subjects design progressive ratio test for morphine, oxycodone, and cocaine. Results show that male and female F1 rats have delayed acquisition and decreased intake of cocaine. In addition, they have blunted PR levels compared to Sal-F1 control rats. Female Mor-F1 rats also demonstrate increased levels of morphine intake during acquisition and increased PR responding for oxycodone. Surprisingly, even following acquisition of morphine self-administration, Mor-F1 males and females still demonstrate blunted effort for cocaine. There were no differences in sucrose self-administration in naïve littermates. MorF0 seminiferous tubules demonstrated increased levels of acetylated histone H3 and there were increased levels of BDNF mRNA in the mPFC in male and female F1 offspring. Together, these data identify systems that are vulnerable to the impact of opioids in the F0 generation.

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.

Evaluation of the Mistakes in Self-Diagnosis of Sexual Dysfunctions in 11,000 Male Outpatients: A Real-Life Study in An Andrology Clinic

Purpose: The aim of this study was to compare the initial request for sexual consultation with the final diagnosis and to evaluate the limits of the active andrological anamnesis concerning unclassified male sexual dysfunction. Methods: In this 12-year observational retrospective study, we collected data from patients referring to an andrological outpatient clinic, evaluating the requests, perceptions, needs, and self-diagnosis at their first visit and comparing them with the final diagnosis reached after a complete clinical, laboratory, and instrumental investigation. Results: A total of 11,200 patients were evaluated. The main request of andrological consultation was erectile dysfunction (ED) (52%), followed by premature ejaculation (PE) (28%), and low sexual desire (11.5%). Among the patients seeking help for ED, about 30% were ultimately found to have a different type of dysfunction and 24% were diagnosed with an “unmet need”, which included issues not present in the current nosography nonetheless affecting sexual and relational life. Among the patients referring for PE, the final diagnosis was lifelong PE for the large majority of them, regardless of whether initially they thought to have an acquired form. Several of those who sought consultation for acquired PE were frequently found to be able to compensate for lifelong PE by a subsequent coitus or were able to induce orgasm in the partner with different modalities. Among the patients referring for low sexual desire, only 57.5% were confirmed to have it; 23% had ED and 18.5% showed a raised threshold of penile sensitivity. Conclusions: The results of this study show that the reason for consultation is frequently misleading and raise the relevance of being aware of the so-called “unmet needs” and to discuss with the patient and the couple to explore the sexual history behind the self-diagnosis. These findings also suggest the need to expand the current taxonomy of male sexual dysfunctions.

Implication of mu opioid receptor in the in vitro maturation of oocytes and its effects on subsequent fertilization and embryo development in mice

Oocyte maturation is the process by which immature oocytes acquire all the necessary characteristics for successful fertilization. The endogenous opioid peptides have been suggested to have a role modulating this process. However, little is known about its implication and the effect of exposing oocyte maturation to opioids on the subsequent fertilization and embryo development. Hence, in the present work, we focused on elucidating the function of the mu opioid receptor (OPRM1) in the modulation of the oocyte maturation. We analyzed the expression and localization of OPRM1 in mice oocytes and granulosa cells by reverse-transcription polymerase chain reaction (RT-PCR) and immunocytochemistry. To observe the activity of the OPRM1, immature oocytes were incubated with morphine agonist and/or naloxone antagonist and we evaluated the PI3K/Akt and MAPK pathways, as well as the effect on the subsequent fertilization and embryo development. OPRM1 was present in mice oocytes and granulosa cells, changing its expression pattern depending on the maturation stage. Moreover, morphine, modulating PI3K/Akt and MAPK pathways, helped oocytes to reach blastocyst stage, which was reverted by naloxone. These results propose the OPRM1 as a possible therapeutic target for in vitro maturation culture medium, as it could improve the blastocyst rates obtained in the actual reproduction assisted techniques.

The Influence of Endogenous Opioids on the Relationship between Testosterone and Romantic Bonding

The endogenous opioid system has received attention and extensive research for its effects on reward, pleasure, and pain. However, relative to other neurochemicals, such as oxytocin, vasopressin and dopamine, the function of opioids in regulating human attachment, sociosexuality, and other aspects of human sociality has not received much consideration. For example, nonapeptides (oxytocin and vasopressin) have been extensively studied in animals and humans for their possible roles in mother-offspring attachment, romantic attachment, fatherhood, and social cognition. Likewise, others have proposed models wherein oxytocin and vasopressin are moderators of the relationship between steroid hormones and human social behaviors. Recently, opioids have generated renewed interest in relation to social pain, and importantly, the brain opioid hypothesis of social attachment (BOTSA), which suggests that endogenous opioids are a key implementer in primate and human bonding, has received some support. Here we focus on romantic bonds by proposing that endogenous opioids are an important mechanism mediating reproductive trade-offs through their inhibitory effects on testosterone production.

Testosterone deficiency in non-cancer opioid-treated patients

PURPOSE

The use of opioids in patients with chronic non-cancer pain is common and can be associated with opioid-induced androgen deficiency (OPIAD) in men. This review aims to evaluate the current literature regarding the prevalence, clinical consequence and management of OPIAD.

METHODS

A database search was performed in Medline, Embase and Cochrane using terms such as "analgesics", "opioids" and "testosterone". Relevant literature from January 1969 to March 2018 was evaluated.

RESULTS

The prevalence of patients with OPIAD ranges from 19 to 86%, depending on the criteria for diagnosis of hypogonadism. The opioid-induced suppression of gonadotropin-releasing and luteinizing hormones represents the main important pathogenetic mechanisms. OPIAD has significant negative clinical consequences on sexual function, mood, bone density and body composition. In addition, OPIAD can also impair pain control leading to hyperalgesia, which can contribute to sexual dysfunction and mood impairment.

CONCLUSIONS

OPIAD is a common adverse effect of opioid treatment and contributes to sexual dysfunction, impairs pain relief and reduces overall quality of life. The evaluation of serum testosterone levels should be considered in male chronic opioid users and the decision to initiate testosterone treatment should be based on the clinical profile of individuals, in consultation with the patient.

The mu (μ) and delta (δ) opioid receptors modulate boar sperm motility

Endogenous and exogenous opioids modulate reproductive functions in target cells via opioid receptors (μ, δ, and κ). Sperm motility is a metric of gamete functionality, and serves as a suitable parameter for in vitro drug-induced toxicity assays. This study identifies the presence and location of opioid receptors in pig spermatozoa as well as their functional response after in vitro challenge with known agonists (morphine [μ]; [D-Pen 2,5]-enkephanile [δ]; and U 50488 [κ]) and antagonists (naloxone [μ]; naltrindole [δ]; and nor-binaltrorphimine [κ]). Only the μ- and δ-opioid receptors were present in the boar sperm plasma membrane, overlying the acrosome, neck, and principal piece. Challenge experiments with agonists and antagonists identified both μ- and δ-opioid receptors as regulators of sperm kinematics, wherein μ maintains or increases sperm movement whereas δ decreases sperm motility over time. Mol. Reprod. Dev. 83: 724-734, 2016 © 2016 Wiley Periodicals, Inc.

Mu opioid receptor in the human endometrium: dynamics of its expression and localization during the menstrual cycle

OBJECTIVE

To study the dynamics of the expression and localization of the mu opioid receptor (MOR) in human endometrium throughout the menstrual cycle.

DESIGN

Analysis of human endometrial samples from different menstrual cycle phases (menstrual, early/midproliferative, late proliferative/early secretory, midsecretory, and late secretory) by reverse transcription-polymerase chain reaction, Western blot, and immunohistochemistry.

SETTING

Academic research laboratory.

PATIENT(S)

Women from the Human Reproduction Unit of the Cruces University Hospital, fulfilling the following criteria: normal uterine vaginal ultrasound; absence of endometriosis, polycystic ovary syndrome, implantation failure, or recurrent miscarriage; and no history of opioid drug use.

INTERVENTION(S)

Endometrial samples of 86 women categorized into groups for the menstrual cycle phases: 12 menstrual, 21 early/midproliferative, 16 late proliferative/early secretory, 17 midsecretory, and 20 late secretory.

MAIN OUTCOME MEASURE(S)

MOR gene and protein expression and localization in the different compartments of the human endometrium at different stages of the menstrual cycle.

RESULT(S)

The expression of MOR mRNA and protein changed throughout the cycle in human endometrium. MOR expression increased during the proliferative phase and decreased during the secretory one. Lower values were found at menstruation, and maximum values around the time of ovulation. Small variations for each endometrial compartment were found.

CONCLUSION(S)

The presence of MOR in human endometrium and the dynamic changes during the menstrual cycle suggest a possible role for opioids in reproduction events related to the human endometrium or endometriosis.

Intermittent Moderate Energy Restriction Improves Weight Loss Efficiency in Diet-Induced Obese Mice

Background

Intermittent severe energy restriction is popular for weight management. To investigate whether intermittent moderate energy restriction may improve this approach by enhancing weight loss efficiency, we conducted a study in mice, where energy intake can be controlled.

Methods

Male C57/Bl6 mice that had been rendered obese by an ad libitum diet high in fat and sugar for 22 weeks were then fed one of two energy-restricted normal chow diets for a 12-week weight loss phase. The continuous diet (CD) provided 82% of the energy intake of age-matched ad libitum chow-fed controls. The intermittent diet (ID) provided cycles of 82% of control intake for 5–6 consecutive days, and ad libitum intake for 1–3 days. Weight loss efficiency during this phase was calculated as (total weight change) ÷ [(total energy intake of mice on CD or ID)–(total average energy intake of controls)]. Subsets of mice then underwent a 3-week weight regain phase involving ad libitum re-feeding.

Results

Mice on the ID showed transient hyperphagia relative to controls during each 1–3-day ad libitum feeding period, and overall ate significantly more than CD mice (91.1±1.0 versus 82.2±0.5% of control intake respectively, n = 10, P<0.05). There were no significant differences between CD and ID groups at the end of the weight loss or weight regain phases with respect to body weight, fat mass, circulating glucose or insulin concentrations, or the insulin resistance index. Weight loss efficiency was significantly greater with ID than with CD (0.042±0.007 versus 0.018±0.001 g/kJ, n = 10, P<0.01). Mice on the CD exhibited significantly greater hypothalamic mRNA expression of proopiomelanocortin (POMC) relative to ID and control mice, with no differences in neuropeptide Y or agouti-related peptide mRNA expression between energy-restricted groups.

Conclusion

Intermittent moderate energy restriction may offer an advantage over continuous moderate energy restriction, because it induces significantly greater weight loss relative to energy deficit in mice.

Intravenous iron replacement therapy in eugonadal males with iron-deficiency anemia: Effects on pituitary gonadal axis and sperm parameters; A pilot study

AIM OF THE STUDY

To evaluate semen parameters and to assess serum FSH, LH, Testosterone (T) concentrations before and 12 weeks after intravenous iron therapy (800-1200 mg elemental iron therapy - IVI) in adults with iron-deficiency anemia (IDA).

MATERIALS AND METHODS

We studied 11 eugonadal adults with IDA, aged 40 ± 5 years, due to defective intake of iron. Anemia was diagnosed when hemoglobin (Hb) was equal or below 10 g/dl. Serum iron, total iron-binding capacity (TIBC) and ferritin concentrations confirmed the diagnosis of IDA. Basal serum concentrations of FSH, LH, and T were measured. Semen parameters were evaluated before and 6-7 weeks after IVI therapy.

RESULTS

After IVI therapy and correction of anemia, a significant increase of Hb from 8.1 ± 1.17 g/dL to 13.1 ± 0.7 g/dL was observed and was associated with an increase of T (from 12.22 ± 1.4 nmol/L to 15.9 ± 0.96 nmol/L; P < 0.001), FSH (from 2.82 ± 0.87 to 3.82 ± 1.08 IU/L; P = 0.007), and LH (from 2.27 ± 0.9 to 3.82 ± 1.5 IU/L; P = 0.0002). Total sperm count (TSC) increased significantly from 72 ± 17.5 million/ml to 158 ± 49 million/mL (P < 0.001), rapid progressive sperm motility (RPM) increased from 22 ± 9.4 to 69 ± 30 million/ml (P < 0.001), and sperms with normal morphology (NM) increased from 33 ± 5 to 56 ± 7 million/ml (P < 0.001). Increment in Hb concentration was correlated significantly with LH, FSH, and T concentrations after IVI (r = 0.69 and r = 0.44, r = 0.75, respectively; P < 0.01). The increment in serum T was correlated significantly with increments in the TSC and total sperm motility and RPM (r = 0.66, 0.43, and 0.55, respectively; P < 0.001) but not with gonadotrophin levels.

CONCLUSION

Our study proved for the first time, to our knowledge, that correction of IDA with IVI is associated with significant enhancement of sperm parameters and increased concentrations of serum LH, FSH, and T. These effects on spermatogenesis are reached by an unknown mechanism and suggest a number of pathways that need further human and/or experimental studies.

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.

Hormone replacement therapy in morphine-induced hypogonadic male chronic pain patients

BACKGROUND

In male patients suffering from chronic pain, opioid administration induces severe hypogonadism, leading to impaired physical and psychological conditions such as fatigue, anaemia and depression. Hormone replacement therapy is rarely considered for these hypogonadic patients, notwithstanding the various pharmacological solutions available.

METHODS

To treat hypogonadism and to evaluate the consequent endocrine, physical and psychological changes in male chronic pain patients treated with morphine (epidural route), we tested the administration of testosterone via a gel formulation for one year. Hormonal (total testosterone, estradiol, free testosterone, DHT, cortisol), pain (VAS and other pain questionnaires), andrological (Ageing Males' Symptoms Scale-AMS) and psychological (POMS, CES-D and SF-36) parameters were evaluated at baseline (T0) and after 3, 6 and 12 months (T3, T6, T12 respectively).

RESULTS

The daily administration of testosterone increased total and free testosterone and DHT at T3, and the levels remained high until T12. Pain rating indexes (QUID) progressively improved from T3 to T12 while the other pain parameters (VAS, Area%) remained unchanged. The AMS sexual dimension and SF-36 Mental Index displayed a significant improvement over time.

CONCLUSIONS

In conclusion, our results suggest that a constant, long-term supply of testosterone can induce a general improvement of the male chronic pain patient's quality of life, an important clinical aspect of pain management.

Delta opioid receptor on equine sperm cells: subcellular localization and involvement in sperm motility analyzed by computer assisted sperm analyzer (CASA)

BACKGROUND

Opioid receptors and endogenous opioid peptides act not only in the control of nociceptive pathways, indeed several reports demonstrate the effects of opiates on sperm cell motility and morphology suggesting the importance of these receptors in the modulation of reproduction in mammals. In this study we investigated the expression of delta opioid receptors on equine spermatozoa by western blot/indirect immunofluorescence and its relationship with sperm cell physiology.

METHODS

We analyzed viability, motility, capacitation, acrosome reaction and mitochondrial activity in the presence of naltrindole and DPDPE by means of a computer assisted sperm analyzer and a fluorescent confocal microscope. The evaluation of viability, capacitation and acrosome reaction was carried out by the double CTC/Hoechst staining, whereas mitochondrial activity was assessed by means of MitoTracker Orange dye.

RESULTS

We showed that in equine sperm cells, delta opioid receptor is expressed as a doublet of 65 and 50 kDa molecular mass and is localized in the mid piece of tail; we also demonstrated that naltrindole, a delta opioid receptor antagonist, could be utilized in modulating several physiological parameters of the equine spermatozoon in a dose-dependent way. We also found that low concentrations of the antagonist increase sperm motility whereas high concentrations show the opposite effect. Moreover low concentrations hamper capacitation, acrosome reaction and viability even if the percentage of cells with active mitochondria seems to be increased; the opposite effect is exerted at high concentrations. We have also observed that the delta opioid receptor agonist DPDPE is scarcely involved in affecting the same parameters at the employed concentrations.

CONCLUSIONS

The results described in this paper add new important details in the comprehension of the mammalian sperm physiology and suggest new insights for improving reproduction and for optimizing equine breeding.

Endocrine consequences of opioid therapy

Gonadal hormones are known to be affected by morphine and other opioids. In this paper, we summarize data collected in recent years which clearly indicate that the opioid-induced effects on steroid hormones depend on the opioid used and in some cases on the sex of the subject. Indeed morphine is able to reduce hormones like testosterone and cortisol in both male and female subjects in just a few hours, probably acting directly on peripheral glands. These depressant effects of morphine on hormones are also present in the treatment of surgical pain and are quickly reversible once opioid administration is suspended. Similar actions were also found to occur in experimental animals and in vitro in glial cells, further confirming the morphine-induced reduction of testosterone cell content. Testosterone and its metabolites are well known substances involved in the development and maintenance of the brain and all body structures. Thus when treating pain with opioids, their effects on hypothalamo-pituitary-gonadal and hypothalamo-pituitary-adrenal-related hormones must be considered and, where possible, hormone replacement therapy should be started.

Psychosocial stress inhibits amplitude of gonadotropin-releasing hormone pulses independent of cortisol action on the type II glucocorticoid receptor

Our laboratory has developed a paradigm of psychosocial stress (sequential layering of isolation, blindfold, and predator cues) that robustly elevates cortisol secretion and decreases LH pulse amplitude in ovariectomized ewes. This decrease in LH pulse amplitude is due, at least in part, to a reduction in pituitary responsiveness to GnRH, caused by cortisol acting via the type II glucocorticoid receptor (GR). The first experiment of the current study aimed to determine whether this layered psychosocial stress also inhibits pulsatile GnRH release into pituitary portal blood. The stress paradigm significantly reduced GnRH pulse amplitude compared with nonstressed ovariectomized ewes. The second experiment tested if this stress-induced decrease in GnRH pulse amplitude is mediated by cortisol action on the type II GR. Ovariectomized ewes were allocated to three groups: nonstress control, stress, and stress plus the type II GR antagonist RU486. The layered psychosocial stress paradigm decreased GnRH and LH pulse amplitude compared with nonstress controls. Importantly, the stress also lowered GnRH pulse amplitude to a comparable extent in ewes in which cortisol action via the type II GR was antagonized. Therefore, we conclude that psychosocial stress reduces the amplitude of GnRH pulses independent of cortisol action on the type II GR. The present findings, combined with our recent observations, suggest that the mechanisms by which psychosocial stress inhibits reproductive neuroendocrine activity at the hypothalamic and pituitary levels are fundamentally different.

Rat RFamide-related peptide-3 stimulates GH secretion, inhibits LH secretion, and has variable effects on sex behavior in the adult male rat

A recently described avian neuropeptide, gonadotropin inhibitory hormone (GnIH), has been shown to have seasonal regulatory effects on the hypothalamic-pituitary-gonadotropin axis (HPG) in several avian species. In the bird, GnIH expression is increased during the photorefractory period and has inhibitory effects on the HPG. A recently described mammalian neuropeptide, RF-amide-related peptide-3 (RFRP-3), may be genetically related and functionally similar to this avian neuropeptide. The purposes of this study were to first see if rat RFRP-3 is expressed in the male rat brain and second to determine if ICV injections of RFRP-3 will have effects on feeding and sex behaviors, as well as hormone release from the anterior pituitary. Results confirm other studies in that immunoreactive cell bodies and fibers are observable in areas of the male rat brain known to control the HPG and feeding and sex behaviors. RFRP-3 fibers are also observed in close proximity to GnRH immunoreactive cell bodies. Behavioral tests indicate that high but not low ICV RFRP-3 (500 vs. 100 ng, respectively) significantly (p<0.05) suppressed all facets of male sex behavior while not having any observable effects on their ability to ambulate. Sex behavior was later exhibited when those same male rats received the ICV vehicle. While suppressing sex behavior, ICV RFRP-3 significantly (p<0.05) increased food intake compared to controls. ICV RFRP-3 also significantly reduced plasma levels of luteinizing hormone but increased growth hormone regardless of the time of day; however, at no time did RFRP-3 alter plasma levels of FSH, thyroid hormone, or cortisol. These results indicate that although RFRP-3 has similar effects on LH as observed with GnIH in avian species, in the rat RFRP-3 has additional roles in regulating feeding and growth.

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.

COMMENTARY: Subclinical Erectile Dysfunction: Proposal for a Novel Taxonomic Category in Sexual Medicine

The definition of erectile dysfunction currently used and accepted worldwide does not encompass all possible changes to male erection. Partial, temporary, or episodic absence of erection is not considered as true erectile dysfunction. This leads to a lack of diagnosis and therapy and perhaps even the risk of the subsequent development of overt impotence. The lack of an evidence-based diagnosis of such a condition may be due to the widespread, pernicious self-prescription of erection drugs, obtained from the illegal market. To define the pathological condition of men experiencing a lack of erection who are unaffected by erectile dysfunction, we propose herein a new taxonomic category, based on new sexological criteria. In addition, we suggest research into biochemical markers to define this condition, which we have named subclinical erectile dysfunction.

Increases in preproenkephalin mRNA levels in the Syrian hamster: The influence of glucocorticoids is dependent on age and tissue

In adult hamsters, basal proenkephalin (Penk) gene expression in adrenals is independent of glucocorticoids and glucocorticoid receptor blockade, by RU 486, increases striatal preproenkephalin (PPenk) mRNA levels. However, glucocorticoids maintain both basal and induced Penk gene expression in rat adrenal (medulla) and striatum. This suggests species and tissue-specific differences in Penk gene regulation. Since studies show temporal coordination in Penk gene expression in developing hamster adrenal and striatum, we tested the hypothesis that increasing PPenk mRNA levels are dependent, while basal levels are independent of glucocorticoids in developing hamsters. To facilitate this study, we examined the influence of glucocorticoids on the temporal increases in developing hamster PPenk mRNA observed in adrenals between postnatal days 0 and 4 and in striatum between postnatal days 12 and 48. PPenk mRNA levels were determined in hamster pups after treatment with increasing doses of metyrapone (an 11beta hydroxylase inhibitor) or with the glucocorticoid receptor antagonist RU 486 +/- metyrapone between postnatal days 2 and 4. Levels were also determined 36 days after hypophysectomy at age 16-17 days. Although plasma glucocorticoid levels and/or the influence from glucocorticoids were reduced, only developmental increases in PPenk mRNA are influenced by glucocorticoids in hamster adrenals, while basal adrenal mRNA levels are unchanged. However, pituitary influence on striatal PPenk mRNA levels appears complex and may involve steroid and/or non-steroid factors. These results suggest that glucocorticoids regulate hamster Penk gene expression via a mechanism that varies with age and tissue and functions during the induction of the Penk gene and not to maintain basal gene expression. Possible mechanisms and species variation are discussed.

Multiple sources of endogenous opioid peptide involved in the hypoglycemic response to 15 Hz electroacupuncture at the Zhongwan acupoint in rats

A decrease in plasma glucose levels was observed in rats which received electroacupuncture (EA) stimulation at the Zhongwan acupoint. In the present study, the role of the adrenal gland in this hypoglycemic response to EA at high frequency (15 Hz) was investigated on adrenalectomized (ADX) normal rats. There was a sharper decrease in plasma glucose by EA stimulation in the fasting ADX group than in the fasting sham-operated group. Naloxone blocked this hypoglycemic response to EA stimulation in rats which received ADX. Stimulation of EA failed to elicit an increase in plasma beta-endorphin and insulin levels in ADX rats. Similar results were observed in sham and ADX mice. EA stimulation of ADX mice can reduce plasma glucose levels. Furthermore, naloxone abolished the hypoglycemic response to EA stimulation in mice. Such a hypoglycemic response to EA stimulation was also observed in micro-opioid receptor knockout mice (MOR-KOM). Mediation by another opioid peptide should also be considered in future experiments. We conclude that multiple sources of endogenous opioid peptide participated in the lowering of plasma glucose in rats induced by EA stimulation at higher frequency (15 Hz) at the Zhongwan acupoint. Increase in beta-endorphin levels from the adrenal gland enhances the secretion of insulin, there by reducing plasma glucose levels, and is partially involved in this EA stimulation.

Neuropeptides of the pituitary adenylate cyclase-activating polypeptide/vasoactive intestinal polypeptide/growth hormone-releasing hormone/secretin family in testis

Mammalian testicular development and the maintenance of spermatogenesis are hormone-dependent processes that are controlled by the pituitary gonadotropins and testosterone. Recent studies have demonstrated the presence of many neuropeptides and their receptors in the testis, suggesting that these peptides operate as local regulators of testicular germ cell development and function. Among these testicular neuropeptides, the peptides that belong to the pituitary adenylate cyclase-activating polypeptide (PACAP) family, particularly growth hormone-releasing hormone and secretin, appear to show some unique common features in terms of intratesticular localization and the time of expression during the spermatogenic cycle. However, their precise physiologic roles and mechanisms of action remain unknown. This review analyzes the available information on the functional interactions among the testicular cells that appear to be mediated by locally produced neuropeptides, with a special emphasis on the peptides of the PACAP family.

Striatal proenkephalin gene induction: coordinated regulation by cyclic AMP and calcium pathways

Enkephalin modulates striatal function, thereby affecting motor performance and addictive behaviors. The proenkephalin gene is also used as a model to study cyclic AMP-mediated gene expression in striatal neurons. The second messenger pathway leading to proenkephalin expression demonstrates how cyclic AMP pathways are synchronized with depolarization. We show that cyclic AMP-mediated regulation of the proenkephalin gene is dependent on the activity of L-type Ca2+ channels. Inhibition of L-type Ca2+ channels blocks forskolin-mediated induction of proenkephalin. The Ca2+-activated kinase, Ca2+/calmodulin kinase, as well as the cyclic AMP-activated kinase, protein kinase A (PKA), are both necessary for the induction of the proenkephalin promoter. Similarly, both kinases are needed for the L-type Ca2+ channel-mediated induction of proenkephalin. This synchronization of second messenger pathways provides a coincidence mechanism that gates proenkephalin synthesis in striatal neurons, ensuring that levels are increased only in the presence of activated PKA and depolarization.

Neuropeptides of the pituitary adenylate cyclase-activating polypeptide/vasoactive intestinal polypeptide/growth hormone-releasing hormone/secretin family in testis

Mammalian testicular development and the maintenance of spermatogenesis are hormone-dependent processes that are controlled by the pituitary gonadotropins and testosterone. Recent studies have demonstrated the presence of many neuropeptides and their receptors in the testis, suggesting that these peptides operate as local regulators of testicular germ cell development and function. Among these testicular neuropeptides, the peptides that belong to the pituitary adenylate cyclase-activating polypeptide (PACAP) family, particularly growth hormone-releasing hormone and secretin, appear to show some unique common features in terms of intratesticular localization and the time of expression during the spermatogenic cycle. However, their precise physiologic roles and mechanisms of action remain unknown. This review analyzes the available information on the functional interactions among the testicular cells that appear to be mediated by locally produced neuropeptides, with a special emphasis on the peptides of the PACAP family.

Acute and long-term effects of AIDS and injection drug use on gonadal function

Hypogonadism has been observed in both the HIV-infected population and injection drug users (IDUs). Considering these populations in conjunction is essential because IDUs and HIV often occur in the same individual. Additionally, although the etiology of hypogonadism may be different in each population, its treatment with respect to the underlying condition is similar. The philosophy of both AIDS and IDU treatment has changed drastically in recent years, due to several factors. Survival rates of HIV patients have been steadily increasing, forcing a closer examination of the long-term effects of AIDS-related symptoms, and the quality of life issues associated therewith. In comparison, IDU is now viewed as a chronic addiction like that for alcoholism, which must be treated, rather than an untreatable personal problem. Therefore, it is logical that the endocrine and metabolic changes associated with both HIV and IDU should be examined to help alleviate these symptoms in a continuing effort to treat the underlying condition.

Effects of morphine on electrically evoked contractions of the vas deferens in two congeneric rodent species differing in sperm competition intensity

An early prediction of sperm competition theory was that males should adjust the number of sperm they deliver according to the risk of double mating and this has received empirical support in recent years. It has been suggested that adaptive regulation of sperm delivery in mammals may depend on changes in vas deferens contractility. In laboratory mice, the vas deferens is sensitive to opioid agonists and the secretion of endogenous opioid peptides can be affected by social interactions that may be predictive of sperm competition risk. The present experiment was conducted to determine whether morphine, an opioid agonist (at the mu-receptor), has different effects on electrically evoked contractions of the isolated vas deferens in two congeneric rodent species differing in sperm competition intensity. Morphine inhibited contractions of the vas deferens in the non-monogamous deer mouse (Peromyscus maniculatus) but not the monogamous California mouse (Peromyscus californicus). This implies that the vas deferens of P. maniculatus possesses functional mu-receptors and, thus, should be able to respond to changes in the circulating levels of endogenous agonists whose secretion can be affected by social interactions predictive of sperm competition risk.

Effects of alcohol on the synthesis and expression of hypothalamic peptides

Studies aimed at analyzing the deleterious effects of excess alcohol in the brain have revealed structural alterations that are often associated with functional and behavioral disturbances. Among the neuronal damage related to prolonged alcohol exposure, alterations in the synthesizing capabilities and levels of expression of neuroactive peptides have been increasingly reported. Actually, such changes frequently represent the sole repercussion of acute and short-term exposure to ethanol. This review gathers the existing data on the effects of ethanol exposure on the synthesis and expression of hypothalamic peptides. Amid those that can act both as neurotransmitters and neurohormones, we allude to vasopressin, corticotropin-releasing hormone, thyrotropin-releasing hormone and pro-opiomelanocortin and related peptides produced by paraventricular, supraoptic and arcuate neurons. With respect to peptides that act exclusively as neurotransmitters, we address the effects of alcohol on vasoactive intestinal polypeptide, gastrin-releasing peptide, somatostatin and vasopressin synthesized by suprachiasmatic neurons. Hypothalamic neurons that produce peptides that act as neurotransmitters are supposed to be modulated primarily by influences exerted by neuronal afferents, whereas those producing peptides that additionally act as neurohormones are also regulated by peripheral stimuli (e.g., plasma levels of circulating hormones, osmotic challenges). These peculiar features endue the hypothalamus with characteristics that are particularly propitious to enlighten the still cryptic mechanisms underlying the ethanol effects on protein synthesis.

In vitro effects of beta-endorphin on testicular release of androgens in the lizard Podarcis sicula Raf

The effects of the proopiomelanocortin-derived opioid peptide, beta-endorphin (beta-EP), and of the opioid antagonist, naloxone (NAL), on both basal and pituitary-stimulated androgen secretion from superfused quiescent and active testes were assessed in the adult lizard, Podarcis sicula. In the absence of the homologous pituitary, in vitro treatment with beta-EP and/or NAL did not affect basal secretion of androgens from quiescent and active testes. Conversely, in the presence of the homologous pituitary, treatment with beta-EP brought about a decrease in androgen secretion in active testes, but no effect on quiescent ones. Naloxone counteracted the inhibitor effect of beta-EP in active testes, and enhanced maximal pituitary-stimulated secretion of androgens in quiescent but not in active testes. The effects produces by beta-endorphin and naloxone were reversible. These results suggest that, in this lizard, opioids might be involved in the control of androgen release. The lack of effect of beta-EP and naloxone when added directly to the testes seems to suggest that the opioid agonist and antagonist act on androgen release by modulating pituitary gonadotrophin output.

Neuroendocrine marker substances in human Leydig cells--changes by disturbances of testicular function

A number of neuroendocrine and neuronal markers were demonstrated in Leydig cells of the testes of 18 men aged between 20 and 81 years. Tissue sections were divided into five groups, i.e. carcinoma of the prostate (control cases; n = 4), seminoma (n = 8), anti-androgen therapy (n = 3), oestradiol therapy (n = 2) and cryptorchidism (n = 1). The following substances were immunocytochemically tested: the monoamine synthesizing enzymes tyrosine hydroxylase, aromatic L-amino acid decarboxylase, dopamine-beta-hydroxylase and phenylethanolamine-N-methyltransferase, the indolamine serotonin, the calcium-binding proteins parvalbumin, calbindin and S-100 protein, the microtubule associated protein-2, as well as neurofilament protein 200, synaptophysin, neuron specific enolase, substance P and chromogranin A + B. All these substances were found in Leydig cells of all sections independently of the pathological changes of the testes. Compared with the control cases, all the other groups showed a significantly weaker immunoreactivity for all markers. The uniformity of staining among the different antibodies allows the deduction that these neuroactive peptides may belong to a basic equipment of Leydig cells probably stabilizing their function in an autocrine manner. On the other hand, Leydig cells themselves seem to be a stable structural component of the testis, which are not essentially involved in the pathogenesis of the disturbances mentioned above.

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

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

Effect of naloxone and beta-casomorphin on the hypothalamic-pituitary-luteinizing hormone axis in vitro

The effect of naloxone and beta-casomorphin on luteinizing hormone (LH) release from pituitary cell aggregates, obtained by three-dimensional culture, with or without mediobasal hypothalamic fragments was studied in vitro. Short-term naloxone perifusion at a concentration of 10(-5)M did not modify either basal or LHRH-stimulated LH release from the pituitary cell aggregates. In contrast, a 12-min naloxone perifusion at the same concentration caused an increase in LH release in the mediobasal hypothalamic-pituitary cell aggregate axis. This increase was rapid (12-16 min after time pulse), marked [up to 10 times (p less than 0.004) the initial base line], short (return to the base line secretion 32-40 min after the beginning of the time pulse) and dose-dependent, with a rise greater than 1000% at a concentration of 10(-4) (p less than 0.006). The same effect was observed when a second pulse was applied 48 min after the first one. LH release induced by naloxone was antagonized 56 +/- 2% (p less than 0.03) by beta-casomorphin (an exogenous opiate) at a concentration of 10(-5) M. beta-casomorphin alone did not modify LH basal secretion, but inhibited 25.1 +/- 2.4% (p less than 0.008) LH release enhanced by LHRH. These results indicate that naloxone, an opiate antagonist, markedly increases LH release via a mu-type opioid receptor mechanism at the hypothalamic level only, during short-term exposure.

Circadian rhythm of plasma testosterone in men with idiopathic hypogonadotrophic hypogonadism before and during pulsatile administration of gonadotrophin-releasing hormone

OBJECTIVE

The aim was to investigate whether a pulsatile discharge of LH from the pituitary is necessary to achieve the circadian secretion of testosterone.

DESIGN

The daily rhythm of the androgen has been studied in patients with idiopathic hypogonadotrophic hypogonadism (IHH) both in the absence of therapy and during pulsatile administration of gonadotrophin releasing hormone (GnRH).

PATIENTS

Six patients with IHH and ten normal subjects were analysed. Blood sampling was performed at 2-hourly intervals, for 24 hours. The IHH patients then received synthetic GnRH i.v. at the rate of one pulse every 2 hours (10 micrograms/pulse). On day 11 of treatment, blood samples were taken for the rhythm analysis every 2 hours, for 24 hours.

MEASUREMENTS

Plasma testosterone and LH were measured in the individual samples by radioimmunoassay. Evaluation of the rhythm was performed by cosinor analysis.

RESULTS

A significant circadian rhythm of plasma testosterone was statistically validated in the normal subjects, whereas no rhythm was detected in the IHH patients in the absence of therapy. On day 11 of GnRH pulsatile administration the IHH patients showed normal testosterone levels and a statistically significant circadian rhythm of the androgen was evident, with acrophase between 0700 and 0800 h. Moreover, the amplitude, acrophase and mesor of testosterone rhythm in IHH patients in the course of treatment were statistically indistinguishable from the corresponding values in the normal subjects. Plasma LH did not show statistically significant circadian variations, either in the control group or in the IHH patients before or during therapy.

CONCLUSIONS

We conclude that a physiological circadian rhythm of plasma testosterone can be obtained, in IHH men, by treatment with GnRH. Since the pulsatile administration of exogenous GnRH at constant doses induced a circadian rhythm in testosterone and no daily variations in LH were evident, we suggest that, although a pulsatile secretion of LH is probably necessary for the synchronization of the circadian rhythm with acrophase in the morning, the testosterone variations might be the results of a local testicular modulation of LH action.