Similar effects of prolactin and dbcAMP upon human spermatozoa metabolism

Prolactin (PRL) and its receptor: actions, signal transduction pathways and phenotypes observed in PRL receptor knockout mice

PRL is an anterior pituitary hormone that, along with GH and PLs, forms a family of hormones that probably resulted from the duplication of an ancestral gene. The PRLR is also a member of a larger family, known as the cytokine class-1 receptor superfamily, which currently has more than 20 different members. PRLRs or binding sites are widely distributed throughout the body. In fact, it is difficult to find a tissue that does not express any PRLR mRNA or protein. In agreement with this wide distribution of receptors is the fact that now more than 300 separate actions of PRL have been reported in various vertebrates, including effects on water and salt balance, growth and development, endocrinology and metabolism, brain and behavior, reproduction, and immune regulation and protection. Clearly, a large proportion of these actions are directly or indirectly associated with the process of reproduction, including many behavioral effects. PRL is also becoming well known as an important regulator of immune function. A number of disease states, including the growth of different forms of cancer as well as various autoimmune diseases, appear to be related to an overproduction of PRL, which may act in an endocrine, autocrine, or paracrine manner, or via an increased sensitivity to the hormone. The first step in the mechanism of action of PRL is the binding to a cell surface receptor. The ligand binds in a two-step process in which site 1 on PRL binds to one receptor molecule, after which a second receptor molecule binds to site 2 on the hormone, forming a homodimer consisting of one molecule of PRL and two molecules of receptor. The PRLR contains no intrinsic tyrosine kinase cytoplasmic domain but associates with a cytoplasmic tyrosine kinase, JAK2. Dimerization of the receptor induces tyrosine phosphorylation and activation of the JAK kinase followed by phosphorylation of the receptor. Other receptor-associated kinases of the Src family have also been shown to be activated by PRL. One major pathway of signaling involves phosphorylation of cytoplasmic State proteins, which themselves dimerize and translocate to nucleus and bind to specific promoter elements on PRL-responsive genes. In addition, the Ras/Raf/MAP kinase pathway is also activated by PRL and may be involved in the proliferative effects of the hormone. Finally, a number of other potential mediators have been identified, including IRS-1, PI-3 kinase, SHP-2, PLC gamma, PKC, and intracellular Ca2+. The technique of gene targeting in mice has been used to develop the first experimental model in which the effect of the complete absence of any lactogen or PRL-mediated effects can be studied. Heterozygous (+/-) females show almost complete failure to lactate after the first, but not subsequent, pregnancies. Homozygous (-/-) females are infertile due to multiple reproductive abnormalities, including ovulation of premeiotic oocytes, reduced fertilization of oocytes, reduced preimplantation oocyte development, lack of embryo implantation, and the absence of pseudopregnancy. Twenty per cent of the homozygous males showed delayed fertility. Other phenotypes, including effects on the immune system and bone, are currently being examined. It is clear that there are multiple actions associated with PRL. It will be important to correlate known effects with local production of PRL to differentiate classic endocrine from autocrine/paracrine effects. The fact that extrapituitary PRL can, under some circumstances, compensate for pituitary PRL raises the interesting possibility that there may be effects of PRL other than those originally observed in hypophysectomized rats. The PRLR knockout mouse model should be an interesting system by which to look for effects activated only by PRL or other lactogenic hormones. On the other hand, many of the effects reported in this review may be shared with other hormones, cytokines, or growth factors and thus will be more difficult to study. (ABSTRACT TRUNCATED)

Binding of 125I-prolactin to spermatozoa from normospermic and asthenospermic men

Scatchard analysis of prolactin binding sites (PRL-BS) from ejaculated spermatozoa showed a single population of binding sites (apparent association constant: 2.51+/-0.186 nmol/l[-1]) with 0.317+/-0.0743 fmol/10(6) sperm binding sites. Different pools of spermatozoa were incubated with increasing concentrations of several hormones. There was a decrease in [125I]-oPRL binding with purified ovine prolactin (oPRL) and human growth hormone (hGH) which was not observed in the presence of synthetic ACTH and recombinant FSH, suggesting that binding was hormone specific. When the patient's samples were analyzed using the single point assay at saturation concentration, asthenospermic patients showed a significantly higher concentration of binding sites compared to normospermic ones. Both groups of patients displayed similar PRL levels in seminal plasma measured by DELFIA. Moreover, individual values of PRL levels in seminal plasma did not correlate with PRL-BS concentrations. We thus conclude that [125I]-oPRL binding to ejaculated spermatozoa was hormone specific and with similar parameters as seen in other target tissues. PRL-BS concentration in asthenospermic patients was significantly higher than in normospermic but this was not due to different levels of PRL in seminal plasma.

Evaluation of semen parameters in man with hyperprolactinemia induced by metoclopramide

Hyperprolactinemia in man decreases libido and potency, but the few reports concerning its influence on spermatogenesis are contradictory. The aim of this study was to evaluate the effect of induced hyperprolactimemia on semen parameters. A total of 15 potentially fertile male volunteers, aged 28.2 +/- 4.3 years, were given 10 mg metoclopramide three times daily for 12 weeks. Serum and seminal plasma prolactin levels and semen parameters were determined before and 4, 8, and 12 weeks following initiation of metoclopramide administration. A fivefold increase of serum prolactin levels was observed, semen volume and abnormal sperm forms decreased, while spermatozoa velocity increased. On the contrary, no influence was noted on the number of spermatozoa per milliliter, the total number of spermatozoa, the percentage of motile spermatozoa, or the index of motility. Hyperprolactinemia seems to improve spermatozoal velocity and morphology, although direct effect of metoclopramide on these parameters cannot be excluded.

Hyperprolactinemia in men with asthenozoospermia, oligozoospermia, or azoospermia

The role of serum prolactin (PRL) in male infertility is still unclear. To assess the clinical significance of PRL determination during infertility studies, serum hormones and semen samples from 167 men attending the Andrology Clinic were analyzed, and PRL seric values were correlated with volume, sperm count, motility, viability, and morphology. The range of PRL levels (ng/mL) was 7.3 +/- 2.1 in the control group (n = 46), 13.9 +/- 6.6 in asthenozoospermic (n = 51), 12.6 +/- 7.8 in oligozoospermic (n = 42), and 10.9 +/- 4.8 in azoospermic patients (n = 28). Significantly higher (p < .0001) levels of PRL were found in the men with asthenozoospermia, oligozoospermia, and azoospermia. In the 121 infertile patients with abnormal semen analysis, serum PRL levels were below 14.0 ng/mL (normal mean + 3 SD) in 81 (66.9%) and above this level in 40 (33.1%) cases. Serum FSH and LH concentrations in azoospermic men were significantly higher (p < .0001) when compared with those of the control group, which indicates some disturbance of the spermatogenic process, and estradiol was significantly higher (p < .02) in oligozoospermic patients. No significant differences were found in serum testosterone. Twenty-one patients with idiopathic oligoasthenozoospermia and hyperprolactinemia were treated with 2.5 mg of bromocriptine daily for 6 months, resulting in a nonmeasurable effect on their sperm analysis. In conclusion, two-thirds of patients with oligozoospermia, asthenozoospermia, and azoospermia have normal PRL levels. Infertility in men due to moderate hyperprolactinemia could be associated with these sperm disturbances, but bromocriptine was of no therapeutic utility.

Sperm motility should be assessed in fresh sperm and after a sperm washing procedure

A prospective study was carried out on semen samples from 118 consecutive unselected men attending our infertility clinic to determine whether sperm motility may be affected by seminal plasma. The incidence of asthenozoospermia as defined by fewer than 50% of spermatozoa with forward progressive motility in the untreated semen was 37.4%. This value was significantly reduced to 23% after washing and removing seminal plasma. Men with asthenozoospermia in untreated semen but normal in the washed sample had a percentage of normal sperm morphology and a percentage of swollen tails in the HOS test similar to those of controls, and higher than those of asthenozoospermics in both the untreated and washed sample. Sperm velocity was also significantly improved after the washing procedure. Spermatozoa selected by swim-down procedure and applied to a seminal plasma medium reduced sperm motility affecting negatively the HOS test. Sperm motility should be assessed after a sperm washing procedure, since seminal plasma contains constituents that decrease sperm motility without affecting membrane integrity.

The secretory activity of the seminal vesicles and its relationship to sperm motility: effects of infection in the male reproductive tract

In 146 males aged between 20 years and 40 years attending an infertility service, the secretory activity of the seminal vesicles was assessed by measurement of corrected seminal fructose concentration. This value was related to the presence of a positive semen culture, other evidence of inflammatory processes in the reproductive tract and sperm motility. Only 48% of subjects with a positive semen culture showed evidence of inflammation in the reproductive tract, as assessed by the presence of more than 20 white blood cells per high power field, and greater than 10% spermagglutination in the ejaculate. There was a relationship between the inflammatory process, hypofunction of the seminal vesicles and poor sperm motility. When the semen culture was positive but there was no evidence of inflammation neither seminal vesicle function nor sperm motility was affected. When the semen culture was negative, i.e. no evidence of inflammation and the subjects were asthenozoospermic, the corrected fructose levels were normal. It is proposed that in these conditions the cause of asthenozoospermia may be factors other than accessory sex organ dysfunction. In conclusion, there was no close relationship between the bacteriological results and evidence of inflammation of the accessory glands. A positive semen culture was related to lower levels of corrected fructose (hypofunction of the seminal vesicles) when the positive sperm culture was associated with inflammation of the reproductive tract and asthenozoospermia.

Seminal prolactin and its relationship to sperm motility in men

Semen assessment and levels of serum and seminal plasma prolactin (PRL) were determined in 81 men. In subjects with both normal sperm concentrations and normal sperm motility, the levels of serum and seminal plasma PRL were 14.7 +/- 1.48 and 10.0 +/- 1.05 ng/ml (mean +/- standard error of the mean, SEM, P less than 0.05), respectively. This difference is not observed either in subjects with polyzoospermia with normal sperm motility, or in those with oligozoospermia. Serum PRL was higher in azoospermia and also in subjects with lower levels of seminal citric acid. Seminal plasma PRL was directly related to sperm motility (r = 0.70, P less than 0.01) and inversely related to sperm concentration (r = -0.42 P less than 0.05). Seminal PRL was increased in subjects with higher levels of seminal citric acid and decreased in subjects with lower levels of corrected seminal fructose. Serum and seminal plasma PRL did not change significantly in subjects with different concentrations of serum testosterone.

Functional structure and ultrastructure of seminal vesicles

The function of the seminal vesicles in animals and man is under androgen control. The use of a new marker of the seminal vesicle function, termed corrected fructose, demonstrates an association between serum testosterone levels and seminal corrected fructose levels. The human seminal vesicles secrete a variety of products, and there is good evidence of a close relationship between functions of the seminal vesicles and sperm motility. Some of their products of secretion, such as potassium, bicarbonate, prostaglandins, and prolactin, directly stimulate the motility of the sperm through actions at the level of the mechanisms of production of the energy necessary for the motion. Several constituents are secreted by the seminal vesicles, some of which have no specific functions.

Hypoprolactinemia as related to seminal quality and serum testosterone

Semen quality and serum testosterone were studied in six men with hypoprolactinemia (less than or equal to 6 ng/ml) and in normoprolactinemic controls. The incidence of hypoprolactinemia in 92 men attending an infertility clinic was 7.5%. Males with hypoprolactinemia showed in high percentage of disorders (oligozoospermia, 50%; asthenospermia, 75%; hypofunction of seminal vesicles, 67%; and hypoandrogenism, 67%). Hypoprolactinemia is a clinical disorder associated mainly with poor sperm motility.

Influences of prolactin upon spermatogenesis and spermatozoa during in vitro fertilization in mice

Hyperprolactinemia, induced by pituitary isografts for 20 weeks in male mice and confirmed by radioimmunoassay using anti-mouse prolactin serum, did not impair spermatogenesis in the testis and maturing processes of spermatozoa in the epididymis. Incubation of freshly obtained epididymal spermatozoa for 90 min in culture media containing various levels of mouse prolactin did not yield any adverse effects on percentage motility rates of epididymal spermatozoa. When the level of mouse prolactin in the preincubation medium for epididymal spermatozoa was 100 ng/ml, the rate of fertilization by these preincubated spermatozoa in the subsequent in vitro fertilization experiment was significantly lowered compared with that observed in controls. However, when the level of prolactin in preincubation media was 10 ng/ml, no significant reduction in the rate of fertilization occurred. The present experiments seem to indicate the existence of some differences in the effects of prolactin on male germ cells until they reach the tail of the epididymis and on the processes of capacitation and/or fertilization by epididymal spermatozoa after they leave the epididymis.

Lack of effect of exogenous prolactin on the fertilizing capacity of human spermatozoa in vitro

The effect of exogenous prolactin (PRL) on the fertilizing capacity of human spermatozoa in vitro was evaluated by the zona-free hamster ova penetration assay. Bovine and ovine PRL, in both physiological and pharmacological concentrations, failed to increase the penetration after 5 hr of incubation in vitro. The percent motility of spermatozoa was not influenced by PRL during the incubation period. Exogenous PRL does not affect the fertilizing capacity of human spermatozoa in vitro. The role of prolactin, normally present in seminal plasma and female reproductive tract fluid, in the human spermatozoal capacitation process merits further investigation.

Characterization of hyperactivated motility by human spermatozoa during capacitation: comparison of fertile and oligozoospermic sperm populations

Suspensions of capacitating human spermatozoa were analyzed for potential hyperactivated movements using videomicrographic methods. Analysis was carried out on aliquots of 22 sperm suspensions, which were proved fertile several hours later during human in vitro fertilization. After approximately 3 h of capacitation, 22.1% of the fertile spermatozoa displayed motility patterns designated as hyperactivated. Over 80% of these hyperactivated spermatozoa moved with a wide-amplitude, two-dimensional whiplash pattern, displaying marked lateral displacement of the head. Only 8.4% of capacitating spermatozoa from oligozoospermic patients showed these hyperactivated movements. The incidence of hyperactivated movements by fertile and oligozoospermic spermatozoa could be significantly increased after exposure to various motility stimulants. The clinical significance of hyperactivation as a functional assay of fertilizing capacity is discussed.

Relationships of seminal plasma prolactin with spermatozoal characteristics and fertilizing capacity in vitro

Seminal plasma prolactin (PRL) levels were determined in 224 semen samples collected from fertile and suspected infertile men, and their relationships with spermatozoal characteristics and fertilizing capacity in vitro were evaluated. PRL concentrations were similar in normospermic and oligospermic samples, but were significantly lower in azoospermic samples. PRL concentrations were significantly higher in samples with high spermatozoal motility than in those with low spermatozoal motility. There were no significant differences in PRL concentrations between normal-morphology and abnormal-morphology samples, and between high-fertilizing capacity and low-fertilizing capacity samples. A low degree of positive correlation was observed between the PRL concentration and the spermatozoal motility. There were no significant correlations between the PRL levels, the other spermatozoal characteristics, and the spermatozoal fertilizing capacity in vitro. These findings indicate that the seminal plasma PRL levels are significantly depressed in azoospermic subjects and suggest that the seminal plasma PRL may play a role in the maintenance of spermatozoal motility. Whether there is a potential function of prolactin in semen on spermatozoal fertilizing capacity, however, cannot be inferred from the present study.

An examination of blood steroid and gonadotropin concentrations in relation to fertility status and testicular function in men

Plasma concentrations of luteinizing hormone (LH), follicle-stimulating hormone (FSH), prolactin (PRL), testosterone (T), and 17 beta-estradiol (E2) have been measured in men complaining of infertility in comparison with men of proven fertility. Subgrouping of patients was achieved on the basis of the presence or absence of sperm in the ejaculate and further by the concentration of sperm or by testicular score. The levels of plasma LH, FSH, PRL, and T were found to be significantly different in the fertile men, compared with both infertile men with sperm in their ejaculates and azoospermic men. There were no significant differences between the groups for E2. There appeared to be an inverse relationship between LH concentrations and sperm count in both fertile and infertile men. FSH levels did not vary significantly in the fertile men in relation to sperm count grouping but were significantly less than those found for the infertile men with sperm. Azoospermic patients with high testicular scores had FSH levels indistinguishable from those of the fertile men. The results are discussed in terms of testicular abnormalities and on the interrelationship between the hormones examined.

Prolactin in seminal fluid

Prolactin appears to modulate male reproduction by regulating hormone receptor levels in the testis and accessory sex organs and by facilitating spermatozoal biochemical processes associated with capacitation. A large portion of immunoreactive prolactin (iPRL) seems to be transported from blood to semen via the accessory sex organs and takes several days to make this transition. The iPRL in semen is heterogeneous in size and a unique portion may be associated with spermatozoa. Data from several clinical studies of seminal fluid prolactin are inconsistent. The variability of patient populations classified as fertile or infertile, the differences in prolactin assays used, and the lack of information about sample processing have been major causes of this difficulty.

Prolactin and male reproduction

Elevated levels of prolactin(PRL) are associated with gonadal dysfunction in men and women, but the relationship between PRL levels and gonadal activity is best defined in women. The purpose of this review is to summarize and discuss the influence of PRL on the male reproductive function in normaprolactinemia and to describe the clinical, diagnostic, and therapeutic aspects of the male hyperprolactinemia syndrome as related to sexual dysfunction and infertility.