The role of prolactin in the regulation of testis function: the synergistic effects of prolactin and luteinizing hormone on the incorporation of (1- 14 C)acetate into testosterone and cholesterol by testes from hypophysectomized rats in vitro

An unusual case of Cushing's syndrome due to bihormonal ACTH-prolactin secreting pituitary macroadenoma with rapid response to cabergoline

A 23-year-old man presenting with florid Cushing's syndrome was found to have high plasma ACTH and very high serum prolactin. Pituitary MRI showed a large invasive macroadenoma. Low-dose cabergoline promptly suppressed both ACTH and prolactin levels within 2 weeks, with unexpected clinical and biochemical hypocortisolism requiring hydrocortisone replacement. Secondary hypogonadism was reversed. Clinical and biochemical remission of his Cushing's syndrome together with significant shrinkage of his macroadenoma has been maintained for 1 year on cabergoline 0.5 mg twice weekly. Reduction in pituitary tumour volume and brisk fall in serum prolactin in response to low-dose cabergoline is regularly observed in patients with macroprolactinomas, but the concurrent fall in the plasma ACTH level and hypocortisolism was a pleasant surprise. We assume that he most likely has a single bihormonal adenoma that is enriched with dopamine-2 receptors.

Carcinogenicity of Monochloro-1,2-Propanediol (α-Chlorohydrin, 3-MCPD)

3-Monochloro-1,2-propanediol (3-MCPD) is a by-product found in trace amounts, generally less than 1 mg/kg (<1 ppm), in hydrolyzed vegetable protein produced through acid hydrolysis. In a chronic study with F344 rats, high doses of 3-MCPD produced benign renal tumors in both sexes and Leydig-cell and mammary tumors in males. 3-MCPD is genotoxic in vitro, but there is no evidence of genotoxicity in vivo. There is some question about the mechanism responsible for the carcinogenicity of 3-MCPD in certain species. Here we present a critical review of the toxicological, metabolic, and mechanistic data on 3-MCPD. On the basis of this review, the tumors reported in F344 rats are concluded to have developed as a result of nongenotoxic mechanisms and are considered not to be relevant to humans exposed to trace amounts of 3-MCPD. This conclusion was based on the lack of carcinogenicity of 3-MCPD in mice or Sprague-Dawley rats; the benign nature of the tumors involved; the dependence of the Leydig-cell and mammary tumors on species-and strain-dependent mechanisms involving chronic changes in hormone balance; the association of the renal tumors with chronic nephropathy and nephrotoxicity; and differences between bacterial and mammalian systems in the metabolism of 3-MCPD that likely account for its genotoxic activity in certain in vitro test systems. At trace levels in foods, 3 MCPD is considered not to pose a carcinogenic risk to humans.

The Lipidosterolic Extract fromSerenoa repens Interferes with Prolactin Receptor Signal Transduction

The lipidosterolic extract from the saw palmetto Serenoa repens (LSESr) is commonly used for medical treatment of benign prostatic hypertrophia due to its ability to inhibit 5alpha-reductase which permits the conversion of testosterone to dihydrotestosterone, the active androgen on prostate cell proliferation. However, the complete action mechanism of LSESr is still unknown. Several lines of evidence suggest that, in addition to inhibition of 5alpha-reductase, it may interfere with the action of prolactin (PRL). We therefore investigated a possible interference of this plant extract with another hormone that controls prostate gland growth, PRL. As the action mechanism of PRL is now fully documented in Chinese hamster ovary cells expressing the PRL receptor, we have conducted our experiments on these cells. In this study, using electrophysiological (whole-cell recording and single-channel recording), microspectrofluorimetric and biochemical techniques, we show that LSESr (1-30 &mgr;g/ml) reduced the basal activity of a K(+) channel and of protein kinase C (PKC) in CHO cells. In addition, pretreatment of the cells with 1-10 &mgr;g/ml LSESr for 6-36 h abolished the effects of PRL on [Ca(2+)](i), K(+) conductance and PKC. LSESr may block PRL-induced prostate growth by inhibiting several steps of PRL receptor signal transduction. LSESr may also be useful for diseases implicating PRL. Copyright 1995 S. Karger AG, Basel

Acute effect of prolactin on ornithine decarboxylase activity in the rat testis

A study was conducted to evaluate the effect of the acute treatment with prolactin (PRL) on ornithine decarboxylase (ODC) activity in the rat testis. Injection of a single SC dose of ovine PRL to puberal rats resulted in the activation of ODC from whole testis. This effect was maximal at 4 h after injection, and statistically significant at the dose of 500 micrograms. The effect of PRL was confined to the interstitial space; no change was observed in seminiferous tubules. PRL was unable to further increase testicular ODC activity when injected together with a stimulatory dose of human chorionic gonadotropin (hCG). The effect of PRL was mimicked by injection of a single dose of the dopamine antagonist sulpiride, which provoked a ninefold increase in serum PRL levels. In contrast, PRL did not stimulate testicular ODC activity in hypophysectomized rats, either under basal conditions or during treatment with PRL-hCG, indicating the requirement of a functional hypophysis for the expression of PRL action. These results suggest that the stimulation of testicular ODC activity by PRL is a marker of the trophic response of the testis to this hormone, different from the stimulation of steroidogenesis. This activity could be useful for the study of PRL action on the testis as well as of the interaction between PRL and LH at the testicular level.

Ontogenic studies of the neural control of adenohypophyseal hormones in the rat. II. Prolactin

1. Serum prolactin levels are low during the first 20 days of life and gradually increase toward puberty, in both male and female rats. 2. There is an age-related increase in the cell population engaged in prolactin secretion, as well as an increase in the synthesis of prolactin and of the amount of prolactin secreted from individual lactotropes. 3. The gradual increase in prolactin levels in the third week of life is not related to a decrease in dopaminergic inhibition but to an increase in the efficiency of prolactin releasing factors such as estrogen, serotonin, opiates, and posterior pituitary extracts. 4. Prolactin release induced by physiological factors, such as stress, cervical stimulation, or the expression of spontaneous diurnal and nocturnal surges, requires maturational events within the hypothalamic-pituitary axis which are evident at the end of the third week of life. 5. In the female rat the steadily increasing levels of prolactin are involved in the timing of puberty eclosion acting at the ovary and at the brain. 6. In the prepubertal male rat increasing titers of prolactin may be involved in testicular and accessory organ development and may facilitate the actions of luteinizing hormone, follicle stimulating hormone, and testosterone on male sexual organs.

Regulation of the testis

The testicular cells are regulated by factors produced locally in the testis. These factors include peptide growth factors, pro-opiomelanocortin derivatives, neuropeptides and steroids. Several agents able to affect steroido- and spermatogenesis can also affect leukocytes and many of the testis-regulating factors are produced by immune cells, suggesting that testicular cells and leukocytes may interact. In the present article, the effects of various testicular cell and leukocyte produced factors on steroido- and spermatogenesis are reviewed. The possibility that leukocytes may produce substances able to affect the testicular functions suggests that inhibition of immune system activation in the testis may be important also for reasons other than protection of autoantigenic germ cells from an autoimmune attack.

Effect of hypo and hyperprolactinemia on the testicular maturation of Wistar rats during puberal transition

In Wistar rats, the structural and metabolic organization of the testis was influenced by the blood concentration of prolactin. The androgen dependent enzyme activities in plasma as well as in testis were higher under hyperprolactinemia and lower under hypoprolactinemia, as induced by bromocriptine. While prolactin had direct effect on the testicular functions, bromocriptine seemed to exert its influence through blocking hypophysial prolactin.

Hyperprolactinemic infertile men

Clinical descriptions of prolactin in states of oversecretion are presented in 49 patients that presented for infertility investigation. Radiological assessment did not reveal microadenomas in these patients. Erectile dysfunction or deficient semen parameters could be early manifestations of hyperprolactinemia in some infertile men.

Prolactin and Leydig cell steroidogenic enzymes in the bonnet monkey (Macaca radiata)

The effect of treatment with prolactin or bromocryptine on testicular steroidogenesis and serum hormone levels were studied in immature and mature bonnet monkeys. Leydig cells alone showed the presence of 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD) and 17 beta-hydroxysteroid dehydrogenase (17 beta-HSD) in normal immature and mature monkeys. Administration of prolactin increased the activity of 3 beta-HSD and 17 beta-HSD in Leydig cells from mature monkeys, and also increased the serum levels of testosterone. Bromocryptine treatment induced exactly the opposite effect. These changes occurred in the absence of any change in serum gonadotrophin levels. In immature monkeys, prolactin and bromocryptine had no significant effect. These results suggest a direct stimulatory effect of prolactin on testicular steroidogenesis in mature monkeys.

Effect of ectopic pituitary homograft on the physiological status of rat testis

Pituitary glands grafted under the kidney capsule provide a continuous supply of prolactin due to the absence of hypothalamic inhibitory factor. Increase in the level of prolactin in the rat may affect availability of hormone for reproductive function. Single pituitaries were transplanted under the kidney capsule of male rats. After six weeks of the transplant, the recipient rats were sacrificed and trophic activity of testosterone and intratesticular functions were assessed. The weights of ventral prostate and seminal vesicles, full and empty, showed significant increase from the control value. The activity of beta-glucuronidase in kidney, an androgen inducible enzyme, also increased in comparison with the control value. Incorporation of 32P in the nucleic acid fraction showed an increase. The increased rate of testosterone production and an alteration in spermatogenesis was associated with increased activity of acid phosphatase and decreased activity of beta-glucuronidase. The active mediation of lysosomal enzyme in testicular function as altered by prolactin was indicated.

The effect of prolactin on human BPH epithelial cell proliferation

Epithelial cell monolayers derived from specimens of human benign prostatic hyperplasia (BPH) tissue by an explant culture technique were cultured with prolactin in the presence and absence of androgens. Proliferation of the cells was measured by both autoradiographic assessment of [3H]-thymidine uptake and stathmokinetic procedures. Prolactin significantly stimulated the growth of these cells in the concentration range 0.5 mIU/ml to 10 mIU/ml but was inhibitory at a concentration of 100 mIU/ml. In the presence of testosterone (1 X 10(-7) M), prolactin at low concentrations (greater than 1 mIU/ml) but not at 10 mIU/ml, the concentration at which all other experiments were performed, produced a further stimulation in the proliferation. The increase in growth seen with cells cultured with 5 alpha-dihydrotestosterone (1 X 10(-7) M) was reduced with addition of prolactin at high concentrations (10-100 mIU). When the fetal calf serum used in the cultures was stripped of endogenous steroids, prolactin still increased cell proliferation, although to a reduced extent. This indicated that the effects of prolactin were not dependent on the presence of androgens.

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.

Twenty-four hour profiles of serum prolactin during male puberty with and without gynaecomastia

Twenty-four hour profiles of circulating prolactin have been documented in eight boys with simple delayed puberty, eleven with gynaecomastia, three of whom were retested following its spontaneous resolution, and two normal adult men. Mean 24 h prolactin levels in four boys with delayed puberty and ten with gynaecomastia exceeded the mean levels for the two adult men. A sleep-associated rise in prolactin levels occurred at all stages of puberty irrespective of the presence or absence of gynaecomastia, and in some subjects peaks also occurred during the daytime. Boys with gynaecomastia had higher 24 h means levels of prolactin (P less than 0.05), higher daytime levels (P less than 0.05) and higher sleep-associated levels (P less than 0.05) than did control subjects. These were not related to the degree or duration of the gynaecomastia, but 24 h mean levels of prolactin and oestradiol were positively correlated. In one subject who had had transient galactorrhoea, high levels of circulating prolactin, oestrone and oestradiol fell following spontaneous resolution of the gynaecomastia. We believe that oestrogen: androgen imbalance during the daytime is the major cause of pubertal gynaecomastia, with hyperprolacinaemia (which may cause galactorrhoea) sometimes occurring as a response to relative hyperoestrogenaemia.

Specific binding of prolactin by the prostate gland of the rat and man

Specific binding sites for 125iodine-prolactin are present in membrane particles obtained from the rat ventral prostate, human benign prostatic hyperplasia and prostatic adenocarcinoma. In the ventral prostate glands of young rats (1 to 4 months old) specific binding of 125iodine-prolactin is higher than in older animals (greater than 8 months old). Subcellular distribution studies revealed that specific 125iodine-prolactin binding activity is associated primarily with the 15,000 and 100,000 g particulate membrane fractions of the rat ventral prostate and human prostate glands. In rats between 2 and 4 months old significant increases in the prolactin binding activity in the 100,000 g membrane fraction of the ventral prostate are observed to occur without concomitant increases in prolactin binding activity in the 15,000 g fraction. The level of specific 125iodine-prolactin binding activity present in the human prostate gland is lower than that observed in the rat ventral prostate gland. Localization of specific prolactin binding sites in the rat ventral psotate and the human prostate gland suggests that prolactin could influence the function of these tissues directly.

Investigations on the influence of prolactin suppression on reproductive function in bulls

In 3 mature bulls 2 injections (i.m.) of 150 mg 2-Br-alpha-ergocryptine (CB-154, Sandoz) within 48 hrs. decreased the plasma prolactin concentrations significantly for about 14 days (first experiment). In a second experiment, where treatment was repeated after 2 weeks, the period of maximal prolaction deficiency could be extended to a length of about 4 weeks. However, intensity of prolactin inhibition was less pronounced. This is attributed to seasonal factors. Neither during the shorter nor during the longer period of prolactin suppression were apparent changes of the LH and testosterone levels observed. Apart from a minor increase in the rate of morphologically abnormal sperm cells, reproductive function as libido, mating behaviour, semen quality, secretory activity of the accessory glands (concentration of fructose, GPC and chloride in seminal plasma and pre-sperm fraction resp.) were not significantly affected. It seems questionable, therefore, whether under physiological conditions prolactin is essential for the regulation of sexual functions in mature bulls.

Evaluation of proteohormon concentrations in serum and seminal fluid and its relationship with sperm count

The measurement of FSH, LH, and PRL in serum and seminal fluid of 105 men attending a male infertility clinic and 21 men of proven fertility (controls) did not reveal an interrelationship between the spermatozoal count and the level of the proteo-hormones in both biological fluid except for FSH, which was significantly higher in the serum of men with low as compared to normal sperm count (p less than 0.01). FSH in seminal fluid was significantly lower (p less than 0.01), and LH-like activity significantly higher (p less than 0.01) than in serum, while there was no difference between the respective levels of PRL. These results could be confirmed in 4 patients with azoospermia due to occlusive disease, and in 1 out of 2 vasectomized men. It was demonstrated for the first time that the higher concentration of "LH" in seminal fluid as compared to serum was due to the presence of HCG-beta or a HCG-like material cross-reacting with the antiserum against LH.

Influence of hyperprolactinaemia due to metoclopramide on gonadal function in men

Five clinically normal male volunteers were given metoclopramide, 10 mg t.d.s. for 6 weeks. During treatment prolactin concentrations were elevated (over 50 ng/ml) in all. LH, FSH, testosterone and cortisol concentrations were not altered. No change was observed in LH or FSH responses to LHRH testing 4 weeks after the beginning of therapy, compared with pre-treatment values. A reduction in seminal volume and total sperm count were observed in each subject. Four noticed a decrease in libido and three lost spontaneous erections. While the metoclopramide-induced hyperprolactinaemia could be the cause of the observed changes in semen and erectile activity, it is possible that this dopamine receptor blocking drug might directly affect central or peripheral mechanism of erection, the testes or accessory organs.

Bromocriptine and prostatic carcinoma: plasma kinetics, production and tissue uptake of 3H-testosterone in vivo

The influence of the anti-prolactin bromocriptine on plasma kinetics, production rate and tissue uptake of testosterone was investigated in 15 patients with newly diagnosed stages C and D prostatic carcinoma. Bromocriptine was given for 5 days in a daily dose of 15 mg. orally. The studies were performed with the single injection technique using the 2-compartment model. Plasma testosterone, serum prolactin, and luteinizing and follicle-stimulating hormones were determined initially. Blood samples were drawn up to 5 hours after the injection of 3H-testosterone. For tissue studies a transrectal needle biopsy was done 3 hours post-injection. Bromocriptine suppressed prolactin and the endogenous testosterone level. Furthermore, it favored the elimination of 3H-testosterone, lowered the production rate of testosterone and hampered the in vivo uptake of the 3H-label into prostatic carcinoma tissue. Finally, the grading of the tumor lesions affected only the pre-bromocriptine uptake of radioactive androgens and not the uptake in response to bromocriptine. The potential clinical impliications of these observations are discussed.

Prolactin binding in rat testis: specific receptors in interstitial cells

Specific receptors for [125I]hPrl (human prolactin) are present in membrane preparations of rat testis. The receptors are specific for lactogenic hormones (prolactin and human growth hormone) but do not bind gonadotropins. The prolactin receptors are localized exclusively in the interstitial cell tissue, and are not present in membrane preparations from isolated seminiferous tubules. The localization of prolactin receptors interstitial tissue suggests that the effect of prolactin on LH/hCG-stimulated testosterone production is due to a direct effect of prolactin of Leydig cells.