Macroprolactinemia: a new cause of hyperprolactinemia

Macroprolactinemia: a mini-review and update on clinical practice

Hyperprolactinemia is common among infertile patients, with up to 15%-20% of women with oligomenorrhea having hyperprolactinemia. Suppression of the hypothalamic-pituitary-gonadal axis via inhibition of pulsatile gonadotropin releasing hormone because of hyperprolactinemia is a common endocrine etiology of infertility. There are 3 forms of human prolactin (PRL): monomeric PRL, dimeric PRL, and macro-PRL. Also known as big-big PRL, macro-PRL has a molecular weight >150 kDa and normally comprises 5%-10% of circulating PRL. When the predominant form of circulating PRL is macro-PRL, macroprolactinemia is diagnosed. Among patients with hyperprolactinemia, 10%-46% have macroprolactinemia. Patients with macroprolactinemia are at risk of unnecessary pituitary imaging and treatment with dopamine agonists if not correctly diagnosed. Given the high prevalence of macroprolactinemia among patients with elevated PRL levels and the different management of patients with macroprolactinemia vs true monomeric hyperprolactinemia, all patients with persistently elevated PRL levels should be screened for macro-PRL.

Evaluation of autoantibodies and immunoglobulin G subclasses in women with suspected macroprolactinemia

BACKGROUND

Macroprolactin mostly composed of an immunoglobulin G (IgG) and a monomeric prolactin (PRL) represents the major circulating PRL form in the patients with macroprolactinemia that are usually asymptomatic and may not require treatment. In this study, we aimed to evaluate the prevalence of antithyroid and antinuclear antibodies, as well as the IgG subclass distributions in the patients suspected for macroprolactinemia.

METHODS

From January to July in 2018, totally 317 patients with elevated PRL were subjected to the polyethylene glycol (PEG) precipitation assay. The patients with recovery rates of ≤60% were subjected for IgG subclass determination and autoantibody testing including thyroid peroxidase antibody (aTPO), antithyroglobulin antibody (aTG), and antinuclear antibodies (ANA).

RESULTS

The higher the post-PEG PRL recovery rates, the less typical hyperprolactinemia symptoms and the higher prevalence of autoantibodies were observed. The IgG1 and IgG3 were the predominant subclasses in the PRL-IgG complexes according to the immunoprecipitation experiments.

CONCLUSION

The patients with post-PEG PRL recovery rates of <40% and 40%-60% were likely to represent two distinct populations of different clinical presentations. The prevalence of autoantibodies and IgG subclasses distribution suggested their pathogenic significance in the development of macroprolactinemia.

Biochemical diagnosis in prolactinomas: some caveats

Prolactinomas are the most frequently seen pituitary adenomas in clinical practice. A correct biochemical diagnosis of hyperprolactinemia is a prerequisite for further investigation but may be hampered by analytical difficulties as well as a large number of potentially overlapping conditions associated with increased prolactin levels. Suspicion should rise in patients whose symptoms and biochemical results do not match. Assay problems, macroprolactinemia, and high-dose hook effect are discussed as possible reasons for false positive or false negative prolactin levels. Physiological and pathological causes of hyperprolactinemia and their implications for interpreting prolactin results are reviewed.

PCOS and Hyperprolactinemia: what do we know in 2019?

Polycystic ovary syndrome (PCOS) and hyperprolactinemia (HPRL) are the two most common etiologies of anovulation in women. Since the 1950s, some authors think that there is a pathophysiological link between PCOS and HPRL. Since then, many authors have speculated about the link between these two endocrine entities, but no hypothesis proposed so far could ever be confirmed. Furthermore, PCOS and HPRL are frequent endocrine diseases and a fortuitous association cannot be excluded. The evolution of knowledge about PCOS and HPRL shows that studies conducted before the 2000s are obsolete given current knowledge. Indeed, most of the studies were conducted before consensual diagnosis criteria of PCOS and included small numbers of patients. In addition, the investigation of HPRL in these studies relied on obsolete methods and did not look for the presence of macroprolactinemia. It is therefore possible that HPRL that has been attributed to PCOS corresponded in fact to macroprolactinemia or to pituitary microadenomas of small sizes that could not be detected with the imaging methods of the time. Recent studies that have conducted a rigorous etiological investigation show that HPRL found in PCOS correspond either to non-permanent increase of prolactin levels, to macroprolactinemia or to other etiologies. None of this recent study found HPRL related to PCOS in these patients. Thus, the link between PCOS and HPRL seems to be more of a myth than a well-established medical reality and we believe that the discovery of an HPRL in a PCOS patient needs a standard etiological investigation of HPRL.

Different Cabergoline Effect on Metabolic and Anthropometric Parameters in Female Prolactinoma Patients Versus Idiopathic Hyperprolactinemia Patients

BACKGROUND

Hyperprolactinemia can lead to weight gain, insulin resistance, abnormal glucose homeostasis and dyslipidemia. Reversibility of these changes after normalization of prolactin with dopamine agonists is still controversial and needs more clarification.

OBJECTIVE

We aimed to: 1) evaluate and compare metabolic and anthropometric profile in female with newly diagnosed prolactin-secreting adenoma versus female idiopathic hyperprolactinemic patients; 2) compare the effects of one year cabergoline therapy on the metabolic profile and anthropometric parameters (by using visceral adiposity index as index for evaluation of adipose tissue dysfunction) in females with prolactinoma to female idiopathic hyperprolactinemic patients.

PATIENTS AND METHODS

We enrolled 40 female patients with newly diagnosed prolactinoma and 40 female patients with idiopathic hyperprolactinemia, who were matched according to: age; weight; BMI; waist; and prolactin levels. We enrolled the participants in this study at the time of diagnosis before therapy and they were followed up for 12 months.

RESULTS

Cabergoline therapy had significant favorable effects on metabolic and anthropometric parameters, visceral adiposity index and in all patients (apart from HDLc in prolactinoma patients). Cabergoline therapy was significantly more effective in patient with idiopathic hyperprolactinemia than prolactinoma patients with regard to BMI, waist circumference, HDLc and visceral adiposity index despite normalization of prolactin levels in both groups.

CONCLUSION

12 months of Cabergoline treatment improved most of the anthropometric and metabolic parameters, and visceral adiposity index as a marker for adipose tissue dysfunction in both idiopathic hyperprolactinemia and prolactinoma patients. However, Cabergoline treatment was more effective in idiopathic hyperprolactinemic than prolactinoma patients.

Pitfalls in the Diagnostic Evaluation of Hyperprolactinemia

An appropriate diagnostic evaluation is essential for the most appropriate treatment to be performed. Currently, macroprolactinemia is the third most frequent cause of nonphysiological hyperprolactinemia after drugs and prolactinomas. Up to 40% of macroprolactinemic patients may present with hypogonadism symptoms, infertility, and/or galactorrhea. Thus, the screening for macroprolactin is indicated not only for asymptomatic subjects but also for those without an obvious cause for their prolactin (PRL) elevation. Before submitting patients to macroprolactin screening and pituitary magnetic resonance imaging, one should rule out pregnancy, drug-induced hyperprolactinemia, primary hypothyroidism, and renal failure. The magnitude of PRL elevation can be useful in determining the etiology of hyperprolactinemia. PRL values >250 ng/mL are highly suggestive of prolactinomas and virtually exclude nonfunctioning pituitary adenomas (NFPAs) and other sellar masses as the etiology of hyperprolactinemia. However, they can also be found in subjects with macroprolactinemia, drug-induced hyper-prolactinemia or chronic renal failure. By contrast, most patients with NFPAs, drug-induced hyperprolactinemia, macroprolactinemia, or systemic diseases present with PRL levels <100 ng/mL. However, exceptions to these rules are not rare. Indeed, up to 25% of patients harboring a microprolactinoma or a cystic macroprolactinoma may also have PRL <100 ng/mL. Falsely low PRL levels may result from the so-called "hook effect," which should be considered in all cases of large (≥3 cm) pituitary adenomas associated with normal or mildly elevated PRL levels (≤250 ng/mL). The hook effect may be unmasked by repeating PRL measurement after a 1:100 serum sample dilution.

Hyperprolactinaemia - a problem in patients from the reproductive period to the menopause

Hyperprolactinaemia especially affects women in reproductive age (90/100,000) but also often is diagnosed in menopause age and leads to disturbances in functioning of LH-RH neurons and, as a consequence, to a decrease of FSH and LH, which causes inhibition of oestradiol production. Prolactin is a peptide hormone, phylogenetically one of the oldest, stimulating cells of various organs, which is produced and secreted mainly by lactotrophic acidophilic cells of the anterior lobe of the pituitary. It influences the increase in the mass of the mammary glands, and stimulation and maintenance of lactation after delivery. There are a number of factors apart of pregnancy, delivery, and lactation than can influence secretion of the hormone in other physiological and pathological circumstances, like high-protein diet, stress, REM sleep, or neoplastic tumours, inflammatory diseases, chronic systematic diseases, thyroid hormonal changes, and drug intake. The purpose of this review is to summarise the current knowledge regarding the proper diagnosis and possible influence of hyperprolactinaemia on fertility and menopause symptoms and current treatment methods.

Urine oligosaccharide pattern in patients with hyperprolactinaemia

Free milk-type oligosaccharides are produced during pregnancy and lactation and may have an impact on several cells in the immune system. Our aim was to investigate if patients with isolated hyperprolactinaemia, not related to pregnancy, also have increased synthesis and urinary excretion of milk-type oligosaccharides and to compare the excretion pattern with that found during pregnancy. Urine samples were collected as morning sample from 18 patients with hyperprolactinaemia, 13 healthy controls with normal prolactin levels and four pregnant women. After purification, lactose and free oligosaccharides were analysed and quantified by high-performance anion-exchange chromatography with pulsed amperometric detection. The identity of peaks was confirmed by exoglycosidase treatment and comparison with oligosaccharide standards. Prolactin was measured in serum collected between 09 and 11 a.m. by a standardized immunochemical method. Patients with hyperprolactinaemia had higher urinary excretion of lactose than normoprolactinemic controls and urinary lactose correlated positively to prolactin levels (r = 0.51, p < 0.05). Increased levels of the fucosylated oligosaccharides 2-fucosyl lactose and lacto-di-fucotetraose were found in urine from three and two patients, respectively. The acidic oligosaccharide 3-sialyl lactose was found in high amount in urine from two patients with prolactin of >10,000 mU/l. However, pregnant women in their third trimester had the highest concentration of all these oligosaccharides and excretion increased during pregnancy. This study is first to show that both lactose and certain fucosylated and sialylated milk-type oligosaccharides are increased in some patients with hyperprolactinaemia. It remains to elucidate the functional importance of these findings.

Effects of prolactin on platelet activation and blood clotting

Increased levels of prolactin often coincide with an increased risk for thromboembolic events, but it is unclear whether a direct causal relation exists. Our aim was to examine the effect of prolactin on platelet function. In addition to using recombinant prolactin for experiments in vitro, we analyzed platelet function by flow cytometry in a group of 13 females with hyperprolactinaemia and 18 healthy female controls. Platelet activation was measured by P-selectin expression and by the amount of platelet-bound fibrinogen after stimulation with adenosine di phosphate (ADP), collagen-related peptide and the protease activated receptor (thrombin receptor) (PAR)-activating peptides PAR4-AP and PAR1-AP. Free oscillation rheometry was used to measure clotting time in whole blood. No significant effect on platelet activation or clotting time could be seen in in vitro experiments by adding recombinant prolactin. However, significantly lower P-selectin expression was found in the hyperprolactinemic group when platelets were activated by ADP (5 and 10 μM) or PAR4-AP. The expression of fibrinogen did not differ between the two groups for any of the activators used. For all samples, inverse significant correlations between P-selectin expression and prolactin concentration were found for both 5 μM ADP (r = - 0.61, p < 0.01), 10 μM ADP (r = - 0.62, p < 0.001) and PAR4-AP (r = - 0.69, p < 0.001). Thrombin cleavage of recombinant prolactin resulting in a 16 kDa C-terminal fragment did not alter the P-selectin expression upon activation. We found an indirect inhibitory effect of prolactin on platelets in hyperprolactinemic patients, suggesting that prolactin might have a protective role in thromboembolic disease.

Macroprolactinemia: new insights in hyperprolactinemia

Hypersecretion of prolactin by lactotroph cells of the anterior pituitary may lead to hyperprolactinemia in physiological, pathological and idiopathic conditions. Most patients with idiopathic hyperprolactinemia may have radiologically undetected microprolactinomas, but some may present other causes of hyperprolactinemia described as macroprolactinemia. This condition corresponds to the predominance of higher molecular mass prolactin forms (big-big prolactin, MW > 150 kDa), that have been postulated to represent prolactin monomer complexed with anti-prolactin immunoglobulins or autoantibodies. The prevalence of macroprolactinemia in hyperprolactinemic populations between 15–46% has been reported. In the pathophysiology of macroprolactinemia it seems that pituitary prolactin has antigenicity, leading to the production of anti-prolactin autoantibodies, and these antibodies reduce prolactin bioactivity and delay prolactin clearance. Antibody-bound prolactin is big enough to be confined to vascular spaces, and therefore macroprolactinemia develops due to the delayed clearance of prolactin rather than increased production. Although the clinical symptoms are less frequent in macroprolactinemic patients, they could not be diff erentiated from true hyperprolactinemic patients, on the basis of clinical features alone. Although gel filtration chromatography (GFC) is known to be the gold standard for detecting macroprolactin, the polyethylene glycol precipitation (PEG) method has off ered a simple, cheap, and highly suitable alternative. In conclusion, macroprolactinemia can be considered a benign condition with low incidence of clinical symptoms and therefore hormonal and imaging investigations as well as medical or surgical treatment and prolonged follow-up are not necessary.

Prevalence of pituitary adenomas in macroprolactinemic patients may be higher than it is presumed

One form of prolactin (PRL) is macroprolactin with high molecular mass. Many macroprolactinemic patients have no pituitary adenomas and no clinical symptoms of hyperprolactinemia, it is controversial whether macroprolactinemia is a benign condition that does not need further investigation and treatment. In this study, we aimed to compare macroprolactinemic patients (group I) with the true hyperprolactinemic patients (group II) for the presence of pituitary adenoma. We investigated 161 patients with hyperprolactinemia, whose magnetic resonance imaging records of the pituitary were taken. All patients were questioned for irregular menses, infertility and examined for galactorrhea. Patients were screened for macroprolactinemia by polyethylene glycol precipitation, and a recovery of ≤40% and normal monomeric PRL level was taken as an indication of significant macroprolactinemia. Of 161 patients with hyperprolactinemia, 60 (37.26%) had macroprolactinemia. PRL levels of group II were lower than those of group I (P = 0.011), although monomeric PRL levels of group II were higher than those of group I (P = 0.0005). Of 60 macroprolactinemic patients, 16 (26.7%) had pituitary adenomas. The prevalence of pituitary adenomas was lower in group I, compared with group II (P = 0.0005). No significant differences were found between the prevalences of irregular menses and infertility of group I and II (P = 0.084, P = 0.361). Prevalence of galactorrhea in group I was lower than that in group II (P = 0.048). Prevalence of pituitary adenomas in macroprolactinemic patients is lower compared with the true hyperprolactinemic patients, but may be higher than that found in other recent studies and in the general population.

Clinical characterization of patients with macroprolactinemia and monomeric hyperprolactinemia

Macroprolactinemia is often a cause of misdiagnosis, unnecessary expensive investigation, and unsuitable treatment. The aim of the present study was to investigate the clinical findings and the concentrations of macroprolactin in patients with hyperprolactinemia in our region. Eighty-four female hyperprolactinemic patients were screened for macroprolactinemia. Prolactin was measured by chemiluminescence method on an Immulite 2000 analyzer (Siemens Health Diagnostics, Deerfield, IL, USA). Recoveries less than or equal to 40% after polyethylene glycol precipitation were indicative of macroprolactinemia. Clinical features and biochemical values were compared in true hyperprolactinemic and macroprolactinemic patients. Macroprolactinemia was detected in 31 patients (36.9%), with 84 hyperprolactinemic female patients. There was no difference in frequency of galactorrhea and oligomenorrhea/amenorrhea between the two groups. When we evaluated the clinical features of patients according to prolactin levels, no significant difference was found between the groups. In conclusion, our initial data show that no clinical features could reliably differentiate macroprolactinemic from true hyperprolactinemic patients, but at least one of these symptoms was present in most macroprolactinemic patients.

Polycystic ovary syndrome or hyperprolactinaemia: a study of mild hyperprolactinaemia

Polycystic ovary syndrome (PCOS) and hyperprolactinaemia are both common causes of secondary amenorrhoea in reproductive women. The relationship between PCOS and hyperprolactinaemia has been reported with controversial results. To evaluate the clinical and laboratory features of women with mild hyperprolactinaemia and PCOS, we studied 474 Taiwan Chinese women: 101 had mild hyperprolactinaemia, 266 had PCOS and 107 were the control group. In this study, we found that 64% of the women with mild hyperprolactinaemia fulfilled the PCOS diagnostic criteria, regardless of their prolactin levels. Obese women with PCOS had significantly lower luteinising hormone (LH) and LH-to-FSH ratios than non-obese women with PCOS. Obese hyperprolactinaemic women had significantly lower follicle-stimulating hormone (FSH), but higher LH-to-FSH ratios than the non-obese hyperprolactinaemic women. For women with PCOS, the BMIs were significantly negative with LH (γ = -0.253, p < 0.001), but not with FSH (γ = -0.061, p = 0.319). For the hyperprolactinaemic women, the BMIs were significantly negative with FSH (γ = -0.353, p < 0.001), but not with LH (γ = -0.021, p = 0.837). Although PCOS-related syndrome was very prevalent in women with hyperprolactinaemia, the patterns of disturbance in gonadotropin secretion were different between the PCOS and the hyperprolactinaemia patients.

Serum prolactin and macroprolactin in heart failure: no relation to established laboratory or clinical parameters

Background

A few smaller studies have reported that the prolactin concentration is elevated in connection with heart failure. As heart failure is combined with disturbances of several biological systems any or all of which may also influence prolactin concentrations, we wanted to evaluate the relation of prolactin to prognosis in elderly patients.

Methods

A total of 462 elderly patients from a primary health-care centre, all with symptoms of heart failure, were included. In addition to clinical examination including echocardiography, concentrations of prolactin, macroprolactin, C-reactive protein, thyroid-stimulating hormone and N-terminal pro B-type natriuretric peptide (NT-proBNP) were measured. Patients were then followed for 10 y, and all incidents of cardiovascular mortality were registered.

Results

After excluding patients with macroprolactin, hyperprolactinaemia was found in 3.7% of the patients. There were no differences in prolactin concentrations or in the frequency of macroprolactin between patients with heart failure and those with normal cardiac function, defined as left ventricular ejection fraction of at least 50%. No significant correlation could be found between NT-proBNP and prolactin. Neither could any association be found between cardiovascular mortality and prolactin concentration during 10 y of follow-up.

Conclusions

Prolactin concentrations were not associated with cardiovascular mortality or any clinical or biochemical marker of heart failure. Macroprolactin was found in similar frequency among patients with and without heart failure, and showed no correlation with mortality risk.

Has Prolactin a Role in the Hypogonadal Status of HIV-Infected Patients?

Most cases of hypogonadism in human immunodeficiency virus (HIV) infection are of hypophyseal— hypothalamic origin, and hyperprolactinemia, also commonly observed in HIV-infected patients, may cause hypogonadism. We studied 188 HIV-infected men who had simultaneous determinations of gonadal and hypophyseal hormones, and we found that prolactin levels were independently predictive of hypogonadism in multivariate analysis.

Diagnosis and treatment of pituitary microadenoma: report of 80 cases

OBJECTIVE

To analyse and discuss the diagnosis and treatment of pituitary microadenoma.

SUBJECTS AND METHODS

Eighty cases of pituitary microadenoma treated with transsphenoidal approach in our department were analysed retrospectively during the last 2 years.

RESULTS

During following-up of 13.0+/-3.2 months, neither remained tumor was found except one patients with microprolactinoma, nor recurrence. Diabetes insipidus occurred in 19 patients, among which 15 patients recovered in 1 week, three in 1 month and one in 7 months. The adrenocorticotrophic hormone deficiency was found in nine of 63 patients with PRL-, GH- and non-functioning microadenoma (12%), but hypoadrenalemia recovered in all patients. Among these nine patients, seven recovered in 3 months and two in 6 months. Dysosphesia occurred in 32 cases: 30 recovered in 1 month and two in 4 months. Thirteen of 15 patients (86.7%) with ACTH-secreting microadenoma achieved chemical remission judged by plasma cortisol levels<or=2 microg/dl within 72 hours of surgery. During the mean 13.0 months of follow-up, the symptoms of amenorrhea, galactorrhea, headache, obesity and sexual disturbance were improved greatly. In total, 93.7% (45/48) of patients had normal post-operative PRL levels in the patients who had no pre-operative treatment history of long time medical therapy and large dose medical therapy in short time.

CONCLUSIONS

(1) Transsphenoidal surgery (TSS) is safe and effective treatment for pituitary microadenoma; (2) TSS is considered to be definitive treatment for ACTH- and GH-secreting microadenoma once the diagnosis is established; (3) in order to obtain better effects, TSS could be offered as first-line treatment for patients with locally non-invasive PRL-secreting microadenoma (tumor larger than 3 mm in diameter) and non-functioning microadenoma.

Anti-prolactin (PRL) autoantibodies suppress PRL bioactivity in patients with macroprolactinaemia

OBJECTIVE

Macroprolactinaemia, mainly caused by anti-prolactin (PRL) autoantibodies, is frequently found in patients with hyperprolactinaemia. Characteristically, these patients lack clinical symptoms of hyperprolactinaemia, but the serum bioactive PRL concentrations in vitro measured by the Nb2 bioassay are usually high. In this study, we investigated the causes of the discrepancy and the true biological features of macroprolactin.

SUBJECTS AND METHODS

Sixteen patients with macroprolactinaemia due to anti-PRL autoantibodies were studied. PRL bioactivity was determined by the phosphorylation of signal transducer and activator of transcription (Stat)5 in T47D human breast cancer cells and the proliferation of Nb2 rat lymphoma cells.

RESULTS

PRL bioactivity by the T47D bioassay, expressed as the density of the band of phosphorylated Stat5/immunoreactive PRL, was significantly lower in sera containing anti-PRL autoantibodies (2.4 +/- 1.1) than in control sera (7.2 +/- 3.1). Dissociation of PRL from the autoantibodies by acidification resulted in an increase in phosphorylated Stat5. PRL bioactivity by the Nb2 bioassay was not significantly different between sera with and without anti-PRL autoantibodies, and free PRL in the medium gradually increased during the incubation in a time-dependent manner in sera containing anti-PRL autoantibodies.

CONCLUSIONS

We conclude that the level of bioactivity of macroprolactin in the Nb2 bioassay is normal due to dissociation of PRL from the autoantibodies as a result of the longer incubation and more dilute assay conditions than in the T47D bioassay. The bioactivity of macroprolactin is low in vivo due to anti-PRL autoantibodies, but monomeric PRL dissociated from the autoantibodies retains full biological activity in patients with macroprolactinaemia.

An infant case of macroprolactinemia with transient idiopathic central precocious puberty

Macroprolactinemia was recognized more than a decade ago as a cause of hyperprolactinemia and the prevalence of macroprolactinemia is thought to be 10%-26% of patients with hyperprolactinemia. However, there are few published reports about macroprolactinemia in childhood. We report a 7-year-and-1-month-old girl with hyperprolactinemia due to macroprolactinemia with the complication of transient idiopathic central precocious puberty (ICPP). At the age of 6 years and 9 months, she was diagnosed with ICPP at another clinic, on the basis of isolated mammary development and increased height velocity with slightly advanced bone age. At that time, the unexpected finding of high PRL level was also observed. Four months later, she was referred to our clinic for persistently high PRL level. At this time, other endocrinological data showed prepubertal stage and we demonstrated macroprolactinemia and the presence of anti-PRL autoantibody. After other causes of hyperprolactinemia such as prolactinoma and stress were ruled out, we finally diagnosed her with hyperprolactinemia due to macroprolactinemia. Because most patients with macroprolactinemia are symptom-free despite hyperprolactinemia and drug therapy would not be indicated, macroprolactinemia should be suspected even in children to avoid unnecessary examinations and treatments.

Development of anti-PRL (prolactin) autoantibodies by homologous PRL in rats: a model for macroprolactinemia

Macroprolactinemia is hyperprolactinemia in humans mainly due to anti-PRL (prolactin) autoantibodies and is a pitfall for the differential diagnosis of hyperprolactinemia. Despite its high prevalence, the pathogenesis remains unclear. In this study, we examined whether anti-PRL autoantibodies develop via immunization with homologous rat pituitary PRL in rats to elucidate what mechanisms are involved and whether they cause hyperprolactinemia with low PRL bioactivity, as seen in human macroprolactinemia. Anti-PRL antibodies were developed in 19 of 20 rats immunized with homologous rat pituitary PRL and 29 of 30 rats with heterogeneous bovine or porcine pituitary PRL but did not develop in 25 control rats. In rats with anti-PRL antibodies, the basal serum PRL levels were elevated, and a provocative test for PRL secretion using dopamine D2 receptor antagonist (metoclopramide) showed a normal rising response with a slower clearance of PRL because of the accumulation of macroprolactin in blood. Antibodies developed by porcine or rat pituitary PRL reduced the bioactivity of rat serum PRL, and gonadal functions in these rats were normal despite hyperprolactinemia. Anti-PRL antibodies were stable and persisted for at least 5 wk after the final injection of PRL. These findings suggest that pituitary PRL, even if homologous, has antigenicity, leading to the development of anti-PRL autoantibodies. We successfully produced an animal model of human macroprolactinemia, with which we can explain the mechanisms of its clinical characteristics, i.e. asymptomatic hyperprolactinemia.

Detection of molecular variants of prolactin in human serum, evaluation of a method based on ultrafiltration

BACKGROUND

In human blood, there are several molecular variants of prolactin with different biological effects. There is a need for new methods to detect and quantify these variants in order to fully understand the pathophysiological role of prolactin.

METHODS

A method based on ultrafiltration was optimized, validated and compared to PEG precipitation. Serum samples from 84 patients were analyzed before and after pre treatment on two immunoassays, Elecsys (Roche) and Access (Beckman). Protein G precipitation was used to confirm presence of macroprolactin.

RESULTS

The recovery of prolactin after ultrafiltration was lower than after PEG precipitation. A limit of 40% recovery after PEG precipitation corresponded to 27% recovery after ultrafiltration. Using these limits there were total agreement regarding detection of macroprolactin (r(s)=0.96). In contrast, recovery of prolactin in samples without macroprolactin showed a considerable disagreement between ultrafiltration and PEG precipitation (r(s)=0.48). Within-run CV was 4% for the ultrafiltration method. The correlation coefficient (r) between the immunoassays was 0.96 after ultrafiltration.

CONCLUSIONS

Ultrafiltration can be used to compare different prolactin immunoassays and to detect macroprolactin in assays with interference from PEG. For samples without macroprolactin ultrafiltration may give additional information reflecting individual variations of other molecular variants of prolactin.

Macroprolactinemia: clinical significance and characterization of the condition

The purpose of this study was to characterize the clinical picture of macroprolactinemic patients and to further assess whether macroprolactinemia was part of an auto-immune syndrome. Eighty-two hyperprolactinemic (serum PRL > 1000 mU/l) patients were investigated and the PEG precipitation test identified 14 patients with macroprolactinemia (bb PRL). They were submitted to a hormonal and autoimmune screening and an IV TRH test. Bioactivity of their serum prolactin was evaluated, using an Nb2 assay. The biochemical nature of bb-PRL was investigated by immunoprecipitation with anti-IgG antibodies. Seventy-nine percent of the studied patients presented with infertility, amenorrhoea, galactorrhoea, mastodynia, gynaecomastia or erectile dysfunction. In most cases, however, these symptoms could be explained by the presence of other non hyperprolactinemia-related pathology. Despite the finding of in vitro biological activity in all macroprolactinemic sera tested, our results suggest a variable in vivo bioactivity of bb-PRL, probably related to a reduced capacity to cross vascular endothelium. In this study, we demonstrated that in 12 out of 13 samples (85%), bb-PRL consisted of PRL-IgG complexes. There was no clinical or laboratory evidence of auto-immunity.

The impact on clinical practice of routine screening for macroprolactin

BACKGROUND

Macroprolactin has reduced bioactivity in vivo and accumulates in the sera of some subjects, resulting in pseudo-hyperprolactinemia and consequent misdiagnosis.

METHODS

We have audited our experience of routine screening for macroprolactin using polyethylene glycol (PEG) precipitation over a 5-yr period in a single center.

RESULTS

Application of a reference range for monomeric prolactin (the residual prolactin present in macroprolactin-depleted serum) for normal individuals revealed that 453 of 2089 hyperprolactinemic samples (22%) identified by Delfia immunoassay were explained entirely by macroprolactin. The percentage of hyperprolactinemic samples explained by macroprolactinemia was similar across all levels of total prolactin (18, 21, 19, and 17% of samples from 700-1000, 1000-2000, 2000-3000, and greater than 3000 mU/liter, respectively). Application of an absolute prolactin threshold after polyethylene glycol treatment of sera, rather than the traditional method, i.e. less than 40% recovery, minimizes the opportunity for misclassification of patients in whom macroprolactin accounted for more than 60% of prolactin and the residual bioactive prolactin was present in excess. Macroprolactinemic patients could not be differentiated from true hyperprolactinemic patients on the basis of clinical features alone. Although oligomenorrhea/amenorrhea and galactorrhea were more common in patients with true hyperprolactinemia (P < 0.05), they were also frequently present in macroprolactinemic patients. Plasma levels of estradiol and LH and the LH/FSH ratio were significantly greater in macroprolactinemic compared with true hyperprolactinemic subjects (P < 0.05). Reduced use of imaging and dopamine agonist treatment resulted in a net cost savings, offsetting the additional cost associated with the introduction of screening.

CONCLUSION

Routine screening of all hyperprolactinemic sera for macroprolactin is recommended.

Hyperprolactinaemia and the regular menstrual cycle in asymptomatic women: should it be treated during therapy for infertility?

It is known that hyperprolactinaemia can cause galactorrhoea and irregular cycles or even amenorrhoea. High serum prolactin (PRL) can disturb follicular maturation and corpus luteum function. Treatment of hyperprolactinaemia in patients with resulting bleeding anomalies is established, but the question is how to manage normal cyclic hyperprolactinaemic women? Studies have shown that in a subgroup of asymptomatic patients the serum contains mainly high molecular weight form (big big PRL), which has a low bioactivity, called macroprolactinaemia. It is evident that macroprolactin does not affect the control of pituitary PRL secretion via the short loop feedback mechanism or the secretion of gonadotrophins as does monomeric PRL. Identification of macroprolactinaemia is therefore clinically important to prevent unnecessary examinations and inappropriate treatment. Prolactinoma can be associated with macroprolactinaemia. Performance of pituitary imaging in asymptomatic patients with hyperprolactinaemia may therefore be justified, but further studies are needed to evaluate the relation of costs and benefit. An unsolved problem is the differentiation between inactive and PRL-secreting tumours. Caution should be exercised concerning medical treatment in unstimulated patients and also in patients during ovarian stimulation alone or in combination with intrauterine insemination or in-vitro fertilization. The potential clinical significance of hyperprolactinaemia/macroprolactinaemia in asymptomatic women must be further evaluated.

Identification of IgG-immunocomplex macroprolactin with an immunometric "sandwich" system: technical and clinical considerations

MacroPRL can be due either to anti-PRL autoantibodies IgG (IgG-macroPRL) or other PRL containing molecules without IgG-PRL immuncomplexes (nIgG-macroPRL), the composition of which is not fully clarified. The aims of this study were: a) testing a new immunometric assay, capable of recognising IgG-macroPRL, b) looking for any biological and/or clinical discrepancy between nlgG-macroPRL and IgG-macroPRL. Clinical, biological and neuroradiological data were recorded from 28 hyperprolactinemic women classified as macroprolactinemic on the basis of PRL recoveries after polyethylene glycol (PEG) precipitation <50% on a Roche Elecsys analyser. Fourteen sera with recoveries >70% were employed as controls for the IgG-macroPRL assay. An immunometric "sandwich" assay for IgG-macroPRL was performed employing an anti-PRL antibody to capture PRL and a second one binding and tracing the immunoglobulin G (IgG) component. For this purpose, 2 kits were simultaneously employed, the first for PRL assay and the second for Anti-Toxoplasma IgG assay. The procedure was applied to both DiaSorin LIAISON and Abbott AxSYM systems. IgG-macroPRL immunometric detection was obtained with DiaSorin LIAISON. Twenty out of 28 (72%) sera gave luminescent signal higher than the maximum control serum and were considered as IgG-macroPRL carriers. Our results confirm the high IgG-macroPRL prevalence in macroprolactinemia. No significant clinical differences appear between IgG and nIgG-macroPRL. Conversely, significantly higher PRL values (p =0,039) and lower recoveries (p = 0.001) were found in IgG-macroPRL. Further studies with reference methods, such as gel chromatography and human IgG (h-IgG) affinity columns, are needed to fully validate this IgG-macroPRL immunometric assay.