Osteo-promoting activity of OSTEOPLANT ANGIOSTAD in vitro.

AIM: There is an increasing need for an appropriate and readily-available material to reconstruct large bone defects, one of the most significant problems in the dental and maxillo-facial fields. The in vitro study examines the effects of OSTEOPLANT ANGIOSTAD, a product developed to increase osteoinductivity. METHODS: The product's biological properties were assessed by examining: the viability of cultured bone-marrow mesenchymal stem cells (MSC) through the methylthiazol tetrazolium assay; transforming growth factor (TGF)-b release by these cells through the enzyme-linked immunosorbent assay (ELISA) and the migration capacity of MSC and endothelial cells, by the in vitro wound closure test and transwell-migration assay, respectively. RESULTS: OSTEOPLANT ANGIOSTAD preserved MSC's viability and improved their capacity to release TGF-b1. It also increased in vitro wound healing by MSC and migration of endothelial cells. CONCLUSION: The results show that, since it increases the production by MSC of proangiogenic factors such as TGF-beta and promotes endothelial cell migration, OSTEOPLANT ANGIOSTAD may be an appropriate adjunct to accelerate the osteointegration of bone substitutes.

Increased intrathecal TGF-beta1, but not IL-12, IFN-gamma and IL-10 levels in Alzheimer's disease patients.

An inflammatory response has been hypothesised to be involved in the pathogenesis of primary dementias, above all Alzheimer's disease (AD). This study was aimed at evaluating interleukin (IL)-12 and a panel of related cytokine levels in paired CSF and sera of demented patients. IL-12 (p70 heterodimer and total IL-12 p40 chain), interferon (IFN)-gamma, IL-10 and transforming growth factor (TGF)-beta1 levels were measured in 30 patients with probable Alzheimer's disease (PrAD), 57 patients with other dementing disorders, including probable vascular dementia (PrVD), Parkinson's disease (PD) and normal pressure hydrocephalus (NPH), and 25 cognitively normal control subjects. In the presence of unchanged concentrations of IL-12, IFN-gamma and IL-10, the mean CSF level of TGF-beta1 and the correspondent TGF-beta1 index, but not the serum level, were significantly increased in PrAD compared to controls and PrVD, whereas no difference was found vs. NPH and PD. Our results support the pathophysiological role of TGF-beta1 system in AD.

[Biological aspects of pancreatic cancer]. / Aspetti bbiologici del carcinoma pancreatico.

Pancreatic ductal carcinoma still is an aggressive disease with a fatal prognosis due to late diagnosis and resistance to pharmacological and surgical treatments. Molecular investigations of pancreatic cancer are complicated by the restricted accessibility of the organ for biopsies. However, recent studies have indicated that pancreatic cancer is a multi-stage process resulting from the accumulation of genetic changes in the somatic DNA of normal cells. These molecular alterations, including overexpression of receptor-ligand systems, oncogene activation and loss of tumour suppressor genes, leads to a profound disturbance in cell cycle regulation and continuous growth. The molecular findings are now integrated in a pancreatic tumour progression model, with genetically and morphological defined precursor lesions. However, it remains unclear whether the initial target cells of this cancer develop from ductal or acinar cells. This review will present recent emerging questions on the biology of pancreatic cancer with particular emphasis on the cell origin and tumour microenvironment.

Interstitial cells of Cajal, enteric nerves, and glial cells in colonic diverticular disease.

BACKGROUND: Colonic diverticular disease (diverticulosis) is a common disorder in Western countries. Although its pathogenesis is probably multifactorial, motor abnormalities of the large bowel are thought to play an important role. However, little is known about the basic mechanism that may underlie abnormal colon motility in diverticulosis. AIMS: To investigate the interstitial cells of Cajal (the gut pacemaker cells), together with myenteric and submucosal ganglion and glial cells, in patients with diverticulosis. PATIENTS: Full thickness colonic samples were obtained from 39 patients undergoing surgery for diverticulosis. Specimens from tumour free areas of the colon in 10 age matched subjects undergoing surgery for colorectal cancer served as controls. METHODS: Interstitial cells of Cajal were assessed using anti-Kit antibodies; submucosal and myenteric plexus neurones and glial cells were assessed by means of anti-PGP 9.5 and anti-S-100 monoclonal antibodies, respectively. RESULTS: Patients with diverticulosis had normal numbers of myenteric and submucosal plexus neurones compared with controls (p = 0.103 and p = 0.516, respectively). All subtypes of interstitial cells of Cajal were significantly (p = 0.0003) reduced compared with controls, as were glial cells (p = 0.0041). CONCLUSIONS: Interstitial cells of Cajal and glial cells are decreased in colonic diverticular disease, whereas enteric neurones appear to be normally represented. This finding might explain some of the large bowel motor abnormalities reported to occur in this condition.

16-year follow-up study of Vena Cava Filters Group.

AIM: The prevalence of venous thromboembolic disease (VTED) is between 0.05% and 0.1% whereas its incidence is approximately 0.1%. Out of 100 patients with deep vein thrombosis (DVT), 5 will develop clinically serious pulmonary embolism (PE), one of which will be fatal. It is well known from the literature that surgical interventions carried out without antithrombotic prophylaxis have a 30% incidence of DVT, which can be halved with adequate prophylaxis. The aim of this study is to evaluate the immediate, middle- and long-term complications of caval filters by identifying any of the problems connected with or independent of the presence of the filter, also in relation to international literature data. METHODS: In view of the evolution of VTED surgical prevention methods, we have analyzed our case record composed of 821 patients (October 1984-October 2002), treated with different surgical solutions for VTED, with indications for the placement of 634 caval filters. RESULTS: The 30-day follow-up of all the 634 filters placed (100%) shows no mortality from the procedure and any of its immediate complications. The middle-term follow-up (from 1 month to 5 years) of 361 filters (57%) shows 0.55% mortality from PE while the long-term follow-up (5-16 years) of 105 filters (17%) shows a percentage decrease in all complications and no mortality from PE. The results also show a progressive annual decrease in the number of filters placed. CONCLUSIONS: The lower incidence of complications, compared to that reported in the literature, can be attributed to both improved operator dexterity in the placement of the filter and correct management of the complications. The lower number of filters used can be explained by improved therapeutic possibilities with new low molecular weight heparins (LMWH) and by current diagnostic as well as instrumental and biochemical monitoring methodologies.

Acute recurrent diverticulitis is prevented by oral administration of a polybacterial lysate suspension.

AIM: The main cause of acute diverticulitis is the abnormal accumulation of fecal bacteria within the diverticular lumen, leading to a balancing between normal probiotic microflora and pathogenic species; Gram negative Entero-bacteriaceae, mainly Escherichia coli and Proteus spp, are the genders that usually cause the disease-related symptoms, due to their ability to adhere to intestinal mucosa. The intestine is well known as the largest human lymphoepithelial organ and daily produces more antibodies, mainly secretory IgAs, than do all other lymphoid tissues. IgAs have different immune and anti-inflammatory properties. The aim of this study was to verify the efficacy of an oral immunostimulant highly-purified, polymicrobial lysate in the prevention of recurrent attacks of diverticulitis and in the improvement of symptoms. METHODS: The study was carried out on 83 consecutive patients suffering from recurrent symptomatic acute diverticulitis and with at least 2 attacks in the previous year; patients were randomly assigned to receive (group A) an oral polybacterial lysate suspension or to a no-treatment clinical follow-up as controls (group B). RESULTS: A total of 76 patients (41 in group A and 35 in group B) terminated the study period. the sums of the scores for symptoms, reported on day schedules, were calculated and examined by means of ANOVA statistical analysis. Statistical differences between group A vs group B were recorded after 1 month (p<0.05) and 3 months (p<0.01) of treatment with the oral polybacterial lysate suspension. CONCLUSIONS: Our data suggest that the administration of an oral enterovaccine for the prophylaxis of recurrent diverticulitis is effective and well tolerated, probably due to a direct stimulation of IgA-mediated mucosal defences.

Are colonic regular contractile frequency patterns in slow transit constipation a relevant pathophysiological phenomenon?

BACKGROUND: Pathogenesis of slow transit constipation still remains elusive. Some studies have shown several colonic motor abnormalities; however, it is not easy to understand the relative importance of the single ones. AIMS: Since it has been hypothesized that an excess of periodic distal motor activity may be of pathophysiological importance in patients with slow transit constipation, we evaluated regular colonic contractile frequencies in a homogeneous cohort of these patients. PATIENTS: A total of 26 female patients (age range 34 to 67 years) fulfilling the Rome II criteria for constipation entered the study. No patient had evidence of secondary forms of constipation and distal obstruction. METHODS: Twenty-four hour colonic manometric studies were obtained for each patient. Regular contractile patterns (with frequencies ranging from 2 to 8 cycles/min) were calculated for the entire recording period and in single colonic segments. RESULTS: Overall, regular patterns accounted for about 3% of the total colonic motor activity (average 30 min/day per subject), with the 3 cycles/min being the predominant contractile rhythm. Most of this activity was present in the sigmoid colon, accounting for >50% of the total amount of motility, and it was more prevalent than in the descending and transverse colon; no differences were revealed in the descending with respect to the transverse colon. No daily fluctuations of regular contractile activity, nor a cyclic pattern, nor migration between recording points were observed. CONCLUSIONS: Regular colonic frequency patterns are probably of minor pathophysiological importance in slow transit constipation, even in the light of the scant amount of such phenomena previously documented in healthy subjects.

Transforming growth factor-beta and interleukin 10 in oral implant sites in humans.

Cross-talk between cells and cytokines in peri-implant tissue is largely unknown. The immune response in the gingival mucosa appears to favor implant integration over rejection, since titanium-implant-retained overdentures show long-term success. This study evaluates pro-inflammatory (interleukin [IL]-2, interferon [IFN]-gamma, IL-12) and anti-inflammatory (IL-4, IL-10, transforming growth factor [TGF]-beta1) cytokine mRNA expression and tissue morphometry in peri-implant soft tissue from patients before and during treatment with Brånemark titanium implants. Immediately after treatment with endosseous implant and overdenture, TGF-beta1 mRNA increased in peri-implant mucosa specimens; transcript accumulation for IL-10 was elevated at 4 months and decreased dramatically thereafter. Transcripts for IL-2, IFN-gamma, IL-12, and IL-4 were absent. Healthy osseointegrated implants showed no histological inflammation in most patients. These findings suggest that newly classified TGF-beta and/or IL-10 secreting T regulatory (r)/T helper (h)-3 cells may populate implant insertion sites.

Expression of transforming growth factor-beta isoforms in the skin, kidney, pancreas and bladder in a German shepherd dog affected by renal cystadenocarcinoma and nodular dermatofibrosis.

The present study was performed to assess the expression of isoforms 1, 2 and 3 of transforming growth factor (TGF)-beta in skin nodular dermatofibrosis lesions, kidney, bladder and pancreas from a 10-year-old female German shepherd dog (GSD) affected by renal cystadenocarcinoma and nodular dermatofibrosis (RCND) compared with normal GSDs (n = 2). Formalin-fixed, paraffin-embedded tissues obtained from the dog affected by RCND, diagnosed by renal ultrasonography and histopathological examination were analysed by immunohistochemistry using polyclonal antibodies to TGF-beta1, 2 and 3, and evaluated semiquantitatively using an immunoreactivity score. Similar expression of TGF-beta2 and TGF-beta3 was observed in all tissue specimens in both the RCND-affected animal and normal dogs. In contrast, TGF-beta1 immunoreactivity was increased in the derma of the RCND canine. Comparable TGF-beta1 serum levels were found between the diseased and normal animals. The increased local cutaneous production of TGF-beta1 in the RCND dog, compared with the normal animals, suggests that this cytokine may play an important role in the induction of nodular dermatofibrosis associated with renal cystadenocarcinoma.

Local effects of atherosclerotic plaque on arterial distensibility.

Hypertension, diabetes, and hypercholesterolemia are characterized by a reduction in arterial distensibility and by accelerated atherosclerosis. Whether arterial stiffening is an inherent feature of these conditions or just the consequence of the atherosclerotic clinical or subclinical lesions is not known, however. Our aim was to obtain information on this issue by directly measuring, in humans, arterial distensibility both at the site of an atherosclerotic lesion and at the proximal normal site. In 10 patients (8 men; mean+/-SEM age, 65.2+/-3.4 years) affected by monolateral hemodynamic significant internal carotid artery stenosis, we measured arterial distensibility (Wall Track System; PIE Medical) bilaterally, both at the internal carotid artery and at the common carotid artery level. In the common carotid artery, measurements were made 3 cm below the bifurcation. In the affected internal carotid artery, measurements were made at the plaque shoulder (wall thickness of 2 mm). Measurements were made in the contralateral internal carotid artery at a symmetrical level. Arterial wall thickness was measured in the same site of arterial distensibility. Arterial distensibility was less in the internal than in the common carotid artery, with a marked reduction at the plaque internal carotid artery level compared with the corresponding contralateral site (-45%, P<0.01). It was also less, however, in the common carotid artery branching into the atherosclerotic internal carotid artery than in the contralateral common carotid artery (-25%, P<0.05). Wall thickness was similar in the 2 common carotid arteries and obviously greater in the affected internal carotid artery than in the contralateral artery. Arterial distensibility was markedly less in the internal carotid artery where there was a plaque compared with the intact contralateral internal carotid artery; it was also less, however, in the common carotid artery of the affected side in comparison with the contralateral common carotid artery. This provides evidence that the effect of a plaque on arterial mechanical properties is not limited to the actual plaque site but rather extends to a considerable degree in a proximal direction.

The 6-F nitinol TrapEase inferior vena cava filter: results of a prospective multicenter trial.

PURPOSE: The authors report the first results of a new 6-F symmetrically designed permanent nitinol inferior vena cava (IVC) filter, the Cordis TrapEase, evaluated in a multicenter prospective study with 6-months of follow-up. MATERIALS AND METHODS: A total of 65 patients (29 men, 36 women) who ranged in age from 37 to 96 years (mean age, 68 years) and who were at high risk of pulmonary embolism (PE) were enrolled in 12 centers in Europe and Canada. The study was approved by the institutional review boards at all centers. Study objectives were to evaluate filter effectiveness, filter stability, and caval occlusion. Indications for filter placement were deep vein thrombosis with recurrent thromboembolism and/or free-floating thrombus with contraindication to anticoagulation in 37 patients, and complications in achieving adequate anticoagulation in 28 patients. Follow-up included clinical examination, plain film, Doppler ultrasound, CT scan, and nuclear medicine. RESULTS: The analysis of the data revealed a technical success of 95.4% (three filter-system related implantations not at the intended site, no events of filter tilting) and a clinical success of 100% at 6 months (no cases of symptomatic PE), the study primary endpoint. There were no cases (0%) of filter migration, insertion site thrombosis, filter fracture, or vessel wall perforation. During the study period, there were two cases of filter thrombosis: one case of early symptomatic thrombosis that was successfully treated in the hospital, and one case of nonsymptomatic filter thrombosis detected at 1-month follow-up, with spontaneous recanalization at 3 months. In the latter patient, some residual thrombus was still detected at 6 months. Of the study population of 65 patients, there were 23 deaths. These deaths were not related to the device or the implantation procedure but to the underlying disease process. CONCLUSION: This study demonstrates the new nitinol permanent IVC filter to be a safe and an effective device, with a low overall complication rate, for use in patients with thromboembolic disease at high risk of PE.

[The pro-apoptotic factors Fas Ligand and Trail. Molecular mechanisms, physiopathological role and therapeutic potential]. / I fattori pro-apoptotici Fas Ligando e Trail. Meccanismi molecolari, ruolo fisiopatologico e potenzialità terapeutiche.

Programmed cell death, also known as apoptosis, is a normal physiologic process which occurs during embryonic development as well as in maintenance of tissue homeostasis. Increasing evidence suggests that alterations in cell death contribute to the pathogenesis of a number of human diseases, including cancer, viral infections, autoimmune diseases and acquired immunodeficiency syndrome (AIDS). The extraordinary research activity of the past few years has resulted in the characterization of the principal proteins involved in the apoptosis machinery. An area of particular interest has been the induction of apoptosis by two death receptor/ligand pairs, Fas/Fas Ligand and DR4-DR5/TRAIL. The identification of these molecules with the recruited signaling pathways could clarify their physiopathological implications, having a significant impact upon potential therapeutic interventions in diseases associated with cell survival alterations.

Aberrant activation of c-kit protects colon carcinoma cells against apoptosis and enhances their invasive potential.

Multiple genetic aberrations contribute to the development of biologically aggressive, clinically malignant colorectal carcinomas (CRCs). Some of these have been linked to inappropriate signaling through the tyrosine kinase moieties of growth factor receptors. We have described previously (G. Bellone et al., J. Cell. Physiol., 172: 1-11, 1997) that human CRCs overexpress both the receptor tyrosine kinase c-kit and its ligand, stem cell factor (SCF), relative to normal mucosa cells, thus establishing an autocrine c-kit-mediated loop. In addition, we noted that exogenous SCF contributes to anchorage-independent growth of HT-29 colon carcinoma cells in semisolid medium. Here, we investigated possible roles of the c-kit/SCF autocrine/paracrine system in survival and invasive capacity of DLD-1 colon carcinoma cells. We report that SCF was required for migration and invasion of DLD-1 cells through reconstituted basement membranes (Matrigel) and up-regulated gelatinase (matrix metalloproteinase-9) activity in DLD-1 cells. Furthermore, we describe that SCF supported survival of DLD-1 cells in growth factor-deprived conditions. These results suggest multiple roles of c-kit activation in support of the malignant phenotype of DLD-1 cells related to growth, survival, migration, and invasive potential.

Differential expression of transforming growth factors-beta1, -beta2 and -beta3 in human colon carcinoma.

Transforming growth factor (TGF)-beta is a protein family which affects multiple cellular functions including survival, proliferation, differentiation and adhesion. Among the three known isoforms, TGF-beta1 is commonly overexpressed in solid malignancies. Recent studies in knock-out mice demonstrated non-redundant roles of different TGF-beta isoforms in development. The present study was performed to assess tumour-associated expression of the three TGF-beta isoforms in colon carcinoma. We report that colon carcinoma progression is associated with gradual and significant increases in expression of TGF-beta1 and TGF-beta2 mRNA and proteins. By contrast, TGF-beta3 expression was detected in normal colonic mucosa and, at slightly higher levels, in tumour tissues. In addition, plasma levels of both TGF-beta1 and TGF-beta2 were significantly higher in cancer patients when compared with unaffected individuals. Taken together, our results indicate distinct expression patterns of the three TGF-beta isoforms in colon carcinoma cells and possible systemic effects of TGF-beta1 and TGF-beta2 in tumour patients.

[Esophageal motility disorders]. / Le alterazioni motorie dell'esofago.

Esophageal motility abnormalities are usually diagnosed when esophageal manometry is performed in patients with unexplained non-cardiac chest pain, non obstructive dysphagia or as a part of the preoperative evaluation for surgery of gastroesophageal reflux. Classification of these abnormalities has been a subject of controversy. These esophageal contraction abnormalities can be separated manometrically from the motor pattern seen in normal subjects, however, their clinical relevance is still unclear and debated. Many patients demonstrate motility abnormalities in the manometry laboratories, but may lack correlation with their presenting symptoms. Medical treatment can decrease symptoms particularly chest pain or acid reflux but there is no significant changes in the manometric patterns. Such motor abnormalities may not reflect a true disease state, but they could be markers of other abnormalities and they can modify the initial manometric findings in time.

In vitro effect of transforming growth factor-beta on adhesion molecule expression by human gingival fibroblasts cultured in the presence of a titanium abutment.

BACKGROUND: There is little information in the literature on the structural basis mediating gingival cell adhesion to the surface of titanium abutments. We cultured gingival fibroblasts on a titanium abutment creating as closely as possible the in vivo state. We analyzed the constitutive and transforming growth factor (TGF) beta-induced expression of the adhesion molecules CD44, CD49b, CD49c, CD51, CD54, and CD61 and extracellular matrix (ECM) components fibronectin, laminin and collagen IV. METHODS: Three totally edentulous patients underwent implant treatment to anchor the mandibular denture on 2 implants. Gingival mucosa cell specimens were collected from the mandible during the first surgical stage and the gingival fibroblast cultures were prepared. Cells were cultured for 48 hours with or without isoforms TGF-beta1, TGF-beta2, and TGF-beta3. The expression of adhesion molecules and ECM components was analyzed by immunofluorescence staining and flow cytometry. RESULTS: The addition of TGF-beta isoforms to the cell culture over the incubation period had little effect on cell growth rate, but significantly influenced cell orientation, which changed from a sun-burst pattern in control conditions to a more elongated organization and perpendicular to abutment surface. In all fibroblast preparations, a marked expression of CD44 and a moderate positivity for anti-CD49b and CD49c were found. By contrast, CD51, CD54, and CD61 expressions were negligible. When fibroblasts were cultured for 48 hours in the presence of TGF-beta, the expression of most of the receptor molecules increased. The cells expressed constitutively moderate levels of laminin and fibronectin and low amounts of collagen IV. By contrast, treatment with any one of the 3 TGF-beta isoforms greatly enhanced the expression levels of fibronectin, laminin, and, especially, collagen IV. CONCLUSIONS: TGF-beta not only seems to affect the orientation of the cultured gingival fibroblasts, but also to induce a clear-cut modification of their adhesion molecule expression.

Production and pro-apoptotic activity of soluble CD95 ligand in pancreatic carcinoma.

We report here that the progression of pancreatic carcinomas in tumor patients is associated with increased serum levels of both the soluble forms of CD95 ligand (CD95L/FasL) and its receptor, CD95 (Fas). Shedding of proteolytically processed soluble CD95L was also observed in pancreatic carcinoma cells in vitro, thus identifying one possible source of CD95L in patients' sera. Because the secreted forms of both CD95 and CD95L have been implicated previously in protection of cells from CD95-mediated cell death, we assessed the effect of soluble CD95L in supernatants of pancreatic carcinoma cells on viability of Jurkat T lymphocytes. We describe that (a) supernatants derived from cultured pancreatic carcinoma cells caused apoptosis of Jurkat cells; (b) soluble tumor-derived CD95L contributed significantly to this effect; and (c) in comparison to Jurkat cells, pancreatic carcinoma cells themselves revealed increased resistance to apoptosis induction by autocrine soluble CD95L. These results are consistent with the notion that in the microenvironment of pancreatic tumors, tumor-derived shed CD95L exerts paracrine pro-apoptotic effects. In addition, because it is released at high levels into the bloodstream, soluble CD95L may have systemic effects in tumor patients that reach beyond the microenvironment of the tumor site.

Manometric investigation of anorectal function in early and late stage Parkinson's disease.

Abnormal gastrointestinal function is relatively frequent in Parkinson's disease, and constipation is a disturbing symptom in many patients. However, it remains to be established whether anorectal abnormalities are characteristic of the late stages of the disease. Clinical and anorectal manometric function were investigated in groups of early and late stage parkinsonian patients. Thirty one patients (19 men, 12 women, age range 22 to 89 years) entered the study. The disease severity was assessed by Hoehn and Yahr staging: there were four (12.9%) stage I, seven (22.6%) stage II, 10 (32.2%) stage III, and 10 (32.2%) stage IV patients. Anorectal variables were measured by standard manometric equipment and techniques. Values obtained in early stage patients (Hoehn and Yahr stage I and II) were compared with those obtained in late stage patients (Hoehn and Yahr stage III and IV). Overall, more than 70% of patients complained of chronic constipation, with chronic laxative use reported in more than 30%. Late stage patients were slightly older than their early stage counterparts. Pelvic floor dyssynergia was documented in more than 60% of patients. Manometric variables were not different in the two groups. In conclusion, defecatory dysfunction is frequent in Parkinson's disease, it is not confined to late stage patients, and it is found early in the course of the disease. This has potential implications for a targeted therapeutic approach.

Association between elevated prolactin levels and circulating erythroid precursors in dialyzed patients.

The prolactin (PRL) receptor (R), a member of the cytokine hemopoietin receptor superfamily, has been shown to activate early differentiation steps along the erythroid pathway. In particular PRL, a product of bone marrow stroma, induces functional erythropoietin (EPO)-R on CD34+ hemopoietic progenitors. In this study, expression of EPO-R mRNA and responsiveness to EPO were assessed on enriched hemopoietic progenitor cells (HPC) from seven hyperprolactinemic and three normoprolactinemic patients and two normal subjects. Expression of EPO-R mRNA by semiquantitative reverse transcriptase-polymerase chain reaction (RT-PCR) was found in HPC of four out of seven hyperprolactinemic patients but not in normoprolactinemic patients or normal donors. Development of EPO-dependent Colony Forming Unit-Erythroid (CFU-E) colonies in semi-solid medium was observed only in hyperprolactinemic patients (six out of seven). A much higher number of CFU-E colonies was observed in the four patients with a positive EPO-R message. We conclude from these data that abnormally high levels of PRL may increase the number of EPO-responsive hemopoietic precursors in vivo as they do in vitro. Since hyperprolactinemia associates in these patients with depressed EPO production, it may be regarded as a compensatory mechanism for the reduced availability of the hemopoietic factor.