Dopamine agonist resistance-related endocan promotes angiogenesis and cells viability of prolactinomas

Dopamine agonists (DAs) are the first-line treatment of prolactinomas. They function through the dopamine 2 receptor (D2R) in the tumor cells. Endocan, also called endothelial cell-specific molecule-1 (ESM1), has been described as a marker of neoangiogenesis. However, whether ESM1 promotes the resistance of prolactinomas to DA therapy is largely unknown. In our study, 25 patients with prolactinomas were divided into resistant- and sensitive- groups according to the clinical response to bromocriptine. We found that ESM1-microvessel density of resistant prolactinomas was significantly higher than that of sensitive prolactinomas (47.9 ± 11.6, n = 8, vs 13.1 ± 2.8, n = 17, p = 0.0006), indicating that ESM1 was a DA resistance-related gene. Immunostaining showed that ESM1 was expressed in tumor vessels and sporadic tumor cells, and ESM1 was overlapped with the Smooth Muscle Actin (SMA) and von Willebrand Factor (VWF) in the tumor vessels. Silencing of ESM1 markedly suppressed the viability of GH3 and MMQ cells in vitro, and furthermore, significantly increased the sensitivity of GH3 and MMQ cells to DA treatment. Additionally, silencing of ESM1 down-regulated the angiogenesis-associated genes, such as VEGFR2, FGF2, CD34, CD31, VWF, and EGFR. Knockdown of ESM1 decreased endothelial tube formation of HUVECs, and significantly increased the sensitivity of HUVECs to Avastin treatment. Therefore, we first demonstrate that DA resistance-related ESM1 promotes the angiogenesis and tumor cells growth of prolactinomas, suggesting that ESM1 may be a novel therapeutic target for prolactinomas.

[Complications of treatment of prolactinoma by dopamine agonists]

Treatment of prolactin-secreting pituitary adenomas by dopamine agonists is highly effective and currently is used as basic treatment in most cases, however, literature sources practically do not contain data about possible complications of this therapy. We described a total of 11 cases of deterioration due to primary treatment of macroprolactinomas by cabergoline in the series of 176 patients. The first group included patients with enlargement of the tumor producing deterioration of the symptoms (onset of visual disorders and/or cephalgia). This occurred in 3 (1.7%) cases due to intratumoral hemorrhage or cystic transformation, and in 1 (0.6%) case as a result of growth of cabergoline-resistant tumor. The second group was made up of 6 (3.4%) cases of nasal CSF leak which developed within 3 to 6 weeks after start of treatment. All patients with CSF leak had adenomas with high sensitivity to the drug which produced rapid and significant shrinking of the tumor. The third group was presented by the single case (0.6%) of visual deterioration due to development of empty sella syndrome with dislocation of chiasm and optic nerves into sellar cavity.

Dopaminergic D2 receptor knockout mouse: an animal model of prolactinoma

Dopamine receptor type 2 (D2R) knockout mice (KO) have chronic hyperprolactinemia, pituitary hyperplasia, and a moderate decrease in MSH content. They are also growth retarded evidencing an alteration in the GH-IGF-I axis. In D2R KO, lactotropes do not show dense secretory granules but degranulated cells and fewer somatotropes, gonadotropes and thyrotropes. Prolactin levels are always higher in female than in male knockouts, and in accordance, pituitary hyperplasia is observed at 8 months only in females. After 16 months of age, highly vascularized adenomas develop, especially in females. Prominent vascular channels in the hyperplastic and adenomatous pituitaries, as well as extravasated red blood cells not contained in capillaries is also a common finding. Prolactin is not the factor that enhances the hyperplastic phenotype in females while estrogen is a permissive factor. VEGF-A expression is increased in pituitaries from D2R KO. VEGF-A is expressed in follicle stellate cells. Because D2R receptors are found in lactotropes and not in follicle stellate cells, it may be inferred that a paracrine-derived factor from lactotropes is acting on follicle stellate cells to increase VEGF-A expression. VEGF-A does not induce pituitary cell proliferation, even though it enhances prolactin secretion. But it may act on adjacent endothelial cells and participate in the angiogenic process that increases the availability of different growth factors and mitogens. The D2R knockout mouse represents a unique animal model to study dopamine-resistant prolactinomas, and VEGF-A may be an alternative therapeutic target in this pathology.

Rat tumor response to the vascular-disrupting agent 5,6-dimethylxanthenone-4-acetic acid as measured by dynamic contrast-enhanced magnetic resonance imaging, plasma 5-hydroxyindoleacetic acid levels, and tumor necrosis

The dose-dependent effects of 5,6-dimethylxanthenone-4-acetic acid (DMXAA) on rat GH3 prolactinomas were investigated in vivo. Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) was used to assess tumor blood flow/permeability pretreatment and 24 hours posttreatment with 0, 100, 200, or 350 mg/kg DMXAA. DCE-MRI data were analyzed using K(trans) and the integrated area under the gadolinium time curve (IAUGC) as response biomarkers. High-performance liquid chromatography (HPLC) was used to determine the plasma concentration of the serotonin metabolite 5-hydroxyindoleacetic acid (5-HIAA) following treatment to provide an index of increased vessel permeability and vascular damage. Finally, tumor necrosis was assessed by grading hematoxylin and eosin-stained sections cut from the same tumors investigated by MRI. Both tumor K(trans) and IAUGC were significantly reduced 24 hours posttreatment with 350 mg/kg DMXAA only, with no evidence of dose response. HPLC demonstrated a significant increase in plasma 5-HIAA 24 hours posttreatment with 200 and 350 mg/kg DMXAA. Histologic analysis revealed some evidence of tumor necrosis following treatment with 100 or 200 mg/kg DMXAA, reaching significance with 350 mg/kg DMXAA. The absence of any reduction in K(trans) or IAUGC following treatment with 200 mg/kg, despite a significant increase in 5-HIAA, raises concerns about the utility of established DCE-MRI biomarkers to assess tumor response to DMXAA.

Inhibitory effect of thalidomide on the growth, secretory function and angiogenesis of estrogen-induced prolactinoma in Fischer 344 rats

The process of angiogenesis has been found to be essential for the development of estrogen-induced pituitary prolactinoma in Fischer 344 rats. Thalidomide [(alpha-(N-phthalimido)-glutarimide] is known to be a potent immunomodulatory drug with antiangiogenic properties, but its effect on lactotroph cell secretory function and pituitary prolactinoma formation has not been described yet. The purpose of this study was to examine the effects of thalidomide on secretion of prolactin (PRL) and vascular endothelial growth factor (VEGF), cell proliferation, apoptosis and angiogenesis within the anterior pituitary gland in long-term diethylstilboestrol (DES)-treated male F344 rats in vivo and in vitro. It was found that DES sharply increased serum PRL and VEGF levels. On the other hand, simultaneous treatment of F344 rats with thalidomide for the last 15 days of the experiment attenuated the stimulatory effect of DES on PRL and VEGF secretion. It also diminished prolactin cell proliferation evaluated as the number of proliferating cell nuclear antigen (PCNA)-positive stained cell nuclei and increased the number of apoptotic bodies determined by the terminal deoxynucleotidyl-mediated dUTP nick-end labeling (TUNEL) method in sections of the DES-induced pituitary prolactinoma. The density of pituitary microvessels evaluated by microscopic counting of CD-31-positive blood vessels was also diminished by the tested drug. In addition, thalidomide (10(-4) to 10(-6) M) inhibited cell proliferation, prolactin and VEGF secretion from rat pituitary prolactinoma cells cultured in vitro. In conclusion, our results provide strong evidence for the antiprolactin and antitumor activity of thalidomide in experimentally DES-induced pituitary adenoma.

Spontaneous remission of functioning pituitary adenomas without hypopituitarism following infarctive apoplexy: two case reports

Functioning pituitary adenomas may exhibit spontaneous remission after pituitary apoplexy usually in association with hypopituitarism. We report two patients who presented with sudden headache and double vision, showed a ring-enhanced sellar tumor on MRI, underwent transsphenoidal surgery that revealed a coagulation necrotic adenoma without massive hemorrhage, and showed normal pituitary function after the surgery. Definitive diagnoses were made based on immunohistochemistry of the necrotic cells. The findings were consistent with the presence of selective infarct of a GH adenoma and a prolactinoma that had led to remission of acromegaly and menstrual disturbance, respectively, without pituitary insufficiency. In contrast to hemorrhagic apoplexy, infarctive apoplexy tends to affect only the tumor and thus presents with mild symptoms and lack pituitary deficiencies.

The Effects of Tumour Blood Flow and Oxygenation Modifiers on Subcutaneous Tumours as Determined by NIRS

Modulation of tumour oxygenation may be used to increase or decrease tumour hypoxia in order to improve the effect of radiotherapy or bioreductive drugs, respectively. Magnetic resonance imaging (MRI) and near infrared spectroscopy (NIRS) are techniques sensitive to blood deoxyhemoglobin concentration (Hb) that can be used to investigate tumour hypoxia indirectly via blood oxygenation levels. In this study we have used NIRS to determine absolute Hb and changes in deoxyhemoglobin and oxyhemoglobin (HbO) in subcutaneous rodent tumours for challenges that alter blood flow and oxygenation, with the aim to better interpret our MRI data. Both carbogen [95% O2 + 5% CO2] and 100% O2 breathing produced a similar and significant reduction in Hb and increase in HbO, but a negligible change in HbT (= Hb + HbO). In contrast, N2 breathing to terminal anoxia and intravenous hydralazine produced a negligible increase in Hb, but large reductions in HbO and HbT. HbT is proportional to blood volume, so our data suggests large blood volume decreases occur with challenges likely to cause reduced arterial blood pressure. Hence MRI techniques that measure the R2* relaxation rate, which varies linearly with total Hb, will underestimate the effects of hypotensive agents at increasing tumour hypoxia.

Angiogenesis in prolactinomas: regulation and relationship with tumour behaviour

Tumours are dependent on angiogenesis for growth and inhibition of angiogenesis has become a target for antineoplastic therapy. In the pituitary, unlike other tissues, vascularization is lower in adenomas compared to the normal gland. Despite this finding, a relationship between increased vascularity and several aspects of prolactinoma behaviour such as size, invasiveness, surgical outcome and malignancy, has been demonstrated. The process of angiogenesis is the result of a balance of stimulating and inhibiting factors. It is likely that an interaction between gene expression (such as pituitary tumour transforming gene (PTTG) and a novel gene located within the Edpm5 quantitative trait locus), hormonal stimuli including oestrogens, dopamine, 16 kDa fragments of prolactin and proangiogenic and antiangiogenic growth factors (for example, vascular endothelial growth factor (VEGF) and fibroblast growth factor (FGF-2), determine the final angiogenic phenotype of prolactinomas, and thus subsequent tumour behaviour. The elucidation of all the factors involved in the regulation of angiogenesis and their interactions might open new possibilities in the treatment of prolactinomas, especially in those cases with resistance or intolerance to dopamine agonists.

Single dose of the antivascular agent, ZD6126 (N-acetylcolchinol-O-phosphate), reduces perfusion for at least 96 hours in the GH3 prolactinoma rat tumor model

Tumor vasculature is an attractive therapeutic target as it differs structurally from normal vasculature, and the destruction of a single vessel can lead to the death of many tumor cells. The effects of antivascular drugs are frequently short term, with regrowth beginning less than 24 hours posttreatment. This study investigated the duration of the response to the vascular targeting agent, ZD6126, of the GH3 prolactinoma, in which efficacy and dose-response have previously been demonstrated. GH3 prolactinomas were grown in the flanks of eight Wistar Furth rats. All animals were treated with 50 mg/kg ZD6126. The tumors were examined with dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) 24 hours pretreatment and posttreatment, and at a single time between 48 and 96 hours posttreatment. No evidence of recovery of perfusion was observed even at the longest (96-hour) time point. Involvement of a statistician at the project planning stage and the use of DCE-MRI, which permits noninvasive quantitation of parameters related to blood flow in intact animals, allowed this highly significant result to be obtained using only eight rats.

Tumour dose response to the antivascular agent ZD6126 assessed by magnetic resonance imaging

ZD6126 is a vascular targeting agent that disrupts the tubulin cytoskeleton of proliferating neo-endothelial cells. This leads to the selective destruction and congestion of tumour blood vessels in experimental tumours, resulting in extensive haemorrhagic necrosis. In this study, the dose-dependent activity of ZD6126 in rat GH3 prolactinomas and murine RIF-1 fibrosarcomas was assessed using two magnetic resonance imaging (MRI) methods. Dynamic contrast-enhanced (DCE) MRI, quantified by an initial area under the time-concentration product curve (IAUC) method, gives values related to tumour perfusion and vascular permeability. Multigradient recalled echo MRI measures the transverse relaxation rate T(2)*, which is sensitive to tissue (deoxyhaemoglobin). Tumour IAUC and R(2)* (=1/T(2)*) decreased post-treatment with ZD6126 in a dose-dependent manner. In the rat model, lower doses of ZD6126 reduced the IAUC close to zero within restricted areas of the tumour, typically in the centre, while the highest dose reduced the IAUC to zero over the majority of the tumour. A decrease in both MRI end points was associated with the induction of massive central tumour necrosis measured histologically, which increased in a dose-dependent manner. Magnetic resonance imaging may be of value in evaluation of the acute clinical effects of ZD6126 in solid tumours. In particular, measurement of IAUC by DCE MRI should provide an unambiguous measure of biological activity of antivascular therapies for clinical trial.

Effects of pentosan polysulfate sodium on the estrogen-induced pituitary prolactinoma in Fischer 344 rats

The development of estrogen-induced pituitary prolactinoma in Fischer 344 (F344) rats is associated with enhanced neovascularization. This type of tumor is a rich source of basic fibroblast growth factor (bFGF), which possesses strong mitogenic and angiogenic properties. Pentosan polysulfate sodium (PPS) has been shown to exert antitumor activity by antagonizing the binding of bFGF to cell surface receptors. We have examined the effects of pentosan on tumor growth, hyperprolactinemia and angiogenesis in diethylstilbestrol-induced anterior pituitary adenoma in F344 rats. Chronic treatment with PPS did not cause any changes in the pituitary weight and serum prolactin concentration in comparison with untreated animals. The density of microvessels identified by CD-31 was also not affected by the tested drug. On the other hand, pentosan has been found to decrease cell proliferation evaluated by a number of PCNA-positive stained cell nuclei. Moreover, the TUNEL method has revealed an increased number of apoptotic bodies within the anterior pituitary after treatment with PPS. Despite the antiproliferative and proapoptotic activity of pentosan, the drug failed to inhibit tumor growth. This fact might be due to the lack of antiangiogenic activity of PPS in this experimental design.

Three-dimensional imaging of hormone-secreting cells and their microvessel environment in estrogen-induced prolactinoma of the rat pituitary gland by confocal laser scanning microscopy

This study focused on the three-dimensional imaging of hormone-secreting cells and their microvascular environment in estrogen-induced prolactinoma of the rat pituitary gland. Adult female Wistar-Imamichi rats were injected with estradiol dipropionate and killed 7 weeks later. Some rats given estrogen for 7 weeks also were injected with bromocriptine before killing. To obtain a detailed three-dimensional image of microvessels, dialyzed fluorescein isothiocyanate (FITC)-conjugated gelatin was injected into the left ventricle of the rat heart. After the perfusion, the pituitary glands were resected and subjected to immunohistochemistry (IHC). To evaluate the effects of estrogen and bromocriptine, IHC was performed with antibodies against prolactin (PRL), adrenocorticotropic hormone (ACTH), and growth hormone (GH). With the combination, microvessels and cells containing PRL, ACTH, and GH could be clearly identified by confocal laser scanning microscopy (CLSM). The PRL cells increased in number and became hypertrophic after prolonged exposure to estrogen. With bromocriptine administration after estrogen treatment, however, PRL cells decreased in number and became atrophic. The current study revealed that estrogen and bromocriptine had significant effects on PRL secretion and the microvascular environment. Therefore, this technique (FITC injection and IHC) with CLSM is suitable for the three-dimensional imaging of hormone-secreting mechanisms under various conditions.

Effects of different levels of hypercapnic hyperoxia on tumour R 2 ∗ and arterial blood gases

The hypercapnia induced by carbogen (95% O(2)/5% CO(2)) breathing, which is being re-evaluated as a clinical radiosensitiser, causes patient discomfort and hence poor compliance. Recent preclinical and clinical studies have indicated that the CO(2) content might be lowered without compromising increased tumour oxygenation and radiosensitisation. This preclinical study was designed to see if lower levels of hypercapnia could evoke similar decreases in the transverse relaxation rate R(2)* of rodent tumours to those seen with carbogen breathing. The response of rat GH3 prolactinomas to 1%, 212% and 5% CO(2) in oxygen, and 100% O(2) breathing, was monitored by non-invasive multi-gradient echo MRI to quantify R(2)*. As the oxygenation of haemoglobin is proportional to the blood p(a)O(2) and therefore in equilibrium with tissue pO(2), R(2)* is a sensitive indicator of tissue oxygenation. Hyperoxia alone decreased R(2)* by 13%, whilst all three hypercapnic hyperoxic gases decreased R(2)* by 29%. Breathing 1% CO(2) in oxygen evoked the same decrease in R(2)* as carbogen. The DeltaR(2)* response is primarily consistent with an increase in blood oxygenation, though localised increases in tumour blood flow were also identified in response to hypercapnia. The data support the concept that levels of hypercapnia can be reduced without loss of enhanced oxygenation and hence potential radiotherapeutic benefit.

Role of matrix metalloproteinase 9 in pituitary tumor behavior

The matrix metalloproteinases (MMPs) are a family of zinc-containing endopeptidases that are able to degrade the extracellular matrix and allow angiogenesis and tumor invasion. The vast majority of pituitary tumors are benign and do not metastasize to distant sites, although they may invade locally. The aim of this study was to determine whether expression of the collagenase MMP-9 may play a role in allowing angiogenesis and invasion by different pituitary tumor types. Tumor expression of MMP-9 was investigated using a monoclonal antibody on a series of well-characterized paraffin-embedded sections of pituitary tumors. Invasive macroprolactinomas (n = 11) were significantly more likely to express MMP-9 than noninvasive macroprolactinomas (n = 8) (P = 0.003). Invasive macroprolactinomas showed higher-density MMP-9 staining than noninvasive tumors (P < 0.05). MMP-9 expression did not differ between noninvasive tumors and normal pituitary gland, or between different sized prolactinomas. MMP-9 expression was related to aggressive tumor behavior. It was higher in invasive macroprolactinomas (P = 0.003) when compared with noninvasive macroprolactinomas or the normal anterior pituitary gland. In addition, although there was no difference in whether MMP-9 was present or not when nonfunctioning adenomas that recurred were compared with those that did not, samples of recurrent tumor at the second presentation were more likely to express MMP-9 (P = 0.01). Pituitary carcinomas were significantly more likely to be MMP-9 positive compared with normal anterior pituitary gland (P = 0.05), but there was no difference from invasive adenomas. Angiogenesis assessed by vascular density was related to MMP-9 expression (P < 0.05). In summary, we have shown the presence of MMP-9 expression in some invasive and recurrent pituitary adenomas, and in the majority of pituitary carcinoma. The mechanisms whereby MMP-9 expression influences tumor recurrence and invasiveness, and its association with angiogenesis, remains to be elucidated. However, these observations suggest that a future potential therapeutic strategy for some pituitary tumors may be administration of a synthetic MMP-9 inhibitor.

[A primary study of microanatomy on blood supplement of large and huge pituitary adenoma]

OBJECTIVE

To explore the blood supplement regularity of large and huge pituitary adenomas. MECHODS: Sixteen large and huge pituitary adenomas were removed by microsurgery via transorbitofrontosphenoidal approach. The blood vessels of the tumors coming from surrounding structures were observed, photographed, videotaped and measured during operation.

RESULTS

The blood supplement of the pituitary adenoma comes from not only the superior and inferior hypophyseal arteries, but also a lot of new arteries originating from meninges, optic nerves, optic chiasm, and arteries which surround the tumors, such as internal carotid artery, anterior cerebral artery and soon.

CONCLUSION

The blood supplement of large and huge pituitary adenomas is increased obviously. The operation results will get much better if this situation is recognized and handled very well.

Effects of nicotinamide and carbogen on tumour oxygenation, blood flow, energetics and blood glucose levels

Both host carbogen (95% oxygen/5% carbon dioxide) breathing and nicotinamide administration enhance tumour radiotherapeutic response and are being re-evaluated in the clinic. Non-invasive magnetic resonance imaging (MRI) and 31P magnetic resonance spectroscopy (MRS) methods have been used to give information on the effects of nicotinamide alone and in combination with host carbogen breathing on transplanted rat GH3 prolactinomas. Gradient recalled echo (GRE) MRI, sensitive to blood oxygenation changes, and spin echo (SE) MRI, sensitive to perfusion/flow, showed large signal intensity increases with carbogen breathing. Nicotinamide, thought to act by suppressing the transient closure of small blood vessels that cause intermittent tumour hypoxia, induced a small increase in blood oxygenation but no detectable change in perfusion/flow. Carbogen combined with nicotinamide was no more effective than carbogen alone. Both carbogen and nicotinamide caused significant increases in the nucleoside triphosphate/inorganic phosphate (betaNTP/Pi) ratio, implying that the tumour cells normally receive sub-optimal substrate supply, and is consistent with either increased glycolysis and/or a switch to more oxidative metabolism. The most striking observation was the marked increase in blood glucose (twofold) induced by both nicotinamide and carbogen. Whether this may play a role in tumour radiosensitivity has yet to be determined.

Angiogenesis in pituitary adenomas - relationship to endocrine function, treatment and outcome

Angiogenesis has been shown to be related to tumour behaviour, prognosis and response to treatment in many different tumour types. The aim of this study was to examine the relationship between angiogenesis and tumour behaviour and response to treatment in pituitary adenomas. The microvessel density (MVD) of pituitary tumours was assessed by counting blood vessels labelled with 3 different endothelial markers using antibodies to CD31, factor eight-related antigen and biotinylated Ulex europaeus (agglutinin I UEAI). One hundred and forty-two surgically removed pituitary adenomas (46 GH secreting, 6 microprolactinomas, 19 macroprolactinomas, 18 ACTH secreting and 53 functionless tumours) were carefully characterized and assessed. There was a significant negative correlation between age and MVD of GH secreting tumours (R(2)=33.8, P=0.005). Age was not related to MVD in other tumour types. Pre-treatment hormone production by the adenomas was related to MVD in prolactinomas (P<0.05), but not in GH secreting tumours. Invasive prolactinomas were significantly more vascular than non-invasive tumours (P<0.05). Drug treatment with metyrapone or bromocriptine did not appear to influence tumour angiogenesis. Surgical cure was more likely in macroprolactinomas and in ACTH secreting tumours with lower MVD. These results show that factors related to angiogenesis are very important in determining a number of clinical features of pituitary tumours, in particular the invasiveness of macroprolactinomas, the effect of age in tumours secreting GH and the outcome of surgical treatment in macroprolactinomas and ACTH secreting tumours.

Proliferation, bcl-2 expression and angiogenesis in pituitary adenomas: relationship to tumour behaviour

The prediction of pituitary tumour behaviour, in terms of response to treatment from which can be derived optimal management strategies, is a challenge that has been approached using several different means. Angiogenesis in other tumour types has been shown to be correlated with poor response to treatment and tumour recurrence. The aim of this paper is to assess the role of measurements of cell proliferation and angiogenesis in predicting pituitary tumour behaviour. The proliferative capacity of the tumour was assessed using the Ki-67 labelling index (LI) while bcl-2 expression was used to assess anti-apoptotic pathways. The microvessel density (MVD) was assessed using antibodies to CD31 and factor VIII-related antigen, and with biotinylated ulex europaeus agglutinin I. There was no difference between Ki-67 LI and MVD of functionless tumours that recurred and those that did not, but bcl-2 expression was significantly lower in tumours that subsequently regrew. Macroprolactinomas had significantly higher LI than microprolactinomas and than all other tumours. Cell proliferation and angiogenesis were not related, showing that both processes are under different control mechanisms in pituitary tumours. In contrast there was a positive relationship between markers of angiogenesis and bcl-2 expression in prolactinomas, GH-secreting tumours and non-recurrent functionless tumours with higher levels of bcl-2 expression being found in the more vascular tumours. These findings may suggest that angiogenesis is related to the ability of tumour cells to survive rather than their proliferative activity.

Angiogenesis in pituitary adenomas and the normal pituitary gland

Angiogenesis is essential for tumor growth beyond a few millimeters in diameter, and the intratumoral microvessel count that represents a measure of angiogenesis has been correlated with tumor behavior in a variety of different tumor types. To date no systematic study has assessed pituitary tumors of different secretory types, correlating vascular count with tumor size. The vascular densities of pituitary tumors and normal anterior pituitary were therefore assessed by counting vessels labeled using the vascular markers CD31 and ulex europaeus agglutinin I. One hundred and twelve surgically removed pituitary adenomas (30 GH-secreting, 25 prolactinomas, 15 ACTH-secreting, and 42 nonfunctioning tumors) were compared with 13 specimens of normal anterior pituitary gland. The vascular counts in the normal anterior pituitary gland were significantly higher (P < 0.05) than those in the tumors using both CD31 and ulex europaeus agglutinin I. In addition, microprolactinomas were significantly less vascular (P < 0.05) than macroprolactinomas, although there was no such difference between vascular densities of microadenomas and macroadenomas producing GH. ACTH-secreting tumors were, like microprolactinomas, of much lower vascular density than the normal pituitary and other secreting and nonsecreting tumor types. In marked contrast to other tumors, pituitary adenomas are less vascular than the normal pituitary gland, suggesting that there may be inhibitors of angiogenesis that play an important role in the behavior of these tumors.

Tumour response to hypercapnia and hyperoxia monitored by FLOOD magnetic resonance imaging

Flow and oxygenation dependent (FLOOD) MR images of GH3 prolactinomas display large intensity increases in response to carbogen (5% CO2/95% O2) breathing. To assess the relative contributions of carbon dioxide and oxygen to this response and the tumour oxygenation state, the response of GH3 prolactinomas to 5% CO2/95% air, carbogen and 100% O2 was monitored by FLOOD MRI and PO2 histography. A 10-30% image intensity increase was observed during 5% CO2/95% air breathing, consistent with an increase in tumour blood flow, as a result of CO2-induced vasodilation, reducing the concentration of deoxyhaemoglobin in the blood. Carbogen caused a further 40-50% signal enhancement, suggesting an additional improvement due to increase blood oxygenation. A small 5-10% increase was observed in response to 100% O2, highlighting the dominance of CO2-induced vasodilation in the carbogen response. Despite the large FLOOD response, non-significant increases in tumour pO2 were observed in response to the three gases. Tissue pO2 is determined by the balance of oxygen supply and demand, hence increased blood flow/oxygenation may not necessarily produce a large increase in tissue PO2. The FLOOD response is determined by the level of deoxygenation of blood, the size of this response relating to vascular density and the potential of high-oxygen content gases to improve the oxygen supply to tumour tissue.

Perfusion MRI in normal and abnormal pituitary gland. A preliminary study

Perfusion MRI (magnetic resonance imaging) of the pituitary gland was performed in 20 healthy volunteers and 63 patients with various lesions involving the pituitary gland. All patients underwent sequential contrast-enhanced MRI using spoiled gradient recalled sequences with high temporal resolution (7 seconds). Four pituitary areas (pituitary stalk, posterior lobe, postero-superior, and antero-inferior adenohypophysis) were tested with a selected region of interest. Maximal contrast percentual variation was calculated. The timing of enhancement in normal patients matched perfectly with normal pituitary vascularization. Abnormal timing in pathological condition was investigated.

Total capsular calcification in a prolactinoma--case report

A 42-year-old male presented with a prolactin-producing pituitary adenoma with an atypical radiological appearance. The tumor was incidentally found by magnetic resonance imaging, which demonstrated a cystic tumor in the enlarged and partially empty sella turcica. Computed tomography revealed the tumor was surrounded by calcification with an egg-shell appearance. The serum prolactin level was 37 ng/ml. The operative finding was a calcified shell-containing cystic tumor. Immunohistochemical staining revealed prolactin-positive cells. The combination of the unusual calcification, and enlarged and partially empty sella was considered to be a sequela of spontaneous degeneration of the tumor.

Modification of tumour perfusion and oxygenation monitored by gradient recalled echo MRI and 31P MRS

Gradient recalled echo (GRE) 1H images can be used to monitor changes in blood oxygenation via the dephasing effects of paramagnetic deoxyhaemoglobin (Hb). We have modulated the blood flow/oxygenation of GH3 rat tumours by i.v. calcitonin gene-related peptide (CGRP) or carbogen (95% O2, 5% CO2) inhalation, and obtained GRE 1H images interleaved with 31P spectra before, during and after the insult. With CGRP the GRE image intensity decreased (6/10) by > 10% with a concomitant 40% decrease (4/4) in beta NTP/P1 and a small decrease in pH. Both the image intensity and 31P spectra returned to near their pre-CGRP levels after 50 min, consistent with a transient episode of hypoxia. Carbogen breathing (5/5) caused > 40% increases in average GRE image intensity, with no significant changes in the 31P spectra (4/4). Three-dimensional GRE images were obtained to confirm that a T2* increase, rather than just an 'in-flow' effect due to increased blood flow, was responsible for the GRE enhancement. Increases in average image intensity > 40% were observed for the three-dimensional GRE images (2/2), indicating a T2* increase. Using Hb as an endogenous contrast agent, the high sensitivity of the GRE technique may provide a method of monitoring heterogeneous tumour perfusion and oxygenation, both in the laboratory and the clinic.

Noninvasive monitoring of carbogen-induced changes in tumor blood flow and oxygenation by functional magnetic resonance imaging

PURPOSE

The response of tumors to radiotherapy can be enhanced if carbogen (95% O2, 5% CO2) is breathed. The timing of carbogen administration is critical, and a noninvasive method of monitoring the response of individual tumors would have obvious utility. Functional gradient recalled echo (GRE) magnetic resonance imaging (MRI) techniques are sensitive to changes in the concentrations of deoxyhemoglobin, which, thus, acts as an endogenous contrast agent for oxygenation status and blood flow.

METHODS AND MATERIALS

Subcutaneous GH3 prolactinomas in three rats were imaged at 4.7 Tesla with a GRE 1H sequence [echo time (TE) = 20 ms, repetition time (TR) = 80 ms, flip angle = 45 degrees, 1 mm slice, 256 phase encode steps, 4 cm field of view, in-plane resolution 0.08 x 0.08 mm, acquisition time = 4 min]. The rats breathed air or carbogen for four periods of 20 min; three control rats breathed only air.

RESULTS

Carbogen breathing caused increases of up to 100% in the GRE image intensity of the tumors. Reversion of air breathing caused the image intensity to fall; essentially the same response was observed with the second cycle of carbogen and air breathing. Control rat tumors showed no significant change.

CONCLUSIONS

The response of tumors to carbogen can be monitored noninvasively by GRE MRI. In principle, this could be due to an increase in oxygen content of the blood, a decrease in tumor cell oxygen consumption, or an increase in tumor blood flow. The very large changes in signal intensity suggest that a blood flow increase is the most probable explanation. If this technique can be successfully applied in man, it should be possible to optimize carbogen treatment for individual radiotherapy patients, and perhaps also to enhance tumor uptake of chemotherapeutic agents.

Blood supply, blood flow and autoregulation in the adenohypophysis, and altered patterns in oestrogen-induced adenomatous hyperplasia

The article addresses the fascinating topic of blood flow in the normal and the adenomatous anterior pituitary gland. This is considered in conjunction with the anatomy and physiology of the area and the neuro secretion. The mechanisms of the control of the development and growth of the prolactinoma and the changes in the microcirculation of the tumour are discussed. It is felt that its altered microvascular pattern and in particular the influx of the systemic low dopamine blood through the supplementary and newly developed blood supply plays an important role in the natural history of these tumours.