3-Acetyl-11-keto-ß-boswellic acid attenuated oxidative glutamate toxicity in neuron-like cell lines by apoptosis inhibition.

3-Acetyl-11-keto-ß-boswellic acid (AKBA), a pentacyclic triterpenic acid present in gum resin of Boswellia serrata, has been found to possess antioxidant and neuroprotective properties. In this study, we aimed to examine protective properties of AKBA against glutamate-induced neuronal injury. To investigate the effects of AKBA (2.5-10 µM) on glutamate injury in neuron-like cells PC12 and N2a, two treatment regimens (incubation for 2 or 0 hours before glutamate exposure) were used. Then, the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide method was used to determine viability of the cells. Cellular redox status was evaluated using fluorimetry and comet assays. Annexin V/propidium iodide double staining and Western blot analysis of relative apoptotic proteins were conducted. Based on the results, 24 hours incubation with glutamate (8 mM) increased the cell mortality of PC12 and N2a (P < .001). However, AKBA (2.5-10 µM) enhanced the cell viability in both treatment regimens (P < .001). Also co- and pretreatment with AKBA significantly attenuated lipid peroxidation, reactive oxygen species production, and DNA injury (P < .05 and P < .001). AKBA also restored the activity of cellular superoxide dismutase under glutamate toxicity; this effect was seen to be more significant during the pretreatment regimen (P < .001). Moreover, Western blot analysis indicated that AKBA inhibited glutamate-induced programmed cell death through depressing the elevation of the expression ratio of Bax/Bcl-2 and cleaved-caspase-3 proteins, concentration-dependently. Overall, the present findings suggest the neuroprotective activities of AKBA against glutamate-induced cell injury probably by inhibiting oxidative damage and reducing apoptotic cell death.

Recurrent Catecholamine-Induced Cardiomyopathy and Hypertensive Emergencies: A presentation of Pheochromocytoma and Related Concerns.

Catecholamine-induced cardiomyopathy (CIC) and pheochromocytoma are both rare entities, and their exact incidence and prevalence are unknown. Pheochromocytoma has been implicated as one of the causes of CIC or Takotsubo syndrome (TTS) by means of case reports and retrospective reviews. However, the evaluation of any patient with TTS and pheochromocytoma is often faced with multiple challenges due to its rarity and atypical presentations, which subsequently leads to delay in diagnosis. Here, we present a case of a 51-year old female who had three distinct episodes of TTS and now presented in a hypertensive emergency with angina, palpitations, headache, nausea, and vomiting. She was treated for non-ST elevation myocardial infarction (NSTEMI) but coronary angiogram revealed patent coronary arteries. Due to the paroxysmal nature of her hypertensive emergencies and variable blood pressure response, pheochromocytoma was suspected. On further evaluation, she was found to have elevated metanephrines and a 6.3 cm left adrenal mass on CT scan. This case emphasizes the importance of considering or identifying pheochromocytoma as an underlying primary etiology for recurrent episodes of TTS and related concerns such as choice of anti-hypertensive agents.

Metoclopramide induced pheochromocytoma crisis.

Metoclopramide (MCP) is a commonly used anti-emetic in the emergency department (ED). Its use is generally well tolerated; although infrequent adverse reactions such as extrapyramidal reactions or tardive dyskinesia are reported. However, many ED providers are not familiar with the potentially life-threatening hypertensive emergency that can be precipitated by MCP administration in patients with pheochromocytoma. A previously healthy 36-year-old woman presented to the ED with headache and nausea. She developed acute hypertensive emergency (acute agitation, worsening headache, chest pain and wide complex tachycardia) when her blood pressure (BP) increased to 223/102mmHg (initial BP, 134/86mmHg) after receiving intravenous MCP. Her hospital course was complicated by multi-organ injury, including acute respiratory distress syndrome requiring venous-venous extracorporeal membrane oxygenation, non-ST elevation myocardial infarction, cardiogenic shock, acute liver failure, and oliguric kidney injury requiring continuous renal replacement therapy. CT scan showed previously undiagnosed large right adrenal mass (5.9cm). The diagnosis of pheochromocytoma was confirmed after adrenalectomy. Drug-induced acute pheochromocytoma crisis is a rare event. Early recognition and appropriate blood pressure management with clevidipine, nicardipine, or phentolamine is essential.

Epoxiconazole caused oxidative stress related DNA damage and apoptosis in PC12 rat Pheochromocytoma.

Epoxiconazole is among the most widely applied pesticides worldwide. The increased use of these products could cause toxic effects on human health which are mainly associated with its residues in food or occupational exposure in agriculture. The brain is the principal target of lipophilic compounds exposure, while the data of brain injury induced by Epoxiconazole remains unclear. The purpose of our investigation was to assess the cytotoxic and genotoxic effects of the epoxiconazole in rat Pheochromocytoma (PC 12). We found that epoxiconazole could reduce the viability and proliferation of PC12 cells, induce the DNA damage, nuclear condensation, cytoskeleton network disruption and enhance the apoptotic cell death. Intracellular biochemical assay proved that EPX induces the loss of mitochondrial membrane potential (ΔΨm) and activates caspase-3. Indeed, EPX instigated ROS generation in neuronal cells, which is accompanied by an increase of lipid peroxidation as confirmed by the high levels of MDA. Interestingly, Pre-treatment of PC12 cells with the ROS scavenger N-acetylcysteine mitigated EPX-provoked DNA fragmentation and enhancement of apoptosis. Our results demonstrate that the genotoxic and cytotoxic outcomes of EPX are mediated through a ROS-dependent pathway in PC12 cells.

Toxicology and carcinogenesis studies of alpha,beta-thujone (CAS No. 76231-76-0) in F344/N rats and B6C3F1 mice (gavage studies).

BACKGROUND: α,ß-Thujone is a component of the essential oils of some plants including wormwood, sage, and cedar. It is used in herbal medicines, food and flavoring, and notably as the principal ingredient of the liqueur absinthe. We studied the effects of α,ß-thujone on male and female rats and mice to identify potential toxic or cancer-related hazards. METHOD: We deposited solutions containing α,ß-thujone in methylcellulose through a tube directly into the stomach to groups of 50 male and female rats and mice five days per week for two years. Exposed rats received either 12.5, 25, or 50 milligrams of α,ß-thujone per kilogram of body weight, and mice received 3, 6, 12, or 25 mg/kg. Control animals received methylcellulose with no chemical added by the same method. At the end of the study, tissues from more than 40 sites were examined for every animal. RESULTS: All male and female rats receiving 50 mg/kg α,ß-thujone died before the end of the study. All of those animals, and most receiving 25 mg/kg, experienced seizures. In male rats there was an increased incidence of cancers of the preputial gland and a slight increase in the incidence of pheochromocytomas of the adrenal gland. Nearly all male and female mice receiving 25 mg/kg α,ß-thujone experienced seizures, and all of the female mice receiving 25 mg/kg died before the end of the study. No increases in cancers were observed in female rats or in male or female mice. CONCLUSIONS: We conclude that α,ß-thujone caused cancers of the preputial gland in male rats, and an increase in adrenal gland tumors in male rats may have been related to α,ß-thujone administration. There was no increase in cancer incidence in female rats or male or female mice. Seizures were seen in almost all rats and mice receiving the highest doses of α,ß-thujone.

Cytochrome 450 metabolites of arachidonic acid (20-HETE, 11,12-EET and 14,15-EET) promote pheochromocytoma cell growth and tumor associated angiogenesis.

The importance of cytochrome P450 (CYP)-derived arachidonic acid (AA) metabolites, 20-hydroxyeicosatetraenoic acid (20-HETE) and epoxyeicosatrienoic acids (EETs) as tumor growth promotors has already been described in several cancer types. The aim of this study was to evaluate the role of these compounds in the biology of pheochromocytoma/paraganglioma. These tumors originate from chromaffin cells derived from adrenal medulla (pheochromocytomas) or extra-adrenal autonomic paraganglia (paragangliomas), and they represent the most common hereditary endocrine neoplasia. According to mutations in the driver genes, these tumors are divided in two clusters: pseudo-hypoxic and kinase-signaling EETs, but not 20-HETE, exhibited a potent ability to sustain growth in a murine pheochromocytoma cell line (MPC) in vitro, EETs promoted an increase in cell proliferation and a decrease in cell apoptosis. In a mouse model of pheochromocytoma, the inhibition of CYP-mediated AA metabolism using 1-aminobenzotriazol resulted in slower tumor growth, a decreased vascularization, and a lower final volume. Also, the expression of AA-metabolizing CYP monooxygenases was detected in tumor samples from human origin, being their apparent abundance and the production of both metabolites higher in tumors from the kinase-signaling cluster. This is the first evidence of the importance of CYP- derived AA metabolites in the biology and development of pheochromocytoma/paraganglioma tumors.

Chemically induced pheochromocytomas in rats: mechanisms and relevance for human risk assessment.

Pheochromocytomas are tumors originating from chromaffin cells of the adrenal medulla, which have been observed in numerous carcinogenicity studies. The authors have evaluated pheochromocytoma concurrence with other effects and the possible mechanisms, in order to assess the relevance of such data for the classification of carcinogenic effects and their relevance to humans. The evaluation revealed that pheochromocytomas occur with relatively higher frequency in male rats, especially when the following conditions are involved: hypoxia, uncoupling of oxidative phosphorylation, disturbance in calcium homeostasis, and disturbance of the hypothalamic endocrine axis. The underlying biochemical mechanisms suggest that other substances that interfere with these biochemical endpoints also produce pheochromocytomas. Such endpoints include enzymes involved in catecholamine synthesis, receptor tyrosine kinase (RET), hypoxia-inducible factor (HIF), succinate dehydrogenase, fumarate hydratase, and pyruvate dehydrogenase. To date, there is no indication that the substances inducing pheochromocytomas in animal experiments also induce corresponding tumors in humans. Because the mechanisms of action identified in rats are to be expected in humans, pheochromocytomas may be induced after exposure conditions similar to those used in the animal studies. Whether hereditary mutations represent a risk factor in humans is not clear. Pheochromocytomas that occur in animal experiments currently appear to have little relevance for conditions at the work place. When sufficiently documented and evaluated, such secondary pheochromocytomas are not relevant for classification and human risk assessment.

Pheochromocytoma presenting with severe hyperglycemia and metabolic acidosis following intra-articular glucocorticoid administration: a case report.

BACKGROUND: There are several reports of pheochromocytoma crisis triggered by systemic glucocorticoid administration. However, pheochromocytoma crisis after intra-articular glucocorticoid administration has been rarely reported. CASE PRESENTATION: A 45-year-old Japanese man presented to our hospital with a sudden, severe headache. He had no history of diabetes. He had received an intra-articular injection of betamethasone (2 mg) for joint pain, 2 days prior to his admission. On examination, his blood pressure was 240/126 mmHg and pulse was 120 beats/minute. The possibility of cerebrovascular events was ruled out by imaging studies and lumbar puncture. Blood tests revealed severe hyperglycemia (523 mg/dL) and metabolic acidosis (pH 7.21, anion gap 26.2 mEq/L, lactate 11.75 mmol/L) with a glycosylated hemoglobin level of 5.7%. Although a urine sample could not be obtained, fulminant type 1 diabetes mellitus and diabetic ketoacidosis were suspected based on these findings. However, after the initial treatment for diabetic ketoacidosis, his insulin secretion was found to be normal and the plasma levels of ketones were not elevated. This excluded the possibility of fulminant type 1 diabetes mellitus and diabetic ketoacidosis. Subsequently, a left adrenal gland tumor and elevated levels of serum catecholamine and urinary catecholamine metabolites were detected, while his other hormone levels were normal. Serum catecholamine levels did not decrease following the clonidine test, and a functional scintigraphy using iodine-131 metaiodobenzylguanidine showed strong uptake in the region of the left adrenal gland. Although no signs of pheochromocytoma crisis, such as paroxysmal hyperglycemia and hypertension, had been observed since admission, a pheochromocytoma was diagnosed based on the investigations. After controlling his blood pressure, a left adrenalectomy was performed. CONCLUSIONS: This case illustrates that intra-articular glucocorticoid administration can induce a pheochromocytoma crisis and an increase in hyperglycemia, and that pheochromocytoma crisis can resemble the clinical picture of fulminant type 1 diabetes mellitus owing to severe hyperglycemia with metabolic acidosis and normal glycosylated hemoglobin levels, especially under the influence of glucocorticoid.

Inhalation carcinogenicity study with nickel metal powder in Wistar rats.

Epidemiological studies of nickel refinery workers have demonstrated an association between increased respiratory cancer risk and exposure to certain nickel compounds (later confirmed in animal studies). However, the lack of an association found in epidemiological analyses for nickel metal remained unconfirmed for lack of robust animal inhalation studies. In the present study, Wistar rats were exposed by whole-body inhalation to 0, 0.1, 0.4, and 1.0 mg Ni/m(3) nickel metal powder (MMAD=1.8 microm, GSD=2.4 microm) for 6 h/day, 5 days/week for up to 24 months. A subsequent six-month period without exposures preceded the final euthanasia. High mortality among rats exposed to 1.0 mg Ni/m(3) nickel metal resulted in the earlier termination of exposures in this group. The exposure level of 0.4 mg Ni/m(3) was established as the MTD for the study. Lung alterations associated with nickel metal exposure included alveolar proteinosis, alveolar histiocytosis, chronic inflammation, and bronchiolar-alveolar hyperplasia. No increased incidence of neoplasm of the respiratory tract was observed. Adrenal gland pheochromocytomas (benign and malignant) in males and combined cortical adenomas/carcinomas in females were induced in a dose-dependent manner by the nickel metal exposure. The incidence of pheochromocytomas was statistically increased in the 0.4 mg Ni/m(3) male group. Pheochromocytomas appear to be secondary to the lung toxicity associated with the exposure rather than being related to a direct nickel effect on the adrenal glands. The incidence of cortical tumors among 0.4 mg Ni/m(3) females, although statistically higher compared to the concurrent controls, falls within the historical control range; therefore, in the present study, this tumor is of uncertain relationship to nickel metal exposure. The lack of respiratory tumors in the present animal study is consistent with the findings of the epidemiological studies.

Inhalation carcinogenicity and chronic toxicity of carbon tetrachloride in rats and mice.

Carcinogenicity and chronic toxicity of carbon tetrachloride were examined by inhalation exposure of 50 F344 rats and 50 BDF1 mice of both sexes to carbon tetrachloride at 0 (clean air), 5, 25, or 125 ppm (v/v) for 6 h/day, 5 days/wk, for 104 wk. Incidences of hepatocellular adenomas and carcinomas in rats and mice of both sexes and of adrenal pheochromocytomas in mice of both sexes were significantly increased dose-dependently. Hepatocellular carcinomas and cirrhosis significantly occurred in the 125-ppm-exposed rats of both sexes, and 3 cases of hepatocellular carcinomas and increased incidences of hepatic altered cell foci were noted in the 25-ppm-exposed female rats. Hepatocellular carcinomas were induced in mice of both sexes at 25 and 125 ppm, and hepatocellular adenomas occurred in females at 5 ppm without any degenerative or necrotic change in hepatocytes. Hepatocellular carcinomas metastasized to the lung. The chronic hepatotoxicity was characterized by cirrhosis, fibrosis, and fatty change in rats, and ceroid deposition, bile-duct proliferation, and hydropic change in mice. Survival rates were decreased in the 125-ppm-exposed rats and mice of both sexes and in the 25-ppm-exposed female mice, in association with decreased body weights. The decreased survival rates were considered to be causally related to both various tumors including hepatocellular carcinomas and severe chronic progressive nephropathy in rats and to hepatocellular carcinomas in mice. This study provided clear evidence of carcinogenicity for carbon tetrachloride in rats and mice. A cytotoxic-proliferative and genotoxic mode of action for carbon tetrachloride-induced hepatocarcinogenesis was suggested.

Long-term studies on carcinogenicity and promoting effect of phenylbutazone in DONRYU rats.

The carcinogenicity and promoting effect of phenylbutazone were investigated in inbred DONRYU rats. In the carcinogenicity study, both sexes were administered the chemical at dietary levels of 0 (control), 0.125, or 0.25% for 2 years. Toxic lesions were associated with phenylbutazone treatment in the kidney and digestive tract, appearing to have an adverse effect on life expectancy. Various tumors were detected in all groups including the controls. With the exception of pheochromocytoma in the female high-dose group, no statistically significant increase in yield of any tumors, including leukemia, was apparent in the treated groups of either sex when the data were analyzed by Fisher's exact probability and/or chi-square tests. Application of an age-adjusted statistical analysis revealed a slight positive effect regarding the occurrence of pheochromocytomas, neoplastic liver nodules, and leukemias in females. However, these tumors are commonly observed to develop spontaneously in this rat strain, and no such effect was apparent in the male groups. In addition, no differences in incidences of relevant preneoplastic lesions were evident between control and treated groups. Thus phenylbutazone showed no carcinogenic activity in DONRYU rats when given continuously in the diet for 2 years. For the investigation of promoting effect, phenylbutazone was given as a dietary supplement for 2 years subsequent to initiation with N-ethyl-N-nitrosourea or N-propyl-N-nitrosourea. No enhancement of nitrosourea-induced leukemogenesis was apparent, although a slight promoting effect was demonstrated for renal and thyroid tumorigenesis.

High incidences of pheochromocytomas after long-term administration of retinol acetate to F344/DuCrj rats.

The carcinogenicity of retinol acetate [(RAC) CAS: 127-47-9], a synthetic derivative of retinol, was tested by continuous oral administration in the drinking water of F344/DuCrj rats for 104 weeks. Groups of 50 male and 50 female rats were given solutions of 0.25 or 0.125% RAC in the form of gelatinized beadlets suspended in distilled water. Control groups consisting of the same numbers of rats were given 0.25% of placebo beadlets. All of the surviving animals were killed at 108 weeks, 4 weeks after the cessation of the RAC treatments. The survival rates were 72-84% and were sufficiently high for statistical comparison of all groups. Inhibition of body weight gain was marked in females of the high-dose group. Higher incidences of malignant pheochromocytomas, benign pheochromocytomas, and hyperplasias of the adrenal medulla were observed in the RAC-treated groups. The combined incidences of tumors of the adrenal medulla in males and females of the high-dose groups and the incidence in females of the low-dose group were significantly higher than the incidence in the controls. Conversely, statistically significant decreases were found in the incidences of the mammary gland tumors in males of the high-dose group, of thyroid tumors in females of the high-dose group, and of clitoral gland tumors in females of both high- and low-dose groups. It was concluded that RAC given orally possesses potential for increasing the incidence of pheochromocytomas in male and female F344 rats in a dose-related manner under the conditions of this bioassay.

[Pseudo-pheochromocytoma due to iproniazid: A case report]. / Pseudo-phéochromocytome médicamenteux sous iproniazide : à propos d'un cas.

INTRODUCTION: Pheochromocytoma is suggested by the presence of severe and paroxysmal hypertension associated with hyperadrenergy clinical signs. If the diagnosis of pheochromocytoma is ruled out, a pseudo-pheochromocytoma should be considered. We report a clinical observation of pseudo-pheochromocytoma due to iproniazid, a non-selective irreversible monoamine oxidase (MAO) A and B inhibitor in a patient with bipolar disorder. CASE REPORT: A 78-year-old Caucasian male patient treated by iproniazid was hospitalized for depressive relapse. After several episodes of syncopes related to orthostatic hypotension, the patient presented hypertensive crisis. Urinary normetanephrines were increased to twice the upper limit of the normal range. Iproniazid was discontinued. Patient hemodynamic was rapidly stabilized and sympathetic hypertonia diminished. The urinary measurements normalized within two months. The abdominal imaging eliminated an adrenal tumor. CONCLUSION: Iproniazid could be responsible for severe irregular blood pressure associated with abnormal catecholamine metabolism (i.e. pseudo-pheochromocytoma).

Differentiation of pheochromocytoma PC12 cells induced by human urine extract and the involvement of the extracellular signal-regulated kinase signaling pathway.

OBJECTIVE: The aim of this study was to investigate the effects of a human urine preparation on the differentiation of tumor cells. DESIGN: The pheochromocytoma PC12 cells were used to examine the effects of a human urine preparation, CDA-2 on the induction of differentiation markers, neurofilaments, and compared with that induced by nerve growth factor (NGF). The MAPK/ERK kinase (MEK) inhibitor U0126 was used to examine the involvement of mitogen-activated protein kinase (MAPK) signaling pathway in this differentiation inducing effect. RESULTS: We find that CDA-2 could induce differentiation of pheochromocytoma PC12 cells, as evidenced by the markedly increased expression of neurofilaments to a level comparable to those induced by NGF. This phenomenon was accompanied by the phosphorylation of extracellular-signal-regulated kinase (ERK) and could be inhibited by the MEK inhibitor, U0126. CONCLUSIONS: Our results demonstrate the presence of active components in the human urine extract that can induce differentiation of PC12 cells and may involve the ERK signaling pathway. This may provide new insights for seeking novel differentiation agents and offer hope for cancer patients.

Accidental provocation of phaeochromocytoma: the forgotten hazard of metoclopramide?

The perilous potential of metoclopramide when used inadvertently in patients harbouring phaeochromocytomas goes largely under-recognised. Despite the rarity of phaeochromocytoma, clinicians should exercise caution in the use of metoclopramide among hypertensives and those with labile blood pressures, given the potentially life-threatening crisis it can readily evoke in those with this tumour. We report a series of three patients with phaeochromocytoma who developed acute crises from metoclopramide.

Transient cardiogenic shock during a crisis of pheochromocytoma triggered by high-dose exogenous corticosteroids.

We report a case of a 39-year-old woman who presented to the emergency department (ED) with symptoms of pharyngitis and fever. Diagnosed with streptococcal pharyngitis, she received antibiotics and dexamethasone, and was discharged. Within 24 h she returned to the ED with signs and symptoms of an acute coronary syndrome; she was thus given ß-blockers. Her coronary angiogram was normal. She developed cardiogenic shock with an ejection fraction (EF) of 10% and apical ballooning on echocardiography. Her condition improved with optimal medical therapy. Subsequent testing weeks later confirmed the presence of a pheochromocytoma. Following prazosin and an adrenalectomy, all her antihypertensive medications were weaned and her EF normalised. We believe the high-dose exogenous corticosteroids triggered a pheochromocytoma crisis. The concomitant use of ß-blockers without preceding α blockade resulted in cardiovascular collapse. Pheochromocytoma crisis must be included in the differential diagnosis of any dramatic haemodynamic collapse after administration of exogenous corticosteroid or ß-blockers.

Long-term carcinogenicity bioassays on three chlorofluorocarbons (trichlorofluoromethane, FC11; dichlorodifluoromethane, FC12; chlorodifluoromethane, FC22) administered by inhalation to Sprague-Dawley rats and Swiss mice.

Three propellant chlorofluorocarbons, namely trichlorofluoromethane (FC11), dichlorodifluoromethane (FC12), and chlorodifluoromethane (FC22) were administered by inhalation at a concentration of 5000, 1000 and 0 ppm, 4 hours daily, 5 days weekly, for 104 and 78 weeks, to rats and mice, respectively. The animals were kept under observation until spontaneous death. Under the experimental conditions, all three compounds failed to show any carcinogenic effects.

Inhalation toxicity and carcinogenicity studies of cobalt sulfate.

Cobalt sulfate is a water-soluble cobalt salt with a variety of industrial and agricultural uses. Several cobalt compounds have induced sarcomas at injection sites in animals, and reports have suggested that exposure to cobalt-containing materials may cause lung cancer in humans. The present studies were done because no adequate rodent carcinogenicity studies had been performed with a soluble cobalt salt using a route relevant to occupational exposures. Groups of 50 male and 50 female F344/N rats and B6C3F1 mice were exposed to aerosols containing 0, 0.3, 1.0, or 3.0 mg/m3 cobalt sulfate hexahydrate, 6 h/day, 5 days/week, for 104 weeks. Survival and body weights of exposed rats and mice were generally unaffected by the exposures. In rats, proteinosis, alveolar epithelial metaplasia, granulomatous alveolar inflammation, and interstitial fibrosis were observed in the lung in all exposed groups. Nonneoplastic lesions of the nose and larynx were also attributed to exposure to all concentrations of cobalt sulfate. In 3.0 mg/m3 male rats and in female rats exposed to 1.0 or 3.0 mg/m3, the incidences of alveolar/bronchiolar neoplasms were increased over those in the control groups. Lung tumors occurred with significant positive trends in both sexes. The incidences of adrenal pheochromocytoma in 1.0 mg/m3 male rats and in 3.0 mg/m3 female rats were increased. Nonneoplastic lesions of the respiratory tract were less severe in mice than in rats. In mice, alveolar/bronchiolar neoplasms in 3.0 mg/m3 males and females were greater than those in the controls, and lung tumors occurred with significantly positive trends. Male mice had liver lesions consistent with a Helicobacter hepaticus infection. Incidences of liver hemangiosarcomas were increased in exposed groups of male mice; however, because of the infection, no conclusion could be reached concerning an association between liver hemangiosarcomas and cobalt sulfate. In summary, exposure to cobalt sulfate by inhalation resulted in increased incidence of alveolar/bronchiolar neoplasms and a spectrum of inflammatory, fibrotic, and proliferative lesions in the respiratory tracts of male and female rats and mice. Adrenal pheochromocytomas were increased in female rats, and possibly in male rats.

Vitamin D3-induced proliferative lesions in the rat adrenal medulla.

Adrenal medullary hyperplasia and pheochromocytomas are induced in rats by a variety of non-genotoxic agents, and we have hypothesized that these agents induce lesions indirectly by stimulating chromaffin cell proliferation. Vitamin D3, which has not been previously associated with adrenal medullary proliferative lesions, is the most potent in vivo stimulus to chromaffin cell proliferation yet identified. The present investigation utilized the vitamin D3 model to prospectively test the relationship between mitogenicity and focal proliferative lesions in the adrenal medulla and to determine early events in the pathogenesis of these lesions. Charles River Crl:CD BR rats were treated with 0; 5000; 10,000; or 20,000 IU/kg/day of vitamin D3 in corn oil (5 ml/kg) by oral intubation. Rats were killed after 4, 8, 12, or 26 weeks of treatment, following a final week of labeling with bromodeoxyuridine (BrdU) using a mini-pump. Adrenal sections were double-stained for BrdU and phenylethanolamine-N-methyl transferase (PNMT) to discriminate epinephrine (E) from norepinephrine (NE) cells or for vesicular acetylcholine transporter (VAchT) to identify cholinergic nerve endings. Vitamin D3 caused a 4-5-fold increase in BrdU labeling at week 4, diminishing to a 2-fold increase by week 26. An initial preponderance of labeled E cells gave way to a preponderance of labeled NE cells. By week 26, 17/19 (89%) animals receiving the 2 highest doses of vitamin D3 had focal adrenal medullary proliferative lesions, in contrast to an absence of lesions in control rats. The lesions encompassed a spectrum including BrdU-labeled "hot spots" not readily visible on H and E sections, hyperplastic nodules, and pheochromocytomas. Lesions were usually multicentric, bilateral, and peripheral in location, and almost all were PNMT-negative. The lesions were not cholinergically innervated, suggesting autonomous proliferation. Hot spots, hyperplastic nodules, and pheochromocytomas appear to represent a continuum rather than separate entities. Their development might involve selective responses of chromaffin cell subsets to mitogenic signals, influenced by both innervation and corticomedullary interactions. A number of non-genotoxic compounds that induce pheochromocytomas in rats are known to affect calcium homeostasis. The results of this study provide further evidence to support the hypothesis that altered calcium homeostasis is indirectly involved in the pathogenesis of pheochromocytomas, via effects on chromaffin cell proliferation.