Pathologic changes in blood vessels following administration of an inotropic vasodilator (ICI 153,110) to the rat

Sampling the Rat Mesenteric Artery

Vascular injury can be induced by different classes of drug candidates, and it can affect the mesenteric vasculature. Sampling of the mesenteric vessels in the rat is crucial for proper assessment of potential adverse or pharmacologic effects of drugs in nonclinical rodent studies. To date, several sampling and processing techniques for the histopathologic evaluation of the mesenteric artery in rodents have been described and used in studies with candidate drugs that may affect the vascular system. However, most of those techniques require a significant amount of time and effort. A less labor-intensive, time-consuming, and expensive technique that allows examination of the mesentery vasculature with abundant longitudinal and cross sections of the vessels when examined microscopically was developed and presented here.

Non-proliferative and Proliferative Lesions of the Cardiovascular System of the Rat and Mouse

The INHAND Project (International Harmonization of Nomenclature and Diagnostic Criteria for Lesions in Rats and Mice) is a joint initiative of the Societies of Toxicologic Pathology from Japan (JSTP), Europe (ESTP), Great Britain (BSTP) and North America (STP) to develop an internationally-accepted nomenclature for proliferative and non-proliferative lesions in laboratory animals. The primary purpose of this publication is to provide a standardized nomenclature for characterizing lesions observed in the cardiovascular (CV) system of rats and mice commonly used in drug or chemical safety assessment. The standardized nomenclature presented in this document is also available electronically for society members on the internet (http://goreni.org). Accurate and precise morphologic descriptions of changes in the CV system are important for understanding the mechanisms and pathogenesis of those changes, differentiation of natural and induced injuries and their ultimate functional consequence. Challenges in nomenclature are associated with lesions or pathologic processes that may present as a temporal or pathogenic spectrum or when natural and induced injuries share indistinguishable features. Specific nomenclature recommendations are offered to provide a consistent approach.

Scientific and Regulatory Policy Committee Points-to-consider Paper*

Drug-induced vascular injury (DIVI) is a recurrent challenge in the development of novel pharmaceutical agents. Although DIVI in laboratory animal species has been well characterized for vasoactive small molecules, there is little available information regarding DIVI associated with biotherapeutics such as peptides/proteins or antibodies. Because of the uncertainty about whether DIVI in preclinical studies is predictive of effects in humans and the lack of robust biomarkers of DIVI, preclinical DIVI findings can cause considerable delays in or even halt development of promising new drugs. This review discusses standard terminology, characteristics, and mechanisms of DIVI associated with biotherapeutics. Guidance and points to consider for the toxicologist and pathologist facing preclinical cases of biotherapeutic-related DIVI are outlined, and examples of regulatory feedback for each of the mechanistic types of DIVI are included to provide insight into risk assessment.

Proceedings of the 2014 National Toxicology Program Satellite Symposium

The 2014 annual National Toxicology Program (NTP) Satellite Symposium, entitled "Pathology Potpourri" was held in Washington, D.C., in advance of the Society of Toxicologic Pathology's 33rd annual meeting. The goal of this annual NTP Symposium is to present current diagnostic pathology or nomenclature issues to the toxicologic pathology community. This article presents summaries of the speakers' presentations, including diagnostic or nomenclature issues that were presented, along with select images that were used for audience voting and discussion. Some lesions and topics covered during the symposium included a pulmonary mucinous adenocarcinoma in a male B6C3F1 mouse; plexiform vasculopathy in Wistar Han (Crl:WI[Han]) rats; staging of the estrous cycle in rats and mice; peri-islet fibrosis, hemorrhage, lobular atrophy and inflammation in male Sprague-Dawley (SD) rats; retinal dysplasia in Crl:WI[Han] rats and B6C3F1 mice; multicentric lymphoma with intravascular microemboli and tumor lysis syndrome, and 2 cases of myopathy and vascular anomaly in Tg.rasH2 mice; benign thymomas in Crl:WI[Han] rats; angiomatous lesions in the mesenteric lymph nodes of Crl:WI[Han] rats; an unusual foveal lesion in a cynomolgous monkey; and finally a series of nomenclatures challenges from the endocrine International Harmonization of Nomenclature and Diagnostic Criteria (INHAND) Organ Working Group (OWG).

Nonclinical Safety Biomarkers of Drug-induced Vascular Injury

Better biomarkers are needed to identify, characterize, and/or monitor drug-induced vascular injury (DIVI) in nonclinical species and patients. The Predictive Safety Testing Consortium (PSTC), a precompetitive collaboration of pharmaceutical companies and the U.S. Food and Drug Administration (FDA), formed the Vascular Injury Working Group (VIWG) to develop and qualify translatable biomarkers of DIVI. The VIWG focused its research on acute DIVI because early detection for clinical and nonclinical safety monitoring is desirable. The VIWG developed a strategy based on the premise that biomarkers of DIVI in rat would be translatable to humans due to the morphologic similarity of vascular injury between species regardless of mechanism. The histomorphologic lexicon for DIVI in rat defines degenerative and adaptive findings of the vascular endothelium and smooth muscles, and characterizes inflammatory components. We describe the mechanisms of these changes and their associations with candidate biomarkers for which advanced analytical method validation was completed. Further development is recommended for circulating microRNAs, endothelial microparticles, and imaging techniques. Recommendations for sample collection and processing, analytical methods, and confirmation of target localization using immunohistochemistry and in situ hybridization are described. The methods described are anticipated to aid in the identification and qualification of translational biomarkers for DIVI.

Mesenteric vascular remodeling in hyperhomocysteinemia

Remodeling by its very nature implies synthesis and degradation of extracellular matrix components (such as elastin, collagen, and connexins). Most of the vascular matrix metalloproteinase (MMP) are latent because of the presence of constitutive nitric oxide (NO). However, during oxidative stress peroxinitrite (ONOO-) activates the latent MMPs and instigates vascular remodeling. Interestingly, in mesenteric artery, homocysteine (Hcy) decreases the NO bio-availability, and folic acid (FA, an Hcy-lowering agent) mitigates the Hcy-mediated mesentery artery dysfunction. Dimethylarginine dimethylaminohydrolase-2 (DDAH-2) and endothelial nitric oxide synthase (eNOS) increases NO production. The hypothesis was that the Hcy decreased NO bio-availability, in part, activating MMP, decreasing elastin, DDAH-2, eNOS and increased vasomotor response by increasing connexin. To test this hypothesis,the authors used 12-week-old C57BJ/L6 wild type (WT) and hyperhomocysteinemic (HHcy)-cystathione beta synthase heterozygote knockout (CBS+/-) mice. Blood pressure measurements were made by radio-telemetry. WT and MMP-9 knockout mice were administered with Hcy (0.67 mg/ml in drinking water). Superior mesenteric artery and mesenteric arcade were analyzed with light and confocal microscopy. The protein expressions were measured by western blot analysis. The mRNA levels for MMP-9 were measured by RT-PCR. The data showed decreased DDAH-2 and eNOS expressions in mesentery in CBS-/+ mice compared with WT mice. Immuno-fluorescence and western blot results suggest increased MMP-9 and connexin-40 expression in mesenteric arcades of CBS-/+ mice compared with WT mice. The wall thickness of third-order mesenteric artery was increased in CBS-/+ mice compared to WT mice. Hcy treatment increased blood pressure in WT mice. Interestingly, in MMP-9 KO, Hcy did not increase blood pressure. These results may suggest that HHcy causes mesenteric artery remodeling and narrowing by activating MMP-9 and decreasing DDAH-2 and eNOS expressions, compromising the blood flow, instigating hypertension, and acute abdomen pain.

Intimal Hyperplasia in Rats after Subcutaneous Injection of a Somatostatin Analog

The somatostatin analog octreotide was administered to male and female Sprague-Dawley rats by subcutaneous injection for thirteen weeks at 0 (saline control), 0 (placebo control [mannitol and lactic acid; pH 4.2]), 1.25 mg/kg/day and 2.5 mg/kg/day to explore its potential effect on cutaneous vascular morphology. The placebo caused an increase in the incidence of intimal hyperplasia compared to saline controls in female rats; octreotide increased the incidence and severity of intimal hyperplasia in males and females. Intimal hyperplasia consisted of increased numbers of cells located between the endothelial cell layer and the internal elastic lamina. Severity was based on the degree of compromise of the vascular lumen (regardless of vessel size and number), with severely affected vessels having no visible lumen. Intimal hyperplasia in rats treated with octreotide was considered to be an unexpected and adverse finding, given that this compound and other somatostatin analogs have been investigated as reducers of intimal proliferation or restenosis after angioplasty in humans and that no such lesion has been reported in the literature for this class of compound to date. The induction of intimal hyperplasia by the placebo is also a notable finding; this may be because of the low pH of the formulation.

Mechanisms and biomarkers of cardiovascular injury induced by phosphodiesterase inhibitor III SK&F 95654 in the spontaneously hypertensive rat

The cardiovascular injury of the type III selective PDE inhibitor SK&F 95654 was investigated in SHR. Twenty-four hours after a single sc injection of 100 or 200 mg/kg of the drug, rats exhibited cardiomyocyte necrosis and apoptosis, interstitial inflammation, hemorrhage and edema, as well as mesenteric arterial hemorrhage and necrosis, periarteritis, EC and VSMC apoptosis, EC activation, and MC activation and degranulation. Elevated serum levels of cTnT and decreased cTnT immunoperoxidase staining on cardiomyocytes were detected in the drug-treated rats. Serum levels of alpha2-macroglobulin and IL-6 were significantly elevated following drug treatment. NMR spectral patterns of urine samples are significantly different between the drug-treated and control rats. These results indicate that measurement of serum cTnT, acute phase proteins, and cytokines as well as metabonomic urine profiles may serve as potential biomarkers for drug-induced cardiovascular injury in rats. Increased expression of CD63 on MC (tissue biomarker of MC), of nitrotyrosine on MC and EC (an indirect indicator of NO in vivo), and of iNOS on MC and EC (source of NO) suggest that NO produced by activated and degranulated MC as well as activated EC play an important role in SK&F 95654-induced mesenteric vascular injury.

Mesenteritis precedes vasculitis in the rat mesentery after subacute administration of a phosphodiesterase type 4 inhibitor

Inhibitors of phosphodiesterase type 4 (PDE4) are currently exploited as potent drugs for pulmonary diseases. Some PDE4 inhibitors induce necrotizing panarteritis in the mesentery of rats, comparable to spontaneous polyarteritis nodosa in rats and vascular alterations that are induced by various vasoactive compounds, such as fenoldopam and inhibitors of PDE3. The mechanism of toxicity is unknown. In order to investigate the development of arteritis in the splanchnic vasculature of rats, a time-course study was performed with high doses of a compound (BYK169171), specifically inhibiting PDE4. Rats were treated orally for 1-28 days, and alterations in the mesentery were evaluated by histology, morphometry, and immunohistology. As early as 3 days after the onset of treatment, a mesenteritis was found, characterized by macrophage infiltration, fibroblast proliferation, neovascularization, and loss of adipocytes. Incidence and severity of the mesenteritis were low during the first 2 weeks of treatment, but increased with duration of treatment, finally affecting 2/3 of all animals. A segmental necrotizing panarteritis was detected in some rats treated for 21 or 28 days, but always followed a mesenteritis, whereas many animals with mesenteric inflammation did not have vascular lesions. We postulate that PDE4 inhibitors do not cause a primary vasculitis/arteritis in rats, but induce a non-purulent inflammation as the predominant initial toxic effect in the mesentery. This renders their toxic effect distinct from that of PDE3 inhibitors.

The toxicity of SCH 351591, a novel phosphodiesterase-4 inhibitor, in Cynomolgus monkeys

SCH351591, a novel phosphodiesterase-4 inhibitor under investigation as a potential therapeutic for asthma and chronic obstructive pulmonary disease (COPD), was evaluated in a 3-month rising-dose study in Cynomolgus monkeys. Four groups, containing four monkeys/sex, received vehicle control or rising doses up to 12, 24, or 48 mg/kg of SCH351591 daily. Although initial exposure produced clinical signs of emesis, reduced food intake, and reduced body weight, tachyphylaxis to the emesis allowed dose escalation up to 48 mg/kg/day. Two monkeys died and 3 were sacrificed in moribund condition over the course of the study. Early mortality, involving monkeys dosed with 12 or 24 mg/kg, was attributed to sepsis (2 monkeys) or colon inflammation (3 monkeys). Leukocyte function assays on low- and mid-dose group survivors revealed an inhibition of T lymphocyte proliferation for 12 mg/kg group males and 24 mg/kg group monkeys of both sexes. Necropsy findings, unassociated with early mortality, included reduced size and weight of the thymus, depletion of body fat, red discoloration of the gastric mucosa, and perivascular hemorrhage of the stomach and heart. Stomach and heart gross findings were present in the high-dose group only. Histopathologic lesions, in addition to those attributed to concurrent bacterial infection, included thymic atrophy, serous atrophy of fat, myocardial degeneration and acute to chronic inflammation of small to medium-sized arteries in various organs and tissues including the heart, kidneys, stomach, salivary glands, pancreas, esophagus, gallbladder, and mesentery. The findings of this study demonstrate the potential of a PDE4 inhibitor to alter immunologic response as well as to produce arteriopathy in nonhuman primates.

SK&F 95654-induced acute cardiovascular toxicity in Sprague-Dawley rats--histopathologic, electron microscopic, and immunohistochemical studies

The characteristics and pathogenesis of the cardiovascular toxicity induced by the type III selective phosphodiesterase inhibitor SK&F 95654 were examined in 2 studies. Sprague-Dawley rats received either a single sc injection of 50, 100, or 200 mg/kg SK&F 95654 and were euthanized at 24 hours after administration of the drug (Study 1), or were given a single subcutaneous (sc) injection of 100 mg/kg SK&F 95654 and euthanized at 1, 2, 4, 6, 8,12, 24 hours, or 2 weeks after treatment (Study 2). Control rats received either DMSO or saline. Myocardial lesions and vascular lesions of the mesentery, spleen, and pancreas were seen 24 hours after dosing with either 50,100, or 200 mg/kg SK&F 95654. The frequency and severity of these lesions (evaluated after the 100 mg/kg dose) increased with time over a period of 1 to 24 hours. By 2 weeks, the lesions subsided. Cardiac lesions consisted of myocyte necrosis with hypercontraction bands, inflammatory cell infiltration, interstitial hemorrhage, and interstitial edema. Vascular lesions of the mesentery were most prominent and consisted of vasodilatation and inflammation in the small-sized vessels, arterial medial necrosis and hemorrhage, and venous thrombosis. The vascular lesions included: leukocyte adhesion to endothelial cells, transendothelial migration of leukocytes, and inflammatory cell infiltration into vessel walls. Affected vessels included arteries, terminal arterioles, capillaries, postcapillary venules, and veins. Apoptosis of endothelial and smooth muscle cells was detected in the mesenteric vasculature by both TUNEL assay and electron microscopy. Evidence of endothelial cell activation in the mesenteric arteries and veins was also observed by electron microscopy. Immunohistochemical staining detected enhanced endothelial cell expression of intercellular adhesion molecule- 1 (ICAM- 1) and von Willebrand factor (vWF) in the mesenteric arteries and veins. Mast cells were noted to be more prevalent in affected mesenteric tissue from drug-treated animals. The present findings suggest that apoptosis of endothelial and smooth muscle cells, activation of endothelial cells, recruitment of mast cells, and increased expression of adhesion molecules are important factors to the overall pathogenesis of SK&F 95654-induced vasculitis.

Histopathological and immunohistochemical studies on arteritis induced by fenoldopam, a vasodilator, in rats

Fenoldopam, a dopaminergic (DA1) agonist, has been reported to induce medial necrosis and adventitial inflammatory response in the splanchnic arteries in rats. This study was carried out to clarify the detailed time course of the inflammatory responses, using antibodies for the inflammatory cell markers, CD3 (T cell), CD20 (B cell) and ED-1 (macrophage), and inflammatory serum factors, IgG, IgM and C3. Rats were administered fenoldopam for 24 hours by intravenous infusion. Histopathologically, medial necrosis with hemorrhage was observed at the end of infusion, but it almost disappeared on day 7 post-infusion. Adventitial inflammatory responses with ED-1-, CD3- and CD20-positive cells were very slight at the end of infusion, became prominent with marked fibrosis on days 3 and 5, decreased on day 7, and subsided on day 14. The serum factors were first present in the area of medial necrosis, then shifted to the subendothelial space or cytoplasm of smooth muscle cells, and disappeared on day 14 post-infusion. Gaps in the external elastic lamina were observed on days 3 and 5 post-infusion, and IgG and IgM were present outside the gaps in the adventitia. These results provided us with more detailed information on the inflammatory responses following medial damage induced by vasodilators.

Pulmonary vascular sclerosis in an albino rat with leukemia

The animal investigated was a two years old male control Sprague-Dawley rat which died spontaneously during a carcinogenicity study. Post-mortem examination disclosed hepatic and splenic enlargement. At microscopical examination, massive leucaemic infiltration was observed in many tissues/organs, including bone marrow, spleen, liver and renal blood vessels. A very unusual finding was observed in the lung, consisting of scattered micronodules which replaced most of the lung parenchyma. They contained collagen, displaying a somewhat circular distribution at the periphery of the lesions, fibrin, leukemic cells and fibroblasts. Immunostaining for desmin revealed the presence of smooth muscle fibers within the nodules, while staining for elastic fibers showed clearly that the internal and external elastic membranes were identifiable within the nodules. The diagnosis of pulmonary vascular sclerosis was made on the basis of microscopical and immunohistochemical findings.

Arterial lesions induced by phosphodiesterase III (PDE III) inhibitors and DA(1) agonists

Compounds that inhibit the low Km, cGMP-inhibitable form of phosphodiesterase (type III) and the DA(1) agonist, fenoldopam, are potent vasodilators that have been associated with segmental medial haemorrhagic necrosis in susceptible arterial beds following administration of suprapharmacological doses to dogs and/or rats. Morphological and haemodynamic investigative studies with PDE III inhibitors support the hypothesis that the arterial toxicity is the consequence of the vasodilator pharmacology of these compounds. Investigative data also suggest that similar mechanisms are involved in the pathogenesis of arterial lesions induced by fenoldopam and the K(+) channel opener, minoxidil.

Phosphodiesterase 4 inhibitors and the treatment of asthma: where are we now and where do we go from here?

Research conducted over the last 20 years has established that inflammation of the airways is central to the airway dysfunction that characterises asthma. Typically, the airway wall is infiltrated by a variety of cells including mast cells, eosinophils and T lymphocytes, which have deviated towards a T(H)2 phenotype. Together, these cells release a plethora of mediators including interleukin (IL)-4, IL-5, granulocyte/macrophage colony-stimulating factor and eotaxin which ultimately cause the histopathology and symptoms of asthma. Glucocorticosteroids are the only drugs currently available that effectively impact upon this inflammation and resolve, to a greater or lesser extent, compromised lung function. However, steroids are nonselective and generally unsuitable for paediatric use. New drugs are clearly required. One group of potential therapeutic agents for asthma are inhibitors of cyclic AMP-specific phosphodiesterase (PDE), of which theophylline may be considered a prototype. It is now known that PDE is a generic term which refers to at least 11 distinct enzyme families that hydrolyse cAMP and/or cGMP. Over the last decade, inhibitors of PDE4 (a cAMP-specific family that negatively regulates the function of almost all pro-inflammatory and immune cells, and exerts widespread anti-inflammatory activity in animal models of asthma) have been developed with the view to reducing the adverse effects profile associated with non-selective inhibitors such as theophylline. Such is the optimism regarding PDE4 as a viable therapeutic target that more than 100 PDE4 inhibitor patent applications have been filed since 1996 by 13 major pharmaceutical companies. This article reviews the progress of PDE4 inhibitors as anti-inflammatory agents, and identifies problems that have been encountered by the pharmaceutical industry in the clinical development of these drugs and what strategies are being considered to overcome them.

Toxicologic and carcinogenic effects of the type IV phosphodiesterase inhibitor RP 73401 on the nasal olfactory tissue in rats

RP 73401, a type IV phosphodiesterase inhibitor, caused toxic effects in the nasal olfactory region of Sprague-Dawley rats when administered by either oral or inhalation exposure. A single oral administration of RP 73401 (at a dose of > or = 50 mg/kg) or 5-day inhalation exposure (1 hr/day) at a dose of approximately 1.0 mg/kg per day caused degeneration and sloughing of the olfactory surface epithelium. Degeneration and loss of Bowman's glands were noted in the underlying lamina propria and submucosa. Electron microscopy of these lesions demonstrated that sustentacular cells and the epithelial cells lining Bowman's glands were the primary target cells in the olfactory mucosa. The earliest ultrastructural changes detected in these cells were dilatation and vesiculation of the endoplasmic reticulum, suggesting that metabolic activation is important for the toxic effects. In repeated-dose studies, 13 wk of oral dosing at 2.0 or 6.0 mg/kg per day resulted in subtle disorganization of the olfactory epithelium, whereas basal cell hyperplasia in the olfactory epithelium was identified in a 6-month inhalation study at a dose of 1.0 mg/kg per day. A 2-yr inhalation carcinogenicity study resulted in tumors of the nasal olfactory region in rats treated at 0.5 and 1.0 mg/kg per day. Most tumors were classified as olfactory neuroblastomas, and immunohistochemistry on selected tumors was consistent with their being of neuroectodermal origin. Of the species studied (rat, mouse, and dog), the olfactory toxicity of RP 73401 was confined to the rat, and the toxicity was likely related to metabolic activation by olfactory epithelial cells rather than the phosphodiesterase activity of the compound.

Systemic histopathology of rats treated with 6-sulfanilamidoindazole, a novel arthritogenic sulfonamide

6-Sulfanilamidoindazole (6SAI) is a sulfonamide that induces acute, self-limiting arthritis in rats, and 6SAI-induced arthritis is thought to be a model for testing anti-inflammatory agents. In this study, in order to clarify the location of arthritis and relationships between arthritis and other changes in this model, we have investigated the detailed pathologic changes in rats administered orally with 6SAI (125, 250, 500 mg/kg) daily for 4 wk in a time-course experiment. Moderate to severe arthritis was observed in rats of middle- and high-dose groups. Histologically, in the affected ankle, exudative synovitis and periarthritis were observed at 1 wk, granulation tissue formation with angiogenesis and periosteal new bone formation at 2 wk, and marked fibrosis of affected area at 4 wk, respectively. In addition to these changes, in periarticular and periosteal tissues of affected ankles, subendothelial insudation of small-sized arteries and medial fibrinoid degeneration of medium-sized arteries were observed at 1 and 2 wk and intimal thickening and medial hypertrophy at 4 wk, respectively. No arterial changes were observed in the unaffected ankles. Similar arterial changes were often observed in the liver, thyroid glands, and lungs and rarely in various organs and tissues. Acute inflammation of serous tissues such as mesentery, mediastinum, and capsule of spleen or thymus were also present in 6SAI-treated groups, and it was sometimes accompanied by arteritis. In addition, in 6SAI-treated rats, follicular hyperplasia of thyroid glands and pituitary changes, which are thought to be related to depression of thyroid hormone production by 6SAI, were observed. These results show that 6SAI induces not only arthritis but also arteritis, serositis, and thyroid change, and it is necessary to take the interaction between these changes into consideration when anti-inflammatory agents are tested in this model.

Mesenteric arteriopathy in the rat induced by phosphodiesterase III inhibitors: an investigation of morphological, ultrastructural, and hemodynamic changes

A reproducible model of a phosphodiesterase III (PDE III) inhibitor-induced arteriopathy has been developed in the rat after subcutaneous administration of SK&F 95654. Administration of this potent PDE III inhibitor induced an arteriopathy of mesenteric arteries within 24 hr that was dose-related in intensity and incidence over the range 0.174, 0.348, 0.523, and 0.697 mmol/kg. The arteriopathy was restricted to muscular arteries of external diameter of 100-800 microns and was shown microscopically to be focal or segmental medial necrosis and hemorrhage. A time-course experiment, conducted from 3 to 24 hr postdosing, showed that the first changes observed 6 hr postdosing were on the endothelium followed by focal hemorrhages into the media at 12 hr postdosing, causing compression, degeneration, and necrosis of myocytes. From 16 hr postdosing, there was focal endothelial cell necrosis and loss of confluence. Leukocytes and activated platelets were found adhering to exposed basement lamina and seen to pass through endothelial gaps into the subintima. By 24 hr postdosing, medial necrosis was extensive with large areas of media replaced by erythrocytes, cell debris, and a few leukocytes and platelets. The effect of 3 structurally dissimilar PDE III inhibitors administered subcutaneously at a dose of 0.697 mmol/kg was compared with that of SK&F 95654. The arteriopathy induced by these compounds were identical to that produced by SK&F 95654 with the incidence and severity of lesions ranked in the following order: SK&F 95654 > WIN 62582 > SK&F 94836, with no macroscopic lesions observed for SK&F 94120. Systolic blood pressure was measured for these 4 PDE III inhibitors at regular intervals over the 24-hr period postadministration by a plesthymographic method. The severity of the arterial lesions correlated with the magnitude of hypotension induced by these agents. It is postulated that the arterial damage is a consequence of profound vasodilation resulting in abnormal endothelial permeability and increased wall tension, resulting in progressive medial necrosis and hemorrhage.

The toxicity of repeated exposures to rolipram, a type IV phosphodiesterase inhibitor, in rats

Rolipram is a selective inhibitor of Type IV phosphodiesterase isozymes (PDE IV) which is often used as a baseline comparator for compounds in this class. To document the toxicological effects of rolipram, it was administered to female rats at 0, 10, 30 or 100 mg/kg/day orally for up to 2 weeks. One treatment-related death in the 100 mg/kg/day dose group was observed on day 3, and all rats at this dose level were considered moribund and euthanatized on day 5. Several clinical signs were observed in treated rats, including increased salivation, slight distention of the abdomen, emaciated appearance, and ataxia. After 14 days of treatment, the rats were necropsied and tissues examined microscopically. A number of compound-related histopathological changes were observed in rats receiving 30 or 100 mg/kg/day. Myocardial degeneration and necrosis, endocardial fibrosis, epicarditis, and arteritis/periarteritis of intramural and extramural coronary arteries were observed in the heart. A necrotizing vasculitis and inflammation were observed in the mesentery and interstitial areas of the liver, affecting medium-sized portal arteries and veins. Focal necrosis was also observed in the glandular mucosa of the stomach at these 2 dose levels. Other treatment-related effects included squamous hyperplasia and hyperkeratosis with or without ulceration in the nonglandular stomach of at least one animal from all treatment groups. Enlarged salivary glands were noted at necropsy in animals treated with 100 mg/kg/day, and this finding correlated microscopically with dilatation and degeneration of ducts and acini in the sublingual gland with secondary inflammation and edema. The results of this study demonstrate that rolipram, a selective inhibitor of the type IV class of PDE, can cause effects on the heart and vasculature of rats which heretofore have been ascribed only to selective inhibitors of the PDE III class of isozymes. Therefore, these organs should be closely examined in studies with other PDE IV inhibitors. In addition, the gastrointestinal tract and salivary glands were sites for rolipram-induced toxicity and may be targets of other PDE IV inhibitors.

Characterization of the arteritis induced by infusion of rats with UK-61,260, an inodilator, for 24 h. A comparison with the arteritis induced by fenoldopam mesylate

Administration of fenoldopam mesylate (FM), a dopaminergic agonist, or of cyclic cAMP phosphodiesterase inhibitors (PDE III), for example theophylline and caffeine, induces arteritis in the rat. In this study we characterized the arteritis induced by UK-61,260, an investigational inotropic agent with vasodilatory properties which displays an inhibitory action on cyclic AMP phosphodiesterase, in comparison with lesions induced by FM. The compounds were administered to Sprague-Dawley rats by intravenous infusion over 24 h (FM and UK-61,260), orally or subcutaneously (UK-61,260); the rats were killed and necropsied for pathological examination at various times between 0 h and 28 days post-infusion. Infusion of UK-61,260 at doses of 100, 300 or 400 mg/kg produced arteritis mainly in the mesenteric arteries and occasionally in the renal, pancreatic, gastric and coronary arteries. There were no arterial lesions after infusion of 30 mg/kg, or after administration of 30, 100 or 200 mg/kg per day subcutaneously for 7 days, or after acute administration of 100, 300, 400 or 600 mg/kg orally. Infusion of rats with 72 or 144 mg/kg FM produced arteritis over a wider range of tissues than did UK-61,260. However, the arterial lesions produced by infusion of either drug have the same initial aspect and a similar evolution with time. Immediately after the end of the infusion, minimal necrosis and haemorrhage occurred in the media only, without involvement of the endothelium or the perivascular space. This indicates that the media of the artery is the primary site of injury. The lesions seen 1 and 3 days post-infusion were characterized by severe medial necrosis and haemorrhage with perivascular acute inflammation and appeared macroscopically as haemorrhagic spots on the vessels. On days 7, 14 and 28 post-infusion, no medial necrosis or haemorrhage were present, while perivascular chronic inflammation and moderate smooth muscle hyperplasia were seen. It appeared, therefore, that the lesions underwent repair in 28 days, but footprints of the damage were still present 28 days post-infusion. The similarity between arteritis induced in rats by fenoldopam or by UK-61,260, at doses inducing PDE III inhibition, is consistent with the view that they have a similar pathogenesis. In our view it is probable that these pharmacologically and chemically distinct drugs trigger an increase in intracellular levels of cAMP which in turn triggers vascular damage. The arterial changes observed in the current study after acute administration may explain the increased incidence of polyarteritis nodosa occurring in long term toxicity studies with FM or PDE III inhibitors.

Long-term effects of an inotropic phosphodiesterase inhibitor (ICI 153,110) on the rat salivary gland, harderian gland, and intestinal mucosa

The inotropic vasodilator, ICI 153,110, a phosphodiesterase inhibitor intended for the treatment of congestive heart failure, was administered to Alderley Park Wistar-derived rats for periods of up to 182 days. Treatment produced hypertrophy of salivary glands, hyperplasia of intestinal mucosa, and dacryoadenitis of the harderian gland. As the functions of these glandular tissues can be modified by factors which alter cyclic nucleotide metabolism, it is postulated that the glandular alterations produced by ICI 153,110 occurred as a result of phosphodiesterase inhibition.