Coprological survey of endoparasite infections in owned dogs and owners' perceptions of endoparasite control in Belgium and the Netherlands.

Infections with endoparasites are common in dogs. Some of these parasites are potentially zoonotic and therefore a public health concern. A survey was conducted in twenty-six small animal practices to evaluate the prevalence of endoparasites in Belgian and Dutch owned dogs older than 6 months as well as risk factors associated with infection. Out of 239 faecal samples screened (168 in Belgium and 71 in the Netherlands), 18 dogs were tested positive for at least one type of endoparasite with three dogs co-infected with two parasitic species. Toxocara sp. was the most frequently found endoparasite (4.6%). Three other dogs were positive for Angiostrongylus vasorum (1.4%) using the Baermann method and confirmed in one dog by the Angiodetect® test. Age and predation behaviour were identified as two risk factors associated with endoparasite infection. Although the majority (77%) of the owners in this study reported to administer at least one anthelmintic treatment per year, only a minority of them (24.3%) were aware of the risk to human health, indicating that owner awareness is sub-optimal. For dog owners, human toxocarosis and other potential zoonoses remain an underestimated health concern. The implementation of sustainable parasite control strategies should be promoted taking also into account the public health risk.

Dispersal capacity of Haematopota spp. and Stomoxys calcitrans using a mark-release-recapture approach in Belgium.

The dispersion potential of mechanical vectors is an important factor in the dissemination of pathogens. A mark-release-recapture experiment was implemented using two groups (unfed and partially fed) of the Tabanidae (Diptera) (Haematopota spp.) and biting Muscidae (Diptera) (Stomoxys calcitrans) most frequently collected in Belgium in order to evaluate their dispersion potential. In total, 2104 specimens of Haematopota spp. were collected directly from horses and 5396 S. calcitrans were collected in a cattle farm using hand-nets. Some of these insects were partially fed in vitro and all were subsequently coloured. Overall, 67 specimens of S. calcitrans (1.2%) and 17 of Haematopota spp. (0.8%) were recaptured directly on horses. Stomoxys calcitrans flew maximum distances of 150 m and 300 m when partially fed and unfed, respectively. Haematopota spp. travelled maximum distances of 100 m and 200 m when partially fed and unfed, respectively. Segregation measures seem essential in order to reduce the risk for pathogen transmission. A distance of 150 m appears to be the minimum required for segregation to avoid the risk for mechanical transmission, but in areas of higher vector density, this should probably be increased.

A comparative test of ixodid tick identification by a network of European researchers.

This study reports the results of a comparative test of identification of ticks occurring in Western Europe and Northern Africa. A total of 14 laboratories were voluntarily enrolled in the test. Each participant received between 22 and 25 specimens of adult and nymphal ticks of 11 species: Dermacentor marginatus, D. reticulatus, Haemaphysalis punctata, Hyalomma lusitanicum, Hy. marginatum, Ixodes ricinus, I. hexagonus, Rhipicephalus annulatus, R. bursa, R. rossicus, and/or R. sanguineus s.l. Ticks were morphologically identified by three of the co-authors and the identification confirmed by a fourth co-author who used molecular methods based on several genes. Then ticks were randomly selected and blindly distributed among participants, together with a questionnaire. Only specimens collected while questing and, if possible, in the same survey, were circulated. Because of the random nature of the test, a participant could receive several specimens of the same species. Species in the different genera had variable misidentification rates (MR) of 7% (Dermacentor), 14% (Ixodes), 19% (Haemaphysalis), 36% (Hyalomma), and 54% (Rhipicephalus). Within genera, the MR was also variable ranging from 5.4% for I. ricinus or 7.4% for D. marginatus or D. reticulatus to 100% for R. rossicus. The test provided a total misidentification rate of 29.6% of the species of ticks. There are no significant differences in MR according to the sex of the tick. Participants were requested to perform a second round of identifications on the same set of ticks, using only purposely prepared keys (without illustrations), circulated to the enrolled participants, including 2 species of the genus Dermacentor, 8 of Haemaphysalis, 10 of Hyalomma, 23 of Ixodes, and 6 of Rhipicephalus. The average MR in the second round was 28%: 0% (Dermacentor), 33% (Haemaphysalis), 30% (Hyalomma) 18% (Ixodes), and 50% (Rhipicephalus). Species which are not reported in the countries of a participating laboratory had always highest MR, i.e. purely Mediterranean species had highest MR by laboratories in Central and Northern Europe. Participants expressed their concerns about a correct identification for almost 50% of the ticks of the genera Hyalomma and Rhipicephalus. The results revealed less than total confidence in identifying the most prominent species of ticks in the Western Palearctic, and underpin the need for reference libraries for specialists involved in this task. Results also showed that a combination of certain genes may adequately identify the target species of ticks.

A retrospective serological survey on human babesiosis in Belgium.

In Europe, most clinical babesiosis cases in humans have been attributed to Babesia divergens and Babesia sp. EU1. Babesia microti infection of humans occurs mainly in the United States; although a case of autochthonous B. microti infection and serological evidence of infection have been reported in Europe. The Indirect Fluorescent Antibody Test was used to screen sera from 199 anonymous Belgian patients with history of tick bite and clinical symptoms compatible with a tick-borne disease. The serological screen detected positive reactivity in 9% (n = 18), 33.2% (n = 66), and 39.7% (n = 79) of the samples against B. microti, B. divergens, and Babesia sp. EU1, respectively. Thus, evidence of contact among three potentially zoonotic species of Babesia and humans has been confirmed in Belgium. Preventive action and development of better diagnostic tools should help in prevention of clinical cases and to clarify the true burden of such infection for individuals and public health.

Foci report on indigenous Dermacentor reticulatus populations in Belgium and a preliminary study of associated babesiosis pathogens.

The occurrence of autochthonous clinical cases of canine and equine babesiosis in Belgium during the last two decades suggests that the vector of the pathogens responsible for these diseases, Dermacentor reticulatus (Ixodida: Ixodidae), may be present in this country. Consequently, evidence for the presence of this tick species in different locations within Belgium was investigated. Four different locations were monitored by flagging in 2010; these included the locations at which D. reticulatus was previously found on a dog in 2009 and on two red deer in 2007. Two different species of tick were identified, Ixodes ricinus (Ixodida: Ixodidae) and D. reticulatus. A total of 282 D. reticulatus adult ticks (98 males, 184 females) were collected from the four sites. Ticks were found mainly from early March until the end of May and a peak in activity was apparent in March. A Babesia spp. (Piroplasmida: Babesiidae) genus-specific polymerase chain reaction test based on the amplification of a fragment of the 18S rRNA gene was used to investigate the potential presence of Babesia spp. All DNA extracts isolated from the total tick samples yielded negative results. Additional studies to accurately determine the distribution and vectorial capacity of this important tick species in Belgium are warranted.

An optimized DNA extraction and multiplex PCR for the detection of Fasciola sp. in lymnaeid snails.

This study deals with the development and validation of an original PCR protocol to assess the presence of Fasciola hepatica in Galba truncatula its main intermediate host in Western Europe. In the present study two DNA extraction techniques are compared and a new multiplex PCR is described. The Chelex(®) DNA extraction technique showed to be more appropriate than the classical Phenol/Chloroform/Proteinase K based method because of the absence of toxic organic solvent, shorter duration and lower cost, and a higher reproducibility regarding DNA concentrations and wavelength ratios. The multiplex PCR was set up to amplify the lymnaeid internal transcribed spacer 2 sequence (500-600 bp) that act as an internal control and a 124 bp Fasciola sp. sequence that is repeated more than 300,000 times in fluke whole genome. Ninety six snails were pooled and 6 snails (6.25%) found positive for Fasciola sp. The limit of detection is lower than the minimal biological infestation unit (one miracidium). DNA extracts from Paramphistomum daubneyi, Dicrocoelium lanceolatum, and Fascioloides magna did not cross react.

TRAIL inhibits angiogenesis stimulated by VEGF expression in human glioblastoma cells.

Tumour growth is tightly related to new blood vessel formation, tissue remodelling and invasiveness capacity. A number of tissular factors fuel the growth of glioblastoma multiforme, the most aggressive brain neoplasm. In fact, gene array analyses demonstrated that the proapoptotic cytokine tumour necrosis factor-related apoptosis-inducing ligand (TRAIL) inhibited mRNA expression of VEGF, along with those of matrix metalloproteinase-2 (MMP-2), its inhibitor tissue inhibitor of matrix metalloproteinases-2 (TIMP-2), as well as the tumour invasiveness-related gene secreted protein acid rich in cysteine (SPARC) in different human glioblastoma cell lines. Particularly, VEGF mRNA and protein expression and release from glioblastoma cells were also inhibited by TRAIL. The latter also exerted antimitogenic effects on human umbilical vein endothelial cells (HUVECs). With the same cells, TRAIL inhibited new vessel formation in the in vitro matrigel model, as well as it exerted powerful inhibition of blood vessel formation induced by an angiogenic cocktail administered in subcutaneous pellets in vivo in the C57 mouse. Moreover, the expression of MMP-2, its inhibitor TIMP-2 and the tumour invasiveness-related protein SPARC were effectively inhibited by TRAIL in glioblastoma cell lines. In conclusion, our data indicate that TRAIL inhibits the orchestra of factors contributing to glioblastoma biological aggressiveness. Thus, the TRAIL system could be regarded as a molecular target to exploit for innovative therapy of this type of tumour.

Congenital insensitivity to pain with Anhidrosis (NTRK1 mutation) and early onset renal disease: clinical report on three sibs with a 25-year follow-up in one of them.

Congenital insensitivity to pain with anhidrosis (CIPA) is an autosomal recessive disorder caused by mutations in the neurotrophic tyrosine receptor kinase 1 (NTRK1) gene which encodes the receptor for nerve growth factor (NGF). We report the clinical course in three sibs with CIPA and proven NTRK1 gene mutations with a follow-up over a 25-year period in one of them. They had the characteristic clinical features of an abnormally high pain threshold, and mental retardation; in addition their clinical course was marked by the occurrence of early onset renal disease with recurrent microhematuria and proteinuria and frequent observations of increased serum creatinine and blood urea levels. Light microscopy study of a renal biopsy performed in one of them at age of 20 months showed focal glomerulosclerosis, interstitial fibrosis and tubular atrophy. This patient and his younger brother died because of renal failure at the age of 25 years and 14 years, respectively. The sister still alive showed renal impairment and deep venous thrombosis associated with lupus anticoagulant activity, decrease of circulating autoreactive CD5 (+) B lymphocytes and increased urinary levels of IgG and kappa and lambda light chains, suggesting a possible defect in regulation of B-lymphocyte function. In the light of the NGF-related molecular defect, the extraneurological tissue involvement in CIPA might in part reflect dysregulation of immune mechanisms which possibly brings about a chronic inflammatory response. This, in turn, could result in renal disease which should be mentioned among the life-threatening complications associated with this disorder.

Experimental study on the toxicity and the local and systemic tolerability of gemcitabine after topical treatment of the rabbit bladder.

This study investigated gemcitabine administered intravesically to establish the local and systemic tolerability necessary for clinical trials. Gemcitabine was directly administered via catheter into the bladders of 24 male New Zealand rabbits weighing an average of 1.9+/-0.08 kg. Three groups received weekly gemcitabine for 5 (50 mg/kg) or 8 (25 mg/kg or controls) weeks. Animals were inspected daily for signs of toxicity and distress, body weight changes, and water and food consumption; electrocardiogram, blood pressure, and urinalysis were recorded before dosing and after 4 and 8 weeks of treatment. The rabbits were euthanized, and a full necropsy was performed on day 1 after the last instillation. Principal organs (spleen, thymus, testis, and muscle) and plasma samples were analyzed for the systemic absorption of gemcitabine. The 25-mg/kg dose was well tolerated with no clinical side effects. At 50 mg/kg, signs of mild myelosuppression and severe symptomatic toxicity (leg weakness, and hair and body weight loss) was evident after 3 weeks of treatment and three of the seven animals in this group died after four doses. Necropsies revealed normal bone marrow cellularity and organ histology at both doses. No significant systemic drug absorption was seen. These findings suggest that intravesical administration of gemcitabine does not produce organ-specific toxicity, but the higher dose (50 mg/kg) may represent the threshold above which increasing morbidity may occur.

Protective effects of estradiol on TRAIL-induced apoptosis in a human oligodendrocytic cell line: evidence for multiple sites of interactions.

Demyelinating diseases are high impact neurological disorders. Steroids are regarded as protective molecules in the susceptibility to these diseases. Here, we studied the interactions between tumour necrosis factor-related apoptosis-inducing ligand (TRAIL), a potent proapoptotic molecule toxic to oligodendrocytes, and 17-beta-estradiol (E-17-beta), in human oligodendrocytic MO3.13 cells. Exposure of cells to TRAIL resulted in the upregulation of both death receptors DR4 and DR5 and apoptosis, as well as the activation of caspase-8 and -3, increased phosphorylation of Jun-N-terminal kinase and p38 kinase, and the reduction of bcl-2 and bcl-xL proteins. TRAIL-mediated MO3.13 cell apoptosis was abrogated by the dominant-negative form of the adaptor protein FADD and by caspase inhibitors. Preincubation with E-17-beta completely prevented both TRAIL-induced DR4 and DR5 upregulation and apoptosis. Estrogen-induced cytoprotection was time and concentration dependent and reverted by antiestrogens. Estrogen treatment per se reduced kinase phosphorylation, and upregulated bcl-2 and bcl-xL proteins. In conclusion, our data show that the detrimental role of TRAIL on oligodendrocytes can be effectively counteracted by estrogens, thus suggesting that the underlying molecular interactions can be of potential relevance in characterizing novel targets for therapy of demyelinating disorders.

Red wine micronutrients as protective agents in Alzheimer-like induced insult.

Plant extract micronutrients are commonly added to diets for health and prevention of degenerative disease. However, there are barriers to the introduction of these products as antioxidant therapies in counteracting chronic human diseases, probably because the molecular bases of their therapeutic potential are poorly clarified. The present study was designed to evaluate the possible protective effect of combined micronutrients present in black grape skin on toxicity induced by 25-35 beta-amyloid peptid or by serum of Alzheimer's disease patients, in human umbilical vein endothelial cells (HUVECs). The hypothesis was tested by examining the results of lactic dehydrogenase (LDH) release to estimate cytoplasmic membrane breakdown; activity of mitochondrial complexes, reactive oxygen species (ROS) production and malonyl dialdehyde (MDA) levels as markers of oxidative stress induction and COMET assay to evaluate DNA fragmentation. The results demonstrate that black grape skin extract reduces the ROS production, protects the cellular membrane from oxidative damage, and consequently prevents DNA fragmentation. The experimental results suggest that this natural compound may be used to ameliorate the progression of pathology in AD disease therapy.

Behavioral and neurochemical effects of dopaminergic drugs in models of brain injury.

The dopaminergic drugs, ropinirole and dihydroergocryptine (DHECP) were injected subcutaneously (s.c.) at doses of 0.5 and 1 mg/kg/day for 7 days into male rats of the Sprague-Dawley strain. The drug pretreatment reverted amnesia induced in rats by hypobaric hypopxia and tested in active and passive avoidance tasks. Furthermore, a partial restoration of memory retention was found in animals with a 2-month brain occlusive ischemia induced by manipulation of the four major arteries of the brain. No major changes were found in spontaneous motor activity, but drug treatment increased ambulation of animals subjected to acute or chronic experimental manipulation. In a model of kainate-induced epilepsy, ropinirole or DHECP did not affect seizure parameters, but reduced mortality rate. At the end of behavioral procedures, in all animals subjected to hypobaric hypoxia or to brain occlusive ischemia glutathione redox index (glutathione reduced/glutathione oxidized ratio) was measured in the frontal cortex, striatum and hippocampus. It was found that experimental models of brain injury were followed by a decrease of reduced glutathione content in all brain areas. The glutathione redox index was augmented by ropinirole or DHECP treatment in all brain areas. These behavioral and neurochemical findings suggest that ropinirole and DHECP may exert either protective activity (as found in animals pretreated with these drugs and exposed to hypobaric hypoxia) or reversal of brain injury (as found in animals treated after two-month occlusive brain ischemia). Thus, both drugs may be studied as therapeutic agents in brain injuries of various origin.

Divergent effects of corticotropin releasing hormone on endothelial cell nitric oxide synthase are associated with different expression of CRH type 1 and 2 receptors.

1. Endothelium is a target for an array of factors involved in inflammation. Endothelial cells express receptors for CRH, a neuropeptide produced during inflammation. We report both the concentration-dependent inhibitory effect of CRH upon cytokine-stimulated nitrite release by H5V murine endothelioma cells, and its stimulatory one in HUVEC cells. 2. Western blot analysis showed that CRH inhibits cytokine-stimulated iNOS protein in H5V cells, and, instead, potentiated it in HUVEC cells. 3. H5V cells expressed both CRH receptors (CRH-R1 and R2) mRNAs, whereas HUVEC cells expressed the CRH-R2 mRNA solely. 4. CRH increased medium nitrites and iNOS protein expression in H5V cells pretreated with the selective CRH-R1 antagonist CP 154,526. However, the selective CRH-R2 antagonist anti-Svg-30 failed to produce similar effects. In fact, anti-Svg-30 inhibited CRH-induced increase of nitrite release and iNOS expression in HUVEC cells. 5. Our results confirm the activating role of CRH on endothelial cells, although it suggests its possible inhibitory role in the late phase of the inflammatory response. NO-mediated effects of CRH on endothelial cells could be exploited in therapeutic strategies related to inflammatory and/or degenerative diseases.

Tamoxifen inhibits nerve growth factor-induced proliferation of the human breast cancerous cell line MCF-7.

An array of polypeptide growth factors contribute to the development of breast cancer, the most common tumor-related cause of death in women of Western countries. Therefore, breast cancer therapy should be aimed at inhibition of growth factor-dependent breast cancerous cell proliferation. However, the relative contribution of each individual factor in the development and maintenance of the transformed phenotype is largely unknown. Here we report for the first time that the proliferative effects of nerve growth factor, (NGF) a typical neurotrophin, are similar to those of epidermal growth factor (EGF) and insulin-like growth factor II, and are enhanced by 17beta-estradiol in the human breast cancer cell line MCF-7. The effect of NGF appeared to be mediated by its trkA receptors (trkA(NGFR)), as suggested by the potent inhibition of both MCF-7 cell proliferation and trkA(NGFR) phosphorylation occurring upon treatment of cultures with the selective trkA(NGFR) inhibitor K252a. Surprisingly, the antiestrogen drug tamoxifen (TAM) inhibited NGF-induced MCF-7 cell proliferation and trkA(NGFR) phosphorylation in a concentration-related fashion. The effect of TAM seemed to be estrogen receptor-independent, because the pure estrogen receptor antagonist ICI 182.780 was unable to block NGF-induced trkA(NGFR) phosphorylation. Our data underline the new emerging role of trkA(NGFR) in breast tumor growth, and suggest a related novel therapeutic use of TAM in breast cancer.

Increased ACTH and cortisol secretion after interleukin-alpha injection in the common marmoset (Callithrix jacchus jacchus).

We have studied the effect of intravenous injection of interleukin-1 (dose range: from 0.25 to 4.5 microg/kg of body weight) on plasma ACTH and cortisol levels in the marmoset, a primate paradygm of peripheral glucocorticoid resistance. Blood sampling were collected and body temperature recorded 0, 15, 30, 60, 120, 180, 240 and 300 min after injection. Interleukin-1 stimulated secretion of ACTH in a dose-dependent fashion. Maximal secretion occurred 120 min after injection, and lasted up to 240 min. Plasma ACTH levels returned to baseline 300 min after interleukin-1 injection. Plasma cortisol levels were related to ACTH levels. Body temperature elevation, which occurred 10-15 min after injection was dose-dependent, and lasted 3 h. Results suggest that the pyrogenic effect of interleukin is associated, in the marmoset, with integrated activation of the hypothalamic-pituitary-adrenal axis. In light of the proneness of marmosets to hyperimmune disorders, our data are consistent with the hypothesized central biological role of IL-1, as well as the pathophysiological relevance of the neuro-endocrine-immune cross-talk during the acute phase response.

Apomorphine, dopamine and phenylethylamine reduce the proportion of phosphorylated insulin receptor substrate 1.

We tested the ability of dopamine, apomorphine, phenylethylamine and pergolide to inhibit the proliferation of fetal calf serum-stimulated human breast cancer (MCF)-7 cells. While the first three compounds were able to block the proliferation of MCF-7 cells, pergolide failed to do so (up to 100 microM). The inhibitory effect of dopamine, apomorphine and phenylethylamine was also evident in serum-starved insulin-stimulated MCF-7 cells. Apomorphine also inhibited the proliferation of the human oestrogen receptor-negative breast cancer (MDA-MB231) and prostate carcinoma (LNCaP) cell lines. In a second set of experiments, we measured the ability of dopamine, apomorphine, phenylethylamine and pergolide to inhibit the phosphorylation (or increase the dephosphorylation) of the insulin receptor substrate (IRS)-1, a major intracellular substrate of the insulin-like growth factor (IGF)-1 receptor. Dopamine, apomorphine and phenylethylamine all reduced to zero the level of phosphorylated IRS-1 with potencies ranging between 0.01 and 1 microM. Finally, we found that fibroblasts from IRS-1 null (-/-) mice were less sensitive to the anti-proliferative effect of apomorphine compared to fibroblasts from wild type-mice, suggesting that the inhibition of IRS-1 phosphorylation by apomorphine is an important aspect of the activity of this compound.

Responsiveness of irradiated rat anterior pituitary cells to hypothalamic releasing hormones is restored by treatment with growth hormone.

Hypopituitarism is a common sequela of irradiation in cancer patients. Here we report that recombinant human growth hormone (r-hGH) prevents cell death and restores secretory capacity of irradiated rat pituitary cells in vitro. Dispersed rat pituitary cells from male Sprague-Dawley rats, irradiated with a 9-Gy sublethal dose, were incubated with r-hGH before, after, or before and after irradiation. Treatment with GH resulted in increased cell survival, which reached its maximum at the concentration of 5 nM, with an EC(50) of 3.5 nM. Protective effects of GH on pituitary cells were more pronounced in cultures treated before and after irradiation. Similarly, beneficial effects of GH were observed on the secretory capacity of surviving cells. In fact, irradiated pituitary cells treated with GH secreted substantial amounts of GH, luteinizing hormone, follicle-stimulating hormone, prolactin, thyroid-stimulating hormone and adrenocorticotropic hormone in response to specific releasing hormones. Such effects of GH were prevented in the presence of the specific GH receptor antagonists B2036 and G120K. Our results show that r-hGH exerts a specific protective effect on irradiated rat pituitary cells and suggest possible use of GH as an adjuvant agent for prevention of postirradiation hypopituitarism.

Thymic hormones, cancer and behavioural adaptive responses.

The effects of thymic hormones are not restricted within the immune system but are rather pleiotropic. Through neuropeptides the neuroendocrine system participates in the regulation of homeostasis as well as in the control of stress response and behavioural outputs. Thymic hormones increase spontaneous behaviour, inhibit anxiety-like responses and improve resistance to stress in tumour-bearing mice. In addition, thymic hormones modulate secretion of pituitary adrenocorticotrophin (ACTH) and beta-endorphin in both primates and rodents. In turn, both ACTH and beta-endorphin influence stress response and behaviour. Besides their neuroendocrine effects, thymic hormones have radioprotective effects either when administered alone or when associated with other radioprotective agents. Thymic hormones are possibly able to reduce postirradiation tissue damage in the bone marrow and in the central nervous system. Finally, evidence suggests a potentiating effect of thymic hormones when associated with current anticancer drugs. From the data reviewed it seems reasonable to conclude that the combination of thymic hormones with cancer therapy is associated with improvement of behaviour and well-being status, protection of tissues from detrimental effects of cancer treatment, and possibly also with potentiation of the antiproliferative effects of other drugs. Thus, thymic hormones could be envisioned as a valuable adjunct to actual cancer therapy.

Adenylate-cyclase-dependent pituitary adrenocorticotropin secretion is defective in the inflammatory-disease-susceptible Lewis rat.

Susceptibility to arthritis in the Lewis rat is associated with a defect of the hypothalamic-pituitary-adrenal axis. We examined the pituitary corticotropes of both intact and dexamethasone-treated male and female inflammatory-disease-susceptible Lewis and inflammatory-disease-resistant Fischer rats. We determined adrenocorticotropin levels in the media from primary cultures of anterior pituitary cells of both strains. In other experiments we have measured intracellular cyclic adenosine monophosphate and inositol monophosphate accumulation. Cells were incubated with corticotropin-releasing hormone, arginine vasopressin, forskolin, phorbol myristate acetate, or thyrotropin-releasing hormone. Corticotropin-releasing hormone stimulated adrenocorticotropin secretion from both male and female Lewis rat pituitary cells in a concentration-dependent manner. Basal and stimulated adrenocorticotropin levels in cells from Lewis rats were lower than those measured in the incubation media of Fischer rat dispersed pituitary cells. Arginine vasopressin, as well as forskolin and phorbol myristate acetate, induced a significant release of adrenocorticotropin from pituitary cells of both strains. Incubation with corticotropin-releasing hormone did not produce a significant accumulation of intracellular cyclic adenosine monophosphate in Lewis rat dispersed pituicytes of both sexes. On the other hand, forskolin induced a significant increase of intracellular cyclic adenosine monophosphate in the same cultures. Finally, inositol monophosphate accumulation was comparable in pituitary cells from both Lewis and Fischer rats of both sexes incubated with thyrotropin-releasing hormone. Adrenocorticotropin secretion from pituitary cells of male Lewis rats treated in vivo with dexamethasone was either reduced or abolished following incubation with different secretagogues. A defect in pituitary adrenocorticotropin secretion could be among the causes of the hyporesponsiveness of the hypothalamic-pituitary-adrenal axis in the Lewis rat. Such a defect appears to be associated with dysfunction of receptor-coupled events related to adenylate cyclase.