New phenotypic cytotoxicity assay for ROS-inducing compounds using rat renal epithelial cells

An important mechanism of chemical toxicity is the induction of oxidative stress through the production of excess reactive oxygen species (ROS). In this study, we show that the level of drug-induced ROS production between NRK52E and HepG2 cells is significantly different for several marketed drugs and a number of Takeda's internal proprietary compounds. Nifedipine, a calcium channel blocker and the initial focus of the study, was demonstrated to promote in vitro ROS production and a decrease in cell viability in NRK52E cells but not HepG2 cells. ROS production after nifedipine treatment was inhibited by a NOX inhibitor (GKT136901) but not the mitochondrial NADH dehydrogenase inhibitor, rotenone, suggesting that nifedipine decreases NRK52E cell viability primarily through a NOX-mediated pathway. To understand the breadth of NOX-mediated ROS production, 12 commercially available compounds that are structurally and/or pharmacologically related to nifedipine as well as 172 internal Takeda candidate drugs, were also evaluated against these two cell types. Over 15 % of compounds not cytotoxic to HepG2 cells (below 50 μM) were cytotoxic to NRK52E cells. Our results suggest that a combination of cell viability data from both NRK52E and HepG2 cells was superior for the prediction of in vivo toxicity findings when compared to use of only one cell line. Further, the NRK52E cell viability assay is a good predictor of NOX-mediated ROS production and can be used as a follow up assay following a negative HepG2 response to aid in the selection of suitable compounds for in vivo toxicity studies.

Endocrine and cellular stress effects of zinc oxide nanoparticles and nifedipine in marsh frogs Pelophylax ridibundus

Freshwater organisms including amphibians experience increasing exposures to emerging pollutants such as nanoparticles and pharmaceuticals, which can affect their fitness and performance. We studied the effects of two common pollutants extensively used in industry, pharmaceutical and personal care products, nano-zinc oxide (nZnO) and a Ca-channel blocker nifedipine (Nfd), on endocrine status and cellular stress markers of the marsh frog Pelophylax ridibundus. Males were exposed for 14days to nZnO (3.1μM), Zn²⁺ (3.1μM, as a positive control for nZnO exposures), Nfd (10μM), and combination of nZnO and Nfd (nZnO+Nfd). Exposure to nZnO and Zn²⁺ led to an increase in Zn burdens, elevated concentrations of the metal-bound metallothioneins (MT-Me) in the liver and increased vitellogenin in the serum, whereas exposures to Nfd and nZnO+Nfd resulted in the metal release from MTs and a significant increase in the ratio of total to metal-bound MTs. This likely reflects oxidative stress caused by Nfd exposures as manifested in the elevated levels of oxyradical production, upregulation of superoxide dismutase activity (SOD) and increase in the total and oxidized glutathione concentrations in Nfd-exposed frogs. Zn-containing exposures upregulated activity of deiodinase (in nZnO and nZnO+Nfd exposures) and serum thyrotropin level (in the case of Zn²⁺). All exposures caused an increase in DNA fragmentation, lipofuscin accumulation as well as upregulation of caspase-3 and CYP450 levels reflecting cytotoxicity of the studied compounds in the liver. Across all experimental treatments, nZnO exposures in the absence of Nfd had the least impact on the cellular stress traits or redox status in frogs. This indicates that at the low environmentally relevant levels of pollution, pharmaceuticals such as Nfd and free metals (such as Zn²⁺) may represent a stronger threat to the health of the frogs than nZnO particles.

The effects of zinc nanooxide on cellular stress responses of the freshwater mussels Unio tumidus are modulated by elevated temperature and organic pollutants

Nanoparticle toxicity is a growing concern in freshwater habitats. However, understanding of the nanoparticle effects on aquatic organisms is impeded by the lack of the studies of the nanoparticles effects in the environmentally relevant context of multiple stress exposures. Zinc oxide nanoparticles (n-ZnO) are widely used metal-based nanoparticles in electronics and personal care products that accumulate in aquatic environments from multiple non-point sources. In this study, we evaluated the effects of n-ZnO in a model organism, a mussel Unio tumidus, and the potential modulation of these effects by common co-occurring environmental stressors. Male U. tumidus were exposed for 14 days to n-ZnO (3.1 μM), Zn(2+) (3.1 μM), Ca-channel blocker nifedipine (Nfd 10 μM), combinations of n-ZnO and Nfd or n-ZnO and thiocarbamate fungicide Tattoo (Ta, 91 μg L(-1)) at 18 °C, and n-ZnO at 25 °C (n-ZnO+t°). Total and metallothionein-bound Zn levels as well as levels of metallothioneins (MT), cellular stress responses and cytotoxicity biomarkers were assessed in the mussels. The key biomarkers that showed differential responses to different single and combined stressors in this study were activities of caspase-3 and lysosomal cathepsin D, as well as protein carbonyl content. At 18 °C, exposures to n-ZnO, organic pollutants and their combinations led to a prominent up-regulation of MT levels (by ∼30%) and oxidative stress response including up-regulation of superoxide dismutase activity, an increase in oxyradical production, and a 2-3-fold decrease in the levels of protein carbonyls in all exposures except nZnO+Ta. Expos ure to n-ZnO in the absence of other stressors also led to a strong (∼7-fold) elevation of cathepsin D activity. Cellular responses to Zn(2+) and n-ZnO were different indicating that n-ZnO was not due exclusively to Zn release. Ca-channel blocker Nfd affected intracellular Zn distribution (reflected in the prominent elevation of Zn-MT levels) and caused reductive stress indicated by elevated levels of reduced glutathione levels and an increase in lactate/pyruvate ratio (reflecting higher NADH/NAD ratio). Elevated temperature (25 °C) abolished most of the typical responses to n-ZnO and induced oxidative injury, DNA fragmentation and caspase-3 mediated apoptosis in n-ZnO-exposed mussels. DNA fragmentation was also induced by exposure to organic toxins (alone and in combination with n-ZnO) but not by n-ZnO alone. These data indicate that n-ZnO toxicity to freshwater organisms is modulated by organic pollutants and enhanced by elevated temperatures.

Carcinogens induce loss of the primary cilium in human renal proximal tubular epithelial cells independently of effects on the cell cycle

The primary cilium is an immotile sensory and signaling organelle found on the majority of mammalian cell types. Of the multitude of roles that the primary cilium performs, perhaps some of the most important include maintenance of differentiation, quiescence, and cellular polarity. Given that the progression of cancer requires disruption of all of these processes, we have investigated the effects of several carcinogens on the primary cilium of the RPTEC/TERT1 human proximal tubular epithelial cell line. Using both scanning electron microscopy and immunofluorescent labeling of the ciliary markers acetylated tubulin and Arl13b, we confirmed that RPTEC/TERT1 cells express primary cilium upon reaching confluence. Treatment with the carcinogens ochratoxin A (OTA) and potassium bromate (KBrO(3)) caused a significant reduction in the number of ciliated cells, while exposure to nifedipine, a noncarcinogenic renal toxin, had no effect on primary cilium expression. Flow cytometric analysis of the effects of all three compounds on the cell cycle revealed that only KBrO(3) resulted in an increase in the proportion of cells entering the cell cycle. Microarray analysis revealed dysregulation of multiple pathways affecting ciliogenesis and ciliary maintenance following OTA and KBrO(3) exposure, which were unaffected by nifedipine exposure. The primary cilium represents a unique physical checkpoint with relevance to carcinogenesis. We have shown that the renal carcinogens OTA and KBrO(3) cause significant deciliation in a model of the proximal tubule. With KBrO(3), this was followed by reentry into the cell cycle; however, deciliation was not found to be associated with reentry into the cell cycle following OTA exposure. Transcriptomic analysis identified dysregulation of Wnt signaling and ciliary trafficking in response to OTA and KBrO(3) exposure.

Verapamil toxicity dysregulates the phosphatidylinositol 3-kinase pathway

OBJECTIVES

Recent animal research and clinical case reports suggest benefit from high-dose insulin therapy (HDIT) for the treatment of calcium channel blocker (CCB) toxicity. One molecular signaling pathway, the phosphatidylinositol 3-kinase (PI3K) pathway, that contributes to CCB toxicity and the efficacy of HDIT, was examined for a role in this phenomenon.

METHODS

A differentiated 3T3-L1 adipocyte model system was utilized to characterize metabolic and molecular signaling events dysregulated in response to acute CCB toxicity. Glucose uptake assays were performed in the presence of representatives of three classes of CCB drugs, and the ability of HDIT to reverse observed inhibition was assessed. Western blot analyses were utilized to probe which insulin-dependent signaling pathway was inhibited by CCB toxicity.

RESULTS

Representative compounds from the dihydropyridine and phenylalkylamine classes of CCBs were more effective at inhibiting glucose uptake in differentiated 3T3-L1 adipocytes than a representative from the benzothiazepine class. Phosphorylation at serine 473 of the Akt protein (P-Akt), a protein representing a common pathway for insulin receptors (IR), insulinlike growth factor receptors (IGFR), and hybrid receptors formed by IR and IGFR subunits, was abolished in the presence of toxic doses of the phenylalkylamine CCB verapamil. Phosphorylation at serine 473 of Akt was rescued in the presence high concentrations of insulin.

CONCLUSIONS

These data suggest that dysregulation of the insulin-dependent PI3K pathway is partially responsible for insulin resistance and the hyperglycemic state observed in response to acute CCB toxicity.

[Histometric analysis of gingival hyperplasia in Wistar rats during nifedipine administration]

BACKGROUND/AIM

The use of calcium channel blockers, especially nifedipine, causes gingival hyperplasia which leads to the destruction of the deeper periodontal tissues. During this process, inflammatory changes and the changes of colagen fibers occur. The aim of this study was to metrically compare the extent of proliferation of connective tissue in the deeper periodontal tissue in experimental animals regarding the dose and duration of nifedipine administration.

METHODS

The study involved 50 Wistar rats to which water solution of nifedipine was given in certain time intervals and doses. Before starting the experiment, i.e. before nifedipine administration, and in the defined time intervals, measuring of the morphology of gingival size was performed including the buccolingual and mesiodistal wideness and vertical altitude of the central interdental papilla. The measurement was performed by the use of a special graduated probe. Histometric analyses of the tissue samples were done on the sagital cross-sections in the direction from the top to the bottom of papilla on five levels. For the statistical analysis of the data, the established values to the extent of the most present changes were used. The mesiodistal and buccolingual diameters for the levels L2 and L3 were quantitively determined and compared. These values were compared to the vertical diameter of gingival growth determined before the onset of patohistologic analyses of the tissue samples.

RESULTS

At the begining of the experiment, the volume of the lower incisive central papilla in the rats was 12 mm(3). The central interdental papilla vertical altitude was 6.6 mm in rats which had received a lower dose of nifedipine, 8 mm in rats which had received a higher dose in the defined time intervals while the value for the control group was 3.8 mm.

CONCLUSION

The obtained results showed that the administration of nifedipine led to the extensive gingival hyperplasia in the experimental animals. Gingival hyperplasia correlates with both the dose of nifedipine and the duration of its administration.

Histopathologic investigations of nifedipine-induced gingival hyperplasia in Wistar rats

Background. Nifedipine, a calcium channel blocker, used in the therapy of cardiovascular diseases, can induce gingival overgrowth. The aim of the study was to assess the influence of nifedipine on the deeper periodontal tissues of the experimental animals concerning connective tissue and blood vessels proliferation. Methods. The research was performed on Wistar rats, and they received the precise doses of nifedipine water suspension while the changes were followed up in pre-determined time intervals. The analyses of samples of tissues were done on the cross-sections of papilla from the top to the bottom on five levels. Results. Considerable level of changes was observed in the area of dental alveolar edge and in the gingivo-dental interspace. Epithelial hyperplasia and inflammatory subepithelial infiltration of lymphoplasmocyte type were also present. Alveolar bone destruction, the increased number of osteoclasts and periodontal destruction were found, as well. Conclusion. The results of this study showed a significant gingival hyperplasia in the experimental animals which received high doses of drug during extended period of time.

Sex difference in induction of hepatic CYP2B and CYP3A subfamily enzymes by nicardipine and nifedipine in rats

Male and female of F344 rats were treated per os with nicardipine (Nic) and nifedipine (Nif), and changes in the levels of mRNA and protein of hepatic cytochrome P450 (P450) enzymes, CYP2B1, CYP2B2, CYP3A1, CYP3A2, CYP3A9, and CYP3A18 were examined. Furthermore, hepatic microsomal activities for pentoxyresorufin O-dealkylation (PROD) and nifedipine oxidation, which are mainly mediated by CYP2B and CYP3A subfamily enzymes, respectively, were measured. Analyses of RT-PCR and Western blotting revealed that Nic and Nif induced predominantly CYP3A and CYP2B enzymes, respectively. As for the gene activation of CYP2B enzymes, especially CYP2B1, Nif showed high capacity in both sexes of rats, whereas Nic did a definite capacity in the males but little in the females. Gene activations of CYP3A1, CYP3A2, and CYP3A18 by Nic occurred in both sexes of rats, although that of CYP3A9 did only in the male rats. Although gene activations of CYP3A1 and CYP3A2 by Nif were observed in both sexes of rats, a slight activation of the CYP3A9 gene occurred only in female rats, and the CYP3A18 gene activation, in neither male nor female rats. Thus, changes in levels of the mRNA or protein of CYP2B and CYP3A enzymes, especially CYP2B1 and CYP3A2, were closely correlated with those in hepatic PROD and nifedipine oxidation activities, respectively. The present findings demonstrate for the first time the sex difference in the Nic- and Nif-mediated induction of hepatic P450 enzymes in rats and further indicate that Nic and Nif show different specificities and sex dependencies in the induction of hepatic P450 enzymes.

Fatality from administration of labetalol and crushed extended-release nifedipine

OBJECTIVE

To report a case in which a crushed extended-release (XL) nifedipine tablet contributed to a patient fatality.

CASE SUMMARY

A 38-year-old woman with multiple medical problems presented to the hospital in acute respiratory distress and was diagnosed with acute pulmonary edema and pneumonia. After initial stabilization, her medications were changed to oral hydralazine, labetalol, and nifedipine XL. These medications were crushed and administered through a nasogastric tube. The patient developed worsening bradycardia with hypotension and experienced asystolic cardiac arrest. She was resuscitated; however, the following morning, another dose of labetalol and nifedipine XL was crushed and administered through the nasogastric tube. She again developed worsening bradycardia with hypotension and ultimately died.

DISCUSSION

The administration of a crushed nifedipine XL tablet resulted in the patient's severe hypotension. The concurrent administration of labetalol prevented a compensatory heart rate increase. The repeat administration of nifedipine XL in the same manner underscores a fundamental problem in healthcare worker communication and drug delivery system comprehension. Use of the Naranjo probability scale indicated a highly probable relationship between the patient's hypotension and the nifedipine and labetalol therapy.

CONCLUSIONS

Simultaneous administration of a beta-blocker and a calcium-channel blocker may produce synergistic effects. The release characteristics of oral controlled-release medications are destroyed when crushed, resulting in the rapid bioavailability of the total drug amount. The importance of education and communication among nurses, physicians, and pharmacists regarding the mechanism of action of controlled-release medications and their administration needs to be emphasized.

Morphological evaluation of combined effects of cyclosporin and nifedipine on gingival overgrowth in rats

It has previously been shown that, while cyclosporin A (CsA) and nifedipine both cause gingival overgrowth in the rat, the combined use of these drugs increases the severity of overgrowth. The aim of this study was to describe the histometry and densities of fibroblasts, collagen fibers and vessels in the gingival tissue of rats that were treated with CsA and nifedipine, either alone or in combination. Rats were treated for 60 days with a daily subcutaneous injection of 10 mg/kg body weight of CsA and/or with 50 mg/kg body weight of nifedipine added to the chow. The results confirmed that CsA causes a more severe overgrowth than nifedipine, and that the combined use of these drugs increases the overgrowth severity. All the rat groups that were studied showed that, as the severity of overgrowth increased, there was a parallel increase in fibroblasts and collagen, and a decrease in vessel content. Therefore, independently of whether the gingival overgrowth was caused by CsA alone, nifedipine alone, or both treatments in combination, the fibroblast and collagen density increased in parallel with the severity of the overgrowth.

Enhanced vincristine neurotoxicity from drug interactions: case report and review of literature

This study reports observed toxicity in a child with acute lymphocytic leukemia who had received vincristine (VCR) with nifedipine and itraconazole. A 5-year-old-child with leukemia developed bilateral cranial nerve palsies, severe peripheral neuropathy involving upper and lower extremities, seizures, hypertension, heart failure, and syndrome of inappropriate antidiuretic hormone secretion after being treated with VCR, nifedipine, and itraconazole. Appropriate management of the above problems including discontinuation of VCR resulted in recovery from neurotoxic manifestations. Concurrent administration of VCR with nifedipine and itraconazole may enhance its neurotoxicity.

Human hepatocyte--a model for toxicological studies. Functional and biochemical characterization

Isolated human hepatocytes (HH) are an accepted model for in vitro experiments for testing liver function and xenobiotic metabolism. Preferred over more traditional animal hepatocyte model used in toxicological studies, it is the model of choice when substances undergoing biotransformation in man are investigated. The aim of this study was to optimize isolation and culture conditions for HH primary culture with regard to cell yield, viability, and metabolic activity, and to evaluate the suitability of donor samples for toxicology experiments. Cell viability, total cytochrome P450 (CYP) content, CYP3A4, CYP1A2 activity, and finally mixed ethoxycoumarin-O-deethylase (ECOD) activity were parameters measured in order to characterize the isolated HH. The quality of the primary cultures, stable and functional for a seven-day period following 24 hour stabilization, was assessed by lactate dehydrogenase (LDH) leakage and response to the model toxin tert-butylhydroperoxide (tBH) and to silybinin, a model cytoprotective substance. Based on HH obtained from livers of five multiorgan donors (average age 44.8 years, three males and two females), the individual variability of donors needs to be considered in evaluating cultures focussing on clinical liver tests. Greater sensitivity to toxins and silybinin was found in the hepatocyte culture from one donor with higher aminotransferase activity. In another case, higher serum bilirubin appeared to be linked to higher ECOD activity. Our conclusion is that values of clinical liver tests ought to suggest a healthy organ thus eliminating previous hepatocyte damage, the crucial factor of primary culture stability and functioning.

Alterations of gingival morphology in nifedipine-fed rats

BACKGROUND

Gingival enlargement induced by nifedipine (NIF), a calcium antagonist, has been reported in human and animal studies. However, three-dimensional morphologic measurements of gingivae have never been used to describe this type of enlargement. We previously established an animal model of cyclosporin-induced gingival enlargement. The present study used morphologic measurements to examine whether or not NIF-induced gingival enlargement occurs in the animal model.

METHODS

Eighty male Sprague-Dawley rats were divided into four groups. Rats in each group received daily NIF, at a dosage of 0, 10, 30 or 50 mg/kg body weight, by gastric feeding for nine weeks. Gingival dimensions (including buccolingual and mesiodistal widths, and vertical height) were assessed from stone models obtained from the mandibular incisor regions every three weeks.

RESULTS

Over the course of the nine-week experiments, significant dimensional changes of the gingivae were observed according to two main factors: 1) the dose or, 2) the treatment duration. Gingival dimensions (including buccolingual and mesiodistal widths, and vertical height) significantly increased with the duration of NIF treatment. Dimensional alterations of gingivae were noted among the different dosage groups, but significant differences were mainly observed in those groups compared to the 50 mg/kg group.

CONCLUSIONS

The finding of increased gingival morphology in NIF-treated rats in this study shows that gingival enlargement can be induced by NIF in rats.

Proliferation of human peripheral blood mononuclear cells during calcium entry blockade. Role of protein kinase C

To evaluate the role of protein kinase C (PKC) and intracellular calcium and particularly Ca(2+)-uptake in the initiation of lymphocyte mitogenesis, the proliferation of human peripheral blood mononuclear cells (PBMC) was investigated during calcium entry blockade with nifedipine (an L-type calcium channel blocker) and mibefradil (an L- and T-type calcium channel blocker with a higher selectivity for T-type channels). The rate of [3H]-thymidine, [3H]-uridine and [3H]-leucine incorporation into control and concanavalin A-stimulated PBMC cultured for 3 days in the presence or absence of the calcium channel blockers nifedipine or mibefradil (1, 10 or 50 microM) is assayed. Nifedipine and mibefradil concentration-dependently reduced cell number and [3H]-thymidine incorporation or de novo DNA synthesis in control and concanavalin A-stimulated PBMC, as well as de novo RNA and protein synthesis. The proliferative response of nifedipine- or mibefradil-treated cells was restored by addition of phorbol-12-myristate-13-acetate (PMA), an exogenous PKC activator. Our data show that PBMC treated with the Ca2+ channel blockers nifedipine or mibefradil are still capable of proliferating in response to PMA. However, in PKC-depleted cells, the proliferative response of PBMC was suppressed.

Photodegraded nifedipine promotes transferrin-independent gallium uptake by cultured tumor cells

It was reported previously that normal soft tissues accumulate 67Ga by a transferrin-dependent route, but uptake by tumors can be transferrin independent. It was also reported that, although overexpression of the transferrin receptor can promote Ga avidity, the transferrin-independent uptake of 67Ga is significant and can be augmented to exceed transferrin-mediated levels by increasing extracellular calcium. In assessing the effect of calcium channel blockers on uptake of 67Ga, it was observed that, after exposure to light (either visible or ultraviolet [UV]), nifedipine strongly potentiates the cellular uptake of 67Ga by a transferrin-independent process.

METHODS

The effect of nifedipine on 67Ga uptake as a function of time, concentration, duration and type of preexposure to light was determined in two cultured Chinese hamster ovary cell lines. One cell line lacks the transferrin receptor. In the other, the human transferrin receptor has been restored by transfection and is overexpressed constitutively.

RESULTS

Although there are some differences in pattern of stimulation of uptake, nifedipine subjected to either UV or fluorescent light strongly promotes the uptake of 67Ga in the cultured cells in a time-dependent and concentration-dependent manner. Maximal uptake of 67Ga occurs when the cells are incubated for 30 min with 25 micromol/L nifedipine preexposed to either 4h of fluorescent or 1h of UV light. Under these conditions, uptake of 67Ga is 1000-fold greater than basal levels and 50-fold greater than can be achieved by the transferrin-dependent route. Light-shielded nifedipine has no effect on 67Ga uptake.

CONCLUSION

The effect of photodegraded nifedipine on the uptake of 67Ga is independent of expression of the transferrin receptor. The potential for photodegraded nifedipine to improve oncologic imaging with 67Ga warrants further investigation.

Pemphigus and pemphigoid-like effects of nifedipine on in vitro cultured normal human skin explants

BACKGROUND

A variety of drugs have been implicated in the onset and exacerbation of pemphigus and bullous pemphigoid. The demonstration of biochemical acantholysis in skin explants to various drugs in the absence of autoantibodies, in which the tested drugs evoke a biochemical reaction that leads to desmosomal function loss, may be a valuable adjunct to patient management by confirming the suspicion of drug-related pemphigus or bullous pemphigoid.

OBJECTIVE

To determine whether a skin explant model might serve as a possible in vitro correlate of drug-induced pemphigus and pemphigoid-like effects related to the calcium channel blocker nifedipine.

METHODS

Normal human breast skin obtained from nonpemphigus and nonpemphigoid patients undergoing mastectomy was cultured with nifedipine at final concentrations of 2, 4, and 8 mM. The drug effect on skin explants evidenced by morphologic changes was evaluated by microscopy by three observers.

RESULTS

Five out of seven explants cultured with nifedipine at concentrations ranging from 2 to 8 mM exhibited obvious morphologic changes of two types: intraepithelial (or pemphigus-type) splittings and subepithelial (or pemphigoid-type) splittings. Two explants showed no acantholysis and no subepithelial splittings. Control cultures without polyethylene glycol 200 (PEG) showed no changes. Skin control samples cultured in medium supplemented with 10% PEG displayed vacuolar degeneration throughout the entire epidermis, but no sign of cell-cell dyshesion or dermo-epidermal detachment.

CONCLUSIONS

A type of skin susceptibility to nifedipine may be genetically determined, with some nifedipine-treated patients developing an acantholytic reaction and others a subepidermal bullous eruption.

A calcium agonist, Bay k 8644, suppresses the embryotoxic effects induced by dihydropyridines calcium channel blockers in cultured rat embryos

Day 9 rat embryos were exposed to 1,4-dihydropyridine calcium channel blockers; nifedipine (NIF), nicardipine (NIC) or nitrendipine (NIT), for 48 hr in the whole embryo culture system. There were dose-dependent growth retardation and abnormalities, predominantly in cardiovascular system. The three compounds exhibited very similar pattern of dysmorphogenic effects, but the potency of these compounds were quantitatively different. The incidences of embryos with the abnormalities were 100%, 100% and 85% following either exposure of NIF, NIC or NIT at concentration of 300, 8 and 15 microM, respectively. This study was to investigate whether these blocker-induced embryotoxicity was due to calcium channel blocking properties themselves in the embryos. Day 9 rat embryos were co-exposed to 1,4-dihydropyridine calcium channel agonist, Bay k 8644 (BAY) and each calcium channel blocker under the same culture condition. The retarded embryonic growth induced by 200 or 300 microM of NIF, 8 microM of NIC and 15 microM of NIT nearly of completely ameliorated when embryos were co-exposed with BAY at one-third or half concentration of each calcium channel blocker. Supplementation of BAY reduced the incidence of abnormalities by NIF-, NIC- and NIT-alone. These results suggested that one of mechanisms for embryotoxicity induced by calcium channel blocker was directly related to channel blocking property of the chemicals.

Nifedipine-induced gingival overgrowth in rats: brief review and experimental study

The first case report of gingival overgrowth induced by nifedipine (NIF), a calcium-beta blocker, was in 1984. However, the association between gingival alterations and the drug therapy of sodium diphenyl hydantoinate was initially described in 1939. The purpose of the experimental study was to examine the effect of NIF on gingival morphology in an animal model. Forty-five male Sprague-Dawley rats were randomly divided into 3 groups. Animals in each group daily received NIF in dimethyl sulfoxide by gastric feeding at a dosage of 0 (control), 30, or 50 mg/kg body weight for 9 weeks. Gingival gross morphology was assessed tri-weekly from stone models obtained from the mandibular incisal region. Animals were sacrificed at the end of study and tissue blocks were processed for histopathologic and histometric evaluation. Histometric analysis was performed at 5 selected tissue levels. Macro- and microscopic significantly increased gingival dimensions were demonstrated in NIF-treated animals compared to control. Although a fibrovascular tissue was observed in the tooth-gingiva interface for both NIF-treated and control animals, it was thicker and appeared earlier in NIF-treated animals. The results of the present study suggest that gingival overgrowth can be induced by NIF in rats and that the gingival overgrowth appears dose dependent.

Electrophysiologic assessment of calcium channel blockers in transplanted hearts: an experimental study

The effects of calcium channel blockers on automaticity, conduction, and refractoriness were studied in a model of heterotopic heart transplantation in dogs, which combined an innervated heart (recipient) and a denervated one (donor). Following the surgical procedure, 0.2 mg/kg verapamil (n = 10), 0.15 mg/kg diltiazem (n = 10), or 5 microg/kg + 30 microg/kg/h nifedipine (n = 10) was administered intravenously. In basal situation and after drug administration, each heart was assessed for AV interval, cycle length, sinoatrial conduction time, atrioventricular node antegrade block point, and atrioventricular node and ventricular refractory periods; electrocardiographic PR and QT intervals and QRS complexes; systemic arterial, pulmonary artery, central venous, and pulmonary capillary wedge pressures; and cardiac output. The depressor effects of these calcium channel blockers on automaticity, refractoriness, and conduction were more intense in the transplanted hearts, very possibly because of the absence of adrenergic reflexes mediated by the autonomic nervous system; in particular, verapamil produced a great depression of sinus automaticity in a large number of cases.

L-2-chloropropionic acid-induced cerebellar granule cell necrosis is potentiated by L-type calcium channel antagonists

We have used the model of L-2-chloropropionic acid (L-CPA)-induced selective cerebellar granule necrosis to study excitatory amino acid-induced necrotic cell death in vivo produced by the activation of N-methyl-D-aspartate (NMDA) receptors. However, the mechanism for the NMDA receptor activation and the biochemical events which dictate the anatomical selectivity for the L-CPA-induced lesion are as yet unknown. We examined whether blockade of sodium and calcium channels may reduce the neurotoxicity through a reduction of glutamate release from granule cells. None of the sodium channel antagonists examined, i.e. phenytoin, lamotrigine or rilazole nor the mixed sodium/calcium channel blocker, lifarazine, altered the L-CPA neurotoxicity. However, L-type calcium channel blockers, verapamil and nifedipine enhanced the L-CPA-induced granule cell necrosis, assessed by measuring the degree of L-CPA-induced reductions in cerebellar aspartate concentration, increases in cerebellar glycine concentrations and the development of cerebellar oedema. In addition, the locomotor activity of rats receiving both L-CPA and either verapamil or nifedipine was significantly lower than when rats received L-CPA alone, suggesting an enhancement of the neurotoxicity of L-CPA by L-type calcium channel blockade. The data suggest that L-CPA may interfere with non-L-type calcium channels located on granule cell bodies and nerve terminals leading to reduction of the calcium entry into the cells. We suggest that a combination of L-type channel blockade and non-L-type channels which are sensitive to L-CPA produces reductions in intracellular calcium concentrations below that required for neuronal survival.

Cardiovascular effects of elgodipine and nifedipine compared in anaesthetized rats

The cardiovascular effects of elgodipine were studied and compared with those of nifedipine in the presence or absence of ganglion blockade. A bolus of elgodipine (5-25 microg/kg) or nifedipine (60-120 microg/kg) was given and sequential cardiovascular effects in rats were recorded. Both dihydropyridines induced a dose-dependent decrease in mean arterial pressure but, whereas nifedipine induced reflex tachycardia, elgodipine induced a dose-dependent bradycardia. Both substances induced decreases in left ventricular d P/dt(max) without significant changes in central venous pressure. Good linear correlation was observed between the elgodipine-induced decrease in mean arterial pressure and those of heart rate and left ventricular dP/dt(max). The profile of the decrease in mean arterial pressure in animals pretreated with hexametonium chloride (20 mg/kg) was the same but the nifedipine-induced tachycardia was abolished without changes in elgodipine-induced bradycardia. These characteristics of elgodipine makes this dihydropyridine a potentially beneficial therapeutic agent in the case of severe hypertension accompanied by obstructive coronopathy.

Anticonvulsant and adverse effects of MK-801, LY 235959, and GYKI 52466 in combination with Ca2+ channel inhibitors in mice

This study was designed to investigate the influence of the calcium (Ca2+) channel inhibitors nicardipine, nifedipine, and flunarizine on the protective action of MK-801, LY 235959 [N-methyl-D-aspartate (NMDA) receptor antagonists], and GYKI 52466 (a non-NMDA receptor antagonist) against electroconvulsions in mice. Unlike nicardipine (15 mg/kg) or flunarizine (10 mg/kg) nifedipine (7.5 and 15 mg/kg) potentiated the protective potency of MK-801 (0.05 mg/kg), as reflected by significant elevation of the convulsive threshold (a CS50 value of the current strength in mA producing tonic hind limb extension in 50% of the animals). The protective activity of LY 235959 and GYKI 52466 was reflected by their ED50 values in mg/kg, at which the drugs were expected to protect 50% of mice against maximal electroshock-induced tonic extension of the hind limbs. Nicardipine (3.75 15 mg/kg), nifedipine (0.94-15 mg/kg), and flunarizine (2.5-10 mg/kg) in a dose-dependent manner markedly potentiated the antiseizure efficacy of LY 235959. Flunarizine (5 and 10 mg/kg) was the only Ca2+ channel inhibitor to enhance the protective action of GYKI 52466 against electroconvulsions. Except with MK-801 + flunarizine (motor performance) or GYKI 52466 + flunarizine (long-term memory), combination of NMDA or non-NMDA receptor antagonists with Ca2+ channel inhibitors produced an impairment of motor performance (evaluated in the chimney test) and long-term memory acquisition (measured in the passive avoidance task) as compared with vehicle treatment.

Effects of nilvadipine (a dihydropyridine-type calcium entry blocker) on cerebral blood flow in acute experimental brain ischemia in rats

The purpose of the present study was to examine the effect of nilvadipine (a dihydropyridine-type calcium entry blocker) on the cerebral circulation, experimental models of cerebral ischemia were used to measure abrupt changes in the cortical cerebral blood flow (CBF) at the 'penumbra' (the boundary region between the anterior cerebral artery (ACA) and the middle cerebral artery (MCA)). Left middle cerebral artery occlusion (MCAO) was performed in Sprague--Dawley rats, and then 8 or 16 micrograms kg-1 of nilvadipine was administered to two groups of the rats. The former group was referred to as the 8-MCAO(+) group (n = 8), and the latter group, the 16-MCAO(+) group (n = 8). To a control group (n = 8), only the solvent of nilvadipine was administered. After the administration in each group, CBF and the mean arterial blood pressure (MAP) were continuously measured for 60 min. The MAP in both the 8-MCAO(+) and 16-MCAO(+) groups was significantly lower than in the control group for 25 min after nilvadipine administration (Wilcoxon 2 sample test, p < 0.05). Also, the CBF in the 16-MCAO(+) group was significantly lower (about 20%) for 55 minutes than that in the control group. On the other hand, the CBF in the 8-MCAO(+) group three minutes after nilvadipine administration was not significantly lower than in the control group (Wilcoxon 2 sample test). Our findings confirmed that nilvadipine (8 micrograms kg-1) maintained CBF while lowering the blood pressure in the experimental model of acute cerebral ischemia.

Calcium channel blockers induce thymic apoptosis in vivo in rats

We investigated the in vivo effect of structurally different calcium channel blockers (CCB) on rat thymus. Administration of verapamil (40 mg/kg ip), diltiazem (90 mg/kg ip), nifedipine (15 mg/kg ip), or nicardipine (10 mg/kg ip) induced apoptotic indices of 4.3, 4.0, 2.0, and 6.5, respectively, compared to 0.5 in the saline-treated control rats. Apoptosis was assessed by morphology and the apoptotic index was calculated using a computer-assisted image analyzer. Diltiazem had a rapid and substantial effect as evidenced by apoptosis at 1.5 hr and a 36% decrease in thymus weight by 24 hr. We were uncertain about the mechanisms by which CCB induced thymic apoptosis in vivo since in vitro studies have shown that increases in intracellular calcium cause apoptosis and that CCB prevent apoptosis. We sought insight into the mechanism by evaluating potential and known in vivo effects of these drugs. Neither verapamil nor diltiazem was found to elevate serum cortisol levels, a known trigger for apoptosis. Hypotension, a known response to CCB, does not appear to be causal factor since the potent hypotensive agent sodium nitroprusside (10 microg/kg, iv) did not cause a significant increase in thymic apoptosis. Calcium signaling may be important since the calmodulin antagonist chlorpromazine (60 mg/kg ip) was found to induce a 15-fold increase in apoptosis. Our observations suggest that calcium signaling is necessary for the survival of the T lymphocytes in the thymus.

Pathogenesis of drug-induced gingival overgrowth. A review of studies in the rat model

Drug-induced gingival overgrowth is a side effect associated principally with 3 types of drugs: anticonvulsant (phenytoin), immunosuppressant (cyclosporine A), and various calcium channel blockers (nifedipine, verapamil, diltiazem). In this review, we describe the features of phenytoin-, cyclosporine A- and nifedipine-induced gingival overgrowth in rats and discuss factors influencing the onset and severity of these disorders. There are several features common to the gingival overgrowth induced by these drugs: 1) gingival overgrowth is more conspicuous in the buccal than in the lingual gingiva and less severe in the maxilla than in the mandible; 2) once the blood concentration of the drug reaches a certain level as a result of increasing the dose, the incidence of gingival overgrowth is 100% and its severity is dependent on the blood level, the most severe overgrowth being induced by cyclosporine A; 3) the duration of drug administration for maximal gingival overgrowth to develop is about 40 days; 4) the gingival overgrowth regresses spontaneously after discontinuing the drug; 5) accumulation of dental plaque is not essential for the onset of overgrowth, but plays a role in its severity; and 6) more severe overgrowth is induced in young than in old rats. Furthermore, male rats are more susceptible than females to nifedipine-induced gingival overgrowth. These results suggest that drug-induced gingival overgrowth in rats is dependent on the oral drug dose, blood drug level, age, and sex and that preexisting gingival inflammation is a factor relevant to its severity. Since these factors have also been suggested to be important determinants for human drug-induced gingival overgrowth, the rat model may prove valuable in the future for elucidating the molecular pathogenesis of the disorder.

Factors influencing nifedipine-induced gingival overgrowth in rats

Factors such as age, the dose of nifedipine administered in the diet, serum drug level, duration of drug administration, and sex which may influence nifedipine-induced gingival overgrowth were examined in a rat model using 20-, 50-, and 90-days-old male and female rats. Oral administration of nifedipine (50 to 250 mg/kg diet) increased the serum level of the drug in a dose-dependent manner in both males and females. However, a higher serum level was required in females than males to attain the same degree of gingival overgrowth. The minimum dietary concentrations of the drug required to elicit gingival overgrowth in males and females were 150 and 100 mg/kg, respectively, which gave respective minimum serum levels of 800 and 1100 ng/ml. The degree of overgrowth depended on the serum concentration of the drug after it had reached the required minimum in male and female animals. Administration of nifedipine (250 mg/kg diet) for 20 days was enough to induce maximal overgrowth, but this induction occurred only in rats that started to receive the drug when they were 20 days old, not in those that started at 50 and 90 days of age for the same administration period of 55 days, and the overgrowth regressed and the gingiva were normal 40 days after ceasing drug administration. These results suggest that gingival overgrowth occurred in accordance with the drug concentration in the diet, as well as that in the serum, and was more likely to occur in males and younger individuals.

Interaction between nifedipine and digoxin in rats

Possible nifedipine-digoxin interaction was investigated in rats by comparing lethal doses of intravenously infused digoxin in control and experimental rats. In the experimental rats, nifedipine was administered intraperitoneally, 30 minutes prior to infusing digoxin at a constant rate of 40mcg per minute. Results indicate that nifedipine administered within the dosage range 0.5-2.0mg per kg rat body weight, lowered the lethal dose of intravenously infused digoxin by 26-38% compared with control rats, thus indicating a synergistic effect between the two drugs. There was very little dose dependence of this effect. It is concluded that concomitant administration of nifedipine and digoxin in humans may lead to drug interactions.

Modulation of cytostatic drugs by nifedipine in two heterotransplanted human testicular-cancer cell lines differing in their sensitivity to standard agents

Drug resistance is an important clinical problem in testicular cancer patients with relapsed or refractory disease after first-line chemotherapy. Here we report that the relative reduction in tumour volume in nude mice heterotransplanted with either H 12.1 or H 23.1 human testicular cancer cell lines was significantly increased by addition of the calcium antagonist nifedipine to the maximum tolerated dose (MTD) of cisplatin (DDP). The mean reduction in relative tumour volume at day 30 (rVR) reached statistical significance for both cell lines following combination therapy of DDP with nifedipine compared to DDP alone (55 +/- 7% versus 12 +/- 4% for H 23.1 and 60 +/- 9% vs. DDP with nifedipine has also been confirmed in H 12.1 cells in vitro. However, in vivo, this combination was associated with a concordant increase in therapeutic toxicity. In contrast, no improvement in in vivo anti-tumour activity was obtained by combining similar dose-schedules of nifedipine with the MTD of epirubicin, or with MTDs of vinblastine or etoposide. These results are in agreement with our immunohistochemical finding that H 12.1 and H 23.1 do not over-express the Pgp 170 glycoprotein which mediates the multiple drug resistance (MDR) phenotype and involves both anthracyclines and vinblastine, but not DDP. We conclude that another Pgp-MDR modulator, nifedipine, is able to increase the anti-tumour activity of DDP in vivo and in vitro via a specific but as yet unknown mechanism, which is most likely not MDR-related. However, the increased anti-tumour activity is, in vivo, associated with a considerable increase in overall toxicity. Further studies are necessary to decrease therapeutic toxicity, before clinically relevant models for modifiers of DDP-resistance could possibly be applied to patients.

Inhibition of the spore polar filament extrusion of the microsporidium, Encephalitozoon hellem, isolated from an AIDS patient

Spores of the microsporidian parasitic protozoan Encephalitozoon hellem were purified and incubated at 37 degrees C in a solution with an electrolyte composition similar to that of mammalian extracellular fluid, and in solution in which the calcium had been replaced with 0.2 mM EGTA. Polar filament extrusion (germination) was monitored by both scanning electron microscopy and light microscopy. Germination was pH-dependent, with optima at pH 7.4 and 9.5, and was significantly greater in the presence of medium calcium. Hydrogen peroxide caused a concentration-dependent increase in germination that was also reduced in a calcium-free medium. Four agents were found to inhibit spontaneous and H2O2-stimulated polar filament extrusion: the microfilament disrupter, cytochalasin D; the microtubule disrupter, demecolcine; the calcium channel blocker, nifedipine; and the antifungal agent, itraconazole. These results are consistent with the existence of a calcium-channel-mediated step, and requirements for an F-actin- and for a tubulin-containing element in the germination process of the spore of this parasite. Nifedipine, cytochalasin D and itraconazole all have different sites of action and were therefore able to potentiate one another when used in paired combination to inhibit germination.

Nifedipine-induced gingival overgrowth in the presence or absence of gingival inflammation in rats

One adverse effect of nifedipine, a long-acting vasodilator, is gingival overgrowth. Preexisting gingival inflammation and/or dental plaque has been suggested to be responsible for the progression of this side effect, but the precise mechanism is uncertain because of a lack of suitable animal models. A study was therefore done to establish an experimental model of gingival overgrowth in rats and to investigate the possible involvement of gingival inflammation and/or dental plaque in its development. Specific pathogen-free Fischer rats (male, 14 days old) were used. Gingival inflammation and dental plaque accumulation were induced by infection with Streptococcus mutans MT8148R. The nifedipine-treated rats (experimental group) were fed a caries-inducing diet containing nifedipine either with or without infection, while the nifedipine-untreated rats (control group) were fed the same diet, similarly with or without the infection. Marked gingival overgrowth was induced in the mandibular molar region of nifedipine-treated rats regardless of S. mutans infection, although the infection resulted in a further increase in the degree of gingival overgrowth. Histological examination of the gingival overgrowth revealed the presence of redundant subepithelial connective tissue in the treated rats, and inflammatory cell infiltration was apparent only in the tissue of the S. mutans-infected rats regardless of the nifedipine administration. These findings suggest that nifedipine induces gingival overgrowth in rats either in the presence or absence of gingival inflammation and/or dental plaque, although these factors can augment the effect of the drug.(ABSTRACT TRUNCATED AT 250 WORDS)

In vitro phototoxicity of nifedipine: sequential induction of toxic and non-toxic photoproducts with UVA radiation

Anecdotal reports suggest that the dihydropyridine calcium antagonist, nifedipine (NIF), may be phototoxic in human skin. We have studied NIF phototoxicity in vitro using UVA fluorescent tubes (Sylvania PUVA). NIF was phototoxic to Candida albicans and induced photohaemolysis both with NIF present during irradiation and with pre-irradiated drug. In V79 hamster fibroblasts, NIF (10 micrograms ml-1) was phototoxic MTT assay) 24 h after irradiation (0-112 kJ m-2); at 7.5 kJ m-2, about 70% of cells were damaged whilst at 37.5 kJ m-2, only about 45% of cells were damaged. A similar pattern was seen with pre-irradiated NIF. Absorption spectroscopy showed that the NIF absorption maximum (Amax approximately 340 nm) blue-shifted to 314 nm at low UVA doses (7.5 kJ m-2 or less) and red-shifted to 345 nm at higher doses (isosbestic point, 325 nm). Thin layer chromatography of irradiated NIF showed a single photoproduct (PP1; Amax approximately 314 nm) formed at 7.5 kJ m-2 or less which disappeared at higher UVA doses to give further photoproducts. PP1 was highly dark toxic to V79 cells (50% damage at about 5 micrograms ml-1) but PP1 pre-irradiated with UVA was non-toxic. Preliminary gas chromatography-mass spectroscopy studies suggest that PP1 is the nitroso derivative of NIF. These results indicate that NIF phototoxicity in vitro is partially mediated by initial formation of a toxic photoproduct (PP1) but, paradoxically, subsequent UVA irradiation may reduce phototoxicity. The NIF concentrations required to induce in vitro phototoxicity are much greater than therapeutic plasma levels. Unless there is skin accumulation of NIF or PP1, our in vitro results suggest that NIF may not be an important skin-photosensitizing agent in vivo.

Identical phalangeal defects induced by phenytoin and nifedipine suggest fetal hypoxia and vascular disruption behind phenytoin teratogenicity

In previous experimental studies in rabbits, we have shown that vasodilating drugs (including nifedipine) cause distal digital defects. These defects were preceded by edema, hemorrhage, and finally necrosis of the developed cartilage in the phalanges. The underlying mechanism is most likely a fetal hypoxic response, secondary to maternal hypotension and decreased uteroplacental blood flow. Since phenytoin is known to cause distal digital defects both in man and rabbits, we decided to compare the defects provoked by oral administration of phenytoin (100 mg/kg) versus nifedipine (8.3 mg/kg) to New Zealand White rabbits on days 6-18 of gestation. In order to investigate phase-specificity, phenytoin (150 mg/kg) was given on days 14-17. The result of single dose administration on day 16 of phenytoin (300 mg/kg) versus nifedipine (33.2 mg/kg) was also studied. In this latter experiment maternal heart rate was measured up to 21 hours after phenytoin administration. Phenytoin induced digital defects identical with those produced by nifedipine and caused marked maternal cardiodepression. The defects consisted of a reduction, absence, or abnormal structure of the distal phalanges. The distal phalanx of the fourth digit on the hindpaw was the first to be affected, with inclusion of other phalanges, both on the hind- and forepaws, with increasing dose. The sensitive period for induction and histological appearance of these defects was identical for phenytoin and nifedipine. These results suggest that vascular disruption due to a fetal hypoxic response lies behind phenytoin teratogenicity, as has been shown for vasodilators. A cardiodepressive action on the maternal and fetal hearts, possibly in combination with decreased uteroplacental blood flow, is discussed as a probable factor behind phenytoin teratogenicity.

Effects of calcium channel blocker overdose-induced toxicity in the conscious dog

STUDY OBJECTIVE

To evaluate the effects of nifedipine, diltiazem, and verapamil overdose on systemic hemodynamics and blood flows to the coronary, superior mesenteric, renal, and iliac arteries in the unanesthetized dog.

DESIGN

Nonblinded, controlled animal study.

SETTING

Research laboratory of a large pharmaceutical company.

TYPE OF PARTICIPANTS

Nineteen healthy mongrel dogs obtained from a commercial supplier.

INTERVENTIONS

Under general anesthesia, flow probes were placed about the ascending aorta, circumflex coronary, superior mesenteric, renal, and iliac arteries; a micromanometer was implanted into the tip of the left ventricle; and a catheter was inserted into the descending aorta. Experiments were performed after a recovery period of at least two weeks.

MEASUREMENTS AND MAIN RESULTS

Arterial blood pressure, heart rate, cardiac output, left ventricular pressure, and regional blood flows were measured prior to drug administration, and after 0.03, 0.1, 0.3, 1.0, and 3.0 mg/kg IV administration of the study drugs. Dogs receiving diltiazem or verapamil also received a dose of 10.0 mg/kg. When the blood pressure had been reduced from baseline by 30%, 1.43 mg/kg nifedipine IV (six dogs) decreased total peripheral resistance by 51%, increased cardiac output by 35%, and increased heart rate by 132%. Coronary blood flow and iliac blood flow increased 93% and 45%, respectively, but mesenteric blood flow and renal blood flow were not significantly altered. Diltiazem (eight) and verapamil (seven) at equivasodepressor doses (1.43 to 4.43 mg/kg) caused less peripheral vasodilation and reflex tachycardia. At severely toxic levels when arterial blood pressure fell by 50%, all three drugs decreased cardiac output. Nifedipine still increased heart rate. Diltiazem and verapamil caused high-grade atrioventricular block, resulting in bradycardia. All three drugs caused a redistribution of cardiac output favoring the coronary bed over the other beds.

CONCLUSIONS

In the conscious dog, calcium channel blocker-induced hypotension at the moderate level is associated with disparate effects on systemic hemodynamics, probably resulting from differential reflex sympathetic activation. However, at a more severe level, their toxic effects are similar and manifested predominantly by their actions on the slow calcium channel.

Opiate tolerance-induced modulation of free intracellular calcium in synaptosomes

Synaptosomes were prepared from morphine-tolerant and non-tolerant mice. Significantly higher levels of basal free intracellular calcium were observed in the synaptosomes from the opiate-tolerant mice compared to synaptosomes from non-tolerant mice (468 nM versus 328 nM, respectively). In addition, morphine (1 microM) failed to attenuate KCl-induced rises in intracellular calcium in the synaptosomes from the tolerant mice. Conversely, morphine produced a concentration-related, naloxone-reversible attenuation of 50 mM KCl-induced rises in intracellular calcium in the synaptosomes from the non-tolerant mice. Omega conotoxin, which blocks both "L" and "N" type calcium channels, attenuated KCl-stimulated rises in intracellular calcium only in synaptosomes from non-tolerant mice. BAY-K 8644, an "L-type" calcium channel agonist, produced nifedipine-reversible increases in intracellular calcium in the synaptosomes from the tolerant animals only. These data suggest that chronic exposure to morphine results in an alteration in either the number of the activation state of calcium channels in the membrane. Changes in intracellular free calcium may be the final common pathway through which neurons adapt to the chronic exposure to morphine.

Nifedipine enhances the cardiac toxicity of magnesium sulfate in the isolated perfused Sprague-Dawley rat heart

Magnesium sulfate is commonly used in tocolytic regimens and as prophylaxis against seizures. Nifedipine may be used simultaneously in either situation. With the isolated perfused rat heart model (Sprague-Dawley rats), we investigated the effects of these agents on cardiac function. Whereas each agent alone depressed cardiac performance, the two drugs together had maximal depressive effects on the heart.

Fetal cardiovascular effects of nifedipine in rats

In this study we clarify the fetal cardiovascular effects of nifedipine. Nifedipine was administered to near-term rats and cardiovascular morphology of the fetus was studied with a rapid whole-body freezing technique. Fetal cardiac failure was estimated by accumulation of pericardial effusion and ventricular dilatation. Dose-response study at 8 h after administration revealed that slight ventricular dilatation occurred with 0.1 mg/kg of nifedipine, and remarkable ventricular dilatation and pericardial fluid accumulation were noted with 10 mg/kg nifedipine. Time-course study with one dose of 10 mg/kg nifedipine revealed early ventricular dilatation at 1 h, peak ventricular dilatation and fluid accumulation at 8 h, and slight effects at 24 h. In conclusion, the cardiodepressive effect of nifedipine in the fetal rat was mild with the therapeutic dose, and its effects increased dose dependently.

[Effect of nifedipine (corinfar) on cerebrovascular circulation in patients with exertion-induced stenocardia]

Headache as a side effect of corinfar treatment courses for angina of effort was more commonly seen in patients with pretreatment dystonic rheoencephalographic changes. A single corinfar dose produced a drop of venous tone. Corinfar-associated headache was less common in patients after long-term treatment with high-dose nitroglycerin.

Safety and efficacy of amlodipine added to hydrochlorothiazide therapy in essential hypertension

We compared amlodipine, a dihydropyridine calcium antagonist, to placebo as add-on therapy to hydrochlorothiazide in 91 hypertensive patients inadequately controlled on hydrochlorothiazide (50 mg/d for four weeks). This was a double-blind, randomized, multicenter, parallel group-trial; 45 patients received placebo and 46 received amlodipine in doses of 2.5 to 10 mg qd (mean 9 mg/d). Supine blood pressure systolic/diastolic, mean +/- SE mm Hg) 24-hour postdose was significantly reduced by 14.2 +/- 2.3/11.7 +/- 1, compared to placebo, 4.5 +/- 2.7/5 +/- 1.2. Standing blood pressure was similarly reduced: amlodipine by 14 +/- 2.7/12.5 +/- 1.2; placebo by 3 +/- 2.1/5.8 +/- 1.2. This reduction in blood pressure was attained without any significant changes in pulse rate, EKG, and serum lipids (triglycerides were reduced in the amlodipine group by 42.9 mg/dL, P = .023). Only two patients had side effects requiring discontinuation from the study (both in the amlodipine group). Side effects occurred in 27 amlodipine-treated patients (11 with peripheral edema) and 18 patients in the placebo (three with peripheral edema) group. Investigator's assessment of therapeutic effect and tolerability, and the percent of responders v nonresponders was also in favor of amlodipine. Thus amlodipine administered once daily is an effective and safe agent for second-step therapy in mild to moderate essential hypertension.

Analgesic action of clonixin, nifedipine and morphine using the formalin test

1. The analgesic effect of ClX, nifedipine, metamizol, indoprofen and morphine in the pain induced by formalin injection (formalin test) was studied. 2. Attempts to demonstrate tolerance to ClX were unsuccessful. 3. In the analgesic test nifedipine and morphine are approximately 10 times more potent than ClX. 4. The present results suggest that the analgesic action of ClX is not mediated by mu 1, delta or kappa-opioid receptors and the anti-nociceptive effect of nifedipine may be associated with the blockade of the transmembrane inward movements of calcium.

Pharmacokinetic study of benidipine hydrochloride in rats and dogs

(+/-) - (R*) - 2,6-Dimethyl-4-(m-nitrophenyl)-1,4-dihydropyridine - 3, 5-dicarboxylic acid (R*)-1-benzyl-3-piperidinyl ester, methyl ester hydrochloride (benidipine hydrochloride, KW-3049) is presently under development as an anti-hypertensive and antianginal agent. A pharmacokinetic study in rat and dog after oral and intravenous administrations revealed that KW-3049 was rapidly absorbed from the gastrointestinal tract, distributed into tissues moderately and comparatively quickly eliminated. After oral administration, non-linearity of bioavailability with increment of doses was observed in both rat and dog. Female and male rats showed similar drug disposition after intravenous administration. Oxidation product of KW-3049 dihydropyridine ring was also measured in some plasma samples. The concentration rates of its pyridine metabolite accounted for 0 to 30% and 0 to 23% of the combined concentration of KW-3049 plus the pyridine metabolite in rat and dog.

Synthesis and pharmacological activity of stereoisomers of 1,4-dihydro-2,6-dimethyl-4-(3-nitrophenyl)-3,5-pyridine-dicarboxylic acid methyl 1-(phenylmethyl)-3-piperidinyl ester

1,4-Dihydro-2,6-dimethyl-4-(3-nitrophenyl)-3,5-pyridinedicarboxylic++ + acid methyl 1-(phenylmethyl)-3-piperidinyl ester 1, a highly potent calcium antagonist, was separated into stereo- and optical isomers to investigate the differences of antihypertensive activities between them. Fractional crystallization of the hydrochlorides of 1 gave alpha- and beta-diastereoisomers. The alpha-isomer (benidipine hydrochloride, KW-3049) showed very strong hypotensive effect, but little activity was observed in the beta-isomer. From optically resolved 1,4-dihydro-5-methoxycarbonyl-2,6-dimethyl-4-(3-nitrophenyl)-3- pyridinecarboxylic acids 2, and 1-benzyl-3-piperidinols 3, four optical isomers of 1 were synthesized, and their absolute configurations were deduced. The hypotensive activity of (+)-alpha, namely (S)-(S)-1, was 30 to 100 times stronger than that of (-)-alpha in intravenously administered spontaneously hypertensive rats.

Gingival hyperplasia in dogs induced by oxodipine, a calcium channel blocking agent

Subchronic oral exposure of dogs to Oxodipine, a new calcium channel blocker of the dihydropyridine-type, resulted in dose-related gingival hyperplastic changes. The doses at which an effect was elicited were 24 and 73 times the intended therapeutic dose for man. The effects were first noted after 7 weeks of treatment, and were limited to the high and intermediate dose groups of both sexes. Macroscopically, a generalized enlargement of the maxillary and mandibular facial and lingual gingivae were noted. The histological changes were similar to those described in man for Nifedipine and hydantoin-related drugs. An increase in the activity of alkaline phosphatase and a decrease in alanine aminotransferase was demonstrated. This article is the first to describe gingival hyperplasia in dogs induced in a dose-dependent manner by a calcium channel blocker.

Diltiazem, nifedipine, and their combination in patients with stable angina pectoris: effects on angina, exercise tolerance, and the ambulatory electrocardiographic ST segment

The efficacy and safety of oral nifedipine and diltiazem were compared in 20 patients with stable angina pectoris with use of a placebo run-in, randomized, double-blind titration to maximal effect crossover protocol. The effects of treatment withdrawal were also analyzed. All patients received placebo for 2 weeks and were then randomly assigned to receive either diltiazem or nifedipine. A 2 week drug titration phase in which patients received either diltiazem (180 to 360 mg/day) or nifedipine (30 to 120 mg/day) in three divided doses was followed by a 1 week maintenance phase. Patients then received placebo for 1 to 2 weeks, followed by crossover to the other treatment regimen and a second placebo washout period of 1 week. Patients (n = 13) who remained symptomatic on both diltiazem and nifedipine during the monotherapy periods entered a 3 week combination treatment phase, followed by a final 1 week placebo washout period. Frequency of angina, nitroglycerin consumption, exercise tolerance (Naughton protocol), and frequency of daily episodes of ST segment deviations on the electrocardiogram (1 mm of ST segment depression persisting for at least 1 min with and without chest pain) on an ambulatory electrocardiographic monitor were assessed during the baseline placebo, active monotherapy, placebo withdrawal, and combination treatment phases. Plasma drug levels were also measured. Compared with initial placebo values, the frequency of angina and the amount of nitroglycerin treatment were reduced by both diltiazem (p less than .001) and nifedipine (p less than .02). Diltiazem was more effective than nifedipine in reducing angina (p less than .02). Exercise duration increased with both drugs (p less than .0001). Diltiazem was significantly better than nifedipine in reducing the episodes of ST segment depression on the ambulatory monitor (p less than .01). Diltiazem reduced the resting heart rate (p less than .01); both drugs reduced the resting blood pressure and rate-pressure product. Overall, combination therapy was more effective in patients who did not maximally respond to diltiazem or nifedipine alone with respect to anginal and exercise variables and in reducing blood pressure at rest and during exercise. Plasma drug levels could not predict an individual patient's treatment response. Diltiazem may increase nifedipine drug levels when the drugs are combined. Fewer side effects were observed with diltiazem than nifedipine; the most side effects were seen with combination treatment. There were no apparent withdrawal effects observed with either treatment regimen.(ABSTRACT TRUNCATED AT 400 WORDS)

Hyperphalangeal bones induced in rat pups by maternal treatment with nifedipine

Hyperphalangeal bones were found in postnatal rat pups of mothers treated with nifedipine during pregnancy. The anomaly occurred only at the region between the middle and distal phalanges of the 3rd and 4th fingers and toes. The critical periods of the anomaly were days 13 and 14 of pregnancy for the fingers, and days 14 and 15 of pregnancy for the toes. The incidences were dose-related, being more than 90% in both fingers and toes at a single dose of 150 mg/kg, and even more marked at the 4th digits than at the 3rd digits. Neither right/left difference nor sex difference was manifested in the incidence of the anomaly.

Cardiovascular effects of NPK-1886, a new dihydropyridine compound with calcium entry blocking activity

The cardiovascular effect of NPK-1886 (NPK), a novel photostable dihydropyridine compound, was studied by comparing it with that of nifedipine (Nif). In normal Wistar rats (NWR), systolic blood pressure was only slightly depressed by NPK or Nif, while in three types of hypertensive rats (i.e., spontaneously hypertensive rats (SHR), renal hypertensive rats (RHR) and DOCA-saline-induced hypertensive rats (DOC-Na-R)), the hypotensive potency of NPK was more than or equal to that of Nif. The effectiveness of NPK on the normal and hypertensive models was in the following order: DOC-Na-R, RHR, SHR, NWR. Coronary perfusion flow in Langendorff's heart was increased almost the same extent by NPK and Nif. On isolated rabbit aortic strips, the antagonistic potencies of NPK, like those of Nif, were greater for calcium than for norepinephrine, serotonin and angiotensin II. The negative ino- and chronotropic potency of NPK in isolated guinea-pig right atria was less than that of Nif. The slow membrane action potentials of guinea-pig papillary muscle were suppressed by NPK, but less than by Nif, with manifestations of a reduction of Vmax and AP-duration. These results indicate that NPK has a potent hypotensive effect on hypertensive models and a weaker cardiac inhibition. The general toxicity of NPK was lower than that of Nif.

Cardiorespiratory effects of isosorbide dinitrate and nifedipine in combination with nadolol: a double-blind comparative study of beneficial and adverse antianginal drug interactions

Combinations of 2 or 3 drugs are often used to treat angina pectoris, but their combined cardiorespiratory effects have not been investigated. Using a randomized, double-blind, placebo-controlled protocol, the effects of nadolol alone and nadolol in combination with isosorbide dinitrate and nifedipine were compared, in low and high doses, on antianginal efficacy, respiratory functions and arterial blood oxygen saturation (SaO2) in 19 patients with stable angina pectoris. A complete assessment including a bicycle exercise test with the measurement of the sum of ST-segment depression in all leads (sigma ST) was carried out every 2 weeks. The frequency of anginal attacks and nitroglycerin consumption was reduced significantly (p less than 0.001) by nadolol alone and in combination with the other drugs. Nadolol caused a slight reduction in the forced expiratory volume in 1 second, which was improved by isosorbide dinitrate and nifedipine. The sigma ST profile (basal, at peak exercise and 2 and 5 minutes after exercise) was decreased by nadolol alone and in combination with the other drugs, although the greatest reduction was achieved with large doses of nifedipine and nadolol. The rest and postexercise SaO2 decreased after nadolol alone and in combination with isosorbide dinitrate, but recovered to pretrial values after nifedipine and nadolol. With all drug combination, sigma ST depression was greater when the postexercise SaO2 was less than 92%, and decreased (p less than 0.05) in the same patients when their postexercise SaO2 was greater than 92%.(ABSTRACT TRUNCATED AT 250 WORDS)

Intracranial pressure during nifedipine-induced hypotension

The effect of nifedipine-induced hypotension on intracranial pressure (ICP) was investigated in cats with normal and artificially increased ICP. Eleven cats were anesthetized with intraperitoneal pentobarbital (25 mg/kg), intubated, and ventilated with nitrous oxide in oxygen. Mean arterial pressure (MAP), heart rate (HR), and mean pulmonary artery pressure (PAP) were continuously recorded. A double 19-gauge needle was inserted into the cisterna magna; ICP was continuously monitored from one needle and the other was used to increase and maintain ICP at 27 +/- 4 mm Hg by infusion of pH-adjusted Ringer's lactate solution. After control measurements were taken, nifedipine was given intravenously in each cat when ICP was normal and increased. Infusion of 96 +/- 12 micrograms (SEM) nifedipine (approximately equal to 33 micrograms/kg) reduced MAP 35-45% for 2.5 +/- 0.8 min when ICP was normal, and for 2.0 +/- 0.6 min when ICP had been increased. When initial ICP was normal, nifedipine-induced hypotension produced a small (2.2 mm Hg) but statistically significant increase in ICP and decrease in cerebral perfusion pressure (P less than 0.01). When ICP was initially elevated, nifedipine-induced hypotension produced a larger increase in ICP (5 +/- 1 mm Hg) and a proportionately larger decrease in cerebral perfusion pressure (P less than 0.01).