Increased thrombin generation in a mouse model of cancer cachexia is partially interleukin-6 dependent.

Essentials Cancer cachexia and cancer-associated thrombosis have not previously been mechanistically linked. We assessed thrombin generation and coagulation parameters in cachectic C26 tumor-bearing mice. C26 mice are hypercoagulable, partially corrected by blocking tumor derived interleukin-6. Coagulability and anti-inflammatory interventions may be clinically important in cancer cachexia. SUMMARY: Background Cancer cachexia and cancer-associated thrombosis are potentially fatal outcomes of advanced cancer, which have not previously been mechanistically linked. The colon 26 (C26) carcinoma is a well-established mouse model of complications of advanced cancer cachexia, partially dependent on high levels of interleukin-6 (IL-6) produced by the tumor. Objectives To assess if cancer cachexia altered the coagulation state and if this was attributable to tumor IL-6 production. Methods In male BALB/c*DBA2 (F1 hybrid) mice with a C26 tumor we used modified calibrated automated thrombogram and fibrin generation (based on overall hemostatic potential) assays to assess the functional coagulation state, and also examined fibrinogen, erythrocyte sedimentation rate (ESR), platelet count, tissue factor pathway inhibitor (TFPI) and hepatic expression of coagulation factors by microarray. C26 mice were compared with non-cachectic NC26, pair-fed and sham control mice. IL-6 expression in C26 cells was knocked down by lentiviral shRNA constructs. Results C26 mice with significant weight loss and highly elevated IL-6 had elevated thrombin generation, fibrinogen, ESR, platelets and TFPI compared with all control groups. Fibrin generation was elevated compared with pair-fed and sham controls but not compared with NC26 tumor mice. Hepatic expression of coagulation factors and fibrinolytic inhibitors was increased. Silencing IL-6 in the tumor significantly, but incompletely, attenuated the increased thrombin generation, fibrinogen and TFPI. Conclusions Cachectic C26 tumor-bearing mice are in a hypercoagulable state, which is partly attributable to IL-6 release by the tumor. The findings support the importance of the coagulation state in cancer cachexia and the clinical utility of anti-inflammatory interventions.

Evaluation of dietary betaine in lactating Holstein cows subjected to heat stress.

Betaine (BET), a natural, organic osmolyte, improves cellular efficiency by acting as a chaperone, refolding denatured proteins. To test if dietary BET reduced the effect of heat stress (HS) in lactating dairy cows, multiparous, lactating Holstein cows (n=24) were blocked by days in milk (101.4±8.6 d) and randomly assigned to 1 of 3 daily intakes of dietary BET: the control (CON) group received no BET, mid intake (MID) received 57mg of BET/kg of body weight, and high dose (HI) received 114mg of BET/kg of body weight. Cows were fed twice daily and BET was top-dressed at each feeding. Cows were milked 2 times/d and milk samples were taken daily for analysis. Milk components, yield, feed intake, and water intake records were taken daily. Rectal temperature and respiration rate were taken 3 times/d at 0600, 1400, and 1800h. Cows were housed in environmentally controlled rooms and were allowed acclimation for 7d at thermoneutral (TN) conditions with a mean temperature-humidity index of 56.6. Cows were then exposed to 7d of TN followed by 7d of HS represented by a temperature-humidity index of 71.5 for 14d. This was followed by a recovery period of 3d at TN. Dietary BET increased milk yield during the TN period. No differences were found between BET and CON in total milk production or milk composition during HS. The increase in water intake during HS was not as great for cows fed BET compared with controls. The cows on CON diets had higher p.m. respiration rate than both MID and HI BET during HS, but lower rectal temperature compared with BET. No difference was found in serum glucose during TN, but cows given HI had elevated glucose levels during HS compared with CON. No differences were found in serum insulin levels between CON and BET but an intake by environment interaction was present with insulin increasing in HI-treated lactating dairy cows during HS. The heat shock response [heat shock protein (HSP) 27 and HSP70] was upregulated in bovine mammary epithelial cells in vitro. Blood leukocyte HSP27 was downregulated at the HI dose under TN conditions and HSP70 was upregulated at the HI dose and this effect was increased by HS. No effect was seen with the MID dose with HSP27 or HSP70. The lack of effect of BET at MID may be associated with uptake across the gut. We conclude that BET increased milk production under TN conditions and was associated with reduced feed and water intake and slightly increased body temperatures during HS of cows fed BET. The effect of BET on milk production was lost during HS with HI BET, whereas serum glucose levels increased during HS.

Tobacco use among low-income housing residents: does hardship motivate quit attempts?

PURPOSE: The purpose of this study was to examine material hardship among smokers to determine whether such hardship was positively associated with current attempts to quit tobacco use. METHODS: We analyzed cross-sectional data from the Health in Common (HIC) study, an observational study to investigate social and physical determinants of cancer risk-related behaviors among residents of low-income housing in three cities in the Boston metropolitan area. In this study, three indicators of hardship were used: food hardship, financial hardship, and material hardship (food and financial hardship combined). Logistic regression models were used to obtain the odds of currently trying to quit among current smokers in the HIC (n = 170) across hardship types experienced, adjusting for sociodemographic and psychosocial factors. RESULTS: Fully adjusted models revealed no statistically significant association between trying to quit tobacco use and indicators of material hardship: food hardship and financial hardship present (OR 1.33 (0.42-4.2); food hardship and no financial hardship OR 3.83 (0.97-15.13); and financial hardship but no food hardship OR 0.5 (0.1-2.39). CONCLUSIONS: These findings suggest that even in the presence of material hardship, low-income housing resident tobacco users are not more likely to quit tobacco use; therefore, cessation efforts focused on the financial benefits of quitting may be insufficient to motivate quit attempts among low-income smokers.

The multidrug transporter ABCG2 (BCRP) is inhibited by plant-derived cannabinoids.

BACKGROUND AND PURPOSE: Cannabinoids are used therapeutically for the palliation of the adverse side effects associated with cancer chemotherapy. However, cannabinoids also inhibit both the activity and expression of the multidrug transporter, P-glycoprotein in vitro. Here we address the interaction of cannabinol (CBN), cannabidiol (CBD) and delta 9-tetrahydrocannabinol (THC) with the related multidrug transporter, ABCG2. EXPERIMENTAL APPROACH: Cannabinoid inhibition of Abcg2/ABCG2 was assessed using flow cytometric analysis of substrate accumulation and ATPase activity assays. The cytotoxicity and chemosensitization by cannabinoids was determined with cell viability assays. Expression of cannabinoid and vanilloid receptors was assessed using reverse transcriptase polymerase chain reaction, and cannabinoid modulation of ABCG2 expression was examined using immunoblotting. KEY RESULTS: CBN, CBD and THC increased the intracellular accumulation of the Abcg2/ABCG2 substrate, mitoxantrone, in an over-expressing cell line. The THC metabolite, (-)-11-nor-9-carboxy-delta 9-THC was much less potent. The plant cannabinoids inhibited both basal and substrate stimulated ATPase activity of human ABCG2. Cannabinoid cytotoxicity occurred in the absence of known cannabinoid cell surface receptors, and only at concentrations higher than those required for Abcg2/ABCG2 inhibition. Sub-toxic concentrations of the cannabinoids resensitized the overexpressing cell line to the cytotoxic effect of Abcg2/ABCG2 substrates, mitoxantrone and topotecan. This occurred in the absence of any effect on ABCG2 expression. CONCLUSIONS AND IMPLICATIONS: Cannabinoids are novel Abcg2/ABCG2 inhibitors, reversing the Abcg2-mediated multidrug-resistant phenotype in vitro. This finding may have implications for the co-administration of cannabinoids with pharmaceuticals that are ABCG2 substrates.

The effects of cannabinoids on P-glycoprotein transport and expression in multidrug resistant cells.

Cannabis is the most widely used illicit drug in the world. Cannabinoids are used therapeutically by some patients as they have analgesic, anti-emetic and appetite stimulant properties which palliate adverse symptoms. Use of these agents in an oncology setting raises the question of whether they act to modulate the effectiveness of concurrently administered anti-cancer drugs. The transporter, P-glycoprotein (P-gp) confers multiple drug resistance (MDR) by effluxing a diverse array of anti-cancer agents. This study was undertaken to examine the effect of cannabinoids on P-gp. Unlike the known P-gp inhibitor, PSC833, short 1h exposure to three plant-derived cannabinoids, cannabinol (CBN), cannabidiol (CBD) and Delta(9)-tetrahydrocannabinol (THC) and the synthetic cannabinoid receptor agonist, WIN55, 212-2 (WIN) did not inhibit the efflux of the P-gp substrate Rhodamine 123 (Rh123) in either a drug-selected human T lymphoblastoid leukaemia cell line (CEM/VLB(100)) or in a mouse fibroblast MDR1 transfected cell line (77.1). However, in CEM/VLB(100) cells, prolonged 72 h exposure to the cannabinoids, THC and CBD, decreased P-gp expression to a similar extent as the flavonoid, curcumin (turmeric). This correlated with an increase in intracellular accumulation of Rh123 and enhanced sensitivity of the cells to the cytotoxic actions of the P-gp substrate, vinblastine. Taken together, these results provide preliminary evidence that cannabinoids do not exacerbate P-gp mediated MDR. Further, plant-derived cannabinoids are moderately effective in reversing MDR in CEM/VLB(100) cells by decreasing P-gp expression.

Multidrug resistance genes in infant acute lymphoblastic leukemia: Ara-C is not a substrate for the breast cancer resistance protein.

Infants with acute lymphoblastic leukemia (ALL) are more resistant to chemotherapeutic drugs than older children with ALL, except for Ara-C. Drug resistance mechanisms in infant ALL, however, remain unknown. Possibly, multidrug resistance (MDR) proteins like P-glycoprotein, MDR-associated protein (MRP1), lung resistance-related protein (LRP/MVP) and the breast cancer resistance protein (BCRP) play a role. Accordingly, we measured the mRNA levels of these proteins in infants (n=13) and non-infants (n=13) with ALL, using quantitative RT-PCR. Infants expressed 2.4-fold less BCRP mRNA (P=0.009) than non-infants with ALL. MDR1, MRP1 and LRP/MVP expression did not differ between both groups. MDR gene expression levels did not correlate to prednisolone, vincristine, daunorubicin or Ara-C cytotoxicity, except for BCRP expression, which correlated with resistance to Ara-C (Rs=0.53, P=0.012), suggesting that Ara-C might be a BCRP substrate. However, culturing patients ALL cells in the presence of the BCRP inhibitor Ko143 had no effect on Ara-C sensitivity. Inhibiting Bcrp1 in the Mdr1a-, Mdr1b- and Mrp1-deficient and Bcrp1-overexpressing mouse cell line Mef3.8/T6400, also did not modulate Ara-C cytotoxicity. Therefore, we conclude that Ara-C is not a substrate for BCRP and that MDR proteins do not play a significant role in drug resistance in infant ALL.

Laparoscopic dismembered pyeloplasty: 50 consecutive cases.

OBJECTIVE: To test the hypothesis that laparoscopic dismembered pyeloplasty offers the same good results as open pyeloplasty, but without the disadvantages of the loin incision (which is painful, prolongs hospitalization and prevents a return to normal activities for several weeks) in the treatment of pelvi-ureteric junction (PUJ) obstruction. PATIENTS AND METHODS: Fifty consecutive consenting patients presenting with PUJ obstruction underwent laparoscopic dismembered pyeloplasty carried out by one surgeon using an extraperitoneal approach. RESULTS: Two (4%) procedures were converted to open surgery. The mean (range) operative duration was 164 (120-240) min. Fifteen (30%) of the patients had their ureter transposed anterior to a crossing lower-pole vessel; 22 (44%) patients had a separate renal pelvic suture line. The mean (range) postoperative parenteral analgesic requirement was 19.1 (0-111) mg of morphine sulphate. The mean (range) hospitalization was 2.6 (2-7) days. Two (4%) patients had complications. After a mean (range) follow-up of 18.8 (3-72) months all but one patient, who had failed endopyelotomy, had a normal renogram and were symptom-free. CONCLUSION: These results suggest that a loin wound is not necessary for a successful outcome after dismembered pyeloplasty, and that in expert hands laparoscopic dismembered pyeloplasty should now be considered the standard of care.

Promoting breast and cervical cancer screening at the workplace: results from the Woman to Woman Study.

OBJECTIVES: This article reports findings from a peer-delivered intervention designed to increase use of breast and cervical cancer screening. METHODS: Twenty-six worksites were randomly assigned to the intervention or comparison group. The 16-month intervention consisted of group discussions, outreach, and educational campaigns. Data were collected from a random sample of women employees stratified by age (baseline n = 2943; final n = 2747). Cross-sectional analyses were conducted to evaluate the impact of the intervention on screening behaviors. RESULTS: Relative to comparison worksites, the intervention group experienced greater increases in the percentage of women who reported a recent mammogram (7.2% vs 5.6%), clinical breast examination (5.8% vs 2.1%), and Papanicolaou (Pap) test (4.7% vs 1.9%). After worksite cluster and age strata were controlled for, the observed increase in Pap tests was significantly greater in the intervention group (odds ratio [OR] = 1.28; 95% confidence interval [CI] = 1.01, 1.62); however, differences in mammography screening rates (OR = 1.14; 95% CI = 0.90, 1.44) and clinical breast examination (OR = 1.19; 95% CI = 0.96, 1.49) were not statistically significant. CONCLUSIONS: Intervention activities produced a modest increase in cervical cancer screening, but they did not accelerate breast cancer screening rates above the observed secular trend.

Inhibition of BCRP-mediated drug efflux by fumitremorgin-type indolyl diketopiperazines.

A library of 42 diastereoisomeric mixtures of fumitremorgin-type indolyl diketopiperazines, prepared by parallel solid-phase synthesis, was screened for Breast Cancer Resistance Protein inhibitory activity and compared with GF120918. Demethoxy-fumitremorgin C was synthesized by solid-phase techniques and tested as well. Structure-activity relationship studies have identified several potent analogues, both in assays using the T6400 mouse and the T8 human cell line, whereas low cytotoxicity was seen at effective concentrations.

Extensive contribution of the multidrug transporters P-glycoprotein and Mrp1 to basal drug resistance.

Despite accumulating evidence that multidrug resistance transporter proteins play a part in drug resistance in some clinical cancers, it remains unclear whether the relatively low levels of multidrug resistance transporter expression found in most untreated tumors could substantially affect their basal sensitivity to antineoplastic drugs. To shed light on this problem, the drug sensitivities of wild-type mouse cell lines were compared with those of lines in which the Mdr1a and Mdr1b genes encoding P-glycoprotein (P-gp) were inactivated and lines in which the Mrp1 gene was inactivated in addition to Mdr1a and Mdr1b. These models permit a clean dissection of the contribution of each transporter to drug resistance at expression levels similar to those in normal tissues and avoid complications that might arise from previous exposure of cell lines to drug selection. For substrate drugs, we found that these contributions can indeed be very substantial. Lines lacking functional P-gp were, on average, markedly more sensitive to paclitaxel (16-fold), anthracyclines (4-fold) and Vinca alkaloids (3-fold). Lines lacking both P-gp and Mrp1 were (compared with wild-type lines) hypersensitive to an even broader array of drugs, including epipodophyllotoxins (4-7-fold), anthracyclines (6-7-fold), camptothecins (3-fold), arsenite (4-fold) and Vinca alkaloids, especially vincristine (28-fold). Thus, even very low levels of P-gp and Mrp1 expression that may be difficult to detect in tumors could significantly affect their innate sensitivity to a wide range of clinically important substrate drugs. An implication is that the use of resistance reversal agents to sensitize drug-naive tumors may be appropriate in more cases than is presently appreciated.

Breast cancer resistance protein is localized at the plasma membrane in mitoxantrone- and topotecan-resistant cell lines.

Tumor cells may display a multidrug resistant phenotype by overexpression of ATP-binding cassette transporters such as multidrug resistance (MDRI) P-glycoprotein, multidrug resistance protein 1 (MRP1), and breast cancer resistance protein (BCRP). The presence of BCRP has thus far been reported solely using mRNA data. In this study, we describe a BCRP-specific monoclonal antibody, BXP-34, obtained from mice, immunized with mitoxantrone-resistant, BCRP mRNA-positive MCF-7 MR human breast cancer cells. BCRP was detected in BCRP-transfected cells and in several mitoxantrone- and topotecan-selected tumor cell sublines. Pronounced staining of the cell membranes showed that the transporter is mainly present at the plasma membrane. In a panel of human tumors, including primary tumors as well as drug-treated breast cancer and acute myeloid leukemia samples, BCRP was low or undetectable. Extended studies will be required to analyze the possible contribution of BCRP to clinical multidrug resistance.

Deletion of cysteine 369 in lysyl hydroxylase 1 eliminates enzyme activity and causes Ehlers-Danlos syndrome type VI.

This study describes the relative contribution of the 10 cysteine residues in lysyl hydroxylase 1 (LH1) to enzyme activity. We have identified a novel mutation of a 15-bp deletion in exon 11 in one LH1 allele, that codes for amino acids 367-371 (DLCRQ), in two unrelated compound heterozygous patients with Ehlers-Danlos type VI. The mutations in their other alleles were a C1119T change (exon 10) and a predicted Q49X (exon 2). We confirmed that the loss of cysteine 369 in the deleted sequence contributed to the diminished enzyme activity by structure/function analysis of mutant LH1 constructs, in which C369 and the nine other cysteines were individually mutated to serine by site-directed mutagenesis of a normal pAcGP67/LH1cDNA construct. Following their expression in an Sf9 insect cell/baculovirus system, SDS-PAGE and Western analysis showed that equivalent levels of correctly-sized (85-kDa) products were secreted. The mutation of residues C369 and also C375, C552 and C687 virtually eliminated LH activity, whereas mutations of C267, C270, and C680 had an intermediate effect. In contrast, the C204S, C484S and C566S constructs had normal activity. Although disulfide bond formation may affect the relative contribution of each cysteine to LH activity, catalytic activity does not appear to be directly related to dimerization of the enzyme.

Beliefs about Papanicolaou smears and compliance with Papanicolaou smear follow-up in adolescents.

OBJECTIVE: To explore qualitatively adolescent girls' understanding of Papanicolaou smears and barriers to compliance with Papanicolaou smear follow-up appointments. DESIGN: Qualitative analysis, using 3 focus groups and 15 in-depth, semistructured individual interviews. SETTING: Adolescent Clinic and Young Parents' Program at Children's Hospital, Boston, Mass. MAIN OUTCOME MEASURES: Beliefs and attitudes about Papanicolaou smears and barriers to compliance with Papanicolaou smear follow-up. RESULTS: The mean (+/- SD) age of the 15 interview participants was 18.7 (+/- 1.9) years. Knowledge about Papanicolaou smears and pelvic examinations was poor. Most participants believed that their peers receive Papanicolaou smear screening and perceived teenagers to be susceptible to cervical cancer. Perceived benefits to getting Papanicolaou smears were prevention and early detection or diagnosis, and reported barriers included pain or discomfort, embarrassment, fear of finding a problem, fear of the unknown, denial, poor communication or rapport with the provider, not wanting to look for trouble, lack of knowledge, and peers' advice. Participant-generated strategies for how providers could overcome barriers to Papanicolaou smear screening included education and the development of trusting, consistent relationships with providers. Participant-generated strategies for how providers could enhance appointment-keeping among adolescents included telephone and written reminders. CONCLUSIONS: These data support a behavioral theory-based model of adolescent compliance with Papanicolaou smear follow-up, which may help to develop strategies to enhance compliance with Papanicolaou smear follow-up appointments. These strategies include providing in-depth education about Papanicolaou smears, addressing barriers to Papanicolaou smear follow-up, focusing on appropriate provider behaviors, and instituting an appointment reminder system.

The mouse Bcrp1/Mxr/Abcp gene: amplification and overexpression in cell lines selected for resistance to topotecan, mitoxantrone, or doxorubicin.

Mouse fibroblast cell lines lacking functional Mdr1a, Mdr1b, and Mrp1 genes were selected for resistance to topotecan, mitoxantrone, or doxorubicin. Each of the resulting drug-resistant lines showed marked gene amplification of Bcrp1, the mouse homologue of the human ATP-binding cassette transporter gene BCRP/MXR/ABCP, and greatly elevated expression of Bcrp1 mRNA. All three of the resistant cell lines were highly cross-resistant to topotecan and mitoxantrone and, to a variable extent, doxorubicin. All showed greatly reduced cellular accumulation and greatly increased efflux of mitoxantrone that was dependent on cellular ATP and efficiently reversed by the compound GF120918. The mouse Bcrp1 cDNA encodes a 657-amino-acid protein with 81% identity (86% similarity) to the human breast cancer resistance protein (BCRP) and a virtually superimposable hydrophobicity profile. Our data argue strongly that mouse Bcrp1 is functionally comparable with human BCRP, conferring multidrug resistance to topotecan, mitoxantrone, doxorubicin, and related compounds. Mouse models and cell lines should, therefore, be highly informative in understanding the clinical, pharmacological, and physiological roles of BCRP.

The relationship between social network characteristics and breast cancer screening practices among employed women.

This study examined the relationship between social network characteristics and breast cancer screening practices among employed women. We hypothesized that larger social networks, higher levels of support from networks, and stronger social influences to undergo screening would be positively associated with regular utilization of mammograms and clinical breast examinations. Data were collected from women aged 52 and over who were employed in 27 worksites (N = 1,045). Social network characteristics, breast cancer screening practices, and sociodemographic factors were assessed in a self-administered survey. Bivariate analyses revealed that social influences were significantly associated with regular screening; social support was only marginally associated with regular screening; and social network size was not at all associated. In multivariate analyses, only the perception that screening is normative among one's peers was predictive of regular screening. Provider recommendation was the single most potent predictor of regular screening. These findings provide support for the importance of social norms in motivating women to adhere to screening guidelines. In addition, they underscore the potent impact of provider recommendations on women's screening practices.

Functional dissociation of the prefrontal cortex and the hippocampus in timing behavior.

Using the peak procedure, rats with aspiration lesions to the medial prefrontal cortex (PFC) or the hippocampus were tested for the acquisition of timing behavior and temporal memory. After surgery, rats were 1st trained to discriminate a 40-s interval and then tested for temporal memory with gap trials. Results indicated that lesions to the medial PFC disrupted the acquisition of timing behavior. Medial PFC animals needed significantly more trials to reach criterion, and their temporal discrimination function was less uniform and steep, indicating a general deficit in timing ability. In hippocampal rats, the ability to estimate the duration of the discriminative stimulus was unaffected by the lesion. It was concluded that the hippocampus is not necessary for the acquisition of timing behavior in this task. Gap trials failed to produce a deficit in the memory for temporal events for either lesion. Thus, it was further concluded that neither the medial PFC nor the hippocampus is necessary for the memory of temporal events.

Intention to have a mammogram in the future among women who have underused mammography in the past.

This study investigated associations between confidence in one's ability to discuss mammography with health providers and to obtain regular mammograms (self-efficacy), social network members' attitudes toward mammograms (social influence), mammography experiences, and intention to have a mammogram in the next 1 to 2 years among women who were not in adherence with screening guidelines. Data were collected as part of a baseline assessment for a work site intervention study. Women 52 years and older completed a self-administered survey. Those not in compliance with screening guidelines (n = 194) were included in the analyses. Logistic regression revealed that self-efficacy and strong supportive social influences were significantly associated with mammography intention (odds ratio [OR] = 2.50, OR = 2.22, respectively), adjusting for prior mammography use. Findings suggest that interventions designed to promote mammography should build women's confidence in their ability to discuss mammography with health providers and to obtain regular mammograms. Intervention among social networks may also be an effective means of promoting mammography.

Pim-2 transgene induces lymphoid tumors, exhibiting potent synergy with c-myc.

Evidence from proviral tagging experiments has suggested that pim-2 is similar in oncogenic behavior to its well characterized relative pim-1. While the basal expression in tissues differs, both genes are highly expressed in mitogenically stimulated hematopoietic cells and their transcription is induced in response to the same cytokines. Expression of a pim-2 transgene in lymphoid cells predisposed mice to T-cell lymphomas like those promoted by pim-1 transgenes. Moreover, strong collaboration with an E mu-myc transgene was manifested as pre-B cell leukemia in neonate bi-transgenic animals. Remarkably, this collaboration was attenuated but not prevented by X-inactivation of one of the transgenes. The addition of pim-2 to the fold increases the prominence of the pim proto-oncogene family in tumorigenesis.

Effects of blockade of fast and slow inward current channels on ventricular fibrillation in the pig heart.

OBJECTIVE: To determine the contribution of fast and slow inward channels to the electrocardiogram (ECG) of ventricular fibrillation. METHODS: Ventricular fibrillation was induced by endocardial electrical stimulation in pigs anaesthetised with pentobarbitone sodium (30 mg/kg intravenously). ECGs simultaneously recorded from the body surface (lead II) and from the endocardium were studied by power spectrum analysis (0-40 Hz). RESULTS: The mean (SEM) dominant frequency of fibrillation (9.0 (1.1) Hz in lead II at 0-40 s) did not change significantly with time in pigs given intravenous saline. However, the dominant frequency was significantly reduced by intravenous pretreatment with the class I antiarrhythmic drugs, lignocaine (3 mg/kg, 6.5 (0.5) Hz; 10 mg/kg, 4.2 (0.6) Hz), mexiletine (3 mg/kg, 6.2 (0.4) Hz; 10 mg/kg, 5.5 (0.4) Hz), and disopyramide (2.5 mg/kg, 5.4 (0.6) Hz). After flecainide (3 mg/kg, 6.9 (0.5) Hz) the reduction in frequency was not significant. Similar data were obtained with endocardial recordings. In contrast pre-treatment with verapamil (0.2 mg/kg, 11.7 (0.8) Hz; and 1.0 mg/kg, 12.9 (1.6) Hz) produced a significantly higher dominant frequency of fibrillation than saline and widened the bandwidth of frequencies around the dominant frequency. CONCLUSIONS: These results indicate that voltage-dependent sodium channel currents contribute to the rapid frequencies of ventricular fibrillation. Blockade of L-type inward calcium channel activity increases the fibrillation frequency and fractionates the frequencies of the fibrillation wavefronts.