Locomotor sensitization to intermittent ketamine administration is associated with nucleus accumbens plasticity in male and female rats.

Clinical evidence suggests superior antidepressant response over time with a repeated, intermittent ketamine treatment regimen as compared to a single infusion. However, the club drug ketamine is commonly abused. Therefore, the abuse potential of repeated ketamine injections at low doses needs to be investigated. In this study, we investigated the abuse potential of repeated exposure to either 0, 2.5, or 5 mg/kg ketamine administered once weekly for seven weeks. Locomotor activity and conditioned place preference (CPP) were assayed to evaluate behavioral sensitization to the locomotor activating effects of ketamine and its rewarding properties, respectively. Our results show that while neither males nor females developed CPP, males treated with 5 mg/kg and females treated with either 2.5 or 5 mg/kg ketamine behaviorally sensitized. Furthermore, dendritic spine density was increased in the NAc of both males and females administered 5 mg/kg ketamine, an effect specific to the NAc shell (NAcSh) in males but to both the NAc core (NAcC) and NAcSh in females. Additionally, males administered 5 mg/kg ketamine displayed increased protein expression of ΔfosB, calcium calmodulin kinase II alpha (CaMKIIα), and brain-derived neurotrophic factor (BDNF), an effect not observed in females administered either dose of ketamine. However, males and females administered 5 mg/kg ketamine displayed increased protein expression of AMPA receptors (GluA1). Taken together, low-dose ketamine, when administered intermittently, induces behavioral sensitization at a lower dose in females than males, accompanied by an increase in spine density in the NAc and protein expression changes in pathways commonly implicated in addiction.

Treating lung inflammation with agonists of the adenosine A2A receptor: promises, problems and potential solutions.

Adenosine A(2A) receptor agonists may be important regulators of inflammation. Such conclusions have come from studies demonstrating that, (i) adenosine A(2A) agonists exhibit anti-inflammatory properties in vitro and in vivo, (ii) selective A(2A) antagonists enhance inflammation in vivo and, (iii) knock outs of this receptor aggravate inflammation in a wide variety of in vivo models. Inflammation is a hallmark of asthma and COPD and adenosine has long been suggested to be involved in disease pathology. Two recent publications, however, suggested that an inhaled adenosine A(2A) receptor agonist (GW328267X) did not affect either the early and late asthmatic response or symptoms associated with allergic rhinitis suggesting that the rationale for treating inflammation with an adenosine A(2A) receptor agonist may be incorrect. A barrier to fully investigating the role of adenosine A(2A) receptor agonists as anti-inflammatory agents in the lung is the side effect profile due to systemic exposure, even with inhalation. Unless strategies can be evolved to limit the systemic exposure of inhaled adenosine A(2A) receptor agonists, the promise of treating lung inflammation with such agents may never be fully explored. Using strategies similar to that devised to improve the therapeutic index of inhaled corticosteroids, UK371,104 was identified as a selective agonist of the adenosine A(2A) receptor that has a lung focus of pharmacological activity following delivery to the lung in a pre clinical in vivo model of lung function. Lung-focussed agents such as UK371,104 may be suitable for assessing the anti-inflammatory potential of inhaled adenosine A(2A) receptor agonists.

Canine tricuspid valve malformation, a model of human Ebstein anomaly, maps to dog chromosome 9.

BACKGROUND: Ebstein anomaly of the tricuspid valve is a congenital cardiac malformation characterised by downward displacement of the attachment of the septal and posterior leaflets of the tricuspid valve. Canine tricuspid valve malformation (CTVM) is morphologically similar to Ebstein anomaly; familial occurrence of CTVM has been described. Several observations suggest a genetic cause but most cases appear to be sporadic. METHODS: Three purebred Labrador Retriever kindreds enriched for CTVM underwent clinical examination and echocardiography. DNA was extracted from whole blood. Genotyping was carried out using polymorphic repeat markers with an average spacing of 15 cM and polymorphic information content of 0.74. RESULTS: Pedigree analysis identified CTVM segregating as an autosomal dominant trait with reduced penetrance. Genome wide linkage analysis in one kindred identified a CTVM susceptibility locus on dog chromosome 9 (CFA9) with a maximum multipoint lod score of 3.33. The two additional kindreds showed a conserved disease haplotype. CONCLUSIONS: This study identifies a CTVM susceptibility locus on CFA9 and a founder effect in apparently unrelated Labrador Retriever kindreds. These results provide the basis for a positional candidate cloning effort to identify the CTVM disease gene. Identification of the CTVM gene will permit mutation screening of patients with Ebstein anomaly, which should provide additional insights into the genetic programmes of valve development.

In vitro and in vivo activity of 1-O-hexadecylpropanediol-3-phospho-ganciclovir and 1-O-hexadecylpropanediol-3-phospho-penciclovir in cytomegalovirus and herpes simplex virus infections.

Human cytomegalovirus (HCMV) and herpes simplex virus (HSV) can cause a wide variety of clinical manifestations in man. Ganciclovir (GCV) is effective against HCMV infection when administered by the intravenous route and may be used orally in large doses for prophylaxis of HCMV infections in organ transplantation patients and in AIDS patients. In previous studies with acyclovir (ACV), we found that covalent attachment of an alkyl glycerol phosphate moiety greatly increased oral bioavailability and increased antiviral activity against hepatitis B virus. Adducts of ACV with alkyl propanediol phosphate were more active than the alkyl glycerol phosphate analogue in vitro in 2.2.15 cells, which constitutively produce hepatitis B virus. To see if this strategy would work for two other poorly absorbed nucleoside analogues, we synthesized 1-O-hexadecylpropanediol-3-phospho-GCV (HDP-P-GCV) and 1-O-hexadecyl-propanediol-3-phospho-penciclovir (HDP-P-PCV), and evaluated the in vitro antiviral activity, selectivity and oral antiviral activity of both compounds versus GCV or PCV in mice infected with HSV-1 or HDP-P-GCV versus murine cytomegalovirus (MCMV). HDP-P-GCV is orally active in both MCMV and HSV-1 infection in mice with antiviral activity equivalent to (HSV-1) or greater than oral GCV (MCMV). Oral HDP-P-PCV was more active than PCV orally versus intranasal HSV-1 infection in mice.

Synthesis and antiviral evaluation of 1-O-hexadecylpropanediol-3-P-acyclovir: efficacy against HSV-1 infection in mice.

We synthesized, 1-O-hexadecylpropanediol-3-P-acyclovir, an orally bioavailable lipid prodrug of acyclovir and evaluated it for in vitro and in vivo activity against herpes simplex virus infections. Although 1-O-hexadecylpropanediol-3-P- acyclovir was less active in vitro than acyclovir, on a molar basis it was 2.4 times more active orally in preventing mortality from acute HSV-1 infection in mice. In vitro, 1-O-hexadecylpropanediol-3-P-acyclovir was also more active than acyclovir in a thymidine kinase negative mutant strain of HSV-1 (DM21) and had somewhat higher activity in cytomegalovirus infection in vitro due to it's ability to bypass thymidine kinase.

Radiofrequency catheter ablation of atrioventricular accessory pathways in 3 dogs with subsequent resolution of tachycardia-induced cardiomyopathy.

Incessant supraventricular tachyarrhythmias are known to result in myocardial dysfunction indistinguishable from idiopathic dilated cardiomyopathy by current testing methods. This tachycardia-induced cardiomyopathy (TICM), however, is uniquely reversible with adequate rhythm control. Two dogs were presented to The Ohio State University for incessant supraventricular tachycardia (SVT) and echocardiographic signs of dilated cardiomyopathy, later proven to be TICM. A 3rd dog presented for frequent paroxysms of SVT and syncope had echocardiographic signs of mild myocardial systolic dysfunction. All 3 dogs had inadequate rhythm control with multiple antiarrhythmic agents, and 1 dog suffered from recurrent left-sided congestive heart failure. Generalized cardiomegaly was found in 1 dog and left-sided dilatation without concurrent right-sided enlargement in 1 dog. Mild-to-severe left ventricular systolic dysfunction was confirmed echocardiographically in all dogs. A total of 4 atrioventricular accessory pathways (APs) were found during invasive electrophysiologic studies in these 3 dogs. All APs were successfully ablated with radiofrequency energy delivered through a thermistor-tipped catheter. Elimination of AP conduction, and thus orthodromic atrioventricular reciprocating tachycardia, resulted in resolution of all clinical and echocardiographic evidence of TICM in these dogs. This result confirms that the cardiomyopathy was, in fact, reversible TICM. All cardiovascular medications were discontinued, and no complications occurred during a 15-25-month follow-up period.

Peritoneal effusion in cats: 65 cases (1981-1997).

OBJECTIVE: To determine signalment, diagnoses, presence of effusions in multiple sites, and outcome in cats with peritoneal effusion. DESIGN: Retrospective case series. ANIMALS: 65 cats. PROCEDURE: Medical records from 1981 to 1997 were reviewed to obtain information on cats with peritoneal effusion identified on physical examination, radiographs, abdominal ultrasonograms, or at necropsy. RESULTS: Conditions most commonly associated with peritoneal effusion in cats, in order of frequency, were cardiovascular disease, neoplasia, hepatic disease, renal disease, feline infectious peritonitis, peritonitis attributable to other causes, and urinary tract trauma. Dilated cardiomyopathy (DCM) was the most common disease associated with peritoneal effusion; however, DCM was diagnosed in most of these cats before taurine deficiency was found to be a primary cause of this form of cardiomyopathy in cats. Neoplasia was the most common cause after 1987. Right-sided congestive heart failure was the most commonly associated disorder in cats < 1 year old, whereas neoplastic disease was more common with increasing age. Most effusions were detected during the initial physical examination and were modified transudates. Peritoneal effusion was commonly accompanied by fluid accumulation elsewhere, particularly pleural effusion. The prognosis for a cat with abdominal effusion in this study was poor (mean survival time, 21 days; range, 1 to 350 days; median, 2.5 days). CLINICAL IMPLICATIONS: The primary differential diagnosis for peritoneal effusion in cats is neoplastic disease in older cats and right-sided heart failure in kittens. Diseases associated with peritoneal effusion generally have poor prognoses.

Retrograde coronary venous infusion of ethanol for ablation of canine ventricular myocardium.

INTRODUCTION: Permanent cure of reentrant ventricular tachycardia (VT) associated with coronary artery disease is difficult to achieve. Retrograde coronary venous infusion of ethanol for ablation of ventricular myocardium associated with reentrant tachyarrhythmias has several potential advantages, including use of physiologic mapping techniques and production of deeper, wider necrotic zones. METHODS AND RESULTS: Nine anesthetized dogs had baseline hemodynamic measurement, left ventriculography, coronary arteriography, occlusive coronary venography, and programmed electrical stimulation of the right ventricular apex and outflow tract. A balloon-tipped infusion catheter was advanced into a distal coronary venous branch, the balloon slowly inflated, and pure ethanol infused at volumes of 1.5, 3, or 5 cc. Hemodynamic measurements, angiography, ventriculography, and programmed electrical stimulation were repeated immediately and 1 week following ablation. Formalin-perfused hearts were serially sectioned and lesion volumes determined. Histologic examination of ablation beds then was performed. No significant difference was found in any hemodynamic measurement before or after ablation. Coronary arteriograms and left ventriculograms were unchanged after ablation. Nonsustained VT occurred in eight dogs during ethanol infusion; however, VT was not inducible in any dog before or after ablation. Infusion volumes of 3 cc or more were required to produce transmural lesions. CONCLUSION: Retrograde coronary venous infusions of ethanol using a balloon-tipped infusion catheter were effective in ablating ventricular myocardium. Retrograde chemical ablation did not itself result in inducible VT or adversely affect hemodynamic measurements or coronary arteries. Transmural myocardial necrosis, necessary in the ablation of VT associated with coronary artery disease, can be produced by higher infusion volumes.

Noncirrhotic portal hypertension and nodular regenerative hyperplasia of the liver in dogs with mucopolysaccharidosis type I.

Nodular regenerative hyperplasia (NRH) is an uncommon hepatic lesion often associated with noncirrhotic portal hypertension (PHT). We have noted that NRH and PHT are frequent occurrences in a colony of dogs with the genetic storage disease, mucopolysaccharidosis I (MPS-I). This observation provides the opportunity to study the histology and pathogenesis of NRH and noncirrhotic PHT in a new animal model. Thirteen of 32 dogs (41%) with MPS-I developed multiple portocaval shunts between 4 and 48 months of age that were grossly visible at necropsy. Seven of the 13 developed marked ascites, whereas all those without shunts and littermates (n = 24) heterozygous for the mutated alpha-L-iduronidase allele (carriers unaffected by the storage disease) did not. The large and medium-sized portal veins were widely patent without thrombosis or vascular malformations. Hepatic parenchymal fibrosis was absent or mild and did not correlate with shunt formation. All 32 livers had varying degrees of diffuse periportal hepatocellular hyperplasia with multifocal atrophy and compression of centrolobular cords (NRH) most prominent in dogs with shunts. Many small portal veins were reduced in diameter or absent, especially in animals with shunts. Noncirrhotic PHT and NRH appear to be related to the obliteration of small portal veins in these dogs, but the pathogenesis of this vascular change remains unknown.

Alkylthioglycerol prodrugs of foscarnet: synthesis, oral bioavailability and structure-activity studies in human cytomegalovirus-, herpes simplex virus type 1- and human immunodeficiency virus type 1-infected cells.

In a previous study, we reported that 1-O-octadecyl-sn-glycero-3-foscarnet (ODG-PFA) was 40 to 93 times more potent than free foscarnet (PFA) in human cytomegalovirus (HCMV)-, herpes simplex virus type 1 (HSV-1)- and human immunodeficiency virus type 1 (HIV-1)-infected cells. To evaluate the effect of substituting a 1-S-alkyl thioether for a 1-O-alkyl ether, we synthesized a series of PFA conjugates of 1-S-alkyl-sn-thioglycerols with varied 1-S-alkyl chain lengths. To establish structure-activity relationships we measured the in vitro antiviral activity of liposomal formulations of the drugs in cells infected with HCMV, HSV-1 or HIV-1. The optimum 1-S-alkyl chain length in the series was 16 to 18 carbon atoms. We compared the antiviral activity of 16- and 18-carbon alkyl thioglycerol versus alkylglycerol prodrugs and did not observe any significant differences in their antiviral activities. The series' most active member, 1-S-octadecyl-sn-glycero-3-foscarnet (ODSG-PFA) was 56-, eight- and 45-fold more active than PFA in HCMV-, HSV-1- and HIV-1-infected cells in vitro. The oral absorption of PFA and 1-S-octadecyl-sn-thioglycero-3-PFA was compared in mice by measuring plasma levels of 14C after oral administration of radiolabelled compounds. The peak plasma level of 14C was sevenfold higher following administration of [14C]ODSG-PFA than following an equimolar dose of [14C]PFA. Area-under-the-curve was 23-fold greater for ODSG-PFA than for PFA. Like previously reported alkyloxyether-lipid PFA conjugates, alkylthioether conjugates provided enhanced antiviral activity and oral bioavailability. However, S-ether conjugates may be metabolized differently than O-ether conjugates. More detailed in vivo pharmacokinetic evaluation of the alkyl-thioether-PFA conjugates is required.

Forearm vasoconstriction during dynamic leg exercise in patients with chronic heart failure.

Previous studies assessing vascular responses in nonexercising beds during exercise in patients with chronic heart failure (CHF) have yielded varying results. We proposed that the clinical and hemodynamic severity of heart failure may explain some of the variation. We reasoned that diastolic ventricular interaction (DVI), by limiting the ability of such patients to increase left ventricular (LV) volume and stroke volume during exercise, would attenuate baroreflex activation, resulting in increased sympathetic activation and hence exaggerated vasoconstriction. We hypothesized therefore that vasoconstriction in nonexercising beds would be exaggerated in patients with symptomatic and hemodynamically severe heart failure, particularly if associated with DVI. We measured forearm vascular resistance (FVR) during semierect cycle exercise in 22 CHF patients and 23 control subjects. DVI was assessed by measuring changes in ventricular volumes (radionuclide ventriculography) during volume unloading (-30 mm Hg lower-body negative pressure) in the heart failure patients and was inferred when LV end-diastolic volume paradoxically increased. Patients with symptoms of heart failure developed larger increases in FVR during exercise than did asymptomatic patients. There were significant correlations between the change in FVR during peak exercise and the resting mean pulmonary arterial pressure and pulmonary vascular resistance. CHF patients with DVI developed exaggerated increases in FVR (median [25th to 75th percentile]) compared with the remaining patients during low-workload exercise (138 [66 to 171] vs 6.4 [-4.3 to 28] units, P = 0.002) and during peak exercise (160 [90 to 384] vs 61 [-7.4 to 75] units, P < 0.02). Vasoconstriction in nonexercising beds is exaggerated in CHF patients with clinically and hemodynamically severe heart failure, particularly if associated with DVI. This may explain some of the reported variation in the degree of sympathetic activation that occurs during exercise in CHF patients.

Enhanced oral absorption and antiviral activity of 1-O-octadecyl-sn-glycero-3-phospho-acyclovir and related compounds in hepatitis B virus infection, in vitro.

Acyclovir (ACV) triphosphate and azidothymidine (AZT) triphosphate inhibit the DNA polymerase of human hepatitis B virus (HBV) by 50% at submicromolar concentrations, but no effects of ACV or AZT treatment have been noted on the clinical manifestations of hepatitis B. We synthesized 1-O-octadecyl-sn-glycero-3-phospho-acyclovir (ODG-P-ACV), 1-O-hexadecylpropanediol-3-phospho-acyclovir (HDP-P-ACV), and 1-O-octadecyl-sn-glycero-3-phospho-azidothymidine (ODG-P-AZT), and evaluated their antiviral activity in human hepatoma cells that constitutively produce HBV (2.2.15 cells). ACV and AZT up to 100 microM caused only slight inhibition of HBV replication in 2.2.15 cells. However, HDP-P-ACV and ODG-P-ACV inhibited viral replication by 50% at 0.5 and 6.8 microM, respectively. ODG-P-AZT also showed increased antiviral activity, with a 50% reduction in HBV replication at 2.1 microM. Based on the EC50, HDP-P-ACV, ODG-P-ACV, and ODG-P-AZT were > 200, > 14.7, and > 48 times more active than their free nucleosides in reducing HBV replication in 2.2.15 cells. To evaluate the biochemical basis for the increased antiviral activity, we studied the uptake and metabolism of 1-O-octadecyl-sn-glycero-3-phospho-[3H]acyclovir (ODG-P-[3H]ACV) in HepG2 cells. Cellular uptake of ODG-P-[3H]ACV was found to be substantially greater than that of [3H]ACV, and cellular levels of ACV-mono-, -di-, and -triphosphate were much higher with ODG-P-ACV. ODG-P-[3H]ACV was well absorbed orally. Based on urinary recovery of tritium after oral or parenteral administration of the radiolabeled compounds, oral absorption of ODG-P-ACV in mice was 100% versus 37% for ACV. ODG-P-ACV plasma area under the curve was more than 7-fold greater than that of ACV. Lipid prodrugs of this type may be useful orally in treating viral diseases.

Diastolic ventricular interaction: a possible mechanism for abnormal vascular responses during volume unloading in heart failure.

BACKGROUND: Baroreflex dysfunction is common in chronic heart failure and contributes to the associated sympathoexcitation. Baroreceptor activity normally decreases during volume unloading, causing an increase in sympathetic outflow and resulting in forearm vasoconstriction. Some heart failure patients develop attenuated vasoconstriction or paradoxical vasodilation. The mechanism for this is unknown. We have recently demonstrated diastolic ventricular interaction in some patients with chronic heart failure as evidenced by increases in left ventricular (LV) end-diastolic volume in association with decreases in right ventricular (RV) volume during volume unloading. We reasoned that such an increase in LV volume, by increasing LV mechanoreceptor activity, would decrease sympathetic outflow and could therefore explain the abnormal vascular responses seen in such patients. METHODS AND RESULTS: We assessed changes in forearm vascular resistance (FVR) during application of -20 and -30 mm Hg lower-body negative pressure (LBNP) in 24 patients with chronic heart failure and 16 control subjects. Changes in LV and RV end-diastolic volumes were assessed during -30 mm Hg LBNP in all heart failure patients. Diastolic ventricular interaction was demonstrated in 12 patients as evidenced by increases in LV end-diastolic volume in association with decreases in RV end-diastolic volume during LBNP. Changes in FVR during LBNP (-20 and -30 mm Hg) were markedly attenuated in these 12 patients (-1.6+/-11.2 and -0.9+/-12.5 U) compared with both the remaining patients (11.9+/-10.0 and 17.0+/-12.3 U) and the control subjects (16.5+/-9.5 and 23.1+/-13.9 U) (P<.01 for both comparisons at each level of LBNP). FVR decreased in 5 of these 12 patients during -30 mm Hg LBNP, a response seen in none of the remaining patients (P=.01). CONCLUSIONS: Diastolic ventricular interaction in patients with chronic heart failure is associated with attenuated forearm vasoconstriction or paradoxical vasodilation during LBNP. This may explain the apparent derangement in baroreflex control of sympathetic outflow during acute volume unloading in heart failure.

Cardiac electrophysiologic measurements in dogs before and after intravenous administration of atropine and propranolol.

OBJECTIVES: To assess baseline cardiac electrophysiologic (EP) measurements in dogs undergoing a clinically used anesthetic protocol, and to study the effects of i.v. administered atropine and propranolol on these EP variables. ANIMALS: 15 adult dogs with cardiac function within reference ranges, as assessed by physical examination, electrocardiography, and echocardiography. PROCEDURE: 13 cardiac EP variables were measured in isofluorane-anesthetized dogs before and after i.v. administration of atropine and propranolol. Multipolar electrode catheters were positioned against the endocardium of the dorsal portion of the right atrium, His bundle region, and right ventricular apex. Incremental pacing and pacing-extrastimulus techniques were used to obtain EP measurements of the sinoatrial node, atrioventricular node, and atrial and ventricular myocardia in the control state and after i.v. administration of 0.04 mg of atropine and 0.2 mg of propranolol/kg of body weight. RESULTS: Only the atrial effective refractory period changed significantly after muscarinic and beta-adrenergic receptor antagonism. Marked individual variation in response to these agents, however, was apparent. Two dogs had substantial decreases in sinoatrial and/or atrioventricular nodal measurements, and 7 dogs had notable increases in atrioventricular nodal measurements. CONCLUSIONS: Cardiac EP measurements vary widely among clinically normal, isofluorane-anesthetized dogs. Individual dogs can have variable degrees of autonomic tone, which can be minimized by pharmacologic receptor antagonism. CLINICAL RELEVANCE: Although effects of receptor antagonism at clinically applicable dosages were not significant for 12 of 13 measurements, withdrawal of vagal tone can induce marked EP changes and may be important during a clinical study.

Effusive-constrictive pericardial disease secondary to osseous metaplasia of the pericardium in a dog.

Osseous metaplasia of the pericardium causing effusive-constrictive pericardial disease has not, to our knowledge, been reported in dogs. Clinical signs of right-sided congestive heart failure prompted examination of the dog of this report. Documented causes of constrictive pericardial disease in dogs include trauma and actinomycotic, mycobacterial, and fungal infections. These causes were ruled out in this dog. Immune-mediated disorders, as have been reported in people, also were considered unlikely on the basis of test results. It was concluded that this dog had idiopathic osseous metaplasia of the pericardium and pleura. Signs of right-sided congestive heart failure resolved after subtotal pericardiectomy was performed.

Liver-targeted antiviral nucleosides: enhanced antiviral activity of phosphatidyl-dideoxyguanosine versus dideoxyguanosine in woodchuck hepatitis virus infection in vivo.

It would be desirable to develop antiviral agents that can be targeted to liver to enhance their antiviral effects and reduce nonhepatic toxicity. 2',3'-Dideoxyguanosine (ddG) has been found to be a potent and selective antihepatitis B agent both in vitro and in vivo. To evaluate ddG and its liver-targeted analog, we synthesized a series of phosphatidyl-ddGs and incubated them with 2.2.15 cells, which chronically produce hepatitis B virus. 1,2-Dipalmitoylphosphatidyl-dideoxyguanosine (DPP-ddG) inhibited the production of hepatitis B virus (HBV) DNA in the culture medium by 90% at 4.5 mumol/L versus 9.1 mumol/L for ddG, while the liposome vehicle itself had no effect. To compare the efficacy of free ddG with its lipid prodrug in vivo, we treated woodchucks that were experimentally infected with woodchuck hepatitis virus (WHV) for 4 weeks by intraperitoneal injection of 2.6 mumol/kg/d of free ddG or liposomes containing 2.6 mumol/kg/d of DPP-ddG. Liposomal DPP-ddG reduced serum WHV DNA by 23- to 46-fold at the end of the fourth week, while free ddG reduced serum WHV DNA by 2.2- to 10.4-fold. Treatment with small unilamellar liposomes containing DPP-ddG is substantially more effective than free ddG in reducing WHV-DNA levels in serum in WHV-infected woodchucks. The data suggest that the use of lipid prodrugs to target the liver may be useful in enhancing antiviral therapy of hepatitis.

Transcatheter modification of the atrioventricular node in dogs, using radiofrequency energy.

OBJECTIVE: To develop a protocol for reliably inducing atrioventricular (AV) block (ideally first- or second-degree), using radiofrequency energy. DESIGN: An electrosurgical unit was coupled to an ammeter, which was connected to the distal pole of an electrode catheter positioned at the AV node. Control settings had previously been calibrated to the power output in a circuit with a 100-ohm resistance. ANIMALS: 10 clinically normal dogs. PROCEDURE: Transcatheter AV nodal modification was attempted, using progressive power applications of 10 to 20 W for progressive durations of 10 to 30 seconds. Atrioventricular nodal conduction and refractivity were measured before and 20 minutes and 1 month after ablation. Electrocardiograms were monitored throughout the 1-month period. RESULTS: Eight of the 10 dogs developed complete AV block, I developed stable 2:1 AV block, and another had no long-term change in AV nodal conduction. Four dogs attained their maximal degree of AV block in 2 to 5 days. Three of these had no AV nodal conduction changes until 2 to 4 days after ablation. CONCLUSIONS: An electrosurgical unit can be economically modified for radiofrequency transcatheter ablation. Stable, incomplete AV block was rarely induced using this protocol, whereas complete AV block often developed. A major finding was frequent delay between energy delivery to the AV nodal region and induction of AV block. CLINICAL RELEVANCE: Induction of complete AV block using this technique, followed by permanent pacemaker placement, is an effective alternative to long-term antiarrhythmic treatment in animals with chronic atrial arrhythmias. Transcatheter ablation could be used to treat other forms of tachycardia, as it is in human medicine.