Correlation between verapamil plasma concentration and P-R prolongation in essential hypertension

Transgenic mice over-expressing ET-1 in the endothelial cells develop systemic hypertension with altered vascular reactivity

Endothelin-1 (ET-1) is a potent vasoconstrictor involved in the regulation of vascular tone and implicated in hypertension. However, the role of small blood vessels endothelial ET-1 in hypertension remains unclear. The present study investigated the effect of chronic over-expression of endothelial ET-1 on arterial blood pressure and vascular reactivity using transgenic mice approach. Transgenic mice (TET-1) with endothelial ET-1 over-expression showed increased in ET-1 level in the endothelial cells of small pulmonary blood vessels. Although TET-1 mice appeared normal, they developed mild hypertension which was normalized by the ET(A) receptor (BQ123) but not by ET(B) receptor (BQ788) antagonist. Tail-cuff measurements showed a significant elevation of systolic and mean blood pressure in conscious TET-1 mice. The mice also exhibited left ventricular hypertrophy and left axis deviation in electrocardiogram, suggesting an increased peripheral resistance. The ionic concentrations in the urine and serum were normal in 8-week old TET-1 mice, indicating that the systemic hypertension was independent of renal function, although, higher serum urea levels suggested the occurrence of kidney dysfunction. The vascular reactivity of the aorta and the mesenteric artery was altered in the TET-1 mice indicating that chronic endothelial ET-1 up-regulation leads to vascular tone imbalance in both conduit and resistance arteries. These findings provide evidence for the role of spatial expression of ET-1 in the endothelium contributing to mild hypertension was mediated by ET(A) receptors. The results also suggest that chronic endothelial ET-1 over-expression affects both cardiac and vascular functions, which, at least in part, causes blood pressure elevation.

Adult heart block is associated with disease activity in primary Sjögren's syndrome

OBJECTIVES

Congenital heart block occurring in the foetus and neonate may be associated with maternal anti-SS-A/anti-SS-B autoantibodies (anti-SSA/anti-SSB). The adult atrioventricular node is generally thought to be resistant to the damaging effects of anti-SSA/anti-SSB. However, case reports suggest that heart block developing in adult Sjögren's syndrome (SS) patients may be associated with these autoantibodies. Therefore, we investigated the relationship between serum antibodies and heart block in adult SS patients.

METHODS

We abstracted data from clinic patient records. Diagnosis of primary SS was based on American-European classification criteria. Electrocardiograms (EKGs), laboratory immunology parameters, lipid profiles, and focus scores from labial salivary gland biopsies were available for 51 SS patients. Fifteen patients had follow-up EKGs. PR interval200 ms was considered to be first-degree heart block.

RESULTS

Five patients showed prolonged PR intervals; the presence of heart block was not related to the presence of anti-SSA antibodies. However, significant differences between patients with prolonged and normal PR intervals were seen for mean focus scores (p<0.0001), anti-cardiolipin immunoglobulin IgG (p = 0.0009), age (p = 0.01), IgG (p = 0.02), anti-SSB antibodies (p = 0.02), and high density lipoprotein (HDL) cholesterol levels (p = 0.03). These parameters correlated with prolonged PR intervals.

CONCLUSIONS

These results suggest an association between disease activity, the presence of anti-SSB antibodies, and the occurrence of first-degree heart block in adults with primary SS.

Efficacy of the novel calcium antagonist R(+)-semotiadil in limiting the ventricular rate during atrial flutter in isolated guinea pig hearts

Ca2+ antagonists slow the ventricular rate by blocking conduction in the anterograde direction through the atrioventricular (AV) node. The aim of this study was to investigate the efficacy of the novel Ca2+ antagonist semotiadil compared with verapamil and diltiazem on the filtering capacity of the AV node during simulated atrial flutter in isolated guinea-pig hearts perfused by the method of Langendorff. During sinus rhythm, semotiadil as well as verapamil and diltiazem induced comparable depressant effects on AV-nodal conduction time and, during tachycardia, a comparable enhancement of this effect. The time constant (tau-on) for the drug-specific rate-dependent effect on AV-nodal conduction slowing was longest in the presence of verapamil compared with the long tau-on of semotiadil and the short tau-on of diltiazem. Verapamil and semotiadil exhibited a significantly greater effect than diltiazem on the mean ventricular cycle length (VCLmeun), on the maximal ventricular cycle length (VCLmax) and on the standard deviation of the VCL (SD(VCL)) during atrial flutter. Therefore the kinetics of the rate adaptation of AV-nodal conduction time in the presence of Ca2+ antagonists predicts the filtering capacity of the AV node during atrial flutter. Semotiadil has a verapamil type of action on ventricular cycle length during atrial flutter, whereas the disadvantageous prolongation of maximal VCL as well as the dispersion of VCL with semotiadil was only about half those found with verapamil.

Effects of verapamil and diltiazem on the ventricular rate during simulated atrial flutter in isolated guinea pig hearts

To compare the direct effects of verapamil and diltiazem on the ventricular rate during atrial flutter, we developed an atrial flutter model in guinea pig isolated hearts. Atrial flutter was simulated by rapid atrial pacing (cycle length = 50 ms). At this atrial pacing cycle length, the shape of the frequency of distribution of the ventricular cycle lengths was comparable to that during spontaneous atrial flutter. Verapamil (0.01, 0.03 microM) and diltiazem (0.03, 0.09 microM) caused a comparable prolongation of the atrioventricular conduction time and atrioventricular refractoriness. Also, the anterograde Wenckebach cycle length was increased to a comparable degree by both substances. The mean ventricular cycle length during atrial flutter was comparable prolonged by both substances. The prolongation of the maximal ventricular cycle length was significantly more pronounced in the presence of verapamil. The time dependence of drug-induced alterations in atrioventricular conduction time during abrupt changes of heart rate is significantly more pronounced in the presence of verapamil compared to diltiazem. In conclusion, the more pronounced effect of verapamil on the maximal ventricular cycle length compared to the action of diltiazem may be explained by the slow binding kinetic of this drug to the Ca2+ channel resulting in a longlasting blockade of the Ca2+ channel.

Comparison of the electrophysiologic effects of oral sustained-release and intravenous verapamil in patients with paroxysmal supraventricular tachycardia

The electrophysiologic effects of intravenous verapamil (0.15 mg/kg) and oral sustained-release verapamil (verapamil-SR) (240 mg once daily for 7 days) were studied in 17 patients with paroxysmal supraventricular tachycardia (SVT). Ten patients had atrioventricular (AV) nodal reentrant tachycardia and 7 had AV reciprocating tachycardia involving an accessory AV pathway. Both preparations significantly prolonged anterograde effective refractory period of the AV node and depressed the retrograde AV nodal conduction system. The sinus cycle length, and atrial and ventricular effective refractory periods were prolonged after oral verapamil-SR. Furthermore, oral verapamil-SR depressed retrograde accessory pathway conduction which was not interfered with by intravenous verapamil. Intravenous verapamil and oral verapamil-SR prevented induction of sustained SVT in 12 of 17 (71%) and 10 of 17 (59%) patients, respectively. Follow-up study with oral verapamil-SR 240 mg once daily in 15 patients for 19 +/- 6 months revealed that among the 8 patients without induction of sustained SVT, 7 have been free of symptomatic arrhythmia; only 1 patient had occasional SVT attacks. For the 7 patients with induction of sustained SVT, 3 patients failed to respond to oral verapamil-SR, 1 patient became symptom free, and the remaining 3 patients had less frequent SVT attacks. Thus, immediate intravenous verapamil testing predicts the electrophysiologic results of oral verapamil-SR therapy, and oral verapamil-SR once daily may be used for long-term prophylaxis of SVT with better patient compliance.

Influence of short term verapamil treatment on glucose metabolism in patients with non-insulin dependent diabetes mellitus

The effect of a sustained-release verapamil preparation on glucose metabolism was investigated in 10 patients with non-insulin dependent diabetes mellitus. In a single blind cross-over study verapamil 240 mg b.d. for 1 week lowered fasting plasma glucose from a mean value of 11.6 mmol/l to 10.3 mmol.l-1, and the fasting glucose appearance rate was decreased from 1.5 to 1.2 mmol.min-1. The decrease in fasting plasma glucose and glucose appearance rate was not related to the steady state plasma concentration of verapamil, nor-verapamil and the metabolites D.617 and D.620. After oral glucose administration a tendency to lower plasma glucose values was found after verapamil administration. Plasma insulin, C-peptide, total and C-terminal glucagon were not significantly different in the placebo and the verapamil studies, neither in the fasting state nor after glucose. It is concluded that brief verapamil treatment decreases fasting plasma glucose and glucose turn-over in non-insulin dependent diabetics, possibly by inhibition of gluconeogenesis.