Reduced acetylation of procainamide by para-aminobenzoic acid

Beta-adrenergic stimulation enhances left ventricular diastolic performance in normal subjects

To determine the effects of beta-adrenergic stimulation on transmitral Doppler echocardiography flow characteristics of left ventricular diastolic filling, we studied 10 healthy volunteers aged 23-31 years (mean age, 26.6 years) during intravenous infusion of isoprenaline in consecutive steps of 0.1, 0.2, 0.4, 0.75, and 1.5 micrograms/min (each for 15 min). Saline control infusion was given in the same manner in a crossover and blinded protocol. Compared with the infusion of placebo, stepwise increasing doses of isoprenaline caused a dose-related increase in early and late diastolic filling velocities and velocity-time integrals, a lengthening of the acceleration time, and a shortening of the deceleration and filling time. The chosen method proved highly sensitive, as statistically significant changes were detectable at the lowest dose of 0.1 microgram/min for all variables except velocity-time integral of late filling and deceleration time (> or = 0.2 microgram/min). The effects related to dose in a log-linear fashion except for the lengthening of the acceleration time (early ceiling), the increase of peak early filling velocity (increased steepness at higher doses), and the shortening of the filling time. Inclusion of the associated increases in heart rate and systolic blood pressure and the decrease in diastolic blood pressure blunted all treatment contrasts except for the increase of peak early filling velocity. In addition, the hemodynamics with respect to heart rate and loading conditions were not altered at low dosages of drug (< 0.4 microgram/min). Effects of at least the peak early filling velocity must be interpreted as an active adrenergically mediated myocardial relaxation process. These findings have potentially important clinical implications for this noninvasive, readily available, and convenient technique in clinical pharmacology, stress testing, and possibly therapeutic interventions in diastolic dysfunction in humans.

Inhibition of N-acetylation of procainamide and renal clearance of N-acetylprocainamide by para-aminobenzoic acid in humans

Procainamide administration often results in excessively high serum N-acetylprocainamide (NAPA) concentrations and subtherapeutic serum procainamide concentrations. Inhibition of N-acetylation of procainamide may prevent accumulation of excessive NAPA while maintaining therapeutic serum procainamide concentrations. The purpose of this randomized, two-way crossover study was to determine if para-aminobenzoic acid (PABA) inhibits N-acetylation of procainamide in healthy volunteers. Eleven (7 female, 4 male) fast acetylators of caffeine received, in random order, PABA 1.5 g orally every 6 hours for 5 days, with a single intravenous dose of procainamide 750 mg administered over 30 minutes on the third day, or intravenous procainamide alone. Blood samples were collected during a 48-hour period after initiation of the infusion. Urine was collected over a 72-hour period. Serum procainamide and NAPA concentrations were analyzed using fluorescence polarization immunoassay. Urine procainamide and NAPA concentrations were measured with high performance liquid chromatography. PABA did not significantly influence total or renal procainamide clearance, elimination rate constant, AUC0-00, amount of procainamide excreted unchanged in the urine, or volume of distribution. However, concomitant PABA administration with procainamide resulted in increases in NAPA AUC0-00 and t1/2 and reductions in NAPA Ke, procainamide acetylation (NAPA formation) clearance, and NAPA renal clearance. Although PABA inhibits metabolic conversion of procainamide to NAPA, it also impairs the renal clearance of NAPA (but not procainamide) in healthy subjects. Therefore, PABA may not be useful for optimizing the safety of efficacy of procainamide in patients.

Left ventricular hypertrophy, compliance and ventricular filling

A total of 20 untreated hypertensive patients were divided into two equal groups matched for sex, age and blood pressure but with [mean diastolic wall thickness (MDWT) greater than 1.2 cm] or without (MDWT greater than 1.2 cm) left ventricular hypertrophy (LVH). All patients underwent pulsed doppler echocardiography and 99Tc radionuclide ventriculography at rest to assess diastolic and systolic abnormalities. In hypertensives with LVH the interventricular wall thickness, posterior wall thickness and relative diastolic wall thickness were significantly (P less than 0.01) higher and peak filling rate was significantly (P less than 0.01) lower than in hypertensives without LVH. The indices of systolic function, however, were not significantly different in the two patient groups. In hypertensives without LVH peak filling rate directly correlated with heart rate, whereas in those with LVH peak filling rate directly correlated with heart rate and the ratio of peak velocity of early left ventricular filling : peak velocity of late left ventricular filling due to atrial contraction. It is concluded that diastolic parameters may be useful tools for assessing myocardial compliance and may be effective markers of diastolic dysfunction.

Noninvasive evaluation of left ventricular diastolic function in patients with angina pectoris--pulsed Doppler echocardiographic technique

To assess the disturbed left ventricular diastolic filling by pulsed Doppler echocardiography in patients with angina pectoris who have normal systolic function, 55 subjects (33 angina patients with, 22 control subjects without significant (⩾75%) coronary artery narrowing) underwent pulsed Doppler echocardiography examination one day before coronary arteriography. From analysis of the transmitral flow velocity curve, diastolic time intervals, peak early and late atrial flow velocities, the ratio of early to atrial peak flow velocity, and deceleration slope after peak early flow velocity were measured. The angina group had a significantly higher peak atrial flow velocity (50.1 ± 10.0 cm/sec vs. 43.7 ± 9.0, p<0.05) and a lower ratio of early to atrial peak flow velocity (0.91 ± 0.24 vs. 1.17 ± 0.30, p<0.005), but peak early flow velocity, deceleration slope, and diastolic time intervals were similar in both groups. Therefore, the pulsed Doppler technique using the transmitral flow velocity curve is thought to be useful in the noninvasive evaluation of diastolic function even in patients with angina pectoris who have normal systolic function and no left ventricular hypertrophy.