Hypersensitivity to adrenergic stimulation after propranolol withdrawal in normal subjects

The cardiac response to isoproterenol after propranolol withdrawal was studied in six normal persons. Serial isoproterenol infusions were done before and after oral propranolol administration, 160 mg daily for 2 days. Changes in electromechanical systole corrected for heart rate (QS2I) and pulse pressure were used to assess the inotropic response to isoproterenol, and changes in heart rate were used to assess the chronotropic response. As shown in previous studies, the negative inotropic effect of propranolol lasted only 12 to 15 h, while the negative chronotropic effect lasted 24 to 36 h. After the disappearance of blockade a hypersensitivity to isoproterenol was found 24 to 48 h after propranolol withdrawal in all three measured determinants. The explanation of this phenomenon most likely lies in the nature of adrenergic receptors that become activated during long-term blockade.

Rapid GLC determination of propranolol in human plasma samples

A rapid GLC method for measuring plasma propranolol levels is reported. 4-Methylpropranolol was utilized as an internal standard. Pentafluoropropionate derivatives of propranolol and the internal standard eluted rapidly and gave good sensitivity under the conditions employed. The advantage of this procedure over previously reported methods is the speed of analysis, which is facilitated by rapid elution of contaminant peaks.

Negative inotropic effect of lidocaine in patients with coronary arterial disease and normal subjects

The effect of administration of lidocaine on left ventricular performance was studied using systolic time intervals in nine normal subjects, eight patients with stable angina, and 15 patients with acute myocardial infarction. The greatest response in systolic time intervals occurred at three minutes after intravenous injection of lidocaine (100 mg), with values returning to baseline at 10 to 15 minutes. Administration of lidocaine produced a significant prolongation of the preejection period (PEP) corrected for heart rate in all groups and a prolongation of the ratio of PEP to left ventricular ejection time (PEP/LVET) in patients with angina. The group with acute myocardial infarction exhibited a hyperadrenergic state, as shown by a short baseline QS2I. The QS I was lengthened by administration of lidocaine in all groups, but this was more profound in those with acute myocardial infarction. These changes in systolic time intervals were still present at two hours after injection in six patients with acute myocardial infarction in whom an infusion of lidocaine followed the initial bolus. The effect of administering lidocaine after intravenous injection of propranolol (5 mg) was also studied in six normal subjects. Although propranolol therapy along prolonged the PEP/LVET, a further significant prolongation followed subsequent injection of lidocaine.

Biliary secretion of methotrexate in rats and its inhibition by probenecid

The biliary secretion of methotrexate was investigated in rats under steady-state conditions. The transport system involved was saturable and displayed Michaelis-Menten-type kinetics. Values for the maximal rate of transport and a transport constant analogous to the Michaelis constant were 12 mg/hr and 32 mg/liter (7 x 10-5 M), respectively. The inhibition of this transport mechanism by probenecid also was investigated, and the relationship between the plasma concentration of probenecid and the biliary clearance of methotrexate was elucidated. The value of Ki, the dissociation constant for the transport carrier-inhibitor complex, was 23 mug/ml (8 x10-5 M).