[Acute effects of metoprolol on blood pressure and heart rate. Value of the nitroglycerin test].

The acute effects of Metoprolol on blood pressure and heart rate were studied with reference to the plasma level of the betablocker in 10 patients (6 male and 4 female) with permanent moderate uncomplicated hypertension. Each patient was given a single oral dose of 200 mg Metoprolol: blood samples were taken over a 12 hour period at given times for Metoprolol estimation. The blood pressure was measured with a mercury manometer; heart rate was measured lying and during a stress test (glyceryl trinitrate). The antihypertensive effect of Metoprolol was significant from the 4th hour; at the 8th hour the systolic pressure was reduced by 15% and the diastolic pressure by 17% (p less than 0.001). The blood pressure then rose progressively. The heart rate in the recumbent position fell 10 to 15% during the study. The heart rate during the trinitrin test varied linearly with time (r = 0.991, p less than 0.001). The variation in systolic and diastolic blood pressure did not correlate with the plasma Metoprolol level (r = 0.03, and 0.19); no correlation was found between the fall in lying heart rate and the plasma betablocker level. On the other hand, the trinitrin heart rate (at the end of the test) correlated negatively with the logarithm of the plasma Metoprolol (n = 56, r = 0.688, p less than 0.001). These results confirm that the antihypertensive effect of Metoprolol is not directly related to the plasma level of the betablocker. On the other hand, the betablocker effect assessed by the trinitrin test, correlated with the plasma Metoprolol level. This relationship is similar to those previously observed with other betablockers; atenolol and oxprenolol.