The relationship between PPC and its effect on minoxidil-induced increases in PHA and heart rate was examined in 9 patients with essential hypertension. Concomitant with the minoxidil-induced depression of mean arterial pressure (30.7 ± 3.5 mm Hg, mean ± SEM), heart rate increased from 79.1 ± 3.0 to 100.4 ± 4.6 BPM, and PHA increased from 1.12 ± 0.28 to 8.58 ± 2.83 nglmllhr. Addition of propranolol to minoxidil caused a decrease in heart rate in proportion to log PPC:~ heart rate = 1.1 -12.8 log PPC (r, 0.59, p < 0.005) The relationship between PPC and the reduction in PHA was more complex. While a maio! reduction in PHA was observed at PPC in the range 20 to 60 nglmllhr, there was no consistent effect on PHA at higher PPC. Therefore, maximum antagonism of adrenergicaUy mediated increases in PHA is produced by much lower concentrations of propranolol than maximum suppression of adrenergically mediated increases in heart rate.
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