Circadian Variation of α1-Adrenoceptor-mediated Pressor Response to Phenylephrine in Man

Publisher Website
Google Scholar
Abstract
The variability in the pressor effects of the α1‐adrenoceptor agonist phenylephrine was observed under placebo conditions in ten healthy subjects in a double blind randomized study. Phenylephrine infusions were administered before administration of placebo (baseline) and 2, 4, 8, 12, 24 and 48 h later. The doses of phenylephrine required to increase systolic blood pressure by 20 mmHg after 8 and 12 h (5.30 and 9.30 pm, 81.4 ± 15.3 and 71.1 ± 16.0 μg min−1, respectively) were significantly (P < 0.01) less than the baseline values (8.30 am, 108.0 ± 27.6 g min−1). These results might indicate a circadian variation in the phenylephrine‐induced α‐adrenoceptor‐mediated vascular response in healthy subjects. These observations lend further insight into circadian variations of vascular tone that might contribute to circadian rhythms in cardiovascular disease.