Abstract
Background
Propofol (2,6-diisopropylphenol) is one of the most frequently used anesthetic agents. One of the main side effects of propofol is to reduce blood pressure, which is thought to occur by inhibiting the release of catecholamines from sympathetic neurons. Here, the authors hypothesized that propofol-induced hypotension is not simply the result of suppression of the release mechanisms for catecholamines.
Methods
The authors simultaneously compared the effects of propofol on the release of norepinephrine triggered by high K+-induced depolarization, as well as ionomycin, by using neuroendocrine PC12 cells and synaptosomes. Ionomycin, a Ca2+ ionophore, directly induces Ca2+ influx, thus bypassing the effect of ion channel modulation by propofol.
Results
Propofol decreased depolarization (high K+)-triggered norepinephrine release, whereas it increased ionomycin-triggered release from both PC12 cells and synaptosomes. The propofol (30 μM)-induced increase in norepinephrine release triggered by ionomycin was dependent on both the presence and the concentration of extracellular Ca2+ (0.3 to 10 mM; n = 6). The enhancement of norepinephrine release by propofol was observed in all tested concentrations of ionomycin (0.1 to 5 μM; n = 6).
Conclusions
Propofol at clinically relevant concentrations promotes the catecholamine release as long as Ca2+ influx is supported. This unexpected finding will allow for a better understanding in preventing propofol-induced hypotension.
Enhancement of catecholamine release from PC12 cells by the traditional Japanese medicine, rikkunshito
