The effects of propofol on heart rate, arterial pressure and Aδ and C somatosympathetic reflexes in anaesthetized dogs

The effects of propofol on mean arterial pressure, heart rate and A delta and C somatosympathetic reflexes, recorded in renal nerves, evoked by repeated individual supramaximal electrical stimuli applied to radial nerves, were observed in anaesthetized, paralysed and artificially ventilated dogs. Propofol was infused at rates from 0.4 to 2.0 mg kg(-1) min(-1). Mean C and A delta reflexes were abolished at plasma concentrations (mean, SEM) of 24.3 (3.3) and 29.2 (2.6) mu g mL(-1) (P < 0.05), respectively, when mean arterial pressure and mean heart rate were reduced by approximately 55% (P < 0.01) and 26% (P > 0.05), respectively. Recovery of A delta and C reflexes occurred at plasma concentrations of 13.1 (2.3) and 9.9 (1.3) mu g mL(-1) (P > 0.05), respectively. There was a log- arithmically linearly related fall in mean arterial pressure by 70% up to a plasma concentration approximate to 97 mu g mL(-1) (r(2) = 0.7) with a 28% reduction in heart rate which was uncorrelated with the plasma concentrations (r(2) = 0.12). In conclusion, propofol abolished A delta and C responses at comparable plasma concentrations and caused a major reduction in both mean arterial pressure and heart rate which is consistent with resetting of the baroreflexes. The reduction in mean arterial pressure was logarithmically, linearly correlated with a progressive increase in plasma concentrations without evidence of a ceiling effect.