Ketamine and sympathetic mechanisms in cardiac and smooth muscle

The effects of ketamine on the response of rat isolated cardiac and smooth muscle to electrical stimulation of intramural sympathetic nerves and to exogenous norepinephrine are reported. Low concentrations of ketamine (1 x 10(-5) to 5 x 10(-5) mol l-1) significantly potentiated, whilst high concentrations (2 x 10(-4) and 4 x 10(-4) mol l-1) significantly depressed the positive inotropic response of left atria to sympathetic nerve stimulation. Ketamine 5 x 10(-5) mol l-1 caused a leftward shift of the concentration-response curves of left atria to norepinephrine (threefold increase in potency) and isoproterenol (twofold increase in potency). Spontaneously beating right atria were slowed in a concentration-dependent manner by ketamine (5 x 10(-5) to 4 x 10(-4) mol l-1). Ketamine 1 x 10(-4) mol l-1 potentiated the positive chronotropic response of right atria to low frequency (2 and 5 Hz) sympathetic nerve stimulation, whilst ketamine 4 x 10(-4) mol l-1 depressed the response to all stimulation frequencies. Ketamine 3 x 10(-5) mol l-1 significantly potentiated the amplitude of the response of both hepatic portal vein and vas deferens to field stimulation of sympathetic nerves, and to exogenous norepinephrine. In the presence of reuptake blockade of norepinephrine by pancuronium 1 x 10(-4) mol l-1, ketamine caused no further potentiation of the response of the vas to nerve stimulation.