Effects of D 600 and papaverine on the inotropic response to isoprenaline on left guinea-pig atria under the graded influence of changes of frequency and temperature

Abstract

Isolated left guinea-pig atria were used to examine the influence of D 600 and papaverine on baseline contractile function and inotropic response to isoprenaline, under variable conditions of temperature (27 degrees to 42 degrees C) and rate of beat (0.125 to 4 Hz). The inotropic stimuli, caused by increasing the frequency of stimulation and decreasing the temperature, could not overcome the depressive action of D 600 on basal systolic tension. In addition the inotropic effects evoked by papaverine at low rates of beat and high temperatures were converted into cardiodepressive effects at high stimulation rates and low temperatures. The inotropic response to isoprenaline appeared to be by far more resistant to the depressive actions of D 600 and papaverine than the baseline contractile function. Only at a stimulation frequency of 2 Hz, high concentrations of D 600 (3 X 10(-7)M) and papaverine(3 X 10(-5)M) reduced the response caused by isoprenaline. At a stimulation frequency of 0.5 Hz, however, D 600 left the inotropic responses to isoprenaline unchanged, whereas papaverine potentiated these responses. It appears from the present results that the frequency of stimulation and the temperature greatly modify the cardiodepressive actions evoked by D 600 and papaverine.