1974 Volume 26 Issue 3 Pages 291-304
In order to know the pharmacological actions of 4-(2-hydroxy-3-isopropylaminopropoxy)-indol (LB-46) in isolated rat heart muscle, the influences of this drug were examined on (a) the spontaneous contraction rate of the right atrium, (b) the contractile tensions of the spontaneously contracting right atrial muscle and of the electrically driven papillary and left atrial muscles, (c) the refractory periods of the papillary and left atrial muscles, and (d) the correspondences of responses to high frequent stimulation in the papillary and left atrial muscles. Methods and Materials
Male adult rats of both sexes weighing 300 to 400g were used. After sacrifice by severing the common carotid arteries, the heart was excised, and tissue preparations of their right and left atria and of papillary muscles were severally suspended in a Magnus' apparatus in a Locke's solution saturated with pure oxygen at 30 to 31°C.
The right atrium was used to examine the drug effects on rate and tension of spontaneous contractions while the papillary and left atrial muscles were used to examine the drug effects on their contractile tensions, refractory periods, and correspondences of responses to high frequency stimulations. When the papillary and left atrial muscle tissues were used, they were driven by electrical stimulations at supramaximal intensities, at duration of 10 and 5 msec, respectively, and 120 cycles per min. The drug applied was added to the medium in which the preparations were contracting, and was expected to act easily on these tissues.
When the refractory periods of the papillary and left atrial muscles were examined, Govier's method was used: basal stimulations were given to the muscles at supramaximal intensities, at durations of 10 and 5 msec, respectively, and at 60,120, and 240 cycles per min;and test stimulations, whose conditions were the same as those of the basal stimulations, were given at from 60 to 480 msec after each corresponding basal stimulation. If the time intervals between the two kinds of stimuli were of shorter durations than the refractory periods proper to the tested muscles, muscular contractile responses corresponding to the test stimulations would hardly appear. When the muscular responses corresponding to the test stimulations began to appear during gradual increase of the time intervals, the estimated time intervals were defined to represent the refractory periods of the muscles tested.
