COMPARATIVE EFFECTS OF BARBITURIC ACID DERIVATIVES ON THE ISOLATED HEART

Experiments were performed on the isolated hearts of turtles by perfusion with barbituric acid derivatives to compare their relative toxicities and to attempt a correlation of the findings with studies upon intact organisms. In recent years the trend has been towards more extensive use of such drugs in general medicine, psychiatry, obstetrics, and in surgery. The increasing number of preparations advertised to the profession confuses it as to their relative merits. METHOD The technique and apparatus were the same as used in earlier investigations (1, 2, and 3). The pH of the sodium salts of these drugs was adjusted to the optimum range of 7.2 to 7.4 before use. RESULTS In graphs 1 o 8, figure 1, time in minutes has been plotted on the horizontal and amplitude of contraction on the vertical. The curves show the rate and degree of fall after standard doses. Figure 2 shows average decrease in amplitude (in millimeters of fall per minute) calculated from the tracings. Graph 4 of figure 1 shows that barbituric acid in the concentra-tion 1/2000 M stops a heart within a few seconds. This effect seems due to the acid form in which it is employed inasmuch as sodium barbiturate of the same molar concentration lowered the tracing only 15 per cent in five minutes. The sodium salt of diethyl barbituric acid (barbital) is no more toxic, as evident whe