Effect of milrinone on myocardial mechanical function and cyclic AMP content in the fetal rabbit.

The effect of milrinone on mechanical function was studied in the isolated arterially perfused heart of the fetal (28th day of gestation) and newborn rabbits. The inotropic effect of milrinone in the fetus was significantly less than in the newborn. After milrinone infusion, myocardial cyclic AMP levels increased significantly in the two age groups and the fetal values before and after milrinone infusion were not significantly different from the newborn values. In our previous study the inotropic effects of dibutyryl cyclic AMP and high extracellular calcium in the fetus were significantly less than in the newborn. These data suggest that the diminished inotropic effect of milrinone in the fetus may be due, at least in part, to the decreased inotropism of cyclic AMP and calcium.