Caffeine effect on myocardial mechanical function in the neonatal rabbit heart.

The effects of 20 mM caffeine on myocardial mechanical function were studied in isolated, arterially perfused cardiac preparations of newborn and adult rabbits. Caffeine caused a significant increase in the maximal rate of tension development in the adult (141% of control) but not in the newborn (111%). The resting tension increased significantly in both age groups. However, the increase in the adult (245% of control) was also significantly greater than in the newborn (132%). At the points of maximum effect, caffeine perfusion in the newborn resulted in a decrease in the maximal rate of relaxation (29% of control) and an increase in the half relaxation time (144% of control) that were significantly greater than they were in the adult (41% and 103%, respectively). These data show distinct age-related differences in the effects of caffeine on myocardial mechanical function. These differences may be due to maturational changes that occur in the sarcoplasmic reticulum and T tubule system of the rabbit heart. However, maturational changes in the activity of phosphodiesterase and/or the sympathetic nervous system may play a role.