Inotropic effects of prostaglandin D2 and E1 on the newborn rabbit heart

This study determines the inotropic effects of prostaglandin D2 (PGD2) and prostaglandin E1 (PGE1) in the isolated, arterial perfused newborn (NB) and adult (A) rabbit heart. Significant positive inotropism of PGD2 was observed at all concentrations studied (1 X 10(-17) to 1 X 10(-7) M) in the two age groups; the effect in the NB was significantly greater (p less than 0.05) than that in the A at PGD2 concentrations higher than 1 X 10(-17) M. Significant positive inotropism of PGE1 was observed at PGE1 concentrations higher than 1 X 10(-8) M in the NB, and only at 1 X 10(-6) M in the A. In the NB, the relaxation parameters [1/2 RT and the ratio of +dT/dt (max) to -dT/dt (max)] decreased to 80% of control after PGE1 infusion, but not after PGD2 infusion. In contrast, relaxation parameters in the A were not different from control. Propranolol (1 X 10(-6) M) did not alter the positive inotropic action of PGD2 and PGE1 in the NB. These data indicate that: 1) the positive inotropic effects of PGD2 and PGE1 in NB are greater than that in the A, 2) PGE1 and not PGD2, enhances myocardial relaxation only in the NB, 3) the contractile effects of PGD2 and PGE1 are not mediated by beta-receptors.