In vitro evaluation of nicorandil, diltiazem, and prostaglandin E1 on hypothermic injury to immature myocytes.

The purpose of the present study was to evaluate the functional and biochemical effects of nicorandil (NRD), diltiazem (DTZ), or prostaglandin E1 (PGE) on cardiac myocytes incubated under hypothermic conditions. Cardiac myocytes were isolated from neonatal rat ventricles and cultured for 4 days with MCDB 107 medium. Myocytes (12.5 x 10(5) myocytes/flask) were then incubated at 4 degrees C for 24 hr in media containing various concentrations of NRD, DTZ, or PGE. After hypothermic incubation, creatine phosphokinase (CPK) and lactate dehydrogenase (LDH) were measured. The myocytes were then cultured for an additional 24 hr at 37 degrees C to evaluate the recovery of myocyte beating rate. In the nicorandil groups, 10(-4) M NRD showed significantly increased beating rate recovery compared to control (44.2% vs 24.6%, respectively, as a percentage of control, i.e., beating rate prior to hypothermic incubation). Treatment with 10(-6) M diltiazem showed no beneficial effects (10(-6) M: 25.2%; control: 29.8%); however, beating was not observed at 10(-4) or 10(-5) M. There were no significant changes among the PGE groups. The release of CPK and LDH was significantly suppressed with 10(-4) M NRD (10(-4) M: 24.1, 257.2 MIU/flask; control: 125.4, 459.5 mIU/flask, respectively). However, 10(-4) M DTZ showed significantly increased CPK and LDH levels compared to the control (10(-4) M: 203.3, 883.4 mIU/flask; control: 112.3, 457.4 mIU/flask, respectively). There were no significant differences for CPK and LDH levels among the PGE groups. In conclusion, nicorandil has protective characteristics for immature myocytes that may be suitable for cardiac preservation in the neonatal period.