Objective  To investigate the effect of ultrasound-activated hematoporphyrin on apoptosis of cardiomyocytes from neonatal SD rats and to explore the underlying mechanism.   Methods  The primary cultured cardiomyocytes from neonatal rats were randomly divided into 4 groups

ultrasound (frequency 300 kHz

sound intensity 1.5 W/cm

2

irradiation 60 s) plus hematoporphyrin (concentration 20 μg/ml)

ultrasound (frequency 300 kHz

sound intensity 1.5 W/cm

2

irradiation 60 s)

hematoporphyrin (concentration 20 μg/ml) and control group. The cell growth inhibitory effect of each

group was observed by MTT assay. Apoptosis was measured by flow cytometry with Annexin V-FITC/PI staining. The expressions of Fas and FasL were identified by immunocytochemistry.  Results  The growth of the cultured cardiomyocytes of neonatal rats was significantly inhibited by hematoporphyrin combined with ultrasound at 24 h after treatment (P0.05). The apoptotic rate of ultrasound plus hematoporphyrin group at early term was obviously higher than those of other groups by Annexin V-FITC/PI assay (P0.05). Compared wtih other groups

hematoporphyrin combined with ultrasound apparently increased the level of Fas/FasL protein (P0.05).   Conclusion  Ultrasound-activated hematoporphyrin enhances the apoptosis of cardiomyocytes of neonatal rats

which is possibly associated with higher expression of Fas/FasL protein.