Cardiovascular toxicity study of forklift and automobile diesel exhaust particles in spontaneously hypertensive rats

Diesel exhaust particles (DEPs), a major contributor of ambient particulate matter, have been reported to be associated with cardiopulmonary diseases and lung cancer. DEPs toxicity, as we know, varies with the complicated physical and chemical properties of particles which are influenced by the engine type, fuel components, sampling procedures, etc, and it is possible that different samples of DEPs may have different toxicity. Therefore, the objective of this study was to compare the effects of two different DEPs samples, forklift-derived DEPs (SRM 2975) and automobile-derived DEPs (A-DEP), on heart rate and heart rate variability (HRV) in spontaneously hypertensive rats (SHR). In order to further investigate the contributions of DEPs components on cardiovascular toxicity, the artifical carbon black (CB) as a surrogate of ultrafine fraction of DEPs is subsequently used to examine the effects of ultrafine particles and particle size on heart rate and HRV in SHR.
13-15 and 20-22 weeks old SHR with implanted radiotelemetry devices were intratracheally administered with both normal saline and SRM 2975 (500 μg/animal, n=3) or (A-DEP 500 μg/animal, n=3) alternatively, so each rat could serve as its own control. ECG signals were recorded for 72 hours after each exposure, and heart rate and parameters of HRV including standard deviation of normal-to-normal intervals (SDNN) and root mean square of successive differences of adjacent normal-to-normal intervals (RMSSD) were analyzed. Significantly decreased heart rate was observed in SHR following SRM 2975 exposure, whereas increased heart rate was found after A-DEP exposure. HRV (SDNN and RMSSD) were increased after SRM 2975 exposure, whereas SDNN and RMSSD were decreased after A-DEP exposure.
SHR with implanted radiotelemetry devices were intratracheally administered with both normal saline and CB (500 or 1000 μg 14 nm CB, or 1000 μg 95 nm CB; n=4 for each 14 nm CB group, and n=3 for 95nm CB). ECG signals collection and analysis were as previously described. After 14nm CB exposure, increased heart rate and HRV (SDNN and RMSSD) were observed in SHR. However, the dose-response relationship was only found in heart rate change. In addition, a decrement of heart rate and an increase of HRV were observed in SHR following 95nm CB exposure.
Our results showed that DEPs may cause autonomic nervous system dysfunction in SHR. Both SRM 2975 and A-DEP samples can alter cardiovascular function, but the directions of the effects are different. These disparities on heart rate and HRV changes may due to the characteristics of these particles. We further tested the effects of ultrafine particles, one of the risk factors of particle toxicity, without conclusion. Thus, more studies are needed to investigate the specific components of DEPs which may explain the discrepancy of above findings.