Changes in sequestered leukocytes and platelets in the pulmonary microvasculature of rats with monocrotaline-induced pulmonary hypertension

The role of leukocytes (WBCs) and platelets (PLTs) in the pulmonary circulation may be important in the development of monocrotaline (MCT)-induced pulmonary hypertension in rats. We investigated the changes in WBCs and PLTs in the pulmonary microvasculature during the development of chronic pulmonary hypertension in MCT rats by real-time confocal scanning laser microscopy. The number of WBCs sequestered in the pulmonary microvasculature increased significantly from day 7 after MCT injection, but no further increase occurred from days 14-28. The number of PLTs sequestered in the pulmonary microvasculature increased significantly from day 7 after MCT injection, and reached a peak on day 14. However, the number of PLTs sequestered on days 21 and 28 after MCT injection was significantly lower than on day 14. These findings suggest that PLTs mainly contribute to the initial and middle stages of the development of MCT-induced pulmonary hypertension in rats, while WBCs mainly contribute to the middle and late stages.