Regional difference of capillary-to-fiber ratio in the heart of monocrotaline-treated rats.

This study was designed to investigate the capillary-to-fiber (CF) ratio, and regional differences in this ratio in the hearts of monocrotaline-induced pulmonary hypertensive rats (MCT rats) as compared with normal rats in an attempt to examine capillary proliferation relative to that of muscle cells responding to the pressure stress on right ventricle (RV). Ten Sprague-Dawley male rats (5 weeks old) were injected with 60 mg/Kg monocrotaline, while eight rats were injected with saline as a control. At the age of 8 weeks they were anesthetized and the heart was excised and immediately frozen. The capillaries were stained enzyme-histochemically by detecting alkaline phosphate and dipeptidylaminopeptidase IV. The main finding in this study was a decrease in the CF ratio of MCT rats in all regions of the heart except in the RV mid-layer and endocardium. The CF ratio in the RV-mid-layer was 1.21 +/- 0.11 (mean +/- SD) in MCT rats and 1.27 +/- 0.12 in control rats (no change), while in the mid-layer of the interventricular septum (IVS) it was 1.13 +/- 0.05 in MCT rats and 1.35 +/- 0.07 in control rats (p < 0.001), and in the left ventricular (LV) mid-layer it was 1.20 +/- 0.06 in MCT rats and 1.40 +/- 0.12 in control rats (p < 0.001). This result indicates that capillary proliferation in the IVS and LV was poor in MCT rats, while in RV capillary proliferation was maintained at the control level. In MCT rats, the CF ratio in the RV endocardium and epicardium was significantly higher than the ratio in the LV epicardium, while in control rats the CF ratio in the LV endo- and mid-cardium was significantly higher than in the RV endo- and epicardium. It was suggested that in the hearts of growing MCT rats capillary proliferation in RV compensated for the suppressed capillary proliferation in the whole heart.