Pulmonary capillary density in rats given monocrotaline. A cast corrosion study.

A mechanism for monocrotaline-induced pulmonary hypertension in experimental animals may be the loss of small blood vessels, but when pulmonary arteries have been studied, the results have been controversial. In this report, the density of the entire lung microvasculature as measured by gray-scale analysis of scanning electron microscopic images of corrosion casts is reported. In the first experiment, monocrotaline, 60 mg/kg, was injected intraperitoneally into Sprague-Dawley rats. After 16 days, the pulmonary vascular tree was cast with methylmethacrylate. The vascular density index of the casts at a magnification x 100 on the alveolar surface was 0.40 for the monocrotaline-treated animals and 0.48 for the saline-treated control animals (p less than 0.01). On the pleural surface, it was 0.51 for the monocrotaline animals and 0.67 for the saline animals (p less than 0.001). A second experiment found no significant difference in vascular density index between different doses of monocrotaline. Light and scanning electron microscopy suggest that capillary and small vessel thrombosis may account for the decrease in the density of vessels in pulmonary microvascular casts that occurs in response to monocrotaline.