Altered elastin and collagen synthesis associated with progressive pulmonary hypertension induced by monocrotaline. A biochemical and ultrastructural study.

Changes in elastin and collagen synthesis in the pulmonary artery wall, assessed both biochemically and ultrastructurally, were related to the development of progressive pulmonary hypertension induced by the toxin monocrotaline. Male Sprague-Dawley rats (200 to 225 gm) were injected subcutaneously in the hind flank with either monocrotaline (60 mg/kg) or an equivalent volume of saline and studied 8, 16 and 28 days later. At each time point, the right ventricle and left ventricle with septum were separated and weighed to follow the development of right ventricular hypertrophy. The hilar pulmonary artery was assessed by light microscopy for medial hypertrophy and by electron microscopy for changes in the endothelium, subendothelium and media. The mainstem pulmonary artery was used to determine synthesis of elastin and collagen by in vitro incorporation of [14C]proline into nonelastin, [14C]hydroxyproline into collagen, and [3H]valine into cyanogen bromide-insoluble elastin. In addition, total content of insoluble elastin was determined by weight of the residue after cyanogen bromide digestion and of collagen by total hydroxyproline content in sodium dodecyl sulfate and cyanogen bromide extracts. Eight days after monocrotaline injection, there was pulmonary artery endothelial swelling and a significant decrease in the number of myoendothelial junctions (p less than 0.05) associated with a decreased proportion of amorphous elastin in the media (p less than 0.01). Sixteen days after monocrotaline injection, a decrease in the proportion of elastin in the media was still evident (p less than 0.01) despite an apparent increase in insoluble elastin synthesis. Moreover, the amorphous elastin was distributed preferentially in small islands rather than in laminae (p less than 0.05). Twenty-eight days after monocrotaline injection, medial and right ventricular hypertrophy had developed (p less than 0.05 and p less than 0.01, respectively). At the same time, there was a striking increase in both insoluble elastin synthesis and total insoluble elastin content (p less than 0.01 for both) and an increase in collagen synthesis and total collagen content (p less than 0.05 for both). In addition, the ratio of insoluble elastin synthesis to collagen synthesis was greater than in controls (p less than 0.01), whereas the ratio of total insoluble elastin to total collagen did not change. On ultrastructural analysis, the proportion of amorphous elastin in the vessel wall relative to other elements remained low (p less than 0.01) and was distributed throughout the media as increased numbers of small islands (p less than 0.01).(ABSTRACT TRUNCATED AT 400 WORDS)