Right ventricular systolic pressure load alters myocyte maturation in fetal sheep

The effects of right ventricular (RV) systolic pressure (RVSP) load on feta l myocyte size and maturation were studied. Pulmonary artery (PA) pressure was increased by PA occlusion from mean 47.4 +/- 5.0 (+/-SD) to 71 +/- 13.6 mmHg (P < 0.0001) in eight RVSP-loaded near-term fetal sheep for 10 days. The maximal pressure generated by the RV with acute PA occlusion increased after RVSP load: 78 +/- 7 to 101 +/- 15 mmHg (P < 0.005). RVSP-load hearts were heavier (44.7 +/- 8.4 g) than five nonloaded hearts (31.8 +/- 0.2 g; P < 0.03); heart-to-body weight ratio (10.9 +/- 1.1 and 6.5 +/- 0.9 g/kg, re spectively; P < 0.0001). RVSP-RV myocytes were longer (101.3 +/- 10.2 mm) t han nonloaded RV myocytes (88.2 +/- 8.1 mu m; P, 0.02) and were more often binucleated (82 +/- 13%) than nonloaded myocytes (63 +/- 7%; P, 0.02). RVSP -loaded myocytes had less myofibrillar volume than did nonloaded hearts (44 .1 +/- 4.4% and 56.1 +/- 2.6%; P < 0.002). We conclude that RV systolic loa d 1) leads to RV myocyte enlargement, 2) has minor effects on left ventricu lar myocyte size, and 3) stimulates maturation (increased RV myocyte binucl eation). Myocyte volume data suggest that RV systolic loading stimulates bo th hyperplastic and hypertrophic growth.