DIFFERENTIAL DEVELOPMENT OF UMBILICAL AND SYSTEMIC ARTERIES - II - CONTRACTILE PROTEINS

In fetal sheep, umbilical responsiveness to ANG II exceeds systemic va scular responsiveness. Fetal systemic vascular smooth muscle (VSM) exh ibits an immature phenotype with decreased contractile protein content s, low 200-kDa myosin heavy chain (MHC) SM2, and significant nonmuscle MHC-B expression, whereas umbilical VSM phenotype is incompletely des cribed. We tested the hypothesis that differences in vascular responsi veness could reflect dissimilarities in VSM phenotype. Actin, MHC, MHC isoforms, and active stresses were compared in strips of femoral arte ries and aorta from near-term fetal (n = 12) and adult (n = 12) sheep to those in external and intra-abdominal umbilical arteries. Actin con tents in fetal femoral artery and aorta were less (P less than or equa l to 0.006) than in external umbilical artery (7.37 +/- 1.4 and 7.53 /- 0.7 vs. 21.6 +/- 2.2 mu g/mg wet wt, respectively) as were MHC cont ents (3.17 +/- 0.4 and 2.84 +/- 0.3 vs. 7.16 +/- 0.7, respectively). W hereas 204- and 200-kDa MHC were expressed equally in fetal systemic a rteries, umbilical and adult arteries predominantly expressed the 204- kDa isoform (SM1); only fetal systemic VSM expressed MHC-B. Fetal syst emic artery stresses and myosin light chain phosphorylation were less than those in umbilical and adult arteries (P < 0.001). Compared with umbilical and adult arteries, fetal systemic VSM is biochemically and functionally immature and thus umbilical VSM demonstrates precocious m aturation resembling adult VSM in protein expression and function.