The neonate is particularly susceptible to the development of hypoxic pulmonary hypertension. The present study was undertaken to observe the effect of hypoxia on DNA synthesis and c-myc gene expression between newborn calf and adult bovine PASMC in vilro. DNA synthesis measured by 3H- TdR incorporation was increased after hypoxic challenge for 24h. Hypoxia enhanced the increment in 3H-TdR incorporation induced by EGF. Northern blot analysis revealed that PASMC cultured in both normoxia and hypoxia expressed c- myc gene transcript of 2. 2Kb

but there is a higher 2. 2Kb mRNA expression in hypoxic PASMC than that in normoxia. We speculate that newborn calf PASMC exhibited potential response to hypoxia than adult

which was augmented by EGF. Enhanced c-myc gene expression may lead to a great understanding of the mechanism of PASMC growth in the development of pulmonary hypertension.