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Phenotypic differences between neonatal and adult ovine carotid arteries predict reactivity to chronic hypoxia and VEGF

Double label confocal studies of smooth muscle α‐actin and SM2 myosin indicate significantly greater colocalization between these markers in adult than neonatal arteries revealing that the fraction of non‐contractile smooth muscle cells is greater in immature than mature arteries. To explore the hypothesis that age‐related differences in phenotype determine responses to chronic hypoxia, and VEGF, which mediates many vascular effects of hypoxia, common carotid arteries were harvested from term fetal and adult non‐pregnant sheep maintained at sea level (FN, AN) or for 110 days at 3820m (FH, AH). Stress‐strain relations were determined in all arteries before organ culture, after 48h of serum starvation (S), or after 24h starvation + 24h treatment with 3 ng/ml VEGF (V). Aside from multiple effects of hypoxia that were similar in both age groups, S and V produced opposing effects in AN (S‐induced increases in diameter were reversed by V) but not AH arteries. Opposing effects of S and V were also observed in FH (S‐induced decreases in stiffness, diameter, maximum myogenic and depolarization‐induced tone were all reversed by VEGF) but not in FN. These results demonstrate that age‐dependent differences in smooth muscle phenotype predict reactivity to both VEGF and chronic hypoxia, and that VEGF modulates multiple functional characteristics of arterial smooth muscle. Supported by USPHS Grants HL54120, HD31266, & HL64867.