Recent studies suggest that VEGF contributes to hypoxic remodeling of arterial smooth muscle, although hypoxia produces only transient increases in VEGF that return to normoxic levels despite sustained changes in arterial structure and function. To explore how VEGF might contribute to long-term hypoxic vascular remodeling, this study explores the hypothesis that chronic hypoxia produces sustained increases in smooth muscle VEGF receptor density that mediate long-term vascular effects of hypoxia. Carotid arteries from adult sheep maintained at sea level or altitude (3,820 m) for 110 days were harvested and denuded of endothelium. VEGF levels were similar in chronically hypoxic and normoxic arteries, as determined by immunoblotting. In contrast, VEGF receptor levels were significantly increased by 107% (VEGF-R1) and 156% (VEGF-R2) in hypoxic compared with normoxic arteries. In arteries that were organ cultured 24 h with 3 nM VEGF, VEGF replicated effects of hypoxia on abundances of smooth muscle α actin (SMαA), myosin light chain kinase (MLCK), and MLC20 and the effects of hypoxia on colocalization of MLC20 with SMαA, as measured via confocal microscopy. VEGF did not replicate the effects of chronic hypoxia on colocalization of MLCK with SMαA or MLCK with MLC20, suggesting that VEGF's role in hypoxic remodeling is highly protein specific, particularly for contractile protein organization. VEGF effects in organ culture were inhibited by VEGF receptor blockers vatalinib (240 nM) and dasatinib (6.3 nM). These findings support the hypothesis that long-term upregulation of VEGF receptors help mediate sustained effects of hypoxia on the abundance and colocalization of contractile proteins in arterial smooth muscle.

Hypoxic increases in VEGF contribute to growth of perivascular nerves, which exert potent trophic effects on cerebral arteries. Here we explore the hypothesis that the perivascular sympathetic innervation (PSI) mediates hypoxic changes in the smooth muscle phenotype, structure and function of fetal lamb middle cerebral arteries (MCA). A right superior cervical ganglionectomy (SANX) was performed on exteriorized sheep fetuses of normoxic (N) and hypoxic (H) time‐dated pregnant sheep. Operated fetuses were returned to the womb and their MCA were harvested 14 days later at term. Chronic hypoxia (CH) decreased norepinephrine (NE) content and uptake capacity in MCA but increased contractile responses to transmural adrenergic stimulation at 8 Hz by up to 10‐ fold. CH significantly increased arterial stiffness by 55%. SANX reduced this hypoxic effect by 69%. NE efficacy decreased with hypoxia from 41% to 24% Kmax. SANX increased NE efficacy 39% in N and 61% in H. Similarly, decreases in NE potency with hypoxia were reversed by SANX. Confocal colocalization of myosin heavy chains with α‐actin increased with CH while MLCK‐MLC20 colocalization in H arteries decreased with SANX compared to controls. In conclusion, CH significantly decreases the density but enhances the function of the PSI in fetal MCA. These nerves appear to help mediate effects of hypoxia on fetal MCA structure and function. Supported by PHS# P01‐HD31226.