Moderate Ascorbate Deficiency Increases Myogenic Tone of Arteries From Pregnant but Not Virgin Ascorbate–Dependent Rats

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Abstract
Plasma ascorbic acid is decreased in women with the pregnancy disorder preeclampsia. We used a mutant strain of rats (Osteogenic Disorder Shionogi), dependent on dietary sources of vitamin C, to investigate whether reduced intake of the vitamin would differentially affect vascular function in late-pregnant (day 19) and age-matched virgin rats. The animals were given either 1 mg/mL of ascorbic acid ad libitum in drinking water [fully supplemented (FS)] or 0.25 mg/mL [marginally supplemented (MS)]. Fetal weights were 21% lower in MS than FS rats, whereas mean maternal weights and pup numbers did not differ. Small mesenteric arteries (diameter, 268±7 μm) were mounted in a pressurized arteriograph. Myogenic reactivity (contractile response to step increases in intraluminal pressure) was increased in arteries from MS pregnant compared with FS pregnant rats to levels observed in virgin rats. Ascorbic acid intake did not affect myogenic responses of arteries from virgin rats. Hence, the normal pregnancy-induced reduction in myogenic reactivity was abrogated in MS pregnant animals. Inhibition of nitric oxide synthase had no effect on the myogenicity of arteries from virgin or MS pregnant rats but increased myogenicity of FS pregnant rats to the level of MS pregnant rats. Free radical scavengers reversed the accentuated myogenicity of MS pregnant rats without affecting FS pregnant or virgin rat arteries. These data indicate that moderate ascorbate deprivation increases mesenteric artery myogenic responsiveness during pregnancy. This increase may result from a decrease in nitric oxide–mediated modulation of the myogenic contractile response.