Plasma retinol transport and clearance in hypervitaminosis A.
Effects of mild and severe hypervitaminosis A on retinol transport and clearance were studied in mature ewes. Excessive vitamin A intake was assoicated with high concentrations of vitamin A in plasma and liver, with elevated serum enzymes, with decreased feed consumption and packed cell volume, and with epithelial hyperplasia. Retinol transport in plasma increased 6- to 8-fold with excessive dietary vitamin A, was greater with mild hypervitaminosis A, and increased exponentially with vitamin A concentration in plasma. Clearance of retinol from plasma increased 2-fold with hypervitaminosis A, exhibited a greater response in the mild group, and increased linearly with vitamin A concentration in plasma. The relationship of clearance to vitamin A concentration in liver was described best by a power function. Retinol clearance represents a mechanism to maintain vitamin A concentration in plasma and may be most effective below vitamin A concentrations of 135 microgram/dl plasma. With severe hypervitaminosis A, massive vitamin A accumulates in liver leading to hepatic dysfunction and a resultant decrease in retinol clearance from plasma.
D000410:Alanine Transaminase / Q000097:blood; D000469:Alkaline Phosphatase / Q000097:blood; D000818:Animals; D001219:Aspartate Aminotransferases / Q000097:blood; D004032:Diet; D004305:Dose-Response Relationship, Drug; D005260:Female; D006400:Hematocrit; D008099:Liver / Q000033:anatomy & histology / Q000378:metabolism*; D009929:Organ Size / Q000187:drug effects; D012756:Sheep / Q000378:metabolism*; D014801:Vitamin A / Q000009:adverse effects* / Q000097:blood / Q000378:metabolism
D014801:Vitamin A; D001219:Aspartate Aminotransferases; D000410:Alanine Transaminase; D000469:Alkaline Phosphatase