Stimulatory effects of ethanol on amino acid transport by rat fetal hepatocytes

Authors

  • David W. Heitman Ph.D.,

    Corresponding author
    1. Department of Medicine, Division of Gastroenterology and Nutrition, The University of Texas Health Science Center at San Antonio, San Antonio, Texas 78284–7878
    • Department of Medicine, Division of Gastroenterology and Nutrition, The University of Texas Health Science Center, 7703 Floyd Curl Drive, San Antonio, Texas 78284
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  • Teri A. Frosto,

    1. Department of Medicine, Division of Gastroenterology and Nutrition, The University of Texas Health Science Center at San Antonio, San Antonio, Texas 78284–7878
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  • Steven Schenker,

    1. Department of Medicine, Division of Gastroenterology and Nutrition, The University of Texas Health Science Center at San Antonio, San Antonio, Texas 78284–7878
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  • George I. Henderson

    1. Department of Medicine, Division of Gastroenterology and Nutrition, The University of Texas Health Science Center at San Antonio, San Antonio, Texas 78284–7878
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Abstract

Previous studies have indicated that acute, and especially chronic, maternal ethanol consumption can depress placental uptake of various amino acids. Since the fetal cell itself represents a second barrier to nutrients, one which may be altered by ethanol exposure, the effects of ethanol on amino acid net uptake by rat fetal hepatocytes was addressed. The present study determined that ethanol stimulated amino acid net uptake by fetal hepatocytes grown in monolayer culture. Fetal liver cells were grown in custom Williams' E medium (without L-arginine and with L-ornithine) and exposed to epidermal growth factor (0, 1, 2 or 5 ng per ml) and ethanol (1.7 ± 0.1 or 3.9 ± 0.2 mg per ml). Addition of ethanol (3.9 mg per ml) to the culture medium completely blocked measurable cell replication during a 48-hr exposure period. Fetal hepatocytes exposed to ethanol accrued both protein and water in a parallel fashion, both in excess of that by control cells. Ethanol (1.7 and 3.9 mg per ml) for 48 hr stimulated α-aminoisobutyric acid net uptake by fetal hepatocytes (p < 0.05). Efflux was not affected (p < 0.05). The onset of this significant stimulation of net uptake was progressive and required in excess of 6 hr of contact with ethanol. This ethanol stimulation of α-aminoisobutyric acid net uptake persisted for at least 24 hr following ethanol withdrawal. The component(s) of α-aminoisobutyric acid net uptake stimulated by ethanol was independent of extracellular Na+. In addition, ethanol stimulated net uptake of two other marker amino acids, methyl-α-aminoisobutyric acid and cycloleucine (54 and 128%, respectively, p < 0.05). In summary, these data suggest: (i) ethanol can stimulate the net uptake of amino acids by fetal hepatocytes while not affecting efflux; (ii) this effect requires an exposure period in excess of 6 hr and is not rapidly reversible, and (iv) ethanol exposure (3.9 mg per ml) totally prevents fetal hepatocyte replication and causes a 3- to 4-fold increase (accumulation) in cellular protein and water.

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