Abstract
Abstract Net transport of α-aminoisobutyric acid (AIB) was increased in liver slices prepared from rats injected with hydrocortisone, epinephrine, or glucagon. When slices from untreated animals were initially incubated for 15 min with glucagon or cyclic adenosine 3',5'-monophosphate (cyclic AMP) subsequent uptake of AIB in the presence of either agent was greater than in control experiments; epinephrine was without effect. If extended preliminary incubation with glucagon or cyclic AMP preceded the final incubation with AIB the net increase in uptake was 4 to 6 times that seen with a short preliminary incubation. Under these conditions epinephrine produced a distinct, but relatively small, increase in AIB transport. 1-Aminocyclopentanecarboxylic acid transport was also stimulated in liver slices from rats injected with glucagon or in slices incubated in vitro with glucagon or cyclic AMP. These experiments show that glucagon, cyclic AMP, and epinephrine can stimulate to varying degrees amino acid transport in liver slices in vitro; therefore, these agents may directly affect hepatic amino acid transport in vivo. AIB uptake was relatively high in control liver slices after preliminary incubation for extended periods in Krebs-Ringer buffer alone. The effect was blocked by initially incubating the tissue in an ice bath or with cycloheximide; actinomycin D was less effective. These drugs also inhibited cyclic AMP-induced stimulation of AIB transport. Amino acid analyses of extracts of incubated slices provided little evidence that exchange diffusion is of major significance in stimulation of AIB transport by cyclic AMP.
Published Version
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