Zonation of the action of ethanol on gluconeogenesis and ketogenesis studied in the bivascularly perfused rat liver

Abstract

Zonation of the actions of ethanol on gluconeogenesis and ketogenesis from lactate were investigated in the bivascularly perfused rat liver. Livers from fasted rats were perfused bivascularly in the antegrade and retrograde modes. Ethanol and lactate were infused into the hepatic artery (antegrade and retrograde) and portal vein. A previously described quantitative analysis that takes into account the microcirculatory characteristics of the rat liver was extended to the analysis of zone-specific effects of inhibitors. Confirming previous reports, gluconeogenesis and the corresponding oxygen uptake increment due to saturable lactate infusions were more pronounced in the periportal region. Arterially infused ethanol inhibited gluconeogenesis more strongly in the periportal region (inhibition constant = 3.99 ± 0.22 mM) when compared to downstream localized regions (inhibition constant = 8.64 ± 2.73 mM). The decrease in oxygen uptake caused by ethanol was also more pronounced in the periportal zone. Lactate decreased ketogenesis dependent on endogenous substrates in both regions, periportal and perivenous, but more strongly in the former. Ethanol further inhibited ketogenesis, but only in the periportal zone. Stimulation was found for the perivenous zone. The predominance of most ethanol effects in the periportal region of the liver is probably related to the fact that its transformation is also clearly predominant in this region, as demonstrated in a previous study. The differential effect on ketogenesis, on the other hand, suggest that the net effects of ethanol are the consequence of a summation of several partial effects with different intensities along the hepatic acini.