Ae. Halseth et al., EFFECT OF PHYSICAL-ACTIVITY AND FASTING ON GUT AND LIVER PROTEOLYSIS IN THE DOG, American journal of physiology: endocrinology and metabolism, 36(6), 1997, pp. 1073-1082
The aim of this study was to determine how gut and liver protein kinet
ics adapt to acute exercise in the 18-h-fasted dog (n = 7) and in dogs
glycogen depleted by a 42-h fast (n = 8). For this purpose, sampling
(artery and portal and hepatic veins) and infusion (vena cava) cathete
rs and Doppler flow probes (portal vein and hepatic artery) were impla
nted with animals under general anesthesia. At least 16 days later, an
experiment, consisting of a 120-min equilibration period, a 30-min ba
sal sampling period, and a 150-min exercise period, was performed. At
the start of the equilibration period, a constant rate infusion of [1-
C-13]leucine was initiated. Gut and liver leucine appearance and disap
pearance rates were calculated in these studies by combining a novel s
table isotopic method and arteriovenous difference methods. In the det
ermination of tissue leucine kinetics the tissue inflow of both alpha-
[C-13]ketoisocaproic acid and [C-13]leucine was taken into account. Th
e results of this study show that I)the splanchnic bed (liver plus gut
) contributes similar to 40% to the whole body proteolytic rate in the
basal state and during exercise in dogs fasted for either 18 or 42 h,
2) the contributions of the gut and liver to splanchnic bed proteolys
is is about equal in the basal state in both 18- and 42-h-fasted dogs,
and 3) exercise in the 18-h-fasted dog leads to a greater emphasis on
gut proteolysis and a lesser emphasis on hepatic proteolysis. These s
tudies highlight the important contribution of gut and hepatic proteol
ysis to whole body proteolysis and the ability of the gut to acutely a
dapt to changes in physical activity.