Tadahisa Fujita

Stimulative effect of epinephrine on glucose production and utilization rates in sheep using a stable isotope

The rates of the production and utilization of blood glucose were measured during intravenous epinephrine infusion (2.0 nmol kg-1 min-1 for 1 hr) in sheep. An isotope dilution method with an infusion of [U-13C]glucose and nonsteady-state equations were used for the determination of blood glucose kinetics. Heart rate and concentrations of blood glucose, plasma free fatty acids, and lactate increased (P < 0.01), whereas plasma insulin concentrations tended to decrease (P < 0.06) during epinephrine infusion. The blood glucose turnover rate was 1.9 +/- 0.1 mg kg-1 min-1 before epinephrine infusion. The rate of blood glucose production increased (P < 0.01) to 6.4 +/- 0.5 mg kg-1 min-1 at 20 min after the initiation of epinephrine infusion. The blood glucose utilization rate increased (P < 0.05) gradually and reached 4.1 +/- 1.2 mg kg-1 min-1 at 60 min after the initiation of epinephrine infusion. These results suggest that in sheep, epinephrine stimulates the rates of both the production and the utilization of blood glucose and that hyperglycemia induced by epinephrine infusion is mainly due to a rapid enhancement in the rate of the production of blood glucose.

Effect of metabolizable protein intake on rates of plasma leucine turnover and protein synthesis in heifers

An isotope dilution method using [1-1 3 C]leucine (Leu) infusion together with open-circuit calorimetry was applied to determine the effect of metabolizable protein (MP) intake on rates of plasma Leu turnover and whole body protein synthesis (WBPS) in six heifers. WBPS rate was estimated from rate of plasma Leu turnover and Leu oxidation to carbon dioxide. The experiment consisted of three levels of MP intake and was conducted in a two 3 × 3 Latin square designs of three 21-day periods. The experimental diet consisted of mixed hay, maize and soybean meal. Dietary MP intake of each dietary treatment was 4.3, 4-5 and 4-9 g/kg BW 0.75 /day by changing maize and soybean meal weights. Metabolizable energy (ME) intake was similar for all dietary treatments. When plasma α-[1- 13 C]keto-isocaproic acid enrichments were used as markers indicating intracellular Leu enrichments, plasma Leu turnover rate (LeuTR) increased (P=0-012) and WBPS tended to increase (P= 0-091) as MP intake increased. In contrast, plasma LeuTR and WBPS were not influenced if plasma [1- 13 C]Leu was taken to indicate intracellular Leu enrichments. Total and plasma Leu oxidation rates did not change but intracellular Leu oxidation increased (P=0-044) with increasing MP intake. In heifers, it is suggested that rates of plasma Leu turnover and WBPS are influenced by dietary MP intake, independent of ME intake, although the change in MP intake was relatively small.

Effects of cold exposure and time relative to feeding on glucose metabolism of sheep using a glucose clamp approach

An experiment combining a hyperinsulinaemic euglycaemic clamp approach and an isotope dilution method determined the effects of cold exposure and time relative to feeding on blood glucose metabolism in four sheep. The sheep, fed 20 g/kg body-weight (BW) of lucerne hay cubes and 5 g/kg BW of maize-based concentrates once daily, were exposed in turn to a thermoneutral environment (20 °C) and a cold environment (0 °C) for 20 days. The combined experiments were performed at four different times relative to feeding, i.e. 3 to 2 h, 2 to 1 h and 1 to 0 h before, and 1 to 2 h after the initiation of feeding for the basal periods, and 1 to 0 h before, and 0 to 1 h, 1 to 2 h and 3 to 4 h after the initiation of feeding for the glucose clamp periods in both environments. [U- 13 C]Glucose was continuously infused for 6 h after a priming injection. Insulin was continuously infused at 6.0 mU/kg BW per min for 2 h, which corresponded to the last 2 h of the [U- 13 C]glucose infusion. Blood glucose concentrations were maintained euglycaemic during the insulin infusion by concomitant variable glucose infusion. Blood glucose turnover rate (GTR) during the basal period was enhanced by cold exposure (P = 0.01) and feeding (P = 0.04). Blood GTR increased (P < 0.01) with the glucose clamp. During the glucose clamp, blood GTR and glucose infusion rate (GIR) were greater (P = 0.003 and P = 0.001, respectively) during cold exposure than in the thermoneutral environment. Time relative to feeding influenced (P = 0.003) the GIR, whereas changes in blood GTR and endogenous glucose production rate were not significant. No significant cold x feeding interaction was observed in these variables. It was suggested that, in sheep, glucose metabolism was enhanced by cold exposure and the glucose clamp. It was probable that blood glucose metabolism during the glucose clamp was influenced by cold exposure and feeding, but the combined effect of cold exposure and feeding was not significant.

Responses to dietary starch or sucrose on protein and glucose kinetics in goats fed a high-concentrate diet

Abstract Responses of whole body protein synthesis (WBPS) and glucose irreversible loss rate (ILR) were compared between dietary starch and sucrose in four male goats. Diets were fed at 1.2 times maintenance requirements of ME and CP with 30% of the ME as starch, starch plus sucrose or sucrose, twice daily. The diets consisted of 33, 32, 11 and 24% of alfalfa hay, corn, soybean meal and the carbohydrates, respectively. The WBPS and glucose ILR during 5 – 7 h after feeding were determined by an isotope dilution method of [2H5]phenylalanine, [2H2]tyrosine, [2H4]tyrosine and [13C6]glucose. Sucrose elevated ammonia nitrogen and lowered acetate concentrations in the rumen, but did not differ from starch in nitrogen retention. Glucose ILR and WBPS were similar between the carbohydrates. It was concluded that dietary sucrose would have effects similar to starch on WBPS and glucose kinetics in the absorptive state in goats fed a high-concentrate diet.

Effect of Mild Cold Exposure on Whole-Body and Net Hindquarters Glucose Metabolism in Sheep

Isotope dilution using [U-13C]glucose was combined with measurement of hindquarters arteriovenous difference and blood flow to examine the effect of mild cold exposure on whole-body and net hindquarters glucose metabolism in sheep. Determinations were carried out in a thermoneutral environment (20 +/- 1 degrees C) and on day 5 of mild cold exposure (4 +/- 1 degrees C). Whole-body blood glucose turnover rate was 1.56 and 1.91 mg kg-1 min-1 in the thermoneutral environment and during mild cold exposure, respectively. Net hindquarters glucose uptake was 0.79 and 1.19 mg kg-1 min-1, corresponding to 50 and 61% of whole-body turnover rate, respectively. These results suggest that in sheep the contribution of glucose uptake by the hindquarters tended to increase during mild cold exposure, even though whole-body blood glucose turnover rate did not increase significantly.

Effect of Dietary Protein Intake on Turnover and Oxidation Rates of Plasma Glucose in Adult Sheep

Abstract Sano, H., Kajita, M. and Fujita, T. 2007. Effect of dietary protein intake on turnover and oxidation rates of plasma glucose in adult sheep. J. Appl. Anim. Res., 31: 177–180. An isotope dilution method of [U-13C]glucose with open circuit calorimetry was applied to determine the effect of dietary crude protein (CP) intake 5.6, 7.7 and 10.8 g/kg BW0.75 Id on turnover and oxidation rates of plasma glucose in four adult sheep. Isotopic enrichments of plasma [U-13C]glucose and exhaled 13CO2 were determined for calculating the parameters of plasma glucose metabolism. Turnover and oxidation rates of plasma glucose did not change with dietary CP intake levels. It is likely that in adult sheep, plasma glucose metabolism is not influenced by dietary CP intake, when sufficient digestible energy is supplied.