Studies on the control of gluconeogenesis in sheep: effect of propionate, casein and butyrate infusions

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Abstract
1. Short-term effects of infusions of propionate, amino acids and butyrate on gluconeogenesis, as indicated by changes in the irreversible loss of plasma glucose, synthesis of glucose from ruminal propionate or fixation of blood bicarbonate into glucose have been examined in sheep given their daily ration in twenty-four equal portions at hourly intervals.Sheep received intravenous infusions of [6-3H]glucose usually, in combination with [U-14C]glucose or NaH14CO3or with intraruminal infusions of [2-14C]propionate. Substrates were infused over a 3–7 h period and followed estimates of pre-infusion kinetic measurements.2. It was demonstrated that intraruminal and intramesenteric vein infusions of sodium propionate and intra-abomasal infusions of casein hydrolysate stimulated gluconeogenesis. Glucose synthesis showed a linear response to the infusion of these substrates, which varied from 0·35–6·35 mmol propionate/min and 50–160 mg casein/min.3. The increment in the measured production rate of propionate in the rumen was consistently less than the rate of addition of propionate to the rumen.4. Intramesenteric vein infusions of sodium butyrate at successive rates of 0·25 and 0·50 mmol/min produced only an initial transient increase in plasma glucose production. Since the rate of glucose synthesis from ruminal propionate was not altered, it was suggested that butyrate initiated glycogen mobilization.