The measurement of entry rates of propionate and of butyrate in sheep

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Abstract
Difficulties associated with the measurement of the entry rates of propionate and of butyrate in sheep by isotope dilution were partially overcome by the continuous infusion of labelled substrate together with sufficient carrier substrate to raise the concentration in the blood to 0.5-1.0 m-mole/1. This procedure allowed measurements to be made with an accuracy of about [plus or minus]20%. Experimentally determined changes in the specific activities of infused sub-strates in portal and peripheral blood were in agreement with predictions based on theoretical analysis of a model system. Entry rates of propionate after feeding were in the range 1.45-3.0 m-moles/hour/kg body weight (2 sheep), declining to 0.57-0.71 m-mole/hour/kg (3 sheep) in the starved (24 hour) animal. No entry of propionate could be detected in 1 animal examined after it had been starved from 48 hours. Entry of butyrate was 0.33-0.48 m-mole/hr./kg (2 sheep) after feeding, but zero entry rates were observed in sheep starved for 24 hours.