DETERMINATION OF SMALL AMOUNTS OF KETONE BODIES IN BLOOD

Metabolism of urea in late pregnancy and the possible contribution of amino acid carbon to glucose synthesis in sheep

1. Metabolism of urea in non-pregnant and pregnant sheep (1–25 d from term) has been examined. Injections of [14C]urea were used to estimate urea entry rate, urea pool size and urea space in sheep given 1000 g of a diet of equal parts of crushed oats and chaffed lucerne hay (daya) and in the same sheep 4 d after the ration had been reduced to 250 g (dayb).

2. On both experimental days (aandb), mean pool size was greater (14% on day α, 29% on dayb) and urea space was greater (54% on day α, 24% on dayb) in pregnant animals than in non-pregnant animals; mean plasma urea concentrations were lower (35%) in the pregnant animals on day a but were not significantly different on dayb.

3. The entry rate of urea was similar in all the animals on daya, but was significantly higher (34%) in pregnant than in non-pregnant animals on dayb. There was a significant decrease in urea entry rate in both pregnant (33%) and non-pregnant (86%) animals on dayb.

4. The rate of excretion of urea was lower (26% on daya, 35% on dayb) in pregnant animals, indicating a higher (31% on day α, 40% on dayb) rate of degradation of urea in the digestive tract of pregnant as compared with non-pregnant sheep.

5. Measurements of urea entry rate have been used to calculate the upper limit of amino acid deamination in pregnant and non-pregnant sheep, and this has been used as an indication of the potential availability of amino acid carbon for glucose synthesis. It is suggested that, at a maximum, amino acids may have contributed the carbon required for 63 g/d and 52 g/d of glucose on daysaandbrespectively.