UREA KINETICS IN HEALTHY WOMEN DURING NORMAL-PREGNANCY

Urea kinetics were measured in normal women aged 22-34 years at weeks 16, 24 and 32 on either their habitual protein intake (HABIT) or a con trolled intake of 60 g protein/d (CONTROL), using primed-intermittent oral doses of [(NN)-N-15-N-15]urea and measurement of plateau enrichme nt in urinary urea over 18 h (ID) or a single oral dose of [(NN)-N-15- N-15]urea and measurement of enrichment of urea in urine over the foll owing 48 h (SD). The intake of protein during HABIT-ID (80 g/d) was gr eater than that on HABIT-SD (71 g/d); urea production as a percentage of intake was significantly greater at week 16 for HABIT-ID than HABIT -SD, whereas urea hydrolysis at week 16 was greater for HABIT-SD than HABIT-ID and urea excretion at week 32 was greater for HABIT-ID than H ABIT-SD. The combined results for HABIT-ID and HABIT-SD showed a signi ficant reduction in urea production at week 32 compared with week 24. Urea excretion decreased significantly from week 16 to week 24 with no further decrease to week 32 and urea hydrolysis was significantly gre ater at week 24 than either week 16 or week 32. Compared with HABIT, o n CONTROL there was a decrease in urea production at week 16, and urea excretion was significantly reduced at week 16. For all time periods urea production was closely related to the sum of intake plus hydrolys is. Hydrolysis was greatest at week 24 and closely related to urea pro duction. There was a significant inverse linear relationship overall f or hydrolysis as a proportion of production and excretion as a proport ion of intake, The results show that on HABIT N is more effectively co nserved in mid-pregnancy through an increase in urea hydrolysis and sa lvage, and during late pregnancy through a reduction in urea formation . Lowering protein intake at any stage of pregnancy increased the hydr olysis and salvage of urea. The staging of these changes was later tha n that in pregnancy in Jamaica.