THE AMINOACIDURIA OF PREGNANCY

Summary

The concentration of free amino acids in plasma and their excretion in urine was measured serially in ten healthy women during pregnancy and again postpartum. Almost all amino acids were excreted in greater amounts during pregnancy than in the non-pregnant state and there appeared to be three definable patterns. The excretion of the five amino acids lost in greatest amount, glycine, histidine, threonine, serine and alanine, increased rapidly in early pregnancy to three or four times the non-pregnant rate and continued to increase as pregnancy proceeded. For seven others: lysine, cystine, taurine, tyrosine, phenylalanine, valine and leucine, there was also a greatly increased excretion in early pregnancy, but there after excretion tended to fall. The remaining six amino acids measured showed little or no increase in excretion.

Renal clearance increased commensurately, approximately 30 ml. per minute for histidine and glycine, and it could be calculated that an average of some 20 per cent of filtered glycine and histidine was lost in the urine.

The pattern of excretion is not related to plasma levels, which for most amino acids are somewhat below non-pregnant levels; nor does it appear to be related to the chemical structure or biological function of the amino acids. The picture is of a variable failure of normal reabsorptive mechanisms, cause unknown.