Increased Excretion of N-Acetylneuramin-(2 → 3)-lactose in the Urine of Pregnant and Lactating Rats

Abstract

The effect of pregnancy and lactation on the urinary excretion patterns of neuramin lactose and neuramin N-acetyllactosamine, as well as on the neuraminic acid levels of tissues and serum, was studied in the rat. The urinary neuramin lactose content, 1.1 mg per 24 hours per kg of body weight in control rats, increased 3-fold during the course of pregnancy. With the onset of lactation there was a dramatic increase, which reached a peak on the 6th day after delivery (176 mg per 24 hours per kg). The urinary neuramin N-acetyllactosamine content, 0.47 mg per 24 hours per kg in control rats, increased 2-fold during pregnancy, but, in contrast to the excretion of neuramin lactose, no further increase occurred during lactation. Structural characterization of the excreted neuramin lactose material based on thin layer chromatography, gas chromatography, and mass spectrometry indicated that the increase in the urinary neuramin lactose content during lactation was due to only one of the three neuramin lactoses present in rat urine, namely N-acetylneuramin-(2 → 3)-lactose. Nonsuckling for 12 hours did not affect the excretion of neuramin lactose in the urine, whereas nonsuckling for longer periods caused a successive decrease. Removal of mammary tissue during lactation reduced the urinary excretion rates of neuramin lactose to one-ninth of the preoperative value in the 10- to 22-hour period after operation, while sham operation only reduced it to one-third. Of intraperitoneally injected neuramin lactose, 60 to 70% was excreted unchanged in the urine during the subsequent 12 hours. The results show that the increased amounts of neuramin lactose found in lactation urine are most probably derived from the mammary tissue and that the rate of production of neuramin lactose is probably at least twice as high as what could be expected on the basis of its concentration in milk.