Renal tubular function in normal pregnancy

Changes in urinary excretion of six biochemical parameters in normotensive pregnancy and preeclampsia

We evaluated renal functions by urinary biochemical parameters in normotensive pregnancy and preeclampsia. The parameters are expected to be altered resulting from different abnormalities of renal glomeruli and tubules. We chose N-acetyl-beta-d-glucosaminidase (NAG), beta2-microglobulin (beta2MG), total protein (TP), albumin (Alb), urea nitrogen (UN), uric acid (UA), and creatinine (Cr). Urinary excretion of these biochemical parameter concentrations (relative to Cr) was measured simultaneously in first morning fasting urine samples from 27 healthy nonpregnant women (group 1), 32 women with normotensive pregnancies (group 2), and 26 women with preeclampsia (group 3). The average gestational age at entry was 36 weeks. Serum UN and serum UA also were measured. All the ratios were significantly higher in group 2 than in group 1. The NAG-to-Cr, TP-to-Cr, and Alb-to-Cr ratios were significantly higher in group 3 than in group 2. In contrast, the UN-to-Cr and UA-to-Cr ratios were significantly lower in group 3 than in group 2. The percent increase in the beta2MG-to-Cr ratio in group 2 relative to that in group 1 was the highest, followed by percent increases in the NAG-to-Cr, TP-to-Cr, Alb-to-Cr, UA-to-Cr, and UN-to-Cr ratios. In contrast, the percent increase in the Alb-to-Cr ratio in group 3 relative to that in group 2 was the highest, followed by percent increases in the TP-to-Cr, NAG-to-Cr, beta2MG-to-Cr, UA-to-Cr, and UN-to-Cr ratios. The percent increases in the NAG-to-Cr and beta2MG-to-Cr ratios rose markedly in normotensive pregnancy, whereas percent increases of the Alb-to-Cr and TP-to-Cr ratios were far greater in preeclampsia than in normotensive pregnancy. Renal tubular damage and reabsorption dysfunction may be impaired markedly even in normotensive pregnancy, and further deterioration in reabsorption dysfunction may be slight in preeclampsia. Renal glomerular permeability of TP and Alb may be enhanced in normotensive pregnancy and markedly enhanced in preeclampsia.

Increased excretion of N-acetyl-beta-D-glucosaminidase and beta2-microglobulin in gestational week 30

BACKGROUND

Little is known about when the urinary excretion of a combination of N-acetyl-beta-D-glucosaminidase (NAG) and beta2-microglobulin (beta2MG) concentration [relative to creatinine (Cr)] reaches maximal values during uncomplicated normotensive pregnancy. This study was thus designed to analyze when urinary excretion of biochemical parameters was increased during normotensive pregnancy.

METHODS

NAG, beta2MG, total protein, albumin, and Cr were simultaneously measured in random (untimed) midstream urine samples from 22 healthy nonpregnant women and from 82 normotensive pregnant women (22 in gestational week 20, 25 in week 30, and 35 in week 37).

RESULTS

NAG/Cr and beta2MG/Cr ratios were significantly higher (P < 0.01-0.05) in the normotensive pregnant women in gestational week 30 than in the nonpregnant control subjects and normotensive pregnant women in gestational week 20. The NAG/Cr and beta2MG/Cr ratios showed maximal values in gestational week 30. The total protein/Cr ratio was significantly higher in gestational weeks 20, 30, and 37 than in the control subjects. The albumin/Cr ratio was significantly higher in women in gestational week 30 and 37 than in women in gestational week 20 and in the control subjects.

CONCLUSIONS

The excretion of both NAG and beta2MG relative to Cr was increased and showed the maximal values in gestational week 30 during normotensive pregnancy. The increase in a tubular enzyme (NAG) might be caused by renal tubular damage, and that in a low molecular weight protein (beta2MG) might result from decreased renal tubular reabsorption. These findings suggest that renal tubular damage and reabsorption dysfunction were increased in gestational week 30.

Circulating beta-2-microglobulin levels during pregnancy and their possible relationship with feto-maternal histocompatibility

Plasma beta 2 microglobulin (beta 2m) levels have been measured by radioimmunoassay in normal pregnant women, in two successive pregnancies of a woman who shares HLA antigens with her husband, in normal twin pregnancies, in toxemic pregnancies and in hydatidiform moles. During normal pregnancy, plasma beta 2m levels decrease reaching a minimum at week 14 and increase thereafter to a maximum at week 34. In the two successive pregnancies of the one patient with HLA compatibility, beta 2m concentrations were significantly lower than in normal pregnancies. Women with monozygotic twins had significantly less beta 2m than women with heterozygotic twins. Toxemic patients bearing female fetuses had also statistically lower beta 2m levels than toxemic women with male fetuses. Patients suffering from hydatidiform moles had beta 2m levels in the range of normal pregnant patients. Since circulating beta 2m is produced by lymphocytes one might assume that low beta 2m levels reflect a reduced activity of lymphocytes. The results presented here allow to propose a hypothesis which will have to be verified that reduced beta 2m levels are associated with an increased feto-maternal histocompatibility.