The excretion of gamma-glutamyl transferase in pregnancy

Urinary excretion of N-acetyl-beta-D-glucosaminidase in normal and complicated pregnancy

The urinary excretion of N-acetyl-beta-D-glucosaminidase activity, a sensitive indicator of renal tubular injury, was monitored during and after pregnancy. During normal pregnancy, enzymuria increased progressively to levels 3-4 times above normal in the third trimester. In diabetic mothers, enzyme excretion followed a similar pattern, but was generally higher than in uncomplicated pregnancies. Also in preeclampsia, enzymuria tended to be higher than in normal pregnancy. Enzyme excretion normalized about a year after normal pregnancies, but remained elevated in diabetic subjects and in patients who had developed preeclampsia. This latter finding indicates that marginal persistent renal damage may occur during preeclampsia.

Urinary excretion of N-acetyl-beta-D-glucosaminidase and alanine aminopeptidase during pregnancy

The assay of enzyme activity in urine seems a reliable and safe method to monitor different kidney diseases. However, its use in pregnant patients might be limited by the modifications of kidney function during pregnancy. The aim of the present study was to evaluate the trend of excretion of the lysosomal enzyme N-acetyl-beta-D-glucosaminidase (NAG) and the brush border enzyme alanine aminopeptidase (AAP) during uncomplicated pregnancies. NAG excretion showed a significant increase (P less than 0.001) throughout pregnancy, while no significant modification of AAP levels was demonstrated. These data support the hypothesis that the two enzymes are excreted into the urine through different mechanisms and might constitute markers for different pathological events. As the increase of NAG excretion may be related to the kidney functional adaptation to pregnancy, different cut-off limits must be established in this period.

Increased tubular enzyme excretion in preeclampsia

The pathophysiology of preeclampsia includes ischemia and microinfarctions of the kidney, which could induce renal tubular cells to release enzymes into urine. We therefore measured the concentrations of two markers of renal tubular damage, N-acetyl-beta-D-glucosaminidase and alanine aminopeptidase, in urine specimens from women with mild or severe preeclampsia and compared the results with those from healthy pregnant and nonpregnant women. The median urinary concentrations of N-acetyl-beta-D-glucosaminidase and alanine aminopeptidase in women without preeclampsia increased progressively through the first, second, and third trimesters and reached maximum values of 1.12 and 0.77 U/mmol creatinine, respectively. Median concentrations of the two enzymes were significantly higher in women with mild preeclampsia (N-acetyl-beta-D-glucosaminidase = 1.40, alanine aminopeptidase = 1.12 U/mmol creatinine) or severe preeclampsia (N-acetyl-beta-D-glucosaminidase = 2.90, alanine aminopeptidase = 1.26 U/mmol creatinine). This increased enzyme excretion indicates subclinical preeclamptic renal tubular damage.

Non-postural serial changes in renal function during the third trimester of normal human pregnancy

Seventeen healthy women were investigated near the beginning and again near the end of the third trimester of their normal pregnancies. Infusion studies were performed in the left lateral position. There was a highly significant decrease in effective renal plasma flow but not in glomerular filtration rate, measured as inulin clearance. Plasma creatinine concentration increased significantly, but the renal handling of creatinine was unchanged; simultaneous 24-hour creatinine clearance showed a tendency to decrease. Serum urate concentration also increased significantly, apparently due to an increase in net tubular reabsorption of urate.

Structural, functional, and clinical aspects of gamma-glutamyltransferase

GGT catalyses the transfer of gamma-glutamyl residues to amino acids or small peptides. A number of publications report the purification of GGT, the rat kidney enzyme being the best characterized. Bromelain treatment liberates an active form with a molecular weight of 68,000 separable into two nonidentical glycopeptides with molecular weights of 46,000 and 22,000; the latter contains the gamma-glutamyl binding site. GGT is intimately concerned in the synthesis and metabolism of glutathione through the gamma-glutamyl cycle. There is good evidence that this plays a role in the absorption of amino acids from the glomerular filtrate and from the intestinal lumen through a translocation mechanism. Many studies indicate that the GGT content of liver is increased by enzyme-inducing drugs and that this increase is reflected in elevated activity of the enzyme in blood serum. The serum assay has potential in monitoring drug compliance. Increased serum GGT activity encountered in chronic alcoholics seems to be partly due to microsomal enzyme induction. Utility of the assay in detecting alcoholism is controversial, but it is a useful index to compliance with therapy. Dramatic increases in activity are found in many chemically-induced animal tumors, and can be recognized in premalignant cells long before any morphological changes become evident. It has been used as a test for hepatic metastases, but its predictive value has shown a wide range in the hands of many authors. A similar controversy applies to its role in monitoring cancer therapy. Many synthetic substrates have been used to measure serum GGT activity. Currently, L-gamma-glutamyl-p-nitroanilide is the most popular. Males have higher values than females; activity is very high in the neonate and rather low in pregnancy. The most universal application of serum GGT assay is in diagnosis of liver and biliary tract disease. It is widely believed that higher values occur in biliary obstruction than in parenchymal disease. However, the percentage incidence of abnormalities and the overlap of values in individual cases in different disease categories are so great that the enzyme cannot be recommended for this purpose. Isoenzyme analyses have been performed in an attempt to improve the diagnostic specificity of the serum GGT assay. Tissue-specific patterns have not been described, and disease-specific patterns cannot be reproduced with confidence. Whereas exciting advances are being made in understanding the molecular structure, mechanism, and functions of the enzyme it has yet to find a genuinely useful diagnostic role substantiated by a convincing body of scientific data.

Renal physiology in pregnancy

The changes which occur in renal excretory function during pregnancy are discussed. The relationship between glomerular filtration rate and effective renal plasma flow is examined in the light of new serial data obtained under conditions of saline diuresis. Changes in the renal handling of nutrients and in the excretion of waste products during pregnancy are reviewed.

Effect of anticonvulsant drugs on urinary excretion of gamma-glutamyl transferase in women

Excretion of gamma-glutamyl transferase was found to be significantly higher in a group of epileptic patients on long-term anticonvulsant therapy than in normal subjects. The losses, which may reflect renal enzyme induction, were unrelated to drug dose or duration of therapy and were significantly lower than those found in normal healthy pregnant women at term.