The excretion of glucose during normal pregnancy and after delivery

Upregulation Of Renal GLUT2 And SGLT2 Is Involved In High-Fat Diet-Induced Gestational Diabetes In Mice

INTRODUCTION

Gestational diabetes mellitus (GDM) is a metabolic disorder during mid- to late-pregnancy characterized by hyperglycemia, insulin resistance and fetal mal-development. Glucose transporter type 2 (GLUT2) and sodium-coupled glucose cotransporters 2 (SGLT2) in the proximal tubules play a critical role in the reabsorption of glucose and have been linked to the occurrence of type 2 diabetes mellitus (T2DM). Our study was designed to investigate the role of GLUT2 and SGLT2 in the pathogenesis of GDM, which is considered a forerunner of T2DM, and investigate the related molecular mechanism.

METHODS

High-fat diet (HFD) was utilized to build a GDM mouse model that closely induces metabolic abnormalities similar to human GDM. Body weight, blood glucose and serum insulin were recorded in the experimental process. Glucose tolerance was determined by the use of an intraperitoneal glucose tolerance test (IPGTT). In addition, levels of GLUT2 and SGLT2 were evaluated to further explore the underlying mechanism of GDM.

RESULTS

HFD feeding induced abnormal glucose metabolism as manifested by increased levels of blood glucose and insulin and prominent glucose intolerance. Additionally, fetal mice from mother feed on HFD showed higher mean body weight. Furthermore, HFD feeding led to an increase in the number of positive cells of GLUT2 and SGLT2 in the renal proximal tubule and the expressions of renal GLUT2 and SGLT2 mRNA and proteins in mice. However, no obvious change was observed in renal morphology.

CONCLUSION

Our study demonstrates a potential involvement of renal GLUT2 and SGLT2 in GDM pathology in an HFD-induced GDM mouse model, which further supports the role of renal GLUT2 and SGLT2 not only in T1DM and T2DM but also in GDM.

Impaired decline in renal threshold for glucose during pregnancy - a possible novel mechanism for gestational diabetes mellitus

BACKGROUND

The renal threshold for glucose (RT(G)) is determined by the nephron's reabsorptive capacity. Glucose is reabsorbed through sodium-coupled glucose cotransporters in the proximal tubules. During pregnancy, renal glucose reabsorptive capacity decreases, possibly, due to reduced glucose transporter expression. Our hypothesis is that inadequate decrease in RT(G) during pregnancy will make women more prone to develop gestational diabetes mellitus (GDM).

METHODS

Pregnant women (n = 40) who were referred to our center for oral glucose tolerance test (OGTT) were included in the analysis. Plasma glucose levels and urinary glucose excretion were measured for 4 h after 100 g oral glucose load. These data were used to calculate RT(G) . The subjects were divided into two cohorts, GDM and non-GDM, according to the OGTT results. Mean RT(G) was compared between the two groups.

RESULTS

Fifteen (37.5%) of the women were diagnosed with GDM. Seventeen participants had only trace amounts of urinary glucose excretion, and no value of RT(G) could be determined; RT(G) was determined in the other 23 subjects. Among these 23 women, 13 were diagnosed as GDM, and 10 had normal OGTT. RT(G) was lower in the non-GDM women (146 ± 14 mg/dL) than in the GDM women (182 ± 18 mg/dL), p < 0.001.

CONCLUSIONS

Gestational diabetes mellitus is associated with higher RT(G) during pregnancy compared with non-GDM. These results support our hypothesis that inadequate decrease of the RT(G) may have a pathophysiological role in the development of GDM.

Renal haemodynamics and tubular function in human pregnancy

In human pregnancy, effective renal plasma flow and glomerular filtration rate increase to levels 50-80% above non-pregnant values. The increments occur shortly after conception, persist throughout the second trimester and reduce slightly in late pregnancy. The hyperfiltration of pregnancy does not seem to be a potentially damaging process, as intraglomerular pressure remains unchanged. The increased excretion of glucose and other nutrients, as well as uric acid and protein, is related in part to altered tubular function. Renal physiology is altered so much in pregnancy that non-pregnant norms cannot be used in antenatal care.

Altered urinary excretion of lysosomal hydrolases in pregnancy

Creatinine concentrations and the activities of five lysosomal hydrolases were measured in the serum and urine of 14 healthy nonpregnant control women and 19 healthy pregnant women. Fractional enzyme excretion (FEE) values for beta-glucuronidase, beta-hexosaminidase, alpha-galactosidase, beta-galactosidase, and alpha-mannosidase were calculated and compared between the two groups of subjects. Fractional enzyme excretion was calculated as the ratio of enzyme clearance to creatinine clearance. The FEE values for beta-galactosidase and alpha-mannosidase between the nonpregnant and pregnant populations were not statistically different; however, relative to the nonpregnant control group, the median FEE values for beta-glucuronidase (P < 0.03), beta-hexosaminidase (P < 0.06), and alpha-galactosidase (P < 0.02) were decreased approximately 1.5-, 1.8-, and 2.7-fold, respectively, in the pregnant population. The median urinary beta-galactosidase activity for the pregnant population, when expressed on the basis of creatinine, was twofold higher than that of the control group (P < 0.0005). These data indicate that with pregnancy there are marked changes in the urinary excretion of selected lysosomal enzymes, particularly alpha-galactosidase and beta-glucuronidase. When the molecular weights of these five hydrolases were compared between kidney homogenate and control urine, a correlation of 0.96 was observed, while the correlation between control serum and control urine was 0.69. This suggests that the FEE value differences between the pregnant and control groups are most likely due to changes in tubule cell metabolism, either decreased secretion or increased reabsorption. These biochemical changes may provide a means of assessing changes in renal function during pregnancy.

Renal haemodynamics and tubular function in human pregnancy

In human pregnancy, effective renal plasma flow and glomerular filtration rate increase to levels 50-80% above non-pregnant values. The increments occur shortly after conception, persist throughout the second trimester and reduce slightly in late pregnancy. The hyperfiltration of pregnancy does not seem to be a potentially damaging process. The increased excretion of glucose and other nutrients, as well as uric acid and protein, is related in part to altered tubular function. Renal physiology is altered so much in pregnancy that non-pregnant norms cannot be used in antenatal care.

Does random blood glucose sampling outdate testing for glycosuria in the detection of diabetes during pregnancy?

A random blood glucose concentration was determined in 2403 pregnant women attending an antenatal clinic at between 28 and 32 weeks' gestation. The calculated 99% cut off values were 6.1 mmol/l (110 mg/100 ml) within two hours after a meal and 5.6 mmol/l (101 mg/100 ml) more than two hours after a meal. Patients with a blood glucose concentration in excess of these values were referred for a 75 g oral glucose tolerance test. Of 59 referred, four were found to have previously unsuspected but unequivocal diabetes mellitus and another four to have impaired glucose tolerance on the basis of the World Health Organisation's criteria. Screening all antenatal patients by randomly measuring blood glucose concentrations is not only cheap and efficient but also does not interfere with the routine of busy antenatal clinics.

Reference intervals for urinary glucose in pregnancy

Reference interval upper limits for glucose in urine from non-fasting pregnant women, estimated by a glucose dehydrogenase method are higher than for non-pregnant women (1.4 mmol/l) and increase with gestational age: week 10-20, 2.0 mmol/l (n = 158); week 21-30, 2.3 mmol/l (n = 124) and week 31-42, 2.7 mmol/l (n = 245). The reagent strip Tes-Tape correctly identified glucosuria above a clinical decision limit of 7 mmol/l and reacted in two-thirds of urine samples with from upper reference interval to 8 mmol/l of glucose. The reagent strip Uristix in no case gave a positive reaction.

Antenatal screening for diabetes mellitus by random blood glucose sampling

A system is described for screening an antenatal population for diabetes mellitus based upon random blood glucose sampling. Samples obtained from 186 healthy pregnant women at 28 weeks gestation provided a range of blood glucose concentrations after normal meals from which it was possible to derive two glucose values to define an upper limit of normality. The first, 6.4 mmol/l if within two hours of eating and the second, 5.8 mmol/l when taken more than two hours postprandial were prospectively applied to the screening of 763 consecutive antenatal patients. Ten women exceeding these limits were referred for an oral glucose tolerance test and three were found to have a diabetic response, an incidence of about four undiagnosed diabetic women per 1000 antenatal population.

Kinetics of glucose handling in renal glucosuria during pregnancy

Renal glucose titration studies were carried out in eight pregnant women with renal glucosuria and six female controls. it could be shown that the kinetics of renal glucosuria in pregnancy are very similar to familial renal glucosuria of type A. The tubular maximum of glucose reabsorption was lowered in our pregnancies to about the half. The data obtained clearly indicate that the renal threshold for glucose can be lowered significantly in humans by a still unknown endogenous factor.

The effect of pregnancy on the renal handling of glucose

Tubular reabsorption of glucose has been measured during glucose infusion in 29 healthy women during and after pregnancy. All the women had normal glucose tolerance to an oral load, and normal glucose excretion when not pregnant, but exhibited a wide range of daily glucose excretion in pregnancy. Throughout pregnancy the renal reabsorption of glucose is less effective than in the non-pregnant state and, in general, the greater the amount fo glycosuria which develops in pregnancy, the less effective is the reabsorption during infusion. Post partum, women with minor degrees of glycosuria during the preceding pregnancy return to a normal highly efficient reabsorption performance during infusion, but women who exhibit greater degrees of glycosuria have a reduced capacity to reabsorb even though they are no longer glycosuric after the pregnancy. It is concluded that pregnancy imposes some specific change in the glucose reabsorptive capacity of the proximal tubule and that women with more than usual degrees of glycosuria in pregnancy may, in addition, have an element of tubular damage. This is discussed in relation to other renal function changes in pregnancy in an attempt to explain the characteristic intermittency of clinical glycosuria in pregnancy.