Insulin receptor binding to monocytes and erythrocytes during normal human pregnancy

Physiological leukocytosis during pregnancy is associated with changes in glucose transporter expression of maternal peripheral blood granulocytes and monocytes

PROBLEM

The scarce data on glucose transporter expression of leukocytes are contradictory and nothing is known about changes accompanying physiological leukocytosis during pregnancy, which imposes acute metabolic demands on the cells.

METHOD OF STUDY

Cytospin preparations of intravascular leukocytes were searched immunocytochemically for the high affinity glucose transporters GLUT1, 3 and 4. Pregnancy-associated quantitative changes in transporter expression were assessed by flow cytometry.

RESULTS

Granulocytes and monocytes stained for GLUT1, 3 and 4. Major changes in cell surface transporter expression during pregnancy were a 36% (P < 0.05) down-regulation of granulocyte GLUT1 at term, and an increase in monocyte GLUT3 levels to 137% (P < 0.05), paralleled by a 24% (P < 0.05) decrease in GLUT4 content in second trimester. Apart from a minor subpopulation, lymphocytes were negative for these carriers.

CONCLUSION

GLUT1, 3 and 4 are abundantly expressed in granulocytes and monocytes. The particular isoforms are differentially regulated during pregnancy, suggesting an individual functional significance.

The genetics and pathophysiology of type II and gestational diabetes

The development of both type II diabetes and gestational diabetes is probably governed by a complex and variable interaction of genes and environment. Molecular genetics has so far failed to identify discrete gene mutations accounting for metabolic changes in NIDDM. Both beta cell dysfunction and insulin resistance are operative in the manifestation of these disorders. Specific and sensitive immunoradiometric assays found fasting hyperproinsulinemia and first-phase hypoinsulinemia early in the natural history of the disorder. A lack of specificity of early radioimmunoassays for insulin resulted in measuring not only insulin but also proinsulins, leading to overestimation of insulin and misleading conclusions about its role in diabetes. The major causes of insulin resistance are the genetic deficiency of glycogen synthase activation, compounded by additional defects due to metabolic disorders, receptor downregulation, and glucose transporter abnormalities, all contributing to the impairment in muscle glucose uptake. The liver is also resistant to insulin in NIDDM, reflected in persistent hepatic glucose production despite hyperglycemia. Insulin resistance is present in many nondiabetics, but in itself is insufficient to cause type II diabetes. Gestational diabetes is closely related to NIDDM, and the combination of insulin resistance and impaired insulin secretion is of importance in its pathogenesis.

Insulin receptor binding to erythrocytes in the first half of pregnancy is increased in healthy pregnant women as compared with non-pregnant or gestational diabetic women

Insulin binding to erythrocytes was measured longitudinally by a competitive radioreceptor assay in 21 healthy pregnant (HP) and 20 well-controlled gestational diabetic women (GD) in 4-week intervals throughout pregnancy and at day 4 post-partum. Maximum insulin binding (maxbdg) at weeks 8-14 was increased (P < 0.001) in HP (median: 6.0%) but not in GD (median: 2.7%) as compared with non-pregnant control subjects (C) (median: 3.6%; previously reported: Clin. Chim. Acta 1992;207:57-71) due to an increased number of high-affinity insulin receptors. Throughout gestation the binding decreased continuously, to reach at term the levels found in C. In GD maxbdg remained close to the level of C throughout pregnancy. Binding differences between HP and GD were independent of the body mass index. Maxbdg did not differ between diet- and insulin-treated patients. It was higher in women whose offspring had low umbilical cord insulin levels (< 10 mu units/ml). The findings suggest that (a) higher insulin binding in HP could contribute to the improved glucose tolerance in early pregnancy and (b) the lack of increase in insulin binding during early pregnancy in gestational diabetes might be one factor leading to the manifestation of the disease in late pregnancy. However, it must be kept in mind that insulin receptors on erythrocytes do not necessarily resemble those on the major target tissues of insulin.

Aetiology of gestational diabetes

Glucose tolerance deteriorates in human pregnancy, but about 97-98% of all pregnant women retain a normal glucose tolerance and only 2-3% develop gestational diabetes. The data reviewed show that the diabetogenicity of pregnancy is not due to diminished secretion of insulin or disproportional secretion of proinsulin or glucagon, nor is an increased insulin degradation involved. Only quantitative differences in insulin secretion have been observed between normal pregnant women and women with gestational diabetes. The insulin responses to an oral glucose load or a test meal are thus lower in gestational diabetic women than in normal pregnant women, despite significantly higher plasma glucose concentrations in the gestational diabetics. Also the insulin responses to intravenous glucose injections or infusions are abnormal in gestational diabetics when compared with normal pregnant women, a difference which is still detectable for some time after the completion of pregnancy in at least a fraction of gestational diabetic women. There is thus ample evidence that the diabetogenicity of pregnancy is related to a pronounced peripheral resistance to insulin. The resistance is of a similar magnitude in normal pregnant women and women with gestational diabetes, and it does not seem to be caused by significant alterations in insulin receptor binding to target tissues. The insulin resistance of the whole body is increased to about three times that seen in the non-pregnant state. The increased resistance is caused by post-insulin receptor events and is probably brought about by the cellular effects of the increased plasma levels of one or more of the pregnancy-associated hormones and free cortisol. There is evidence that the resistance is predominantly located to the muscle tissue, where significant reductions in certain key enzymes in glucose and lipid metabolism have been demonstrated. Published evidence points to a similar degree of insulin resistance in normal pregnant women and normal weight women with gestational diabetes. Most normal pregnant women are able to counteract the peripheral resistance by a significant augmentation of their basal and nutrient-stimulated insulin secretion. However, a few (2-3%) of the women do not appear to have the capability to produce a sufficiently large increase in insulin secretion and hence cannot overcome the peripheral resistance. These are the women who become glucose intolerant to such an extent that the diagnostic criteria for gestational diabetes are fulfilled.

Red blood cell insulin receptors in health and disease

CONTENTS

Structure and characteristics of erythrocyte insulin receptor. Red blood cell age and insulin receptors. Insulin receptors in human disease states. Obesity. Chronic renal failure. Acanthosis nigricans. Miscellaneous disease states. Insulin receptors in children. Insulin receptors in women during pregnancy. Insulin binding and other hormones. Comparison of biosynthetic insulin, pancreatic human insulin and porcine insulin binding to erythrocytes. Effect of exercise on insulin binding to red blood cells of normal human volunteers. Miscellaneous insulin binding studies. Insulin internalization and degradation. Insulin and erythrocyte metabolism. Summary and conclusion.

Adipocyte insulin receptor binding and lipogenesis at term in normal pregnancy

Lipogenesis in subcutaneous abdominal adipocytes during late human pregnancy was investigated by studying insulin receptor binding, 3-O-methyl-(14C-(U]-glucose flux and incorporation of (14C(U]-glucose into CO2 (oxidation) and total lipids (lipogenesis) in adipocytes from 18 health pregnant women undergoing Caesarean section at term, and 19 non-pregnant women undergoing gynaecological surgery. The cell diameter and fasting insulin were increased in the pregnant women, compared with controls (P less than 0.01 and P less than 0.05, respectively). The insulin receptor binding, 3-O-methyl-glucose flux, and basal oxidation were similar in both groups. Basal lipogenesis was higher in adipocytes from pregnant women than from controls (P less than 0.05), but the maximally stimulated increment was similar in both groups. Basal and maximally stimulated lipogenesis correlated positively with the cell diameter (P less than 0.001 and P less than 0.05, respectively). The findings indicate that lipogenesis in subcutaneous abdominal adipocytes from pregnant women is increased due to post-receptor events and that adipocytes do not contribute to the insulin resistance in late pregnancy.

Glucose tolerance and insulin receptor binding to monocytes and erythrocytes in patients with cystic fibrosis

Cystic fibrosis (CF) is the most frequent life threatening hereditary disease in the Western World with an incidence of approximately 1:2000. Due to increasing survival rates the high frequency of abnormal glucose tolerance has become an important problem. We compared insulin concentrations during oral glucose tolerance test and insulin receptor binding to both monocytes and erythrocytes from 9 patients with CF, with results from 10 healthy controls of similar body weight. The insulin: glucose ratio was increased in the fasting state (p less than 0.05) in patients with CF compared to controls, indicating an increased insulin resistance in CF-patients. The total insulin secretion during oral glucose tolerance test as judged by the area beneath the insulin curve was similar in the two groups, but insulin secretion was significantly delayed in patients with CF. Insulin receptor binding to monocytes and the number of receptors were significantly increased (p less than 0.01 and 0.02, respectively) in patients with CF whereas the dissociation constant was similar in patients with CF and controls. No difference was observed in insulin receptor binding to erythrocytes between the two groups. No correlations were found between insulin receptor binding to monocytes or erythrocytes and glucose tolerance or insulin concentrations.