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Changes in activity of enzymes related to glycolysis, gluconeogenesis and lipogenesis in placentae from diabetic women
Placenta (I984), 5, 55-6o
Changes in Activity of Enzymes Related to Glycolysis, Gluconeogenesis and Lipogenesis in Placentae from Diabetic Women YORAM
Z. D I A M A N T a' c, R I T A
KISSILEVITZ a & ELEAZAR
SHAFRIR b
Department of Obstetrics and Gynaecology, and bDepartment of Clinical Biochemistry, Hadassah University Hospital and Hebrew University-Hadassah Medical School, Jerusalem, Israel c Present address: Department of Obstetrics and Gynaecology, Bikur Holim Hospital, Jerusalem, Israel Address correspondenceto: Professor Eleazar Shafrir, Department of Biochemistry, Hebrew University-Hadassah Medical School, PO Box II72, Jerusalem 9 z oio, Israel
INTRODUCTION It has repeatedly been shown that babies of diabetic mothers tend to be heavier than normal, but in fact a decrease in birth weight occurs throughout the White Classes A-D, and in class F, the infants are small for gestational age (Emmrich and G6del, i97 i; Pedersen, i976). Clinical studies suggest that placental functional disturbance is associated with retarded fetal growth, increased morbidity and fetal death, but no clear pathological changes underlying this disturbance have so far been identified. Abnormalities in the structure of the trophoblast, stroma and vasculature of the terminal villi have been held responsible for intrauterine fetal deprivation, perinatal death and respiratory distress syndrome (Werner and Schneiderman, 1972; Burstein, Soule and Blumenthal, I975), but no correlation with the severity of diabetes has been shown (Fox, 1975)Similar placental changes have been observed in gestational diabetes and in normal pregnancies (Jones and Fox, 1976a, I976b), but whether these alterations affect placental transport or metabolism is not known. Adequate placental transport function is linked to normal placental intermediary metabolism and substrate supply from maternal plasma. Diabetes is known to produce pronounced changes in the maternal plasma levels of glucose, free fatty acids, triglycerides and amino acids, as well as hormonal alterations, all of which may affect the activity of enzymes and the metabolic pathways of various tissues. In a previous study (Diamant et al, 1982) we have shown that the contents of glycogen, triglycerides and phospholipids are increased in term placentae, when expressed either as per gram of tissue weight, per gram of DNA or as total placenta. This was particularly significant in insulin-dependent class B-F patients. Less impressive increases were seen in gestational diabetics. We now wish to report that these compositional changes are also accompanied by alterations in the activity of enzymes of intermediary metabolism in the placenta.
Y. Z. Diamant, R. Kissilevitz, E. Shafrir
56
M A T E R I A L S AND M E T H O D S Placentae were obtained immediately after delivery from 23 women with gestational diabetes, i2 insulin-dependent diabetic women and 5~ non-diabetic women. Placentae were weighed, placed in plastic bags for storage at - 2o~ and examined within a week. A detailed description of the patients from whom the placentae were obtained is included in an earlier publication pertaining to the same material (Diamant et al, 1982 ). On the day of investigation, samples were removed from all quandrants of the frozen placentae, thawed, cut into thin slices and pooled. Tissue D N A was extracted and determined by diphenylamine reaction, according to the method of Richards (I974). Placental slices were homogenized (i : 3, w/v) in a 0.2 .M sucrose solution containing triethanolamine (2 m i , pH 7-4), disodium E D T A (I raM) and dithioerythreitol (1 m i ) . The homogenates were centrifuged at lOOOOOg at 4~ for 3omin. The supernatant fluids were used for enzyme assays. The cytoplasmic protein content was measured by the method of Lowry et al (195I). The activities of enzymes related to the glycolytic pathway (pyruvate kinase, EC 2.7.1.4o), gluconeogenic pathway (phosphoenolpyruvate carboxylase, EC 4. i. 1.32, aspartate aminotransferase, EC 2.6.I.i), pentose shunt (glucose-6-phosphate dehydrogenase, EC 1.1.1.49 and 6phosphogluconate dehydrogenase EC 1.1.1.43 ) and N A D P H generation (NADP-malate dehydrogenase, 'malate enzyme' EC i. i. 1.4o) were determined by the methods used in liver and adapted for placental tissue as described elsewhere (Diamant and Shafrir, 1972; Diamant et al, I975). All enzyme activities were expressed as nmol substrate metabolized per mg protein or per mg D N A at 37~ Student's t-test was used for statistical evaluation of the results.
RESULTS The data on placentae, babies and maternal fasting glucose values are presented in Table 1. The placenta and baby weight in gestational diabetic patients was higher than in normal and insulindependent diabetic groups. The one-minute Apgar score of 8.9 + o.8 of the normal newborn was reduced to 6.3 + o.9 in the insulin-dependent diabetic group ( P < o.os). The activity of placental enzymes is recorded in Tables 2 and 3. Pyruvate kinase activity was significantly increased in the gestational diabetic group and significantly decreased in the insulin-dependent group, when compared with the control group. The activity of glucose-6phosphate and 6-phosphogluconate dehydrogenase was significantly elevated in both diabetic groups. The activity of the enzymes related to gluconeogenesis, phosphoenolpyruvate carboxylase and aspartate aminotransferase was virtually unchanged. The activity of NADPmalate dehydrogenase involved in N A D P H generation increased significantly in the insulinTable z. Maternal serum glucose levels and data on placentae and babies from normal and diabetic pregnancies
Pregnancy Normal (50) Gestational diabetes (23) Insulin--dependent diabetes (i2)
Maternal serum glucose (mg/dl)
Placentalweight (g)
Baby weight (g)
82 + 6 ioi + 7 t32 +__IOa
550 + 28 664 + 60 615 + i io
3222 + 99 3840 + I26a 3238 + 315
The values are mean+ s.e. for the number of cases given in parentheses. Denotes a significant difference from normal pregnancyat P < o.o5 at least.
Placental E n z :rues in Diabetes
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58
Y. Z. Diamant, R. Kissilevitz, E. Shaflr
dependent diabetic group and slightly in the gestational diabetic group. All these changes were evident when calculated per whole placenta, per DNA or per cytoplasmic protein content. DISCUSSION Both human and rat placentae in diabetic pregnancy accumulate triglycerides, phospholipids and glycogen in correlation to the elevation in their metabolic precursors in the maternal circulation (Diamant et al, 1982; Shafrir and Khassis, 1982). Our present results demonstrate that these changes in composition are accompanied by modifications in the activities of several enzymes regulating the intermediary metabolism. The increase in the activity of pyruvate kinase and pentose shunt enzymes in the placentae from the gestational diabetes group might be construed to be related to hyperinsulinaemia (maternal and/or fetal) since these enzymes are known to be insulin-dependent in the liver or adipose tissue. This is difficult to reconcile with our previous results in diabetic rats (Diamant and Shafrir, I978) which have indicated that, in general, placental enzymes do not exhibit adaptive properties. Their activity does not respond to severe insulin deficiency. It should be borne in mind, however, that the experimental diabetes produced in our rat model on day 12 of pregnancy (Diamant and Shafrir, 1978) was short in duration compared with human gestation and may have been not sufficient in time to induce the adaptive changes. Therefore, any extrapolation of these interpretations to human placenta must await further definition of the properties of placental enzymes in general. On the other hand, there is evidence that the enzymes of the placenta and other tissues may be influenced by a prolonged abundance of fuels, such as glucose or fatty acids, rather than by hormonal alterations. Hyperglycaemia alone may be responsible for the increased activity of NADPH-generating enzymes in analogy to other insulin-independent tissues. Kidneys (Sochor, Baguer and Mclean, I979) and jejunal mucosa (Tyrrel and Anderson, 1971) were shown, for example, to respond with increased activity of pentose shunt and other glycolysis-related enzymes in diabetic rats. In this respect, the placenta may be regarded as an insulin-independent tissue. The metabolic factor causing the decrease in pyruvate kinase activity in the placentae of the insulin-dependent group is not readily apparent. Pyruvate kinase may be affected by inadequate insulinization, inhibition by certain amino acids known to be elevated in diabetes and/or by the reduced glycolytic flow resulting from the inhibition of glycolysis at the fructose-6-phosphate step through products of fatty acid oxidation, as it is known to occur in muscle (Newsholme and Randle, i96i , 1964; Neely, Whitfield and Morgan, I97o; Whitmer et al, i978). In addition, the reduced blood flow and long-standing hypoxia caused by the diabetes-induced placental vascular abnormalities (Driscoll, I964) may also be instrumental in curtailing glycolysis and pyruvate kinase activity. It may be mentioned that a similar pattern of enzyme activity changes was observed in placentae from pregnancies complicated by fetal distress, due to prolonged cord compression, where hypoxia and over-exposure to locally accumulating glucose may be expected (Diamant and Kissilevitz, I98o). Although pyruvate kinase is not a rate-limiting enzyme, in general, and is present in the placenta in great excess, nevertheless an adaptive decrease in its optimal activity signals a diminished capacity of anaerobic glucose metabolism, the main source of placental energy (CO2/lactate ratio = i/io; Beyth et al, 1977). Thus even a small decrease in placental glycolysis may in turn result in an appreciable reduction in the energy-dependent substrate transport across the placenta, which is essential for fetal development (e.g., amino acids).
59
Placental Enzymes in Diabetes
Pedersen (1976) observed that the low baby birthweight throughout the White classes A - F is accompanied by a decrease in amino acid content in the fetal circulation. In our study, the mean baby weight in the insulin-dependent groups (which included B - C classes o f patients) was not decreased, but in the gestational diabetic groups with increased glycolytic capacity it was significantly higher than in the control. No cases of intrauterine or intrapartum fetal death occurred in our series, but as mentioned the one-minute Agpar score was low in the insulindependent group of pregnancies.
SUMMARY The activity o f enzymes with a regulatory function in the pathways of glycolysis, gluconeogenesis and NADPZgeneration was investigated in 5o placentae from normal pregnancies and deliveries, 2 3 placentae from women with gestational diabetes, and 12 placentae from insulindependent patients. In placentae from the gestational diabetic group, the activity of pyruvate kinase and of NADPH-generating enzymes was raised and the activity of enzymes connected to glucogenesis was unchanged. These alterations were attributed to the oversupply of glucose and insulin to morphologically normal and well-oxygenated placental tissue. In the placentae from the insulin-dependent group, the activity o f pyruvate kinase was reduced, the activity of NADPH-generating enzymes was enhanced and the activity of those related to the gluconeogenesis was unchanged. It is suggested that this pattern of enzyme changes reflects a reduction in the glycolytic capacity in these placentae, which may be due to inhibition by products of enhanced fatty acid oxidation in diabetes, amino acids and/or by long-term anoxia as a result of uteroplacental circulatory disturbances. T h e possible relation of reduced energy-forming capacity of the placenta in diabetes to its transport function is discussed.
REFERENCES
Beyth, Y., Neuman, S., Gutman, A. & Shafrir, E. (i977) Effectof prolongedgestationon placentaland maternalliver enzyme activities in the rat. Diabetes and Metabolism, 3, 91-96. Burstein, R., Soule, S. D. & Bhunenthal, H. T. (1975) Histogenesisof pathologicalprocessin placenta of metabolic disease in pregnancy: I I. The diabetic state. American Journal of Obstetrics and Gynec~?logy, 74, 96-IO49 Diamant, Y. Z. & Kissilevltz, R. (198o) Placentain intrauterine fetal deprivation:I I. Biochemicalprofileof placentas from deliveries associatedwith fetal distress. Israel Journal of Medical Sciences, 16, 7-14. Diamant, Y. Z. & Shafrlr, E. 0972) Enzymes of carbohydrate and lipid metabolism in the placenta and liver of pregnant rats. Biochimica et Biophysica Acta, 279, 424-43o. Diamant, Y. Z. & Shafrir, E. (i978) Placentalenzymesof glycolysis,gluconeogenesisand lipogenesisin diabetic rats and in starvation. Diabetologia, 15, 481-485. Diamant, Y. Z., Mayorek, N., Neuman, S. & Shafrir, E. (I975) Enzymesof glucose and fatty acid metabolismin early and term human placenta. American Journal of Obstetrics and Gynecology, x2I, 58-61. Diamant, Y. Z., Metzger, B. E., Freinkel, N. & Shafrir, E. (i 982) Placentallipid and glycogencontent in human and experimental diabetes mellitus. American Journal of Obstetrics and Gynecology, I44, 5-1 I. Driscoll, S. (1964)The pathologyof pregnancycomplicatedby diabetes mellitus.Medical Chnics of North America, 49, 1o53-Io67. Emmrich, P. & G6del, E. (1971) Der Zustand des Neugeborenen in Abh/ingigkeit vom morphologischen Plazentabefund beim muetterlichen Diabetes mellitus. Deutsche Gesundheitswesen, 26, 1732-1735. Fox, H. (1975) Morphologicalpathologyof placenta. In The Placenta and Its Maternal Supply Line (Ed.) Gruenwald,P. pp. i97-22o. Baltimore, MD: University Press. Ginsburg, T. & Jeacock, M. K. 0966) Some aspectsof placentalcarbohydratemetabolismin human diabetes.Journal of Obstetrics and Gynaecology of the British Commonwealth, 73, 452-455. Jones, C. J. P. & Fox, H. (1976a) An uitrastructural and uhrahistochemicalstudy of the placenta of diabetic women. Journal of Pathology 119, t23-I24. Jones, C. J. P. & Fox, H. (I976b) Placental changes in gestationaldiabetes: an ultrastructural study. Obstetrics and Gynecology, 48, 274-280.
6o
Y. Z. Diamant, R. Kissilevitz, E. Shafnr
Lowry, O. H., Rosebrough, N. J., Farr, A. Z. & Randall, R. J. (i951) Protein measurement with the Folin phenol reagent. Journal of Biological Chemistry, x93, 265-27I. Neely, J. R., Whitfield, C. F. & Morgan, H. E. (197o) Regulation of glycogenolysis in hearts: effects of pressure development, glucose and FFA. AmericanJournal of Physiology, 2x9, io83-Io88. Newsholrne, E. A. & Randle, P. J. (1961) Regulation of glucose uptake by muscle: 5. Effect of anoxia, insulin, adrenaline and prolonged starving on concentrations of hexose phosphates in isolated rat diaphragm and perfused isolated rat heart. BiochemicalJournal, 80, 655-662. Newsholme, E. A. & Randle, P. J. (i964) Effects of fatty acids, ketone bodies and pyruvate and of alioxan diabetes, starvation, hypophysectomy and adrenalectomy on the concentration of hexose phosphates, nucleotides and inorganic phosphate in perfused rat heart. BiochemicalJournal, 93, 641-65 I. Pedersen, J. (1976) Birth weight of newborn infants of diabetic women. Proceedingsof the I X CongressInternational Diabetes, New Delhi~ pp. 353-36o. Richards, G. M. (1974) Modification of the diphenylamine reaction giving increased sensitivity and simplicity on the examination of DNA. Analytical Biochemistry, 57, 369-376. Shafrir, E. & Khassis, S. (I982) Maternal-fetal fat transport versus new fat synthesis in the pregnant diabetic rat. Diabetologia, 22, i i i - i 17. Sochor, M., Baguer, N. Z. & McLean, P. (1979) Glucose overutilization in diabetes: evidence from studies on the changes in hexokinase, the pentose phosphate pathway and glucuronate pathway in rat kidney cortex in diabetes. Biochemical and Biophysical Research Communications, 86, 32-39 . Tyrrel, J. B. & Anderson, J. W. (197 i) Glycolytic and pentose phosphate pathway enzymes in jejunal mucosa, adaptive responses to aUoxan diabetes and fasting in the rat. Endocrinology, 89, xx78-I 185. Werner, C. & Scheiderrnan, W. (1972) Placentmorphologie und Placentafunction in Abh~ingigkeit v o n d e r diabetischen Stoffwedselfuhrung. Geburtshilfe und Frauenheilkunde, 32, 959-966. Whitmer, J. T., Idell-Wenger, J. A., Rovetto, M. J. & Neely, J. R. (I978) Control of fatty acid metabolism in ischemic and hypoxic hearts. Journal of Biological Chemistry, 253 , 43o5-43o9.
Changes in Activity of Enzymes Related to Glycolysis, Gluconeogenesis and Lipogenesis in Placentae from Diabetic Women YORAM
Z. D I A M A N T a' c, R I T A
KISSILEVITZ a & ELEAZAR
SHAFRIR b
Department of Obstetrics and Gynaecology, and bDepartment of Clinical Biochemistry, Hadassah University Hospital and Hebrew University-Hadassah Medical School, Jerusalem, Israel c Present address: Department of Obstetrics and Gynaecology, Bikur Holim Hospital, Jerusalem, Israel Address correspondenceto: Professor Eleazar Shafrir, Department of Biochemistry, Hebrew University-Hadassah Medical School, PO Box II72, Jerusalem 9 z oio, Israel
INTRODUCTION It has repeatedly been shown that babies of diabetic mothers tend to be heavier than normal, but in fact a decrease in birth weight occurs throughout the White Classes A-D, and in class F, the infants are small for gestational age (Emmrich and G6del, i97 i; Pedersen, i976). Clinical studies suggest that placental functional disturbance is associated with retarded fetal growth, increased morbidity and fetal death, but no clear pathological changes underlying this disturbance have so far been identified. Abnormalities in the structure of the trophoblast, stroma and vasculature of the terminal villi have been held responsible for intrauterine fetal deprivation, perinatal death and respiratory distress syndrome (Werner and Schneiderman, 1972; Burstein, Soule and Blumenthal, I975), but no correlation with the severity of diabetes has been shown (Fox, 1975)Similar placental changes have been observed in gestational diabetes and in normal pregnancies (Jones and Fox, 1976a, I976b), but whether these alterations affect placental transport or metabolism is not known. Adequate placental transport function is linked to normal placental intermediary metabolism and substrate supply from maternal plasma. Diabetes is known to produce pronounced changes in the maternal plasma levels of glucose, free fatty acids, triglycerides and amino acids, as well as hormonal alterations, all of which may affect the activity of enzymes and the metabolic pathways of various tissues. In a previous study (Diamant et al, 1982) we have shown that the contents of glycogen, triglycerides and phospholipids are increased in term placentae, when expressed either as per gram of tissue weight, per gram of DNA or as total placenta. This was particularly significant in insulin-dependent class B-F patients. Less impressive increases were seen in gestational diabetics. We now wish to report that these compositional changes are also accompanied by alterations in the activity of enzymes of intermediary metabolism in the placenta.
Y. Z. Diamant, R. Kissilevitz, E. Shafrir
56
M A T E R I A L S AND M E T H O D S Placentae were obtained immediately after delivery from 23 women with gestational diabetes, i2 insulin-dependent diabetic women and 5~ non-diabetic women. Placentae were weighed, placed in plastic bags for storage at - 2o~ and examined within a week. A detailed description of the patients from whom the placentae were obtained is included in an earlier publication pertaining to the same material (Diamant et al, 1982 ). On the day of investigation, samples were removed from all quandrants of the frozen placentae, thawed, cut into thin slices and pooled. Tissue D N A was extracted and determined by diphenylamine reaction, according to the method of Richards (I974). Placental slices were homogenized (i : 3, w/v) in a 0.2 .M sucrose solution containing triethanolamine (2 m i , pH 7-4), disodium E D T A (I raM) and dithioerythreitol (1 m i ) . The homogenates were centrifuged at lOOOOOg at 4~ for 3omin. The supernatant fluids were used for enzyme assays. The cytoplasmic protein content was measured by the method of Lowry et al (195I). The activities of enzymes related to the glycolytic pathway (pyruvate kinase, EC 2.7.1.4o), gluconeogenic pathway (phosphoenolpyruvate carboxylase, EC 4. i. 1.32, aspartate aminotransferase, EC 2.6.I.i), pentose shunt (glucose-6-phosphate dehydrogenase, EC 1.1.1.49 and 6phosphogluconate dehydrogenase EC 1.1.1.43 ) and N A D P H generation (NADP-malate dehydrogenase, 'malate enzyme' EC i. i. 1.4o) were determined by the methods used in liver and adapted for placental tissue as described elsewhere (Diamant and Shafrir, 1972; Diamant et al, I975). All enzyme activities were expressed as nmol substrate metabolized per mg protein or per mg D N A at 37~ Student's t-test was used for statistical evaluation of the results.
RESULTS The data on placentae, babies and maternal fasting glucose values are presented in Table 1. The placenta and baby weight in gestational diabetic patients was higher than in normal and insulindependent diabetic groups. The one-minute Apgar score of 8.9 + o.8 of the normal newborn was reduced to 6.3 + o.9 in the insulin-dependent diabetic group ( P < o.os). The activity of placental enzymes is recorded in Tables 2 and 3. Pyruvate kinase activity was significantly increased in the gestational diabetic group and significantly decreased in the insulin-dependent group, when compared with the control group. The activity of glucose-6phosphate and 6-phosphogluconate dehydrogenase was significantly elevated in both diabetic groups. The activity of the enzymes related to gluconeogenesis, phosphoenolpyruvate carboxylase and aspartate aminotransferase was virtually unchanged. The activity of NADPmalate dehydrogenase involved in N A D P H generation increased significantly in the insulinTable z. Maternal serum glucose levels and data on placentae and babies from normal and diabetic pregnancies
Pregnancy Normal (50) Gestational diabetes (23) Insulin--dependent diabetes (i2)
Maternal serum glucose (mg/dl)
Placentalweight (g)
Baby weight (g)
82 + 6 ioi + 7 t32 +__IOa
550 + 28 664 + 60 615 + i io
3222 + 99 3840 + I26a 3238 + 315
The values are mean+ s.e. for the number of cases given in parentheses. Denotes a significant difference from normal pregnancyat P < o.o5 at least.
Placental E n z :rues in Diabetes
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58
Y. Z. Diamant, R. Kissilevitz, E. Shaflr
dependent diabetic group and slightly in the gestational diabetic group. All these changes were evident when calculated per whole placenta, per DNA or per cytoplasmic protein content. DISCUSSION Both human and rat placentae in diabetic pregnancy accumulate triglycerides, phospholipids and glycogen in correlation to the elevation in their metabolic precursors in the maternal circulation (Diamant et al, 1982; Shafrir and Khassis, 1982). Our present results demonstrate that these changes in composition are accompanied by modifications in the activities of several enzymes regulating the intermediary metabolism. The increase in the activity of pyruvate kinase and pentose shunt enzymes in the placentae from the gestational diabetes group might be construed to be related to hyperinsulinaemia (maternal and/or fetal) since these enzymes are known to be insulin-dependent in the liver or adipose tissue. This is difficult to reconcile with our previous results in diabetic rats (Diamant and Shafrir, I978) which have indicated that, in general, placental enzymes do not exhibit adaptive properties. Their activity does not respond to severe insulin deficiency. It should be borne in mind, however, that the experimental diabetes produced in our rat model on day 12 of pregnancy (Diamant and Shafrir, 1978) was short in duration compared with human gestation and may have been not sufficient in time to induce the adaptive changes. Therefore, any extrapolation of these interpretations to human placenta must await further definition of the properties of placental enzymes in general. On the other hand, there is evidence that the enzymes of the placenta and other tissues may be influenced by a prolonged abundance of fuels, such as glucose or fatty acids, rather than by hormonal alterations. Hyperglycaemia alone may be responsible for the increased activity of NADPH-generating enzymes in analogy to other insulin-independent tissues. Kidneys (Sochor, Baguer and Mclean, I979) and jejunal mucosa (Tyrrel and Anderson, 1971) were shown, for example, to respond with increased activity of pentose shunt and other glycolysis-related enzymes in diabetic rats. In this respect, the placenta may be regarded as an insulin-independent tissue. The metabolic factor causing the decrease in pyruvate kinase activity in the placentae of the insulin-dependent group is not readily apparent. Pyruvate kinase may be affected by inadequate insulinization, inhibition by certain amino acids known to be elevated in diabetes and/or by the reduced glycolytic flow resulting from the inhibition of glycolysis at the fructose-6-phosphate step through products of fatty acid oxidation, as it is known to occur in muscle (Newsholme and Randle, i96i , 1964; Neely, Whitfield and Morgan, I97o; Whitmer et al, i978). In addition, the reduced blood flow and long-standing hypoxia caused by the diabetes-induced placental vascular abnormalities (Driscoll, I964) may also be instrumental in curtailing glycolysis and pyruvate kinase activity. It may be mentioned that a similar pattern of enzyme activity changes was observed in placentae from pregnancies complicated by fetal distress, due to prolonged cord compression, where hypoxia and over-exposure to locally accumulating glucose may be expected (Diamant and Kissilevitz, I98o). Although pyruvate kinase is not a rate-limiting enzyme, in general, and is present in the placenta in great excess, nevertheless an adaptive decrease in its optimal activity signals a diminished capacity of anaerobic glucose metabolism, the main source of placental energy (CO2/lactate ratio = i/io; Beyth et al, 1977). Thus even a small decrease in placental glycolysis may in turn result in an appreciable reduction in the energy-dependent substrate transport across the placenta, which is essential for fetal development (e.g., amino acids).
59
Placental Enzymes in Diabetes
Pedersen (1976) observed that the low baby birthweight throughout the White classes A - F is accompanied by a decrease in amino acid content in the fetal circulation. In our study, the mean baby weight in the insulin-dependent groups (which included B - C classes o f patients) was not decreased, but in the gestational diabetic groups with increased glycolytic capacity it was significantly higher than in the control. No cases of intrauterine or intrapartum fetal death occurred in our series, but as mentioned the one-minute Agpar score was low in the insulindependent group of pregnancies.
SUMMARY The activity o f enzymes with a regulatory function in the pathways of glycolysis, gluconeogenesis and NADPZgeneration was investigated in 5o placentae from normal pregnancies and deliveries, 2 3 placentae from women with gestational diabetes, and 12 placentae from insulindependent patients. In placentae from the gestational diabetic group, the activity of pyruvate kinase and of NADPH-generating enzymes was raised and the activity of enzymes connected to glucogenesis was unchanged. These alterations were attributed to the oversupply of glucose and insulin to morphologically normal and well-oxygenated placental tissue. In the placentae from the insulin-dependent group, the activity o f pyruvate kinase was reduced, the activity of NADPH-generating enzymes was enhanced and the activity of those related to the gluconeogenesis was unchanged. It is suggested that this pattern of enzyme changes reflects a reduction in the glycolytic capacity in these placentae, which may be due to inhibition by products of enhanced fatty acid oxidation in diabetes, amino acids and/or by long-term anoxia as a result of uteroplacental circulatory disturbances. T h e possible relation of reduced energy-forming capacity of the placenta in diabetes to its transport function is discussed.
REFERENCES
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