Direct relationship of antepartum glucose control and fetal erythropoietin in human Type 1 (insulin-dependent) diabetic pregnancy

Summary In the present study the antepartum relationship between maternal diabetic glucose control and fetal hypoxaemia was examined in 44 Type 1 (insulin-dependent) diabetic and 23 non-diabetic control pregnancies. Maternal HbA_1C was used to assess maternal integrated blood glucose control while fetal metabolic control was evaluated by antepartum glucose, insulin, and C-peptide determinations in amniotic fluid at elective caesarean delivery. Fetal hypoxaemia was assessed indirectly by fetal umbilical vein plasma erythropoietin level at delivery. A prospectively developed statistical pathway model was used to examine the relationship of these variables. In applying forced stepwise multiple regression with this model, we observed in the diabetic subjects that mean maternal HbA_1C during the last month of pregnancy correlated significantly with fetal umbilical venous erythropoietin at delivery (r=0.57, p<0.001). Additional significant contributions to umbilical venous erythropoietin were found for amniotic fluid glucose and amniotic fluid insulin when these two independent variables were added in stepwise fashion (p<0.01). We conclude that in diabetic pregnancy, antepartum control of maternal hyperglycaemia is a significant factor associated with fetal hypoxaemia. We speculate that this effect is mediated through perturbations which accelerate fetal metabolism and which is expressed by amniotic fluid levels of glucose and insulin.     

FETAL ORIGIN OF AMNIOTIC FLUID INSULIN IN THE HUMAN MOTHER

To investigate the origin of insulin in amniotic fluid amniocenteses were carried out in pregnancies with live, dead and anencephalic fetuses. Amniotic fluid insulin of pregnant women bearing live fetuses was 9.0 ± 2.1 μU/ml; in six women with dead foetuses amniotic fluid insulin was not detected. A significant positive correlation was observed between gestational age and the amniotic fluid concentration of insulin. In the amniotic fluid of the four women bearing anencephalic fetuses, the amount of hormone was within normal limits (10.0 ± 1.4 μU/ml). Intravenous glucose administration (0.33 g/kg body weight) to the mother does not influence levels of insulin in amniotic fluid, but brought about changes in amniotic fluid glucose concentration. These findings support the conclusion that human amniotic fluid insulin is of fetal rather than maternal origin.     

Amniotic fluid C-peptide in normal and insulin-dependent diabetic pregnancies

Summary Glucose, insulin and C-peptide were determined in amniotic fluid from 28 normal and 46 insulin-treated diabetic pregnant women. Glucose, insulin and C-peptide concentrations in amniotic fluid were higher in the diabetics than in the normal subjects. In diabetic women insulin levels did not correlate with birth weight or birth weight adjusted for gestational age, but C-peptide did. C-peptide correlated poorly with insulin (p<0.05) in diabetics but closely (p<0.002) in normal subjects. These results suggest that amniotic fluid investigations in insulintreated diabetic women should use C-peptide assays as these seem to reflect more closely the insulin production of the fetus than do insulin assays. There were no differences in amniotic fluid glucose, insulin and C-peptide concentrations where the amniotic fluid lecithin-sphingomyelin ratio indicated fetal pulmonary maturity or immaturity.     

Early detection of insulin sensitivity and beta-cell function with simple tests indicates future derangements in late pregnancy

OBJECTIVE: Insulin sensitivity and secretion during early and late pregnancy were assessed in women with normal glucose tolerance and gestational diabetes mellitus (GDM). RESEARCH DESIGN AND METHODS: The oral glucose tolerance test (OGTT) was performed in 903 women at 16-20th gestational week, of whom 37 had GDM (GDM1 group), and 859 repeated the OGTT at wk 26-30. At the second test, 55 had GDM (GDM2 group); the others remained normotolerant (ND group). Insulin sensitivity from OGTT (as quantitative insulin sensitivity check index and OGTT insulin sensitivity) and beta-cell function (as the ratio of the areas under the insulin and glucose concentration curves, adjusted for insulin sensitivity) were assessed in both tests. RESULTS: In early pregnancy the quantitative insulin sensitivity check index was not different in the three groups, whereas OGTT insulin sensitivity was lowest in GDM2, intermediate in GDM1, and highest in ND. In late pregnancy both indices were reduced in GDM compared with ND and lower than in early pregnancy. In early pregnancy GDM1, but not GDM2, had lower beta-cell function than ND. During the late visit, GDM2 also showed impaired beta-cell function compared with ND; furthermore, the adaptation to the increase to insulin resistance from early to late pregnancy was defective in GDM2. CONCLUSIONS: In early pregnancy insulin sensitivity, as assessed from the OGTT but not from fasting measurements, is impaired in women who developed GDM. beta-Cell function impairment is evident only when GDM is manifest and is characterized by inappropriate adaptation to the pregnancy induced increase in insulin resistance.     

Determination of insulin-like growth factor-2 in feto-maternal circulation during human pregnancy.

In order to clarify the roles of insulin-like growth factors (IGFs) on the human maternal-fetal environment, IGF-2 and IGF-1 levels were investigated in human plasma and amniotic fluid during pregnancy. Initially, new radio-immunoassay (RIA) systems for human IGF-2 could be developed. The sensitivity of this assay was 17.5 pg/tube and the cross-reactivity with IGF-1 was 0.64%. The pattern of change of maternal plasma IGF-2 in early pregnancy differed from that of IGF-1, but both IGF levels increased progressively in the second half of gestation, and decreased to non-pregnancy levels in the puerperium. Maternal levels of IGF-2 were approximately seven times greater than those of IGF-1. The ratio of IGF-2 to IGF-1 was 3.2 in amniotic fluid. The IGF concentrations in amniotic fluid obtained in the second trimester were significantly greater than those of term specimens, and closely related to those of prolactin (PRL) in amniotic fluid. The highest IGF-2 to IGF-1 ratio (15.9) was found in umbilical vein plasma. On Sephadex G-150 gel-chromatography of maternal and fetal plasma at term, two apparent peaks of unsaturated IGF-2 binding protein (BP) could be detected in both 150 and 40 kilo dalton (kD) regions. One main peak of unsaturated IGF-2 BP could be determined in the 40 kD region in the amniotic fluid at term. High concentration of IGF-2 could be detected in feto-maternal circulation during human pregnancy.(ABSTRACT TRUNCATED AT 250 WORDS)     

Glucose metabolism during and after pregnancy in normal and gestational diabetic women. 1. Influence of normal pregnancy on serum glucose and insulin concentration during basal fasting conditions and after a challenge with glucose.

Glucose and insulin concentrations during basal fasting conditions and after an oral challenge with glucose have been studied during early, mid and late pregnancy and also after delivery in a group of 9 normal women. No significant changes in the fasting serum glucose concentration was observed during pregnancy. In contrast the fasting serum insulin gradually increased. No changes in the mean glucose concentration curve were observed until the second half of pregnancy where the level of the curve was significantly elevated, but statistically calculated limits of normality derived from a special study of non-pregnant normal controls were not exceeded. The serum insulin response to glucose was significantly increased at all stages of gestation and in parallel the insulin-to-glucose index calculated for the total areas below the insulin and glucose concentration curves increased significantly. The fasting insulin-to-glucose index also increased and was found to be significantly correlated to the stage of gestation. The shape of the glucose and insulin curves was modified in the opposite direction by pregnancy: the peak value of glucose was delayed whereas that of insulin was advanced. The results indicate that in pregnancy a diminished "peripheral sensitivity" to endogenous insulin apparently develops.     

Effect of insulin on glucose uptake and metabolism in the human placenta

The effect of insulin on glucose uptake, transfer, and metabolism was investigated in the human placenta perfused in vitro. Insulin concentrations in maternal perfusion medium were varied from 0-1200 microU/ml, whereas the glucose concentration was kept constant in maternal and fetal perfusion media. Despite significant uptake of insulin by the perfused placenta, neither glucose uptake and transfer nor lactate release were significantly modified during a 1-h insulin perfusion. The MCR of insulin by the placenta was 0.29 +/- 0.03 (+/- SEM) ml/min X g at physiological insulin levels. These data suggest that placental glucose transport and metabolism are insensitive to maternal plasma insulin variations and that the low clearance rate of insulin by the placenta is not a major determinant of maternal insulin adjustments during pregnancy.     

Amniotic fluid concentrations of dimeric inhibins, activin A and follistatin in pregnancy

OBJECTIVE: The feto-placental unit is the major source of circulating concentrations of inhibin A and activin A in human pregnancy. The aim of this study was to measure the amniotic fluid concentrations of inhibin A, inhibin B, activin A and follistatin in pregnancies bearing male and female fetuses. DESIGN AND METHOD: Amniotic fluid samples collected by amniocentesis were stored at -20 degrees C. Dimeric inhibins, 'total' activin A and 'total' follistatin were measured using specific two-site enzyme immunoassays. Samples were assayed blindly and the information on fetal sex was obtained from the cytogenetics laboratory. RESULTS: Data show that amniotic fluid concentrations of inhibin A, inhibin B and activin A gradually increase with gestation whilst concentrations of follistatin are similar between weeks 15 and 20 of pregnancy. Mean amniotic fluid levels of inhibin A and inhibin B at 16 and 17 weeks gestation and mean activin A levels at 15 and 16 weeks gestation are considerably lower in pregnancies with male (n=24) compared with female (n=28) fetuses. Levels of follistatin are not different in the male and female fetal pregnancies at any studied gestation. CONCLUSIONS: The results indicate that amniotic fluid contains high concentrations of inhibins (A and B), activin A and follistatin in early pregnancy suggesting that these hormones are produced by the fetal membranes and may be involved in the development of the fetus.     

Thyroxine-binding globulin and its molecular variant in human amniotic fluid

Total thyroxine--binding globulin (TBGt) and its pregnancy-associated molecular variant (TBG-1) were detected by radioimmunoassay in human amniotic fluid collected at the time of delivery. TBGt purified from amniotic fluid by affinity chromatography and hydroxylapatite chromatography, displayed electrophoretic properties, immunoreactivity, a molecular mass, affinity for thyroxine and TBG-1 content identical to those of pure TBGt from human pregnancy serum. The concentrations of TBGt and TBG-1 in maternal venous blood serum were 49 +/- 7 mg/ml and 3.8 +/- 1.3 mg/ml (n = 23), respectively, and those in amniotic fluid were 2.0 +/- 0.5 mg/ml and 0.19 +/- 0.12 mg/ml (n = 30), respectively. The analysis of paired samples showed that the serum and amniotic fluid TBGt levels closely correlated (r = 0.91), whereas the correlation between the respective TBG-1 levels was poor (r = 0.63). The TBG-1/TBGt ratio in amniotic fluid was 20% higher than that in serum. These findings suggested a maternal origin of the most of the amniotic fluid TBG which may possibly enter amniotic fluid by passive diffusion through fetal membranes. An alternative mechanism can exist for TBG-1 transfer from maternal serum to amniotic fluid. It corresponds to a special role that TBG-1 may play in the fetoplacental system.     

Diagnosis and new approaches in the therapy of gestational diabetes mellitus

Gestational diabetes mellitus (GDM) is one of the most common complications in pregnancy. It affects 3-15% of women, depending on the background diabetes risk of the population and applied diagnostic criteria. GDM is associated with neonatal problems such as macrosomia and neonatal hypoglycemia as well as a long term increased risk of diabetes and obesity of offspring. Current therapy of GDM focuses on tightly controlling maternal glucose levels, resulting in insulin therapy in up to 50% of women to reach the fasting glucose target of< 90 mg/dl and 2h-postprandial glucose < 120 mg/dl. However, the rate of macrosomia and C-sections remains increased in pregnancy with GDM despite therapy. This review introduces the diagnosis and implications of GDM and then examines two strands of research aimed at improving current therapy: first, research into predictive markers of GDM pregnancies requiring intensified insulin therapy, and second, research into hypoglycaemic agents for therapy or even prevention of GDM in high risk women such as women with polycystic ovarian syndrome. Predictive markers include amniotic fluid insulin, which requires an invasive amniocentesis procedure, and measures of fetal abdominal circumference early in the third trimester, which have successfully been used to reduce rates of macrosomia. Potential hypoglycemic agents include glyburides and metformin, which have been shown not to have adverse outcomes on neonates, although oral agents are generally contra-indicated because of possible teratogenic and toxic effects observed in animal studies and missing long term outcome data.     

Fetal outcome in gestational diabetes with elevated amniotic fluid insulin levels. Dietary versus insulin treatment

Of 228 women with gestational diabetes between 28 and 32 gestational weeks, 195 had a normal amniotic fluid insulin level (4.8 +/- 3.6 microU/ml) while 33 (14.5%) had an elevated level (23.1 +/- 10 microU/ml). Women with a normal amniotic fluid insulin level were treated by diet alone. Fourteen of the women with an elevated level were treated by diet alone; 19 received insulin treatment additionally. The fetal outcome of patients with a normal amniotic fluid insulin level and dietary therapy and of those with an elevated level and insulin treatment was similar to that of metabolically healthy women. The newborns of gestational diabetics with elevated amniotic fluid insulin treated by diet alone showed a significantly higher incidence of neonatal hyperinsulinism, hypoglycemia, hyperbilirubinemia, high birth weight, respiratory distress syndrome and hypocalcemia. While 2/14 (14%) of the neonates in the dietary group had fatal respiratory distress syndrome, there were no deaths in the group with elevated amniotic fluid insulin and insulin treatment. The data demonstrate that in gestational diabetics with normal amniotic fluid insulin (low-risk group), dietary therapy is sufficient while insulin therapy is required to ensure healthy offspring in patients with elevated amniotic insulin (high-risk group).     

Distribution of catecholamines between fetal and maternal compartments during human pregnancy with emphasis on L-dopa and dopamine

This study was undertaken to determine the differential distribution of catecholamines, in particular L-dihydroxyphenylalanine (L-dopa) and dopamine, between the fetal and maternal compartments during human pregnancy. Amniotic fluid and fetal and maternal blood were obtained from two groups of pregnant women with uncomplicated pregnancies. One group was at 15-20 weeks of gestation and the second group was in labor after 36-41 weeks of gestation. Samples were analyzed for L-dopa, dopamine, norepinephrine, and epinephrine by radioenzymatic assays. L-Dopa constituted about 80% of the total circulating fetal catecholamines, and levels were 2- to 3-fold higher in fetal than maternal plasma. Marked increases in norepinephrine, small rises in epinephrine, but no changes in L-dopa or dopamine concentrations occurred in fetal plasma from mid- to late gestation. Maternal plasma catecholamines did not change. Towards the end of gestation, dopamine in the amniotic fluid increased 15-fold, and norepinephrine increased 5- to 6-fold; L-dopa remained high and unchanged. We conclude that L-dopa is the predominant catecholamine in fetal plasma and amniotic fluid during human pregnancy. No significant changes in its concentrations occur in either compartment between mid- and late gestation. In contrast, dopamine levels, which are 30- to 50-fold lower than those of L-dopa in amniotic fluid during midgestation, show a striking elevation toward the time of labor. Neither the sources nor the possible physiological functions of either L-dopa or dopamine during fetal life are known.     

Influence of severe diabetes mellitus early in pregnancy in the rat: effects on insulin sensitivity and insulin secretion in the offspring

Summary We studied the influence of severe diabetes early in pregnancy on insulin sensitivity and insulin secretion in the offspring. Diabetes (blood glucose >20 mmol/l) was induced in female Sprague-Dawley rats before mating. Diabetic dams were insulin treated during the second half of pregnancy (mean blood glucose 10.6 mmol/l). The offspring were reared by foster mothers. Offspring of both sexes were insulin resistant at four and seven months of age as evidenced by normal glucose tolerance after glucose (2 g/kg body weight intraperitoneally) concomitant with higher than normal rises in insulin levels. Regardless of fetal environment the male rats had higher glucose and insulin levels than the female rats. Insulin responses to glucose (27 mmol/l) in vitro in perfused pancreases were not increased by maternal diabetes, male gender or higher age. Conversely responses to 3-isobutyl-1-methylxanthine (1.0 mmol/l) were enhanced by all three conditions. The pancreatic content of insulin was only marginally affected by maternal diabetes. We conclude that severe diabetes during early pregnancy affects glucose homeostasis in the offspring primarily by diminishing insulin sensitivity and that susceptibility to this effect is not sex- or age-dependent.     

Measurement and characterization of insulin-like growth factor binding protein-3 in human biological fluids: discrepancies between radioimmunoassay and ligand blotting.

The inability to detect insulin-like growth factor binding protein-3 (IGFBP-3) in some circumstances by Western ligand blot analysis has emphasized the need to characterize IGFBPs by both ligand binding and immunological techniques. In this study, we have: 1) characterized and quantified IGFBP-3 in nonpregnancy, pregnancy, and fetal cord serum, follicular, peritoneal, and amniotic fluid, seminal plasma, cerebrospinal fluid (CSF), and urine; 2) established a new IGFBP-3 RIA that detects both intact and fragments of IGFBP-3; 3) identified both intact and fragments of IGFBP-3 by Western immunoblot techniques; and 4) addressed the discordance between Western ligand blot analysis and RIA by assessing fluids for IGFBP proteolytic activity. All fluids examined, except pregnancy serum, CSF, and amniotic fluid, displayed a 44-34-kilodalton (kDa) IGFBP-3 doublet by Western ligand blot analysis. Western immunoblot analysis using specific IGFBP-3 antiserum showed a 44-34-kDa IGFBP-3 doublet and a 28-kDa fragment in nonpregnancy serum, fetal cord serum, follicular fluid, and peritoneal fluid. The immunoreactive 42-38-kDa doublet was faint in urine and seminal plasma. IGFBPs in CSF did not cross-react with IGFBP-3 antiserum. Pregnancy serum and amniotic fluid contained only the 28-kDa fragment when compared against equal volumes of nonpregnancy serum. With the development of an IGFBP-3 RIA, IGFBP-3 could be accurately measured; urine, CSF, and seminal plasma contained the lowest levels of IGFBP-3 at 27 +/- 3 ng/ml (mean +/- SEM), 110 +/- 26 ng/ml, and 209 +/- 56 ng/ml, respectively. In increasing concentration: fetal cord serum contained 753 +/- 101 ng/ml; peritoneal fluid, 1124 +/- 130 ng/ml; follicular fluid, 2356 +/- 211 ng/ml; nonpregnancy serum, 3556 +/- 508 ng/ml; pregnancy serum, 3718 +/- 842 ng/ml; and amniotic fluid, 5150 +/- 688 ng/ml. The measurable concentrations of IGFBP-3 in CSF and the high concentrations measured in pregnancy serum and amniotic fluid conflicted with Western blot analysis. Thus, fluids were assessed for IGFBP proteolytic activity by incubation with a source of IGFBP-3, either nonpregnancy serum or purified IGFBP-3. All fluids displayed some proteolytic activity with either assay. Fluids with little protease activity (nonpregnancy serum, follicular fluid, and urine) showed a close relationship between immunoassayable IGFBP-3 by RIA and IGFBP-3 band intensity by Western ligand blot. Fluids with high proteolytic activity (pregnancy serum, CSF, seminal plasma, peritoneal fluid, and amniotic fluid) gave discrepant IGFBP-3 values between RIA and Western ligand blot.(ABSTRACT TRUNCATED AT 400 WORDS)     

Serum proinsulin in normal and gestational diabetic pregnancy

Summary The concentration of proinsulin-like components (PLC) in serum has been determined by gel filtration on samples obtained from eight normal pregnant women and eight nonobese gestational diabetics. The normal women were investigated early in pregnancy and all subjects were investigated in mid pregnancy, late pregnancy, and postpartum. At each occasion, samples were obtained after an overnight fast and after glucose ingestion. In both groups, the concentration of PLC in serum after overnight fast rose with gestation as well as after glucose ingestion, but there were no significant differences between mean levels of PLC of the normals and the gestational diabetics. With gestation, serum insulin rose in parallel with PLC in either group. The proportion of total insulin immunoreactivity composed by PLC thus remained constant and, furthermore, the proportions of PLC in gestation were equal to those observed postpartum. Four to six weeks after delivery, the basal concentration of PLC in serum was higher in the gestational diabetics than in the normals, whereas the concentrations of insulin were equal. Since the biological potency of proinsulin is much less than that of insulin, the results exclude the possibility that the decrease of glucose tolerance in normal pregnant women and gestational diabetics is due to an increased concentration of proinsulin in serum.     

Glucose decreases steady state mRNA content of hydrophobic surfactant proteins B and C in fetal rat lung explants

The streptozotocin-induced diabetic (STZ-DB) rat model is associated with fetal hyperglycemia, but with low to normal plasma insulin concentration. Because surfactant protein (SP) mRNA content in fetal rat lung is decreased in STZ-DB pregnancy, we investigated the effect of increasing concentrations of glucose on SP gene expression in lung organ cultures. SP mRNA content (SP-A, SP-B, SP-C) was assessed by Northern blot analysis in fetal day 20 lung explants (term = 22 days) cultured for 44 hours in medium containing 10, 25, 50, or 100 mM glucose. Our findings were (1) No consistent alteration in SP-A mRNA content was observed at different glucose concentrations (P > .05); (2) SP-B and SP-C mRNA content were reduced in a dose-dependent manner when glucose concentration was increased from 10 mM to 100 mM. The mRNA content, compared to 10 mM glucose, decreased to 50-60% at 25 mM glucose, to 20-25% at 50 mM glucose, and to lower than 10% at 100 mM glucose (P < .01). These findings indicate that the decrease in SP-B and SP-C mRNA in fetuses of STZ-DB rats may be, in part, due to a direct effect of hyperglycemia, whereas the decrease in SP-A mRNA content in STZ-DB rats appears to be due to other effects of diabetes in pregnancy.     

MEASUREMENT OF SEX HORMONE BINDING GLOBULIN IN HUMAN AMNIOTIC FLUID: ITS RELATIONSHIP TO PROTEIN AND TESTOSTERONE CONCENTRATIONS, AND FETAL SEX

Sex hormone binding globulin (SHBG) has been identified and quantified in human amniotic fluid. Identification was based on its electrophoretic mobility on polyacrylamide gels and its steroid binding characteristics, which were identical to those attributed to SHBG in pregnancy serum. Amniotic fluid SHBG binding capacity was measured by competitive saturation analysis using [³H]-5α-dihydrotestosterone as the labelled ligand, after removal of endogenous steroids with dextran-coated charcoal. Similar amniotic fluid SHBG binding capacities were found in samples taken during early (13–20 weeks, 8.5 ± 5.1 (SD) nmol/l, n= 10) and late (36–37 weeks, 8.7 ± 3.0 nmol/l, n= 28) pregnancy. In comparison with pregnancy serum SHBG levels (390 ± 140 nmol/l, n= 5), amniotic fluid SHBG was not enriched in relation to the relative concentrations of total proteins, albumin or transferrin. Amniotic fluid is therefore not a better source for the purification of SHBG than pregnancy serum. There were no differences in amniotic fluid SHBG levels with respect to fetal sex, but positive correlations were observed between SHBG binding capacities and testosterone concentrations in amniotic fluid from both male (r= 0.68, P < 0.001) and female (r= 0.53, P < 0.05) fetuses. It is suggested that SHBG may sequester free testosterone in amniotic fluid, and that measurements of SHBG in amniotic fluid may help to more accurately identify fetal sex in cases where borderline amniotic fluid testosterone concentrations are found.     

Effects of Diet and Exercise on Insulin Resistance during Pregnancy

Current evidence suggests that both diet and exercise can alter the usual increase in insulin resistance seen in Western societies during mid and late pregnancy. A low-glycemic diet combined with a low-volume exercise regimen during pregnancy decreases the glucose and insulin response to both mixed caloric intake and exercise, and probably lowers both 24-h blood glucose concentrations and the maternal substrate utilization ratio of carbohydrate/fat. The end result is a marked decrease in both maternal weight gain and size at birth. Regular weight-bearing exercise alone lowers markers of insulin resistance and lowers blood glucose concentration during and immediately after exercise during pregnancy. Changes in diet and/or physical activity appear to prevent the onset of gestational diabetes mellitus in at-risk women and may be of value in the treatment of those who develop gestational diabetes.     

Leptin administration prevents spontaneous gestational diabetes in heterozygous Lepr(db/+) mice: effects on placental leptin and fetal growth.

Gestational diabetes mellitus (GDM) results from an interaction between susceptibility genes and the diabetogenic effects of pregnancy. During pregnancy, mice heterozygous for the lepin receptor (db/+) gain more weight, are glucose intolerant, and produce macrosomic fetuses compared with wild-type (+/+) mothers, suggesting that an alteration in leptin action may play a role in GDM and fetal overgrowth. To investigate whether leptin administration or pair-feeding can reduce adiposity and thereby prevent GDM and neonatal overgrowth, we examined energy balance, glucose and insulin tolerance, and fetal growth in pregnant db/+ and +/+ mice treated with recombinant human leptin-IgG during late pregnancy. Leptin reduced food intake and adiposity in pregnant db/+ mice to levels similar to pregnant +/+ mice and significantly reduced maternal weight gain. Maternal glucose levels were markedly lower during glucose and insulin challenge tests in leptin-treated db/+ mice relative to db/+ and pair-fed controls. Despite reduced energy intake and improved glucose tolerance, leptin administration did not reduce fetal overgrowth in offspring from db/+ mothers. Fetal and placental leptin levels were 1.3- to 1.5-fold higher in offspring from db/+ mothers and remained unchanged with leptin administration, whereas leptin treatment in +/+ mothers or pair-feeding decreased placental leptin concentration and reduced fetal birth weight. Our results provide evidence that leptin administration during late gestation can reduce adiposity and improve glucose tolerance in the db/+ mouse model of spontaneous GDM. However, fetal and placenta leptin levels are higher in db/+ mothers and are subject to reduced negative feedback in response to leptin treatment. These data suggest that alterations in placenta leptin may contribute to the regulation of fetal growth independently of maternal glucose levels.     

Peptidergic regulation of maturation of the stimulus-secretion coupling in fetal islet beta cells

The stimulus-secretion coupling of the insulin-producing pancreatic islet beta cell is subject to functional maturation during fetal life. We studied the maturation of a glucose-responsive insulin release from fetal rat islets and specifically investigated the impact of peptidergic regulation. To this end, islets were isolated from 21-day-old fetal rats and maintained for 7 days in tissue culture at 3.3 or 11.1 mM glucose and various supplements. In islets cultured in low glucose, acutely raising the ambient glucose concentration to 16.7 mM evoked a modest stimulation of short-term insulin release that was more pronounced in islets maintained in high glucose. Moreover, the insulin content was much higher in islets cultured in high than in low glucose. Culture with growth hormone (GH) markedly amplified both basal and stimulated short-term insulin secretion from islets maintained in either low or high glucose. Additionally, GH significantly elevated the insulin content in islets maintained in low glucose. Transforming growth factor alpha (TGF-alpha) increased basal, but not glucose-stimulated, insulin release and insulin content in islets cultured in low glucose. Gastrin, expressed in islets during fetal life, did not affect basal or glucose-stimulated insulin release, or insulin content, in islets maintained in either low or high glucose. The addition of gastrin to TGF-alpha did not affect the results obtained with the latter peptide. Gastrin-releasing peptide failed to influence basal or glucose-responsive insulin secretory rates, and insulin content, at either glucose concentration during culture. The somatostatin analog Sandostatin (octreotide acetate) neither influenced basal nor stimulated short-term insulin release at any glucose concentration present during culture, whereas the hormone significantly decreased the insulin content of islets cultured in high glucose. Pancreastatin, produced by porcine islet beta and delta cells, failed to influence basal or glucose-responsive insulin secretory rates, and islet insulin content, at either glucose concentration during culture. Culture with gastric inhibitory peptide (GIP) or glucagon-like peptide I (GLP-1), two proposed incretins, did not affect short-term insulin secretion in response to 3.3 or 16.7 mM glucose irrespective of the ambient glucose concentration during culture. To the contrary, GLP-1, but not GIP, increased the content of insulin in islets cultured in low glucose. We conclude that islet beta-cell differentiation and functional maturation of the stimulus-secretion coupling can be modulated in vitro in fetal rat pancreatic tissue by peptidergic regulation and glycemic stimulation. We suggest that GH and TGF-alpha stimulate, while somatostatin, through paracrine interaction, may inhibit, these processes. These effectors may be of regulatory significance in the in vivo development of glucose-sensitive beta cells, and defects in these mechanisms may result in glucose intolerance in adult subjects.