Metabolism and placental transfer of 125I-proinsulin and 125I-tyrosylated C-peptide in the pregnant rhesus monkey

Reappearance of C-Peptide During the Third Trimester of Pregnancy in Type 1 Diabetes: Pancreatic Regeneration or Fetal Hyperinsulinism?

OBJECTIVE

We assessed longitudinal patterns of maternal C-peptide concentration to examine the hypothesis of β-cell regeneration in pregnancy with type 1 diabetes.

RESEARCH DESIGN AND METHODS

C-peptide was measured on maternal serum samples from 127 participants (12, 24, and 34 weeks) and cord blood during the Continuous Glucose Monitoring in Women With Type 1 Diabetes in Pregnancy Trial (CONCEPTT). C-peptide was measured using a highly sensitive direct and solid-phase competitive electrochemiluminescent immunoassay.

RESULTS

Three discrete patterns of maternal C-peptide trajectory were identified: pattern 1, undetectable throughout pregnancy, n = 74 (58%; maternal C-peptide <3 pmol/L); pattern 2, detectable at baseline, n = 22 (17%; maternal C-peptide 7-272 pmol/L at baseline); and pattern 3, undetectable maternal C-peptide at 12 and 24 weeks, which first became detectable at 34 weeks, n = 31 (24%; maternal C-peptide 4-26 pmol/L at 34 weeks). Baseline characteristics and third trimester glucose profiles of women with pattern 1 and pattern 3 C-peptide trajectories were similar, but women in pattern 3 had suboptimal glycemia (50% time above range) at 24 weeks' gestation. Offspring of women with pattern 3 C-peptide trajectories had elevated cord blood C-peptide (geometric mean 1,319 vs. 718 pmol/L; P = 0.007), increased rates of large for gestational age (90% vs. 60%; P = 0.002), neonatal hypoglycemia (42% vs. 14%; P = 0.001), and neonatal intensive care admission (45% vs. 23%; P = 0.023) compared with pattern 1 offspring.

CONCLUSIONS

First maternal C-peptide appearance at 34 weeks was associated with midtrimester hyperglycemia, elevated cord blood C-peptide, and high rates of neonatal complications. This suggests transfer of C-peptide from fetal to maternal serum and is inconsistent with pregnancy-related β-cell regeneration.

Factors determining insulin requirements in women with type 1 diabetes mellitus during pregnancy: a review

Most women with type 1 diabetes mellitus (T1DM) have increased insulin requirements during pregnancy. However, a minority of women have a fall in insulin requirements. When this occurs in late gestation, it often provokes concern regarding possible compromise of the feto-placental unit. In some centres, this is considered as an indication for delivery, including premature delivery. There are, however, many other factors that affect insulin requirements in pregnancy in women with type 1 diabetes mellitus and the decline in insulin requirements may represent a variant of normal pregnancy. If there is no underlying pathological process, expedited delivery in these women is not warranted and confers increased risks to the newborn. We will explore the factors affecting insulin requirements in gestation in this review. We will also discuss some novel concepts regarding beta-cell function in pregnancy.

In vivo biodistribution and pharmacokinetics of (18)F-labeled human C-peptide: evaluation in monkeys using positron emission tomography

The recently observed beneficial effects exerted by C-peptide in insulin-dependent diabetes patients (IDDM) have instigated research into the mechanisms of C-peptide action as well as the location for it. Here we report in vivo biodistribution studies performed in monkeys using positron emission tomography (PET) and C-peptide labeled in the N-terminal with fluorine-18. Following iv injection of the radiotracer, dynamic decay data were collected over the chest and/or abdomens of the monkeys. The radioactivity distributed mainly to the kidneys, less to the heart and to some extent to the liver. Excretion of radioactivity into the urinary bladder was observed. Brain uptake was not detected in a static emission scan of the head performed at late times. Accumulation of radioactivity in the skeleton as a result of in vivo defluorination was not observed. Pharmacokinetic modeling of the regional concentrations of radioactivity over time resulted, for most organs, in two-compartment models. The organs with the highest radioactivity concentrations have been identified, enabling dose estimations for studies in humans with low or no C-peptide.

Prostanoid production in the umbilicoplacental arterial tree relative to impaired glucose tolerance

The purpose of this study was to investigate prostanoid synthesis in different segments of the umbilicoplacental vascular tree and its relationship to impaired maternal glucose tolerance. Segments from the umbilical artery and vein, allantochorionic artery branches, and the cotyledon artery from 21 women with diabetes or impaired glucose tolerance and 10 healthy women were studied. Production of prostacyclin (PGI2) and thromboxane (TxA2) metabolites was determined. The Mann-Whitney U test, Wilcoxon signed-ranks matched-pairs test, Kruskal-Wallis test, analysis of variance, and simple linear regression analysis were used. A two-tailed P value of < 0.05 was considered statistically significant. From the umbilical artery distal to the cotyledon artery, the PGI2 synthesis decreased and the TxA2 synthesis increased gradually towards the periphery in normal pregnancy. The PGI2/TxA2 ratio was more than 200 times higher in the umbilical artery than in the cotyledon artery. The TxA2 production tended in general to be higher in the diabetic group than in the control group, resulting in significantly lower PGI2/TxA2 ratios in some vessels. The prostanoid production was not significantly correlated to maternal HbA1c or cord C-peptide concentrations. The balance between vascular prostacyclin and thromboxane synthesis in the umbilicoplacental arterial tree changed gradually towards the periphery: the more peripheral, the lower the prostacyclin and the higher the thromboxane production. The physiological role of this phenomenon is unknown, but may be of importance for the equilibration of vascular tone between arteries of different calibers. The altered prostanoid balance found in diabetic pregnancy was not directly attributable to the degree of maternal glycemic control, but may reflect increased free radical activity and peroxide production in diabetes.

Insulin-like growth factors and neonatal cardiomyocyte development: ventricular gene expression and membrane receptor variations in normotensive and hypertensive rats

Defined factors regulating or influencing mammalian ventricular myocyte (cardiomyocyte) development are not known at this time. During early neonatal ventricular growth, cardiomyocytes begin a 'transition phase' of development toward cellular maturation (hypertrophy) that entails terminal proliferation and cellular binucleation. Insulin-like growth factor-I and -II (IGFs) are believed to play a major role in mammalian postnatal and fetal growth, possibly functioning in local environments which facilitate autocrine or paracrine tissue growth characteristics. Therefore, we examined the expression of the IGF genes and their corresponding membrane receptors in ventricles of normotensive and spontaneously hypertensive (SHR) rat pups during the first 7-14 days of age. We have determined: (1) by receptor crosslinking that neonatal ventricular membranes possess type 1 and type 2 IGF receptors; (2) by receptor binding analysis that type 1 IGF receptor concentration is elevated between days 1-7 in the SHR and shows an age-related decline in concentration and an increase in affinity in both strains; (3) by Northern blot analysis that neonatal rat ventricular tissue expresses primarily IGF-II RNA transcripts of 3.6, 2.3 and 1.7 kilobases (kb) in size, with low levels of IGF-I transcripts detected; (4) by slot-blot hybridization that SHR ventricles contain higher levels of IGF-II transcripts at 3 days of age; and (5) localized the IGF transcripts to ventricular myocytes by tissue in situ hybridization. These observations support a role for cardiomyocyte-produced IGFs that may be locally produced and act in an autocrine or paracrine fashion to modulate cardiomyocyte growth and maturation in the developing rat heart. Because both IGF receptor and IGF RNA transcript parameters differed in SHR hearts, genetically predisposed to hypertrophy, a potentially important biochemical alteration may be associated with the fetal/neonatal growth abnormalities of the developing heart in this rat strain.