Biomedical subjects

I H Gewolb

Publications and source records attributed to I H Gewolb.

43 records · Page 3Linked to original sources

PubMedDate not supplied

Effects of insulin and glucose on pulmonary insulin receptors in late gestation fetal rats.

The effects of high glucose and insulin concentrations on fetal lung insulin receptors and tyrosine kinase activity were studied in an in vitro system utilizing 19- or 20-d fetal rat lung explants. Exposure of the explants to 100 mM glucose and insulin (0.1 unit/mL) for 72 h resulted in a significant decrease in specific binding of insulin to partially purified receptors [5.78% +/- 0.66 (SEM) vs. 9.64% +/- 1.68; P less than .01] when compared with lung explants exposed to 10 mM glucose alone. When individual effects of high insulin and glucose were studied, down-regulation of specific insulin binding was also observed, but to a lesser extent than that observed using both high glucose and insulin. Differences in insulin receptor affinity were not noted. Insulin receptor tyrosine kinase activity was also significantly decreased (52% of control values) under high-glucose/high-insulin conditions. Total phosphatidylcholine and disaturated phosphatidylcholine concentrations were significantly decreased in explants grown under high-glucose/high-insulin conditions, consistent with delayed pulmonary maturation. High glucose and insulin levels thus result in down-regulation of fetal lung insulin receptors and insulin receptor tyrosine kinase activity late in gestation. These results may have implications for substrate availability in the developing fetal lung.

Animals↗

PubMedDate not supplied

Fluorescence anisotropy as an index of fetal lung maturation in vitro.

Fluorescence techniques have been used to assess the viscosity of surfactant-containing fluids in vivo and have been successfully employed clinically as indices of lung maturity. However, fluorescence measurements have not been previously used as indicators of fetal lung maturation in an in vitro system. Lung explants derived from 19-, 20-, and 21-day fetal rats were cultured in F-12 medium for 24-72 h. Tissue homogenates and culture medium were eluted on Sephacryl S-300 columns, a diphenylhexatriene (DPH) probe was added to each fraction, and fluorescence anisotropy and intensity were measured after excitation at 357 nm and emission at 435 nm. Elution fractions containing the major fluorescence peak were demonstrated to correspond to the phosphatidylcholine-containing fraction and were shown to contain lamellar bodies. Fluorescence anisotropy of tissue homogenates obtained from 19-day lung explants decreased after 72 h in culture, suggesting lower microviscosity of the surfactant-containing fractions. Assessment of culture media collected at 24-h intervals revealed significant decreases in anisotropy by 48 h for the 19-day explants, and by 24 h for the 20- and 21-day explants. Anisotropy of the final (48-72 h) culture media aliquots was significantly lower for 21-day explants (0.144 +/- 0.004, SE), than for 20-day (0.172 +/- 0.013) or 19-day explants (0.197 +/- 0.008), p < .005. Anisotropy of culture medium tended to be lower than anisotropy of corresponding tissue homogenates, suggesting that viscosity of recently secreted surfactant may be different from viscosity of surfactant within lamellar bodies in type II cells. Relative fluorescence intensity of tissue homogenates also increased with time in culture. These results indicate that fluorescence anisotropy can be used to assess the viscosity of surfactant in vitro and serve as another index of fetal lung maturation in in vitro systems. Estimation of the microviscosity of the surfactant phospholipid bilayer using anisotropy measurements may provide additional insight into such roles of surfactant function as adsorption and spreading.

Animals↗

PubMedDate not supplied

High glucose causes delayed fetal lung maturation in vitro.

The diabetic pregnancy is characterized by a delay in the process of fetal lung maturation. To determine whether high glucose conditions per se have an adverse impact on fetal lung phospholipid metabolism, 20-day fetal rat lung explants were cultured in F-12 medium (10 mM glucose) to which glucose was added to achieve final concentrations of 10, 25, 50, and 100 mM. Significant dose-dependent decreases in the rate of incorporation of [H3]choline into PC were noted at high glucose concentrations: Rate of choline incorporation was decreased by 19 and 28% under 50 and 100 mM glucose conditions, respectively (p < .001). Similar results were obtained when choline incorporation into DSPC was assayed. Equiosmolar mannitol concentrations did not result in comparable decreases, indicating a specific adverse effect attributable to glucose. Total PC and DSPC contents were also decreased by approximately 25% under high glucose conditions (p < .001). Glycogen concentrations were increased two- to threefold in the explants grown under high glucose conditions, consistent with a less mature lung. The addition of 1 unit/mL of insulin to F-12 medium did not result in decreases in choline incorporation into PC or DSPC; the addition of this amount of insulin to medium containing 100 mM glucose did not result in further decreases in choline incorporation rate. These results indicate that high glucose alone can have an adverse effect on fetal lung maturation in vitro and may be involved in the pathogenesis of the delay in fetal lung development observed in the diabetic pregnancy.

Animals↗

PubMedDate not supplied

Effect of high glucose on fetal lung maturation at different times in gestation.

Hyperglycemia has been implicated as a cause of delayed fetal lung maturation in the diabetic pregnancy. It has been previously demonstrated that high glucose levels inhibit biochemical and morphological maturation of fetal rat lung in vitro. To explore whether there is a critical period for maximal effects of high glucose, fetal rat lung explants from day 18-22 (term) were examined after culture for 44 h in media containing 10 or 100 mM glucose. Rate of choline incorporation into PC and DSPC was significantly decreased in explants derived from day 20-22 fetuses after culture with high glucose. Paradoxically, in explants derived from day 18-19 fetuses choline incorporation rate was increased. Significant decreases in total PC and DSPC were seen in the high glucose group on days 20-21; however, earlier in gestation no differences in PC and DSPC were noted, despite the higher rate of choline incorporation into PC and DSPC, suggesting an increased turnover rate. High glucose levels also resulted in significantly decreased incorporation of labeled glycerol and palmitate into PC. Morphologic analysis of right upper lobe explants revealed significant decreases in the number of type II pneumocytes and lamellar bodies per alveolar lining cell in high glucose treated explants derived from days 19-20, but not before or after that time in gestation. Prior to day 20 there were few luminal lamellar bodies in potential airspaces. By day 20, the high glucose group had significantly fewer luminal lamellar bodies, although by day 21 the difference was no longer significant. These results suggest that high glucose may have a greater inhibitory effect late in gestation and that there may be critical periods in lung development when differences in substrate availability and utilization have differing effects.

Animals↗

PubMedDate not supplied

Surfactant secretion by type II pneumocytes is inhibited by high glucose concentrations.

Delayed fetal lung maturation is observed in poorly controlled diabetic pregnancies. To investigate whether elevated glucose levels inhibit basal surfactant secretion and synthesis in type II cells and whether inhibitory effects on secretion can be reversed by secretagogues, type II cells isolated from 20-day fetal rat lung explants were initially cultured in [H3] choline containing media with glucose concentrations of 5.5, 10, 25, 50, and 100 mM, or in equiosmolar mannitol controls. Further incubation in nonradioactive media containing matched glucose levels with and without 1 x 10(-5) M terbutaline 1 x 10(-6) M and 1 x 10(-8) M 12-O-tetradecanoylphorbol 13-acetate (TPA) allowed assessment of incorporation of choline into phosphatidylcholine (PC) and its subsequent secretion. PC secretion was inhibited by culture in high glucose conditions, resulting in an approximately 30% reduction in secretion under 50 and 100 mM glucose conditions compared to culture at 5.5 or 10 mM glucose (p < .01); this decrease could not be explained by changes in osmolarity or in all viability after culture in high glucose. Insulin (1 unit/mL) had no significant impact on secretion (92 +/- 7% of control). Terbutaline-stimulated cells grown under 50 and 100 mM glucose conditions had significantly lower secretion rates than did terbutaline-stimulated cells cultured in 5.3 mM glucose (p < .05). Exposure to TPA resulted in significant increase in surfactant secretion by cells grown in both 5.5 and 100 mM glucose; however, the percentage increase (39.5 +/- 6.8% and 94.8 +/- 8.0% with 10(-8) M and 10(-6) MTPA, respectively) was significantly lower than in controls (87.8 +/- 8.0% and 152.1 +/- 18.8%, respectively) (p < .001). Choline incorporation into PG was also decreased by 100 mM glucose to 77 +/- 9% of control (p < .01). These data indicate that high glucose levels inhibit both surfactant synthesis and baseline and secretagogue-stimulated surfactant secretion by type II cells. This inhibitory effect on surfactant secretion may further exacerbate the decrease in surfactant synthesis and the pulmonary maturational delay seen in infants of diabetic pregnancies.

Animals↗

PubMedDate not supplied

Fluorescence anisotropy of tracheal and oropharyngeal aspirates as an indicator of lung disease in neonates.

Fluorescence anisotropy was assessed in tracheal and oropharyngeal aspirates to evaluate its use in the diagnosis of respiratory distress syndrome. Samples from 31 neonates at birth were purified by using Sephacryl S-300 column chromatography. After the addition of the molecular probe, 1,6-diphenyl 1,3,5 hexatriene fluorescence was measured and anisotropy calculated. Ten neonates with normal respiratory function had a mean anisotropy (+/- SD) of 0.226 +/- 0.023. Fourteen infants with a diagnosis of respiratory distress syndrome had a mean anisotropy of 0.260 +/- 0.014 (p < 0.001). Seven neonates with respiratory problems other than respiratory distress syndrome had a mean anisotropy of 0.211 +/- 0.027 (p < 0.001 vs respiratory distress syndrome). A diagnosis of respiratory distress syndrome was associated with higher tracheal fluid anisotropy, indicating a qualitative difference in the characteristics of the pulmonary surfactant. We conclude that this 30-minute test could help identify neonates who benefit from surfactant replacement therapy.

Birth Weight↗

PubMedDate not supplied

Evolution and variability of pulmonary mechanics during postnatal transition in term infants.

This study was designed to assess whether progressive changes related to the transition to extrauterine life explain in part the interassay variability of pulmonary mechanics in the immediate postnatal period. We performed sequential pulmonary function tests in 21 normal term infants with the use of a pneumotachometer and an esophageal balloon. The average percent increase in values from the first period (2 to 10 hours) to the last period of study (66 to 78 hours) was 27% for tidal volume, 24% for minute ventilation, and 42% for dynamic compliance. The maximum difference between two pulmonary function measurements obtained within 30 minutes of each other ranged between 10% for dynamic compliance and 27% for minute ventilation. The coefficient of variation for dynamic compliance over a 2-hour period (12%) was less than half the 3-day coefficient of variation (31%). The reliability coefficient ranged between 0.72 for tidal volume and 0.92 for dynamic compliance. We conclude that dynamic compliance in term infants increases progressively during the first 3 days of life, whereas tidal volume and minute ventilation increase mostly during the first day. The variability of pulmonary mechanics reflects in part those progressive physiologic changes during postnatal transition.

Female↗