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Biomedical subjects

N Freinkel

Publications and source records attributed to N Freinkel.

At least 55 records · Page 3Linked to original sources
PubMed1983

Biphasic modulation of K+ permeability in pancreatic islets during acute stimulation with glucose.

The regulation of 86Rb+ efflux (marker of K+ permeability) during acute secretagogic stimulation with glucose was studied with cultured as well as freshly isolated pancreatic islets from rats and freshly isolated islets from mice. A perifusion system with minimal dead-space and "flow-through" characteristics conductive to abrupt, steep increases in ambient glucose was combined with multiple samplings of effluent to achieve high temporal resolution. Under these conditions, acute increases in perifusate glucose concentration from 4 to 16.7 mM or from 1 to 27.8 mM effected a biphasic change of the 86Rb+ fractional efflux rate. A rapid reduction of 86Rb+ efflux was interrupted by an evanescent increase in 86Rb+ outflow, which appeared to be temporally coincident with the initiation of the first phase of stimulated insulin release. It is suggested that the glucose-induced biphasic oscillations in K+ permeability may contribute to the well-known initial biphasic changes in beta-cell membrane potential and insulin release during the inception of beta-cell stimulus secretion coupling.

Animals↗
PubMed1983

The honeybee syndrome: teratogenic effects of mannose during organogenesis in rat embryo culture.

The relevance of our present findings should not rest on the possible role of mannose as an important teratogen in man. Excessive exposure to mannose during pregnancy via dietary intake seems unlikely since mannose is absorbed poorly from the gastrointestinal tract and intestinal hydrolysis of mannosidic linkages may be minimal. Moreover, although some plasma mannose may be generated continuously from endogenous sources via the cleavage of mannose-6-phosphate by hepatic glucose-6-phosphatase or mannosidic linkages by other hydrolases, our ongoing surveys have not uncovered any specimens of plasma or amniotic fluid containing mannose in amounts which could compete effectively with prevailing levels of glucose. Although we are continuing to monitor clinical samples for unusual mannose levels, we believe that the major significance of our experiences with this hexose pertains to its applications as a physiological tool for evaluating the metabolic determinants of early organogenesis. Within the above context, our findings must be viewed in relation to the known features of energy metabolism in the embryo during the interval that we have studied (Fig. 9). The classic studies of Shepherd and colleagues, similar findings by others, and more recent experiments in our own laboratory have indicated that glycolysis constitutes the chief energy source for the post-implantation embryo prior to the establishment of the yolk sac circulation on day 10 1/2. Almost all of the assimilated glucose goes to lactic acid, mitochondrial electron transfer is poorly developed, and oxidative metabolism via the Krebs' cycle is minimal. Meaningful Krebs' cycle activity does not become operative until day 10 1/2 and full expression is not found until the establishment of the allantoic circulation on day 11 (Fig. 9). The present experiences with mannose provide the first documentation of how precariously development is balanced during that transitory 9 1/2-10 1/2 day phase of organogenesis when glycolysis predominates. We have shown that even minor perturbations of glycolytic flux during that interval can result in major dysmorphogenic sequelae. Thus, the proposition by Kalter and Warkany that "any meaningful attempt to reduce infant mortality further will have to address the still unresolved causes of congenital malformations" prompts our speculation that major congenital lesions may result from relatively minor disturbances in glycolysis occurring prior to oxidative maturation in the embryo unit. Such effects on glycolysis during this vulnerable phase of embryogenesis could provide a common basis for the teratogenic actions of many unrelated and as yet unidentified agents.(ABSTRACT TRUNCATED AT 400 WORDS)

Abnormalities, Drug-Induced↗
PubMed1982

Placental lipid and glycogen content in human and experimental diabetes mellitus.

To assess whether placental DNA, glycogen, and fat are affected by diabetes mellitus and whether the changes correlate with the disturbance in maternal fuels, placentas were examined at delivery in women with normal carbohydrate metabolism, gestational diabetes mellitus, and Classes B to F diabetes and in rats rendered diabetic by the administration of streptozotocin 2 weeks before mating. Plasma glucose values during late pregnancy were higher in patients with Classes B to F diabetes than in the patients with gestational diabetes mellitus so that they were judged to have more severe metabolic disturbances; rats were also divided into groups with "mild" or "severe" diabetes on the basis of blood sugar. In rats, as in humans, diabetes tended to increase placental mass, DNA, glycogen, and lipids. However, the relative changes in glycogen and fat exceeded the alterations in mass and DNA, especially in those with more severe diabetes, so that a true increase in glycogen and fat per placental cell may have occurred. Thus, placental glycogen/DNA and placental triglycerides/DNA significantly exceeded control values in patients with Classes B to F diabetes and in rats with severe diabetes but not in women with gestational diabetes mellitus or rats with mild diabetes. Total placental triglycerides and total placental glycogen were significantly correlated (r = 0.952; p less than 0.001) in rats with experimental diabetes, which suggests that these alterations in placental composition during late pregnancy may share communal dependencies.

Animals↗
PubMed1982

"Accelerated starvation" and the skipped breakfast in late normal pregnancy.

After dinner at 6 P.M. food was withheld from non-pregnant women and women in the third trimester of pregnancy: there were lean and obese women in each group, and all had normal carbohydrate metabolism. Levels of circulating fuels and glucoregulatory hormones were monitored between 6 A.M. (12 h fast) and noon (18 h fast) the following day. In non-pregnant women plasma levels of glucose, alanine, free fatty acids (FFA) beta-hydroxybutyrate, insulin, and glucagon remained constant between 6 A.M. and noon except for slight fall in plasma alanine in the obese women and slight increases in beta-hydroxybutyrate in the lean. By contrast, in pregnant women the concentrations of all substances measured changed profoundly after extension of the overnight fast. Levels of plasma glucose, which were significantly lower than those in non-pregnant women at 6 A.M., fell further during the subsequent 6 h; plasma alanine levels declined significantly during the same interval, and there were coincident rises in plasma FFA and beta-hydroxybutyrate and reductions in plasma insulin. The changes in lean and obese women were of similar magnitude; habitus did not therefore seem to have effects additional to those of pregnancy on the response to skipping breakfast. In all the pregnant women final levels of FFA and beta-hydroxybutyrate were strongly correlated and inversely related to final levels of plasma glucose. The studies indicate that "accelerated starvation" can be unmasked during pregnancy even with the minor dietary deprivation common in conventional clinical circumstances. Thus, insofar as it may be desirable to avoid ketonaemia during pregnancy, the common practice of skipping breakfast whether by personal preference or for doctor-initiated laboratory testing should be avoided in pregnant women.

3-Hydroxybutyric Acid↗
PubMed1982

The effect of gestational age on amniotic fluid glucose in pregnancy complicated by diabetes mellitus.

Amniotic fluid glucose was measured in 189 amniotic fluid samples from 117 well-controlled Class A to F diabetic pregnant women from 32 to 40 weeks' gestation. A simultaneous maternal plasma glucose level was determined at each amniocentesis. Samples were obtained with the mother in the fasting or nonfasting (3.8 hours after breakfast) state. Amniotic fluid glucose correlated significantly with simultaneous maternal glucose (r = 0.562; p = 0.001). A significant downward linear trend of mean amniotic fluid glucose with advancing gestational age was demonstrated (p less than 0.01). No trend of mean simultaneous maternal glucose with gestational age was seen. These results were not affected by maternal prandial status at the time of amniocentesis. It is concluded that amniotic fluid glucose decreases with advancing gestational age in well-controlled diabetic pregnant women independent of maternal glycemic levels. Studies of amniotic fluid glucose and/or its relationship to other metabolic hormones must take this into account.

Amniocentesis↗
PubMed1982

Alterations in uterine and placental prostaglandin F and E with gestational age in the rat.

Experiments were designed to determine the chronological alterations in placental and uterine prostaglandin F and E (PGF and PGE) during pregnancy in the rat. Pregnant rats (sperm in the vagina = day 0) were sacrificed at days 15, 18, 19, 20, 21 and delivery (day 21 1/2) and placental and uterine tissues assayed (RIA) for PGF and PGE immediately ("in vivo") or after 1 hour incubation ("in vitro"). Uterine content of PGF and PGE in vivo (ng Pg/mg DNA) was increased significantly by day 19 and further increases were seen through delivery. Incubation of uterine tissue resulted in enhanced net production of PGF and PGE (p less than .05) per mg DNA (as judged by tissue content and release into the incubation medium) by day 18 of pregnancy vs. day 15. Net production in vitro peaked around the time of delivery thus paralleling the alterations in tissue content in vivo. By contrast, no differences with gestational age were found in placental content of PGF and PGE in vivo, the concentrations throughout late gestation remaining in the range of uterine PGs at day 15. However, production of PGs per mg placental DNA increased markedly during incubation in vitro with significant enhancement detected by day 19 vs. 15, achieving levels even greater than the uterus in vitro. The in vivo and in vitro findings for the uterus are consistent with the hypothesis that increases in uterine PGs levels at the end of pregnancy may play an important role in parturition. The in vitro experiences with placental tissue suggest that the potential for PG production per placental cell may also increase in late gestation and thereby contribute to the augmented intrauterine availability of PGs at that time.

Animals↗
PubMed1981

Carbohydrate metabolism in pregnancy. XVII. Diurnal profiles of plasma glucose, insulin, free fatty acids, triglycerides, cholesterol, and individual amino acids in late normal pregnancy.

Diurnal profiles have been constructed for glucose, free fatty acids (FFA), triglycerides, cholesterol, and ten neutral amino acids in subjects with normal carbohydrate metabolism during late pregnancy and in age- and weight-matched nongravid women. Samples of blood were secured during a 24 hour period while the subjects were receiving a liquid formula diet (containing 2,110 kcal with 275 gm carbohydrate and 75 gm protein) in three equal feedings at 0800, 1300, and 1800 hours. Postprandial excursions for most nutrients, as well as plasma concentrations after overnight fast and before each meal, were significantly different in the pregnant subjects. The studies indicate that criteria of normalcy based on observations in nongravid women cannot be invoked assess fuel homeostasis in late pregnancy, and that separate criteria are necessary to evaluate nutrient regulation at this time.

Adult↗
PubMed1981

Carbohydrate metabolism in pregnancy XVI: longitudinal estimates of the effects of pregnancy on D-(63H) glucose and D-(6-14C) glucose turnovers during fasting in the rat.

We measured blood glucose concentrations and glucose turnover rates in 24 hr fasted, conscious, unrestrained pregnant rats and nongravid controls on days 18, 19, and 20 of gestation. Turnover measurements were secured with simultaneous equilibrium infusions of D-(6-3H) and D-(6-14C) glucose so that gluconeogenic recycling could also be determined. "Steady state" values for blood glucose in the mother after 24 hr of fasting did not significantly differ on each of the days, and these concentrations were significantly lower than the values in 24 hr fasted nongravid rats. At 18 days gestation, glucose turnover did not differ from nongravid values. By contrast, values for glucose turnover after 24 hr fasting increased significantly and progressively in the 19 and 20 day pregnant rats. The increase in turnover correlated with the increasing growth of the conceptus. The ratio between D-(6-14C) glucose and D-(6-3H) turnover remained constant (and the same as in the nongravid rats) during all 3 days of gestation suggesting that rates of glucose recycling remained unaltered. These longitudinal studies indicate that the factors contributing to the pattern of "accelerated starvation" during dietary deprivation in pregnancy may vary as pregnancy progresses. The exaggerated lowering of blood glucose which accompanies fasting occurs before total glucose turnover increases. This could provide a potential mechanism for conserving maternal glucose. Since transplacental transfer of glucose is concentration-dependent, the early establishment of a lower "steady state" for circulating glucose could diminish the magnitude of loss of this key nutrient to the fetus.

Animals↗
PubMed1981

Quick-freeze fixation and freeze-drying of isolated rat pancreatic islets: application to the ultrastructural localization of inorganic phosphate in the pancreatic beta cell.

A bounce-free mechanical quick-freeze assembly and a Coulter-Terracio freeze-dry apparatus were successfully coupled to obtain high quality ultrastructural preservation of pancreatic beta cells in a simple and dependable manner. Except for obvious shrinkage spaces, morphological relationships at the tissue, cellular, and subcellular levels were all intact. Beta cell secretory granules demonstrated a dense core surrounded by an electron lucent halo as typically described in specimens after aqueous fixation. Cell membranes and intracellular membranes demonstrated a trilaminar appearance. Golgi apparatus were well preserved. Two clearly defined populations of mitochondria were found. One group of very dark mitochondria had extremely dense matrices in which cristae were barely visible. A second group of mitochondria had light matrices with prominent cristae. The combined quick-freeze fixation and freeze-drying was applied to reevaluate the ultrastructural localization of inorganic phosphate that had been precipitated with lead in the beta cells of pancreatic islets. Accumulation of inorganic phosphate adjacent to the plasma membrane and over the nucleolus of the beta cell in nonstimulated islets was documented with better detail than heretofore possible.

Animals↗
PubMed1981

Hepatic insulin and glucagon receptors in pregnancy: their role in the enhanced catabolism during fasting.

The response to dietary deprivation in late pregnancy, as compared to the non-pregnant condition, is more rapid and profound in terms of mobilization of fuels frm peripheral tissues as well as hepatic ketogenesis and gluconeogenesis ("accelerated starvation"). We examined the potential role of hepatic insulin and glucagon receptors in mediating these changes by comparing 48-h fasted 18-day pregnant and age-matched nongravid rats. Molar ratios for insulin:glucagon in peripheral and portal blood were significantly higher in the pregnant rats. Insulin binding to purified liver plasma membrane receptors, when appropriately corrected for differences in insulin degradation by the membrane system, was marginally diminished in the pregnant animals. Glucagon binding and adenylate cyclase activation by glucagon was indistinguishable in the two groups of animals. On the basis of portal vein hormone concentrations and the values for receptor binding, liver insulinization relative to glucagonization appears to be unchanged or slightly increased in the fasted pregnant rat compared to the fasted nongravid rat. Thus, it seems unlikely that much of the "accelerated starvation" response in late pregnancy can be ascribed to diminished insulin and/or increased glucagon availability at the hepatocellular level. Instead, it is hypothesized that postreceptor events play the major role in sustaining the intrahepatic realignments of established fasting in late pregnancy.

Adenylyl Cyclases↗
PubMed1980

Serial ultrasonography to assess evolving fetal macrosomia. Studies in 23 pregnant diabetic women.

Serial ultrasound estimates of fetal biparietal diameter and abdominal circumference were used as differential indices of intrauterine growth of insulin-insensitive and insulin-sensitive structures, respectively, in 23 White's classes A to C diabetic women. Biparietal diameter in all fetuses conformed to growth patterns for fetuses of nondiabetic mothers. However, two patterns were noted for abdominal circumference. Normal increases occurred in 13 fetuses; in the remaining ten, growth of abdominal circumference exceeded upper normal limits from weeks 28 to 32 of gestation onward. This latter group with putative "accelerated somatic growth" in utero had more immunoreactive insulin in amniotic fluid, weighed more at birth, and had more subcutaneous fat. Serial differential ultrasonography may be useful for detecting evolving macrosomia in diabetic pregnancies, and fetal insulin or insulin-like principles may contribute to the macrosomia.

Birth Weight↗
PubMed1980

Morphologic study of cultured pancreatic fetal islets during maturation of the insulin stimulus-secretion mechanism.

We recently described a tissue culture system in which 21.5-day-old fetal rat islets underwent an in vitro maturation of insulin stimulus-secretion coupling over a period of 7 days. During the same period, the acinar part of the explanted fragments degenerated and the islets became isolated, seeming to increase in mass. In the present study, we have utilized these characteristic morphologic changes in an attempt to evaluate the extent that apparent islet growth reflects multiplication of preformed beta cells or the neogenesis of these cells from ductular or acinar cells. In the first days of culture, continuity between islets and ducts could be demonstrated, and the islets appeared to "bud" from the ducts. During this time, only insulin- and glucagon-positive cells could be demonstrated immunocytochemically, and the 3H-thymidine incorporation index of the beta cells (expressed as the percentage of beta cells labeled during 24 h or exposure to 3H-thymidine and 3 h of "chase") in the "budding" islets was 28.7 +/- 2.6. After 7 days in culture, i.e., after maturation of the insulin stimulus-secretion mechanism, the islets were no longer associated with ductular epithelium. At this stage, insulin-, glucagon-, and occasional somatostatin-positive islet cells could be demonstrated, and the 3H-thymidine incorporation index of the beta cells was significantly decreased to 16.7 +/- 2.8. These observations are taken to support previous suggestions of a possible neogenesis of beta cells from duct epithelium in the rat. This tissue culture technique appears well suited for further detailed studies of this neogenesis.

Animals↗
PubMed1980

Banting Lecture 1980. Of pregnancy and progeny.

A profile characteristic of fuel economy in the mother during normal pregnancy has been delineated. The evidence indicates that pregnancy changes the metabolism of every class of foodstuff. The mechanisms by which the conceptus may be implicated are reviewed. The gestational interactions create a pattern of "accelerated starvation" whenever food is withheld, especially in late pregnancy, and they tend to "facilitate anabolism" when food is ingested. The consequent heightened metabolic oscillations during the shuttlings from fed to fasted state provide a basis for more aggressive therapy with exogenous insulin when endogenous insulin is lacking in pregnancy. It is emphasized that developing fetal structures may be exquisitely attuned to fine alterations in maternal fuel economy and that pregnancy complicated by diabetes may merely exaggerate these normal dependencies since maternal insulin affects all maternal fuels. The manifest changes in the offspring of mothers with even the mildest limitations in insulin reserve, i.e., gestational diabetes, attest to the sensitivity of the relationships. It is suggested that concepts of teratogenesis should be expanded to include alterations occurring subsequent to organogenesis during the differentiation and proliferation of fetal cells. Such changes could cause long-range effects upon behavioral, anthropometric, and metabolic functions. It is hypothesized that all of these could constitute expressions of fuel-mediated teratogenesis and that the potentialities should be incorporated into any evaluation of the outcome of pregnancy in gestations attended by disturbances in maternal fuel metabolism.

Adult↗
PubMed1979

Alterations in pancreatic islet phosphate content during secretory stimulation with glucose.

Isolated rat pancreatic islets were perifused and analyzed for phosphate content immediately following the transient increase in the efflux of orthophosphate which occurs when insulin secretion is stimulated by glucose. In some instances, islets were perifused directly following isolation to minimize preparative delay; in others, islets were prelabeled during incubation with [32P]orthophosphate for 90 min prior to perifusion. In both experimental situations, total islet phosphate content declined 40--50% following exposure to stimulating concentrations of glucose and initiation of enhanced insulin release. In the experiments with prelabeled islets, tissue content of [32P]orthophosphate fell to a similar extent so that the specific radioactivity of islet orthophosphate was unaffected. Inhibited of heightened insulin release with Ni2+ did not modify the decrements in total or radioactive tissue orthophosphate, thus indicating that these responses to islet stimulation reflect events which are proximal to activated exocytosis. Simultaneous analyses for tissue ATP and ADP demonstrated that the efflux in orthophosphate and reduction in tissue orthophosphate content were not mediated via net changes in islet adenine nucleotides. The observations represent the first documentation that a net reduction of tissue inorganic phosphate is one of the early components of stimulus-secretion coupling in isolated pancreatic islets.

Adenine Nucleotides↗