Localization of inorganic phosphate in the pancreatic B cell and its loss on glucose stimulation.

Perifusion experiments have shown that there is a discharge of inorganic phosphate into the medium when insulin secretion from isolated islets is stimulated by glucose. Histochemical and microprobe examination of resting pancreatic islets in the electron microscope shows a specific accumulation of inorganic phosphate adjacent to the plasmalemma and nucleolus of the B (beta) cells. This phossphate is lost from the cells during secretory stimulation of islets with high concentrations of glucose.

Carbohydrate metabolism in pregnancy. VI. Plasma fuels, insulin, liver composition, gluconeogenesis, and nitrogen metabolism during late gestation in the fed and fasted rat.

The effects of late pregnancy on metabolic fuels, liver composition, gluconeogenesis, and nitrogen metabolism have been examined in fed and fasted rats. Plasma free fatty acid (FFA) and immunoreactive insulin (IRI) are greater and glucose and ketones are lower in fed 19-day pregnant than they are in agematched virgin rats. A 48 hr fast elicits greater increases in FFA and ketones and more profound reductions in glucose in the pregnant rats and obliterates the differences in IRI. Fetal weight is not modified by such fasting but maternal weight losses exceed that of the nongravid rats. Livers from rats 19 days pregnant contain more and larger hepatocytes. Per mumole hepatic deoxyribonucleic acid (DNA)-phosphorus, water and protein are more abundant, whereas glycogen is unaffected. Livers from fed pregnant rats contain more lipid phosphorus and less neutral lipid fatty acid. After a 48 hr fast, hepatic steatosis supervenes in gravid animals due to accumulated neutral fat. The contents of hepatic acetyl-coenzyme A (CoA) and citric acid are not different in fed pregnant and virgin rats but are greater in the pregnant rats after fasting. Formation of glucose-(14)C and glycogen-(14)C from administered pyruvate-(14)C are the same in fed pregnant and virgin rats, but greater in the pregnant ones after a 24 or 48 hr fast. Pregnancy does not affect creatinine excretion, and urinary urea is not different in fed pregnant, virgin, and postpartum animals. Contrariwise, more nitrogen, potassium, and phosphorus are excreted by the pregnant animals during a 2 day fast. The increment in urinary nitrogen is due largely to urea on the 1st day, whereas heightened ammonia accounts for half the increase on the 2nd and correlates with the enhanced ketonuria. Muscle catabolism, gluconeogenesis, and diversion to fat are activated more rapidly and to a greater degree when food is withheld during late gestation in the rat. These catabolic propensities are restrained in the fed state. The capacity for "accelerated starvation" may confer survival benefit upon an intermittently eating mother in the presence of a continuously feeding fetus.

Carbohydrate metabolism in pregnancy. 8. Metabolism of adipose tissue isolated from fed and fasted pregnant rats during late gestation.

The effects of late pregnancy on adipose tissue metabolism have been examined in fed and fasted rats. Lumbar fat was excised from 19-day pregnant and age-matched virgin rats which had been given unrestricted access to food ("fed") or fasted for 48 hr before sacrifice. In the fed state, adipose tissue from pregnant rats displayed an increased content of free fatty acids (FFA). This coincided with augmented cleavage of preformed glycerides during incubation in vitro as evidenced by greater net production of FFA and glycerol, and altered disposition of labeled glucose. The enhanced lipolysis was independent of the availability of glucose and was not accompanied by impaired responsiveness to the antilipolytic or to the lipogenic actions of added insulin. In the presence of glucose and albumin, esterification as well as lipolysis was greater in adipose tissue from pregnant than nongravid animals. All the differences were exaggerated by prior fasting. These properties of adipose tissue during late gestation have been ascribed to a primary activation of lipolysis rather than impaired esterification or resistance to insulin. It has been suggested that the hormones of pregnancy may be responsible. Although increased intake of food and heightened availability of insulin may offset the net lipolytic effects in the fed state, a heightened turnover of adipose stores is always present. Thus, the pregnant animal appears better poised to mobilize preformed fat whenever exogenous nutrients are withheld.

Embryotoxic effects of brief maternal insulin-hypoglycemia during organogenesis in the rat.

To test whether maternal hypoglycemia can impair organogenesis, we induced brief glucopenia with insulin in conscious pregnant rats during either the headfold stage or the early neural tube closure stage of embryogenesis. At each time, 10 pairs of animals received identical insulin infusions for 1 h. Half the animals were maintained at euglycemia during the infusions, while the others were allowed to become hypoglycemic. Euglycemia was maintained or restored in all animals immediately after the insulin was stopped. Spontaneous activity was diminished during the hypoglycemia but consciousness was preserved. Embryos were removed from mothers and examined 2 d later. This examination revealed that embryos from the hypoglycemic mothers were growth-retarded and displayed a small but significant incidence of gross developmental anomalies compared with embryos from the insulin-infused euglycemic mothers. Thus, brief, mild maternal hypoglycemia during early organogenesis can disrupt normal embryo development in the rat. The effect is due to the hypoglycemia per se rather than to the insulin employed for its induction.

Rapid transient efflux of phosphate ions from pancreatic islets as an early action of insulin secretagogues.

Anionic fluxes during the membrane realignments of stimulated insulin release have not been characterized previously although cations have been implicated in stimulus-secretion coupling. We have shown that a limited packet pulse of phosphate release ("phosphate flush") begins at the same time that the first phase of insulin secretion may occur. To demonstrate this phenomenon, we have prelabeled islets, obtained from rat pancreas by collagenase digestions, by incubation with [(32)P]orthophosphate. When such prelabeled islets are perifused with Krebs-Ringer bicarbonate containing 0.5 mg/ml D-glucose, a basal rate of efflux of radioactivity is established; transfer to perifusates containing 3.0 mg/ml D-glucose elicits an increased (32)P efflux within 1-2 min to peak values which are 7- to 21-fold greater than basal. The total duration of this "phosphate flush" approximates 10 min and exceeds the duration of the first phase of stimulated insulin secretion. With lesser concentrations of glucose, the flush exhibits dose-response relationships, and with 3 mg/ml glucose, a second flush can be elicited by restoring basal conditions and stimulating anew with 3 mg/ml glucose. The phenomenon is highly specific and can be reduplicated by other secretagogues (L-leucine) or sugars (D-mannose) which are also known to elicit insulin release but not by sugars which fail to affect insulin secretion (D-galactose, D-fructose, i-inositol, L-glucose). The efflux of radioactivity consists entirely of [(32)P]orthophosphate. Phosphate flush persists in phosphate-free media, Ca(++)-free media, and when insulin release is obtunded by adding Ni(++) (2 mM) to the perifusates. Thus, efflux of [(32)P]orthophosphate can be dissociated from insulin extrusion, and from net influx of ionic phosphate or calcium. Membrane stabilization with D(2)O or 1.0 mM tetracaine reversibly inhibits phosphate flush. Although the mechanism by which this effect occurs has not yet been established, the phosphate flush appears to constitute one of the earliest and hitherto unknown indices of the excitatory state in pancreatic islets.

Fuel-mediated teratogenesis. Use of D-mannose to modify organogenesis in the rat embryo in vivo.

The unique embryotoxic properties of D-mannose have been used as the basis for a new technique to secure precise temporal correlations between metabolic perturbations during organogenesis and subsequent dysmorphogenesis. Conscious, pregnant rats were infused with D-mannose or equimolar amounts of D-glucose by "square wave" delivery during the interval in which the neural plate is established and early fusion of neural folds takes place, that is, days 9.5-10.0 of gestation. Infusions of mannose to maternal plasma levels of 150-200 mg/dl did not elicit any toxicity in the mothers: motor activity, eating behavior, and serum components (electrolytes, osmolality, bilirubin) did not differ in glucose- vis-à-vis mannose-infused dams. Embryos were excised by hysterotomy on day 11.6 for evaluation of development. Examination with a dissecting microscope did not disclose developmental abnormalities in any of the 136 embryos from glucose-infused mothers or in 62 additional embryos from mothers that had not received any infusions. By contrast, dysmorphic changes were seen in 17 of 191 embryos (8.9%) from mannose-infused mothers. 14 of the 17 had abnormal brain or neural tube development with incomplete neural tube closure in 9 instances. Abnormal axial rotation was present in 8 of the 191 embryos (4.2%) and lesions of the heart or optic vesicles were seen in 4 (2.1%) and 3 (1.6%), respectively. Embryos from mannose-infused mothers displayed significant retardations in somite number, crown-rump length, and total protein and DNA content. These stigmata of growth retardation were more marked in the 17 dysmorphic embryos. The experiments indicate that D-mannose may be employed in model systems with rodents for precisely timed interruptions of organogenesis in vivo. Initial applications are consistent with our earlier suggestion that multiple dysmorphic changes may supervene after interference with communally observed metabolic dependencies during organogenesis. The studies do not identify the vulnerable site(s) within the conceptus (e.g., investing membranes, embryos, or both). However, the findings suggest that dysmorphic events are manifest most markedly in a general setting of embryo growth retardation.

Relationship between efflux of ionic calcium and phosphorus during excitation of pancreatic islets with glucose.

Simultaneous rates of [32P]orthophosphate and 45Ca2+ efflux from prelabeled rat pancreatic islets have been evaluated to assess whether these ions move in concert throughout all phases of "stimulus-secretion coupling". Perifusion with stimulatory concentrations of glucose elicited immediate but transitory increases in 32P outflow accompanied by initial retardations and subsequent augmentations in net 45Ca2+ outflows. These monophasic 32P and biphasic 45Ca2+ responses to secretory stimulation were abolished completely by membrane stabilization with tetracaine. However, certain manipulations enabled individual components to be modified separately. During stimulation with glucose, inhibition of insulin release by Ni2+ abolished the late increases in 45Ca2+ outflow without affecting the initial retentions of 45Ca2+ or the increased releases of 32P. Under basal conditions, the ionophore A23187 "triggered" increased releases of 45Ca2+ and insulin without prior retentions of 45Ca2+ or enhancements of 32P efflux. Thus, the immediate retardations of 45Ca2+ outflow and heightened efflux of 32P may reflect early events in stimulus-secretion coupling which can be dissociated from the augmented release of 45Ca2+ accompanying activated emiocytosis.

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.

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.

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.

Phosphate metabolism and glucose-initiated efflux of phosphate ions in islets of fetal pancreas.

Elsewhere we have proposed that the rapid transient efflux of 32P orthophosphate that occurs when prelabeled pancreatic islets are exposed to nutrient secretagogues (the "phosphate flush") reflects one of the earliest steps in islet stimulus-secretion coupling. We have now shown that the "phosphate flush" is much smaller with islets from fetal rats 21 1/2 days old. This could be attributed to decreased cellular stores of radioactivity, especially inorganic orthophosphate (32P), at the onset of stimulation, which may have been due, in part, to the diminished ability of fetal islets to retain the radiophosphorus accumulated during the labeling period. Certain other differences in phosphate metabolism were also observed. With prelabeled islets from adult rats, exposure to 3.0 mg. per milliliter glucose effected acute increases in the tissue content of AT32P and GT32P. Comparable stimulation of prelabeled fetal islets with 3.0 mg. per milliliter glucose did not elicit detectable changes in the labeling of ATP or GTP. The findings indicate that selected aspects of phosphate metabolism may be immature in fetal islets and, perhaps, implicated in their obtunded secretion of insulin in response to stimulation with glucose.

Growth retardation during early organogenesis in embryos of experimentally diabetic rats.

Embryos from rats rendered diabetic with streptozotocin for 1 wk or more before conception were examined on day 11.5 of gestation (i.e., at the 26-29-somite stage of normal rat embryonic development). The studies were designed to assess whether poorly regulated maternal diabetes is associated with demonstrable abnormalities even during this early phase of embryogenesis. We found that manifest retardations in growth and development were invariably present as judged by significant reductions in crown-rump length and somite number, respectively. Total protein and DNA content of the embryos were also reduced, although not symmetrically, so that protein/DNA ratios were increased. Gross dysmorphogenic lesions in neural tissue disproportional to the overall growth retardation at 11.5 days could not be demonstrated. The findings suggest that maternal diabetes can compromise intra-uterine growth and development during the period preceding and coinciding with the establishment of circulation in the allantoic placenta. The possible multifactorial determinants remain to be elucidated. It also remains to be established whether the early embryotoxicity provides a setting conducive to the increased dysmorphogenesis that is traditionally recognized during the later stages of pregnancy complicated by diabetes.

Insulin receptors in embryo and extraembryonic membranes of early somite rat conceptus.

Intact rat conceptuses were cultured from day 9.5 of gestation on. Individual components of the conceptus, including the embryo and the extraembryonic membranes (consisting of yolk sac, amnion, and allantoic placenta), were isolated and examined for insulin receptors at two time points during organogenesis: day 10.4 of gestation (approximately 10-12 somites) when the yolk sac had become vascularized and just before closure of the anterior neuropore and day 11.6 (approximately 27-31 somites) when vascularization of the chorioallantoic placenta had been established and the neural tube was closed completely. The studies were designed to provide inferential insights about the possible role of insulin in embryogenesis during different phases of nutrient delivery. Active insulin degradation occurred with embryo as well as membrane homogenates during incubation at 37 degrees C. Degradation was markedly reduced at 4 degrees C, and binding of 125I-labeled insulin by embryo or membrane homogenates prepared on day 10.4 or 11.6, respectively, of gestation approached equilibrium after a 20-h incubation at this temperature. Values for the specific binding of tracer (0.4 ng/ml) or carrier (10.4 ng/ml) insulin by embryo and membrane homogenates were the same on days 10.4 and 11.6; specific binding was significantly greater with preparations of membranes than embryo at both time points. Full binding curves on day 11.6 showed similar affinities for insulin by embryo and membranes (Ke = 1.2 X 10(8)/M and 4.6 X 10(8)/M, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Uptake of myo-inositol by early-somite rat conceptus. Transport kinetics and effects of hyperglycemia.

We have shown that myo-inositol in the cultured rat embryo is diminished whenever malformations are induced by hyperglycemia and that the malformations and reductions of tissue myo-inositol content are not corrected by aldose reductase inhibitors. This study was designed to evaluate the kinetics of myo-[3H]inositol uptake in vitro during 1-, 3-, and 24-h intervals in the 10.5-day rat conceptus (10-12 somites). We found that the equilibration between tissue and medium is relatively slow and that the concentration of free myo-inositol in tissue is only approximately threefold greater than in the medium even after 24 h. The integrated uptake of free myo-inositol by the intact 10.5-day conceptus is a saturable process with a Km (246 +/- 16 microM) consistent with a low-affinity system. The net rate of accumulation into the tissue pool of free myo-inositol exceeds the rate of incorporation of the accumulated myo-inositol into lipid components. Ambient glucose inhibits net myo-inositol uptake in a concentration-dependent fashion, and the inhibition is competitive in nature. The glucose-mediated inhibitions of myo-inositol transport also compromise the concurrent incorporation of myo-[3H]inositol into lipid components, although to a lesser extent. These inhibitory effects are relatively specific for D-glucose and not replicated by equimolar additions of D-mannose or D-galactose. myo-Inositol accumulation by the 10.5-day rat conceptus is also impaired by relatively specific inhibitors of D-glucose transport such as phloridzin or ouabain.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Epidemiologic findings on the relationship of time of day and time since last meal to glucose tolerance.

Data from 10,559 men and women, age 30-64, participating in the morning and afternoon in a Chicago Health Department multiphasic screening project, were used to determine the effects of time of day and time since last meal on the values for plasma glucose one and two hours following oral challenge with 100 gm. of glucose. Mean plasma glucose values and rates of suspect glucose intolerance (based on several cutpoints) were sizeably higher in the afternoon than in the morning. In addition, plasma glucose values increased with time elapsed since the last meal, up to 10 hours postprandially. Thereafter, both one- and two-hour plasma glucose values tended to exhibit a decline. Analysis of covariance confirmed that fluctuations in glucose tolerance were related to time of day and time since last meal, but the effects of each parameter were exerted independently.

Differential effects of age versus glycemic stimulation on the maturation of insulin stimulus-secretion coupling during culture of fetal rat islets.

We have cultured islets from 21.5-day-old fetal rats for 1-7 days in RMPI 1640/10% fetal calf serum containing 2.8 or 11.1 mM glucose to evaluate the differential effects of age vis-à-vis glycemic stimulation on the maturation of selected components of stimulus-secretion coupling. After 1 day of culture in either media, acute stimulation with 3.0 mg/ml glucose during basal perifusion with 0.5 mg/ml glucose elicited only a small first phase of stimulated insulin secretion and no second phase. The acute exposure to 3.0 mg/ml glucose produced no change in the prevailing high rates of oxygen consumption (QO2) and caused only minor increments in phosphate efflux (i.e., peak values for phosphate flush of 126 +/- 16% of baseline for islets that had been cultured in 11.1 mM glucose and 162 +/- 30% for islets cultured in 2.8 mM glucose). After 7 days of culture in 11.1 mM glucose, acute stimulation with 3.0 mg/ml glucose increased Qo2 (as in adult islets) and effected acute increases in the AT32P and GT32P content of prelabeled islets. The 3.0 mg/ml glucose also triggered phosphate flush to 599 +/- 45% of baseline and elicited first as well as early second phases of stimulated insulin secretion that replicated the performance of adult islets. By contrast, after 7 days of culture in 2.8 mM glucose, similar acute exposures of fetal islets to 3.0 mg/ml glucose effected only a small first phase and a negligible second phase of stimulated insulin secretion despite the occurrence of the same increments in Qo2 as after culture in 11.1 mM glucose, highly significant increases in AT32P and GT32P, and phosphate flushes that peaked at 306 +/- 16% of basal values. Thus, the ontogeny of individual components of stimulus-secretion coupling may occur in asynchronous fashion and varying require glycemic stimulation in addition to aging per se. The capacities to augment efflux of orthophosphate, enhance respiration, and heighten nucleotide turnover in response to acute stimulation with glucose seem to mature in large measure in time-dependent fashion, whereas some chronic exposure to ambient glucose in excess of basal levels may be required to establish and/or maintain the other coupled components that underlie biphasic stimulated insulin release. However, we did not achieve full exocytotic maturation even after 7 days of culture with 11.1 mM glucose.(ABSTRACT TRUNCATED AT 400 WORDS)

Gestational diabetes mellitus. Correlations between the phenotypic and genotypic characteristics of the mother and abnormal glucose tolerance during the first year postpartum.

We evaluated glucose tolerance during the first year postpartum in 113 women with gestational diabetes mellitus (GDM) diagnosed according to the criteria of the First International Workshop-Conference on GDM and the National Diabetes Data Group. The high incidence of abnormal postpartum glucose tolerance (38% "diabetes mellitus" plus 19% "impaired glucose tolerance") was correlated with certain of the heterogeneous characteristics of the population at the time of antepartum diagnosis. Virtually all women with antepartum fasting plasma glucose (FPG) greater than or equal to 130 mg/dl (GDM class B1) remained abnormal postpartum (21/22 [95%]), which suggests that this group may include women with preexisting glucose intolerance unrecognized before pregnancy. In the remainder, those with FPG greater than or equal to 105-129 mg/dl (GDM class A2) were more likely to be abnormal postpartum than those with FPG less than 105 mg/dl (GDM class A1). Within the A1 and A2 groups, increasing maternal age, relative insulinopenia, and hyperglycemia at 2 h during antepartum OGTT were also associated with a greater likelihood of abnormal glucose tolerance postpartum. The presence of HLA-DR3 and/or -DR4 antigens was not predictive of the status of glucose tolerance during the first year postpartum, although the increased frequency of cytoplasmic islet cell antibodies in A2 and B1 subjects was associated with a high incidence of abnormal postpartum glucoregulation. The high incidence of abnormal postpartum glucose tolerance in all GDM classes makes a compelling case for careful, early, and continuing follow-up of all women with a diagnosis of GDM.(ABSTRACT TRUNCATED AT 250 WORDS)

Gestational diabetes mellitus. Heterogeneity of maternal age, weight, insulin secretion, HLA antigens, and islet cell antibodies and the impact of maternal metabolism on pancreatic B-cell and somatic development in the offspring.

We have examined gravida with gestational diabetes mellitus (GDM), as defined by the National Diabetes Data Group (Diabetes 1979; 28:1039), for phenotypic and genotypic heterogeneity. Fasting plasma glucose (FPG) at diagnosis was used for further stratification of GDM according to putative metabolic severity into class A1 (FPG less than 105 mg/dl [N = 129]), class A2 (FPG 105-129 mg/dl [N = 47]), and class B1 (FPG greater than or equal to 130 mg/dl [N = 23]). All GDM classes tended to be older and heavier than consecutive gravida with documented normal glucose tolerance (controls, N = 148). Subdivision into "lean" and "obese" indicated that plasma immunoreactive insulin (IRI) was greater after overnight fast in the obese of all groups except B1. However, absolute increases in IRI above fasting levels in response to glucose during OGTT were significantly enhanced by obesity only in class A2 gravida. Adjustment for the effects of age and weight by covariate analysis indicated that the IRI response to glycemic stimulation is usually attenuated in all forms of GDM. Mean values for increases in IRI above fasting values during the first 15 min and IRI increments relative to the increases in plasma glucose throughout the 180-min OGTT were below control values in all GDM groups and progressively so, i.e., A1 less than A2 less than B1. The absolute insulinopenia was not invariable; a small number of gravida from all GDM groups displayed well-preserved IRI responses to oral glucose. Genotypic evaluation of the GDM population disclosed an increased occurrence of "markers" known to be associated with type I diabetes mellitus.(ABSTRACT TRUNCATED AT 250 WORDS)

32P-labeling patterns in rat pancreatic islets: tissue source of the radiophosphate released after glucose stimulation.

Immediately after stimulation with glucose in vitro, isolated rat pancreatic islets prelabeled with [32P]orthophosphate release a pulse of [32P]orthophosphate into the media (the "phosphate flush"). Islets have been rapidly frozen before, during, and after this pulse to assess the concurrent changes in the distribution of tissue radioactivity. Under the present experimental conditions, approximately 90% of the islet radioactivity was soluble in perchloric acid (PCA-soluble) immediately before stimulation and slightly more than half of that was present as [32P]orthophosphate. The tissue pool of [32P]orthophosphate declined 55% and 62% after 7 and 14 min of stimulation which, respectively, incorporated the peak and the end of the heightened efflux of radioactivity. The net decrementa in tissue orthophosphate could account for all of the radioactivity which was released during the "phosphate flush." During the 14-min period of stimulation, labeled ATP and GTP (which had accounted for 13% and 4% of total PCA-soluble radioactivity before stimulation) increased 51% and 35%, respectively, and labeled ADP and AMP (which had accounted for 5.4% and 1.5% of PCA-soluble counts) fell 36% and 77%, respectively. Certain other PCA-soluble components, such as phosphorylcholine and phosphorylethanolamine, and total PCA-insoluble radioactivity were not demonstrably altered. The findings indicate that the "phosphate flush" originates from a labile pool of tissue orthophosphate. It remains to be established whether the simultaneous changes in the turnover of selected nucleotides are coupled to the translocation of orthophosphate or are mediated separately.