Prolactin, progesterone, and dexamethasone coordinately and adversely regulate glucokinase and cAMP/PDE cascades in MIN6 beta-cells

Islet cells undergo major changes in structure and function to meet the demand for increased insulin secretion during pregnancy, but the nature of the hormonal interactions and signaling events is incompletely understood. Here, we used the glucose-responsive MIN6 beta-cell line treated with prolactin (PRL), progesterone (PRG), and dexamethasone (DEX, a synthetic glucocorticoid), all elevated during late pregnancy, to study their effects on mechanisms of insulin secretion. DEX alone or combined with PRL and PRG inhibited insulin secretion in response to 16 mM glucose-stimulating concentrations. However, in the basal state (3 mM glucose), the insulin levels in response to DEX treatment were unchanged, and the three hormones together maintained higher insulin release. There were no changes of protein levels of GLUT2 or glucokinase (GK), but PRL or PRG treatment increased GK activity, whereas DEX had an inhibitory effect on GK activity. alpha-Ketoisocaproate (alpha-KIC)-stimulated insulin secretion was also reduced by DEX alone or combined with PRL and PRG, suggesting that DEX may inhibit distal steps in the insulin-exocytotic process. PRL treatment increased the concentration of intracellular cAMP in response to 16 mM glucose, suggesting a role for cAMP in potentiation of insulin secretion, whereas DEX alone or combined with PRL and PRG reduced cAMP levels by increasing phosphodiesterase (PDE) activity. These data provide evidence that PRL and to a lesser extent PRG, which increase in early pregnancy, enhance basal and glucose-stimulated insulin secretion in part by increasing GK activity and amplifying cAMP levels. Glucocorticoid, which increases throughout gestation, counteracts only glucose-stimulated insulin secretion under high glucose concentrations by dominantly inhibiting GK activity and increasing PDE activity to reduce cAMP levels. These adaptations in the beta-cell may play an important role in maintaining the basal hyperinsulinemia of pregnancy while limiting the capacity of PRL and PRG to promote glucose-stimulated insulin secretion during late gestation.     

Hormonal profile and glucose tolerance in late pregnancy and postpartum

Oral glucose tolerance, plasma insulin and basal levels of glucagon, hGH, hPRL, hPL, TSH, T4, T3, thyroxine-binding globulin (TBG), cortisol, corticosteroid-binding globulin (CBG) and estriol were measured in 23 normal pregnant women in late gestation (31 +/- 0.4 weeks of pregnancy). Twelve of these subjects could be re-examined 14 +/- 2 weeks postpartum. Blood glucose was lower basal and after glucose load (100 g) in the pregnant group. Fasting plasma insulin and glucose-induced insulin release were higher in pregnancy. The insulinogenic index and the beta cell response were significantly greater antepartum, while peripheral insulin activity was unchanged. The insulin:glucagon ratio as well as TSH and hGH showed no significant differences between ante- and postpartum values. However, T4, T3, TBG, cortisol, CBG, estriol, hPRL and hPL were significantly higher during gestation than after delivery. T4:TBG and T3:TBG ratios were much lower antepartum, while the cortisol:CBG ratio was comparable ante- and postpartum. To our knowledge this is the first report in which such an extensive hormonal and metabolic analysis was performed in the same women ante- and postpartum. It could be shown that glucose tolerance is not worsened during pregnancy in healthy subjects. The higher gestational insulin values are discussed with respect to the various significant hormonal changes.     

Downregulated IRS-1 and PPARgamma in obese women with gestational diabetes: relationship to FFA during pregnancy

Gestational diabetes mellitus (GDM) is associated with elevated postprandial free fatty acids (FFA) and insulin resistance; however, little is known about the cellular mechanisms underlying insulin resistance to suppress lipolysis during gestation. We evaluated the longitudinal changes in insulin suppression of FFA before pregnancy and in early (12-14 wk) and late (34-36 wk) gestation in obese subjects with normal glucose tolerance and in obese GDM subjects. Abdominal subcutaneous adipose tissue biopsies were also obtained during cesarean delivery from normal obese pregnant (Preg-Con), GDM, and nonpregnant obese control (Non-Preg-Con) subjects during gynecological surgery. GDM subjects had higher basal plasma FFA before pregnancy (P = 0.055). Insulin's ability to suppress FFA levels declined from early to late gestation in both GDM and Preg-Con subjects and was significantly less in GDM subjects compared with Preg-Con subjects over time (P = 0.025). Adipose tissue insulin receptor substrate (IRS)-1 protein levels were 43% lower (P = 0.02) and p85alpha subunit of phosphatidylinositol 3-kinase was twofold higher (P = 0.03) in GDM compared with Preg-Con subjects. The levels of peroxisome proliferator-activated receptor-gamma (PPARgamma) mRNA and protein were lower by 38% in Preg-Con (P = 0.006) and by 48% in GDM subjects (P = 0.005) compared with Non-Preg controls. Lipoprotein lipase and fatty acid-binding protein-2 mRNA levels were 73 and 52% lower in GDM compared with Preg-Con subjects (P < 0.002). Thus GDM women have decreased IRS-1, which may contribute to reduced insulin suppression of lipolysis with advancing gestation. Decreased PPARgamma and its target genes may be part of the molecular mechanism to accelerate fat catabolism to meet fetal nutrient demand in late gestation.     

Treatment with constitutive androstane receptor ligand during pregnancy prevents insulin resistance in offspring from high-fat diet-induced obese pregnant mice

The constitutive androstane receptor (CAR) has been reported to decrease insulin resistance even during pregnancy, while exposure to a high-fat diet (HFD) in utero in mice can induce a type 2 diabetes phenotype that can be transmitted to the progeny. Therefore, we examined whether treatment with a CAR ligand during pregnancy could prevent hypertension, insulin resistance, and hyperlipidemia in the offspring from HFD-induced obese pregnant mice (OH mice). We employed four groups of offspring from HFD-fed and control diet-fed pregnant mice with or without treatment with a CAR ligand. Treatment with a CAR ligand during pregnancy improved glucose tolerance and the levels of triglyceride and adipocytokine and restored the changes induced by HFD with amelioration of hypertension in the adult OH mice. This treatment also increased adiponectin mRNA expression, suppressed leptin expression in adipose tissues of OH mice, and abolished the effect of HFD on the epigenetic modifications of the genes encoding adiponectin and leptin in the offspring during immaturity and adulthood. Our data suggest that CAR might be a potential therapeutic target to prevent metabolic syndrome in adulthood of offspring exposed to an HFD in utero.     

Using PGFM (13,14-dihydro-15-keto-prostaglandin F2α) as a non-invasive pregnancy marker for felids

Understanding the complex endocrine interactions that control reproduction in felids is essential for captive breeding management. The most important demand is a quick and reliable pregnancy diagnosis. However, the occurrence of pseudopregnancies in felids complicates matters. We investigated whether the fecal prostaglandin metabolite (PGFM) recently suggested for pregnancy diagnosis in the lynx is suitable for all felid species. We found that increased levels of PGFM during the last trimester indicate pregnancy in seven of the eight main lineages of the carnivore family Felidae. PGFM levels in a sand cat (domestic cat lineage) were basal at mating and remained so until Day 40 post-mating. Day 41 marked the beginning of a distinct increase culminating in peak levels of 6.5 μg/g before parturition and decreasing again to baseline thereafter. Similar pregnancy profiles were obtained from the domestic cat, the leopard cat, the lynx, the ocelot and the caracal lineage, whereas in pseudopregnant individuals (sand cat, Iberian and Eurasian lynx) fecal PGFM remained at basal levels. In pregnant cheetahs (puma lineage) PGFM increased above basal following day ∼48 peaking before pregnancy but remained at baseline in pseudopregnant females. Discrepancies existed in the Panthera lineage. While Chinese leopard, Sumatran tiger, and the black panther showed marked increases of PGFM during the last weeks of pregnancy, only moderate increases in PGFM levels were found in the Indochinese tiger and the Persian leopard. Altogether, PGFM as tool for pregnancy diagnosis has been proven to be useful in breeding management of felids.     

PPARalpha activation reverses adverse effects induced by high-saturated-fat feeding on pancreatic beta-cell function in late pregnancy

We examined whether the additional demand for insulin secretion imposed by dietary saturated fat-induced insulin resistance during pregnancy is accommodated at late pregnancy, already characterized by insulin resistance. We also assessed whether effects of dietary saturated fat are influenced by PPARalpha activation or substitution of 7% of dietary fatty acids (FAs) with long-chain omega-3 FA, manipulations that improve insulin action in the nonpregnant state. Glucose tolerance at day 19 of pregnancy in the rat was impaired by high-saturated-fat feeding throughout pregnancy. Despite modestly enhanced glucose-stimulated insulin secretion (GSIS) in vivo, islet perifusions revealed an increased glucose threshold and decreased glucose responsiveness of GSIS in the saturated-fat-fed pregnant group. Thus, insulin resistance evoked by dietary saturated fat is partially countered by augmented insulin secretion, but compensation is compromised by impaired islet function. Substitution of 7% of saturated FA with long-chain omega-3 FA suppressed GSIS in vivo but did not modify the effect of saturated-fat feeding to impair GSIS by perifused islets. PPARalpha activation (24 h) rescued impaired islet function that was identified using perifused islets, but GSIS in vivo was suppressed such that glucose tolerance was not improved, suggesting modification of the feedback loop between insulin action and secretion.     

Adaptations of adipose tissue metabolism and number of insulin receptors in pregnant sheep

The endocrine control of adipose tissue metabolism during pregnancy in sheep has been investigated. The number of insulin receptors of sheep adipocytes was increased during pregnancy. There was no apparent change in the concentration of serum insulin during pregnancy in sheep while the rise in serum progesterone concentration was smaller and more gradual than in rats. Net lipid deposition in adipocytes occurred during the first 55 days of pregnancy, probably due primarily to increased lipoprotein lipase activity. Net deposition of lipid had ceased by mid-pregnancy while by 125 days of pregnancy, the rate of fatty acid synthesis in adipose tissue was decreased and the serum fatty acid concentration had risen, suggesting the onset of net lipid mobilization in the tissue. Results are compared with those from other studies with rats; it would appear that different mechanisms regulate lipid deposition during pregnancy in sheep and rats.     

Adipose tissue metabolism during early pregnancy in the rat: temporal relationships of changes in the metabolic activity, number of insulin receptors, and serum hormone concentrations

The temporal relationships between changes in rates of fatty acid and acylglycerol glycerol synthesis; the activity of lipoprotein lipase of parametrial adipocytes and their capacity to bind insulin; and the serum concentrations of insulin, progesterone, prolactin, and total lactogenic activity have been examined in rats during the first 15 days of pregnancy. The rate of fatty acid and acylglycerol synthesis showed a transient increase at Days 9 and 12 of pregnancy, whereas there was no change in the activity of lipoprotein lipase activity except for a fall between Days 12 and 15 of pregnancy. The capacity of adipocytes to bind insulin was increased by Day 6 of pregnancy and remained elevated until at least Day 15; no changes in the affinity for insulin were observed. Serum progesterone, insulin, and total lactogenic activity were elevated by Days 3, 9, and 12 of pregnancy, respectively. The results show that progesterone but not placental lactogen could be responsible for the rise in the insulin-binding capacity of rat adipocytes during pregnancy, whereas the fall in lipogenic capacity at about Day 12 of pregnancy coincides with the rise in serum placental lactogen.     

New developments in the treatment and monitoring of type 1 diabetes mellitus

In recent years, insulin analogues are the benefits of the use in functional intensive insulin therapy for the treatment of diabetes. Shortacting insulin (lispro, aspart and glulisine) and long-acting insulin (glargine and detemir) have been developed for the management of diabetes. Short-acting insulin analogues are an alternative to regular human insulin before meals. These new short-acting insulin analogues show more rapid onset of activity and a shorter duration of action. As a result of these pharmacokinetic differences, an improved postprandial glycemic control is achieved, without increasing the risk of hypoglycemia. In addition, these insulin analogues can be administered immediately before a meal. The long-acting insulin analogues provide basal insulin levels for 24 h when administered once (glargine) or two (detemir) daily. Compared with previous intermediate- or long-acting conventional insulin, these insulins shows a flat profile of plasma insulin levels . The use of these long-acting insulin analogues appears to be associated with a reduced incidence of hypoglycemia, especially at night. The availability of these new insulin analogues has the potential to significantly improve long-term control over blood glucose in diabetic patients. In recent years more and more frequently the method of multiple daily injections (MDI) of insulin is being replaced by the method of continuous subcutaneous insulin infusion (CSII). It is the most physiological way to administer insulin. In recent years treatment with insulin pumps has been used more frequently in the pediatric patients and in the treatment of diabetes in pregnancy. Use of continuous glucose monitoring systems enables detection of glycemia fluctuations unrevealed by selfmonitoring of blood glucose, such as night hypoglycemias and early postprandial hyperglycemias. Real-time systems allow to reduce HbA1c levels and limit number of excursions. Non-invasive glucose measurement devices are introduced. Fully automated continuous glucose monitoring systems integrated with insulin pumps operating in closed-loop model, requiring no patient assistance, are still being researched. Commercially available systems operate in open-loop model, where the patient has to decide on administration and dose of insulin.     

Selection for and initiation of continuous subcutaneous insulin infusion. Proceedings from a workshop

Continuous subcutaneous insulin infusion (CSII) has been used in the paediatric age group for more than 20 years. The technique is not yet widely used in most countries but there has recently been increasing interest in pump therapy for young children and adolescents. In 1999, 7.5% of Swedish children and adolescents with diabetes used pumps, now the figure is approaching 12%. The indication for starting pump therapy has usually been a medical problem, but today quality of life issues are becoming increasingly important. One technique sometimes used is to start CSII by wearing the pump only at night. Daily insulin requirements are usually decreased compared with injection therapy. Studies have shown that it is possible to lower HbA1c when using an insulin pump and that the risk of severe hypoglycaemia can be lowered. The use of CSII has also been successful in preventing recurrent admission for diabetic ketoacidosis. While starting pump therapy does take an extra effort from both the diabetes team and the family, routine visits are generally no more time-consuming than for patients on multiple injection therapy. CSII can be initiated during admission to hospital but most pumps are started on an outpatient basis. Our department has the patients on the day care ward for 3-4 days of 'pump school'. Parents wear a saline pump for practice. The total daily insulin dose is usually lowered 15-20% compared with multiple injections; on average 40-50% (sometimes up to 60%) of the daily dose is given as basal rate. We start all pumps on rapid-acting analogues and use 40 IU/ml if the basal rate is <0.3 IU/h. In conclusion, the use of CSII in children and adolescents is well accepted and can be managed safely.     

Long-term antidiabetic activity of vanadyl after treatment withdrawal: Restoration of insulin secretion?

In its vanadate (V⁵⁺) or vanadyl (V⁴⁺) forms, vanadium has been demonstrated to possess antidiabetic activity. Oral treatment of streptozotocin (STZ)-diabetic animals with either form is associated with correction of hyperglycemia, and prevention of diabetes-induced complications, although weight gain is unaffected. Vanadium treatment of non-diabetic animals lowers plasma insulin levels by reducing insulin demand, as these animals remain normoglycemic. These results suggest that vanadium hasin vivo insulin-mimetic or insulin-enhancing effects, in agreement with severalin vitro observations.Chronic treatment with vanadium has also been shown to result in sustained antidiabetic effects in STZ-diabetic animals long after treatment has ceased. Thus, at 13 weeks after withdrawal from treatment, corrected animals had normalized glucose and weight gain, and improved basal insulin levels. In addition, near-normal glucose tolerance was found despite an insignificant insulin response. Since vanadium accumulates in several tissue sites (e.g. bone, kidney) when pharmacological doses are administered, it is possible that stored vanadium may be important in maintaining near-normal glucose tolerance at least in the short-term following withdrawal from treatment. Recently, following withdrawal of vanadyl treatment up to 30 weeks, diabetic animals which had remained normoglycemic and had normalized glucose tolerance showed improvements in plasma insulin levels both in the basal state and in response to oral glucose, as compared to those which had reverted to hyperglycemia. The observed significant improvements in insulin capacity over the long-term (>3 months) suggests that a restored and/or preserved insulin secretion may be essential for maintained reversal of the diabetic state over a prolonged period after treatment is withdrawn.     

Integration of physiological mechanisms that influence fertility in dairy cows

Fertility in dairy cows has been declining for the past three decades. Genetic selection for increased milk production has been associated with changes in key metabolic hormones (growth hormone, insulin, IGF and leptin) that regulate metabolism by homoeostasis and homeorhesis. These metabolic hormones, particularly insulin, provide signals to the reproductive system so that regulation of ovarian function is coordinated with changes in metabolic status. Studies have shown, for example, that increasing circulating insulin concentrations during the early post partum period can advance the resumption of oestrous cycles by enhancing follicular growth. However, high concentrations of insulin can be detrimental to the developmental competence of oocytes, which is also influenced by the supply of fatty acids at the systemic level and at the ovarian level. Insulin status is also associated with the incidence and characteristics of abnormal ovarian cycles. These changes can occur without significant variation in circulating gonadotrophin concentrations. This suggests that additional factors, such as peripheral metabolites, metabolic hormones and locally produced growth factors, may have a modulating role. Recent evidence has demonstrated that ovarian responses to metabolic signals and nutrient profile vary according to the stage of the reproductive cycle. Improved understanding of this multifactorial process enables nutrition to be matched to genotype and milk production, with a positive impact on pregnancy rate.     

Effect of Pregnancy for Females Born Small on Later Life Metabolic Disease Risk

There is a strong inverse relationship between a females own birth weight and her subsequent risk for gestational diabetes with increased risk of developing diabetes later in life. We have shown that growth restricted females develop loss of glucose tolerance during late pregnancy with normal pancreatic function. The aim of this study was to determine whether growth restricted females develop long-term impairment of metabolic control after an adverse pregnancy adaptation. Uteroplacental insufficiency was induced by bilateral uterine vessel ligation (Restricted) or sham surgery (Control) in late pregnancy (E18) in F0 female rats. F1 Control and Restricted female offspring were mated with normal males and allowed to deliver (termed Ex-Pregnant). Age-matched Control and Restricted Virgins were also studied and glucose tolerance and insulin secretion were determined. Pancreatic morphology and hepatic glycogen and triacylglycerol content were quantified respectively. Restricted females were born lighter than Control and remained lighter at all time points studied (p<0.05). Glucose tolerance, first phase insulin secretion and liver glycogen and triacylglycerol content were not different across groups, with no changes in β-cell mass. Second phase insulin secretion was reduced in Restricted Virgins (−34%, p<0.05) compared to Control Virgins, suggestive of enhanced peripheral insulin sensitivity but this was lost after pregnancy. Growth restriction was associated with enhanced basal hepatic insulin sensitivity, which may provide compensatory benefits to prevent adverse metabolic outcomes often associated with being born small. A prior pregnancy was associated with reduced hepatic insulin sensitivity with effects more pronounced in Controls than Restricted. Our data suggests that pregnancy ameliorates the enhanced peripheral insulin sensitivity in growth restricted females and has deleterious effects for hepatic insulin sensitivity, regardless of maternal birth weight.     

Insulin resistance and impaired baroreflex gain during pregnancy

Pregnancy decreases baroreflex gain, but the underlying mechanism is unclear. Insulin resistance, which has been associated with reduced transport of insulin into the brain, is a consistent feature of many conditions exhibiting impaired baroreflex gain, including pregnancy. Therefore, using conscious pregnant and nonpregnant rabbits, we tested the novel hypothesis that the pregnancy-induced impairment in baroreflex gain is due to insulin resistance and reduced brain insulin. Baroreflex gain was determined by quantifying changes in heart rate in response to stepwise steady-state changes in arterial pressure, secondary to infusion of nitroprusside and phenylephrine. We found that insulin sensitivity and baroreflex gain were strongly correlated in nonpregnant and term pregnant rabbits (r2 = 0.59). The decrease in insulin sensitivity and in baroreflex gain exhibited similar time courses throughout pregnancy, reaching significantly lower levels at 3 wk of gestation and remaining reduced at 4 wk (term is 31 days). Treatment of rabbits with the insulin-sensitizing drug rosiglitazone during pregnancy almost completely normalized baroreflex gain. Finally, pregnancy significantly lowered cerebrospinal fluid insulin concentrations. These data identify insulin resistance as a mechanism underlying pregnancy-induced baroreflex impairment and suggest, for the first time in any condition, that decreased brain insulin concentrations may be the link between reductions in peripheral insulin sensitivity and baroreflex gain.     

Breastfeeding and the Basal Insulin Requirement in Type 1 Diabetic Women

ObjectiveTo evaluate whether breastfeeding in women with type 1 diabetes mellitus is associated with a decreased insulin requirement.MethodsIn this prospective study conducted between September 2006 and August 2008, type 1 diabetic pregnant women were recruited before the third trimester of pregnancy. Eligible women had no evidence of diabetes-related complications and were treated with continuous subcutaneous insulin infusion pump therapy. During pregnancy and in the first 8 weeks of the postpartum period, participants performed daily fingerstick blood glucose monitoring with at least 12 measurements per day; insulin dosages were adjusted to maintain normoglycemia. Participant characteristics, diabetic parameters, and neonatal growth were compared between women who breastfed exclusively and women who did not breastfeed.ResultsOf 18 women, 12 breastfed and 6 did not. Compared with nonbreastfeeding mothers, breastfeeding mothers showed a decreased need for total daily basal insulin (0.21 ± 0.05 units/kg per day vs 0.33 ± 0.02 units/kg per day). The mean value of total daily basal insulin was significantly lower in the breastfeeding group than in the nonbreastfeeding group. The mean number of hyperglycemic episodes in the first 2 weeks post partum and during the third to eighth weeks was not different between the groups.However, the mean number of hypoglycemic episodes in the first 2 weeks post partum in the breastfeeding group was significantly higher than in the nonbreastfeeding group (11.9 ± 2.6 episodes vs 5.5 ± 1.6 episodes, P < .001). No differences were observed between the groups in neonatal birth weight or infant weight after 8 weeks of age.ConclusionsDecreased need in total daily basal insulin is caused by increased glucose use during lactation. We recommend that the starting total daily basal insulin dosage for type 1 diabetic women who breastfeed be calculated as 0.21 units times the weight in kg per day. This regimen results in normoglycemia and minimizes the risk of severe hypoglycemia associated with lactation. (Endocr Pract. 2009;15:187-193)     

Insulin Glargine Use During Pregnancy

ObjectiveTo review the literature regarding the use of insulin glargine during pregnancy, specifically addressing the issues and concerns surrounding mitogenicity, placental transfer, and maternal and fetal safety.MethodsWe performed a systematic literature search using MEDLINE and BIOSIS Previews up to March 2011. Additional studies were identified by hand-searching reference lists from original articles. Inclusion was limited to studies and abstracts in the English language.ResultsA total of 23 reports with 1001 pregnancies managed with insulin glargine contained relevant information regarding the maternal and fetal safety of its use during pregnancy. Insulin glargine does not appear to have enhanced mitogenic activity when compared with the mitogenic activity of native human insulin. The transplacental transfer of insulin glargine appears to be negligible, although it is possible that antibody-bound insulin glargine may gain access to the fetal compartment. The available data suggest that there are no identifiable, consistent adverse maternal or fetal outcomes with the use of insulin glargine during pregnancy, including during the first trimester.ConclusionsUse of insulin glargine during pregnancy should be seriously considered in uncontrolled diabetes during pregnancy and in those patients taking insulin glargine before conception, because the benefits from improved glycemic control would be expected to outweigh any, as yet, unproven risks of insulin glargine exposure.(Endocr Pract. 2011;17:448-455)     

Free fatty acid-induced hepatic insulin resistance: a potential role for protein kinase C-delta

The mechanisms of the impairment in hepatic glucose metabolism induced by free fatty acids (FFAs) and the importance of FFA oxidation in these mechanisms remain unclear. FFA-induced peripheral insulin resistance has been linked to membrane translocation of novel protein kinase C (PKC) isoforms, but the role of PKC in hepatic insulin resistance has not been assessed. To investigate the biochemical pathways that are induced by FFA in the liver and their relation to glucose metabolism in vivo, we determined endogenous glucose production (EGP), the hepatic content of citrate (product of acetyl-CoA derived from FFA oxidation and oxaloacetate), and hepatic PKC isoform translocation after 2 and 7 h Intralipid + heparin (IH) or SAL in rats. Experiments were performed in the basal state and during hyperinsulinemic clamps (insulin infusion rate, 5 mU. kg(-1). min(-1)). IH increased EGP in the basal state (P < 0.001) and during hyperinsulinemia (P < 0.001) at 2 and 7 h. Also, 7-h infusion of IH induced resistance to the suppressive effect of insulin on EGP (P < 0.05). Glycerol infusion (resulting in plasma glycerol levels similar to IH infusion) did not have any effect on EGP. IH increased hepatic citrate content by twofold, independent of the insulin levels and the duration of IH infusion. IH induced hepatic PKC-delta translocation from the cytosolic to membrane fraction in all groups. PKC-delta translocation was greater at 7 compared with 2 h (P < 0.05). In conclusion, 1) increased FFA oxidation may contribute to the FFA-induced increase in EGP in the basal state and during hyperinsulinemia but is not associated with FFA-induced hepatic insulin resistance, and 2) the progressive insulin resistance induced by FFA in the liver is associated with a progressive increase in hepatic PKC-delta translocation.     

Insulin-stimulated Glut 4 translocation in human skeletal muscle: a quantitative confocal microscopical assessment

Summary Insulin stimulation of glucose transport in skeletal muscle is considered to involve translocation of the skeletal muscle_adipose tissue glucose transporter isoform, Glut 4, from cytosolic vesicles to the cell surface. The current study was undertaken to investigate Glut 4 translocation in skeletal muscle of healthy volunteers during euglycaemic insulin infusion. Previous quantitative studies of glucose transport have depended on differential centrifugation methods, which demand large biopsy samples. In this study we have developed and applied a quantitative method using confocal laser microscopy, well suited to the small needle biopsies that are typically available clinically. Percutaneous biopsy of vastus lateralis skeletal muscle was performed during basal and euglycaemic insulin-stimulated conditions, and Glut 4 translocation was assessed using immunohistochemical labelling and confocal laser microscopy imaging in 14 healthy lean subjects. At physiological hyperinsulinaemia (536 _ 16 pm), mean systemic glucose utilization was 9.27 _ 0.78 mg_kg-min, indicative of normal insulin sensitivity. The presence of Glut 4 at the sarcolemma increased significantly (p· 0.01), with a ratio of insulin-stimulated to basal sarcolemmal Glut 4 of 1.85 _ 0.33, indicative of insulin-stimulated Glut 4 translocation. The area of Glut 4-labelled sites also increased significantly (p· 0.01) in response to insulin infusion; this ratio was 1.56 _ 0.13. Thus, at physiological hyperinsulinaemia, the amount of Glut 4 at the cell surface of skeletal muscle in healthy, lean individuals increases approximately twofold over basal conditions, and this process can be measured using immunohistochemical labelling imaged by confocal laser scanning microscopy. This revised version was published online in November 2006 with corrections to the Cover Date.     

Iodothyronine 5''-deiodinase activity and thyroid hormone content in brown adipose tissue during the breeding cycle of the rat.

Brown adipose tissue iodothyronine 5'-deiodinase activity is significantly lower in 17-day pregnant rats compared with virgin controls and remains low during late pregnancy and lactation. It fully recovers with abrupt weaning, but only partially with spontaneous weaning. Even though this profile of changes is remarkably in step with the known pattern of modifications in brown fat thermogenesis during the breeding cycle, the lowered iodothyronine 5'-deiodinase activity appearing between days 15 and 17 of pregnancy occurs earlier than the reduction in brown adipose tissue thermogenesis. Brown fat 3,3',5-tri-iodothyronine content is also reduced in late pregnant, early and mid-lactating rats, most probably as a consequence of the lowered 5'-deiodination of thyroxine in situ. Acute insulin treatment increases brown fat iodothyronine 5'-deiodinase activity in virgin animals as well as in late-pregnant and lactating rats, despite the lowered basal enzyme activity levels in the latter groups. Thus an impaired response to insulin in brown fat does not appear to be a factor leading to the lowered iodothyronine 5'-deiodinase activity during late pregnancy and lactation.     

Effect of treatment with different doses of 17-beta-estradiol on the insulin receptor

The mechanism for the development of insulin resistance in normal pregnancy is complex and is associated with serum levels of sex hormones. However, the influence of these hormones on the early steps of insulin action has not been extensively studied, although the potentially beneficial effect of estradiol on glucose homeostasis has been reported. In this paper, we attempted to determine the effect of 17-beta-estradiol on the insulin receptor of ovariectomized rats treated with different doses of hormones. Our results showed a tissue-dependent response to estradiol. We found that low doses of estradiol increased the amount of insulin receptors in liver and muscle on days 6 and 11 of treatment but not in adipose tissue, and after 16 days only the muscle responsed in this way. On the other hand, high doses of estradiol significantly decreased the amount of insulin receptors, at least in muscle and adipose tissue. We believe that the low concentrations of 17-beta-estradiol (similar to early pregnancy) could be responsible for the increase in insulin sensitivity by increasing the amount of insulin receptors in peripheral tissues. When the hormone levels were high (similar to late pregnancy) the amount of insulin receptors decreased in peripheral tissues, and insulin sensitivity is diminished just as in late pregnancy. The specific molecular mechanism for this action is as yet unknown.