Circulating metabolite utilization by periuterine adipose tissue in situ in the pregnant rat

To study the use of glucose for lipid synthesis by the periuterine adipose tissue in situ, 14C-glucose was infused through the left uterine artery of anesthetized, fed pregnant and virgin control rats. A greater amount of 14C-lipid always appeared in the adipose tissue from the left uterine horn than in the tissue from the right uterine horn, indicating direct utilization of the infused 14C-glucose by the tissue. Glucose utilization for both glycerol and fatty acid synthesis increased from day 0 (virgin rats) to day 20 of gestation and then decreased dramatically on day 21. In virgin and 12-day pregnant rats, glucose was incorporated into either lipidic moiety at similar rates, whereas in late pregnant rats glucose utilization for glyceride glycerol synthesis was four to five times greater than for fatty acids. The utilization of circulating fatty acids and the lipoprotein triglyceride-derived fatty acids was studied by infusing 14C-palmitate or 14C-triolein-labeled very-low-density lipoprotein (VLDL) through the left uterine artery in both virgin and 20-day pregnant rats. Incorporation of fatty acids from either one of these plasma sources was significantly higher in the pregnant than in virgin rats. This high amount of fatty acid acquisition did not account for the very active glyceride glycerol synthesis observed in pregnant rats and can only be explained by the intracellular reesterification of some lipolytic fatty acids. The results suggest a highly accelerated triacylglycerol/fatty acid substrate cycle in adipose tissue during late pregnancy, which would allow active esterification (contributing to fat accumulation) and responsive lipolysis (permitting rapid fat mobilization) by the mother.     

Streptozotocin-induced diabetes decreases mammary gland lipoprotein lipase activity and messenger ribonucleic acid in pregnant and nonpregnant rats

Diabetes mellitus is associated with a reduction of lipoprotein lipase (LPL) activity in adipose tissue and development of hypertriglyceridemia. To determine how a condition of severe insulin deficiency affects mammary gland LPL activity and mRNA expression during late pregnancy, streptozotocin (STZ) treated (40 mg/kg) and non-treated (control) virgin and 20 day pregnant rats were studied. In control rats, both LPL activity and mRNA were higher in pregnant than in virgin rats. When compared to control rats, STZ-treated rats, either pregnant or virgin, showed decreased LPL activity and mRNA content. Furthermore, mammary gland LPL activity was linearly correlated with mRNA content, and either variable was linearly correlated with plasma insulin levels. Thus, insulin deficiency impairs the expression of LPL in mammary glands, revealing the role of insulin as a modulator of the enzyme at the mRNA expression level.     

Changes in dietary fatty acids modify the decreased lipolytic beta3-adrenergic response to hyperinsulinemia in adipocytes from pregnant and nonpregnant rats

The effect of dietary olive oil and fish oil on the lipolytic dose-response of the beta3-adrenergic agonists, epinephrine, isoproterenol, BRL-37344, and CGP-12177, in adipocytes was studied in pregnant and virgin rats either untreated or under hyperinsulinemic-euglycemic conditions. Rats were fed a semisynthetic diet containing 5% of either olive oil or fish oil and studied at day 20 of treatment and/or gestation. Plasma glucose was lower and plasma insulin, triglycerides, and free fatty acids (FFAs) were higher in pregnant versus virgin rats, and the insulin sensitivity index was lower in the former. Lumbar adipose tissue phospholipid fatty acids showed a significantly higher monounsaturated fatty acid and a lower (n - 3) fatty acid content in rats fed the olive oil diet versus the fish oil diet. The lipolytic dose-response curve of either adrenergic agent was always lower in adipocytes from untreated pregnant rats versus virgin rats, and whereas the hyperinsulinemic-euglycemic clamp decreased these responses in adipocytes from virgin rats fed the olive oil diet only, adipocytes from pregnant rats always showed a decreased dose-response lipolytic curve. Thus, the lipolytic responsiveness of beta3-adrenoceptor (beta3-AR) agonists by adipocytes is impaired in cells from rats made hyperinsulinemic chronically by pregnancy or acutely by the hyperinsulinemic-euglycemic clamp, but such response to the acute condition disappears when the adipocyte phospholipid composition is modified by changes in dietary fatty acids.     

In vivo insulin resistance during pregnancy in the rat

Summary The glucose disappearance rate measured after IV glucose injection (1 g/kg body wt) remained unchanged between 12 and 21 day of gestation in the rat. In contrast, insulin secretion in response to IV glucose was markedly increased on day 19 and 21 of pregnancy, suggesting resistance to endogenous insulin. Glucose kinetics (glucose production, utilization and clearance) in response to various doses of IV insulin have been studied in anaesthetised postabsorbtive 19 day pregnant and virgin rats using 6-³H glucose. With the supramaximal dose of insulin (4 U/kg body wt) no differences in glucose kinetics were found between pregnant and virgin rats. In contrast, with the two lower doses of insulin (0.15 and 0.05 U/kg body wt) glucose production was inhibited by 36±3% and 13±2% (Mean±SEM) respectively in virgin rats, but was not decreased in pregnant rats. When the effect of insulin on glucose clearance was expressed as % of the maximal effect obtained with 4 U/kg body weight, the rise in glucose clearance in response to the two lower doses of insulin (0.15 and 0.05 U/kg body wt) was lower in pregnant (57.5±6 and 27.4±4%) than in virgin rats (73.3±6 and 42.2±7%). These results suggest that a decreased sensitivity to insulin appears in late pregnancy in the rat and could involve both liver and skeletal muscle.     

Appearance of circulating and tissue 14C-lipids after oral 14C-tripalmitate administration in the late pregnant rat

Studies were performed to determine whether and/or how dietary lipids participate in maternal hypertriglyceridemia during late gestation in the rat. After oral administration of glycerol-tri(1-14C)-palmitate, total radioactivity in plasma increased more rapidly in 20-day pregnant rats than in either 19-day pregnant rats or virgin controls. At the peak of plasma radioactivity, four hours after the tracer was administered, most of the plasma label corresponded to 14C-lipids in triglyceride-rich lipoproteins (d less than 1.006), and when expressed per micromol of triglyceride, values were higher in pregnant than in virgin rats. The difference was less after 24 hours, although at this time the level of 14C-lipids in d less than 1.006 lipoproteins was still higher in 20-day pregnant rats than in virgins. Tissue 14C-lipids, as expressed per gram of fresh weight, were similar in pregnant and virgin rats, but the values in mammary glands were much higher in the former group. Estimated recovery of administered radioactivity four hours after tracer in total white adipose tissue, mammary glands, and plasma lipids was higher in pregnant than in virgin rats. No difference was found between 20-day pregnant and virgin rats either in the label retained in the gastrointestinal tract or in that exhaled as 14C-CO2 during the first four hours following oral administration of 14C-tripalmitate. These findings plus the known maternal hyperphagia, indicate that in the rat at late pregnancy triglyceride intestinal absorption is unchanged or even enhanced and that dietary lipids actively contribute to both maternal hypertriglyceridemia and lipid uptake by the mammary gland.     

Relative effects of pregnancy and corticosterone administration on skeletal muscle metabolism in the rat

The effects of pregnancy and corticosterone treatment on skeletal muscle metabolism were compared using a noncyclically perfused rat hindlimb preparation. Animal groups studied included 3-week-pregnant animals, rats injected with corticosterone (7.5 mg/100 g BW . day) for 3 days, and age-matched control rats. All were fasted 24 h before perfusion. In baseline perfusions devoid of insulin, no differences were observed among the groups with respect to muscle glucose uptake and the release of lactate, pyruvate, and glycerol. Baseline alanine and phenylalanine release were significantly increased in corticosterone-treated rats compared to values observed in control and pregnant animals. In perfusions with 100 or 500 microU/ml insulin, glucose uptake was increased 5-fold above baseline uptake in the control group. At 100 microU/ml insulin concentrations, glucose uptake in pregnant and corticosterone-treated rats achieved only 50% of the increase seen in control experiments. With 500 microU/ml insulin, glucose uptake was decreased 20% in pregnant animals and 40% in rats receiving corticosterone relative to control values. Alanine release was significantly reduced below baseline after the administration of 500 microU/ml insulin in control rats. In these rats, phenylalanine release, an index of net protein degradation, also was reduced with both 100 and 500 microU/ml insulin. Similar insulin concentrations did not suppress the efflux of either amino acid below baseline in pregnant or corticosterone-treated groups. Corticosterone administration to nonpregnant rats appears to duplicate changes in skeletal muscle metabolism that occur during late rat pregnancy. Insulin resistance in both states is manifested by a decrease in insulin-stimulated glucose uptake and an inability of insulin to suppress net muscle proteolysis. Since plasma free glucocorticoid concentrations are increased in late human as well as rat gestation, these steroids may have an important role in the development of insulin resistance at skeletal muscle sites in this state.     

Differential metabolic responses to tumor necrosis factor with increase in age.

Previous studies have shown varied responses to the effects of tumor necrosis factor (TNF) on glucose and lipid metabolism. To elucidate possible causes for this variation, the present study compared sequential changes in plasma glucose, lactic acid, triglyceride (TG), free fatty acids (FFA), and plasma insulin levels in 1.5- and 16-month-old, normal, fed, male rats, 1 to 6 hours after different doses of intravenous (IV) TNF. In addition, assessment was made of TNF injected intraperitoneally (IP) in precannulated and intact young (1.5 months) rats and of the dose-response (0.25 to 50 micrograms/100 g rat) and the sensitivity to insulin in intact rats. Finally, the metabolic responses and changes in serum insulin and corticosterone concentration after IP TNF were compared in 1.5-, 5-, and 16-month-old rats. Data show that metabolic responses vary with increase in age and experimental conditions. Dose-dependent decreases in plasma glucose (1.4 to 3.9 mumol/mL) and elevations in lactic acid (0.8 to 3.0 mumol/mL) were greater in 1.5- versus 16-month-old rats, were delayed in cannulated rats, and were preceded by hyperglycemia following larger IV doses. Plasma TG levels were elevated after TNF in all groups except precannulated rats, and also showed differences with age. In young rats, the elevation in TG peaked 2 hours after IP injection with return to baseline and was preceded by an elevation in FFA levels. In older rats, which were hypertriglyceridemic at base line, the elevation in TG by TNF occurred by suppressing the decrease in TG of controls, was not accompanied by an increase in FFA levels, was sustained for 5 hours, and was of greater magnitude than in young rats. Significant changes in plasma insulin did not occur in young and older rats after IV TNF. However, young rats had a significant decrease (P less than .02) in plasma insulin and an elevation in corticosterone levels after IP TNF, whereas older rats exhibited an increase in plasma insulin (P less than .02) and a comparable elevation in plasma corticosterone. Young rats also showed an increase in plasma insulin following IP TNF when hypoglycemia was prevented by the infusion of glucose. However, when insulin levels were held comparable (2.4 ng/mL), glucose uptake was enhanced (P less than .05) compared with controls. These findings indicate that mobilization of energy substrates occurs during the initial exposure to TNF, which is altered by the nutritional state of the rats and the dose and route of administration.(ABSTRACT TRUNCATED AT 400 WORDS)     

Glucose tolerance tests and "in vivo" response to intravenous insulin in the unanaesthesized late pregnant rat and their consequences to the fetus

In the late pregnant rat, blood glucose levels were lower and plasma RIA-insulin levels were slightly higher than in virgin animals. Oral and intravenous glucose tolerance tests produced parallel changes in blood glucose in both groups whereas plasma RIA-insulin increased more in the pregnant animals. Blood glucose levels after either low (0.1-1 IU/kg) or high (10 IU/Kg) doses of intravenous insulin decreased more slowly and less in pregnant than in virgin rats. Fetal blood glucose levels were not affected by maternal insulin treatment. Results show that in the unanaesthesized late pregnant rat both insulin sensitivity and responsiveness decreased and it is proposed that this insulin resistance may represent a mechanism to delay disposal of ingested nutrients by maternal tissues, ensuring their availability to the fetus.     

Hyperglycaemia induced by glucose infusion in the unrestrained pregnant rat during the last three days of gestation: Metabolic and hormonal changes in the mother and the fetuses

Summary Continuous glucose infusion was used to induce mild hyperglycaemia in unrestrained pregnant rats during the last three days of pregnancy. Control pregnant rats were infused with distilled water. Fetuses were studied after normal or prolonged pregnancy. Fetuses from glucose-infused rats, compared with controls, showed higher plasma glucose levels, increased plasma insulin and lower plasma glucagon concentrations. Pregnancy prolonged until day 23.5 resulted in a rise in the glucagon/insulin ratio from 6.5 to 67 in fetuses from control rats and from 1.3 to 13 in fetuses from glucose-infused rats. Concurrently in fetuses from control rats, liver phosphoenolpyruvate carboxykinase activity increased markedly and liver glycogen stores decreased sharply. In fetuses from glucose-infused rats, liver phosphoenolpyruvate carboxykinase activity rose and glycogen content decreased, but to a lesser extent. These results show that both the A and B cells of the rat fetal pancreas are sensitive to chronic glucose stimulation.     

The set point for maternal glucose homeostasis is lowered during late pregnancy in the rat: the role of the islet beta-cell and liver

Summary The aim of this study was to determine the effects of late pregnancy on the ability of insulin to suppress maternal hepatic glucose production in the rat. Unlike in most previous studies, suppression of hepatic glucose production was measured at levels of glycaemia above the relatively hypoglycaemic basal pregnant level. Glucose kinetics were measured using steady-state tracer methodology in chronically catheterised, conscious virgin control and pregnant rats, firstly, during basal and low-dose hyperinsulinaemic euglycaemic clamp conditions and secondly, during a three-step glucose infusion protocol (glucose infusion rates of 0, 60 and 150 μmol · kg⁻¹· min⁻¹). During the clamps, plasma glucose levels were not different (6.1 ± 0.4 vs 6.5 ± 0.3 mmol/l, pregnant vs virgin; N. S.), but plasma insulin levels were higher in the pregnant rats (242 ± 30 vs 154 ± 18 pmol/l, pregnant vs virgin; p < 0.05) most probably due to stimulated endogenous insulin release in this group. Hepatic glucose production was suppressed from basal levels by 41 % in virgin and 90 % in pregnant rats. During the glucose infusion studies, at matched insulin levels (147 ± 10 vs 152 ± 14 pmol/l), but at plasma glucose levels which were much lower in the pregnant rats (5.5 ± 0.2 vs 8.4 ± 0.6 mmol/l, pregnant vs virgin; p < 0.0001), hepatic glucose production was shown to be suppressed by a similar degree in both groups (41 ± 5 vs 51 ± 5 % from basal, pregnant vs virgin; N. S.). Both the plasma insulin and percentage suppression of hepatic glucose production dose responses to plasma glucose were markedly shifted to the left indicating that the plasma glucose set point is lowered in pregnancy. In conclusion, suppression of hepatic glucose production by insulin is not impaired and the set point for plasma glucose homeostasis is lowered during late pregnancy in the rat. [Diabetologia (1996) 39: 785–792] Received: 2 October 1995 and in final revised form: 1 February 1996     

Free fatty acids increase hepatic glycogen content in obese males

Obesity is associated with increased hepatic glycogen content. In vivo and in vitro data suggest that plasma free fatty acids (FFA) may cause this increase. In this study we investigated the effect of physiological plasma FFA levels on hepatic glycogen metabolism by studying intrahepatic glucose pathways in lean and obese subjects. Six lean and 6 obese males were studied twice during a 16- to 22-hour fast, once with and once without acipimox, an inhibitor of lipolysis. Intrahepatic glucose fluxes were measured by infusion of [2-(13C1)]glycerol, [1-(2H1)]galactose, and [U-(13C6)]glucose. Acetaminophen was administered as a glucuronate probe. In both lean and obese control studies, plasma FFA levels increased progressively, whereas acipimox completely suppressed plasma FFA levels for the whole study period. In lean males glycogenolysis did not change in the acipimox study, but decreased in the control study (P < .01). In lean males, neither glycogen synthesis, glycogen synthesis retained as glycogen, nor glycogen balance differed between control and acipimox studies. In obese males glycogenolysis did not change in the acipimox study, but decreased in the control study (P < .01). Glycogen synthesis did not change in either study. Glycogen synthesis retained as glycogen did not change in acipimox study, but increased in the control study (P = .03). Glycogen balance did not change in the acipimox study, but increased in the control study (P < .01). This study demonstrates that in obese males physiological levels of FFA contribute to the retention of hepatic glycogen during short-term fasting by inhibiting breakdown of glycogen and increasing glycogen synthesis retained as glycogen, whereas in lean males this effect was absent due to unaltered glycogen synthesis retained as glycogen.     

Stimulation of insulin secretion in man by oral glycerol administration.

The effects of an orally administered glycerol load (1 g/Kg body weight) on blood glucose, plasma FFA, and plasma insulin levels have been determined in eight normal fasting or glucose loaded (1 g/Kg body weight) volunteers. Blood glucose levels were not affected by glycerol loading while glicemia followed the same pattern of a glucose tolerance test in the group treated with glucose plus glycerol. Plasma FFA were significantly lowered only 90 min after glycerol loading while they had markedly and persistently decreased by glycerol plus glucose per os. Finally, though glicemia did not change, insulinemia was markedly increased by glycereol, 90 min after loading; moreover, plasma IRI was significantly higher in the group treated with glycerol plus glucose than in the group treated with glucose alone. These data suggest that the release of insulin may be stimulated by a very small increment of blood glucose, which derives from glycerol.     

Different diabetogenic response to moderate doses of streptozotocin in pregnant rats, and its long-term consequences in the offspring

Diabetes during pregnancy results in congenital malformations and long-term postnatal diseases. Experimental models are still needed to investigate the mechanism responsible for these alterations. Thus, by the administration of different doses of streptozotocin (STZ) (0, 25, 30, or 35 mg/kg body weight, intravenous) at the onset of pregnancy in rats, the present study sought an appropriate animal model for this pathology. At day 6 of pregnancy, plasma glucose was progressively higher with an increasing STZ dose, and in rats receiving the 35-mg dose, 2 subgroups were detected: some animals had plasma glucose levels above controls but below 200 mg/dL (mildly diabetic, MD), whereas others had levels above 400 mg/dL (severely diabetic, SD). At day 20 of pregnancy, the MD rats had normal glycemia, but after an oral glucose load (2 g/kg body weight), plasma glucose increased more and insulin increased less than in controls. The SD rats maintained their hyperglycemia and had a greatly impaired oral glucose tolerance. At day 20, fetuses of SD dams were fewer, weighed less, and had enhanced plasma glucose and triglycerides and decreased insulin, whereas those from MD dams did not differ from controls. At birth, newborns from MD dams had higher body weight, plasma insulin, and liver triglycerides as well as total body lipid concentrations than controls, and on day 21, remained macrosomic and showed higher plasma glucose and liver triglyceride concentrations. At 70 days of age, offspring of MD dams had impaired oral glucose tolerance but normal plasma insulin change in the case of females, whereas plasma insulin increased less in males. These alterations were manifest more in those offspring from dams that had >50% macrosomic newborns than in those from dams that had <50% macrosomic newborns. In conclusion, whereas our MD rats mimic the changes taking place in gestational diabetic women and show the long-term risk of macrosomia, the SD rats are more similar to uncontrolled diabetics. Thus these two rat models, obtained with moderate amounts of STZ, could be used to study the pathophysiological consequences of these different diabetic conditions.     

Effect of feeding a high-fat diet during pregnancy on glucose metabolism in the rat

To alter glucose homeostasis in a period of great glucose demand, pregnant rats were submitted to a high-fat diet and compared to virgin rats. In virgin rats, blood glucose, ketone bodies, plasma insulin, and free fatty acids were not affected by the diet consumed. Glucose turnover measured in the postabsorptive period was slightly decreased in virgin rats fed a high-fat diet compared to rats fed a standard diet. Assuming that the glucose turnover rate is representative for the 24-hour average endogenous glucose production, in rats fed a standard diet the daily carbohydrate intake (9.2 +/- 0.7 g/d) exceeded the glucose turnover rate (4 +/- 0.2 g/d) and could meet the glucose requirement. In rats fed a high-fat diet the carbohydrate intake (2.7 +/- 0.2 g/d) was lower than the glucose turnover rate (3.8 +/- 0.2 g/d), which demonstrated the need for an active endogenous glucose production. Blood glucose, ketone bodies, plasma insulin, and free fatty acid concentrations followed the same patterns during pregnancy in rats fed a standard diet compared to rats fed a high-fat diet. The glucose turnover rate in the postabsorptive period was no more decreased by the high-fat diet in pregnant rats compared to virgin rats despite the greater glucose demand. In late pregnancy the glucose turnover rate was increased up to 70%.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of acute inhibition of lipolysis on operation of the glucose-fatty acid cycle in hepatic cirrhosis.

Hepatic cirrhosis is frequently associated with glucose intolerance and insulin resistance, but the mechanisms underlying the insulin insensitivity are unknown. Plasma concentrations of nonesterified fatty acids (NEFA) are typically elevated in cirrhosis, and the glucose-fatty acid cycle provides a mechanism by which fatty acids may play a role in regulating glucose metabolism. We have therefore investigated the effect of acute inhibition of lipolysis, using the nicotinic acid analogue, acipimox, in 10 male patients with cirrhosis. All subjects were studied in the postabsorptive state after a 10- to 12-hour fast and were given either acipimox 250 mg or a placebo orally 2 hours before a 75-g oral glucose tolerance test (OGTT) and an infusion of insulin (50 mU/kg/h) and glucose (6 mg/kg/min) (insulin sensitivity tests [IST]). The drug was taken in a double-blind crossover design for each test. During the 2 hours following acipimox, there were rapid decreases in plasma NEFA, glycerol, and 3-hydroxybutyrate, confirming inhibition of lipolysis, while there were significant decreases in glucose, insulin, and C-peptide (P less than .001) compared with patients receiving the placebo. Acipimox blunted the increase in glucose after oral glucose loading and decreased incremental glucose concentration (from 579 +/- 76 to 445 +/- 65 mmol/min/L, P less than .02) and incremental insulin concentration (from 13.4 +/- 2.5 to 9.0 +/- 1.4 U/min/L, P = .056) in the OGTT. Improvements in classification of glucose tolerance were seen in five subjects. During the IST, significant reductions occurred in steady-state blood glucose (to 8.8 +/- 1 mmol/L, P less than .02) and C-peptide (to 3.0 +/- 0.5 nmol/L, P less than .05).(ABSTRACT TRUNCATED AT 250 WORDS)     

The nicotinic acid analogue acipimox increases plasma leptin and decreases free fatty acids in type 2 diabetic patients

The effect of 3 days of intensive treatment with acipimox, an antilipolytic nicotinic acid derivative, on plasma leptin levels was studied in eight patients with Type 2 diabetes mellitus in a double-blind, placebo-controlled, cross-over study. Acipimox reduced plasma free fatty acids (FFA) markedly and lowered plasma triglycerides, glucose and insulin. Plasma leptin levels were elevated in all eight patients during 3 days of acipimox treatment (mean increase+/-s.e.: 2.38+/-0.57ng/ml, P<0.005) and the 24h mean effect of acipimox on leptin levels increased during the experimental period (P<0.03). The effect on plasma insulin and glucose resembled a mirror image of the effect on plasma leptin during 3 days of treatment. The suggestion that leptin mediates insulin resistance and may be involved in the development of the diabetic syndrome cannot be supported by the present results. It has been reported that FFA stimulates leptin secretion. Surprisingly, despite a markedly reduced FFA level, leptin concentration increased in the present study. We suggest that a primary acipimox effect is to increase leptin secretion, and that this prevails over the reduced FFA stimulus.     

Sustained reduction in plasma free fatty acid concentration improves insulin action without altering plasma adipocytokine levels in subjects with strong family history of type 2 diabetes

To investigate the effect of a sustained (7-d) decrease in plasma free fatty acid (FFA) concentration in individuals genetically predisposed to develop type 2 diabetes mellitus (T2DM), we studied the effect of acipimox, a potent inhibitor of lipolysis, on insulin action and adipocytokine concentrations in eight normal glucose-tolerant subjects (aged 40 +/- 4 yr, body mass index 26.5 +/- 0.8 kg/m(2)) with at least two first-degree relatives with T2DM. Subjects received an oral glucose tolerance test (OGTT) and 120 min euglycemic insulin clamp (80 mU/m(2).min) with 3-[(3)H] glucose to quantitate rates of insulin-mediated whole-body glucose disposal (Rd) and endogenous (primarily hepatic) glucose production (EGP) before and after acipimox, 250 mg every 6 h for 7 d. Acipimox significantly reduced fasting plasma FFA (515 +/- 64 to 285 +/- 58 microm, P < 0.05) and mean plasma FFA during the OGTT (263 +/- 32 to 151 +/- 25 microm, P < 0.05); insulin-mediated suppression of plasma FFA concentration during the insulin clamp also was enhanced (162 +/- 18 to 120 +/- 15 microm, P < 0.10). Following acipimox, fasting plasma glucose (5.1 +/- 0.1 vs. 5.2 +/- 0.1 mm) did not change, whereas mean plasma glucose during the OGTT decreased (7.6 +/- 0.5 to 6.9 +/- 0.5 mm, P < 0.01) without change in mean plasma insulin concentration (402 +/- 90 to 444 +/- 102 pmol/liter). After acipimox Rd increased from 5.6 +/- 0.5 to 6.8 +/- 0.5 mg/kg.min (P < 0.01) due to an increase in insulin-stimulated nonoxidative glucose disposal (2.5 +/- 0.4 to 3.5 +/- 0.4 mg/kg.min, P < 0.05). The increment in Rd correlated closely with the decrement in fasting plasma FFA concentration (r = -0.80, P < 0.02). Basal EGP did not change after acipimox (1.9 +/- 0.1 vs. 2.0 +/- 0.1 mg/kg.min), but insulin-mediated suppression of EGP improved (0.22 +/- 0.09 to 0.01 +/- 0.01 mg/kg.min, P < 0.05). EGP during the insulin clamp correlated positively with the fasting plasma FFA concentration (r = 0.49, P = 0.06) and the mean plasma FFA concentration during the insulin clamp (r = 0.52, P < 0.05). Plasma adiponectin (7.1 +/- 1.0 to 7.2 +/- 1.1 microg/ml), resistin (4.0 +/- 0.3 to 3.8 +/- 0.3 ng/ml), IL-6 (1.4 +/- 0.3 to 1.6 +/- 0.4 pg/ml), and TNFalpha (2.3 +/- 0.3 to 2.4 +/- 0.3 pg/ml) did not change after acipimox treatment.We concluded that sustained reduction in plasma FFA concentration in subjects with a strong family history of T2DM increases peripheral (muscle) and hepatic insulin sensitivity without increasing adiponectin levels or altering the secretion of other adipocytokines by the adipocyte. These results suggest that lipotoxicity already is well established in individuals who are genetically predisposed to develop T2DM and that drugs that cause a sustained reduction in the elevated plasma FFA concentration may represent an effective modality for the prevention of T2DM in high-risk, genetically predisposed, normal glucose-tolerant individuals despite the lack of an effect on adipocytokine concentrations.     

The effect of long-term pharmacological antilipolysis on substrate metabolism in growth hormone (GH)-substituted GH-deficient adults

The lipolytic properties of GH are essential for the acute effects on glucose metabolism and insulin sensitivity, whereas its more long-term impact on substrate metabolism is uncertain. The aim of the study was to evaluate the influence of pharmacological antilipolysis on substrate metabolism during constant and continued GH exposure. Seven adult GH-deficient (GHD) patients were studied twice in a double-blind randomized order: 1) after 4 wk of acipimox treatment (250 mg, orally, three times daily) and 2) after 4 wk of placebo treatment. Daily GH replacement was continued throughout both study periods. At the end of each period glucose and lipid oxidation rates were assessed by indirect calorimetry, and the protein oxidation rate was estimated by urinary excretion of urea. Endogenous glucose production and whole body protein metabolism were assessed by isotope dilution techniques using tritiated glucose and stable phenylalanine and tyrosine isotopes, respectively. GH and IGF-I levels were not different between periods, whereas FFA and glycerol levels were distinctly suppressed after 4 wk of pharmacological antilipolysis [FFA, 256 +/- 63 (acipimox) vs. 596 +/- 69 (placebo) micromol/liter; P = 0.001]. Likewise, plasma levels of total and low density lipoprotein cholesterol as well as triglycerides were significantly reduced after acipimox. Despite this, lipid oxidation rates were identical at the end of the two treatment periods [589 +/- 106 (acipimox) vs. 626 +/- 111 (placebo) kcal/24 h; P = 0.698]. The total and oxidative rates of glucose as well as protein oxidation and urea excretion were identical at the end of the two treatment periods (P > 0.05). Phenylalanine flux, a measure of protein turnover, was increased [34.62 +/- 1.83 (acipimox) vs. 33.15 +/- 1.61 (placebo) micromol/kg.h; P = 0.049] as was phenylalanine incorporation into protein, a measure of protein synthesis [30.79 +/- 1.67 (acipimox) vs. 28.97 +/- 1.51 (placebo) micromol/kg.h; P = 0.035]. The following conclusions were reached: 1) prolonged antilipolysis by means of acipimox stimulates protein turnover without affecting net protein balance; and 2) acipimox in combination with constant GH exposure results in sustained suppression of circulating levels of FFA, glycerol, and triglycerides without a reduction in the rate of lipid oxidation. The site and origin of lipid fuels for oxidation during suppression of lipolysis remain to be determined.     

Streptozotocin-induced diabetic pregnant rats exhibit signs and symptoms mimicking preeclampsia

The number of patients with hypertension, obesity, diabetes, and hyperlipidemia is increasing. This tendency is observed in pregnant women, in whom many obstetrical and perinatal complications occur. The prevention of these abnormalities is important in reducing perinatal mortality and the risk of coronary disease. We established a pregnant rat model with diabetes and signs and symptoms mimicking preeclampsia. On day 6 of pregnancy, streptozotocin (STZ) or citrate buffer was injected into the tail vein. After STZ administration, plasma glucose was increased within 48 hours and sustained at a high level until day 20 of pregnancy, and plasma insulin was decreased. Fetuses from STZ-treated mothers were growth-restricted, and plasma glucose was 6-fold higher in fetuses of STZ-treated versus control rats. The systolic blood pressure, urinary protein, and hematocrit were increased significantly in STZ-treated rats. Total cholesterol and triglycerides were also elevated in STZ-treated rats, but plasma leptin levels were decreased. The STZ-induced diabetic pregnant rat model exhibited preeclampsia, hemoconcentration, hyperlipidemia, hypoleptinemia, and intrauterine growth restriction. This model closely mimics the features of human pregnancy complicated by diabetes and is useful for the basic study of the pathophysiology of pregnancy with diabetes.     

Uptake of alpha-tocopherol by the mammary gland but not by white adipose tissue is dependent on lipoprotein lipase activity around parturition and during lactation in the rat

This study was undertaken to test the potential role of changes in lipoprotein lipase (LPL) activity in the mammary gland and adipose tissue around parturition and lactation on the uptake of alpha-tocopherol in the rat. Plasma levels of alpha-tocopherol and triglycerides were higher in 20-day pregnant rats than in virgin rats, whereas its concentration was higher in the mammary gland of the former, and no differences were detected in adipose tissue between the groups. After an oral alpha-tocopherol and triglyceride load, both appeared in plasma faster in pregnant rats than in virgin rats, the change being even faster for alpha-tocopherol than for triglycerides. After 24 hours, both alpha-tocopherol and triglycerides in d < 1.006 lipoproteins were higher in pregnant rats than in virgin rats, LPL activity was higher in the mammary gland, and lower in adipose tissue in the former, whereas alpha-tocopherol concentration also appeared higher in the mammary gland of pregnant rats, and no differences were detected between the groups in adipose tissue. At day 13 of lactation, an oral load of alpha-tocopherol and triglycerides caused a higher increase of plasma alpha-tocopherol levels than triglycerides, and this effect decreased when rats had their litter removed 48 hours before analysis. In these litter-removed rats, the appearance of alpha-tocopherol and triglycerides in plasma was higher in d < 1.006 lipoproteins than in lactating rats. Also, both LPL activity and alpha-tocopherol concentration in the mammary gland plus milk was lower in litter-removed rats than in the lactating rats, whereas LPL in adipose tissue was higher in the former, although no difference in alpha-tocopherol was found. Thus, data are consistent with the role of LPL activity in the mammary gland modulating the uptake of alpha-tocopherol during pregnancy and lactation, although this is not true in adipose tissue.