The effect of peripheral administration of peptides on food intake, glucose and insulin in wolf pups

In the studies reported here we demonstrate that bombesin decreases food intake in wolf (Canis lupus) pups without altering glucose or insulin levels. A high dose of cholecystokinin-octapeptide (CCK, 5 μg/kg) decreased food intake. CCK produced a transient increase in insulin, without altering glucose. Glucagon (0.5 mg/kg) failed to decrease food intake despite producing a marked hyperglycemia and hyperinsulinemia. Calcitonin was ineffective at decreasing food intake, although it did decrease the time spent feeding. These studies suggest a potential role for peripheral peptides in food regulation in the wolf.     

Role of insulin and glucagon in oxytocin effects on glucose metabolism.

Oxytocin (OT) infusion in normal dogs increases plasma insulin and glucagon levels and increases rates of glucose production and uptake. The purpose of this study was to determine whether the effects of OT on glucose metabolism were direct or indirect. The studies were carried out in normal, unanesthetized dogs in which OT infusion was superimposed on infusion of either somatostatin, which suppresses insulin and glucagon secretion, or clonidine, which suppresses insulin secretion only. Infusion of 0.2 microgram/kg/min of somatostatin suppressed basal levels of plasma insulin and glucagon and inhibited the OT-induced rise of these hormones by about 60-80% of that seen with OT alone. The rates of glucose production and uptake by tissues, measured with [6-3H] glucose, were significantly lower than those seen with OT alone, and the rise in glucose clearance was completely inhibited. Clonidine (30 micrograms/kg, sc), given along with an insulin infusion to replace basal levels of insulin, completely prevented the OT-induced rise in plasma insulin and markedly reduced the glucose uptake seen with OT alone, but did not reduce the usual increase in plasma glucose and glucagon levels or glucose production. To determine whether the OT-induced rise in plasma insulin was in response to the concomitant increase in plasma glucose, similar plasma glucose levels were established in normal dogs by a continuous infusion of glucose and an OT infusion was superimposed. OT did not raise plasma glucose levels further, but plasma insulin levels were increased, indicating that OT can stimulate insulin secretion independently of the plasma glucose changes. Studies by others have shown that the addition of OT to pancreatic islets or intact pancreas can stimulate insulin and glucagon secretion, indicating a direct effect. Our studies agree with that and suggest that in vivo, OT raises plasma insulin levels, at least in part, through a direct action on the pancreas. These studies also show that OT increases glucose production by increasing glucagon secretion and, in addition, a direct effect of OT on glucose production is likely. The OT-induced increase in glucose uptake is mediated largely by increased insulin secretion.     

Physiological aspects of free and immobilized Aspergillus niger cultures producing citric acid under various glucose concentrations

Similarities and differences between cultures of free and immobilized Aspergillus niger were identified under various glucose concentrations. Growth and citric acid production rates were compared, and the macro-morphology and fine structure of the mycelia examined to determine which parameters were significant in the production of citric acid. With free cultures the diameter of pellets was inversely related to glucose concentration, while biomass levels were lower for immobilized cultures than the equivalent free cultures. Rates of citric acid production were higher with immobilized mycelium, especially at higher glucose levels. The morphology that characterized high citric acid productivity was that of swollen hyphal tips which were seen at concentrations over 100 kg/m³ glucose in both free and immobilized mycelium. Although there is a characteristic morphology associated with high productivity it does not account for the difference observed between free and immobilized mycelia. The increased glucose uptake and productivity was not due to an increased surface area either, since the immobilized system was slightly lower in total surface area than the equivalent free cultures. The major difference was in the mean diffusion path in the two systems.     

Insulin secretion and glucose uptake in hypomagnesemic sheep fed a low magnesium, high potassium diet

Hyperglycemic and euglycemic clamp experiments were conducted to evaluate insulin secretion and glucose uptake in the hypomagnesemic sheep fed a low magnesium (Mg), high potassium (K) diet. Five mature sheep were fed a semipurified diet containing 0.24% Mg and 0.56% K (control diet) and five were fed 0.04% Mg and 3.78% K (low Mg/high K diet) for at least 2 weeks. In the hyperglycemic clamp experiment, plasma glucose concentrations were raised and maintained at a hyperglycemic steady-state (approximately 130 mg/100 ml) by variable rates of glucose infusion during the experimental period (120 minutes). The insulin response in the sheep fed the low Mg/high K diet (31.0 microU/ml) were significantly (P < 0.01) lower than those (111.7 microU/ml) of the sheep fed the control diet. In the euglycemic clamp experiment, insulin was infused at rates of 5, 10, 15, or 20 mU/kg/min, each followed by variable rates of glucose infusion to maintain a euglycemic steady-state (basal fasting levels). Hypomagnesemic sheep fed the low Mg/high K diet had significantly (P < 0.01) lower mean glucose disposal (3.72 mg/kg/min) across the insulin infusion rates compared with those of the sheep fed the control diet (5.37 mg/kg/min). These results suggest that glucose-induced insulin secretion and insulin-induced glucose uptake would be depressed in hypomagnesemic sheep and are caused by feeding the low Mg/high K diet.     

Interactions between oxytocin, glucagon and glucose in normal and streptozotocin-induced diabetic rats

Oxytocin has been suggested to have glucoregulatory functions in rats, man and other mammals. The hyperglycemic actions of oxytocin are believed to be mediated indirectly through changes in pancreatic function. The present study examined the interaction between glucose and oxytocin in normal and streptozotocin (STZ)-induced diabetic rats, under basal conditions and after injections of oxytocin. Plasma glucose and endogenous oxytocin levels were significantly correlated in cannulated lactating rats (r = 0.44, P less than 0.01). To test the hypothesis that oxytocin was acting to elevate plasma glucose, adult male rats were injected with 10 micrograms/kg oxytocin and killed 60 min later. Oxytocin increased plasma glucose from 6.1 +/- 0.1 to 6.8 +/- 0.2 mM (P less than 0.05), and glucagon from 179 +/- 12 to 259 +/- 32 pg/ml (P less than 0.01, n = 18). There was no significant effect of oxytocin on plasma insulin, although the levels were increased by 30%. A lower dose (1 microgram/kg) of oxytocin had no significant effect on plasma glucose or glucagon. To eliminate putative local inhibitory effects of insulin on glucagon secretion, male rats were made diabetic by i.p. injection of 100 mg/kg STZ, which increased glucose to greater than 18 mM and glucagon to 249 +/- 25 pg/ml (P less than 0.05). In these rats, 10 micrograms/kg oxytocin failed to further increase plasma glucose, but caused a much greater increase in glucagon (to 828 +/- 248 pg/ml) and also increased plasma ACTH. A specific oxytocin analog, Thr4,Gly7-oxytocin, mimicked the effect of oxytocin on glucagon secretion in diabetic rats. The lower dose of oxytocin also increased glucagon levels (to 1300 +/- 250 pg/ml), but the effect was not significant. A 3 h i.v. infusion of 1 nmol/kg per h oxytocin in conscious male rats significantly increased glucagon levels by 30 min in normal and STZ-rats; levels returned to baseline by 30 min after stopping the infusion. Plasma glucose increased in the normal, but not STZ-rats. The relative magnitude of the increase in glucagon was identical for normal and diabetic rats, but the absolute levels of glucagon during the infusion were twice as high in the diabetics. To test whether hypoglycemia could elevate plasma levels of oxytocin, male rats were injected i.p. with insulin and killed from 15-180 min later. Plasma glucose levels dropped to less than 2.5 mM by 15 min. Oxytocin levels increased by 150-200% at 30 min; however, the effect was not statistically significant.(ABSTRACT TRUNCATED AT 400 WORDS)     

Impact of continuous and pulsatile insulin delivery on net hepatic glucose uptake

The pancreas releases insulin in a pulsatile manner; however, studies assessing the liver's response to insulin have used constant infusion rates. Our aims were to determine whether the secretion pattern of insulin [continuous (CON) vs. pulsatile] in the presence of hyperglycemia 1) influences net hepatic glucose uptake (NHGU) and 2) entrains NHGU. Chronically catheterized conscious dogs fasted for 42 h received infusions including peripheral somatostatin, portal insulin (0.25 mU x kg(-1) x min(-1)), peripheral glucagon (0.9 ng x kg(-1) x min(-1)), and peripheral glucose at a rate double the glucose load to the liver. After the basal period, insulin was infused for 210 min at either four times the basal rate (1 mU x kg(-1) x min(-1)) or an identical amount in pulses of 1 and 4 min duration, followed by intervals of 11 and 8 min (CON, 1/11, and 4/8, respectively) in which insulin was not infused. A variable peripheral glucose infusion containing [3H]glucose clamped glucose levels at twice the basal level ( approximately 200 mg/dl) throughout each study. Hepatic metabolism was assessed by combining tracer and arteriovenous difference techniques. Arterial plasma insulin (microU/ml) either increased from basal levels of 6 +/- 1 to a constant level of 22 +/- 4 in CON or oscillated from 5 +/- 1 to 416 +/- 79 and from 6 +/- 1 to 123 +/- 43 in 1/11 and 4/8, respectively. NHGU (-0.8 +/- 0.3, 0.4 +/- 0.2, and -0.9 +/- 0.4 mg x kg(-1) x min(-1)) and net hepatic fractional extraction of glucose (0.04 +/- 0.01, 0.04 +/- 0.01, and 0.05 +/- 0.01 mg x kg(-1) x min(-1)) were similar during the experimental period. Spectral analysis was performed to assess whether a correlation existed between the insulin secretion pattern and NHGU. NHGU was not augmented by pulsatile insulin delivery, and there is no evidence of entrainment in hepatic glucose metabolism. Thus the loss of insulin pulsatility per se likely has little or no impact on the effectiveness of insulin in regulating liver glucose uptake.     

Determination of synthesis, recycling and body mass of glucose in rats and rabbits in vivo with 3H- and 14C-labelled glucose

1. Glucose labelled with (3)H in position 2 and uniformly with (14)C was administered simultaneously to rabbits and rats either as a single injection or by continuous infusion. Plasma glucose specific radioactivity and the yield of (3)H in the plasma water were monitored. 2. The rates of synthesis, recycling of carbon and total body mass of glucose were calculated, without assuming a multicompartmental model and without fitting data by exponential expressions. 3. The rate of synthesis of glucose in starved-overnight rabbits was 4mg/min per kg (range 3-4.5mg/min per kg) and 25-35% of the glucose carbon was recycled. The mass of total body glucose in starved rabbits was 290mg/kg (range 220-390mg/kg). About one-third of the total body glucose equilibrates nearly instantaneously with plasma glucose. 4. In rats starved overnight, glucose synthesis was about 10mg/min per kg and recycling of carbon ranged from 30-40%. Total body mass (per kg body weight) is similar to that in rabbits. 5. The activity in plasma water after injection of [2-(3)H]glucose was determined. The initial rate of (3)H(2)O formation is rapid, indicating that the major site of glucose catabolism is in the rapidly mixing pool. The curve of total body glucose radioactivity was obtained from the (3)H(2)O yield, and total mass of glucose was calculated. This agrees with that obtained from the (3)H specific-radioactivity curve.     

Purification and site-specific immobilization of genetically engineered glucose dehydrogenase on thiopropyl-sepharose

The gene encoding glucose dehydrogenase (EC 1.1.1.47) from Bacillus subtilis was inserted in a plasmid 1.0 kb downstream from a lac promoter, resulting in a 70-fold higher production of the enzyme when expressed in Escherichia coli. A glucose dehydrogenase mutant containing a cysteine residue at position 44 could also be expressed at the same high level. This single cysteine residue was used as an ‘affinity tag’ to simplify the purification procedure as well as for site-specific immobilization of glucose dehydrogenase on Thiopropyl-Sepharose. This enzyme was purified to homogeneity with a final recovery of 65% and a specific activity of 240 U/mg. The oriented immobilization resulted in increased thermal stability.     

Renal hemodynamic response to galanin: importance of elevated plasma glucose

Although recent data point to a possible indirect role for galanin in modulating renal blood flow (RBF) and fluid homeostasis in experimental animals, there have been no systematic studies exploring the possible direct effects of the peptide on the mammalian kidney. We ascertained the RBF, glomerular filtration rate (GFR) and plasma glucose responses to direct intrarenal infusion of three progressively increasing doses of synthetic galanin in anesthetized dogs. A 50 ng/kg per min dose (n = 6) failed to affect RBF, GFR or arterial plasma glucose (APG). Yet, a 100 ng/kg per min dose elevated RBF and GFR by 13 and 14%, respectively, while concomitantly increasing APG by 38%. At 200 ng/kg per min, galanin elevated RBF and GFR by 32 and 33%, respectively, while elevating APG by 57%. Intrarenal infusion of glucose (12.5 mg/kg per min; n = 6), reproducing the percentage rise in glucose (62%) elicited by the highest dose of galanin, elevated RBF and GFR by 20 and 23%, respectively. These data indicate that the elevated plasma glucose level, stimulated by galanin infusion, may account for about 63 and 70% of the RBF and GFR responses, respectively, elicited by galanin infusion at the 200 ng dose. The factors mediating the remaining renal hyperemia and hyperfiltration await resolution.     

Comparison of the effect of semisynthetic human insulin and porcine insulin on glucose kinetics, plasma free fatty acid and amino acid levels in man

The effect of semisynthetic human insulin on hepatic glucose output, peripheral glucose clearance, plasma levels of C-Peptide, free fatty acids and amino acids was compared with purified pork insulin using the glucose clamp technique. 8 normal overnight-fasted subjects received intravenous infusions of either human or porcine insulin at 20 mU/m2.min(-1) during 120 min achieving plasma insulin levels of approximately equal to 50 mU/l. Plasma glucose levels were maintained at euglycaemia by variable rates of glucose infusion. Hepatic glucose production measured by continuous infusion of 3-(3) H-glucose was similarly suppressed by both insulins to rates near zero. The metabolic clearance rate of glucose increased during infusion of human insulin by 120%, C-peptide levels decreased by 41% and plasma FFA concentrations fell by 74%. The respective changes during infusion of pork insulin were similar, 118%, 48% and 72%. Both insulins decreased the plasma levels of branched-chain amino acids, tyrosine, phenylalanine, methionine, serine and histidine similarly. Thus, the results demonstrate that semisynthetic human and porcine insulin are aequipotent with respect to suppression of hepatic glucose output, stimulation of glucose clearance, inhibition of insulin secretion, lipolysis and proteolysis.     

Whole body insulin responsiveness is higher in beef steers selected for increased muscling

The aim of this experiment was to evaluate the impact of selection for greater muscling on whole body insulin responsiveness in cattle, as reflected by greater uptake of glucose in response to constant insulin infusion and greater glucose disappearance following an intravenous glucose tolerance test. This study used 18-month-old steers from an Angus herd visually assessed and selected for divergence in muscling over 15 years. Eleven high-muscled (High), 10 low-muscled (Low) and 3 high-muscled steers, which were heterozygous for a myostatin polymorphism (HighHet), were infused with insulin using the hyperinsulineamic-euglyceamic clamp technique. Insulin was constantly infused at two levels, 0.6 μIU/kg per min and 6.0 μIU/kg per min. Glucose was concurrently infused to maintain euglyceamia and the steady state glucose infusion rate (SSGIR) indicated insulin responsiveness. An intravenous glucose tolerance test was also administered at 200 mg/kg live weight. Sixteen blood samples were collected from each animal between -30 and 130 min relative to the administration of intravenous glucose, plasma glucose and insulin concentration was determined in order to analyse insulin secretion and glucose disappearance. Insulin-like growth factor-1 (IGF-1) was also measured in basal plasma samples. At the low insulin infusion rate of 0.6 mU/kg per min, the SSGIR was 73% higher for the High muscling genotype animals when compared to the Low (P<0.05). At the high insulin infusion rate of 6.0 mU/kg per min, these differences were proportionately less with the High and the HighHet genotypes having only 27% and 34% higher SSGIR (P<0.05) than the Low-muscled genotype. The High-muscled cattle also had 30% higher plasma IGF-1 concentrations compared to the Low-muscled cattle. There was no effect of muscling genotype on basal insulin or basal glucose concentrations, glucose disappearance or insulin secretion following an intravenous glucose tolerance test. The increased whole body insulin responsiveness in combination with higher IGF-1 concentrations in the High-muscled steers is likely to initiate a greater level of protein synthesis, which may partially explain the increased muscle accretion in these animals.     

Dose-related involvement of CCK in bombesin-induced pancreatic growth.

We examined the role of CCK in bombesin-induced pancreatic growth in rats using the CCK receptor antagonist L-364,718. Rats (155 +/- 1 g, 8-10 per group) received subcutaneous injections every 8 h for 5 days with bombesin (0.6, 1.7 and 5 nmol/kg) or bombesin in combination with L-364,718 (1 mg/kg). After 5 days the pancreas was removed and pancreatic weight, protein content, DNA, amylase and chymotrypsin contents were determined. Bombesin produced a significant increase (48-475%) of pancreatic weight, tissue contents of protein, DNA, amylase and chymotrypsinogen (F = 82, P less than 0.001). When a large dose of bombesin (5 nmol/kg) was combined with L-364,718 a significant inhibition (up to 70%) of all tissue parameters was observed (P less than 0.001). L-364,718 did not affect the growth response to a small dose of bombesin (0.6 nmol/kg). Plasma CCK levels 15 min after a single injection of bombesin (0.6, 1.7 and 5 nmol/kg) were significantly increased in response to the 5 nmol/kg dose (2.0 +/- 0.7 to 3.4 +/- 0.8 pM, F = 6.9, P less than 0.01). No increases of CCK plasma levels were found in response to the 0.6 and 1.7 nmol/kg doses of bombesin, corresponding to the lack of effects of L-364,718 on growth parameters at these doses. Measuring the time-course of CCK plasma levels after a single injection of 5 nmol/kg bombesin revealed an increase from basal values of 1.4 +/- 0.3 pM to maximal levels of 3.5 +/- 0.5 pM after 15 min (F = 7.1, P less than 0.001). Values returned to basal after 60 min. These results suggest that low doses of bombesin act directly at the acinar cell or through release of non-CCK growth factors whereas high doses of bombesin act in part through CCK release.     

Effects of medium-chain triglyceride feeding or glucose infusion on glucose kinetics in the newborn rat

Hypoglycaemia which develops in starved newborn rats (0.15 +/- 0.01 mg/ml) is reversed by feeding medium-chain triglycerides (0.66 +/- 0.05 mg/ml). Despite similar glycaemia (0.71 +/- 0.07 mg/ml) starved newborns infused with glucose (10.7 mg/min/kg) show a 30% higher glucose turnover rate than medium-chain triglyceride fed animals (14.1 +/- 0.6 versus 10.6 +/- 0.3 mg/min/kg, p less than 0.01). For a comparable [6-3H]glucose turnover rate (10.5 +/- 0.3 mg/min/kg), glucose-infused (5.25 mg/min/kg) newborns have a 30% lower glycaemia (0.50 +/- 0.03 mg/ml, p less than 0.01) than medium-chain triglyceride-fed newborns. Thus, medium chain triglyceride feeding leads to a 30% decreased capacity of the tissues to utilize glucose. For a similar glucose turnover rate, medium-chain triglyceride-fed newborns have a higher blood lactate concentration than glucose-infused newborns (0.26 +/- 0.03 versus 0.15 +/- 0.02 mg/ml). However, in medium-chain triglyceride-fed newborns, the increase of blood lactate is not only due to the Cori cycle, as glucose recycling is less increased than glucose production. Thus medium-chain triglyceride increases the release of gluconeogenic precursors which are not derived from blood glucose. In presence of a glucose infusion (15.25 mg/min/kg) producing hyperglycaemia (1.35 +/- 0.05 mg/ml), endogenous glucose production is suppressed by only 37%. If 3-mercaptopicolinate, an inhibitor or gluconeogenesis, is given concomitantly, hyperglycaemia is prevented (0.72 +/- 0.08 mg/ml) and endogenous glucose production is suppressed. Glucose infusion in the hypoglycaemic newborn rat might thus lead to a precarious glucose homeostasis.     

Immunoreactive cholecystokinin in human and rat plasma: correlation of pancreatic secretion in response to CCK

Immunoreactive cholecystokinin (CCK) levels in human and rat plasma are described using a radioimmunoassay specific for the biologically active sulfated end of CCK. This assay detected significant changes in plasma cholecystokinin levels during intrajejunal administration of amino acids and intravenous infusions of CCK-8 which were followed by increased pancreatic secretion. In humans, the concentration (pg/ml) of plasma cholecystokinin increased from 10.8 to 18.9 following intrajejunal amino acid instillation and from 15.4 to 31.1 during CCK infusion, while pancreatic trypsin secretion increased more than 15 fold. Ingestion of a test meal also caused a rapid and significant elevation (P less than 0.05) in both plasma CCK (14.5-21.7 pg/ml) and gastrin (50-160 pg/ml) levels. In the rat, an injection of 46 ng of CCK-8 produced a 300% increase in immunoreactive plasma CCK levels (2 min) and caused peak pancreatic protein secretion within 5 min; 4 fold lower doses (11.5 ng) elevated plasma CCK by 38% and pancreatic protein secretion to a small but significant extent. The ability of this assay to detect various forms of sulfated CCK in human plasma was also determined. Following gel chromatography on Sephadex G-50, at least three different immunoreactive peaks were found in plasma from fasted subjects and after intrajejunal amino acid stimulation. While the lower molecular weight CCK peptides (CCK-8 and CCK-12) were detected in plasma from both fasted and stimulated subjects, the larger form (CCK-33) was only present in measurable concentrations after amino acid infusion. The simultaneous measurement of increased plasma CCK levels and pancreatic secretion and the changes in the distribution of CCK peptides following amino acid infusion provides strong support that this assay detects physiologically relevant changes in biologically active CCK peptides.     

Rapid translocation of hepatic glucokinase in response to intraduodenal glucose infusion and changes in plasma glucose and insulin in conscious rats

The rate of liver glucokinase (GK) translocation from the nucleus to the cytoplasm in response to intraduodenal glucose infusion and the effect of physiological rises of plasma glucose and/or insulin on GK translocation were examined in 6-h-fasted conscious rats. Intraduodenal glucose infusion (28 mg.kg(-1).min(-1) after a priming dose at 500 mg/kg) elevated blood glucose levels (mg/dl) in the artery and portal vein from 90 +/- 3 and 87 +/- 3 to 154 +/- 4 and 185 +/- 4, respectively, at 10 min. At 120 min, the levels had decreased to 133 +/- 6 and 156 +/- 5, respectively. Plasma insulin levels (ng/ml) in the artery and the portal vein rose from 0.7 +/- 0.1 and 1.8 +/- 0.3 to 11.8 +/- 1.5 and 20.2 +/- 2.0 at 10 min, respectively, and 12.4 +/- 3.1 and 18.0 +/- 4.8 at 30 min, respectively. GK was rapidly exported from the nucleus as determined by measuring the ratio of the nuclear to the cytoplasmic immunofluorescence (N/C) of GK (2.9 +/- 0.3 at 0 min to 1.7 +/- 0.2 at 10 min, 1.5 +/- 0.1 at 20 min, 1.3 +/- 0.1 at 30 min, and 1.3 +/- 0.1 at 120 min). When plasma glucose (arterial; mg/dl) and insulin (arterial; ng/ml) levels were clamped for 30 min at 93 +/- 7 and 0.7 +/- 0.1, 81 +/- 5 and 8.9 +/- 1.3, 175 +/- 5 and 0.7 +/- 0.1, or 162 +/- 5 and 9.2 +/- 1.5, the N/C of GK was 3.0 +/- 0.5, 1.8 +/- 0.1, 1.5 +/- 0.1, and 1.2 +/- 0.1, respectively. The N/C of GK regulatory protein (GKRP) did not change in response to the intraduodenal glucose infusion or the rise in plasma glucose and/or insulin levels. The results suggest that GK but not GKRP translocates rapidly in a manner that corresponds with changes in the hepatic glucose balance in response to glucose ingestion in vivo. Additionally, the translocation of GK is induced by the postprandial rise in plasma glucose and insulin.     

Role of calcium in the bombesin-induced intestinal CCK release in rats

In the isolated vascularly perfused rat duodenojejunum, vascular infusion of bombesin (100 nM) provoked an early, transient (6 min) release of CCK (500% of basal), followed by a sustained response (400% of basal). The calcium chelator EGTA (2 mM) reduced the early peak and abolished the second phase of CCK release. A similar variation was evoked by verapamil (10 μM), whereas diltiazem (100 μM), nifedipine (50 μM), and ω-conotoxin (100 nM) had no significant effect. It is concluded that bombesin-induced CCK release from rat intestine is dependent on the availability of extracellular calcium and on the activation of calcium channels sensitive to blockers of the phenylalkylamine family.     

Reciprocal changes of plasma glucose and ketone bodies in fasted and acutely diabetic rats after CNS stimulation

To assess the effect of chemical stimulation of the central nervous system (CNS) on ketogenesis, we injected neostigmine (5 x 10(-8)mol) into the third cerebral ventricle in normal rats fasted for 48 h and fed rats with diabetes induced by streptozotocin (STZ, 80 mg/kg). The hepatic venous plasma levels of ketone bodies (3-hydroxybutyrate and acetoacetate), free fatty acids (FFA), and glucose were measured for 120 min after the injection of neostigmine under pentobarbital anesthesia. In the normal rats, plasma glucose levels were significantly increased but neither ketone bodies nor FFA were affected by CNS stimulation with neostigmine. In contrast the plasma levels of ketone bodies and FFA were significantly increased in STZ-diabetic rats, while glucose levels remained unchanged. The intravenous infusion of somatostatin (1.0 microgram/kg/min) suppressed the increase in plasma ketone bodies following CNS stimulation in STZ-diabetic rats. These findings suggest that CNS stimulation with neostigmine may accelerate ketogenesis by promoting the lipolysis, which may be induced by glucagon, in fed diabetic rats but not in normal fasted rats.     

Differential effect of saturated and polyunsaturated fatty acids on hepatic glucose metabolism in humans

Prolonged infusions of lipid and heparin that achieve high physiological free fatty acid (FFA) concentrations inhibit hepatic (and peripheral) insulin sensitivity in humans. These infusions are composed largely of polyunsaturated fatty acids (PUFA; linoleic and linolenic). It is not known whether fatty acid composition per se affects hepatic glucose metabolism in humans. To address this issue, we examined the impact of enteral infusions of either palm oil (48% palmitic, 35% oleic, and 8% linoleic acids) or safflower oil (6% palmitic, 12% oleic, 74% linoleic acids) in 14 obese nondiabetic subjects. (2)H(2)O was administered to determine the contribution of gluconeogenesis to endogenous glucose production (EGP), and a primed continuous infusion of [6,6-(2)H]glucose was administered to assess glucose appearance. As a result of the lipid infusions, plasma FFA concentrations increased significantly in both the palm oil (507.5 +/- 47.4 to 939.3 +/- 61.3 micromol/l, P < 0.01) and safflower oil (588.2.0 +/- 43.0 to 857.8 +/- 68.7 micromol/l, P < 0.01) groups after 4 h. EGP was similar at baseline (12.4 +/- 1.8 vs. 11.2 +/- 1.0 micromol x kg FFM(-1) x min(-1)). During a somatostatin-insulin clamp, the glucose infusion rate was significantly lower (AUC glucose infusion rate 195.8 +/- 50.7 vs. 377.8 +/- 38.0 micromol/kg FFM, P < 0.01), and rates of EGP were significantly higher (10.7 +/- 1.4 vs. 6.5 +/- 1.5 micromol x kg FFM(-1) x min(-1), P < 0.01) after palm oil compared with safflower oil, respectively. Baseline rates of gluconeogenesis and glycogenolysis were also similar. However, after lipid infusion, rates of glycogenolysis were suppressed by safflower oil but not by palm oil. Thus these studies demonstrate, for the first time in humans, a differential effect of saturated fatty acids and PUFA on hepatic glucose metabolism.     

Differences in the infectivity of Babesia incubated in plasma and serum and the role of glucose in prolonging viability

Babesia rodhaini was less infective to mice after incubation in rat serum than in rat plasma. This was explained by lower levels of glucose in serum than in plasma. Both serum and plasma were found to become metabolically depleted of glucose following prolonged contact with clotted and unclotted blood cells, respectively. When glucose concentrations in depleted samples were restored to those in freshly separated samples, infectivities of parasites were similar. This was shown for both B. rodhaini and B. argentina. Products of blood cell metabolism, produced when separation of plasma or serum was delayed for 24 h, were not shown to have any detrimental effects on the parasites. Average glucose values for plasma from rats and cattle were 153 mg/100 ml and 63 mg/100 ml, respectively, whereas serum and plasma remaining in contact with blood cells contained as little as 2 mg glucose/100 ml. Lactate values were correspondingly low in plasma and high in serum. Fibrinogen and platelets, factors involved in clotting, did not affect infectivity of B. rodhaini or B. argentina. The relevance of these findings to living babesial vaccines in which plasma- and serum-based diluents may be used is discussed.     

Indomethacin does not affect endogenous glucose production in type 2 diabetes mellitus.

In healthy subjects, basal endogenous glucose production is partly regulated by paracrine intrahepatic factors. It is currently unknown whether paracrine intrahepatic factors also influence the increased basal endogenous glucose production in patients with type 2 diabetes mellitus. Administration of indomethacin to patients with type 2 diabetes mellitus stimulates endogenous glucose production and inhibits insulin secretion. Our aim was to evaluate whether this stimulatory effect on glucose production is solely attributable to inhibition of insulin secretion. In order to do this, we administered indomethacin to 5 patients with type 2 diabetes during continuous infusion of somatostatin to block endogenous insulin and glucagon secretion and infusion of basal concentrations of insulin and glucagon in a placebo-controlled study. Endogenous glucose production was measured 3 hours after the start of the somatostatin, insulin and glucagon infusion, for 4 hours after administration of placebo/indomethacin, by primed, continuous infusion of [6,6-(2)H(2)] glucose. At the time of administration of placebo or indomethacin, there were no significant differences in plasma glucose concentrations and endogenous glucose production rates between the two experiments (16.4 +/- 2.09 mmol/l vs. 16.6 +/- 1.34 mmol/l and 17.7 +/- 1.05 micromol/kg/min and 17.0 +/- 1.06 micromol/kg/min), control vs. indomethacin). Plasma glucose concentration did not change significantly in the four hours after indomethacin or placebo administration. Endogenous glucose production in both experiments was similar after both placebo and indomethacin. Mean plasma C-peptide concentrations were all below the detection limit of the assay, reflecting adequate suppression of endogenous insulin secretion by somatostatin. There were no differences in plasma concentrations of insulin (76 +/- 5 vs. 74 +/- 4 pmol/l) and glucagon (69 +/- 8 vs. 71 +/- 6 ng/l) between the studies with levels remaining unchanged in both experiments. Plasma concentrations of cortisol, epinephrine, and norepinephrine were similar in the two studies and did not change significantly. We conclude that indomethacin stimulates endogenous glucose production in patients with type 2 diabetes mellitus by inhibition of insulin secretion.