Glucose Entry Rate Research Articles

GLUCOSE AND ALANINE METABOLISM IN CHRONICALLY COLD-EXPOSED SHEEP

Glucose and alanine metabolic interrelationships (measured with 3H-glucose and 14C-alanine) were examined in closely shorn wethers subjected to thermoneutral (TN) temperatures or chronic cold exposure (CE, < 21 d). Three treatments (n = 5–6 per treatment) were used: (1) fed to maintain weight at 18–20 °C (TN-Low); (2) fed to maintain weight at 0–4 °C (1.5 × TN-Low intake, CE-Hi); and (3) fed at CE-Hi intake at 18–20 °C (TN-Hi) to distinguish effects of the higher feed intake in the CE-Hi sheep from the cold per se. Plasma glucose pool size increased (P < 0.1) in CE-Hi sheep from 1.81 (TN-Low) and 1.83 (TN-Hi) to 2.40 mmol kg−0.75. Plasma glucose entry rates increased (P < 0.001) from 0.91 (TN-Low) to 1.29 (TN-Hi) to 1.78 (CE-Hi) mmol h−1 kg−0.75. Plasma alanine entry rates showed a tendency (P = 0.19) to increase in the CE-Hi sheep. Percentage alanine converted to glucose increased (P < 0.1) from 14.2% (TN-Low) and 13.4% (TN-Hi) to 21.5% (CE-Hi). These results indicate that increased glucose metabolism in cold-exposed sheep is a chronic adaptation. The data also suggest that the rate of alanine conversion to glucose increases during chronic cold exposure. Key words: Alanine, glucose, chronic cold exposure, sheep

Lupins and energy-yielding nutrients in ewes. 1. Glucose and acetate biokinetics and metabolic hormones in sheep fed a supplement of lupin grain

Measurements were made of metabolism of glucose and acetate and changes in plasma hormones in sheep fed a basal ration to meet maintenance requirements for metabolizable energy (ME) or fed the same level of basal ration and given either a supplement of 750 g day-1 lupin grain (Experiment I) or intravenous glucose infusions over periods of 17 h (Experiment 2).In ewes given supplementary lupins, concentrations of volatile fatty acids (VFAs) in rumen liquor increased but molar proportions of VFAs were unchanged. Plasma concentrations of glucose, acetate and propionate increased; entry rates of glucose, acetate and CO2 increased and glucose oxidation (but not acetate oxidation) increased during supplementation with lupins. Other changes measured during lupin supplementation included increased plasma urea, a transient and marked increase in plasma insulin and a concomitant decrease in plasma growth hormone during the first three days, and an increase in plasma tri-iodothyronine (T3) with no changes in plasma thyroxine (T4).When glucose was infused intravenously at rates ranging from 0 to 46.8 mmoles h-1 (cf. 31 mmoles h-1 due to lupins) endogenous entry rate of glucose only increased at the highest infusion rate. There was a negative linear relationship between infusion rate of glucosc and plasma urea, whereas positive linear relationships were found between glucose infusion rate and both plasma insulin and T3.It was concluded that ewes on a maintenance basal diet and fed a supplement of 750 g day-1 lupin grain would rapidly switch to the anabolic mode concomitant with increases in glucose entry rate by more than 100% and acetate entry rate by more than 50%. Long-term intravenous infusion of the amount of glucose equivalent to that promoted by the lupin grain supplement would probably not suppress endogenous glucose production.

Glucose metabolism in shorn and unshorn pregnant sheep.

1. Whole-body, hind-limb and uterine tissue metabolism of glucose was studied using a combination of isotopic and arterio-venous difference techniques in shorn and unshorn pregnant sheep over the final 4 weeks of pregnancy. This was combined with the measurement of the concentrations of oxygen and carbon dioxide in arterial blood and plasma concentrations of lactate, acetate, non-esterified fatty acids, 3-hydroxybutyrate, glycerol, growth hormone (GH), insulin, glucagon, cortisol, thyroxine and 3,5,3'-triiodothyronine (T3). 2. Glucose entry rate was 28% higher in shorn ewes compared with unshorn controls, even though there was no difference in the arterial plasma concentration of glucose. This effect may have been caused by a decrease in the molar rate, insulin: glucagon (I:G), which was 40% lower in shorn ewes as a result of a significant decrease in the plasma concentration of insulin. There was no difference in the plasma concentration of cortisol or GH. 3. Blood flow across the hind-limb or uterine tissues was not significantly different between shorn and unshorn groups, neither were the net glucose uptake, glucose oxidation rate or contribution of glucose to O2 consumption across these tissues. 4. Insulin-tolerance tests performed on a separate group of shorn and unshorn ewes showed an increased sensitivity to the hypoglycaemic effects of insulin in the shorn group. 5. There was no significant difference between shorn and unshorn animals in the contribution of glucose to CO2 output or in the proportion of glucose entry rate oxidized. CO2 entry rate was 18% higher in shorn ewes compared with unshorn controls which resulted in a 26% higher estimated value for heat production. There was a 47% increase in glucose oxidation rate in shorn ewes but there was no significant difference in the proportion of total heat production which was derived from glucose. The arterial concentrations of O2 and CO2 were significantly higher in shorn ewes, which may be an indication of the higher metabolic rate in these animals. This effect may be mediated via a significant rise in plasma T3 concentration in the shorn group. 6. It is concluded that as a result of long-term cold exposure there is a significant increase in whole-body glucose entry and oxidation rates in the shorn pregnant ewe. The increase in insulin sensitivity at the same time as a decrease in plasma insulin concentration may represent a mechanism to ensure continued glucose supply to insulin-sensitive tissues while the concomitant decrease in plasma I:G stimulates hepatic gluconeogenesis.

Use of fetal streptozotocin injection to determine the role of normal levels of fetal insulin in regulating uteroplacental and umbilical glucose exchange.

The present study was performed to determine the role of the normal fetal concentration of insulin in regulating placental-fetal glucose exchange. Fetal insulin deficiency was produced by streptozotocin injection into near term fetal sheep, and the effects of this insulin deficiency on net uteroplacental glucose uptake and net umbilical glucose uptake were measured. Each fetus received two or three doses of streptozotocin, 100 mg.kg-1.dose-1, given on separate days. This dosage of streptozotocin produced a 97.6% reduction in fetal pancreatic insulin content, a fall in fetal plasma insulin concentration (21 +/- 2 to 10 +/- 1 microU.ml-1), a rise in fetal plasma glucagon concentration (57 +/- 4 to 114 +/- 19 pg.ml-1), a rise in fetal blood glucose concentration (20.4 +/- 0.9 to 33.4 +/- 4.4 mg.dl-1), and a failure of insulin secretion in response to glucose infusion. Fetal blood oxygen content and umbilical oxygen uptake were normal and did not change during the entire study. Umbilical glucose uptake was reduced by 66% (5.98 +/- 0.38 to 2.02 +/- 1.31 mg.min-1.kg-1) after the streptozotocin-induced hypoinsulinemia and hyperglycemia but was returned to the control level by an insulin infusion into the fetus that reestablished the control maternal to fetal glucose concentration gradient. Net uteroplacental glucose uptake (consumption) did not change throughout the study. Because glucose concentration and umbilical glucose uptake could be normalized by an insulin infusion, it is unlikely that direct or toxic effects of streptozotocin on fetal or placental glucose metabolism were primarily responsible for the hyperglycemia and the reduced rate of umbilical glucose uptake.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of insulin and glucose concentrations on glucose utilization in fetal sheep.

Glucose and insulin clamp experiments were performed in vivo in chronically catheterized, late-gestation fetal lambs to quantify the effects of glucose and insulin on fetal glucose metabolism. Fetal glucose uptake from the placenta via the umbilical circulation (umbilical glucose uptake) was measured by application of the Fick principle, and fetal glucose utilization rate (GUR) was measured using [U-14C]glucose tracer. Fetal plasma insulin concentrations ranged from 2 to 119 microU.ml-1 and fetal blood glucose concentrations ranged from 7.3 to 62.6 mg.dl-1. GUR varied from 2.82 to 15.12 mg/min/kg and the exogenous glucose entry rate (umbilical glucose uptake + glucose infusion) varied from 2.46 to 13.95 mg/min/kg. The mean GUR [6.53 +/- 0.28 (SEM) mg/kg/min] was not different from the mean exogenous glucose entry rate [6.29 +/- 0.30 (SEM) mg/kg/min]. Multiple linear regression analysis on a glucose-by-insulin surface demonstrated a best-fit model of fetal glucose utilization following the quadratic equation: GUR = -0.322 + [0.289 (glucose)] + [0.108 (insulin)] - [0.00319 (glucose)2] - [0.000673 (insulin)2], r = 0.883 (all terms significant at p less than 0.02). This model predicted a GURmax of 10.56 mg/min/kg at blood glucose concentration = 45.3 mg/dl and plasma insulin concentration = 80 microU/ml and Km values for blood glucose concentration and plasma insulin concentration of 20.6 mg/dl and 10 microU/ml, respectively. According to this model, the glucose and insulin effects were additive. Furthermore, change in GUR was not proportionate to change in glucose concentration, accounting for a decreasing metabolic clearance rate at higher glucose concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)

Responses to nitrogen and maize supplements by young cattle offered a low-quality pasture hay

Twenty-seven Hereford steers (227�3 kg) were offered ad libitum low-quality grass pasture hay containing 4.3 g N/kg DM. These steers were offered one of three maize supplements (nil, 570 g/day crushed maize or 680 g/day whole maize) alone or with one of two nitrogen (N) supplements (1 12 g/day urea: 250 g/day molasses, or 800 g/day pelleted protein meals). The crushed maize, whole maize and protein meal supplements were calculated to be isoenergetic on a metabolisable energy basis, and the urea and protein meal supplements were isonitrogenous.Both urea and protein meal supplements increased the intakes of hay and total digestible organic matter (DOMI), but there was a significant interaction between maize and N supplements such that maize increased hay and DOM intakes when offered alone. Unsupplemented steers ate only 1.98 kg OM of hay/day, whereas N supplemented steers ate 3.96-4.40 kg OM/day, and those supplemented with crushed and whole maize alone ate 2.45 and 2.85 kg OM/day respectively. The intakes of hay by the urea and protein meal supplemented groups were not significantly different.Both N and maize supplements had positive effects on liveweight change (P < 0.01), with N having the largest effect. Steers supplemented with protein meal gained 210 g/day more than those offered urea (P < 0.05), although DOMI was only 110 g/day more, indicating an effect of protein on the efficiency of utilisation of absorbed nutrients.N supplements increased rumen ammonia concentrations from 10�3.0 mg NH3-N/l in unsupplemented steers to 169� 19.3 and 105� 19.0 mg NH3-N/l in steers offered urea and protein meal respectively; there was a significant interaction between the form of N supplement and form of maize supplement (P < 0.05). Total volatile fatty acid concentrations in the rumen (65� 1.9 mM) did not differ significantly between supplements.Glucose entry rate was positively related to liveweight change and was increased by both the N supplements and whole maize. Glucose entry rate, adjusted for DOMI, was higher in protein meal supplemented steers than those receiving urea or no N supplement (P < 0.01), and these steers had the highest growth rate.Urea pool size, and synthesis rate in the body, were greater in steers given the urea and protein meal supplements (P < 0.05), but there were no significant differences in these measurements between urea and protein meal supplements.

Glucose kinetics in the oestrogen-treated male chicken ( Gallus domesticus), measured after administration of [6- 3H]glucose and [U- 14C]glucose in vivo

1. 1. Male chickens ( Gallus domesticus) were treated with 17β-oestradiol then injected with a mixture of [6- 3H]glucose and [U- 14C]glucose. Subsequently, blood samples were taken to determine plasma lipid levels and several parameters of glucose metabolism, including entry rate, carbon recycling, mean transit time, the total body glucose mass, the mass of the sampling pool and the rate of outflow from this pool. 2. 2. Oestrogen-treated birds exhibited typical hyperlipidaemia, with significantly elevated plasma levels of triacylglycerol and nonesterified fatty acids. 3. 3. Oestrogen administration significantly decreased the glucose entry rate, the total body glucose mass and the rate of outflow from the sampling pool.

Changes in metabolic and reproductive characteristics associated with lactation and glucose infusion in the postpartum ewe.

This study examined mechanisms whereby the metabolic environment interacts with basic reproductive function. Ewes lambing during the breeding season were fed to maintain (MAINT, n = 10) or gain (GAIN, n = 11) body weight during the last 4 mo of gestation. From d 7 to 22 postpartum, ewes were infused iv with saline (n = 10) or glucose at a rate calculated to increase normal glucose entry rate by 75% (n = 11). Blood samples were collected daily to determine plasma concentrations of nutritive metabolites and insulin and at frequent intervals on d 14 and 21 to determine serum gonadotropin concentrations. Hypothalami and pituitaries were collected on d 22 to determine hormone content and receptor concentrations. Plasma concentrations of nutritive metabolites and insulin indicated that MAINT ewes mobilized more (P less than .01) body fat and protein reserves during gestation and early lactation than ewes in the GAIN group. Glucose infusion elevated plasma concentrations of glucose (P less than .05) and insulin (P less than .07) and reduced (P less than .05) fat and protein mobilization, even though it depressed feed intake (P less than .001), compared with saline infusion. Hypothalamic gonadotropin-releasing hormone (GnRH), pituitary luteinizing hormone (LH) and follicle-stimulating hormone (FSH) content and pituitary GnRH receptor concentration were similar between treatments.(ABSTRACT TRUNCATED AT 250 WORDS)

Glucose Absorption and Hepatic Gluconeogenesis in Dairy Cows Fed Diets Varying in Forage Content

One dry and four lactating Holstein cows were prepared with chronic catheters in the mesenteric, hepatic and portal veins and used to study glucose absorption and hepatic gluconeogenesis. The dry cow was used in a preliminary assessment of the methods. In the main experiment high concentrate and high forage diets, providing equal energy intake, were delivered in hourly portions from an automatic feeder as total mixed rations. A few data were collected with the high concentrate ration fed ad libitum in early lactation. A few additional observations were made with limited feed intake by using the same cows subsequent to the main experiment. Portal and hepatic vein blood flow rates were determined by using para-aminohippuric acid. Glucose entry rates were significantly higher during ad libitum feeding of the high concentrate diet than during feeding of the two diets with restricted intake. There was no difference between high concentrate and high forage diets when fed at equal energy intakes. Net glucose appearance in portal blood was demonstrated. Data from this study and from the literature were used to develop general relationships between digestible energy intake and 1) portal vein blood flow, 2) rate of portal appearance of glucose and 3) total splanchnic glucose entry rate.

Postprandial hyperglycemia in patients with noninsulin-dependent diabetes mellitus. Role of hepatic and extrahepatic tissues.

Patients with noninsulin-dependent diabetes mellitus (NIDDM) have both preprandial and postprandial hyperglycemia. To determine the mechanism responsible for the postprandial hyperglycemia, insulin secretion, insulin action, and the pattern of carbohydrate metabolism after glucose ingestion were assessed in patients with NIDDM and in matched nondiabetic subjects using the dual isotope and forearm catheterization techniques. Prior to meal ingestion, hepatic glucose release was increased (P less than 0.001) in the diabetic patients measured using [2-3H] or [3-3H] glucose. After meal ingestion, patients with NIDDM had excessive rates of systemic glucose entry (1,316 +/- 56 vs. 1,018 +/- 65 mg/kg X 7 h, P less than 0.01), primarily owing to a failure to suppress adequately endogenous glucose release (680 +/- 50 vs. 470 +/- 32 mg/kg X 7 h, P less than 0.01) from its high preprandial level. Despite impaired suppression of endogenous glucose production during a hyperinsulinemic glucose clamp (P less than 0.001) and decreased postprandial C-peptide response (P less than 0.05) in NIDDM, percent suppression of hepatic glucose release after oral glucose was comparable in the diabetic and nondiabetic subjects (45 +/- 3 vs. 39 +/- 2%). Although new glucose formation from meal-derived three-carbon precursors (53 +/- 3 vs. 40 +/- 7 mg/kg X 7 h, P less than 0.05) was greater in the diabetic patients, it accounted for only a minor part of this excessive postprandial hepatic glucose release. Postprandial hyperglycemia was exacerbated by the lack of an appropriate increase in glucose uptake whether measured isotopically or by forearm glucose uptake. Thus as has been proposed for fasting hyperglycemia, excessive hepatic glucose release and impaired glucose uptake are involved in the pathogenesis of postprandial hyperglycemia in patients with NIDDM.

The effect of triamcinolone on glucose metabolism in ketotic sheep

SUMMARYThe withdrawal of food from Clun Forest ewes pregnant with twins produced signs of pregnancy toxaemia accompanied by a significant decrease in the concentration of glucose, a significant increase in the concentration of ketones, non-esterified fatty acids (NEFA) and 3-hydroxybutyrate in plasma and a significant decrease in total entry rate and irreversible loss of glucose. A single intramuscular injection of 0·05 or 0·2 mg/kg of triamcinolone acetonide had no significant effect on the concentration of glucose, ketones or 3-hydroxybutyrate in plasma or on the total entry, irreversible loss or recycling of glucose in ketotic or in normal pregnant sheep. The low dose had a significant effect on the concentration of NEFA in plasma. Recovery from the clinical signs was slow after either dose of steroid but appeared to be hastened by the onset of parturition which was more rapid after the higher dose.

The effects of chronic fetal hyperglycemia on substrate uptake by the ovine fetus and conceptus.

Hyperglycemia in fetal sheep has been shown to increase the fetal metabolic rate. Fetal venous glucose infusion was performed in eight late gestation, chronically catheterized fetal lambs to assess any changes in substrate uptake by the ovine uterus and conceptus. Fetal glucose infusion (11.9 +/- 0.6 mg glucose X kg-1 X min-1) caused a stable increase in fetal plasma glucose concentration approximately 3-fold above baseline. The fetal glucose entry rate increased from 6.6 +/- 0.7 to 9.3 +/- 0.6 mg X kg-1 X min-1 by day 3 of infusion (p less than 0.01) despite a net umbilical glucose excretion during the period of fetal hyperglycemia. Due to a concomitant increase in fetal oxygen consumption, no change in fetal glucose/O2 quotient was observed. A significant relationship was noted (p less than 0.02) between the fetal glucose entry rate and the rate of fetal oxygen consumption. Fetal glucose infusion caused a decrease in uterine glucose uptake as well. No changes were observed in calculated net placental glucose uptake although the relative fetal contribution increased from net placental exit to fetus to a placental uptake amounting to 20.8 +/- 5.8% of the total placental glucose uptake (p less than 0.01). Although no changes in fetal lactate concentration occurred, both maternal and fetal lactate entry rates increased, the magnitude of increase being significantly related to fetal glucose concentration. Both maternal and fetal insulin concentrations rose during the period of fetal hyperglycemia and were related to the respective increases of maternal or fetal substrate uptakes but not to fetal oxygen consumption.(ABSTRACT TRUNCATED AT 250 WORDS)

The roles of energy- or protein-rich supplements in the subtropics for young cattle consuming basal diets that are low in digestible energy and protein

SUMMARYTwenty-seven Hereford weaner steers (mean age 11 months, and live weight 142±17 kg) were used to study the effect of supplementation of an energy-rich grain (sorghum), and/or a protein meal on the live-weight change of cattle on a basal diet of low-quality grass hay over 48 days (Expt 1). The basal hay had an estimated energy value of 6·2 MJ metabolizable energy (ME)/kg dry matter (D.M.) and a nitrogen content of 6·2 g/kg D.M. Corresponding values for the sorghum supplement were 12·4 and 14·4, and for the protein meal 9·6 and 65. The daily rates of supplementation in Expt 1 were (g/head) 0 (nil), 600 (P1) or 1200 (P2) of protein meal pellets or 0 (nil), 560 (S1) or 1120 (S2) of sorghum and all combinations of P1or P2with S1or S2. The carry-over effect of such supplementation on subsequent growth was recorded in Expt 2 when the steers grazed a kikuyu grass pasture for 100 days.In Expt 1, organic-matter intake of hay (HOMI) was increased (P< 0·01) by protein but decreased (P< 0·01) by the sorghum supplements. By 48 days, P1-supplemented steers were eating 29·5% more hay than non-supplemented steers, and P2steers were eating 43·5% more hay than the non-supplemented steers. S1supplemented steers were eating 29·5% less, and S2steers 23% less hay than non-supplemented steers. Steers lost weight on the basal hay diet, and at the lower level of sorghum (S1) supplementation, but were able to maintain weight at the higher level (S2) of supplementation. In contrast, steers supplemented with protein gained weight (P< 0·01): 430 g/day on P1and 700 g/day on P2treatments. None of the steers offered combinations of P and S had live-weight changes as high as those offered only protein supplements. There was no evidence of compensatory gain by the smaller steers in Expt 2 when grazing and unsupplemented.Glucose kinetics in plasma were studied in each steer on day 35 of Expt 1 by means of a single intravenous injection of [2-3H]glucose. The quantity of glucose in the sampled pool and the total rate of glucose entry into the pool (GER) were higher (P< 0·01) in steers that were protein supplemented, with GER being related to both ME intake and to N intake per unit ME intake.Urea pool size and entry rate were also estimated on day 35 of Expt 1 using a single intravenous injection of [14C]urea. The quantity of urea in the sampled pool, and entry rate into the pool were increased significantly (P< 0·01) by protein, but reduced (P< 0·05) by sorghum, supplementation. Rumen ammonia concentrations were low in steers given the hay alone, and when supplemented with sorghum (10–15 mg N/l), but were significantly higher (70 mg N/l;P< 0·01) during protein supplementation.It was concluded that growth of cattle on the basal ration was restricted by low voluntary intakes of hay. Intake was increased substantially by protein supplementation. The consequent increase in live weight was due to a greater intake of organic matter which was accompanied by a greater synthesis of glucose and availability of amino acids in the animals.

Lactate and glucose metabolism in the resting and diving harbor seal (Phoca vitulina)

The rates of lactate and glucose production, removal, and oxidation were measured in harbor seals before and after 10 min restrained dives using radioisotope tracer techniques. The results show: 1. Net turnover rates were 24 μmol·min−1·kg−1 for lactate and 12 μmol·min−1·kg−1 for glucose at rest (Table 2). 2. Only 21% of lactate turnover and 3% of glucose turnover were oxidized. Their combined oxidation contributed less than 9% to resting energy production. 3. During 10 min dives, there was 9 fold increase in lactate production. 4. Less than 27% of the lactate produced during diving was oxidized during recovery. 5. The blood glucose concentration decreased 1 mM during diving, but increased and remained elevated for 2 h after the dive (Fig. 5 and 6). The postdive hyperglycemia resulted from a high glucose entry rate which lasted 10–15 min after the dive. A peak entry rate of 168 μmol·min−1·kg−1 was measured 30 sec after a dive. 6. In spite of the postdive hyperglycemia, glucose oxidation was only 11% higher than predive levels. 7. The predive concentration of plasma free fatty acids (FFA) was similar to other arctic carnivores (Fig. 9).

Rates of Entry and Oxidation of D(-)-3-Hydroxybutyrate and Glucose in Fed and Fasted Chickens

Rates of entry and oxidation of D(-)-3-hydroxybutyrate (DBHB) and glucose and their contribution to the total metabolic production of CO2 were studied in fed and 48-hr fasted Leghorn roosters using primed constant intravenous infusions of NaH14CO3, D(-)-3-[3-14C] -hydroxybutyrate, and D-[U-14Cl glucose. Fasting increased plasma DBHB concentrations sixfold but did not change plasma glucose levels. In both states of nutrition, rates of CO2 production were identical (P>.05). Mean fractions of the total CO2 derived from DBHB and glucose in fed and fasted chickens, respectively, were: DBHB, 1.7 and 9.9% (P<.001); glucose, 29 and 10% (P<.001). Entry rates of DBHB and glucose in fed chickens were 276 and 5936 μmoles/hr per kg (P<.001), respectively, and in starved birds were 1703 and 2204 μmoles/hr per kg (P<.001), respectively. Fasting increased the oxidation rate of DBHB from 124 to 737 μmoles/hr per kg (P<.001) and decreased the oxidation rate of glucose from 1491 to 525 μmoles/hr per kg (P<.0Ol). During fasting, glucose homeosta

EFFECT OF FASTING ON PLASMA GLUCOSE KINETICS IN DOUBLE-MUSCLED CATTLE

The effect of a 4-day fast on plasma glucose kinetics was determined with three 14-mo-old carrier bulls and three of their double-muscled (DM) half-siblings. Glucose entry rate and irreversible loss were less (P &lt; 0.05) during fasting for both animal types. Glucose pool size was greater (P &lt; 0.05) in carrier than in DM bulls. Key words: Plasma, glucose kinetics, double-muscled bulls

Glucose metabolism in vivo in fed and 48 h starved goats during pregnancy and lactation.

1. Glucose turnover (i.e. glucose entry and utilization rates) in fed and 48 h starved goats during pregnancy and lactation was determined using a continuous infusion of [U-14C)- and [3-3H]glucose. 2. Glucose synthesis and utilization increased during pregnancy and lactation in fed but not in starved goats. 3. Recycling of glucose-C was approximately 10% in fed animals and 15-20% in starved animals and was unaffected by the stage of pregnancy or lactation. 4. Plasma glucose concentrations were maintained during pregnancy and lactation in fed goats but decreased during 48 h starvation in pregnant goats. Little change was seen in the plasma concentration of lipids and their metabolites during pregnancy and lactation in fed goats, but increases were observed after 48 h starvation. 5. The control of glucose metabolism in ruminants during pregnancy and lactation is discussed.

Gluconeogenesis from glycerol by ketotic sheep pregnant with twins

The concentrations of glycerol and glucose in plasma, the entry rates of glycerol and glucose into the plasma pool and the production of glucose from glycerol were measured in four normal sheep pregnant with twins and in the same sheep after the induction of ketosis and after the oral administration of 3 ml/kg body-weight of glycerol in two doses six hours apart. After starvation there was a significant fall in the concentration of glucose and a rise in that of ketone bodies in the plasma. The rise in the concentration of glycerol was not significant. The divided oral dose of glycerol was followed by significant increases in the concentrations of glycerol and glucose and a significant fall in that of ketone bodies in plasma. After starvation, glucose and glycerol entry rates fell significantly from 42.0 +/- 3.5 to 18.1 +/- 1.4 mmol per hour and from 28.1 +/- 4.6 to 13.5 +/- 2.9 mmol per hour respectively. The amount of glucose formed from glycerol decreased from 5.4 +/- 1.2 to 3.0 +/- 0.5 mmol per hour. After a divided oral dose of glycerol, glycerol entry in the ketotic sheep rose significantly from 13.5 +/- 2.9 to 320 +/- 24.1 mmol per hour and glucose entry rate rose significantly from 18.1 +/- 1.4 to 71.5 +/- 10.1 mmol per hour. The amount of glucose produced from glycerol increased from 3.0 +/- 0.5 to 62.1 +/- 9.2 mmol per hour after the administration of glycerol. The oral dose of glycerol had no obvious effect on the clinical signs of induced ketosis.

The utilisation of glycerol by sheep

Increased but steady concentrations of glycerol and glucose in carotid, jugular and portal plasma of sheep were obtained between 2.5 and 3.5 h after the second of two oral doses of glycerol (2 and a ml/kg body weight with a 6 h interval between) and the concentration of glycerol in portal plasma was greater than in the other vessels. During the last hour of a 3.5 h continuous infusion of [14C]glycerol and [3H]glucose, ie, between 2.5 and 3.5 h after the second dose of glycerol, specific radioactivity(SRA) of glycerol and of [14C] an [3H] glucose were measured in plasma obtained from the three previously mentioned sites in dosed and undosed sheep. Although in dosed sheep the SRA of glycerol in portal plasma was lower than that in jugular plasma, the difference was such that the SRA in jugular plasma could be used to calculate entry rates and the rate of production of glucose from glycerol. Mean (+/- SE) glycerol entry rate in four fed sheep increased from 9.2 +/- 1.2 to 62.7 +/- 0.9 mg C/min after a divided oral dose of glycerol. Mean glucose entry rate increased from 29.0 +/0 3.4 to 58.3 +/- 7.6 mg C/min. The amount of glucose which was derived from glycerol increased from 5.4 +/- 1.6 to 35.5 +/- 3.7 mg C/min. This increase accounted for the increase in total glucose entry.

Glucose metabolism in feeding and postabsorptive lambs and mature sheep

1. 1. In growing sheep, fasting results in a reduction in plasma glucose concentration and in glucose pool size, irreversible loss and total entry rate estimated by isotope dilution using [U- 14C]glucose. 2. 2. Glucose space ( S, % body weight) in fed and fasted lambs decreased exponentially with body weight ( W, kg), S = 120 W −0.62), while the mean (+- SE) turnover time was 49 ± 2 min. 3. 3. During fasting the mean glucose concentration was 0.58 ± 0.03 mg/ml, irreversible loss was 23.9 ± 1.2 mg/min whereas total entry rate increased significantly with body weight. 4. 4. Total entry rate and irreversible loss of glucose were correlated with pool size, suggesting that the mass of glucose available to tissues exerts an important control over glucose metabolism in the lamb.