Rate Of Ketogenesis Research Articles

Reversal of Ketosis in Type 1 Diabetes Is Not Adversely Affected by SGLT2 Inhibitor Therapy.

We have shown that "euglycemic DKA" in patients with type 1 diabetes receiving a sodium-glucose cotransporter 2-inhibitor (SGLT2i) is due to normal increases in rates of ketogenesis but blunted increases in plasma glucose levels. In this analysis, we assessed whether rescue treatment of early ketoacidosis with insulin is altered by SGLT2i use. Participants received 0.2 U/kg of aspart insulin after two 6-h interruptions of basal insulin that increased beta-hydroxybutyrate (BHB) by 1.2 ± 0.7 mmol/L before and by 1.5 ± 0.2 mmol/L during canagliflozin treatment. BHB and free fatty acid (FFA) were monitored every 30 min for 120 min after receiving a 0.2 U/kg subcutaneous injection of aspart insulin. Ten adults (23 ± 5 years) were studied. During the 120 min after rescue therapy with insulin, the reductions in BHB and FFA were nearly identical between the pre- and during canagliflozin treatment studies, respectively (-1.27 ± 0.76 and -1.13 ± 0.69, P = 0.671 for BHB and -0.50 ± 0.35 vs. -0.41 ± 0.41, P = 0.603 for FFA). These data indicate that turning ketogenesis off, as well as on, does not appear to be affected by SGLT2i use.

Reciprocal effects of dietary sesamin on ketogenesis and triacylglycerol secretion by the rat liver.

The effects of dietary sesamin (a mixture of sesamin and episesamin, 1:1, w/w) on ketone body production and lipid secretion were studied in isolated perfused liver from rats given sesamin. Feeding sesamin at the dietary level of 0.2% from 14 to 16 d resulted in an enlargement of liver weight. Ketone body production was significantly elevated in the livers perfused with oleic acid in comparison with those perfused without an exogenous-free fatty acid, and sesamin feeding caused a stimulation of ketone body production, especially when exogenous oleic acid was provided. On the other hand, the ratio of beta-hydroxybutyrate to acetoacetate, an index of mitochondrial redox potential, tended to increase in the livers perfused with oleic acid compared with those without fatty acid, thought it was consistently lowered by dietary sesamin. The cumulative secretion of triacylglycerol, but not of cholesterol, by the livers from sesamin-fed rats was decreased markedly, especially when exogenous oleic acid was provided, suggesting an inverse relationship between the rates of ketogenesis and triacylglycerol secretion. These results suggest that dietary sesamin exerts its hypotriglyceridemic effect at least in part through an enhanced metabolism of exogenous-free fatty acid to oxidation at the expense of esterification in rat liver.

ALTERED HEPATIC METABOLISM OF FATTY ACIDS IN RATS FED A HYPOLIPIDAEMIC DRUG, FENOFIBRATE

The aim of this study was to examine the effects of dietary fenofibrate (0.05% in the diet) on ketone body production and lipid secretion in isolated perfused rat liver. Feeding with fenofibrate for 7–9 days caused an increased liver weight. Ketone body production was significantly greater in the livers perfused with oleic acid than in those perfused without fatty acid, with the elevation of the ratio of β-hydroxybutyrate:acetoacetate indicating an increased redox potential in mitochondrial compartments by exogenous fatty acid. On the other hand, fenofibrate feeding caused a further stimulation of ketone body production from both endogenous and exogenous fatty acid substrates, respectively, with a decreased ratio of β-hydroxybutyrate:acetoacetate as compared to respective control livers, indicating a decreased redox potential. Hepatic secretion of triglyceride, but not of cholesterol, was decreased markedly in the fenofibrate-fed rats, especially when oleate was provided, suggesting an inverse relationship between rates of ketogenesis and triglyceride secretion. These results suggest that the altered hepatic metabolism of long-chain fatty acids between oxidation and esterification caused by fenofibrate may thus be a factor responsible for the decreased secretion of triglyceride, hence leading to hypotriglyceridaemia in vivo.

Interrelation between mitochondrial respiration, substrate supply and redox ratio in perifused permeabilized rat hepatocytes

A one-step perifusion technique is described for studying the regulation of energy metabolism in intact hepatocytes and in mitochondria of the same cells after their permeabilization by digitonin. Cell count and activities of glutamate dehydrogenase, the latter being used as an indicator of mitochondrial integrity, were found to be nearly unchanged after permeabilization and perifusion for at least 40 min at 37°C. The residual activity of lactate dehydrogenase after permeabilization indicated that permeabilized cells were almost depleted of soluble cytosolic components. The composition of the perifusion medium was chosen so that various metabolic states could be adjusted of both intact and permeabilized hepatocytes without the need to change the perifusion medium. Oxidative phosphorylation of mitochondria within permeabilized hepatocytes remained intact throughout the perifusion as indicated by the response of respiration to the addition of ADP, carboxyatractyloside and uncoupler. The application of the perifusion technique allows us to sample indicator metabolites in the effluent medium like acetoacetate (AcAc) and 3-hydroxybutyrate (HB) for calculating the mitochondrial redox ratios and rates of ketogenesis. In the presence of octanoate and ADP, an improvement of substrate supply by glutamate and malate led to increases in the intramitochondrial HB/AcAc ratio and the respiration rate. Glutamate/malate concentrations of 1 mM resulted in maximal respiration rates, whereas concentrations of 5 mM further enhanced the HB/AcAc ratio. Mitochondria responded to increasing ATP/ADP ratios in the perifusion medium by decreased respiration rates at higher HB/AcAc ratios. By comparing respiration rates and redox ratios of mitochondria in permeabilized cells with those before permeabilization (gluconeogenic conditions of hepatocytes), it is concluded that in the intact cell oxidative phosphorylation is limited with respect to substrate supply as well as by the ATP demand.

Inhibition of β-oxidation by 3-mercaptopropionic acid produces features of Reye's syndrome in perfused rat liver

Background/Aims: The cause of Reye's syndrome has not been completely defined. The rate of ketogenesis in the liver is a key determinant of, and reciprocally related to, triglyceride secretion. In the present study, 3-mercaptopropionic acid (MPA), a known inhibitor of mitochondrial long-chain acyl coenzyme A (CoA) dehydrogenase, was used to investigate the relationship between ketone body production, triglyceride secretion, and triglyceride accumulation in perfused rat liver. Methods: Livers from fasted rats were perfused 225 minutes with or without MPA in the presence of [1-14C]oleic acid. Morphology was studied by light and electron microscopy. Results: Inhibition of fatty acid oxidation by the liver with MPA resulted in a decrease in ketone body production. Treatment with MPA caused an accumulation of small-droplet triglycerides in liver, whereas the net secretion of triglyceride ceased after an initial period of increased secretion with continued decreased ketogenesis. At the end of the perfusion period, mitochondria in the MPA group appeared to be damaged. Conclusions: The rates of both ketogenesis and triglyceride secretion by the liver appear to be the major determinants of hepatic triglyceride content. In addition, the MPA-mediated biochemical and morphological findings are quite similar to those of Reye's syndrome.

Food restriction and stimulation of monooxygenation of p-nitroanisole in perfused rat liver

This study assessed the effects of food restriction on the metabolism of model monooxygenase substrates in the perfused rat liver. Female Sprague-Dawley rats had access ad lib. to a Purina 5001 nonpurified diet (control) or were given 65% of the intake of controls for 3 weeks. Livers were perfused with oxygenated Krebs-Henseleit buffer using a non-recirculating system, and the rates of monooxygenation of p-nitroanisole and 7-ethoxycoumarin were measured. The results indicate that food restriction stimulated p-nitroanisole O-demethylation from 2.9 ± 0.2 to 4.6 ± 0.5 μmol/(g.hr) when saturating concentrations of p-nitroanisole were infused. Concomitantly, the ratio of β-hydroxybutyrate to acetoacetate (B/A) and the rates of ketogenesis (B + A) were increased significantly by food restriction. Further, p-nitroanisole (200 μmnol/L) increased hepatic malate concentration nearly 3-fold in liver extracts from food-restricted rats. However, infusion of either a low concentration of p-nitroanisole (50 μmol/L) or 7-ethoxycoumarin (200 μmol/L) did not alter these parameters. On the other hand, food restriction did not alter rates of monooxygenation in isolated microsomes supplemented with excess NADPH. Taken together, these data support the hypothesis that high concentrations of p-nitroanisole increased monooxygenation in food-restricted rats by stimulating fatty acid oxidation, which elevates the mitochondrial NADH/NAD + ratio. This, in turn, increases the availability of reducing equivalents in the form of NADPH by a malate-pyruvate exchange system, leading to increased drug metabolism.

Ketogenesis from lactate in rat liver during the perinatal period.

Lactate, which accumulates in neonatal plasma during the first hours after delivery, is used by neonatal tissues as a source of energy and carbon skeleton. In this work, lactate use by rat liver during late gestation (last 3 d) and early neonatal life (6 h postpartum) has been studied. The rate of lactate use by liver was compared with that found with oleate, inasmuch as fatty acids are the main substrates for the liver after the onset of lactation. The main fate of lactate in the liver during the perinatal period was ketone bodies, preferentially over CO2 and lipids. The rate of oxidation of lactate and its incorporation into lipids decreased during late gestation, but the rate of ketogenesis from lactate remained high during this period. After birth, the rate of lactate oxidation sharply increased, but lipogenesis decreased and ketogenesis was maintained. The rates of oleate oxidation and ketogenesis from oleate were two orders of magnitude lower than those from lactate. However, the rate of oleate incorporation into lipids was only 4-fold lower than that observed from lactate under the same circumstances. Our results suggest that lactate is a major substrate for the liver during the perinatal period because it is mainly incorporated into ketone bodies. This may target lactate carbons to different neonatal tissues.

Relationships between fatty acid synthesis and lipid secretion in the isolated perfused rat liver: Effects of hyperthyroidism, glucose and oleate

Various studies on the effects of thyroid status on hepatic fatty acid synthesis have produced conflicting results. Several variables (e.g., plasma free fatty acid and glucose concentrations) are altered simultaneously by thyroid status and can affect fatty acid synthesis. To evaluate the effects of these variables, hepatic fatty acid synthesis (lipogenesis) was studied in isolated perfused livers from normal and triiodothyronine-treated rats. Livers were perfused with media containing either 5.5 or 25 mM glucose without fatty acid, or 5.5 mM glucose and 0.7 mM oleate. Rates of lipogenesis were determined by measurement of incorporation of 3H2O into fatty acids. Lipogenesis in livers from hyperthyroid animals exceeded that of controls, when perfused with 5.5 mM glucose with or without oleate. Perfusion with 25 mM glucose increased lipogenesis in both euthyroid and hyperthyroid groups to the same level, abolishing this difference between them. Perfusion with oleate reduced rates of lipogenesis by livers from euthyroid and hyperthyroid rats to a similar extent, but stimulated secretion of radioactive fatty acid in phospholipid and free fatty acid fractions. Oleate increased ketogenesis by livers from normal and triiodothyronine-treated rats, with higher rates of ketogenesis in the triiodothyronine-treated group. When oleate was omitted, ketogenesis in the presence of 5.5 mM glucose by the hyperthyroid group was similar to that of euthyroid controls, while ketogenesis was decreased in the hyperthyroid group relative to controls when perfused with 25 mM glucose. About 30% of the radioactivity incorporated into the total fatty acid of both groups was recovered in palmitate, with the remainder in longer chain saturated and unsaturated fatty acids. In both euthyroid and hyperthyroid groups, the ratio of triacylglycerol:phospholipid fatty acid radioactivity was not only less than predicted (based on synthetic rates of PL and TG) but also was decreased in perfusions with exogenous oleate compared to perfusions without oleate. In perfusions with oleate, both groups incorporated twice as much radioactivity into phospholipid as into triacylglycerol. The data suggest the following concepts: while hepatic fatty acid synthesis and oxidation are increased simultaneously in the hyperthyroid state, de novo synthesized fatty acids seem to be poorer substrates for oxidation than are exogenous fatty acids, and are preferentially incorporated into phospholipid, while exogenous fatty acids are better substrates for oxidation and esterification to triacylglycerol. The preferential utilization of de novo synthesized fatty acid for phospholipid synthesis may be an important physiologic adaptation insuring a constant source of fatty acid for membrane synthesis.

Effect of lactation on gluconeogenesis and ketogenesis in ovine hepatocytes

1. 1. Rates of glucose synthesis from radioactive precursors and ketogenesis were determined in hepatocytes from control and lactating sheep. 2. 2. Gluconeogenesis from propionate was the same in both groups. Gluconeogenesis from lactate + pyruvate was three-fold higher in hepatocytes from lactating sheep. Palmitate stimulated gluconeogenesis from lactate + pyruvate in both groups. 3. 3. Rates of ketogenesis from palmitate but not butyrate were slightly higher in hepatocytes from lactating sheep. No other differences in the metabolism of palmitate or butyrate were seen in the two groups. Exogenous carnitine stimulated ketogenesis from palmitate. Propionate inhibited ketogenesis from palmitate and butyrate. Lactate + pyruvate also inhibited ketogenesis slightly but stimulated oxidation and esterification. 4. 4. It is concluded that the major changes in glucose and ketone production seen in the lactating ruminant are not the result of long-term changes within the hepatocyte but occur because of the changes in substrate supply to the liver and changes in intracellular concentrations of metabolites.

Altered hepatic metabolism of free fatty acid in rats fed a threonine-imbalanced diet.

The effects of a threonine-imbalanced diet (8% casein supplemented with 0.3% methionine, TI) on the ketone body production and the secretion rate of lipids were examined in the isolated perfused rat liver. Feeding a TI diet compared to an 8% casein (C) diet resulted in an enlargement of liver, presumably due to 2-4-fold accumulation of triglyceride. Serum triglyceride likewise increased significantly in rats fed a TI diet. No significant difference was found in the other lipid components both in serum and liver. When the livers from rats fed C or TI diets were isolated and perfused in the presence of an exogenous oleate substrate, the TI diet decreased the ketone body production and conversely increased the secretion rate of triglyceride, suggesting an inverse relationship between rates of ketogenesis and triglyceride secretion. The proportion of oleate in the perfusate triglyceride obtained at the end of perfusion was comparable between the C and TI groups, whereas in the post-perfused liver it was higher in the former than in the latter, suggesting a stimulatory effect of the TI diet on the secretion of the oleate in the form of triglyceride. These results indicate that altered hepatic metabolism of long-chain free fatty acids between the pathways of oxidation and esterification is one of the causative factors for triglyceride accumulation in the liver produced by threonine imbalance.

Metabolism of octanoyl- and palmitoylcarnitine by intact rat hepatocytes

Ketogenesis from extracellular substrates was quantified using intact rat hepatocytes. Rates of ketogenesis from octanoylcarnitine and palmitoylcarnitine were 20 and 30%, respectively, of the rates observed from the corresponding free acids. In contrast, the free acids and the acylcarnitines were converted to ketone bodies at similar rates in a liver homogenate system. These results suggest that medium- and long-chain acylcarnitines may be relatively poor substrates for metabolism by intact liver cells.

Renal and hepatic aspects of ketoacidosis: a quantitative analysis based on energy turnover.

The central theme explored is that the rate of ATP production cannot exceed its rate of use in any organ or compartment. Thus the rate of ATP turnover exerts an absolute control over the rates in pathways that synthesize it. This is manifested in two major ways: substrate competition for oxidation and the influence of changes in oxygen consumption rate on the rate of fuel oxidation. By direct measurement, the rate of ketogenesis in the liver is as high as 1500 mmol/day during chronic ketoacidosis of fasting. Given the limited ate of hepatic oxygen consumption, ketogenesis and glucose synthesis from amino acids compete as precursors for hepatic ATP synthesis. Thus There is little room to increase the rate of ketoacid production further in these subjects. Energy turnover considerations in the kidney during chronic fasting seem to limit renal NH4+ production. In this case, there is competition between glutamine and ketone bodies as ATP precursors. This aspect may be important in the regulation of lean body mass catabolism of fasting. There is a "trade-off" in maintaining high circulating ketone body concentrations during fasting. The benefit is primarily for the CNS, and the cost is small loss of lean body mass owing to the need for high rates of NH4+ excretion.

Hypophysectomy does not alter the acinar zonation of gluconeogenesis or the mitochondrial redox state in rat liver.

The biochemical and functional heterogeneity of hepatocytes in different zones of the liver acinus may be related to the concentrations of hormones within the liver acinus. We examined the effects of hypophysectomy, which causes marked changes in plasma hormone levels and in activities of hepatic enzymes that are normally heterogeneously distributed, on the degree of metabolic zonation within the liver acinus. In hypophysectomized rats the activity of alanine aminotransferase was increased, but its normal zonation (predominance in the periportal zone) was preserved. The activity in cultured periportal and perivenous hepatocytes was increased by dexamethasone, but not by glucagon. Periportal hepatocytes from hypophysectomized rats expressed higher rates of gluconeogenesis in culture than did perivenous hepatocytes, irrespective of the absence or presence of dexamethasone, glucagon or insulin. Similar differences in rates of ketogenesis and in the mitochondrial redox state in response to glucagon were observed between periportal and perivenous hepatocytes from hypophysectomized rats as between cell populations from normal rats. Although hypophysectomy causes marked changes in hepatic enzyme activities, it does not alter the degree of zonation of alanine aminotransferase, gluconeogenesis or the mitochondrial redox state within the liver acinus.

Effects of ethanol feeding on the activity and regulation of hepatic carnitine palmitoyltransferase I

The effects of ethanol administration on activity and regulation of carnitine palmitoyltransferase I (CPT-I) were studied in hepatocytes isolated from rats fed a liquid, high-fat diet containing 36% of total calories as ethanol or an isocaloric amount of sucrose. Cells were isolated at several time points in the course of a 5-week experimental period. Ethanol consumption markedly decreased CPT-I activity and increased enzyme sensitivity to inhibition by exogenously added malonyl-CoA. Changes in enzyme activity occurred sooner than those in enzyme sensitivity. Fatty acid oxidation to CO 2 and ketone bodies was depressed in hepatocytes from ethanol-fed animals during the first part of the treatment. At the end of the 35-day period, there were no longer differences in the rate of ketogenesis between the two groups. At that time, however, the rate of CO 2 formation was still impaired in the ethanol-fed animals. Furthermore, addition of ethanol or acetaldehyde to the incubation medium strongly depressed CPT-I activity and rates of fatty acid oxidation in hepatocytes from ethanol-treated rats, whereas these effects were much less pronounced in cells from control animals. The response of CPT-I activity to insulin, glucagon, vasopressin, and phorbol ester was blunted in cells derived from ethanol-fed rats. These changes in the regulation of CPT-I activity corresponded with those observed in the rate of fatty acid oxidation. It is concluded that CPT-I may play a role in the generation of the ethanol-induced fatty liver.

Glucagon regulation of gluconeogenesis and ketogenesis in periportal and perivenous rat hepatocytes. Heterogeneity of hormone action and of the mitochondrial redox state.

Hepatocytes isolated from the periportal or perivenous zones of livers of fed rats were used to study the long-term (14 h) and short-term (2 h) effects of glucagon on gluconeogenesis and ketogenesis. Long-term culture with glucagon (100 nM) resulted in a greater increase (P less than 0.01) in gluconeogenesis in periportal than in perivenous cells (93 +/- 16 versus 30 +/- 14 nmol/h per mg of protein; 72% versus 30% increase), but short-term incubation (2 h) with glucagon resulted in similar stimulation in the two cell populations. Rates of ketogenesis (acetoacetate and D-3-hydroxybutyrate production) were not significantly higher in periportal cells cultured without glucagon, compared with perivenous cells. However, after long-term culture with glucagon, the periportal cells had a significantly higher rate of ketogenesis (from either palmitate or octanoate as substrate), but a lower 3-hydroxybutyrate/acetoacetate production ratio, suggesting a more oxidized mitochondrial NADH/NAD+ redox state despite the higher rate of beta-oxidation. Periportal hepatocytes had a higher activity of carnitine palmitoyltransferase but a lower activity of citrate synthase than did perivenous cells. These findings suggest that: (i) glucagon elicits greater long-term stimulation of gluconeogenesis in periportal than in perivenous hepatocytes maintained in culture; (ii) after culture with glucagon, the rates of ketogenesis and the mitochondrial redox state differ in periportal and perivenous hepatocytes.

Fatty acid uptake and metabolism to ketone bodies and triacylglycerol in rat and human hepatocyte cultures is dependent on chain-length and degree of saturation Effects of carnitine and glucagon

Rat and human hepatocyte cultures were incubated with 5 common plasma longchain fatty acids (C16–C18). Rates of fatty acid uptake were similar in rat and human hepatocytes and were of the order: 16:1 > 16:0; 18:2 > 18:1 > 18:0. Rates of ketogenesis were lower in human compared to rat hepatocytes. In rat hepatocytes glucagon stimulated ketogenesis only in the presence of exogenous carnitine and rates of ketogenesis were higher from unsaturated compared to corresponding saturated fatty acids. Glucagon decreased triacylglycerol secretion irrespective of the fatty acid substrate and it increased intracellular triacylglycerol accumulation. The latter effect of glucagon was more marked in the absence of carnitine supplementation.

Effects of propionate and carnitine on the hepatic oxidation of short- and medium-chain-length fatty acids.

Accumulation of propionate, or its metabolic product propionyl-CoA, can disrupt normal cellular metabolism. The present study examined the effects of propionate, or propionyl-CoA generated during the oxidation of odd-chain-length fatty acids, on hepatic oxidation of short- and medium-chain-length fatty acids. In isolated hepatocytes, ketone-body formation from odd-chain-length fatty acids was slow as compared with even-chain-length fatty acid substrates, and increased as the carbon chain length was increased from five to seven to nine. In contrast, rates of ketogenesis from butyrate, hexonoate and octanoate were all approximately equal. Propionate (10 mM) inhibited ketogenesis from butyrate, hexanoate and octanoate by 81%, 53% and 18% respectively. Addition of carnitine had no effect on ketogenesis from the even-chain-length fatty acids, but increased the rate of ketone-body formation from pentanoate (by 53%), heptanoate (by 28%) and from butyrate or hexanoate in the presence of propionate. The inhibitory effect of propionate could not be explained by shunting acetyl-CoA into the tricarboxylic acid cycle, as CO2 formation from butyrate was also decreased by propionate. Examination of the hepatocyte CoA pool during oxidation of butyrate demonstrated that addition of propionate decreased acetyl-CoA and CoA as propionyl-CoA accumulated. Addition of carnitine decreased propionyl-CoA by 50% (associated with production of propionylcarnitine) and increased acetyl-CoA and CoA. Similar changes in the CoA pool were seen during the oxidation of pentanoate. These results demonstrate that accumulation of propionyl-CoA results in inhibition of short-chain fatty acid oxidation. Carnitine can partially reverse this inhibition. Changes in the hepatocyte CoA pool are consistent with carnitine acting by generating propionylcarnitine, thereby decreasing propionyl-CoA and increasing availability of free CoA. The data provide further evidence of the potential cellular toxicity from organic acid accretion, and supports the concept that carnitine's interaction with the cellular CoA pool can have a beneficial effect on cellular metabolism and function under conditions of unusual organic acid accumulation.

The characteristics and site of inhibition of gluconeogenesis in rat liver cells by bacterial endotoxin. Stimulation of phosphofructokinase-1.

The characteristics and site of inhibition of gluconeogenesis by endotoxin were investigated in liver cells isolated from control and endotoxin-treated rats. Endotoxin treatment was associated with inhibition (40-50%) of gluconeogenesis from lactate plus pyruvate over a range of concentrations of substrate and of oleate and with or without glucose or glucagon. Similar inhibition was observed with asparagine, proline, glutamine, alanine and a substrate mixture, but not with glycerol, glyceraldehyde, dihydroxyacetone or endogenous substrates. There was no change in cellular ATP content or in the rates of ketogenesis or ureogenesis from asparagine, proline or glutamine. Other effects on isotopic fluxes, metabolite contents, enzyme activities and control coefficients were consistent with the suggestion that the effects of endotoxin on gluconeogenesis are exerted at the level of phosphofructokinase-1, and not at phosphoenolpyruvate carboxykinase, pyruvate kinase, pyruvate carboxylase or glucokinase.

Interrelationships between dietary carbohydrates, B cell function and rate of ketogenesis during underfeeding in obese patients.

Six matched groups of obese patients underwent 3-week selective hypocaloric regimens which consisted of a 240 or 480 kcal/day liquid formula diets for groups 1-4 and an 800 kcal/day conventional diet for groups 5 and 6. Carbohydrate intake ranged from 19 to 112 g/day so that for each energy level two different amounts of carbohydrates were administered. Body weight loss was similar in groups 1-4 and significantly lower in groups 5 and 6. During treatment fasting serum insulin (but not serum C-peptide) levels and the daily urine excretion rate of C-peptide showed quite a similar fall in all groups. Fasting glucagon levels did not change. The rate of ketogenesis which developed during each nutritional treatment was inversely related to the amount of dietary carbohydrates; moreover, a significant correlation was found between percent variation of ketoacids and those of fasting IRI (r = -0.42; p less than 0.01) and glucose (r = -0.52; p less than 0.01) concentrations, but not with those of fasting C-peptide and its daily urine excretion rate. In conclusion, it seems that during underfeeding (1) low- and high-carbohydrate-containing regimens are substantially equipotent stimuli secretagogues of insulin secretion, and (2) carbohydrate (or glucose) availability affects ketogenesis even through noninsulin-mediated mechanisms.

Ketone body metabolism during pregnancy in the rabbit

The aim of this study was to test the effect of lipid store mobilization on changes in ketone body metabolism in pregnant rabbits. Related blood parameters were studied in pregnant animals fed either ad libitum or submitted between days 21 of gestation and parturition first to 50% food restriction for 4 days and then to a complete fast. Ketogenesis from oleate, butyrate and endogenous substrates was measured on days 0, 8, 18 and 28 of gestation in isolated liver cells prepared from females fasted for 48 h. In the does fed ad libitum, the concentration of non-esterified fatty acids (NEFA) was higher than in non-pregnant animals and then increased about 2-fold in the last week before term. Total ketone body concentrations increased slightly but significantly from day 27 until term. In the same period, glycemia decreased significantly. No variations were observed in lactate, alanine and total amino acid concentrations. Food restriction on days 21 to 24 induced a quick rise in the plasma concentrations of NEFA, ketone bodies and glycerol. Further fasting resulted in the development of hyperketonemia which was more than 3 times that observed during prolonged fasting in non-pregnant rabbits. There was no further increase in plasma NEFA level after day 27 of gestation. Food restriction and fasting decreased only the plasma level of total amino acids but had no significant effect on plasma concentrations of lactate and alanine. In isolated liver cells, a marked and significant increase in the rate of ketogenesis from oleate, butyrate and endogenous substrates was noted on day 28 of gestation in comparison with the preceding periods. It is concluded that ketonemia was enhanced in late gestation, particularly with restricted feeding or in fasted animals; this enhancement was partly related to the increase of plasma NEFA concentrations and partly to the enhancement of hepatic ketogenesis in the mothers. The fact that the rate of hepatic ketogenesis was increased equally with butyrate and oleate indicated that it could not be explained by a modification of acylcarnitine transferase activity as butyrate directly crosses the mitochondrial membrane without using this pathway.