Effects of beta-hydroxybutyrate, glycerol, and free fatty acid infusions on glucagon and epinephrine secretion in dogs during acute hypoglycemia

Transcriptomic and metabolomic insights into the roles of exogenous β-hydroxybutyrate acid for the development of rumen epithelium in young goats

Beta-hydroxybutyric acid (BHBA), as one of the main metabolic ketones in the rumen epithelium, plays critical roles in cellular growth and metabolism. The ketogenic capacity is associated with the maturation of rumen in young ruminants, and the exogenous BHBA in diet may promote the rumen development. However, the effects of exogenous BHBA on rumen remain unknown. This is the first study to investigate the mechanisms of BHBA on gene expression and metabolism of rumen epithelium using young goats as a model through multi-omics techniques. Thirty-two young goats were divided into control, low dose, middle dose, and high dose groups by supplementation of BHBA in starter (0, 3, 6, and 9 g/day, respectively). Results demonstrated the dietary of BHBA promoted the growth performance of young goats and increased width and length of the rumen papilla (P < 0.05). Hub genes in host transcriptome that were positively related to rumen characteristics and BHBA concentration were identified. Several upregulated hub genes including NDUFC1, NDUFB4, NDUFB10, NDUFA11 and NDUFA1 were enriched in the gene ontology (GO) pathway of nicotinamide adenine dinucleotide (NADH) dehydrogenase (ubiquinone) activity, while ATP5ME, ATP5PO and ATP5PF were associated with ATP synthesis. RT-PCR revealed the expression of genes (HMGCS2, BDH1, SLC16A3, etc.) associated with lipolysis increased significantly by BHBA supplementation (P < 0.05). Metabolomics indicated that some metabolites such as glucose, palmitic acid, cortisol and capric acid were also increased (P < 0.05). This study revealed that BHBA promoted rumen development through altering NADH balance and accelerating lipid metabolism, which provides a theoretical guidance for the strategies of gastrointestinal health and development of young ruminants.

The past, present, and future physiology and pharmacology of glucagon

The evolution of glucagon has seen the transition from an impurity in the preparation of insulin to the development of glucagon receptor agonists for use in type 1 diabetes. In type 2 diabetes, glucagon receptor antagonists have been explored to reduce glycemia thought to be induced by hyperglucagonemia. However, the catabolic actions of glucagon are currently being leveraged to target the rise in obesity that paralleled that of diabetes, bringing the pharmacology of glucagon full circle. During this evolution, the physiological importance of glucagon advanced beyond the control of hepatic glucose production, incorporating critical roles for glucagon to regulate both lipid and amino acid metabolism. Thus, it is unsurprising that the study of glucagon has left several paradoxes that make it difficult to distill this hormone down to a simplified action. Here, we describe the history of glucagon from the past to the present and suggest some direction to the future of this field.

Role of beta-hydroxybutyric acid in the central regulation of energy balance

Although the phenomenon of beta-hydroxybutyric acid (BHBA) impact on satiety and thermogenesis has been described in the past decades, the underlying molecular mechanisms involved remain unresolved. Other metabolites such as glucose, fatty or branched chain amino acids are known to activate the AMP kinase pathway leading to an increase of anorexic and a decrease of orexigenic neuropeptides in the hypothalamus, one of the central regulators of energy homeostasis. Since BHBA is utilized as an energy source by the brain particularly in suckling newborns and under starving conditions, it is supposed to be a further central signal and energy providing substrate involved in the regulation of food intake. Moreover, BHBA might present a therapeutic approach for treating neuronal diseases because of its neuroprotective properties. Therefore, the purpose of this review is to summarize the known central effects of BHBA and to point out the importance of the identification of cellular pathways triggered in response to BHBA.

Stimulatory influence of D(-)3-hydroxybutyrate feeding on sympathetic nervous system activity in the rat

To examine the effect of ketone body utilization on sympathetic nervous system (SNS) activity, norepinephrine (NE) turnover was measured in heart and interscapular brown adipose tissue (IBAT) of rats fed diets enriched with D(-)3-hydroxybutyrate (3OHB), the naturally occurring isomer of hydroxybutyrate. Isoenergetic substitution of 3OHB for chow for 4 days increased cardiac [3H]NE turnover (P < .025), with a slightly less marked (P < .06) effect in IBAT. When [3H]NE turnover was measured in rats fed chow diets supplemented with 3OHB or sucrose and compared with that in animals fed chow alone, [3H]NE turnover rates in heart and IBAT were similar in the ketone-supplemented and chow-fed groups. Animals fed the sucrose-supplemented chow displayed lower rates of [3H]NE turnover in IBAT than rates found in those given the 3OHB-containing chow (-36%, P < .025 in IBAT). In addition, the stimulatory effect on SNS activity of a 4-day exposure to a sucrose-enriched diet after 2 days of fasting was significantly enhanced by concomitant ketone ingestion. Fractional NE turnover in IBAT was increased from 9.3% +/- 1.3%/h in control rats to 14.2% +/- 0.9%/h in rats refed with 3OHB (P < .005). These observations indicate that increased ketone body utilization does not suppress SNS activity and may stimulate it in a manner quantitatively similar to that seen with carbohydrate or fat ingestion.

The influence of ketosis on the metabolic response to skeletal trauma

Intravenous glucose and ketone body feeding were compared for their potential in altering urinary nitrogen losses by the traumatized rat. Eighteen male rats were traumatized by bilateral femoral fracture. The rats were fed totally by vein for 3 days prior and 3 days after injury and the infusion rate was held constant over the 6 days of infusion. Group GT rats were fed glucose as the source of nonprotein energy while group MT rats were fed a mixture of 72% monoacetoacetin (the monoglyceride of acetoacetate)-28% glucose for the nonprotein energy. Total urinary nitrogen excretion on a 24-hr basis was measured for each of the 6 days of intravenous feeding. On the third day post-trauma, each rat was evaluated for leucine kinetics using a continuous infusion of L-[1-14C]leucine and measurement of breath and plasma specific activities. Rats from group MT were hyperketonemic and normoglycemic and rats from group GT were normoketonemic and hyperglycemic. Urinary nitrogen losses, leucine oxidation, and leucine turnover were similar for the two groups. We conclude that ketone bodies are as good an intravenous source of energy as is glucose, and the ketone bodies do not cause hyperglycemia.

Glucose counterregulation during prolonged hypoglycemia in normal humans

To study glucose counterregulation under conditions approximating those of clinical disorders in which hypoglycemia develops gradually and is reversed over a prolonged period, we injected regular insulin subcutaneously, in a dose (0.15 U/kg) selected to produce two- to threefold increases in plasma insulin, in 11 normal human volunteers and measured plasma glucose, insulin, C-peptide, and counterregulatory hormone concentrations as well as rates of glucose production, glucose utilization, and insulin secretion over 12 h. The data suggest that the mechanisms of gradual recovery from prolonged hypoglycemia may differ from those of rapid recovery from short-term hypoglycemia produced by intravenous injection of insulin in that 1) both stimulation of glucose production and limitation of glucose utilization contribute to recovery from prolonged hypoglycemia; 2) increases in glucagon, epinephrine, growth hormone, and cortisol secretion as well as a decrease in insulin secretion may all participate in glucose counterregulation during prolonged hypoglycemia; 3) epinephrine may play a more important role than glucagon during prolonged hypoglycemia. The latter two conclusions are based primarily on the temporal relationships between changes in the rates of glucose turnover and changes in plasma hormone concentrations and should not be considered proved. However, they provide the basis for testable hypotheses concerning the physiology of gradual recovery from prolonged hypoglycemia that can be expected to be relevant to the pathophysiology of clinical hypoglycemia.

Effect of ketone bodies on glucose production and utilization in the miniature pig

The effect of ketone bodies on glucose production (Ra) and utilization (Rd) was investigated in the 24-h starved, conscious unrestrained miniature pig. Infusing Na-DL-beta-OH-butyrate (Na-DL-beta-OHB) and thus shifting the blood pH from 7.40 to 7.56 resulted in a decrease of Ra by 52% and of Rd by 45%, as determined by the isotope dilution technique. Simultaneously, the concentrations of arterial insulin and glucagon were slightly enhanced, whereas the plasma levels of glucose, lactate, pyruvate, alanine, alpha-amino-N, and free fatty acids (FFA) were all reduced. Infusion of Na-bicarbonate, which yielded a similar shift in blood pH, did not mimick these effects. Infusion of equimolar amounts of the ketoacid, yielding a blood pH of 7.35, induced similar metabolic alterations with respect to plasma glucose, Ra, Rd, and insulin; however, plasma alanine and alpha-amino-N increased. Infusing different amounts of Na-DL-beta-OHB resulting in plasma steady state levels of ketones from 0.25 to 1.5 mM had similar effects on arterial insulin and glucose kinetics. No dose dependency was observed. Prevention of the Na-DL-beta-OHB-induced hypoalaninemia by simultaneous infusion of alanine (1 mumol/kg X min) did not prevent hypoglycemia. Infusion of Na-DL-beta-OHB plus insulin (0.4 mU/kg X min) showed no additive effect on the inhibition of Ra. Ketones did not inhibit the insulin-stimulated metabolic clearance rate (MCR) for glucose. Infusion of somatostatin (0.2 micrograms/kg X min) initially decreased plasma glucose, Ra, and Rd, which was followed by an increase in plasma glucose and Ra; however, on infusion of somatostatin plus Na-DL-beta-OHB, hypoglycemia and the reduced Ra were maintained. In the anaesthetized 24-h starved miniature pig, Na-DL-beta-OHB infusion decreased the hepatic exchange for glucose, lactate, and FFA, whereas the exchange for glycerol, alanine, and alpha-amino-N as well as liver perfusion rate were unaffected. Simultaneously, portal glucagon and insulin as well as hepatic insulin extraction rate were elevated. Leg exchange for glucose, lactate, glycerol, alanine, alpha-amino-N, and FFA were decreased, while ketone body utilization increased. Repeated infusion of Na-DL-beta-OHB at the fourth, fifth, and sixth day of starvation in the conscious, unrestrained mini-pig resulted in a significant drop in urinary nitrogen (N)-excretion. However, this effect was mimicked by infusing equimolar amounts of Na-bicarbonate. In contrast, when only the ketoacid was given, urinary N-excretion accelerated. To summarize: (a) Ketone bodies decrease endogenous glucose production via an insulin-dependent mechanism; in addition, ketones probably exert a direct inhibitory action on gluconeogenesis. The ketone body-induced hypoalaninemia does not contribute to this effect. (b) The counterregulatory response to hypoglycemia is reduced by ketones. (c) As a consequence of the decrease in R(a), glucose utilization declines during ketone infusion. (d)The insulin-stimulated MCR for glucose is not affected by ketones. (e) Ketones in their physiological moiety do not show a protein-sparing effect.

Sex differences in the adrenergic response to hypoglycemic stress in human

We have found different patterns of adrenergic response to insulin-induced hypoglycemia in men and women. The differences involve the readiness of adrenergic reactivity, the magnitude of the responses, and the nature of secreted amines. In men, a strong and transient discharge of epinephrine (E) is observed in plasma, corresponding to a great increase in the urinary level of this amine in the 2 h period following insulin. In women, the adrenergic response is delayed and consists of moderately increased amounts of E and norepinephrine (NE) which persist in plasma for a longer period. From the correlations observed between urinary amount and the increase of plasmatic catecholamines after 30, 45, and 60 min, it may be assumed that urinary data may reflect the cumulative plasma levels of catecholamines in the corresponding period, but not the precise pattern of plasmatic changes. Our findings show that the differences in adrenergic behavior previously observed in men and women under the effect of psychological stress, may also be induced by a metabolic stimulus such a insulin hypoglycemia; however, women, but not men, exhibit a mild release of NE under this metabolic stress.

Effect of oleic acid on arginine-induced glucagon secretion by the isolated perfused rat pancreas

The isolated perfused rat pancreas was used to investigate the effect of oleic acid on glucagon secretion in response to 10 mmol/l arginine. In the absence of oleic acid and at 2.5 mmol/l calcium, arginine induced a biphasic glucagon secretion. At lower extracellular calcium concentration (1.0 mmol/l), the second phase of glucagon release was reduced, the first phase being unchanged. In the presence of 1,500 mumol/l oleic acid, the glucagon response to arginine was also biphasic, but second phase release was markedly inhibited, the first phase glucagon release being unchanged. Such an effect was not obtained when oleic acid concentration in the medium was 750 mumol/l. These results demonstrate that high concentrations of oleic acid inhibit glucagon secretion in response to arginine from the isolated perfused rat pancreas and support the concept that circulating free fatty acid levels are involved in the control of glucagon secretion.

Influence of elevated plasma free fatty acids on the glucagon response to hypoglycemia in normal and in pregnant women

We investigated the influence of an insulin-induced hypoglycemia on plasma glucagon in nonpregnant healthy young women and in women during the last month of gestation. Both groups were tested either in the basal state or during a period where free fatty acid plasma levels were increased by infusion of a lipid emulsion supplemented with heparin. Regular insulin was injected intravenously at the dose of 0.1 U/kg body wt in controls and 0.3 U/kg in pregnant women in order to obtain a similar lowering of blood glucose in all groups. In controls, the increase in plasma glucagon was maximum 30 and 45 min after insulin injection and averaged 130 pg/ml; the infusion of triglycerides and heparin which raised plasma FFA to about 1300 muEq/liter decreased basal plasma glucagon levels and reduced, by about 70%, the glucagon response to hypoglycemia. During the last month of pregnancy, the glucagon response to insulin-induced hypoglycemia was reduced by 60% (mean maximal increase 52 pg/ml); furthermore, raising plasma FFA to about 1500 muEq/liter completely abolished the glucagon rise induced by the insulin hypoglycemia. These results support the view that the glucagon release from A-cells can be modulated by the level of circulating plasma FFA.

Effects of exogenous glucagon and epinephrine in physiological amounts on the blood levels of free fatty acids and glycerol in dogs

Exogenous glucagon or epinephrine were infused into normal overnight fasted dogs to raise circulating hormone levels to concentrations within the physiologic range. Plasma levels of glycerol and free fatty acids remained unchanged during the glucagon infusion, but rose significantly during the administration of epinephrine. Plasma insulin in the systemic circulation remained unchanged during the glucagon infusion and increased slightly during the infusion of thecatecholamine. The data suggest that in normal dogs glucagon in physiological amounts has no lipolytic effect. The importance of the sympathetic nervous system in regulating lipolysis in normal mammals is stressed.