Excess portal venous long-chain fatty acids induce syndrome X via HPA axis and sympathetic activation

We tested the hypothesis that excessive portal venous supply of long-chain fatty acids to the liver contributes to the development of insulin resistance via activation of the hypothalamus-pituitary-adrenal axis (HPA axis) and sympathetic system. Rats received an intraportal infusion of the long-chain fatty acid oleate (150 nmol/min, 24 h), the medium-chain fatty acid caprylate, or the solvent. Corticosterone (Cort) and norepinephrine (NE) were measured as indexes for HPA axis and sympathetic activity, respectively. Insulin sensitivity was assessed by means of an intravenous glucose tolerance test (IVGTT). Oleate infusion induced increases in plasma Cort (Δ = 13.5 ± 3.6 µg/dl; P < 0.05) and NE (Δ = 235 ± 76 ng/l; P < 0.05), whereas caprylate and solvent had no effect. The area under the insulin response curve to the IVGTT was larger in the oleate-treated group than in the caprylate and solvent groups (area = 220 ± 35 vs. 112 ± 13 and 106 ± 8, respectively, P < 0.05). The area under the glucose response curves was comparable [area = 121 ± 13 (oleate) vs. 135 ± 20 (caprylate) and 96 ± 11 (solvent)]. The results are consistent with the concept that increased portal free fatty acid is involved in the induction of visceral obesity-related insulin resistance via activation of the HPA axis and sympathetic system.

Overfeeding, Autonomic Regulation and Metabolic Consequences

The autonomic nervous system plays an important role in the regulation of body processes in health and disease. Overfeeding and obesity (a disproportional increase of the fat mass of the body) are often accompanied by alterations in both sympathetic and parasympathetic autonomic functions. The overfeeding-induced changes in autonomic outflow occur with typical symptoms such as adiposity and hyperinsulinemia. There might be a causal relationship between autonomic disturbances and the consequences of overfeeding and obesity. Therefore studies were designed to investigate autonomic functioning in experimentally and genetically hyperphagic rats. Special emphasis was given to the processes that are involved in the regulation of peripheral energy substrate homeostasis. The data revealed that overfeeding is accompanied by increased parasympathetic outflow. Typical indices of vagal activity (such as the cephalic insulin release during food ingestion) were increased in all our rat models for hyperphagia. Overfeeding was also accompanied by increased sympathetic tone, reflected by enhanced baseline plasma norepinephrine (NE) levels in both VMH-lesioned animals and rats rendered obese by hyperalimentation. Plasma levels of NE during exercise were, however, reduced in these two groups of animals. This diminished increase in the exercise-induced NE outflow could be normalized by prior food deprivation. It was concluded from these experiments that overfeeding is associated with increased parasympathetic and sympathetic tone. In models for hyperphagia that display a continuously elevated nutrient intake such as the VMH-lesioned and the overfed rat, this increased sympathetic tone was accompanied by a diminished NE response to exercise. This attenuated outflow of NE was directly related to the size of the fat reserves, indicating that the feedback mechanism from the periphery to the central nervous system is altered in the overfed state.

Exploiting open source 3D printer architecture for laboratory robotics to automate high-throughput time-lapse imaging for analytical microbiology

Growth in open-source hardware designs combined with the low-cost of high performance optoelectronic and robotics components has supported a resurgence of in-house custom lab equipment development. We describe a low cost (below USD700), open-source, fully customizable high-throughput imaging system for analytical microbiology applications. The system comprises a Raspberry Pi camera mounted on an aluminium extrusion frame with 3D-printed joints controlled by an Arduino microcontroller running open-source Repetier Host Firmware. The camera position is controlled by simple G-code scripts supplied from a Raspberry Pi singleboard computer and allow customized time-lapse imaging of microdevices over a large imaging area. Open-source OctoPrint software allows remote access and control. This simple yet effective design allows high-throughput microbiology testing in multiple formats including formats for bacterial motility, colony growth, microtitre plates and microfluidic devices termed ‘lab-on-a-comb’ to screen the effects of different culture media components and antibiotics on bacterial growth. The open-source robot design allows customization of the size of the imaging area; the current design has an imaging area of ~420 × 300mm, which allows 29 ‘lab-on-a-comb’ devices to be imaged which is equivalent 3480 individual 1μl samples. The system can also be modified for fluorescence detection using LED and emission filters embedded on the PiCam for more sensitive detection of bacterial growth using fluorescent dyes

Central and Peripheral Control of Sympathoadrenal Activity and Energy Metabolism in Rats

The role of adrenoceptors in the hypothalamus and the peripheral sympathetic nervous system in the regulation of sympathoadrenal activity and glucose and FFA mobilization was investigated in exercising rats. Apparent close relations within the two parts of the sympathoadrenal system and between factors that regulate glucose and FFA mobilization during exercise were completely disrupted by local hypothalamic infusions of adrenoceptor antagonists or anesthetic drugs. The experiments actually identified specific areas in the hypothalamus that integrate the information regarding the substrate levels in the blood with the "central command" from higher centers in the brain. Furthermore, the results of experiments with exercising intact and adrenodemedullated (Adm) rats, with and without administration of selective adrenoceptor agonists and antagonists, suggest that the activity of the sympathetic nervous system is also regulated at the level of the peripheral sympathetic nerve endings. In particular, presynaptic adrenergic regulatory mechanisms can markedly influence the outflow of NE from the sympathetic nerve endings. In conclusion, the data show that an organ-specific organization of sympathetic output during exercise may take place at different levels within the sympathetic nervous system.

Effects of Monosodium Glutamate (Umami Taste) With and Without Guanosine 5'-Monophosphate on Rat Autonomic Responses to Meals

Monosodium glutamate (MSG) is used as a food additive to improve the taste of food. The effect of MSG on sweet taste is enhanced by guanosine 5'-monophosphate (GMP). Because increased palatability is known to increase the vagally mediated preabsorptive insulin response (PIR), we hypothesized that MSG and GMP will enhance the PIR. To study this, male Wistar rats were provided with permanent cannulas for venous blood sampling and intragastric drug administration. The MSG and GMP were either added to a test meal or infused into the stomach during a test meal. Blood samples were taken to measure concentrations of glucose, insulin, epinephrine (E), and norepinephrine (NE). Addition of 56 mg MSG to a control meal markedly reduced both phases of the meal-induced increase in plasma insulin and had no effects on blood glucose and plasma E and NE responses. Infusion of 56 mg MSG into the stomach at the onset of food intake reduced the PIR with no effect on glucose, E, NE, or the second phase insulin release. Addition of 2 mg MSG in combination with GMP to the test meal or gastric administration of these drugs did not affect the changes in any of the blood components measured. It is concluded that addition of a high dose of MSG to a test meal leads to a reduction in the vagal response to food.

Metabolic and Hormonal Responses to Hypothalamic Administration of Norfenfluramine in Rats

The effects of intrahypothalamic administration of norfenfluramine (NFFL), an anorectic agent that increases serotonergic transmission, on plasma concentrations of glucose, free fatty acids (FFA), and their regulating hormones were investigated in resting and exercising rats. Infusion of 5 µg NFFL in 0.125 µl aCSF/min into the nucleus paraventricularis of the hypothalamus (PVN) caused a significant increase of blood glucose, plasma epinephrine (E), and corticosterone concentrations. Plasma levels of FFA, insulin, or norepinephrine (NE) remained unchanged. Lower doses of NFFL (0.5 and 0.05 µg/min) did not affect peripheral metabolism. The effects of NFFL in the PVN were completely prevented by prior administration of a 5-HT1 antagonist, (S)-(-)propranolol. The exercise-induced increase of plasma NE was reduced after prior administration of 5 µg NFFL/min into the PVN. Plasma E responses tended to be increased. The exercise-induced alterations in glucose, FFA, corticosterone, and insulin were not affected by NFFL infusion into the PVN. The data suggest that activation of serotonergic mechanisms in the PVN might change the neurohormonal response to a stressor favouring the release of adrenal hormones above activation of the neuronal branch of the sympathetic nervous system.

Paraventricular hypothalamic adrenoceptors and energy metabolism in exercising rats

The role of adrenoceptors in the paraventricular nucleus (PVN) in the exercise-induced changes in plasma norepinephrine (NE), epinephrine (E), corticosterone, free fatty acids (FFA), and blood glucose was investigated in rats. Exercise consisted of strenuous swimming against a countercurrent for 15 min. Before, during, and after swimming, blood samples were withdrawn through a permanent heart catheter for determination of E, NE, corticosterone, FFA, and glucose, In control rats receiving artificial cerebrospinal fluid through permanent bilateral cannulas into the PVN, the levels of all blood components increased during exercise. Infusion of the α-adrenoceptor antagonist phentolamine into the PVN completely reduced the exercise-induced increases in blood glucose and plasma corticosterone concentrations. Plasma NE, E, and FFA were not affected. Infusion of the β-adrenoceptor antagonist timolol into the PVN reduced blood glucose and plasma NE concentrations. Plasma E, corticosterone, and FFA remained unchanged. It is concluded that α- and β-adrenergic receptors in the PVN are involved in the central nervous regulation of blood glucose levels during exercise, partly by influencing sympathetic outflow. α-Adrenoceptors in the PVN play an important role in the release of corticosterone during exercise.