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.

Mapping physiological G protein-coupled receptor signaling pathways reveals a role for receptor phosphorylation in airway contraction.

G protein-coupled receptors (GPCRs) are known to initiate a plethora of signaling pathways in vitro. However, it is unclear which of these pathways are engaged to mediate physiological responses. Here, we examine the distinct roles of Gq/11-dependent signaling and receptor phosphorylation-dependent signaling in bronchial airway contraction and lung function regulated through the M3-muscarinic acetylcholine receptor (M3-mAChR). By using a genetically engineered mouse expressing a G protein-biased M3-mAChR mutant, we reveal the first evidence, to our knowledge, of a role for M3-mAChR phosphorylation in bronchial smooth muscle contraction in health and in a disease state with relevance to human asthma. Furthermore, this mouse model can be used to distinguish the physiological responses that are regulated by M3-mAChR phosphorylation (which include control of lung function) from those responses that are downstream of G protein signaling. In this way, we present an approach by which to predict the physiological/therapeutic outcome of M3-mAChR-biased ligands with important implications for drug discovery.This study is funded by the Medical Research Council (MRC) through funding of program leaders provided by the MRC Toxicology Unit (to A.B.T.)

Effect of ISO-1 and dexamethasone on ozone-induced lung inflammation.

<p>Cytokine mRNA (A, C, E & G) and protein (B, D, F & H) expression levels in the lung of ozone exposed and ISO-1- or dexamethasone-treated mice. KC (A&B), GM-CSF (C&D), TNF-α (E&F), and MIF (G&H). Data are expressed as mean±SD for 6 animals per group. *<i>p</i><0.05 and **<i>p</i><0.01 compared to air controls, ^#<i>p</i><0.05 compared to ozone exposed group.</p

Effect of ISO-1 and dexamethasone on ozone-induced changes in AHR and lung function.

<p>Mouse lung function measurements of pulmonary resistance (R_L; A), -logPC₁₀₀ (B), FEV₇₅ (C), lung compliance (C_chord; D), total lung capacity (TLC; E) and functional residual capacity (FRC; F). Data are expressed as mean±SD for 6 animals per group. *<i>p</i><0.05 and **<i>p</i><0.01 compared to air controls, ^#<i>p</i><0.05 compared to ozone-exposed group.</p