Mercaptoacetate blocks fatty acid-induced GLP-1 secretion in male rats by directly antagonizing GPR40 fatty acid receptors

Mercaptoacetate (MA) is an orexigenic agent reported to block fatty acid (FA) oxidation. Recently, however, we reported evidence from isolated nodose ganglion neurons that MA antagonizes the G protein-coupled long- and medium-chain FA receptor GPR40. GPR40 mediates FA-induced secretion of the satietogenic incretin peptide glucagon-like peptide 1 (GLP-1), by enteroendocrine L cells, as well as FA-induced enhancement of glucose-stimulated insulin secretion. Our results in cultured nodose neurons suggest that MA would also block GPR40 in enteroendocrine cells controlling GLP-1 secretion. If so, this would suggest an alternative mechanism by which MA increases food intake. We tested the hypothesis that MA blocks FA-induced GLP-1 secretion in vitro using cultured STC-1 cells (a murine enteroendocrine cell line) and in vivo in adult male rats. In vitro, MA blocked the increase in both cytosolic Ca2+ and GLP-1 release stimulated by FAs and also reduced (but less effectively) the response of STC-1 cells to grifolic acid, a partial agonist of the GPR120 FA receptor. In vivo, MA reduced GLP-1 secretion following olive oil gavage while also increasing glucose and decreasing insulin levels. The carnitine palmatoyltransferase 1 antagonist etomoxir did not alter these responses. Results indicate that MA's actions, including its orexigenic effect, are mediated by GPR40 (and possibly GPR120) receptor antagonism and not by blockade of fat oxidation, as previously believed. Analysis of MA's interaction with GPR40 may facilitate understanding of the multiple functions of this receptor and the manner in which FAs participate in the control of hunger and satiety.

Abstract P220: Congestive Heart Failure in the Rat Induces Subtle Renal Damage via Neurogenic Pathways

Background: Cardiomyopathy in experimental renal insufficiency is putatively influenced by neurogenic pathways of renal origin. We wondered if cardiac neurogenic effects in congestive heart failure could likewise harm the kidney. We hypothesized that increased renal sympathetic nerve activity (RSNA) in rats with congestive heart failure after myocardial infarction (CHF) induces renal structural damage. Methods: 21 day after induction of CHF renal morphology was evaluated by immunohistology (interstitial and glomerular mononuclear cell infiltration (ED1), cell proliferation (PCNA), collagen I,III,IV,V,VI, laminin und fibronectin). RSNA was assessed by volume challenge (VE) to decrease RSNA. CHF and control rats were investigated with and without renal denervation (DNX). Blood pressure (BP), heart rate (HR) and RSNA were recorded. Nodose ganglion neurons (NGN) with vagal cardiac afferents were cultured for 1 day. Whole cell recordings were obtained and current-voltage relationships established. Cells were characterized by osmomechanical stress with a mannitol solution. Results: In CHF rats with intact renal nerves (nonDNX) formation of collagen I occurred, that was reduced after DNX (12.2+0.7 %area vs. 9.1+1.1 %area*, n=6, * p<0.05). VE-induced RSNA decreases were impaired in CHF vs controls suggesting increased RSNA (-α 34+8% vs. -α[[Unable to Display Character: &#61472;]]54+6% *, n=6, * p<0.05). NGN from CHF exhibited altered conductance in response to mechanical stress as compared to controls (change in holding current at -80 mV: control_normoosmotic: -144±30 pA; control_hypoos.: -282±34 pA vs CHF_normosmotic: - 230±55 pA; CHF_hypos.: -540±100* pA; *p<0.05 CHF vs. control). Conclusion: CHF induced subtle renal structural damage due to increased renal sympathetic tone which was likely due to altered NGN mechanosensitivity. Afferent nerve units from cardiovascular organs obviously form a complex sympathomodulatory network.