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 Ca(2+)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.

Chronic Alcohol Consumption in Rats Leads to Desynchrony in Diurnal Rhythms and Molecular Clocks.

BACKGROUND: Circadian rhythms are essential for adapting to the environment. Chronic alcohol consumption often leads to sleep and circadian disruptions, which may impair the life quality of individuals with alcohol use disorders and contribute to the morbidity associated with alcoholism. METHODS: We used a pair-feeding liquid diet alcohol exposure protocol (6 weeks duration) in PER1::LUC transgenic rats to examine the effects of chronic alcohol exposure on: (i) diurnal rhythms of core body temperature and locomotor activity, (ii) plasma corticosterone (CORT) concentrations, and (iii) rhythms of ex vivo Period1 (Per1) expression in the suprachiasmatic nucleus (SCN), pituitary, and adrenal glands. We followed multiple circadian outputs not only to examine individual components, but also to assess the relative phase relationships among rhythms. RESULTS: We found that chronic alcohol consumption: (i) reduced 24-hour body temperature and locomotor activity counts in the dark period, (ii) advanced the acrophase of diurnal rhythms of body temperature and locomotor activity, (iii) abolished the phase difference between temperature and activity rhythms, (iv) blunted and advanced the diurnal CORT rhythm, and (v) advanced Per1 expression in the adrenal and pituitary glands but not in the SCN. We found that chronic alcohol altered the phase relationships among diurnal rhythms and between the central (SCN) and peripheral (adrenal and pituitary) molecular clocks. CONCLUSIONS: Our findings suggest that desynchrony among internal rhythms is an important and overlooked aspect of alcohol-induced circadian disruptions. The misalignment of phases among rhythms may compromise normal physiological functions and put individuals with chronic alcohol use at greater risk for developing other physical and mental health issues. How this desynchrony occurs and the extent to which it participates in alcohol-related pathologies requires further investigation.