Dysfunctional lipid and glucose metabolism contribute to metabolic syndrome; a major public health concern that enhances cardiovascular disease risk. Arsenic (As(III)) exposure may increase metabolic syndrome and cardiovascular disease risk by impairing adipose tissue differentiation, function, and insulin sensitivity through pathogenic mechanisms that remain unclear. We hypothesized that As(III) signals through the Pertussis toxin (Ptx) sensitive, Gi protein-coupled (GPCR) to impair adipogenesis, as previously demonstrated for its stimulation of vascular oxidant generation, angiogenesis, and remodeling. Since both As(III) and GPCR ligands inhibit progenitor cell differentiation into adipocytes, we investigated the hypothesis in an model of low passage human mesenchymal stem cells (hMSC). As(III) (0.1-1.0 μM) suppressed dexamethasone/insulin-induced hMSC adipogenesis, as indicated by: decreased transcriptional promoters of differentiation; decreased fat droplet formation; and decreased expression of differentiated adipocyte markers, such as adiponectin (ADIPOQ) and perilipin (PLIN1). Pre-incubating hMSC with Ptx prevented 90% of the suppressive effect of As(III). Selective competitive antagonists of Gi-coupled endothelin-1 type A and B receptors were approximately 60% effective in blocking As(III) inhibition and combination of antagonists to both receptors were 85% effective. In contrast, antagonists to the sphingosine-1-phosphate type 1 receptor (previously shown to mediate As(III) vascular effects) or the angiotensin II type 1 receptor were ineffective in blocking As(III) effects. These studies suggest a majority of arsenic-inhibited adipocyte differentiation and metabolism requires endothelin-1 GPCRs and that As(III) effects on GPCR signaling are tissue and context specific. This may represent a significant mechanism for the contribution of arsenic exposure to increased metabolic and cardiovascular diseases.