C16 Lactosylceramide is an endogenous bioactive sphingolipid. It forms membrane microdomains with Lyn kinase and the αi subunits of inhibitory G protein-coupled receptors (GPCRs), suggesting a role in cell signaling. Plasma levels of C16 lactosylceramide are elevated in insulin-resistant cattle. C16 Lactosylceramide is also upregulated in a mouse model of Niemann-Pick type C1 disease, a neurodegenerative cholesterol-sphingolipid lysosomal storage disorder.