1-Butyryl-glycerol (monobutyrin) is a simple lipid product of adipocytes with angiogenic activity. Recent studies have shown that the biosynthesis of this compound is tightly linked to lipolysis, a process associated with changes in blood flow. We now present data indicating that monobutyrin is an effective vasodilator of rodent blood vessels using a fluorescent retinal angiogram assay. The vasodilatory activity of monobutyrin is potent (ED50 = 3.3 x 10(-7) M), dose dependent, and stereospecific. Because diabetes represents a catabolic, lipolytic state with numerous vascular complications, we examined the action and regulation of monobutyrin in insulin-deficient diabetic rats. Serum levels of monobutyrin in streptozotocin-induced diabetic rats were greatly elevated compared to normal animals. At the same time, the retinal vessels of the diabetic animals develop a resistance to the vasodilatory activity of monobutyrin. These results demonstrate a role for monobutyrin in the control of vascular tone and suggest a possible involvement in the pathology of diabetes.