ADP ribosyl (ADPR) cyclases comprise a family of ectoenzymes recently shown to influence cytosolic Ca²⁺ concentration in a variety of cell types. At least two ADPR cyclase family members have been identified in mammals: CD38 and CD157. We recently found reduced renal vascular reactivity to angiotensin II (Ang II), endothelin-1 (ET-1), and norepinephrine (NE) in the presence of the broad ADPR cyclase inhibitor nicotinamide. We hypothesized that CD38 mediates effects attributed to ADPR cyclase. We found expression of ADPR cyclases CD38 and CD157 mRNA in spleen, thymus, skin, and preglomerular arterioles of wild type (WT) animals. Mice lacking CD38 showed decreased CD157 expression in most tissues tested. No difference in systolic or mean arterial pressure (AP) was observed between strains in either conscious or anesthetized states, whereas heart rate was reduced 10-20% in CD38-/- animals (P<0.05). During anesthesia, CD38-/- mice had similar renal blood flow (RBF) and reduced urine excretion (P<0.005). RBF responses to iv injection of Ang II, ET-1 and NE were attenuated ~50% in CD38-/- vs. WT mice (P<0.01 for all). The systemic pressor response to Ang II was decreased in the absence of CD38 (P<0.01), whereas that to NE was normal (P>0.05); ET-1 was administered at a non-pressor dose. Nicotinamide effectively inhibited Ang II-induced renal vasoconstriction in WT mice (P<0.001), but had no effect on renal responses to Ang II in CD38-/- mice (P>0.5). Overall, our observations indicate the presence of two ADPR cyclase family members in renal preglomerular resistance arterioles and the importance of CD38 participation in acute vascular responses to all three vasoconstrictors in the renal microcirculation.