Kallikrein Messenger RNA in Rat Arteries and Veins

Glandular kallikrein (EC 3.4.21.8) belongs to a subgroup of serine proteases coded by a multigene family. A kininogenase resembling glandular kallikrein has been identified in vascular tissue; however, it is not clear whether it is synthesized by vascular tissue or taken up from plasma. To determine the potential for kallikrein synthesis in vascular tissues, we tested whether messenger RNA (mRNA) for glandular kallikrein is present in rat arteries and veins. Poly(A) RNA was isolated from pools of arteries or veins (n=3, 30 rats each). Poly(A) RNA from the kidney and liver was used as a positive and negative control, respectively. As a probe, we used rat pancreatic kallikrein P-labeled complementary DNA, which recognizes mRNA of the entire rat kallikrein family. Slot-blot analysis indicated that kallikrein mRNA was present in mRNA from the arteries, veins, and kidney but not from the liver. Poly(A) RNA from arteries and veins contained ∼1% as much kallikrein mRNA as that from the kidney. To confirm the slot-blot results and determine whether the mRNA for true glandular kallikrein was present in vascular tissue, we employed a polymerase chain reaction assay, first using primers specific for the entire kallikrein family (which amplify a 430-bp fragment) and then using primers specific for true glandular kallikrein mRNA (which amplify a 370-bp fragment). After the polymerase chain reaction assay, both arteries and veins showed fragments of these sizes when tested with rat kallikrein complementary DNA probe, thus confirming the presence of glandular kallikrein mRNA. Similar results were obtained when the polymerase chain reaction assay was applied to mRNA isolated from vascular smooth muscle cells in culture and from the kidney. No signal was obtained with liver mRNA. We concluded that kallikrein is synthesized by the vascular wall, possibly by smooth muscle cells. The presence of locally synthesized kallikrein indicates that the vascular kallikrein-kinin system may play a role in the regulation of vascular tone.