Distribution of immunoreactive kallikrein along the rat nephron

We have used a direct radioimmunoassay to localize kallikrein along the corticomedullary axis of the rat kidney and in microdissected rat cortical nephron segments. As previously seen in rat and dog, kallikrein content was highest in the outer cortex and decreased progressively toward the papillary tip. In microdissected cortical nephron segments, the highest kallikrein content was found in the connecting tubule [176 +/- 16 (SE) pg/mm tubule length (n = 12)]. In addition, a significant amount of kallikrein was found in distal convoluted tubules [53 +/- 4 pg/mm (n = 14)], initial collecting tubules [75 +/- 10 pg/mm (n = 14)], and cortical collecting ducts [37 +/- 4 pg/mm (n = 13)]. Little or no kallikrein was found in glomeruli, proximal convoluted tubules, proximal straight tubules, and cortical thick ascending limbs. These results are compatible with a site of action of the kallikrein-kinin system in the cortical segments of the rat distal nephron.