A Kininogenase Resembling Glandular Kallikrein in the Rat Pituitary Pars Intermedia

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Abstract
The purpose of this study was to determine the distribution and characteristics of kinin-generating proteases (kininogenases) in rat pituitary tissue. Male rat pituitaries were dissected into their various lobes, sonicated in saline containing 12 mM deoxycholic acid, and assayed for protease activity at pH 8.5 using kininogen and chromogenic peptide substrates; kinin generation was measured by RIA. The rat pituitary was found to contain kininogenase activity highly concentrated in the pars intermedia; this activity was strongly inhibited by aprotinin and was resistant to soybean trypsin inhibitor. Antiserum against rat urinary kallikrein also inhibited the intermediate pituitary kininogenase. The kininogenase product was identified as bradykinin by reversed-phase high performance liquid chromatography. Homogenization of neurointermediate pituitaries in 0.25 M sucrose buffer (pH 7.5) followed by differential centrifugation (1,000 × g, 5 min; 10,000 × g, 20 min; 105,000 × g, 70 min) demonstrated that most of the kininogenase activity was in the 10,000 × g pellet. Kinin generation by neurointermediate pituitary extracts had a pH optimum of 8.0, and such extracts also hydrolyzed chromogenic peptide substrates for kallikreins. In addition, neurointermediate pituitary extracts were found to contain a distinct protease which hydrolyzed a chromogenic peptide substrate for thrombin. The intermediate pituitary kininogenase resembles glandular kallikrein and possibly may participate in prohormone processing.