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Evidence for Trypsin-tike Proteases in Pituitaries of Dahl Salt Sensitive and Salt-Resistant Rats 1

Abstract The pituitary cleft of Dahl hypertension-resistant rats (R) contains significant amounts of a protein-rich fluid (colloid) which is not observed in pituitary glands of Dahl salt-sensitive hypertensive (S) rats. The accumulation of colloid has been found to correlate inversely with blood pressure. In this study we have shown that the pituitaries of Dahl R rats have significantly higher levels of protease activity than salt-sensitive S rats. Protease activity was measured using the synthetic substrate α-N-p-tosyl-L-arginine-[3H]methyl ester. Protease activity was found to increase with age and was highest in male R rats. The following lines of evidence suggest that colloid itself contains significant amounts of protease activity. (a) Protease activity correlated significantly with the accumulation of colloid in the R rats. (b) Protease activity could be measured directly by assaying a sample of colloid obtained by micropuncture. (c) A subline of the R rat which lacked colloid also lacked protease activity. The protease activity from R male pituitaries could be resolved into two components by Sephacryl S-200 molecular sieve chromatography. The molecular weights were estimated to be 128,000 and 64,000 daltons. Inhibitor studies showed that neither lima bean nor soybean trypsin inhibitors were potent inhibitors of protease activity. The 128,000-dalton component was more sensitive to inhibition by trasylol (Aprotinin) than the 64,000-dalton component. The role of these proteases in regulating blood pressure is not yet known.