Effect of chymotrypsin on rat blood pressure

1. 1. Chymotrypsin (Cht) administration (14 mg/kg, i.v.) to rats always caused hypertension; hypotension preceded this effect in 64% of the observations ( n = 11). 2. 2. A 68% reduction of circulating kininogen but not of angiotensinogen was observed after Cht administration. 3. 3. Cht effects were not affected by captopril, [Sar 1-Leu 8]-angiotensin II and alpha-adrenoceptor antagonists. In 70% of the observations ( n = 10) hypotension was abolished by a mixture of histamine H 1-and H 2-antagonists. Therefore histamine release may explain hypotension. 4. 4. Cht released in vitro from rat plasma, a substance producing hypertension in the rat and contraction of the guinea-pig ileum. Both effects were antagonized by [Sar 1-Leu 8]-angiotensin II. 5. 5. In spite of this angiotensin release in vitro, the hypertensive component of the in vivo response to Cht seems to be due to some other substance.