The effects of elastase on blood pressure (B.P.) and the urinary excretions of prostaglandins (PGs) and catecholamines in the spontaneously hypertensive rat (SHR) were investigated. Male SHRs (n = 20), castrated at 4 weeks of age, were divided into 2 groups. Elastase was then dissolved in saline (5 mg/ml) and injected subcutaneously (10 mg/kg of body weight) into the SHRs of one of the 2 groups (n = 10) at 5 to 13 weeks of age, and the same dose of saline only was injected subcutaneously into the SHRs of the other group (n = 10) as a control during the same period. B.P. was measured by the tail-cuff method every 2 weeks. Urine sampling and measurement of body weight (B.Wt.) were also performed every 2 weeks. The B.P. in the elastase-administered group (184.1 +/- 3.3 mmHg) was found to be significantly lower (p less than 0.02) than that of the control group (198.0. +/- 4.3) at 9 weeks of age. A significant difference (p less than 0.01) in B.P. between the control group (204.0 +/- 4.5) and the elastase-administered group (187.3 +/- 2.7) was also observed at 13 weeks of age. The urinary excretion of 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha) in the control group (5.1 +/- 0.4 ng/day/100 g B.Wt.) at 11 weeks of age was significantly lower (p less than 0.05) than that of the elastase-administered group (10.4 +/- 1.3).(ABSTRACT TRUNCATED AT 250 WORDS)