The vascular tissue angiotensin I-converting enzyme activity and aortic elastin content in stroke-prone spontaneously...

1. Stroke-prone spontaneously hypertensive rats (SHRSP) were fed a diet with fish meal as the protein source (fish diet) during the progressive stage of hypertension, and its effects on the activity of angiotensin I-converting enzyme (ACE) in serum and vascular tissues and on the aortic elastin content were studied. The effects of the antihypertensive drugs captopril and hydralazine were also studied. 2. Stroke-prone spontaneously hypertensive rats fed the fish diet showed a distinctly lower level (P < 0.05) of serum ACE activity than the control group fed a commercial stock chow. 3. ACE activity was enhanced in the SHRSP which was administered with captopril. 4. Serum ACE activity was similar in the SHRSP receiving the hydralazine treatment and the control group. 5. The thoracic aorta ACE activity was lowered more (P < 0.05) in the fish diet group and the captopril-treated group than in the control group. In the hydralazine-treated group however, the activity was similar to the control group. 6. The ratio of aorta weight to bodyweight was significantly lower (P < 0.05) in the fish diet group and the captopril-treated group than in the control group, but there was no difference in the hydralazine group. Higher levels of aortic elastin were observed in the drug-treated groups (P < 0.05). 7. No differences were seen between the fish diet and captopril-treated groups by electron-microscopy. 8. The results suggest that suppression of hypertrophy and ameliorations of reduction in elasticity of the vascular wall in the SHRSP fed a fish diet were due to inhibition of vascular tissue ACE activity.