ANGIOTENSIN-CONVERTING ENZYME-INHIBITION PREVENTS THE INCREASE IN AORTIC COLLAGEN IN RATS

Four groups of 4-week-old spontaneously hypertensive rats were treated during 4 months with the angiotensin converting enzyme inhibitor quin april at 1 mg/kg per day (Q1) or 10 mg/kg per day (Q10), hydralazine a t 15 mg/kg per day (H), or placebo (P). In the first set of experiment s, blood pressure was measured in conscious rats, and plasma and aorti c angiotensin converting enzyme activities were evaluated. In the seco nd set of experiments, histomorphometric parameters of the thoracic ao rta were evaluated. Mean blood pressure was lower in the Q10 and H gro ups (136+/-16 and 149+/-11 mm Hg) compared with the P group (190+/-23 mm Hg) (P<.01). The Q1 group showed mean blood pressure values (171+/- 15 mm Hg) lower than the P group (P<.05) but significantly higher than the Q10 and H groups (P<.01 and P<.05, respectively). Aortic medial c ross-sectional area was significantly lower in the H and Q10 groups (4 55+/-61 and 487+/-57 x 10(3) mu m(2)) than in the P group (636+/-72 x 10(3) mu m(2)) (P<.001). In the Q1 group, medial cross-sectional area was lower(550+/-65 x10(3) mu m(2)) than the P group (P<.01) but higher than the Q10 and H groups. In the Q10 and Q1 groups, the collagen con tent of the aortic media was significantly lower than in the two other groups (P<.01) (Q1, 15.3+/-4.6; Q10, 14.3+/-4.0; H, 18.6+/-5.0; P, 21 .9+/-4.7x10(3) mu m(2)/mm of aorta). Aortic angiotensin converting enz yme activity was inhibited by approximately 60% in both groups treated with quinapril, whereas plasma angiotension converting enzyme activit y was reduced only in the Q10 rats. These results show that, whereas b oth hydralazine and quinapril prevented the development of aortic hype rtrophy in a pressure-dependent manner, the prevention of the increase in aortic collagen was observed only after quinapril treatment. This latter effect of angiotensin converting enzyme inhibition was not rela ted to the blood pressure reduction but was associated with the reduct ion of aortic and not plasma converting enzyme.