DIRECT EFFECTS OF ANGIOTENSIN-I, ANGIOTENSIN-II, AN ACE-INHIBITOR ANDA SERINE PROTEINASE-INHIBITOR ON CULTURED HEART-CELLS FROM SPONTANEOUSLY HYPERTENSIVE RATS

1. The purpose of the present study was to investigate how angiotensin I(AI), angiotensin II (An), an angiotensin converting enzyme inhibito r (ACE inhibitor; ACE-I) and a serine proteinase inhibitor contribute to the protein metabolism of cultured newborn spontaneously hypertensi ve rats (SHR) heart cells. We examined the uptake of [H-3]-uridine and [H-3]-proline into cultured cardiac myocytes and fibroblasts, respect ively. 2. Both AI and AII increased the uptake of [H-3]-uridine into m yocytes in a concentration-dependent manner. However, the effect of AI was denied in the presence of the ACE-I with the concentration of 10( -6) g/mL. Both AI and AII increased the uptake of [H-3]-proline into c ardiac fibroblasts in a concentration-dependent manner. However, this effect was only partially abolished in the presence of 10(-6) g/mL of the ACE-I, which was the maximal concentration that did not exert any effect on the [H-3]-proline uptake. In the presence of AII receptor an tagonist, [Sar(1), Leu(8)]-AII, the uptake of [H-3]-proline into cardi ac fibroblasts was completely inhibited. Moreover, the stimulatory eff ects of AI on the uptake of [3H]proline into cardiac fibroblasts were completely inhibited in the presence of a serine proteinase inhibitor in addition to the ACE-I.3. These results suggest that an ACE-I has di fferent effects on protein metabolism in the heart and also suggest th e presence of serine proteinase in cultured cardiac fibroblasts from S HR.