[Sar1]angiotensin II receptor-mediated stimulation of protein synthesis in chick heart cells

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Abstract
Cardiac hypertrophy is a process that occurs in response to various mechanical or hormonal stimuli. Stimulation of the renin-angiotensin system is involved in the process of cardiac hypertorphy through mechanisms related to increased peripheral vascular resistance and increased cardiac afterload. In this study we determined whether [Sar1]angiotensin II (ANG II) directly stimulated protein synthesis and cell growth in embryonic chick myocytes in cell culture. Eighteen-day-old embryonic chick myocytes in subconfluent cell culture, incubated in a chemically defined serum-free media, showed a significant increase in total protein content, 18.5, 26.2, and 22.2%, respectively, when exposed to [Sar1]ANG II (1 .mu.M/day) for 5, 7, and 9 days, respectively. The increase in total protein resulted in part from an increase in the fractional protein synthesis rate of 21.7, 16.5, and 14.9% at 5, 7, and 9 days, respectively. Total DNA and RNA levels did not change significantly following a 4-day exposure to [Sar1]ANG II in subconfluent culture. The relative rate of protein synthesis, determined by pulse labeling for 3 h with [3H]phenylalanine, showed increases of 23.4, 22.9, and 17.8% over control after 4, 5, and 6 days of exposure to [Sar1]ANG II. The incorporation of [3H]-phenylalanine was blocked by the specific ANG II-receptor antagonist [Sar1,Ile8]ANG II. The data demonstrate a receptor-mediated increase in the rate of protein synthesis in cultured chick myocytes in resonse to [Sar1]ANG II, with a resultant increase in total cellular protein. This angiotensin peptide appears to directly stimulate protein synthesis in cultured embryonic chick myocytes. The left ventricular hypertrophy that develops in response to angiotensin peptides in vivo may, in part, be direct and independent of increases in cardiac afterload.