Influence of recombinant human erythropoietin on blood pressure and tissue renin-angiotensin systems.

In humans, blockade of the renin-angiotensin system with angiotensin converting-enzyme inhibitors (ANG CEI) prevents the rise in blood pressure associated with the administration of recombinant human erythropoietin (rhEPO). This study was conducted to determine whether rhEPO elevates blood pressure in normal Wistar rats and whether the renin-ANG system is affected. Groups of 10 rats each were given rhEPO, ANG CEI (enalapril), rhEPO + ANG CEI, or vehicle. Renin and/or renin substrate mRNA was measured in aortas, kidney, and heart; renin activity (PRA), inactive renin, and renin substrate were measured in plasma. rhEPO raised blood pressure in the normal rat without changing the plasma renin system. ANG CEI prevented this blood pressure rise. Renin-specific mRNA was increased by rhEPO in renal tissue, and renin substrate mRNA was significantly elevated in the kidney and aorta. mRNA for renin and renin substrate were not altered in the heart. In both aorta and kidney, a significant correlation was observed between renin substrate mRNA and blood pressure. The data indicate that rhEPO modulates specific tissue renin-ANG systems, which may contribute to blood pressure elevation.

Production of angiotensinogen by cultured rat aortic smooth muscle cells.

This study was conducted to further investigate angiotensinogen synthesis in rat aortic smooth muscle cells (SMC) grown in culture. tissue cultures maintained in defined medium neither grew nor synthesized angiotensinogen. However, in the presence of 5% homologous serum both cell proliferation and angiotensinogen synthesis became apparent. Substitution of normal control serum with that of bilaterally nephrectomized rats or animals given dexamethasone (10mg/kg, ip) led to a further significant increase in angiotensinogen production. In contrast, serum from adrenalectomized rats suppressed angiotensinogen synthesis below the rate observed with normal serum. A positive linear correlation (r = 0.96, p less than 0.01) was evident between the serum angiotensinogen level and the rate of de novo synthesis of this protein. No correlations were found between cell proliferation and either angiotensinogen synthesis or serum angiotensinogen levels. Dexamethasone added to serum did not stimulate the rate of angiotensinogen synthesis and appeared to inhibit cell proliferation. Stimulation or suppression of angiotensinogen synthesis was not accompanied by a statistically significant change in angiotensinogen specific mRNA. The data indicate a complex regulation of angiotensinogen in vascular smooth muscle cells in culture.