Guanine nucleotide-binding proteins in aortic smooth muscle from hypertensive rats

To explore the hypothesis that altered vascular muscle signal transduction may underlie some of the vascular changes observed in hypertensive models, we measured expression of GTP-binding protein (G protein) o-subunits, G, G_i and G_q, in aortic muscle of reduced renal mass and sham-operated rats and proximal and distal aortic segments from rats with interrenal aortic coarctation (IR-AC). G protein expression was measured by immunoblot analysis. When we probed aortic muscle membrane with G_i, and G_q a-subunit antibodies, we identified 41- and 42-kD immunoreactive proteins, respectively. Three immunoreactive bands specific to G, a-subunit antibody were resolved. Immunoreactive blot densities were compared. In aortic muscle membrane of reduced renal mass rats (blood pressure, 148 ±7 mm Hg), we found significantly reduced G, and G, blot densities compared with sham-operated controls (blood pressure, 99±12 mm Hg). There were no differences in G_q blot densities between re- duced renal mass and control rats. G, and G, blot densities were significantly lower in IR-AC proximal aortic segments (carotid pressure, 165±5 mm Hg) and distal aortic segments (femoral pressure, 121 ±4 mm Hg) than in aortas of shamoperated controls. In contrast, G_q expression was significantly increased in the high-pressure proximal aortic segments compared with low-pressure distal aortic segments from IR-AC rats. Thus, altered G protein expression occurs in aortic muscle from nongenetic rat models of hypertension. Given the differences between reduced renal mass and IR-AC models, it is clear that pressure is not the only variable regulating G protein expression and that hormonal and/or metabolic influences probably play a larger role.