SELECTIVE ANTAGONISM OF THE AT(1) RECEPTOR INHIBITS THE EFFECT OF ANGIOTENSIN-II ON DNA AND PROTEIN-SYNTHESIS OF RAT PROXIMAL TUBULAR CELLS

The proliferation and hypertrophy of renal tubular cells are primary f eatures in the progression of both acute and chronic renal disease oft en indicating a poor prognosis. Angiotensin II (ANG II), acting alone or in combination with other growth factors, has been implicated in th is process. The aims of this study were to identify the importance of both ANG II and serum-derived factors upon cellular DNA synthesis and protein synthesis in renal proximal tubular cells and to identify the roles of the ANG II receptor subtypes in these processes together with the underlying intracellular signalling mechanisms involved. Primary cultures of renal proximal tubular cells were prepared from freshly is olated rat kidney cortex. Cells were cultured in either serum-replete Dulbecco's modified Eagle's/Ham's F12 or serum-deplete defined medium containing insulin, hydrocortisone, sodium selenite, transferrin, and tri-iodothyronine. Cells were incubated with ANG II (10(-10), 10(-8), 10(-6) M) for 24-120 h either alone or in combination with losartan, P D123319, or pertussis toxin. Incubation of proximal tubular cells in t he presence of serum and ANG II (10(-8) M) induced a significant early (24 h) increase in DNA synthesis, together with a significant late (9 6 h) increase in protein content. [H-3]thymidine uptake increased by 5 6% (p < 0.001) and total protein content by 23% (p < 0.05). In defined media, ANG II (10(-8) M) stimulated protein synthesis only. [H-3]urid ine uptake, [H-3]leucine uptake, and total protein content increased b y 25, 57, and 17% (p < 0.05), respectively. In both serum-replete and serum-deplete media, the effects upon protein synthesis of ANG II were inhibited by pertussis toxin and losartan, but not by PD 123319. ANG II is clearly a potent stimulator of renal tubular cell DNA and protei n synthesis - a response mediated via the AT(1) receptor coupled to a pertussis toxin sensitive G(i) protein.