Abstract
Epidermal growth factor (EGF), an endogenous mitogenic peptide, has recently been shown to be a potent vasoconstrictor of vascular smooth muscle. In view of its potential role in proliferative and inflammatory renal glomerular diseases, we examined the effects of EGF both on cultured rat mesangial cells and on in vivo glomerular hemodynamics. Mesangial cells possess specific, saturable EGF receptors of differing affinities, with Kd's of 0.1 and 1.7 nM, respectively. EGF produced a rapid increase in intracellular pH of 0.12 +/- 0.01 pH U, which was sodium dependent and amiloride inhibitable. The addition of EGF to mesangial cells cultured on either glass or dimethylpolysiloxane substratum induced reproducible cell contraction. Intrarenal EGF infusion did not affect systemic blood pressure or hematocrit but reversibly decreased GFR and renal blood flow from 4.19 +/- 0.33 to 3.33 +/- 0.26 and from 1.17 +/- 0.09 to 0.69 +/- 0.07 ml/min, respectively. Glomerular micropuncture confirmed decreases in single nephron plasma flow and in single nephron GFR (from 142 +/- 9 to 98 +/- 8 and from 51.6 +/- 11.7 to 28.5 +/- 3.5 nl/min, respectively) which were due to significant increases in both pre- and postglomerular arteriolar resistances (from 1.97 +/- 0.31 to 2.65 +/- 0.36 and from 1.19 +/- 0.11 to 2.00 +/- 0.15 10(10) dyn.s.cm-5 respectively) and to a significant decrease in the ultrafiltration coefficient, Kf, which fell from 0.100 +/- 0.019 to 0.031 +/- 0.007 nl/(s.mmHg). These studies demonstrate that mesangial cells possess specific receptors for EGF, and exposure of these cells to physiologic concentrations of EGF results in an in vitro functional response characterized by activation of Na+/H+ exchange and by resultant intracellular alkalinization, as well as by cell contraction. EGF administration in vivo significantly reduces the glomerular capillary ultrafiltration coefficient, Kf, which, in combination with EGF-induced constriction of both preglomerular and postglomerular arterioles, results in acute major reductions in the rates of glomerular filtration and perfusion.