Interlobular arteries and afferent arterioles are involved in autoregulation of renal blood flow (RBF) and glomerular filtration rate (GFR). The question of whether the contractile mesangial cells are also involved in autoregulation was investigated in Wistar rats. Autoregulation of RBF was examined before and 1 h after infusion of antithymocyte (anti-Thy 1-1) antibodies, and both RBF and GFR autoregulation were examined 30 h after the infusion of antibodies. Mesangial cell destruction was present 30 h after the infusion of antibodies. The angiotensin II-induced contraction of isolated glomeruli (70% of control volume, P less than 0.001) was abolished after the glomeruli had been exposed to anti-Thy 1-1 in vitro. RBF, as well as the lower limit of RBF autoregulation, were not different from control 30 h after the infusion (82 +/- 5 vs. 79 +/- 4 mmHg, P greater than 0.10). Autoregulation of GFR was maintained in the control group but was restricted in the experimental group (autoregulatory index: 0.71 +/- 0.42 for left kidney, 0.02 +/- 0.35 for control; P less than 0.05). The afferent arteriolar diameter was unchanged 30 h after the infusion of antibodies (17.8 +/- 0.8 vs. 17.6 +/- 0.4 microns, P greater than 0.10). One hour after infusion of the antibodies, RBF autoregulation was normal. It is concluded that mesangial cells do not seem to be involved in RBF autoregulation, but may in part influence autoregulation of GFR during pressure reduction.