50% reduction in efferent aeriolar resistance would cause a large decrease in GFR--greater than 10%. A decrease in renal aery pressure from 100 to 85 mm Hg would cause only a slight decrease in GFR in a normal, autoregulating kidney. A decrease in afferent aeriole resistance, a decrease in plasma colloid osmotic pressure, or an increase in the glomerular capillary filtration coefficient would all tend to increase GF