Constriction of either the afferent or efferent aeriole increases resistance, and according to Equation Q = DP/R, an increase in resistance (R) decreases flow (Q) (i.e., RBF). Dilation of either the afferent or efferent aeriole increases flow (i.e., RBF). Constriction of the afferent aeriole (A) decreases P GC because less of the aerial pressure is transmitted to the glomerulus, thereby reducing GFR. Dilation of the afferent aeriole increases P GC because more of the aerial pressure is transmitted to the glomerulus, thereby increasing GFR.Reference: Berne and Levy Medical Physiology; 6th edition; Page no: 574