The myorelaxant effect of theophylline on smooth muscle cells of the afferent arterioles and glomerular tuft.

Theophylline, infused i.v. into rats increased the diameter of the glomerular afferent arterioles by 35.78%; when added to a suspension of isolated glomeruli, it increased the diameter of the capillary tuft within the glomerulus by 25-30%. These variations in diameter can be explained by the myorelaxant effect of theophylline on the smooth contractile fibers present in the arteriolar cells and in certain glomerular cells, such as the mesangial cells. These observations explain, in part, the marked changes in glomerular hemodynamics caused by the injection of theophylline.