Angiotensin-Converting Enzyme Inhibitors, Animals, Arterioles, Blood Pressure, Calcium, Calcium-Transporting ATPases, Enalaprilat, Enzyme Inhibitors, Estrenes, Indoles, Juxtaglomerular Apparatus, Male, Microscopy, Video, Muscle, Smooth, Vascular, Nephrons, Perfusion, Pressure, Pyrrolidinones, Rats, Rats, Sprague-Dawley, Thapsigargin, Type C Phospholipases, Vasoconstriction