Vascular tonicity plays a major role in regulating the blood pressure and the perfusion of organs, and hypertension is a major cause of morbidity and mortality in humans. We use phenylephrine, a vasoconstrictor, to create a model of hypertension in the rat. This work demonstrates the use of a micro-X-ray digital subtraction angiography (DSA) system to image pharmacologically mediated changes in the vascular system of the rat. Imaging physiological function in the rodent calls for high spatial and temporal resolutions and the use of a reproducible image acquisition chain. Dynamic vascular images and quantitative perfusion metrics were acquired before and after a vasoconstrictor, phenylephrine drug injection. Dramatic effects of the vasoconstrictor on vascular dynamics are seen in the prolonged blood flow mean transit time, amount of ventricular filling, the size increase of the pulmonary arteries and aorta, and a substantial increase in mean arterial pressure.