The most common cause of renal artery stenosis is atherosclerosis, the same condition that causes narrowing of the arteries in coronary heart disease and stroke, and the risk factors are the same as well. Cholesterol plaques build up along the walls of the renal artery and gradually cause narrowing.
Oxytocin is a commonly used uterotonic that can cause significant and even fatal hypotension, particularly when given as a bolus. The resulting hypotension can be produced by a decrease in systemic vascular resistance or cardiac output through a decrease in venous return.
Oxytocin is controlled by a positive feedback mechanism where release of the hormone causes an action which stimulates more of its own release. When contraction of the uterus starts, for example, oxytocin is released which stimulates more contractions and more oxytocin to be released. In this way, contractions increase in intensity and frequency. There is also a positive feedback involved in the milk-ejection reflex.