Nitric Oxide deficit may play a role in POTS symptoms. Nitric Oxide (NO) is a very simple molecule whose job it is to control blood vessel size with changes in blood flow, changes in blood vessels during inflammation and blood vessel leakiness (Stewart, 2005). Some POTS patients have a deficit of nitric oxide (Stewart, Taneja, Glover & Medow, 2008.). This deficit may relate to the nitric oxide synthase molecule called nNOS, but it also has a compelling relationship with the hormone angiotensin-II.Together angiotensin-II and NO may help to regulate sympathetic nerve activity in the brain and also in certain peripheral nerves (such as the splanchnic circulation). Moreover, angiotensin-II can result in increased oxidative stress which can itself reduce NO (Dr. Julian Stewart, personal communication, November 28, 2007).
Researchers have found that NO levels can be increased by blocking the most important receptor for angiotensin-II. This may lead to treatments in the future in select groups of POTS patients.