All of the following about prostaglandins are TRUE, EXCEPT:

Prostacyclin is produced by endothelial cells and thromboxane A2 by platelets from their common precursor, arachidonic acid. Prostaglandins are a series of 20-carbon unsaturated fatty acids containing a cyclopentane ring. It was first isolated from semen but are synthesized in most and possibly in all organs in the body. Respiratory smooth muscle is relaxed by PGE2 and PGI2 and contracted by PGD2, TXA2, and PGF2a. Ref: Barrett K.E., Barman S.M., Boitano S., Brooks H.L. (2012). Chapter 1. General Principles & Energy Production in Medical Physiology. In K.E. Barrett, S.M. Barman, S. Boitano, H.L. Brooks (Eds), Ganong's Review of Medical Physiology, 24e.